JPS61104280A - Surface sonic passive transponder with amplitude and phase varying surface pad - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention comprises an interrogation device that transmits an interrogation signal, one or more "labels or passive transponders that generate a response signal containing encoded information in response to the interrogation signal, and a A ``passive question label system'' (
PILS).

A passive question labeling system of the type involved in the present invention is based on H
No. 3,706,094, Col. and Va.
U.S. Pat. No. 3,755.803 to Van Ghan and U.S. Pat. No. 4,058,217 to Vaughan and Cole. The systems disclosed in these patents utilize electromagnetic energy R
It is equipped with a high frequency transmitter capable of transmitting F pulses. These pulses are received by the passive transponder's antenna and sent to the piezoelectric "launch" transducer. This transducer is
The electrical energy received from the antenna is converted into sound wave energy in the piezoelectric material. When a pulse is received, a sound wave is generated in the piezoelectric material and sent along a defined sound wave path. Further, ``tap'' one-lanced transducers placed at regular intervals along this sound wave path convert the sound waves back into electrical energy, which is then reconverted into electrical energy by the launch transducer described above. The presence of a tap transducer at a defined location determines whether a response pulse is transmitted with a particular time delay in response to an interrogation pulse.

This determines the information code contained in the transponder's response.

When the sound pulse is reconverted into an electrical signal, this signal is sent to the transponder's antenna and RF = m
transmitted as energy. This energy is received at a receiver/decoder, preferably co-located with the interrogation transmitter, and the information contained in this response to the interrogation is decoded.

In this -membrane type system, an information code associated with and identifying the passive transducer is incorporated into the transponder when the tap transducer is attached to the piezoelectric substrate. As discussed above, the presence of a tap transducer at a defined location along the acoustic wave path determines whether a response pulse is transmitted with a particular time delay in response to the interrogation pulse. When the encoding format is such, the number of possible codes is 2 to the N power, where N is the number of tap transducers. For many codes, it is necessary to have a significant number of tap transducers, but increasing the number of transducers reduces the efficiency of energy conversion and also inserts spurious signals into the response signal.

OBJECTS OF THE INVENTION It is an object of the invention to provide a passive transponder for use in an interrogation system, so as to transmit a response signal containing encoded information in response to receiving an interrogation signal.

Another object of the invention is to provide a substrate having a substrate surface defining a path of travel of a sound wave, an element of a launch transducer disposed on the surface of the substrate for converting an interrogation signal into a sound wave propagating along the path of travel; Most tap transducer elements are placed on the surface of the substrate at intervals along the path of travel to convert the sound waves into individual output signals, and to mix the output signals of the transducer elements into a response signal. It is an object of the present invention to provide a passive transponder of the above type, comprising a circuit connected to an element of a tap transducer.

Yet another object of the invention is to provide a passive transponder of the above type in which a large number of codes can be generated with a minimum of transducers.

SUMMARY OF THE INVENTION The above objects, as well as other objects that will become apparent from the following description, are: 1. According to the invention, a sound wave is applied to the surface of a support along the path of travel of the sound wave to control the propagation time of the sound wave between transducers. This is accomplished by placing delay pads.

Advantageously, certain delay pads are configured to also control the attenuation of sound waves passing beneath these pads. To create this attenuation, at least one end of the pad is saw-toothed in a plane perpendicular to the sound wave propagation path. The width of the sawtooth in the direction of the travel path is
If N is an odd integer and λ is the wavelength of the center of the sound wave, then
Effectively equal to times nλ/2. In this manner, the sawtooth pad causes the portion of the sound wave passing under one end of the sawtooth to be out of phase by 180 degrees at each point.

In accordance with the present invention, this delay pad is used in a passive question label system. In this system, the interrogation device transmits a first interrogation signal having a first frequency that in turn assumes the majority of frequencies within a defined frequency range. For example, the first frequency is 905, which is a frequency band in which short-distance chick transmission is freely available in many places around the world.
to 925MHz.

A remote passive transponder in communication with the interrogator receives a first signal as an input signal and provides a second signal as an output signal. The conversion method of the signal is communicated,
The first signal is transformed in such a way as to transmit a known information code in the second signal that identifies a particular passive transponder.

The interrogation device of the system includes a receiver for receiving a second signal from the passive transponder and for receiving both the first signal and the second signal, i.e., a signal derived therefrom;
A mixer configured to mix these two signals and generate a further signal is combined. For example, the further signals include the sum and difference of the first and second signals, respectively.

