CA1134939A - Polymeric piezoelectric microprobe having a damper - Google Patents
Polymeric piezoelectric microprobe having a damperInfo
- Publication number
- CA1134939A CA1134939A CA000361678A CA361678A CA1134939A CA 1134939 A CA1134939 A CA 1134939A CA 000361678 A CA000361678 A CA 000361678A CA 361678 A CA361678 A CA 361678A CA 1134939 A CA1134939 A CA 1134939A
- Authority
- CA
- Canada
- Prior art keywords
- housing
- transducer assembly
- probe
- assembly according
- sound absorbing
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 239000000463 material Substances 0.000 claims abstract description 22
- 229920001971 elastomer Polymers 0.000 claims abstract description 10
- 238000001514 detection method Methods 0.000 claims abstract description 5
- 239000010408 film Substances 0.000 claims description 19
- 239000006096 absorbing agent Substances 0.000 claims description 12
- 125000006850 spacer group Chemical group 0.000 claims description 8
- 230000001902 propagating effect Effects 0.000 claims description 6
- 229910052729 chemical element Inorganic materials 0.000 claims description 4
- 239000011104 metalized film Substances 0.000 claims description 4
- 239000011358 absorbing material Substances 0.000 claims description 2
- 239000000523 sample Substances 0.000 abstract description 53
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 abstract description 23
- 239000007788 liquid Substances 0.000 abstract description 7
- 238000005259 measurement Methods 0.000 abstract description 4
- 230000002745 absorbent Effects 0.000 abstract description 3
- 239000002250 absorbent Substances 0.000 abstract description 3
- 229920000642 polymer Polymers 0.000 abstract 1
- 229910001220 stainless steel Inorganic materials 0.000 description 11
- 239000010935 stainless steel Substances 0.000 description 11
- 239000004020 conductor Substances 0.000 description 8
- 239000002033 PVDF binder Substances 0.000 description 4
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 4
- 238000006243 chemical reaction Methods 0.000 description 3
- 238000003384 imaging method Methods 0.000 description 3
- 239000012212 insulator Substances 0.000 description 3
- 229910052451 lead zirconate titanate Inorganic materials 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- ISWSIDIOOBJBQZ-UHFFFAOYSA-N phenol group Chemical group C1(=CC=CC=C1)O ISWSIDIOOBJBQZ-UHFFFAOYSA-N 0.000 description 3
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- 229910052782 aluminium Inorganic materials 0.000 description 2
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 2
- 230000008901 benefit Effects 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 239000000919 ceramic Substances 0.000 description 2
- 229910010293 ceramic material Inorganic materials 0.000 description 2
- 230000007797 corrosion Effects 0.000 description 2
- 238000005260 corrosion Methods 0.000 description 2
- 238000000151 deposition Methods 0.000 description 2
- 230000008021 deposition Effects 0.000 description 2
- 238000002592 echocardiography Methods 0.000 description 2
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- 239000011810 insulating material Substances 0.000 description 2
- 239000002923 metal particle Substances 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 230000004044 response Effects 0.000 description 2
- 238000000926 separation method Methods 0.000 description 2
- 229920002799 BoPET Polymers 0.000 description 1
- 239000005041 Mylar™ Substances 0.000 description 1
- 239000006098 acoustic absorber Substances 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000005219 brazing Methods 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 230000030808 detection of mechanical stimulus involved in sensory perception of sound Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000005684 electric field Effects 0.000 description 1
- 238000010292 electrical insulation Methods 0.000 description 1
- 125000001153 fluoro group Chemical group F* 0.000 description 1
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 1
- 229910052737 gold Inorganic materials 0.000 description 1
- 239000010931 gold Substances 0.000 description 1
- 230000036039 immunity Effects 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
- 238000002955 isolation Methods 0.000 description 1
- HFGPZNIAWCZYJU-UHFFFAOYSA-N lead zirconate titanate Chemical compound [O-2].[O-2].[O-2].[O-2].[O-2].[Ti+4].[Zr+4].[Pb+2] HFGPZNIAWCZYJU-UHFFFAOYSA-N 0.000 description 1
- 230000013011 mating Effects 0.000 description 1
- 238000001465 metallisation Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000000178 monomer Substances 0.000 description 1
- 239000003208 petroleum Substances 0.000 description 1
- 239000002985 plastic film Substances 0.000 description 1
- 229920006255 plastic film Polymers 0.000 description 1
- 229920006254 polymer film Polymers 0.000 description 1
- 229920000131 polyvinylidene Polymers 0.000 description 1
- 230000010255 response to auditory stimulus Effects 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 229920002379 silicone rubber Polymers 0.000 description 1
- 239000004945 silicone rubber Substances 0.000 description 1
- 230000001702 transmitter Effects 0.000 description 1
Classifications
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
- A61B8/08—Detecting organic movements or changes, e.g. tumours, cysts, swellings
- A61B8/0875—Detecting organic movements or changes, e.g. tumours, cysts, swellings for diagnosis of bone
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
- B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
- B06B1/00—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
- B06B1/02—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy
- B06B1/06—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction
- B06B1/0688—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction with foil-type piezoelectric elements, e.g. PVDF
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N30/00—Piezoelectric or electrostrictive devices
- H10N30/30—Piezoelectric or electrostrictive devices with mechanical input and electrical output, e.g. functioning as generators or sensors
- H10N30/302—Sensors
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S310/00—Electrical generator or motor structure
- Y10S310/80—Piezoelectric polymers, e.g. PVDF
Abstract
PIEZOELECTRIC MICROPROBE
Abstract of the Disclosure A probe detects sonic energy in liquids and in mater-ials containing liquids such as the flesh of living beings, the probe being particularly adapted for medical ultrasonics.
The probe is constructed of materials having acoustic imped-ances substantially equal to that of water to maximize the transfer of sonic energy in a living being to an electric signal within the probe for accurate detection of high fre-quency pulses having a duration less than a microsecond. A
piezoelectric polymer serves as the transducer and is mounted at the end of the probe housing between a thin metallic window which serves as one electrode, and a metallized rubber rod which serves as the second electrode and sonically insulates the transducer from the housing. An acoustically absorbent ring affixed to the perimeter of the face of the probe, and a flaring of the back end of the probe, reduce the diffraction and reflection of acoustic waves for improved accuracy in the measurement of submicrosecond pulses.
Abstract of the Disclosure A probe detects sonic energy in liquids and in mater-ials containing liquids such as the flesh of living beings, the probe being particularly adapted for medical ultrasonics.
The probe is constructed of materials having acoustic imped-ances substantially equal to that of water to maximize the transfer of sonic energy in a living being to an electric signal within the probe for accurate detection of high fre-quency pulses having a duration less than a microsecond. A
piezoelectric polymer serves as the transducer and is mounted at the end of the probe housing between a thin metallic window which serves as one electrode, and a metallized rubber rod which serves as the second electrode and sonically insulates the transducer from the housing. An acoustically absorbent ring affixed to the perimeter of the face of the probe, and a flaring of the back end of the probe, reduce the diffraction and reflection of acoustic waves for improved accuracy in the measurement of submicrosecond pulses.
Description
-~34~
Background o.f the Invention This invention relates to sonar transducers and, more particularly, to a transducer probe assembly adapted for detection of short pulses of high frequency sonic energy as is utilized in medical ultrasonics.
Transducers for the conversion of sonic energy into elec-trical signals are employed aboard ships for the detection of underwater sounds, and also in probes for the detection of sounds propagating within the tissues of living beings. The transducers are generally reciprocal devices in that electrical signals applied to the transducers are converted into sound waves which can propagate within the ocean and within living tissues.
In the past, transducers have generally been constructed of a piezoeiectric ceramic material such as lead-zirconate-titanate (P2T). PZT is relatively dense as compared to water and has a much higher acoustic impedance than does water. In sonar applications, the transducer has generally been mounted in strong metallic casings with relatively heavy weights me-
Background o.f the Invention This invention relates to sonar transducers and, more particularly, to a transducer probe assembly adapted for detection of short pulses of high frequency sonic energy as is utilized in medical ultrasonics.
