JPS6056262A - Surface acoustic wave accelerometer - Google Patents

Abstract

PURPOSE:To reduce the number of parts, by forming a comb shaped electrode to one surface of one cantilevered plate while constituting a surface acoustic wave oscillation from said electrode and an active circuit. CONSTITUTION:A pair of comb shaped electrodes 9, 10 are formed to a cantilevered plate 8 through a piezoelectric element and a surface acoustic wave oscillator is formed of said comb shaped electrodes 9, 10 and an active circuit 11. When acceleration is applied to the cantilevered plate 8, the cantilevered plate 8 is bent and an interval L is changed between the electrodes 9, 10 to change oscillation frequency. Therefore, by detecting the change in oscillation frequency is, for example, by a frequency discriminator 13, acceleration applied to the cantilevered plate 8 can be known. Because a surface acoustic wave is utilized as mentioned above, the electrodes 9, 10 may be formed to at least one surface of one cantilevered plate 8 and the number of parts can be reduced.

Description

[Detailed description of the invention] This invention applies to acceleration analysis using surface acoustic waves.

Acceleration detection methods include servo type, piezoelectric type, and vibration type. iυ forms etc. are being considered. This invention relates to improvements in vibrating acceleration detectors.

<Prior Art> Figure 1 shows the structure of a conventional vibrating acceleration detector. In the figure, 1 indicates a pair of piezoelectric vibrators. For example, a crystal or the like is used as this piezoelectric vibrator. One end of the pair of piezoelectric vibrators 1 is fixed to a support 3, the other ends are connected to each other, and a weight 4 is attached to the connection point. Electrodes 2 are bonded to the front and back sides of the piezoelectric vibrator 1, and oscillation circuits 5a and 5b are connected to these electrodes 2, respectively, and oscillates at a frequency fa and fb that are compared to the state of the piezoelectric vibrator 1. Circuits 5a, 5
a11 so that b oscillates. has been completed. When the acceleration applied to the switching weight 4 is zero, the oscillation circuit 5a,
The oscillation frequencies fa and fb of 5b are set so that fa=fb, and the frequency θ difference detector 6 detects fa-fb, and the ia of fa-fb-0 is set so that fa=fb.
When a-fbNO, acceleration is detected according to the value.

For example, as shown in the figure, when acceleration in the direction shown by the arrow 7 is applied to the weight 4, tensile stress acts on one vibrator 1, and compressive stress acts on the other vibrator 1. At this time, the crystal Using an A'T-cut plate of The wave number fa of the oscillation j-1 of the shore oscillation circuit 5a is 1a<mu. Also the other bracket.

Since pressure stress acts on the rotor, the oscillation local wave number of the oscillation circuit 5b decreases. Therefore, the acceleration given by the difference fa-fb can be detected.

<Conventional disadvantages> Fig. 1 (According to the conventional vibrating acceleration detector shown in
There is a drawback that two piezoelectric vibrators are required and the number of parts increases. In addition, by using two piezoelectric vibrators, we arranged the arrangement so that it becomes fa-fb-o when acceleration is zero, and so that the oscillation frequency changes symmetrically when tensile stress and compressive stress are applied. Therefore, the adjustment is plane fl].

The knob and mover 1 have a slight difference in thickness, and this difference in thickness causes a difference in the oscillation wave numbers of the oscillation circuits 5a and 5b, and adjusting to the above conditions is a troublesome adjustment work. is required.

<Object of the Invention> The present invention aims to provide a neutral wave acceleration detector that does not require any cleaning work and can reduce the number of parts.

<Summary of the Invention> In this invention, a comb-shaped electrode is formed on at least one surface of one cantilever plate via a piezoelectric machine, and a surface acoustic wave oscillator is formed by <r'T by this electrode and an active circuit. The oscillator is configured to oscillate at a frequency corresponding to the spacing between the electrodes,
The acceleration applied to the cantilever plate is detected based on changes in the oscillation frequency.

Therefore, according to this invention, the number of parts can be reduced, and since it can be configured with one oscillator, there is no need to adjust the frequency between the oscillators, and the amount of yPi L can be reduced. It becomes a structure.

<Embodiments of the invention> An embodiment of the present invention is shown in FIGS. 2 and 3.

The force 2 figure shows the front view, and the 3rd factor shows the side view 1. In this invention, the cantilever plate 8 includes a piezoelectric squid. Through a pair of combs′
b, electrodes 9 and o: 1a are shaped like J, and these 'electrodes 9 and ]0
The active circuit 11 forms a surface acoustic wave oscillator, and the change in the oscillation frequency of the surface acoustic wave oscillator is used to detect the acceleration applied to the strip plate 8.

The cantilever plate 8 itself may be a piezoelectric machine or may be made of an insulating material such as frozen glass. If the cantilever plate 8 itself is made of a piezoelectric material such as a crystal, it is preferable to form a pair of electrodes 9 and 10 directly on one side of the plate 8.Also, if the cantilever plate 8 is made of an insulating material such as glass, For example, zinc oxide (ZnO
A piezoelectric thin film 12 as shown in FIG.

