WO2006030060A1

WO2006030060A1 - Testing arrangement for rfid transponders

Info

Publication number: WO2006030060A1
Application number: PCT/FI2005/000388
Authority: WO
Inventors: Francisco Nieto Montesano; Juan Carlos Pênás MANRIQUE
Original assignee: Upm Rafsec Oy
Priority date: 2004-09-14
Filing date: 2005-09-09
Publication date: 2006-03-23
Also published as: FI20045341A0; FI116989B

Abstract

The invention relates to a device (2) for testing a transponder (6). The device (2) comprises at least a radiating element (2.1) for radiating RF energy to the transponder (6), and a receiving element (2.2) for receiving RF energy coupled from the radiating element (2.1) via a resonant circuit of the transponder (6). The radiating element (2.1) and the receiving element (2.2) are antennas. The invention also relates to a system and a method.

Description

Testing arrangement for RFID transponders

Field of the Invention

The present invention relates to a device for testing a transponder), the device comprising at least a radiating element for radiating RF energy to the transponder , and a receiving element for receiving RF energy coupled from the radiating element via a resonant circuit of the transponder. The invention also relates to a system for testing a transponder , the system comprising a measurement probe which comprises at least a radiating element for radiating RF energy to the transponder , and a receiving element for receiving RF energy coupled from the radiating element via a resonant circuit of the transponder. The invention further relates to a method for testing a transponder, the method comprising connecting RF energy to a radiating element of a measurement probe for radiating the RF energy to the transponder, and receiving by a receiving element RF energy coupled from the radiating element via a resonant circuit of the transponder.

Background of the Invention

Passive RFID transponders get their energy from the RF field generated by a device usually referred as a RFID Reader or Coupler. There are several normalized frequencies to provide this RF field, and the transponder has to be matched to operate in one of these standard frequencies. It means that the electrical characteristics of the transponders have to be optimised to give maximum response at the required frequency, according to a set of design specifications.

The accurate and repeatable measurement of the electrical characteristics of RFID transponders is a key factor for the transponder manufacturing industry at the design and manufacturing stages of the process.

At design time, a method for comparing performance of the different design alternatives being evaluated should be provided. The transponder resonant frequency has to match the design criteria, in order to give its maximum response (that is, the maximum energization distance), while the Quality factor (Q), has to be chosen to allow the required signal bandwidth for the data transmission (reader to transponder and transponder to reader communication).

At manufacturing stage, it is necessary to check the electrical characteristics against specified manufacturing limits. Transponders whose resonant frequency and/or Q factor lies outside the specification limits, will not perform as required, and as a consequence have to be rejected.

Some contactless methods have been developed to avoid the need to connect a measuring probe to the transponder under test. In a Japanese patent application JP 07-248347 a testing device for contactless testing is presented. The testing device comprises two inductances which are located coaxially parallel. When the RFID transponder is to be tested the testing device needs to be positioned near the antenna resonance circuit preferably in such a way that the axes of the inductances of the testing device and the inductance of the antenna resonance circuit are coaxial. One of the inductances of the testing device radiates electromagnetic energy at a certain frequency. The other inductance of the testing device is used as a receiver for the radiated electromagnetic energy. The ratio between the radiated and received energy is affected by the mutual inductances between the radiating inductance and the inductance of the antenna resonance circuit of the RFID transponder and between the receiving inductance and the inductance of the antenna resonance circuit of the RFID transponder.

However, this kind of approach can only be used for lower frequencies but it becomes impractical as the frequency gets higher. Further, the electrical characteristic of the sensor and detector windings have to be measured.

Summary of the Invention

In the present invention there is provided a contactless method for measuring electrical characteristics of RFID transponders, based on the coupling of two uncoupled antennas through the transponder resonant circuit. One of the antennas is used as a transmission antenna. It radiates RF energy in the frequency range of interest. The other antenna is used as a reception antenna. The geometry and environment of the antennas have been carefully designed to provide as much isolation as possible between them in order to minimize coupling. In this condition, the energy detected by the RX antenna coming from the TX antenna is kept below a certain level in the frequency range of interest. This level will define the sensitivity of the measuring antenna.

To put it more precisely, the device according to the present invention is primarily characterised in that the radiating element and the receiving element are antennas. The system according to the present invention is primarily characterised in that the radiating element and the receiving element are antennas. The method according to the present invention is primarily characterised in that the method comprises using antennas as the radiating element and the receiving element .

The antenna according to the present invention solves the problem of the coupling between the transponder under test, and the testing device (e.g. a spectrum analyser or a network analyser). The antenna constitutes a specialised test probe for the measurement of this type of electronic devices.

The contactless method according to the invention offers some advantages over previous contact methods based on RF measurements using standard RF probes. First, it is easier to implement in particular in manufacturing environments because no precise mechanics is needed to make the electrical contact with the transponder circuit. It also reduces (when properly designed) the effect of the measuring device on the measurement.

In manufacturing environments, only a functional test was usually performed (reading and/or writing the transponder memory contents). The possibility to include electrical tests on the test procedure provides additional data to accept/reject samples, and to take decisions based on statistical information to control the manufacturing process.