Transducers for the conversion of sonic energy into elec-trical signals are employed aboard ships for the detection of underwater sounds, and also in probes for the detection of sounds propagating within the tissues of living beings. The transducers are generally reciprocal devices in that electrical signals applied to the transducers are converted into sound waves which can propagate within the ocean and within living tissues.
In the past, transducers have generally been constructed of a piezoeiectric ceramic material such as lead-zirconate-titanate (P2T). PZT is relatively dense as compared to water and has a much higher acoustic impedance than does water. In sonar applications, the transducer has generally been mounted in strong metallic casings with relatively heavy weights me-
2~ chanically coupled to the transducer in order to provide a measure of impedance matching between the impedances of the transducer and of the water. Probe's employing smaller quan-tities of PZT and utilizing reduced weight of the impedance matching structures have been employed in medical ultrasonic research for the observation of sound waves within living tissues. However, such probes have not been completely satis-factory due to the large difference of impedance between the transducer and the living tissue, the living tissue having an acoustic impedance substantially e~ual to that of water. The large difference of impedance has reduced the efficiency of ~3493~
conversion of sonic energy to electric energy thereby re-ducing the sensitivity of the probe. Furthermore, the ce-ramic materials utilized in transducers, in combination with their mechanical acoustic matching structures, provide a structure which is sufficiently resonant acoustically to inhibit the measurement of sonic pulses of relatively short durations, less than a microsecond duration, as are advan-tageously utilized in medical ultrasonics.
With a view towards providing transducers which are capable of receiving the foregoing submicrosecond sonic sig-nals with minimal distortion, consideration has been given to a material, other than the ceramics, which has piezoelec-tric properties and an acoustic impedance more nearly equal to that of water than is the impedance of the ceramics. One such material, polyvinylidene fluoride is commercially avail-able from the Penwalt Corporation of King of Prussia, Pennsyl-vania and EMI Limited, Middlesex, England. However, this polymeric material is presently obtainable only in thin ~ilms, typically 30 microns thick. The films are produced with met-allized layers on the top and the bottom surfaces by a depos-ition of, typically, aluminum on the surfaces. A problem a- -rises in that the physical structures which have been utilized in the fabrication of sonar transducers employing the relatively massive, rugged ceramic materials do not admit the use of the relatively light, fragile polymeric film.
Summary of the Invention The aforementioned problems are overcome and other advan-tages are provided by a transducer probe which is capable of receiving acoustic signals propagating in liquid media and living tissues wherein the acoustic signals include frequencies ranging up to one megahertz (MHz) and even higher frequencies with signal durations as short as a fractional microsecond interval. In accordance with the invention, the probe is provided with a transducer element formed of a piezoelectric ma'erial having an acoustic impedance substantially equal to that of water, and having metallization on the surfaces of the material for applying electric signals to the material.
Due to the substantial equality of impedance of the transducer element with the impedance of water, the transducer element may be viewed as being transparent to acoustic energy. The probe is preferably immersed fully in water for detecting sounds propagating in the water, the acoustic transparency minimizing interference of the transducer element to the propagation of sonic waves to permit observation of submicro-second sonic pulses.
- In a preferred embodiment of the invention, the trans-ducer element is formed of a film of a polymeric piezoelec-tric material such as polyvinylidene fluoride. The probe is formed with an elongated cylindrical or frusto-conical housing terminated by an acoustic window. The housing is typically fabricated of stainless steel to prevent a de-velopment of corrosion from liquids in which the probe may be immersed. The window is fabricated of a material which is substantially lossless to acoustic energy, and to further insure against acoustic losses, is fabricated with a thick-1~3493~
ness which should be less than approximately ten percent of the wavelength of the acoustic energy propagating through the window. In the preferred embodiment of the invention, a window thickness of less than one percent of the wave-length has been utilized. The window has been fabricated of stainless steel in a thickness of 0.025 millimeter (mm) since the stainless steel is sufficiently strong to permit the fabrication of such a thin window and for providing acoustical cond~ctivity through the window. In addition, the electrical conductivity of the stainless steel provides for electrical shielding of the transducer.
The transducer element is placed in physical contact with the window so that the window and the housing serve as an electrical contact for the transducer element. A second electrical contact is made by means of an electrically con-ducting sonic insulator. The sonic insulator is, preferably, a rubber rod for attenuating any sonic reverberations which might otherwise be induced within the housing. The rubber rod is formulated with metal particles to provide an elec-trical conductivity thereto, the rubber rod abutting the transducer element to secure it against the window while the electrical conductivity enables the rod to serve as the second electrical contact for the transducer élement. The cylinder of insulating material, such as a phenolic material, sur-rounds the rubber rod to serve as a spacer element and to provide electrical insulation between the rod and the housing.
A cylinder of insulating material also serves as an acoustic insulator to further attenuate any sonic reverberations which might otherwise develop within the housing. Any voids between the transducer element, the rod, and the insuIating cylinder, 1~39193~
are filled with oil to insure an acoustic transmission path which is free of resonance effects associated with an air pocket. An acoustically absorbent ring affixed to the peri-meter of the face of the probe, and a flaring of the back end of the probe, reduce the diffraction and reflection of acoustic waves for improved accuracy in the measurement of submicrosecond pulses.
In accordance with the present invention, there is provided a transducer assembly comprising: a polymeric piezo-electric element having front and back surfaces thereof; anelongated housing enclosing said piezoelectric element and having a substantially transparent acoustic window at an end thereof in contact wit~ said first surface of said piezoelectric element;
an elongated sound absorbing member in contact with said second surface of said piezoelectric element; a spacer member disposed circumferentially around said sound absorbing member and located between said sound absorbing member and said housing, said piezoelectric element having an acoustic impedance substantially equal in magnitude to the impedance of a medium to which said transducer assembly is acoustically coupled for the detection of sonic signals propagating in said medium; and means for isolating said polymeric piezoelectric element from sound waves diffracted from the edge of said acoustic window.
In accordance with the present invention, there is also provided a transducer assembly comprising: a piezoelectric element comprising a polymerized film having front and back surfaces thereof, there being front and back metallized films - ~ :
deposited, respectivelyl on said front and said back surfaces of said polymerized film; a housing enclosing said piezoelectric 30 element and having a window in contact with said first surface ~:
of said piezoelectric elément, said window being electrically conductive and transmissive of sonic energy, said window serving ~4S~39 as a first electrical terminal for said piezoelectric element;
a sound absorbing member in contact with said second metallized film, said sound absorbing member being electrically conductive and serving as a second electrical terminal for said piezoelec-tric element; and an amplifier disposed within said housing and electrically coupled to said polymerized film.
- 5a -,.t~
3L~'~
Brief Description of the Drawings _ _ _ The aforementioned aspects and other features of the invention are explained in the following description taken in connection with the accompanying drawings wherein:
Figure 1 is a sectional view of an acoustic probe con-structed in accordance with the invention;
Figure 2 is an enlarged view of a face of the probe of Figure 1 designated by an encircled region in Figure l;
Figure 3 is an end view of the probe of Figure 1 taken along the lines 3-3 of Figure 2;
Figure 4 shows a portion of a polymer film with metallized layers thereon which i.s utilized in forming the transducer ele ment seen in Figures 1 and 2;
Figure 5 is an alternative embodiment of the invention wherein the housing as provided with a frusto-conical shape for reducing sonic reverberations within the housing; and for reducing electrical capacitance between an electrically conducting rubber rod and the housing;
Figure 6 shows a sonic echo system.utilizing a conven-tional sound transmitter and the probe of Figure 1 for por-traying an image of the internal structure of living tissues;
Figure 7 is an alternative arrangement of the sound transmitter and probe of Fiyure 6 wherein the transmitter and the probe are immersed in a liquid for imaging an object submerged within the liquid.
Descrlption of the Preferred Embodlment Referring now to Figures 1, 2 and 3, an acoustic probe 20 which is constructed in accordance with the invention is seen to comprise a cylindrically shaped neck 22 and a pod 24 secured to the end of the neck 22, the neck 22 housing the acoustic sensing elements while the pod 24 houses the ele-ments of an electrical amplifier 26. The amplifier 26, which is of conventional design, for low noise figure, is shown diagrammatically and is seen to be mounted on a circuit board 28 which is enclosed by a housing 30 of the pod 24.