The electrodes 9 and 10 are arranged in the direction in which the cantilever plate 8 extends, and the spacing between the electrodes 9 and 100 changes when the cantilever plate 8 bends about the fulcrum.

An active circuit 11 is connected 12) between electrodes 9 and 10. This active circuit 11 is an amplifier in this example.

<Operation of the Invention> According to the above-described configuration, a slight electrical signal generated on the input side of the active circuit 11 is amplified by the active circuit 11 and applied to one electrode 9. When an electric drive signal is applied to the electrode 9, a surface acoustic wave is generated in the thin film 12 under pressure π, and a bullet,
When the surface waves reach the other electrode 10, an electrical signal is generated at the electrode 10.

As a result, the input and output Δh'' of the active circuit 11 are coupled by the propagation path of the surface acoustic wave, and are constituted by a return loop, resulting in an oscillation state.The oscillation frequency f is −L・(1).

Here, V is the propagation velocity of the surface acoustic wave, and L is the distance between the electrodes 9 and 10.

Since the oscillation frequency of the surface acoustic wave oscillator is defined by the first equation, acceleration is applied to the cantilever plate 8, and when the cantilever plate 8 is bent and the distance between the electrodes 9 and 10 changes, the oscillation frequency f changes. Therefore, this change in oscillation frequency can be detected by, for example, frequency discrimination:'=:r13.
You can find out the acceleration applied to.

<Another Embodiment of the Invention> FIG. 4 shows another embodiment of the invention. In this example, 'electrodes 9, 1o and 9' are provided on both the front and arrow sides of the cantilever plate 8.

10', these two sets of electrodes and the active circuit 11°1
1' constitutes a pair of surface acoustic wave oscillators, the frequency difference detection circuit 14 detects the difference in oscillation frequency between the pair of surface acoustic wave oscillators, and the acceleration is detected from the frequency difference. .

In other words, when acceleration is applied to the cantilever plate 8, the distance between the electrodes 9 and 10 formed on one surface becomes dog, and the distance L' between the electrodes 9' and 10' on the other side becomes smaller. . Therefore, these electrodes 9. ] The oscillation frequencies fa and fb of the pair of oscillators constituted by the active circuits 11 and 11' change in opposite directions, decreasing and increasing. Therefore, this frequency difference is detected by the frequency difference detection circuit 14.
Acceleration can be known by detecting it.

According to the embodiment shown in FIG. 4, the following great advantages can be obtained. This method calculates the difference in the oscillation frequencies of two surface acoustic wave oscillators and determines the acceleration from the value of the difference. Therefore, even if the oscillation frequencies of the two oscillators drift due to temperature changes, for example, the oscillation frequency cannot be changed. The drifts of the oscillators are approximately equal and deviate in the same direction.

Therefore, by calculating the difference between the oscillation frequencies of the two oscillators, the drift in the oscillation frequency is canceled out, and measurement errors due to the drift can be eliminated. Therefore, a surface acoustic wave accelerometer having a temperature correction function can be obtained.

<Effects of the Invention> As explained above, since the present invention utilizes surface acoustic waves, an electrode 9 is provided on at least one surface of one cantilever plate 8.
10 is easy to form, the number of parts is small, and the vapor deposition can be performed on only one side, making it easy to manufacture, suitable for mass production, and expected to reduce costs.

1. As explained in FIG. 4, electrodes 9,
10, 9', and 10' are formed, and these two sets of electrodes constitute a pair of surface acoustic wave oscillators, and the acceleration is calculated from the difference in the oscillation frequency of these two surface acoustic wave oscillators. What is the acceleration detector that removes the constant error of 1jllll due to temperature fluctuation? ! I can do J. Therefore, a highly accurate accelerometer can be provided.

Furthermore, since a non-piezoelectric material such as glass can be used as the cantilever plate 8, the degree of freedom in selecting the material for the cantilever plate 8 is increased, and therefore, the material with excellent spring properties can be used as the material for surface acoustic waves. If selected, it is possible to obtain a surface acoustic wave accelerometer with good performance, and also to reduce the cost. In this way, significant effects can be obtained both in manufacturing and in practical use.゛

[Brief explanation of drawings]

Fig. 1 is a side view (2) for explaining the structure of a conventional vibrating acceleration detector, Fig. 3 is a front view showing an embodiment of the present invention, and Fig. FIG. 4 is a front view showing another embodiment of the present invention. 8: Cantilever plate, 9.10: Electrode constituting the surface acoustic wave oscillator, 11: Active circuit constituting the surface acoustic wave oscillator (1j; 12: Piezoelectric a-base membrane. Patent applicant: Japan Aviation Electronics Industry, Ltd.) Agent Kusano
Table left 1 Figure o 2 Figure well 3 Figure 7i74 Also

Claims (1)

[Claims] (1) A pair of 1′ west]-shaped electrodes are formed on at least one of the front and back sides of the cantilever plate, a surface acoustic wave oscillator that oscillates at a frequency corresponding to the spacing between the electrodes is configured, and the surface A surface acoustic wave accelerometer that detects the acceleration applied to the cantilever plate from the oscillation frequency of an elastic wave oscillator.