JPH0214611A - Transversal type signal processing element - Google Patents

Abstract

PURPOSE:To realize amplitude modulation AM and phase modulation PM by using an interdigital transducer as an analog modulation element so as to use a plate mode ultrasonic wave. CONSTITUTION:Interdigital transducers IDT 2, 3 for carrier input/output are provided to the left and right edges of a piezoelectric substrate 1 and an interdigital transducer IDT 4 for modulation is arranged in the middle. With a termination resistor 5 connected to the modulation IDT 4 varied, it is possible to change the transmission characteristic of an acoustic wave propagated between the carrier input/output IDTs 2, 3. The termination resistor 5 is set so as to make the phase of the acoustic wave nearly constant and to change the amplitude statistically especially to apply PM modulation. Thus, the plate mode ultrasonic wave is used to realize amplitude modulation AM and phase modulation PM.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to transversal signal processing elements, and in particular to amplitude modulation (AM) and phase modulation (PM) using plate mode ultrasonic waves in the field of signal processing and sensors. ) Regarding elements.

(Prior Art) At present, electro-mechanical (hereinafter referred to as E
Components (abbreviated as M) are being replaced by pure electronic circuit elements such as filters and resonators because they are small and highly functional.

(Problems to be Solved by the Invention) An object of the present invention is to realize amplitude modulation (AM) and phase modulation (PM) using plate mode ultrasonic waves, which are attracting attention in the fields of signal processing and sensors.

(Means for Solving the Problems) In order to achieve this object, the present invention includes a transducer for modulation disposed in the center of a piezoelectric substrate, and a transducer for modulation disposed at the left and right ends of the piezoelectric substrate. The present invention is characterized by the provision of interdigital transducers for carrier wave input/output placed on both sides of the interdigital transducer, and a terminating resistor connected to the interdigital transducer for modulation. be.

(Function) According to the present invention having the above configuration, the terminating resistor is changed to reduce the sound propagating between the interdigital transducers for carrier wave input and output via the interdigital transducer for modulation. Wave passing characteristics can be changed.

In particular, AM modulation is performed by setting a terminating resistor so that the phase of the acoustic wave is substantially constant and the amplitude is statically varied. Furthermore, PM modulation is performed by setting a terminating resistor so that the amplitude of the acoustic wave is approximately constant and the phase is statically changed.

Therefore, the present invention can achieve the above object, and utilize plate mode ultrasound to perform amplitude modulation (AM) and phase modulation (PM).
can be realized.

(Example) Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 is a plan view of a device in one embodiment of the invention. In the figure, there are interdigital transducers (hereinafter abbreviated as IDT) 2 and 3 for carrier wave input/output at the left and right ends of a piezoelectric substrate 1, and an IDT 4 for modulation is arranged in the center! has been done. Further, by changing the terminating resistor 5 connected to the IDT 4 for modulation, the acoustic wave passage characteristics can be changed.

This operation is similar to the crossed-field method of Sm1th et al.
It is possible to calculate theoretically using a model.

The design of a modulation element operating at about I MHz is achieved by setting the following variables and constants. Here, IDT capacitance per pair: Cs□40pF, logarithm of IDT: N=4. Free surface velocity: vo=2212 m/s, velocity under metal film:
v, = 1683 m/s, electrode finger gap: '2 g
”0.46 mm, electrode finger width: (1,=Q,54
mm, input/output IDT logarithm: 8. Then, the center frequency f0 of the IDT can be expressed by the following equation.

fo= (x, /V6+ 12+m /V+s) −
172 = 945.5 kHz In order to evaluate how the IDT terminated with electrical resistance "R" operates as an AM and PM element, we tested two acoustic terminals with different frequencies and termination resistances. The complex transfer characteristic T between
Figure 2 shows the results of (f, R). In a short-circuit state, the amplitude is flat over all frequencies, and the phase changes linearly, but the resistance value is large (as a result, an attenuation region appears on the higher frequency side than the center frequency. At 10QOkHz, the phase does not change.null1 There is a point, and from that point, the low frequency side becomes an advanced phase region, and the high frequency side becomes a slow phase region.Also,
In the phase advance region, a phase shift of about 30'' occurs for a change in the resistance value of Ω from 100 to 1. Therefore, when operating at the frequency of one null point, AM modulation occurs, and around a frequency of 900 kHz, PM modulation occurs. It is possible.The piezoelectric ceramic (NEPECN-10) used in the experiment is 45X 8X
O, 15mm size horizontally polarized substrate, 5haer
Horizontal (SH) waves are excited. Figure 3 is a diagram showing the dependence of the pass characteristics in the IDT section for modulation on the terminating resistance. It is expressed as a relative value with respect to 0Ω.The amplitude attenuates as the termination condition becomes open, but there is almost no change in the phase. Modulation is possible.

FIG. 4 is a diagram showing observed waveforms when acoustic AM modulation is performed using a J-FET (2SK117-Y) as a variable resistance element. The upper part of the figure shows a 1OkHz modulation signal (
0, IV/divL lower stage is AM modulated carrier wave [5
fflV/div), and the modulation index is m = 33.3%
(It is AMI.

The frequency that can be modulated by PM is 800 to 970 kHz, and FIG. 5 shows the pass characteristic at 862 kHz, where the amplitude change is small. As can be seen from the figure, in the range of 200 to lkΩ, a phase shift of about 30° was obtained with almost no amplitude change.

Figure 6 is a diagram showing the result of PM modulation using a 1OKHz modulation signal, where m = 0.19 from a carrier wave shifted by ±11°.
(PM) is required.

(Effects of the Invention) As explained above, according to the present invention, in order to use a blind transducer as an analog modulation element, Sm1t
As is clear from the theoretical results obtained using the equalization circuit of H et al., amplitude modulation (AM) and phase modulation (PM) could be realized using plate mode ultrasound. These results are effective in providing design guidelines when introducing traveling wave ultrasonic devices into the field of signal processing.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an embodiment of the present invention, FIG. 2 is a diagram showing the frequency characteristics of the IDT for modulation in this embodiment, and FIG. 3 is a diagram showing the pass characteristics of the AM element in this embodiment. FIG. 4 is a diagram showing the observed waveform of the AM modulated signal in this example, and FIG. 5 is a diagram showing the resistance dependence in this example.
FIG. 6 is a diagram showing the resistance dependence of the pass characteristics of the M element, and a diagram showing the observed waveform of the PM-modulated signal in this example. 1...Piezoelectric substrate 2.3... Withdrawal wave IDT for input/output, 4... IDT for modulation, 5... Termination resistor.

Claims (3)

[Claims] (1) A modulating interdigital transducer disposed in the center of the piezoelectric substrate, and carrier wave input/output disposed at the left and right ends of the piezoelectric substrate so as to sandwich the modulating interdigital transducer. and a terminating resistor connected to the modulating interdigital transducer, the terminating resistor being varied to create a transducer for carrier wave input/output via the modulating interdigital transducer. A transversal signal processing element characterized by changing the passage characteristics of acoustic waves propagating between transducers. (2) The transversal type signal processing element according to claim 1, wherein the terminating resistor is set so that the phase of the acoustic wave is substantially constant and the amplitude is varied. (3) The transversal type signal processing element according to claim 1, wherein the terminating resistor is set so that the amplitude of the acoustic wave is substantially constant and the phase thereof is varied.