Finally, the system includes a signal processing device (processor) that responds to the signal produced by the mixer, which detects the frequencies contained in this signal to determine the information code that communicates with the passive transponder.

For a complete understanding of the invention, reference is now made to the following detailed description of a preferred embodiment of the invention, and to the accompanying drawings.

The present invention will be described with reference to the drawings of FIGS. 1 to 8, in which identical components in each of the six drawings are designated by the same reference numerals.

1 to 7 show a signal transponder with a surface acoustic wave transponder constituting the invention. 1st
The illustrated transmitter, receiver and decoder system consists of a ramp signal generator 20 providing a sawtooth wave to a voltage controlled oscillator (vCO) 22. vCO is frequency 90
It generates an output signal with a frequency f that repeatedly rises linearly from 5 MHz to a frequency of 925 M1 (z). This signal is amplified by the RF amplifier 24,
Sent to 6. Switch 26 switches the amplified signal to either a transmission amplifier 28 or a decode mixer 30. The switch 26 is connected to the lO generated by the clock 32.
Controlled by OKHz square waves.

The output signal S1 of the amplifier 26 is supplied to an external circulator or transmit/receive (TR) switch 34 and transmitted as 'remagnetizing radiant energy by an antenna 36.

A block diagram of a transponder combined with the system of FIG. 1 is shown in FIG. The transponder receives signal S1 at antenna 38 and sends it to a series delay device with indicated delay times TO and ΔT.

After sending a signal to each successive delay device, signaler 0, signaler 1, I2 . ,.

, IN are retrieved and sent to summation device 111. Intermediate signal Io1.1. . The combined signal S2 of the sum of IN is transmitted to the antenna 36 of the system of FIG.
It is fed back to the antenna 38.

Transponder response signal S2 is received at antenna 36 and passed through circulator or TR switch 34 to receive amplifier 44. The output signal S of this amplifier 44
4 is mixed with the signal S3 sent intermittently by the switch 26 in the mixer.

The output signal S5 of the mixer 30 includes the sum and difference frequencies of the signals S3 and S4. This output signal is sent to a bandpass filter with a passband width of 1 to 3 KHz. The output signal of the filter is passed through the anti-12-adjusting filter 4.
8 to the sample-and-hold circuit.

A sample-and-hold device provides samples to an A/D converter 52. This A/D converter then sends the sampled digital values to a processor 54 which analyzes the frequencies contained in the signal by means of a Fourier transform. Sample-hold device 50 and A/D converter 5
2, when the frequency of the VCO output signal increases monotonically,
In time, it is strobed with a sample signal that compensates for non-linearities.

To provide compensation, the signal at frequency f generated by VCO 22 is sent through buffer amplifier 56 to delay device 58 with a constant signal delay time Ts.

Both the delayed and undelayed signals are fed to a mixer 60 which generates a signal S7 containing the sum and difference frequencies. This signal S7 is fed to a low pass filter 62 which passes only the part of this signal that contains the difference frequency. The output signal of the low pass filter is provided to a zero crossing detector 64 which generates a pulse at each positive (negative) zero crossing. These pulses are used to strobe sample-and-hold device 50 and A/D converter 52.

3-5 illustrate the operation of the circuit of FIG. 1. FIG. FIG. 3 shows the output frequency of the 100K) lz of the clock 32, and FIG. 4 shows the sweep frequency of the signal generated at vCO. FIG. 5 shows the frequency of the signal S1 transmitted over a plurality of single lines 66, and the broken line shows the frequency of the signal S2 received from the transponder. Signal 68 is received between transmissions of signal 66. These intervals are selected to be the same or approximately the same as the round trip delay time between transmitting the signal to the transponder and receiving the transponder response signal. As shown by the many dashed lines, the response signals of the transponders have different delay times (To, To+ΔT
, To+2ΔT1011. .

, TO+NΔT) are combined (
) As a result, it contains many frequencies at a given instant.

6 and 7 illustrate an embodiment of a passive transponder implementing the block diagram of FIG. 2. This transponder converts the received signal S1 into a sound wave and further converts the sound wave energy back into an electrical signal S2 for transmission from the dipole antenna. In more detail, the signal conversion element of the transponder is made of lithium acid (
It includes a substrate 72 of piezoelectric material, such as LiN b O3). On the surface of this substrate are placed full-flex fortresses, such as aluminum, forming a pattern as shown in detail in FIG. for example.