Description of the Drawings

In the following the invention will be described in more detail with reference to the appended drawings, in which Fig. 1 depicts a system according to an example embodiment of the present invention as a block diagram,

Fig. 2 depicts an example of a measurement probe according to the present invention, and

Fig. 3 shows an example of measurement results of a test performed by the system according to the present invention.

Detailed Description of the Invention

In Fig. 1 an example of the system 1 of the present invention is illustrated as a block diagram. In this example the system comprises a measurement probe 2, a frequency generator 3, a receiver 4, and an analysing device 5 which comprises e.g. a display 5.1 for presenting measurement results and memory 5.2 for storing the measurement results. The probe 2 comprises a radiating element 2.1 and a receiving element 2.2. There is also a shielding 2.3 between the radiating element 2.1 and the receiving element 2.2 to minimize the mutual coupling between the radiating 2. land the receiving elements 2.2. The frequency generator 3 is connected to the radiating element 2.1 for providing RF energy to the radiating element 2.1. The receiving element 2.2 is connected to the receiver 4 for connecting the RF energy received by the receiving element 2.2 to the analysing device.

When the device 6, e.g. a passive RFID transponder, is to be tested the frequency generator 3 is set to generate RF energy at a certain frequency. The frequency depends on the planned operating frequency of the device 6 to be tested and allowed tolerances in the operating frequency. For example, the device may be designed to operate on a frequency range between a first frequency f1 and a second frequency f2. The frequency generator 3 is then set to produce RF signal at a frequency which is in the frequency range f1-f2 i.e. between the first f1 and the second frequency f2. The measurement probe 2 is placed near the device 6, preferably near the antenna 6.1 of the device 6. The antenna 6.1 is part of a resonant circuit through which energy is supplied to the device 6 and information is transmitted from the device 6. The radiating element 2.1 radiates RF energy to the device 6. Some of the energy is coupled through the resonant circuit of the device 6 to the receiving element 2.2 of the measurement probe 2. The receiver 4 receives the RF energy coupled to the receiving element 2.2 and forms a low frequency signal or a DC signal on the basis of the field strength of the received RF energy. The signal is connected to the analysing device 5 which may store information on the signal to the memory 5.2 and display the information on the display 5.1. The analysing device 5 may also display the reference information which may have been stored previously to the memory 5.2 of the analysing device 5. Now it is possible to compare the amount of energy coupled from the radiating element 2.1 without the device 6 and when the device 6 is under test. The difference in the energy levels indicates the amount of coupling and hence the electrical characteristics of the device 6 on the measurement frequency.

In an example embodiment of the present invention the electrical properties of the measurement probe 2 are analysed and stored into the memory 5.2 of the analysing device 5 before performing the measurements for the device 6. Therefore, it is possible to analyse the difference of the RF energy coupled from the radiating element 2.2 to the receiving element 2.2 without the device 6 and when the device 6 is near the measurement probe 2.

It is not always enough to use only one measurement frequency. Therefore, the testing may also be performed in steps in the following way. The operational frequency range f1-f2 in which the device 6 should operate is determined. The frequency range to be measured is defined so that it is includes the operational frequency range. The frequency generator 3 is set to a starting frequency which is, for example, the first frequency f1. Then the measurement is performed on that frequency and the result is stored. The frequency of the frequency generator 3 is changed a little towards the second frequency and the measurement process is repeated on that frequency. The measurements are repeated on the whole frequency range f1-f2. Therefore, after the frequency range is measured the characteristics of the device 6 on that frequency range f1-f2 are known. The number of steps of the above described range measurement method depends inter alia on the accuracy on which the device 6 should be analysed. The changes in the measurement frequency between the repetitions is not necessarily linear but may also be logarithmic. In other words, the change of the : frequency is smaller near the lower limit of the frequency range than near the higher limit of the frequency range.

When the radiating element 2.1 with a given electrical characteristic (like usually found in transponders) is placed near the receiving element 2.2, some of the transmitted energy will be coupled to the receiving element 2.2 through the device 6 under test (DUT), being the amount of energy coupled, proportional to the electrical response of the device 6 under test at the transmission frequency. The situation is described in Fig. 2.

As a consequence, the level of the signal detected in the receiving element 2.2 is a direct measure of the electrical response of the device 6 under test. If the RF signal is swapped through the frequency range of interest, a plot of the frequency response of the device 6 under test will be easily obtained.

The elements 2.1, 2.2 of the measurement probe 2 should be designed to provide good impedance and flat response over the frequency range of interest. Usually a couple of radiating elements 2.1, 2.2 used as TX and RX antennas with its resonance at a frequency much higher than this frequency range is used.

On the other hand, while the mutual coupling has to be minimized, the coupling of both radiating elements 2.1 , 2.2 with the device 6 under test should to be maximized, in order to obtain enough dynamic range for a given measurement.