The board 28 is secured to a cover 32 of the housing 30 to facilitate the making of electrical connections between the amplifier 26 and the following terminals, namely, a terminal 34 which is a coaxial cable connector for the supplying of power to the amplifier 26, a terminal 36 which is a coaxial cable connector for providing the output signal of the ampli-fier 26, and a grounding terminal 38. The terminals 34, 36 and 38 are mounted on the cover 32. A socket 39 is coupled to the amplifier 26 and is secured to the board 28 for slid-: 20 ably mating with a terminal 40 which is coupled to a trans-ducer element 42 as wlll be descrlbed hereinafter.
Referring also to Figure 4, the transducer element 42-is fabricated in the form of a thin circular disc by cutting out a disc from a piezoelectric polymeric film 52, such as polyvinylidene fluoride having metallized layers 55-56 there-on. The layers 55 and 56 are formed by the deposition of a metal, such as aluminum or gold upon the front and back sur-faces of the film 52. The transducer element 42 has been con-structed with a diameter of l.S mm in one embodiment of the invention, the film 52 having a thickness of 30 microns. The ~L3g~3~
layers 55 and 56 are utilized Eor detecting an electric field which is generated within the film 52 in response to sound waves incident thereupon. While a film 52 having the afore-mentioned 30 micron thickness has been utilized in constructing the probe 20, it is believed that a thicker film would provide a greater efficiency in the conversion of sonic energy to elec-trical signals. With the use of piezoelectric poly~er o great-er thickness, the relatively thin disc shape of the transducer element 42 would have a thicker shape such as that of a tile.
Also, it is noted that, while the transducer element 42 has been fabricated with a circular shape, the transducer element 42 may alternatively be fabricated of a square shaped tile.
A feature of the invention is the mounting of the trans-ducer element 42 within a housing 60 of the neck 22 wherein the neck housing 60 provides both isolation from radio-fre-quency interference and sonic reverberations. The neck housing 60 is formed of a tubular section of an electrically conducting material, such as stainless steel, and is termin-ated at its front end with a window 62 which is constructed of an electrically conductive material which is resistant to corrosion and transmissive of sonic energy. In the preferred embodiment of the invention, the window 62 has been construc-ted of stainless steel since stainless steel, as has been noted hereinabove, is sufficiently strong to permit the fab-rication of the window 62 with a thickness of 0.025 mm, this thickness being less than one percent of a wavelength of the sound which is to be detected by the probe 20. Since stainless steel is propagative of sonic energy, and since the thickness is substantially less than the sonic wavelength, sound waves can propagate through the window 62 with essentially no reflec-. .
~13q~9 tion or attenuation, even though the acoustic impedance of bulk stainless steel r many wavelengths in thickness, is many times greater than that of water.
The acoustic impedance of the transducer element 42 closely approximates that of water so that, upon the con-tacting of the window with liviny tissue or a body of water as will be seen in Figures 6 and 7, sonic energy is able to propagate through the transducer element 42 with substantially no reflection therefrom, the transducer ele-ment 42 being essentially transparent to the sonic energy.
The metallized layers 55 and 56 have substantially less thickness than that of the film 52 and of the window 62 so as to appear essentially transparent to the sonic energy.
As seen in Figure 3, the transducer element 42 is placed in the front end of the neck 22 in contact with a back sur-face of the window 62 so that sonic energy can readily pro-pagate through the window 62 and into the transducer element 42. In addition, the contacting of the transducer element 42 with the window 62 provides for a path of electrical con-duction wherein the neck housing 60 and the window 62 with the front layer 55 provide an electrode for the transducer element 42.
A second electrode for the transducer 42 is provided by a rod 64 which is electrically coupled between the terminal 40 and the back layer 56 of the transducer element 42~ The rod 64 is constructed of electrically conductive, sound ab-sorbing material such as rubber which has been impregnated with metal particles. A disc 66 on the front end of the ter-minal 40 mates with the bac~ end of the rod 64 to insure elec-trical conduction between the rod 64 and the terminal 40. The ' ':, 31~3~39 terminal 40 is conveniently fabricated of a copper wire.
The rubber of the rod 64 has an acoustic impedance with a magnitude similar to that of the acoustic impedance of water so that the propagation of sonic energy from the transducer element 42 into the rod 64 is accomplished with a minimum oE
reflected energy thereby minimizing any ringing by the super-position of incident and reflected waves, and, thus, facili-tating the observation of short-duration acoustic signals in the submicrosecond range.
A further feature of the invention is the enclosing of the transducer element 42 and the rod 64 and the terminal 40 by an acoustic absorber 68, the absorber 68 having been fab-ricated of a phenolic material in the preferred embodiment of the invention. It is noted that the diameter of the trans-ducer element 42 is approximately equal to the length of two wavelengths of the sonic energy at a frequency of approximate-ly two megahertz (MHz), which frequency is often utilized in ultrasonic research. As may be seen in ~igure 3, the diam-eter of the neck housinq 60 is greater than that of the trans-ducer element 42 with the result that the interior dimensions of the neck 22 are su~ficiently large to admit the development of sonic reverberations in the absence of sound absorbing material such as that provided by the absorber 68 and the rod 64. Both the absorber 68 and the rod 64 absorb sonic energy, and thereby inhibit the formation of reverberations, while their acoustic impedances, which have`a magnitude similar to that of water and of the transducer element 42, promotes the propagation of sonic energy through the transducer element 42 with a minimum of reflection. Thereby, sonic signals detected by the transducer element 42 are essentially free of the in-- 10 ~
.
~3~l~3~
fluence of reflection and reverberation with the result that the aforementioned short-duration pulses of sonic energy can be observed.
To further improve the response of the probe 20 to the short-duration pulses of sonic energy, a ring 70 of an acous-ticly absorbingly material, such as rubber, is provided around the periphery of the window 62. The ring 70 has a smooth tapered outer surface to inhibit the diffraction of an incoming sonic wave about the edges of the window 62. Also, the pod housing 30 is provided with a front section 71 having a frusto-conical shape with a cone angle of approximately 20 to 40. The frusto-conical shape gives the probe 2n an increasing outer diameter which de-flects sound waves, travelling parallel to and alongside the neck housing 60, away from the probe 20. Thereby, there is substan-tially no reflection of the sound waves off the discontinuity formed by the back end of the probe 20. It has been found that, with a probe constructed in accordance with the preerred embodi-ment of the invention, sonic pulse durations of less than a half wavelength of the carrier frequency of the sound wave can be ob-served.
With respect to the electrical connections between the transducer element 42 and the amplifier 26, it is noted that the pod housing 30 is formed of a metal for electrical conduction, such as stainless steel, and is secured to the back end of the neck housing 60 in a conventional manner as by brazing or by screw threads. Similarly, the cover 32 is fabricated of metal and is secured to the pod housing 30 by a threaded ~etallic retainer ring 72. Thus, the terminal 38- is electrically con-nected via the c:over 32 and the pod housing 30 to the neck housing 60. Secure electrical contact between the disk 66 and , ~34~3~
the rod 64 is maintained by a center-bored screw 73 affixed to the terminal 40, the screw being threadedly secured to the back end of the absorber 68 for urging the disk 66 against the rod 64. Accordingly, the electrical conductors of the neck 22 are seen to be in a coaxial arrangement wherein the inner con-ductor is formed of the rod 64 and the terminal ~0 while the outer conductor is formed of the housings 60 and 30. The ab-sorber 68 thus serves as a dielectric spacer between the inner and the outer conductors.
In selecting a length of the rod 64, it is no-ted that in- :
creasing length of the rod 64 provides for increased attenua-tion of sonic reverberation, and also results in increased elec-tric capacitance between the inner and outer conductors of the coaxial arrangement. While Figure 1 shows a length of the rod 64 which is approximately one third the length of the neck hous-ing 60r a longer length of the rod 64 may be utilized, for exam-ple, a length of the rod 64 equal to approximately two thirds the length of the neck housing 60. While the shorter length of the rod 64 results in a somewhat reduced attenuation of sonic reverberations, since the terminal 40 has been found experimen-tally to contribute to the presence of the reverberations as does the neck housing 60, the reduced length of the rod 64 pro-vides the advantage of reduced capacitance between the inner and outer conductors with a resultant increase in the amplitude of the electric signal applied via the terminals 40 and 38 to the amplifier 26. A still further reduction in capacitance results by a reduction in the length of the neck housing 60.