This pattern consists of two buspars 74 and 76 connected to a dival antenna 70, a "launch" transducer 78, and a plurality of "tap" transducers 80. Bars 74 and 76 thus define a travel path 82 for the sound waves generated by the launch transducer and traveling substantially straight to reach each tap transducer in turn. The tap transducers reconvert the sound waves into electrical signals that are collected and summed by buspers 74 and 76. This electrical signal then activates the dipole antenna 7o and is converted into electromagnetic radiation and transmitted as signal S2.

The tap transducers 80 are equally spaced along the surface acoustic wave path 82 as shown in FIG.
By providing a selected number of "delay pads" 84 between the tap transducers, an information code associated with the transponder is provided. These delay pads, shown in detail in FIG. 7, are preferably formed of the same material and co-located with buspars 74.76 and transducers 78.8o. Each delay pad slows the propagation of surface acoustic waves from tap transducer 80 to the next tap transducer at an operating frequency (
It is wide enough to delay an undelayed sound wave at approximately 915 MHz) by 1/4 cycle, or 90''.
By providing a position for two delay pads, what is the phase φ of the surface acoustic wave received by the tap transducer? Control can be performed to provide the following four types of phases.

1. Knee 90' if no pad is provided between successive tap transducers 2. Knee 90' if one pad is provided between successive tap transducers 3. Knee 90' if two pads are provided between successive tap transducers @ 4. When three pads are provided between successive tap transducers: +180' To explain Fig. phase) and φ1, φ2
,...φN (the phase of the signal picked up by successive tap transducers) is the synthesizer (adder)
In the embodiment of FIG.
4 and 76. Signal s2 by antenna 7o
This phase information, transmitted as , contains the information code of the transponder.

As shown in FIG. 7, the width of each of the three delay pads 84 provided between the two tap transducers 80 (
L) is of such width as to give the propagation of the sound wave from one tap transducer to the next a 90° phase delay compared to the phase it would be in the absence of such a delay pad. This width (L) is based on the materials of the base and the delay pad itself, the thickness of the delay pad, and the wavelength of the surface acoustic wave. As described above, the material of the base is preferably lithium niobate (LiNb○), and the material of the delay pad is preferably aluminum.

In the following equation, Vo is “
equal to the propagation velocity of the sound wave on the free surface (Vo = 3488 m/s for lithium niobate substrate), Vs
is the propagation velocity of the sound wave in a surface shorted with an infinitely short delay pad, φ is the normal phase delay in the sound wave transmission from one tap transducer to the next tap transducer when there is no delay pad, and Δφ is the additional phase delay provided by one delay pad. Here, it is defined as follows.

Vo-Vs I Vo 2 where 5 is the "coupling constant" for the metallized (aluminum) piezoelectric (lithium niobate) surface.

φ ■0 λ and λ , where Kt/λ is an approximation term for the mass loading by the pad, and further, where K is a proportionality constant based on the substrate and pad materials, and t is , is the thickness of the pad, so it is as follows.

2πL 2 λ and 2π[1/2 K” + (Kt/λ)] The preferred thickness of the delay pad membrane is about 0.1 micrometer. Initially three delay pads are placed between every tap transducer. , and then selectively removing the delay pad to provide the code for that transponder facilitates the manufacture of the transponder.

If the pads provide a delay of 90@, four types of codes are possible for each set of three delay pads. Therefore, in the case of the transponder shown in FIG. 6 with 7 sets of delay pads, 47 codes are possible.

Figure 8 shows how to control the amplitude and phase of the sound waves.

A delay pad 86 that can be used is shown. Such amplitude changes can be detected by the receiver-decoder device and provide further codes to the transponder without the need for further tap transducers and delay pads.

In this case, the amplitude change of a surface sound wave takes the form of a prescribed attenuation or attenuation. This attenuation is achieved by canceling waves at the edges of the delay pad.6 As shown in FIG. These are the traveling paths 9 of surface sound waves.
2 but offset from each other by a distance in the direction of the path of travel. The first edge 88 has a total length a, while the second edge has a total length b. Although the serrations are shown as having only two sections in FIG. 8, it will be appreciated that the edges may be divided into multiple sections for each edge. the entire section of the first edge has a delay pad width L1;
On the other hand, it is only necessary that the second edge section has a delay pad width L2.

Therefore, distance a is the sum of all sections of the first edge, while distance a is the sum of all sections of the second edge.

