RU2326405C1 - Device of identification at surface acoustic waves - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: identification device consists of casing, receiver-transmitter antenna, several acoustic channels, which are installed in different acoustic ducts. In every acoustic channel there is receiver-transmitter IDT and reflecting IDT in parallel acoustic channels with the same period L_0i, which is different in different acoustic ducts, and frequency-selective multiple-stripe directional coupler between them. The distance between transducers is different in different acoustic ducts. Receiver-transmitter IDT in all acoustic ducts are made unidirectional with internal reflectors and connected to antenna in parallel.

EFFECT: increases reflection factor of surface acoustic waves from reflecting IDT in different acoustic channels.

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Description

 The invention relates to the field of radio engineering and can be used to identify and protect various objects.

Known passive identification device / 1 /, in which there is no power source. In these devices, using inductive coupling through an alternating magnetic field, remote power supply of the microcircuit is performed, which gives a specific code through the same coupling inductance to the recognition device. The disadvantage of this system is the small radius of action (up to a meter), as well as a sufficiently strong signal that provides power to the microcircuit, which can harm an identifiable object (especially if it is an animal or a person).

To eliminate these disadvantages allows a passive device for radio frequency identification on surface acoustic waves (SAW), comprising a housing, a transceiver antenna, a sound duct, on the working surface of which there are transceiver interdigital transducer (PPVShP) connected to the antenna, and reflective IDT ( OVShP) placed in one acoustic channel with PPVShP / 2 /. In this device, the interrogating signal is received by the antenna, then it is converted using SAWB into SAWs, which are then reflected from the OWFS, forming a code sequence, which is converted into an electromagnetic signal by means of the SSWB and radiated to a recognition device. In this case, there is no need to power the microcircuit, therefore, the interrogating signal can be attenuated to values that do not harm the identified object. Identification distance can also be increased by proper selection of operating frequencies and antenna. The disadvantage of this design is a sufficiently large attenuation of the reflected signal compared to incident on the antenna (which reduces the dynamic range and reduces the distance at which the identification of the object can be made) due to the fact that the reflection coefficient from reflective IDTs should be significantly less than 1, so that the reflected signals from neighboring reflective IDTs would not distort the code sequence.

The problem to which the invention is directed, is to create an identification device for a surfactant devoid of these disadvantages. The technical result that the implementation of the invention provides is to increase the reflection coefficient of the surfactant from the OVShP located in various acoustic channels.

This is achieved by the fact that several acoustic channels are introduced into it, located on different sound ducts, in each of which PPVShP and OVShP are located in parallel acoustic channels with the same period L _0i , which is different in different sound ducts, and a frequency-selective multiband directional coupler between them , the distance between these converters is also different in different sound ducts, the receiving and transmitting IDTs in all sound ducts are made unidirectional with internal reflectors and connected in parallel us to the antenna.

Figure 1 shows the topological structure of a device for surfactants in accordance with the invention.

The device contains sound ducts 1, transceiver IDT 2 and reflective IDT 3 in parallel acoustic channels with the same period L _0i , which is different in different sound ducts. Between these IDTs there is a frequency-selective multiband directional coupler 4. IDT2 in different sound ducts is made with internal reflectors and connected in parallel to the antenna 5. Sound ducts 1 together with IDT 2, 3 and coupler 4 are placed in a sealed enclosure 6.

Figure 2 shows one of the embodiments of the frequency selective directional coupler and the principle of its operation.

The coupler 4 consists of several sections, each of which contains an upper comb of electrodes 7, a lower comb of electrodes 8 and a meander electrode 9. A beam of surfactants with a width of two less than the aperture of the sections of the coupler, which can be represented as symmetrical 10 and asymmetric, falls on it. 11 mod.