In the assembly of the components of the probe 20, it is noted that a petroleum based oil, such as SAE 30 weight oil, has been placed along the interfaces between the transducer ~L~3~39 element 42, the window 62, the rod 64 and the absorber 68 for filling any voids along the interfaces which would otherwise be air pockets which tend to be resonant and introduce acou-stic discontinuities with attendant reverberations. The in-sertion of the oil into such voids removes such resonances and reverberations. The interior of the pod housing 30 is also filled with the oil. After insertion of the transducer element 42, the rod 64, and the terminal 40, the absorber 68 is then inserted via the pod 24 into the nec~ 22 in the space between the rod 64 and the neck housing 60. The circuit board 28 having the amplifier 26 thereon and attached to the cover 32, is then inserted into the pod 24 and positioned by the cover 32. An o-ring 74 is placed between the cover 32 and a shelf of the pod housing 30, the O-ring 74 and the oil within the pod housing 30 serving to prevent the entry of water or other contaminents into the pod 24 when the probe 20 is immersed as will be seen in Figure 7. The retainer ring 72 tightens the cover 32 against the O-ring 74. Upon insertion of the circuit board 28 into the pod 24, the socket 39 slidably mates with the terminal 40 to electrically connect the amplifier 26 with the transducer element 42.
Referring now to Figure 5, there is seen an alternative embodiment of the probe 20 of Figures 1-3, the embodiment of Figure 5 being identified as the probe 20A. The transducer element 42 and the window 62 are the same as that shown in Figure 1. Similarly, the amplifier 26 and the electrical connections made thereto are the same as that shown in Fig-ure 1. In Figure 5, improved immunity to reverberations is attained by modifying the cylindrical shape of the neck hous-ing 60 of Figure 3 to become a frusto~conical shaped housing - 13 ~
~349~9 60A in Figure 5. Similarly, the outer cylindrical surface of the absorber 68 of Figure 3 has assumed a frusto-conical shape in the absorber 68A of Figure 5. The ring 70 of Fig-ure 3 has been similarly modifled to provide the ring 70A of Figure 5 which mates with the housing 60A of Figure 5. The the rod 64 and the terminal 40 appear in the same form in the embodiments of both Figures 3 and 5. The reduced reverbera-tions are believed to be obtained by virtue of the fact that a sonic wave impinging upon the interior wall of the housing 60A in Figure 5 is re~lected in a direction generally along the axis of the probe 20A for attenuating the sound in the ab,sorber 68A. An additional feature of the embodiment of Figure 5 is found in the increasing separation between the rod 64 and the housing 60A with progression along the axis of the probe 20A towards the amplifier 26, the increasing separation providing for an increasing diminution in the magnitude of the electrical capacitance with a resultant in-crease in the magnitude of an,electrical signal coupled from the transducer element 42 to the amplifier 26.
Referring now to Figures 6 and 7, there is seen a system for sonic range finding and imaging. In Figure 6, there is shown one arrangement using the probe 20 and a transmitting transducer 80 for imaging living tissue such as that of a human leg 82. A signal generator 8~, in response to cloc~
pulses of a timer 86 provides electrical signals which are converted by the transducer 80 to sound waves which propagate into the leg 82, The transducer 80 and the probe 20 contact the leg 82 to provide a good acoustic path between the trans-mitter 80 and the leg 82, and between the probe 20 and the leg 82. If desired, the face of the probe 20 and of the -trans-;~ ~
313~
mitter 80 may be coated with a gel to insure that there are no air pockets, or voids, between the faces of the probe 20 and the transducer 80.
A preferred arrangement for the use of the probe 20 and the transmitting transducer 80 is shown in Figure 7 wherein a subject 88 which is to be imagecl is submerged within a liquid, such as water 90 enclosed within a container 92.
Good acoustical contact between the water and the probe 20 and the transducer 80 are obtained by emersing the complete probe 20 and the face of the transducer 80 into the water 90. To minimi~e the e~ect on the received sonic signal of interference with sound waves reflected from the surface of the water and the walls of the container 92, the probe 20 is spaced at a distance, thirty centimeters having been found to be sufficient, from the water surface and the walls o~ the container 92. Echoes obtained from material within the leg 82, or from material within the subject 88, are reflected back through the probe 20 to be presented on a display 9~. The timer 86 provides clock pulse signals to the display 94 so that the difference in times between the transmission and reception of the sonic signal appear as a measurement of depth of reflecting surfaces within the leg 82 or the subject 88.
The terminal 36 (seen in Figure 3) of the probe 20 is coupled to the display 94 while the terminal 34 of the probe 20 is coupled to a power supply 96 for powering the amplifier 26 of Figure 3 to amplify the echoes received by the probe 20.
In constructing the preferred embodiment, the rod 64 is `
formed of a silicone rubber which is absorbent of acoustic en-ergy, the rod 64 has a diameter of 1.5 millimeter (mm) and a length of 22 mm, the rod being available from Chomerics of ~1391~
Woburn, Massachusetts. The absorber 68 is 75 mm long and 5.5 mm in diameter, and is fabricated oE a linen phenolic material.
Terminal 40 is a copper rod of 1.0 mm diameter, the rod extend-ing a distance of 75 mm. The stainless steel tube of the neck housing 60 has an outer diameter of approximately 60 mm, and 0.25 mm wall thickness~ The cylindrical portion of the pod housing 30 has a length of 38 mm, while the flared portion is 25 mm in length as measured along the axis of the probe 20. The outer diameter of the pod 24 is 18 mm.
Returning to Figure 4, it is noted hy way of alternative embodiments, that other piezoelectric polymeric material having an acoustic impedance similar to that of water may be utilized since such materials would be essentially transparent to the propagation of sonic energy as is the polyvinylidene fluoride, also known as polyvinylidene di1uoride due to the two fluorine atoms in each monomer. For example, a plastic film, known commercially as Mylar, may be utilized, the film being metallized to serve as the electrodes. The reverber ation inhibiting structure of the rod 6~, the absorber 68 and the ring 70 of Figure 1 in combination with the acoustically transparent window 62 and the elongated neck housing 60 is applicable to a transducer element which is transparent to sonic energy coupled ~rom water, or material of similar acou-stic impedance, into the transducer element.
It is understood that the above described embodiments of the invention are illustrative only and that modifications thereof may occur to those skilled in the art. Accordingly, it is desired that this invention is not to be limited to the ~ embodiments disclosed herein but is to be limited only as de-fined by the appended claims.
conversion of sonic energy to electric energy thereby re-ducing the sensitivity of the probe. Furthermore, the ce-ramic materials utilized in transducers, in combination with their mechanical acoustic matching structures, provide a structure which is sufficiently resonant acoustically to inhibit the measurement of sonic pulses of relatively short durations, less than a microsecond duration, as are advan-tageously utilized in medical ultrasonics.
With a view towards providing transducers which are capable of receiving the foregoing submicrosecond sonic sig-nals with minimal distortion, consideration has been given to a material, other than the ceramics, which has piezoelec-tric properties and an acoustic impedance more nearly equal to that of water than is the impedance of the ceramics. One such material, polyvinylidene fluoride is commercially avail-able from the Penwalt Corporation of King of Prussia, Pennsyl-vania and EMI Limited, Middlesex, England. However, this polymeric material is presently obtainable only in thin ~ilms, typically 30 microns thick. The films are produced with met-allized layers on the top and the bottom surfaces by a depos-ition of, typically, aluminum on the surfaces. A problem a- -rises in that the physical structures which have been utilized in the fabrication of sonar transducers employing the relatively massive, rugged ceramic materials do not admit the use of the relatively light, fragile polymeric film.
Summary of the Invention The aforementioned problems are overcome and other advan-tages are provided by a transducer probe which is capable of receiving acoustic signals propagating in liquid media and living tissues wherein the acoustic signals include frequencies ranging up to one megahertz (MHz) and even higher frequencies with signal durations as short as a fractional microsecond interval. In accordance with the invention, the probe is provided with a transducer element formed of a piezoelectric ma'erial having an acoustic impedance substantially equal to that of water, and having metallization on the surfaces of the material for applying electric signals to the material.
