WO2006011831A1

WO2006011831A1 - Device for encoding on a surface acoustic waves for a passive transponder unit

Info

Publication number: WO2006011831A1
Application number: PCT/RU2005/000390
Authority: WO
Inventors: Sergei Aleksandrovich Zabuzov; Sergei Mikhailovich Larionov; Vladimir Grigoryevich Mikheev; Sergei Anatolievich GOLOVIN; Andrei Evgenyevich Tyulin; Vasily Nikolaevich Tikmenov; Nikolai Yakovlevich Markov
Original assignee: Sergei Aleksandrovich Zabuzov; Sergei Mikhailovich Larionov; Vladimir Grigoryevich Mikheev; Golovin Sergei Anatolyevich; Andrei Evgenyevich Tyulin; Vasily Nikolaevich Tikmenov; Nikolai Yakovlevich Markov
Priority date: 2004-07-20
Filing date: 2005-07-19
Publication date: 2006-02-02
Also published as: RU2270517C1

Abstract

The invention relates to radar engineering and can be used for recording an individual code combination in the passive transponders of systems for radiofrequency identification of mobile and stationary objects. The aim of said invention is to increase the number of admissible code combinations without increasing the overall size of the crystal of a piezoelectric substrate, thereby increasing a transponder information capacity. The inventive device for encoding on surface acoustic waves comprises a piezoelectric substrate and N pairs of opposite-finger transducers which are placed on the substrate. Each pair consists of an input and an output opposite-finger transducer and is tuned on a determined operating frequency. N input opposite-finger transducers to which the request signal is transmitted are arranged along the substrate width on the same plane one under another and electrically in parallel connected to each other. N output opposite-finger transducers from which a response signal is transmitted are step-wisely disposed along the substrate width in corresponding positions with respect to the input opposite-finger transducers. Said output opposite-finger transducers are arranged in the adjacent rows either to the left of the output opposite-finger transducer disposed in the previous row or to the right thereof and are electrically in parallel connected to each other

Description

DESCRIPTION

Surface acoustic wave coding device for passive transponder.

The proposed technical solution relates to radar technology, in particular, to transponders for radio-frequency identification systems of moving and stationary objects.

Radio frequency identification and registration systems (RFID systems) became widespread in the early 90s. In these systems, the object is identified by a unique digital code emitted by a transponder tag attached to the object. The transponder is polled automatically using a transceiver (reader). Currently, depending on the requirements of the system, both active, powered by a built-in battery, and passive transponders are used. The energy necessary for the formation of the response signal, the passive transponder receives from the energy of the request signal of the reader. The reader can interrogate a transponder due to ultrasonic, light or other energy.

The existing RFID systems of various manufacturers, as a rule, differ in the radius of action, the carrier frequency of the signals used, the type of modulation, the radio protocol and the amount of information returned by the transponder tag.

At the moment, high-frequency transponder devices that allow the identification of objects on

SUBSTITUTE SHEET (RULE 26) distances large enough to 15 meters and moving at speeds of up to 200 km / h.

A significant reduction in the cost of high-frequency equipment is possible due to the use of surface acoustic wave (SAW) devices in RFID systems.

Known marker device according to the patent of the Russian Federation JVa 2176092, IPC ⁷ GOlS 13/79, published November 20, 2001. The marker device for the RFID system contains a board and a receiving and emitting antenna placed on it, as well as a device for surface acoustic waves made in the form of a substrate of piezoelectric material, on which the input and output interdigital transducers (VPS) are located. Moreover, the output IDT is a pair of electrodes connected to the summing buses in accordance with a pre-selected code. The maximum number of code combinations for this device is 2 ^N , where N is the number of pairs of output electrodes. With the actually acceptable dimensions of the device for surfactants for markers, the number of N characters varies from 16 to 32. A further increase in the number N leads to unacceptably large sizes of the substrate of the device. In addition, the maximum number of output electrodes is limited by the attenuation of the surfactant propagating through the sound duct. The closest analogue to the claimed technical solution is a device for surfactants with parallel acoustic wave propagation paths described in US patent J64620191, IPC GOlS 013/80, published on 10/28/86.

The known surface acoustic wave (SAW) coding device for a passive transponder used in object identification systems comprises a piezoelectric substrate and N pairs of interdigital

REPLACING LTSY ^{^} Щ ^ ВЫЛb ^' iб) ^' transducers (IDT) located on the surface of the piezoelectric substrate in parallel rows along its width, and each pair of IDTs consists of one input IDT and one output IDT and is tuned to a specific operating frequency. The input IDTs to which the request signal arrives are located across the width of the substrate in one plane, one below the other. While the output IDTs can be arranged stepwise across the width of the substrate, or in different parts of the substrate. Electrically input and output IDTs can be interconnected both in series and in parallel.