The device operates as follows. When applying the interrogating signal with a carrier frequency F _0i to the antenna 5, it passes to IDT 2 and excites SAWs in the sound duct, which are reflected from the reflective IDT 3 and are received by IDT 2, and then the signal enters the antenna 5 and is transmitted to the recognition device. In each channel there is only one reflective IDT, there is no re-reflection from neighboring IDTs, therefore the reflection coefficient from it is made close to 1, which significantly increases the reflected signal compared to the prototype. Since IDT 2 is made in each sound duct with a certain period, which is different in different sound ducts, the conductivity of IDT 2 near its frequency of acoustic synchronism is f _0i = V _SAW / L _0i , where V _SAW is the speed of the SAW under the IDT, L _0i is the period IDT 2 in the i-th acoustic channel, there will be much more conductivity IDT 2 in other sound ducts in which the frequencies of acoustic synchronism are different from that of this sound duct. Therefore, when all IDTs 2 are connected in parallel to the antenna, the maximum current will flow where the frequency of acoustic synchronism coincides with the carrier frequency of the interrogating pulse. Thus, it is possible to achieve signal suppression in adjacent channels by 13 dB if the frequency of the acoustic synchronism of the neighboring channel differs by the minimum value Δf = f _0i / N, where N is the number of IDT periods 2, since its amplitude-frequency characteristic (AFC) has the form sinX / X, where X = πN (ff ₀ ) / f ₀ . Next, the surfactant emitted by IDT 2, is fed to a frequency-selective directional coupler (see figure 2). In this coupler, the upper comb of electrodes 7 and the meander electrode 9, as well as the lower comb of electrodes 8 and the meander electrode 9 in each section form an IDT embedded in each other. The length of each section is chosen equal to the length of IDT 2. Moreover, its frequency response has the form sinX / X, i.e. the same as IDT 2. Since the aperture of the IDT coupled into each other is twice as large as IDT 2, and IDT 3 is in a parallel acoustic channel, we can consider the SAW radiated by IDT 2 in the form of symmetric 10 and asymmetric 11 modes (see figure 2). For an asymmetric mode, the IDTs inserted into each other appear to be short-circuited and its propagation velocity under the IDT is equal to the propagation velocity of the surfactant under the short-circuited piezoelectric surface with a length equal to the width of all electrodes of all sections of the coupler. Symmetrical fashion when passing surfactant under IDTs undergoes an additional phase shift by an amount Ga / ωC _T, where C _T - static capacitance GSW, ω = 2πf, Ga = 8f ₀ k ² M ² (sinX / X) ^2, k ² - square coefficient electromechanical communication surfactant, M - the number of pairs of IDT electrodes. With the passage of several sections, this shift can become equal to π and the surfactant will transition to a parallel acoustic channel. The amplitude of these surfactants will be proportional to the additional phase shift, i.e. proportional to (sinX / X) ² . Therefore, the amplitude of the SAW, whose frequencies differ from the frequency of acoustic synchronism of the ith sound duct by Δf, will be suppressed by more than 20 dB. When reflected from IDT 3 and the surfactant passes again through the coupler, the surfactant again at frequencies more than Δf different from the frequency of acoustic synchronism of the ith sound duct will experience additional attenuation of more than 20 dB. Thus, in the i-th sound duct, SAWs with frequencies of the neighboring sound duct will experience more than 40 dB suppression. The symmetric mode will also be reflected from the IDT coupler. To prevent this from happening, IDTs embedded in each other are used. In this case, the distance between the centers of these IDTs is much smaller than the length of the IDT itself. Therefore, positioning nested IDT so that the distance between their centers is _^3/4 surfactants length can suppress reflected signals in the pass band is much greater than the band IDT bandwidth because the signals reflected from the two IDTs are located in protifofaze and frequency, at which these signals will be added in phase, will be far from the frequencies lying in the passband of the IDT coupler, and will not affect the signals reflected from IDT 3.

Since in the i-th sound duct the distance between IDTs 2 and 3 is different from the distances in other sound ducts, and in the rest of the sound ducts the SAWs are suppressed by more than 40 dB, the signal received by antenna 5 will only get into the given channel and exit through antenna 5 to Recognizing device with a certain delay. When f _0i changes, the signal is effectively reflected in another acoustic channel, experiencing a different delay. Thus, for different f _{0i, the} signals are reflected from IDT 3 with different delays, forming a frequency-delay code.

Execution example. The identification device is made in a sealed enclosure 6, in which there are 6 sound conductors 1 (channels) of lithium niobate YX / 128 ⁰ cut. On each sound duct there are transceiver unidirectional IDTs 2, containing 17 active sections and having an aperture of 50 SAW lengths at the center frequency of the channel. Each channel has its own center frequency. With the center frequency of the first channel equal to 1200 MHz, the center frequencies of the remaining channels are shifted relative to each other by 40 MHz in the direction of increasing frequency. Reflective IDTs 3 are similar to transceivers and are located in parallel acoustic channels of different sound ducts with a minimum shift of 0.25 μs, which provides a distance of 0.5 μs between the reflected pulses. The coefficient of reflection from IDT 3 is 0.96. With a maximum distance between IDT of 10 mm, it is possible to provide 10 gradations in delay after 0.25 μs. Then with 6 channels, the maximum number of delay / frequency combinations will be 10 ⁶ . Between IDTs 2 and 3, in each sound duct there is a frequency-selective coupler consisting of 3 sections, each of which consists of IDTs embedded in each other, containing 17 pairs of electrodes. The distance between the centers of nested IDT is equal to _^3/4 the length of the surfactant. The amplitude of the signal reflected from the identification device with the carrier coinciding with the frequency of acoustic synchronism of the ith channel is 12-15 dB less than the amplitude of the signal received at the device, which is explained by the shunting effect of the IDT of 3 neighboring channels, as well as insignificant losses (2-3 dB) in taps. The amplitude of the signal reflected from the identification device with a carrier that does not coincide with the frequency of the acoustic synchronism of the ith channel is more than 40 dB less than the amplitude of the signal received at the device, which means the isolation between the channels is more than 40 dB.

List of references

1. PCT Patent (WO) 94/06104 A1.

2. The patent of Germany No. 1279785 A.

3. Morgan D. Signal processing devices for surfactants.

Claims (1)

An identification device for surface acoustic waves, comprising a housing, a transceiver antenna, a sound duct, on the working surface of which there is a transceiver interdigital transducer (IDT) connected to the antenna, reflective IDTs in one acoustic channel, characterized in that introduced several acoustic channels located on different sound ducts, in each of which there are transceiver IDTs and reflective IDTs in parallel acoustic channels with the same period L _{0 i,} which is different in different acoustic lines, and a frequency selective directional coupler multistrlp therebetween, the distance between the transducers are also different in different acoustic line transceivers IDT all unidirectional acoustic lines formed with internal reflectors and parallel connected to the antenna.

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