Due to the substantial equality of impedance of the transducer element with the impedance of water, the transducer element may be viewed as being transparent to acoustic energy. The probe is preferably immersed fully in water for detecting sounds propagating in the water, the acoustic transparency minimizing interference of the transducer element to the propagation of sonic waves to permit observation of submicro-second sonic pulses.
- In a preferred embodiment of the invention, the trans-ducer element is formed of a film of a polymeric piezoelec-tric material such as polyvinylidene fluoride. The probe is formed with an elongated cylindrical or frusto-conical housing terminated by an acoustic window. The housing is typically fabricated of stainless steel to prevent a de-velopment of corrosion from liquids in which the probe may be immersed. The window is fabricated of a material which is substantially lossless to acoustic energy, and to further insure against acoustic losses, is fabricated with a thick-1~3493~
ness which should be less than approximately ten percent of the wavelength of the acoustic energy propagating through the window. In the preferred embodiment of the invention, a window thickness of less than one percent of the wave-length has been utilized. The window has been fabricated of stainless steel in a thickness of 0.025 millimeter (mm) since the stainless steel is sufficiently strong to permit the fabrication of such a thin window and for providing acoustical cond~ctivity through the window. In addition, the electrical conductivity of the stainless steel provides for electrical shielding of the transducer.
The transducer element is placed in physical contact with the window so that the window and the housing serve as an electrical contact for the transducer element. A second electrical contact is made by means of an electrically con-ducting sonic insulator. The sonic insulator is, preferably, a rubber rod for attenuating any sonic reverberations which might otherwise be induced within the housing. The rubber rod is formulated with metal particles to provide an elec-trical conductivity thereto, the rubber rod abutting the transducer element to secure it against the window while the electrical conductivity enables the rod to serve as the second electrical contact for the transducer élement. The cylinder of insulating material, such as a phenolic material, sur-rounds the rubber rod to serve as a spacer element and to provide electrical insulation between the rod and the housing.
A cylinder of insulating material also serves as an acoustic insulator to further attenuate any sonic reverberations which might otherwise develop within the housing. Any voids between the transducer element, the rod, and the insuIating cylinder, 1~39193~
are filled with oil to insure an acoustic transmission path which is free of resonance effects associated with an air pocket. An acoustically absorbent ring affixed to the peri-meter of the face of the probe, and a flaring of the back end of the probe, reduce the diffraction and reflection of acoustic waves for improved accuracy in the measurement of submicrosecond pulses.
In accordance with the present invention, there is provided a transducer assembly comprising: a polymeric piezo-electric element having front and back surfaces thereof; anelongated housing enclosing said piezoelectric element and having a substantially transparent acoustic window at an end thereof in contact wit~ said first surface of said piezoelectric element;
an elongated sound absorbing member in contact with said second surface of said piezoelectric element; a spacer member disposed circumferentially around said sound absorbing member and located between said sound absorbing member and said housing, said piezoelectric element having an acoustic impedance substantially equal in magnitude to the impedance of a medium to which said transducer assembly is acoustically coupled for the detection of sonic signals propagating in said medium; and means for isolating said polymeric piezoelectric element from sound waves diffracted from the edge of said acoustic window.
In accordance with the present invention, there is also provided a transducer assembly comprising: a piezoelectric element comprising a polymerized film having front and back surfaces thereof, there being front and back metallized films - ~ :
deposited, respectivelyl on said front and said back surfaces of said polymerized film; a housing enclosing said piezoelectric 30 element and having a window in contact with said first surface ~:
of said piezoelectric elément, said window being electrically conductive and transmissive of sonic energy, said window serving ~4S~39 as a first electrical terminal for said piezoelectric element;
a sound absorbing member in contact with said second metallized film, said sound absorbing member being electrically conductive and serving as a second electrical terminal for said piezoelec-tric element; and an amplifier disposed within said housing and electrically coupled to said polymerized film.
- 5a -,.t~
3L~'~
Brief Description of the Drawings _ _ _ The aforementioned aspects and other features of the invention are explained in the following description taken in connection with the accompanying drawings wherein:
Figure 1 is a sectional view of an acoustic probe con-structed in accordance with the invention;
Figure 2 is an enlarged view of a face of the probe of Figure 1 designated by an encircled region in Figure l;
Figure 3 is an end view of the probe of Figure 1 taken along the lines 3-3 of Figure 2;
Figure 4 shows a portion of a polymer film with metallized layers thereon which i.s utilized in forming the transducer ele ment seen in Figures 1 and 2;
Figure 5 is an alternative embodiment of the invention wherein the housing as provided with a frusto-conical shape for reducing sonic reverberations within the housing; and for reducing electrical capacitance between an electrically conducting rubber rod and the housing;
Figure 6 shows a sonic echo system.utilizing a conven-tional sound transmitter and the probe of Figure 1 for por-traying an image of the internal structure of living tissues;
Figure 7 is an alternative arrangement of the sound transmitter and probe of Fiyure 6 wherein the transmitter and the probe are immersed in a liquid for imaging an object submerged within the liquid.
Descrlption of the Preferred Embodlment Referring now to Figures 1, 2 and 3, an acoustic probe 20 which is constructed in accordance with the invention is seen to comprise a cylindrically shaped neck 22 and a pod 24 secured to the end of the neck 22, the neck 22 housing the acoustic sensing elements while the pod 24 houses the ele-ments of an electrical amplifier 26. The amplifier 26, which is of conventional design, for low noise figure, is shown diagrammatically and is seen to be mounted on a circuit board 28 which is enclosed by a housing 30 of the pod 24.
The board 28 is secured to a cover 32 of the housing 30 to facilitate the making of electrical connections between the amplifier 26 and the following terminals, namely, a terminal 34 which is a coaxial cable connector for the supplying of power to the amplifier 26, a terminal 36 which is a coaxial cable connector for providing the output signal of the ampli-fier 26, and a grounding terminal 38. The terminals 34, 36 and 38 are mounted on the cover 32. A socket 39 is coupled to the amplifier 26 and is secured to the board 28 for slid-: 20 ably mating with a terminal 40 which is coupled to a trans-ducer element 42 as wlll be descrlbed hereinafter.
Referring also to Figure 4, the transducer element 42-is fabricated in the form of a thin circular disc by cutting out a disc from a piezoelectric polymeric film 52, such as polyvinylidene fluoride having metallized layers 55-56 there-on. The layers 55 and 56 are formed by the deposition of a metal, such as aluminum or gold upon the front and back sur-faces of the film 52. The transducer element 42 has been con-structed with a diameter of l.S mm in one embodiment of the invention, the film 52 having a thickness of 30 microns. The ~L3g~3~
layers 55 and 56 are utilized Eor detecting an electric field which is generated within the film 52 in response to sound waves incident thereupon. While a film 52 having the afore-mentioned 30 micron thickness has been utilized in constructing the probe 20, it is believed that a thicker film would provide a greater efficiency in the conversion of sonic energy to elec-trical signals. With the use of piezoelectric poly~er o great-er thickness, the relatively thin disc shape of the transducer element 42 would have a thicker shape such as that of a tile.
Also, it is noted that, while the transducer element 42 has been fabricated with a circular shape, the transducer element 42 may alternatively be fabricated of a square shaped tile.
A feature of the invention is the mounting of the trans-ducer element 42 within a housing 60 of the neck 22 wherein the neck housing 60 provides both isolation from radio-fre-quency interference and sonic reverberations. The neck housing 60 is formed of a tubular section of an electrically conducting material, such as stainless steel, and is termin-ated at its front end with a window 62 which is constructed of an electrically conductive material which is resistant to corrosion and transmissive of sonic energy. In the preferred embodiment of the invention, the window 62 has been construc-ted of stainless steel since stainless steel, as has been noted hereinabove, is sufficiently strong to permit the fab-rication of the window 62 with a thickness of 0.025 mm, this thickness being less than one percent of a wavelength of the sound which is to be detected by the probe 20. Since stainless steel is propagative of sonic energy, and since the thickness is substantially less than the sonic wavelength, sound waves can propagate through the window 62 with essentially no reflec-. .