Maximum wave cancellation effect on the serrations is achieved when the distances are chosen such that the difference in delay provided by the pads at the first and second edges is each n180' (where n is an odd number). . In particular, D is φ1−φ2=n
Preferably it is selected to be π radians. where φ1 is the additional delay provided by the delay pad over distance L1 and φ2 is the additional delay provided by the delay pad over distance L2.

The above equation for a width delay pad gives the following equation:

However, 2 λ 2πX D=L1-L2=(Δ φ 1- Δ φ 2) [λ/
2 π Alternatively, it can be controlled by changing the relative total lengths a and b of the first and second edges.Here, if W is the damping weighting coefficient, then under the optimal delay condition, 1+1=(a-b)/(a+b).

As is clear from this equation, when a is equal to b (W=O
), maximum attenuation occurs. When either a or b is equal to 0 (W=1) - the attenuation is minimum.

As shown in FIG. 8, amplitude varying delay pads 88 are preferably formed in mirror images before and after tap transducer 94. Such a configuration compensates for variations in the acoustic wavefront caused by these delay pads.

There has been illustrated and described a novel surface acoustic wave passive transponder having amplitude and phase varying delay pads and achieving all of the objects and possible advantages of the present invention. However.

Numerous changes, modifications, and various other uses and applications will become apparent to those skilled in the art in view of the foregoing description and accompanying drawings disclosing the preferred embodiments of the invention. Such changes, modifications, and various other uses and applications that do not depart from the spirit and scope of the invention are intended to be defined by the following claims.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a system for transmitting an interrogation signal, receiving a response signal, and decoding information encoded in the response signal; FIG. 2 is a passive transponder used in the system of FIG. 1; 3 is a timing diagram showing the clock output of the system of FIG. 1; and FIG. 4 is a frequency-time diagram showing the transmission signals of the system of FIG. 5 is a frequency-time diagram showing both transmitted and received signals for the system of FIG. 1; FIG. 6 is an enlarged plan view of a particular embodiment of the transponder of FIG. 2; FIG. FIG. 6 is a greatly enlarged plan view of the embodiment shown, and FIG. 8 is a greatly enlarged plan view of a sonic delay pad with serrated edges for controlling sound attenuation. 20... Gradient signal generator 22... Voltage controlled oscillator (VCO) 24... RF
Amplifier 26...Transmission/reception switch 28...Power amplifier 30...Decode mixer 32...Clock 34...Transmission/reception switch 36.38...Antenna 4o...Delay Element 44...Amplifier 52...Analog-digital converter 54...Processor FIG, 1 FIG, 2 FIG, 3 FIG, 4 FIG, 5 Procedural amendment (method) 1. Indication of the case 1988 Patent Application No. 225649 2, Title of the Invention Surface Acoustic Passive Transponder with Amplitude and Phase Changing Surface Pad 3, Relationship to the Amendment Case Applicant Name: X-Site Incorvore Terrado 4
, agent

Claims (5)

[Claims] (1) In a passive transponder used in an interrogation system to transmit a response signal containing coded information in response to receiving an interrogation signal, a substrate having a substrate surface defining a path of travel for acoustic waves; launch transducers disposed on a surface for converting the interrogation signal into sound waves propagating along the travel path; and launch transducers spaced along the travel path on the surface for converting the sound waves into respective output signals. a plurality of tap transducers spaced apart from each other and circuit means connected to the tap transducers to combine the output signals to form the response signal, A transponder further comprising at least one sonic delay pad disposed along the travel path on the surface of the substrate to control time. (2) The transponder according to claim (1), wherein a plurality of the pads are provided, and these pads are arranged between the tap transducers so as to control the delay time between each tap transducer. . (3) Width (L) of the pad in the direction of propagation of the sound wave
) and its thickness (t), where the phase delay given by the pad is Δφ, the center wavelength of the sound wave is λ, and the constant is K
If s and K, then L=(Δφλ)/{2π[1/2K^2s+(Kt/λ
)]} The transponder according to claim 1, wherein the transponder is selected based on the formula: (4) The transponder of claim 1, wherein at least one end of the pad is serrated at its edge perpendicular to the travel path to control attenuation of the sound wave. (5) said serrated edges form first and second edges, which are perpendicular to said path of travel but offset from each other by a distance D in the direction of said path of travel; 1st and 2nd
The difference in delay imparted by the pads at the edges of each n1
The transponder according to claim 4, wherein the angle is 80° (n is an odd number).