The location of the output converters proposed in the prototype is due to the need to reduce the influence of interference from one acoustic surfactant propagation channel to another. Phase coding of the response signal is performed by the so-called phase pads, i.e. metallization sites of sections of the sound duct in front of the electrodes of the output transducers, on which the SAW propagation speed is lower than on the free surface of the sound duct due to shorting the tangential component of the electric field.

The disadvantages of the above device is the complexity of the topological execution of the output Converter and the inability to obtain a large number of code combinations on the limited working area of the substrate of the device for surfactants. For a SAW device, the accuracy of performing phase pads for frequencies of about 1 GHz should be at least 0.01 μm, which is very difficult for the modern development of the technical level of precision lithography. In addition, the number of code variations in a line of such a device, not exceeding four characters in a horizontal line, is 2, that is, 16. It is difficult to imagine the implementation of such a device at a frequency of 2.45 GHz, since there are currently no technical manufacturing tools for its implementation.

SUBSTITUTE SHEET (RULE 26) Thus, in the presence of the number of parallel acoustic channels (5-7), which corresponds to the actual dimensions of the maximum width of the manufactured substrates from synthetic piezoelectric materials, the maximum possible number of code combinations for this device does not exceed 120. The objective of the present invention is to provide such a SAW encoding device for a transponder in which a significant increase in the number of possible code combinations is achieved without increasing the overall crystal size of the piezoelectric substrate.

The problem is solved in that in a coding device for surface acoustic waves (SAW) for a passive transponder used in object identification systems containing a piezoelectric substrate and N pairs of interdigital transducers (IDT) located on the surface of the piezoelectric substrate in parallel rows along its width and each pair of IDTs consists of one input IDT and one output

IDT and tuned to a specific operating frequency,

The N input IDTs to which the request signal arrives are located across the width of the substrate in one plane one below the other and are connected electrically in parallel with each other, N output IDTs, from which the response signal is taken, are located stepwise along the width of the substrate at the base positions relative to the corresponding input IDTs, moreover, the output IDTs are located in adjacent rows either to the left of the output IDT in the previous row, or to the right of it, and are also electrically connected in parallel with each other,

SUBSTITUTE SHEET (RULE 26) it is proposed that at least two IDT pairs have different operating frequencies selected from M different values, the alternation of IDT pairs having different operating frequencies would be individual for each SAW device and correspond to a pre-selected code combination. Each of the N output IDTs can be set along the length of the substrate with a shift relative to the base position in one of the fixed positions, individual for each SAW device and the corresponding pre-selected code combination. Thus, the maximum number of code combinations for this device will be - (MxL) ^N , where M is the number of operating frequencies of the device, L is the number of fixed positions of the output IDT, including the base, N is the number of IDT pairs.

Due to the use in the proposed device of various operating frequencies that are configured with different pairs of converters and the introduction of additional spatial positioning of the output IDTs, it is possible to significantly increase the number of possible code combinations that the device can contain. In this case, the dimensions of the substrate do not increase, because the distances between the additional positions on which it is proposed to shift the output IDTs and the basic positions of the output IDTs are insignificant. An additional feature of the encoding device is that one of the IDT pairs in which the output IDT is located at a fixed distance from the input ID at a minimum distance is made in the form of a reference one, which sets the initial delay of operation of the output IDTs.

SUBSTITUTE SHEET (RULE 26) The introduction of an additional line with reference transducers makes it possible to achieve a more accurate reference of time intervals in the output signal, which is equivalent to the exact determination of the spatial position of the output IDTs.

The distance between the input and output reference converters determines the initial, reference delay of the device (Tnach).

Another additional difference is that in a SAW device for a passive transponder, M is chosen to be two and L is three, which corresponds to the most optimal ratio between the number of code combinations of the device and the cost of its manufacture. The essence of the inventive coding device for SAW for the transponder is illustrated by drawings.

In FIG. 1 shows the general case of the implementation of a coding device for SAWs, where 1 piezoelectric substrate, 2 input reference IDT, 3 output reference IDT, 4 input IDT, 5 output IDF frequency (spatial period) of reference IDT,

N is the number of input and output IDTs. Its maximum value is determined by the ratio of the maximum possible width of the substrate to the minimum possible aperture of the IDT constituting the row.

M is the number of frequencies (spatial periods) of the device. The maximum value is determined by the quotient of the division of the allowed working band and the IDT band.

L-number of fixed positions that each output IDT in a row can occupy. The maximum number L is determined by the maximum length of the sound duct and the number of partial output IDTs (the maximum possible number of lines).

In real technically feasible devices, N can reach 10-12, M can be 5-7, and L can be 3-4.

SUBSTITUTE SHEET (RULE 26) Figure 2 shows an example implementation of the inventive device with four operating frequencies, to graphically simplify IDTs are shown in the form of rectangles.

On Fig.3 shows the amplitude-frequency characteristic (module gain) for an example implementation of the device shown in figure 2.