~13q~9 tion or attenuation, even though the acoustic impedance of bulk stainless steel r many wavelengths in thickness, is many times greater than that of water.
The acoustic impedance of the transducer element 42 closely approximates that of water so that, upon the con-tacting of the window with liviny tissue or a body of water as will be seen in Figures 6 and 7, sonic energy is able to propagate through the transducer element 42 with substantially no reflection therefrom, the transducer ele-ment 42 being essentially transparent to the sonic energy.
The metallized layers 55 and 56 have substantially less thickness than that of the film 52 and of the window 62 so as to appear essentially transparent to the sonic energy.
As seen in Figure 3, the transducer element 42 is placed in the front end of the neck 22 in contact with a back sur-face of the window 62 so that sonic energy can readily pro-pagate through the window 62 and into the transducer element 42. In addition, the contacting of the transducer element 42 with the window 62 provides for a path of electrical con-duction wherein the neck housing 60 and the window 62 with the front layer 55 provide an electrode for the transducer element 42.
A second electrode for the transducer 42 is provided by a rod 64 which is electrically coupled between the terminal 40 and the back layer 56 of the transducer element 42~ The rod 64 is constructed of electrically conductive, sound ab-sorbing material such as rubber which has been impregnated with metal particles. A disc 66 on the front end of the ter-minal 40 mates with the bac~ end of the rod 64 to insure elec-trical conduction between the rod 64 and the terminal 40. The ' ':, 31~3~39 terminal 40 is conveniently fabricated of a copper wire.
The rubber of the rod 64 has an acoustic impedance with a magnitude similar to that of the acoustic impedance of water so that the propagation of sonic energy from the transducer element 42 into the rod 64 is accomplished with a minimum oE
reflected energy thereby minimizing any ringing by the super-position of incident and reflected waves, and, thus, facili-tating the observation of short-duration acoustic signals in the submicrosecond range.
A further feature of the invention is the enclosing of the transducer element 42 and the rod 64 and the terminal 40 by an acoustic absorber 68, the absorber 68 having been fab-ricated of a phenolic material in the preferred embodiment of the invention. It is noted that the diameter of the trans-ducer element 42 is approximately equal to the length of two wavelengths of the sonic energy at a frequency of approximate-ly two megahertz (MHz), which frequency is often utilized in ultrasonic research. As may be seen in ~igure 3, the diam-eter of the neck housinq 60 is greater than that of the trans-ducer element 42 with the result that the interior dimensions of the neck 22 are su~ficiently large to admit the development of sonic reverberations in the absence of sound absorbing material such as that provided by the absorber 68 and the rod 64. Both the absorber 68 and the rod 64 absorb sonic energy, and thereby inhibit the formation of reverberations, while their acoustic impedances, which have`a magnitude similar to that of water and of the transducer element 42, promotes the propagation of sonic energy through the transducer element 42 with a minimum of reflection. Thereby, sonic signals detected by the transducer element 42 are essentially free of the in-- 10 ~
.
~3~l~3~
fluence of reflection and reverberation with the result that the aforementioned short-duration pulses of sonic energy can be observed.
To further improve the response of the probe 20 to the short-duration pulses of sonic energy, a ring 70 of an acous-ticly absorbingly material, such as rubber, is provided around the periphery of the window 62. The ring 70 has a smooth tapered outer surface to inhibit the diffraction of an incoming sonic wave about the edges of the window 62. Also, the pod housing 30 is provided with a front section 71 having a frusto-conical shape with a cone angle of approximately 20 to 40. The frusto-conical shape gives the probe 2n an increasing outer diameter which de-flects sound waves, travelling parallel to and alongside the neck housing 60, away from the probe 20. Thereby, there is substan-tially no reflection of the sound waves off the discontinuity formed by the back end of the probe 20. It has been found that, with a probe constructed in accordance with the preerred embodi-ment of the invention, sonic pulse durations of less than a half wavelength of the carrier frequency of the sound wave can be ob-served.
With respect to the electrical connections between the transducer element 42 and the amplifier 26, it is noted that the pod housing 30 is formed of a metal for electrical conduction, such as stainless steel, and is secured to the back end of the neck housing 60 in a conventional manner as by brazing or by screw threads. Similarly, the cover 32 is fabricated of metal and is secured to the pod housing 30 by a threaded ~etallic retainer ring 72. Thus, the terminal 38- is electrically con-nected via the c:over 32 and the pod housing 30 to the neck housing 60. Secure electrical contact between the disk 66 and , ~34~3~
the rod 64 is maintained by a center-bored screw 73 affixed to the terminal 40, the screw being threadedly secured to the back end of the absorber 68 for urging the disk 66 against the rod 64. Accordingly, the electrical conductors of the neck 22 are seen to be in a coaxial arrangement wherein the inner con-ductor is formed of the rod 64 and the terminal ~0 while the outer conductor is formed of the housings 60 and 30. The ab-sorber 68 thus serves as a dielectric spacer between the inner and the outer conductors.
In selecting a length of the rod 64, it is no-ted that in- :
creasing length of the rod 64 provides for increased attenua-tion of sonic reverberation, and also results in increased elec-tric capacitance between the inner and outer conductors of the coaxial arrangement. While Figure 1 shows a length of the rod 64 which is approximately one third the length of the neck hous-ing 60r a longer length of the rod 64 may be utilized, for exam-ple, a length of the rod 64 equal to approximately two thirds the length of the neck housing 60. While the shorter length of the rod 64 results in a somewhat reduced attenuation of sonic reverberations, since the terminal 40 has been found experimen-tally to contribute to the presence of the reverberations as does the neck housing 60, the reduced length of the rod 64 pro-vides the advantage of reduced capacitance between the inner and outer conductors with a resultant increase in the amplitude of the electric signal applied via the terminals 40 and 38 to the amplifier 26. A still further reduction in capacitance results by a reduction in the length of the neck housing 60.
In the assembly of the components of the probe 20, it is noted that a petroleum based oil, such as SAE 30 weight oil, has been placed along the interfaces between the transducer ~L~3~39 element 42, the window 62, the rod 64 and the absorber 68 for filling any voids along the interfaces which would otherwise be air pockets which tend to be resonant and introduce acou-stic discontinuities with attendant reverberations. The in-sertion of the oil into such voids removes such resonances and reverberations. The interior of the pod housing 30 is also filled with the oil. After insertion of the transducer element 42, the rod 64, and the terminal 40, the absorber 68 is then inserted via the pod 24 into the nec~ 22 in the space between the rod 64 and the neck housing 60. The circuit board 28 having the amplifier 26 thereon and attached to the cover 32, is then inserted into the pod 24 and positioned by the cover 32. An o-ring 74 is placed between the cover 32 and a shelf of the pod housing 30, the O-ring 74 and the oil within the pod housing 30 serving to prevent the entry of water or other contaminents into the pod 24 when the probe 20 is immersed as will be seen in Figure 7. The retainer ring 72 tightens the cover 32 against the O-ring 74. Upon insertion of the circuit board 28 into the pod 24, the socket 39 slidably mates with the terminal 40 to electrically connect the amplifier 26 with the transducer element 42.
Referring now to Figure 5, there is seen an alternative embodiment of the probe 20 of Figures 1-3, the embodiment of Figure 5 being identified as the probe 20A. The transducer element 42 and the window 62 are the same as that shown in Figure 1. Similarly, the amplifier 26 and the electrical connections made thereto are the same as that shown in Fig-ure 1. In Figure 5, improved immunity to reverberations is attained by modifying the cylindrical shape of the neck hous-ing 60 of Figure 3 to become a frusto~conical shaped housing - 13 ~
~349~9 60A in Figure 5. Similarly, the outer cylindrical surface of the absorber 68 of Figure 3 has assumed a frusto-conical shape in the absorber 68A of Figure 5. The ring 70 of Fig-ure 3 has been similarly modifled to provide the ring 70A of Figure 5 which mates with the housing 60A of Figure 5. The the rod 64 and the terminal 40 appear in the same form in the embodiments of both Figures 3 and 5. The reduced reverbera-tions are believed to be obtained by virtue of the fact that a sonic wave impinging upon the interior wall of the housing 60A in Figure 5 is re~lected in a direction generally along the axis of the probe 20A for attenuating the sound in the ab,sorber 68A. An additional feature of the embodiment of Figure 5 is found in the increasing separation between the rod 64 and the housing 60A with progression along the axis of the probe 20A towards the amplifier 26, the increasing separation providing for an increasing diminution in the magnitude of the electrical capacitance with a resultant in-crease in the magnitude of an,electrical signal coupled from the transducer element 42 to the amplifier 26.
