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BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing an example of the
relationship between the gap h (k is the wave number of the surface acoustic wave) between the
surface of the piezoelectric substrate and the short circuit plate and the propagation velocity v8
of the surface acoustic wave, FIG. 3 is a bird's-eye view showing a pressure-sensitive element
according to the present invention, FIG. 3 is a graph showing the relationship between the load
W of the pressure-sensitive element according to an embodiment of the present invention Is a
graph showing the relationship between the load W of the pressure sensitive element and the
change Δf / f of the oscillation frequency according to the prior art. In each figure, 1 is a surface
acoustic wave delay line, 2 is a spacer, 3 is a conductive thin plate, and 4 is a pressure.
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pressure
sensitive device that utilizes the entire surface acoustic wave oscillator. Heretofore, this type of
pressure-sensitive element is formed as an oscillator gold electrode as a surface acoustic wave
delay-return circuit, and the surface acoustic wave propagation path is used as a pressuresensitive portion. The principle of operation is to detect as a change in the phase change of the
delay line that occurs when the pressure is applied to the substrate. This phase change is caused
by a change in propagation path length due to distortion and a change in the propagation speed
plate, but the amount of change is usually very small such as 10-1 to 10 '. Therefore, the change
in oscillation frequency is also small. The amount of change does not depend so much on the
substrate material, and this method can not improve the pressure sensitive sensitivity t −. (1) / r,
71 y 9 This invention provides a pressure sensitive element which has significantly increased
pressure sensitive sensitivity as compared with the prior art. Generally, the surface acoustic wave
on the surface of the piezoelectric substrate is accompanied by an electromagnetic wave based
on the piezoelectric action, and the electromagnetic wave seeps between the walls on the surface
of the substrate. Therefore, when the substrate surface is electrically shorted, it is well known
that the propagation speed changes, and the amount of change is larger as the coupling
coefficient is larger. Therefore, if the short-circuit plate is installed in a gap rhk that does not
adhere to the surface, the propagation velocity vs changes as shown in FIG. FIG. 1 shows a
piezoelectric crystal 1. In the calculation result in the case of propagating the surface acoustic
wave in the Z-axis direction using the Y plate of jNbOs, the horizontal axis is 槓 hk of the air gap
and the wave number of the surface acoustic wave. Therefore, as shown in FIG. 2, a spacer 2t ′
′ is provided in the propagation path in the surface acoustic wave delay lsl, and the thin
conductor plate 3 is replaced with the conductive thin plate 3 as a pressure sensitive portion. Is
obtained. That is, when the thin conductor plate is deformed by the pressure 4, the air gap on the
propagation path changes, and (2) the delay time changes based on the calculation result of FIG.
Therefore, when the oscillator is configured using this delay line, it is possible to obtain an
oscillation frequency change which is one to two digits larger than that of the conventional
element for the same pressure. An embodiment is shown in FIG. In the example, the substrate
was made to propagate in the surface acoustic wave tube Z-axis direction using a LIN plate of LIN
') Os. The period of the interdigital electrodes of the delay line is 120 μm, and the distance
between the interdigital electrodes is 8 m. As a spacer, a mica plate having a thickness of about
15 μm was used, and a tube obtained by At-vapor deposition on a glass plate polished to about
50 μm as a conductive thin plate was used. An oscillator was constructed using such a delay
line, and pressure was applied to the conductive thin plate.
A weight of 1 to 5 g was used to press the conductive thin plate. In FIG. 3, the horizontal axis is
the load W, and the vertical axis is the change .DELTA.f / f of the oscillation frequency. FIG. 4
shows experimental results according to the conventional method for comparison. In this case, φ
of the LINbOJs board is φ, -2. A load of 1 to 100 g was applied by me. As is apparent from FIGS.
3 and 4, in the pressure-sensitive element of the present invention, it is possible to obtain a
change in the ejection frequency by about 2 digits with a load (8) of about l / 10 compared to the
conventional one. I understand. As described above, in the element, the pressure sensitivity can
be adjusted by the material and thickness of the conductive thin plate, the thickness of the
spacer, and the like. Possible applications include micro displacement detection, microphones,
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