Figure 4 shows the spatial frequency-coded pulse train of the transponder responses for an example implementation of the device shown in figure 2 (impulse response of the device).

A description of the operation of the device in the implementation example shown in figure 2.

Each line, consisting of an input and output partial IDT, has its own frequency channel Δfi, Δfг, Δfз, and Δ £ t. In addition, each frequency channel has its own central frequency: fϊ, fg, fz and £ ". Since the input and output partial IDTs in each of its group are electrically connected in parallel, the general view of the frequency response of the device has a comb structure, shown in Fig. 4

The order of change of these frequencies in the vertical line of the input IDT is the frequency encoding of the device. For the device in question, the frequency code will look like this: f2-fz-fi- £ t (if you assign a binary code to each frequency, then this frequency sequence can be expressed in a digital binary code).

At the same time, each output IDT in its row can occupy one of the fixed positions, relative to the basic ones. These are: 0, + Δt, - Δt, +2 Δt, -2 Δt.

The output IDTs can occupy in their line either the basic - zero position, indicated in figures 1 and 2 by the number 0, or one of the additional positions,

SUBSTITUTE SHEET (RULE 26) close to the base and shifted from it by any discrete value - plus / minus (s Δt), where s is an integer (Fig. 2). The encoding is the spatial arrangement of the output IDTs in rows in accordance with a pre-selected code combination. The minimum spatial shift of the output IDT, corresponding to the minimum discrete value Δt, can be half the wavelength of the surfactant corresponding to the frequency of this series of devices. In this case, the phase shift of the output signal will be 180 degrees relative to the input signal, i.e. phase manipulation of the output signal will be carried out.

When interrogating a transponder with such an encoding device with a short radio pulse coming from the reader, a pulse with a wide spectrum that covers the entire operating band - ΔF of the device, the response will be the spatial frequency-coded sequence shown in Fig. 4. In this sequence, the first from the origin, i.e. reference radio pulse, and the first in time of arrival is a pulse with a frequency f ₂ . The next in the sequence will be a radio pulse with a frequency fz. Then a signal with a frequency ft will follow, with fi <fg <fz. For another instance of a device for a SAW, the frequency alternation will be different, for example, fz, U, fg and fi, and the temporal position of the sequence pulses may also change. The second pulse can be shifted relative to its reference position along the direction of surfactant propagation by +2 Δt, and the third pulse by -Δt. Thus, for each specific instance of a device on a SAW, a unique code is implemented that is unique to it, and the number of searches of such codes is determined from the expression - (M ^χ L) ^N. A device similar to that described can be manufactured on high-precision photo-typing equipment with an accuracy of positioning elements of 0.02-0.03 μm,

SUBSTITUTE SHEET (RULE 26) with minimum element sizes of 0.35 - 0.40 microns, which corresponds to operating frequencies of a surfactant of about 2.5 GHz.

The technical and economic effect of the proposed technical solution consists in the fact that, while maintaining the technical requirements for the accuracy of technological equipment and the fixed geometric dimensions of the sound duct of a SAW device, it is possible to increase by more than two orders of the information capacity of a transponder for a SAW while maintaining its geometric dimensions. So, for example, over 4.5 billion code options can be achieved on sound ducts measuring 10xl0x0.5mm.

SUBSTITUTE SHEET (RULE 26)

Claims

CLAIM

1. A coding device for surface acoustic waves for a passive transponder used in object identification systems containing a piezoelectric substrate and

N pairs of interdigital transducers (LIS) located on the surface of the piezoelectric substrate in parallel rows along its width, each pair of IDTs consisting of one input IDT and one output IDT and tuned to a specific operating frequency, N input IDTs to which a request signal is received are located across the width of the substrate in one plane one below the other and are electrically connected in parallel with each other,

N output IDTs from which the response signal is taken are arranged in steps along the width of the substrate in basic positions relative to the input IDTs, the output IDTs being located in adjacent rows either to the left of the output IDT in the previous row or to the right of it, and are also electrically connected in parallel , characterized in that at least two IDT pairs have different operating frequencies, selected from M different values, the alternation of IDT pairs having different operating frequencies, individually for each device on the SAW and corresponds to her selected code combination, each of N output IDTs may be set with a shift relative to the reference position in one of the fixed positions for each individual SAW devices and the corresponding pre-selected code,

SUBSTITUTE SHEET (RULE 26) thus, the maximum number of code combinations for this device is - (M ^χ L) ^N , where M is the number of operating frequencies of the device, L is the number of fixed positions of the output IPS, including the base, N is the number of IDT pairs.

2. The device according to p. 1, characterized in that one of the pairs of IDT, in which the output

IDT is located from the input at the minimum possible distance in the base position is selected as the reference, which sets the initial delay of the output IDT.

3. The device according to claims 1 to 2, characterized in that M is two and L is three.

SUBSTITUTE SHEET (RULE 26)