In Fig. 2 an example of the measurement probe 2 according to the present invention is shown. The measurement probe 2 comprises a substrate 2.3 on which the radiating element 2.1 and the receiving element 2.2 are formed. The first radiating element 2.1 is partly surrounded by a first shielding 2.4 and he receiving element 2.2 is partly surrounded by a second shielding 2.5. However, the invention is not restricted to such construction but one of the shieldings 2A_Λ 2.5 may not be required. The purpose of the shieldings 2.4, 2.5 is to minimize the direct coupling of RF signals between the radiating element 2.1 and the receiving element 2.2 so that the measurement results would be as reliable as possible. The measurement probe 2 also comprises a signal input wiring 2.6 for inputting RF energy from the frequency generator 3 and a signal output wiring 2.7 for outputting the measurement results to the receiver 4.

In an example embodiment of the invention the radiating element 2.1 and the receiving element 2.2 are monopole antennas but also other antenna structures are possible. The use of antennas instead of resonance circuits enables that the measurement probe 2 can be used on a broader frequqency range than measurement probes of prior art. The radiating element 2.1 and the receiving element 2.2 can be produced, for example, by using wires, by forming them on a printed circuit board, etc. The elements 2.1, 2.2 may also be provided with radiators.

In Fig. 3 an example of measurement results of a test performed by the system according to the present invention are shown. The curve 301 represents the properties of the measurement probe without the device 6 (a weak coupling between the elements 2.1, 2.2) and the curve 302 represents the properties of the measurement probe 2 when it is located near the device 6 under test (a strong coupling between the elements 2.1, 2.2).

It is obvious that the present invention is not solely limited to the above described embodiments but it can be modified within the scope of the appended claims.

Claims

Claims:

1. A device (2) for testing a transponder (6), the device (2) comprising at least a radiating element (2.1) for radiating RF energy to the transponder (6), and a receiving element (2.2) for receiving RF energy coupled from the radiating element (2.1) via a resonant circuit of the transponder (6), characterised in that the radiating element (2.1) and the receiving element (2.2) are antennas.

2. A device (2) according to claim 1 , characterised in that the resonance frequencies of the radiating (2.1) and the receiving elements (2.2) are higher than the resonance frequency of the resonant circuit of the transponder (6).

3. A device (2) according to claim 1 or 2, characterised in that it comprises at least a first shielding between the radiating element (2.1 ) and the receiving element (2.2) for decreasing the mutual coupling between the radiating element (2.1) and the receiving element (2.2).

4. A device (2) according to claim 1 , 2 or 3, characterised in that it comprises an input (2.6) for inputting RF energy to the radiating element (2.1), and an output for outputting the RF energy coupled from the radiating element (2.1) via a resonant circuit of the transponder (6) , wherein electric properties of the transponder (6) are arranged to be determined on the basis of the RF energy output from the device (2) in relation to the RF energy input to the device (2).

5. A device (2) according to claim 4, characterised in that a multiple of frequencies near the resonance frequency of the resonant circuit of the transponder (6) are arranged to be input (2.6) at a time.

6. A system (1) for testing a transponder (6), the system (1) comprising a measurement probe (2) which comprises at least a radiating element (2.1) for radiating RF energy to the transponder (6), and a receiving element (2.2) for receiving RF energy coupled from the radiating element (2.1) via a resonant circuit of the transponder (6), characterised in that the radiating element (2.1) and the receiving element (2.2) are antennas.

7. A system (1) according to claim 6, characterised in that the resonance frequencies of the radiating (2.1) and the receiving elements (2.2) are higher than the resonance frequency of the resonant circuit of the transponder (6).

8. A system (1) according to claim 6 or 2, characterised in that measurement probe (2) comprises at least a first shielding between the radiating element (2.1) and the receiving element (2.2) for decreasing the mutual coupling between the radiating element (2.1) and the receiving element (2.2).

9. A system (1) according to claim 6, 7 or 8, characterised in that it comprises:

- a frequency generator (3) for generating RF energy,

- a receiver (4) for receiving RF energy, - an analysing device (5) for analysing at least the coupled RF energies, and the measurement probe (2) comprises

- an input (2.6) for inputting RF energy from the frequency generator (3) to the radiating element (2.1), and

- an output for outputting the RF energy coupled from the radiating element (2.1) via a resonant circuit of the transponder (6) to the receiver (4), wherein the analysing device (5) is adapted to determine electric properties of the transponder (6) on the basis of the RF energy output from the measurement probe (2) in relation to the RF energy input to the measurement probe (2).

10. A system (1) according to claim 9, characterised in that a multiple of frequencies near the resonance frequency of the resonant circuit of the transponder (6) are arranged to be generated by the frequency generator (3) at a time.

11. A method for testing a transponder (6), the method comprising:

- connecting RF energy to a radiating element (2.1) of a measurement probe (2) for radiating the RF energy to the transponder (6), and - receiving by a receiving element (2.2) RF energy coupled from the radiating element (2.1) via a resonant circuit of the transponder (6), characterised in that the method comprises using antennas as the radiating element (2.1) and the receiving element (2,2).