Referring now to Figures 6 and 7, there is seen a system for sonic range finding and imaging. In Figure 6, there is shown one arrangement using the probe 20 and a transmitting transducer 80 for imaging living tissue such as that of a human leg 82. A signal generator 8~, in response to cloc~
pulses of a timer 86 provides electrical signals which are converted by the transducer 80 to sound waves which propagate into the leg 82, The transducer 80 and the probe 20 contact the leg 82 to provide a good acoustic path between the trans-mitter 80 and the leg 82, and between the probe 20 and the leg 82. If desired, the face of the probe 20 and of the -trans-;~ ~
313~
mitter 80 may be coated with a gel to insure that there are no air pockets, or voids, between the faces of the probe 20 and the transducer 80.
A preferred arrangement for the use of the probe 20 and the transmitting transducer 80 is shown in Figure 7 wherein a subject 88 which is to be imagecl is submerged within a liquid, such as water 90 enclosed within a container 92.
Good acoustical contact between the water and the probe 20 and the transducer 80 are obtained by emersing the complete probe 20 and the face of the transducer 80 into the water 90. To minimi~e the e~ect on the received sonic signal of interference with sound waves reflected from the surface of the water and the walls of the container 92, the probe 20 is spaced at a distance, thirty centimeters having been found to be sufficient, from the water surface and the walls o~ the container 92. Echoes obtained from material within the leg 82, or from material within the subject 88, are reflected back through the probe 20 to be presented on a display 9~. The timer 86 provides clock pulse signals to the display 94 so that the difference in times between the transmission and reception of the sonic signal appear as a measurement of depth of reflecting surfaces within the leg 82 or the subject 88.
The terminal 36 (seen in Figure 3) of the probe 20 is coupled to the display 94 while the terminal 34 of the probe 20 is coupled to a power supply 96 for powering the amplifier 26 of Figure 3 to amplify the echoes received by the probe 20.
In constructing the preferred embodiment, the rod 64 is `
formed of a silicone rubber which is absorbent of acoustic en-ergy, the rod 64 has a diameter of 1.5 millimeter (mm) and a length of 22 mm, the rod being available from Chomerics of ~1391~
Woburn, Massachusetts. The absorber 68 is 75 mm long and 5.5 mm in diameter, and is fabricated oE a linen phenolic material.
Terminal 40 is a copper rod of 1.0 mm diameter, the rod extend-ing a distance of 75 mm. The stainless steel tube of the neck housing 60 has an outer diameter of approximately 60 mm, and 0.25 mm wall thickness~ The cylindrical portion of the pod housing 30 has a length of 38 mm, while the flared portion is 25 mm in length as measured along the axis of the probe 20. The outer diameter of the pod 24 is 18 mm.
Returning to Figure 4, it is noted hy way of alternative embodiments, that other piezoelectric polymeric material having an acoustic impedance similar to that of water may be utilized since such materials would be essentially transparent to the propagation of sonic energy as is the polyvinylidene fluoride, also known as polyvinylidene di1uoride due to the two fluorine atoms in each monomer. For example, a plastic film, known commercially as Mylar, may be utilized, the film being metallized to serve as the electrodes. The reverber ation inhibiting structure of the rod 6~, the absorber 68 and the ring 70 of Figure 1 in combination with the acoustically transparent window 62 and the elongated neck housing 60 is applicable to a transducer element which is transparent to sonic energy coupled ~rom water, or material of similar acou-stic impedance, into the transducer element.
It is understood that the above described embodiments of the invention are illustrative only and that modifications thereof may occur to those skilled in the art. Accordingly, it is desired that this invention is not to be limited to the ~ embodiments disclosed herein but is to be limited only as de-fined by the appended claims.
Claims (15)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A transducer assembly comprising:
a polymeric piezoelectric element having front and back surfaces thereof;
an elongated housing enclosing said piezoelectric ele-ment and having a substantially transparent acoustic window at an end thereof in contact with said first surface of said piezo-electric element;
an elongated sound absorbing member in contact with said second surface of said piezoelectric element;
a spacer member disposed circumferentially around said sound absorbing member and located between said sound absorbing member and said housing, said piezoelectric element having an acoustic impedance substantially equal in magnitude to the impedance of a medium to which said transducer assembly is acoustically coupled for the detection of sonic signals propa-gating in said medium; and means for isolating said polymeric piezoelectric element from sound waves diffracted from the edge of said acoustic window.
a polymeric piezoelectric element having front and back surfaces thereof;
an elongated housing enclosing said piezoelectric ele-ment and having a substantially transparent acoustic window at an end thereof in contact with said first surface of said piezo-electric element;
an elongated sound absorbing member in contact with said second surface of said piezoelectric element;
a spacer member disposed circumferentially around said sound absorbing member and located between said sound absorbing member and said housing, said piezoelectric element having an acoustic impedance substantially equal in magnitude to the impedance of a medium to which said transducer assembly is acoustically coupled for the detection of sonic signals propa-gating in said medium; and means for isolating said polymeric piezoelectric element from sound waves diffracted from the edge of said acoustic window.
2. A transducer assembly according to claim 1 wherein said sound absorber and said spacer member are fabricated of materials which attenuate sound waves substantially, said materials having acoustic impedances which are substantially equal in magnitude to the impedance of said polymeric piezo-electric element.
3. A transducer assembly according to claim 2 wherein said sound absorber is electrically conductive for conducting an electrical signal to a terminal of said transducer element, and wherein said housing is electrically conducting for conducting electrical signals to another terminal of said piezo-electric element.
4. A transducer assembly according to claim 1 further comprising:
means for substantially eliminating reflections of sound waves from the exterior of said housing.
means for substantially eliminating reflections of sound waves from the exterior of said housing.
5. A transducer assembly according to claim 4 wherein:
said reflection eliminating means comprise an out-wardly flaring portion of said housing.
said reflection eliminating means comprise an out-wardly flaring portion of said housing.
6. A transducer assembly according to claim 1 wherein:
said isolating means comprise an acoustically absorb-ing element disposed along the periphery of said acoustic window.
said isolating means comprise an acoustically absorb-ing element disposed along the periphery of said acoustic window.
7. A transducer assembly according to claim 2 wherein:
said sound absorbing member comprises a metallized resilient rod.
said sound absorbing member comprises a metallized resilient rod.
8. A transducer assembly according to claim 3 further comprising:
an amplifier disposed in close proximity and electri-cally coupled to said polymeric piezoelectric element.
an amplifier disposed in close proximity and electri-cally coupled to said polymeric piezoelectric element.
9. A transducer assembly according to claim 3 wherein:
the relative dimensions of said electrically conduc-tive sound absorbing member, said spacer member and said housing reduce the electrical capacitance of said assembly.
the relative dimensions of said electrically conduc-tive sound absorbing member, said spacer member and said housing reduce the electrical capacitance of said assembly.
10. A transducer assembly comprising:
a piezoelectric element comprising a polymerized film having front and back surfaces thereof, there being front and back metallized films deposited, respectively, on said front and said back surfaces of said polymerized film;
a housing enclosing said piezoelectric element and having a window in contact with said first surface of said piezoelectric element, said window being electrically conductive and transmissive of sonic energy, said window serving as a first electrical terminal for said piezoelectric element;
a sound absorbing member in contact with said second metallized film, said sound absorbing member being electrically conductive and serving as a second electrical terminal for said piezoelectric element; and an amplifier disposed within said housing and electri-cally coupled to said polymerized film.
a piezoelectric element comprising a polymerized film having front and back surfaces thereof, there being front and back metallized films deposited, respectively, on said front and said back surfaces of said polymerized film;
a housing enclosing said piezoelectric element and having a window in contact with said first surface of said piezoelectric element, said window being electrically conductive and transmissive of sonic energy, said window serving as a first electrical terminal for said piezoelectric element;
a sound absorbing member in contact with said second metallized film, said sound absorbing member being electrically conductive and serving as a second electrical terminal for said piezoelectric element; and an amplifier disposed within said housing and electri-cally coupled to said polymerized film.
11. A transducer assembly according to claim 6 wherein said sound absorbing member comprises a metallized rubber rod for securing said polymerized film against said window.
12. A transducer assembly according to claim 6 further comprising:
means for reducing the electrical capacitance between said housing and said sound absorbing member.
means for reducing the electrical capacitance between said housing and said sound absorbing member.
13. A transducer assembly according to claim 12 wherein:
said capacitance reducing means comprise an electri-cally insulating spacer member of sound absorbing material, said spacer member being located between said electrically conductive sound absorbing member and said housing.
said capacitance reducing means comprise an electri-cally insulating spacer member of sound absorbing material, said spacer member being located between said electrically conductive sound absorbing member and said housing.
14. A transducer assembly according to claim 6 further comprising:
a sound absorbing ring member disposed along the periphery of said window.
a sound absorbing ring member disposed along the periphery of said window.
15. A transducer assembly according to claim 12 wherein:
said polymerized film has a size of the order of a wavelength of the sonic energy used.
"
said polymerized film has a size of the order of a wavelength of the sonic energy used.
"
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/099,438 US4316115A (en) | 1979-12-03 | 1979-12-03 | Polymeric piezoelectric microprobe with damper |
| US099,438 | 1979-12-03 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1134939A true CA1134939A (en) | 1982-11-02 |
Family
ID=22275011
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000361678A Expired CA1134939A (en) | 1979-12-03 | 1980-10-07 | Polymeric piezoelectric microprobe having a damper |
Country Status (2)
| Country | Link |
|---|---|
| US (1) | US4316115A (en) |
| CA (1) | CA1134939A (en) |
Families Citing this family (29)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4410825A (en) * | 1981-04-10 | 1983-10-18 | Lobastov George S | Piezoelectric pressure transducer with threaded damper bar |
| US4628928A (en) * | 1982-08-09 | 1986-12-16 | Medtronic, Inc. | Robotic implantable medical device and/or component restoration system |
| US4771772A (en) * | 1982-08-09 | 1988-09-20 | Medtronic, Inc. | Robotic implantable medical device and/or component restoration system |
| US4628907A (en) * | 1984-03-22 | 1986-12-16 | Epley John M | Direct contact hearing aid apparatus |
| US4608507A (en) * | 1984-06-29 | 1986-08-26 | Micro Pure Systems, Inc. | Damping device for focused piezoelectric transducer |
| DE8507700U1 (en) * | 1985-03-15 | 1985-08-22 | Rheintechnik Weiland & Kaspar Kg, 6680 Neunkirchen | Device for determining the pregnancy of female pets |
| FR2646309B1 (en) * | 1989-04-24 | 1997-01-31 | Technomed Int Sa | METHOD FOR MANUFACTURING AN ACOUSTIC SENSOR AND ACOUSTIC SENSOR THUS OBTAINED, WITH A PROTECTIVE LAYER |
| EP0425716B1 (en) * | 1989-10-30 | 1994-01-19 | Siemens Aktiengesellschaft | Ultrasonic layered transducer with astigmatic sound lobe |
| US5125137A (en) * | 1990-09-06 | 1992-06-30 | Cardiometrics, Inc. | Method for providing a miniature ultrasound high efficiency transducer assembly |
| US5059851A (en) * | 1990-09-06 | 1991-10-22 | Cardiometrics, Inc. | Miniature ultrasound high efficiency transducer assembly, guidewire using the same and method |
| US5811680A (en) * | 1993-06-13 | 1998-09-22 | Technion Research & Development Foundation Ltd. | Method and apparatus for testing the quality of fruit |
| US5724315A (en) * | 1996-05-29 | 1998-03-03 | The United States Of America As Represented By The Secretary Of The Navy | Omnidirectional ultrasonic microprobe hydrophone |
| US5899847A (en) * | 1996-08-07 | 1999-05-04 | St. Croix Medical, Inc. | Implantable middle-ear hearing assist system using piezoelectric transducer film |
| US6339961B1 (en) * | 1996-11-15 | 2002-01-22 | Ue Systems, Inc. | Ultrasonic detecting lubrication apparatus with acoustically isolated transducer |
| AU6531200A (en) * | 1999-08-09 | 2001-03-05 | Cross Match Technologies, Inc. | Piezoelectric film fingerprint scanner |
| US6324907B1 (en) * | 1999-11-29 | 2001-12-04 | Microtronic A/S | Flexible substrate transducer assembly |
| US20030001459A1 (en) * | 2000-03-23 | 2003-01-02 | Cross Match Technologies, Inc. | Secure wireless sales transaction using print information to verify a purchaser's identity |
| KR100887275B1 (en) * | 2000-03-23 | 2009-03-06 | 크로스 매치 테크놀로지스, 인크. | Piezoelectric identification device and applications thereof |
| US7132780B2 (en) * | 2000-03-23 | 2006-11-07 | Cross Match Technologies, Inc. | Method for obtaining biometric data for an individual in a secure transaction |
| US7067962B2 (en) | 2000-03-23 | 2006-06-27 | Cross Match Technologies, Inc. | Multiplexer for a piezo ceramic identification device |
| US20060008432A1 (en) * | 2004-07-07 | 2006-01-12 | Sebastiano Scarampi | Gilsonite derived pharmaceutical delivery compositions and methods: nail applications |
| US20060006361A1 (en) * | 2004-07-08 | 2006-01-12 | Joseph Callerame | Clathrate of chlorine dioxide |
| US8334637B2 (en) * | 2006-09-18 | 2012-12-18 | Liposonix, Inc. | Transducer with shield |
| US7652411B2 (en) * | 2006-09-18 | 2010-01-26 | Medicis Technologies Corporation | Transducer with shield |
| EP1923145A1 (en) * | 2006-11-15 | 2008-05-21 | Nederlandse Organisatie voor toegepast-natuurwetenschappelijk Onderzoek TNO | Remote ultrasonic transducer system |
| US8264126B2 (en) * | 2009-09-01 | 2012-09-11 | Measurement Specialties, Inc. | Multilayer acoustic impedance converter for ultrasonic transducers |
| US9673604B2 (en) * | 2015-05-05 | 2017-06-06 | Gregory L. Weipert | Coaxial cable terminator assembly having a substrate with inner and outer termination connections carried by a cap |
| DE102016101154B4 (en) * | 2016-01-22 | 2024-03-14 | Krohne Ag | Ultrasonic transducer |
| CZ201984A3 (en) | 2019-02-13 | 2020-04-01 | České vysoké učenà technické v Praze | Miniature sound pressure sensor in liquids and gases |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1967130C2 (en) * | 1968-01-25 | 1982-04-01 | Pioneer Electronic Corp., Tokyo | Mechanical-electrical or electrical-mechanical converter |
| US3553501A (en) * | 1968-02-16 | 1971-01-05 | Us Interior | Ultrasonic piezoelectric transducer cartridge |
| JPS5123439B2 (en) * | 1971-11-05 | 1976-07-16 | ||
| US3855847A (en) * | 1972-06-20 | 1974-12-24 | Westinghouse Electric Corp | Acoustic emission transducer and monitoring system |
| US3794866A (en) * | 1972-11-09 | 1974-02-26 | Automation Ind Inc | Ultrasonic search unit construction |
| US3921442A (en) * | 1973-11-28 | 1975-11-25 | Automation Ind Inc | Acoustic couplant for use with an ultrasonic search unit |
| US3925692A (en) * | 1974-06-13 | 1975-12-09 | Westinghouse Electric Corp | Replaceable element ultrasonic flowmeter transducer |
-
1979
- 1979-12-03 US US06/099,438 patent/US4316115A/en not_active Expired - Lifetime
-
1980
- 1980-10-07 CA CA000361678A patent/CA1134939A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| US4316115A (en) | 1982-02-16 |
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