JPS6135324A - Lithium tantalate resonator - Google Patents

Abstract

PURPOSE:To minimize the tensile force or compressive force onto a resonator which is generated by a temp. change by cutting a Z plate at the angle rotating 30-60 deg. the plate around the X-axis as the axis f rotation. CONSTITUTION:The lithium tantalate resonator 1 cut at 30-60 deg. cutting angle is the refractive mode lithium tantalate resonator connected at both ends and fixed at both ends. Said resonator is supported and fixed at both ends 3 thereof by an adhesive material 4, etc. onto supporting pedestals 2. The pedestals 2 are made of an insulating material such as ceramics. The resonator has consequently the advantage that said resonator is strong to disturbance, particularly strong impact force, unlike a cantilever type. Since the lithium tantalate is used as a sensor, the reduction in the size is possible and the electromechanical coupling coefft. as the resonator is larger than the coefft. of a rock crystal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a vacuum sensor lithium tantalate oscillator used as a vacuum sensor to measure the degree of vacuum. In particular, it relates to flexural mode lithium oxide oscillators.

[Prior art]

Vacuum gauges have been used in a variety of devices since ancient times. Among these, Villany vacuum gauges have been particularly widely used.

[Problem that the invention seeks to solve]

However, recently, as devices have become smaller and lighter,
At the same time, vacuum gauges are required to be smaller and lighter. The Villany vacuum gauge described above is large in size and heavy, so it cannot adequately meet recent demands. Therefore, the present invention proposes a new sensor for vacuum gauges that improves the above-mentioned drawbacks, and particularly provides a vacuum sensor lithium tantalate vibrator using lithium tantalate. In other words, the present invention provides a vacuum sensor lithium tantalate vibrator that is small, shock resistant, and highly reliable.

[Means for solving problems]

Figure 1 shows the degree of vacuum in bending mode vibration of the present invention and the C6 process value (Orymtal process value) of the lithium tantalate oscillator.
The horizontal axis represents the degree of vacuum (Tor).
The C1 engineering value (KΩ) is plotted with r ) on the vertical axis. According to experiments, the C0 value continues to rise as the degree of vacuum deteriorates.

When the degree of vacuum changes from 0.1 Torr to 1'rorr, the C0 value increases accordingly, that is,
The present invention focuses on the dependence of the C9 work value on the degree of vacuum, and uses this relationship to accurately measure the degree of vacuum. In reality, a change in the C0T value of the vibrator is equivalent to a change in the current flowing through the crystal resonator, and an actual vacuum gauge converts the flowing current into the degree of vacuum and displays it. Further, in order to make the vibrator of the present invention strong against impact, a fixed-end type is used instead of a cantilever type.

More specifically, the crystal resonator is set on a support base made of a material such as ceramics, and is supported and fixed at both ends of the crystal resonator using an adhesive or the like. Therefore, the crystal resonator of the present invention has the advantage of being resistant to external disturbances, particularly strong impact forces. however,
Since the coefficient of linear expansion of the lithium tantalate oscillator is different from that of the support pedestal, stress F acts on the lithium tantalate oscillator due to changes in temperature, and for this reason, the frequency of the lithium tantalate oscillator, i.e., This changes the C0 value and causes a decrease in vacuum measurement accuracy. The present invention solves this problem by reducing the stress sensitivity even when stress F is applied to the lithium tantalate vibrator.

In other words, the problem is solved by selecting the cutting angle of the vibrator. FIG. 5 is a model diagram for theoretically analyzing the vibrator of the present invention. The shape of the vibrator is rod-like and the width is W.
, length l, thickness t, and density P, and both ends are fixed. Now, assuming that the lithium tantalate vibrator and the support base are fixed at room temperature (20°C), the linear expansion coefficient α1 of the lithium tantalate vibrator, the linear expansion coefficient α7 of the support base, and the temperature t. Then, the following relationship holds. That is, the tensile force and compressive force are as shown in (1). Now, for the sake of simplicity, if we consider the case where a tensile force y acts on both ends of the lithium tantalate oscillator as shown in Figure 3 (compressive force can be replaced with -F), the vibration equation can be expressed as potential energy and kinetic energy. By applying the variational principle, it can be expressed as follows.

EI distortion! +ρA÷t−, q= 0 ・・・・・・(2
) alpha

Equation (2) can be solved approximately, and when solved for the frequency f, it becomes as follows.

However, ξ is a correction term. Further, α is a constant determined by the boundary conditions of the oscillator, and is the root of 1 when both ends are fixed.

Also, the resonance frequency when no force F is applied is 10
Then, equation (8) becomes as follows.

Now, considering the fundamental wave vibration of the rod fixed at both ends, ξ is calculated to be -0,53057, and α=4,730, so equation (4) becomes as follows.

Equation (5) shows the frequency when force F is applied, and is 40
．． 64EiI ......(6), then (6)
The formula shows the sensitivity to force F. That is, the smaller K is, the smaller the frequency change per unit power becomes. Next, if we consider the value of K in detail, we can see that in order to reduce the sensitivity (
From Equation 6), it can be seen that it is sufficient to shorten the length of the vibrator, increase the moment of inertia, and increase the Young's modulus (reduce the elastic compliance). In other words, l and f are determined by the shape of the vibrator. On the other hand, Young's modulus E is determined by the cutting direction of the vibrator. The present invention theoretically calculates the cut angle that provides the minimum force sensitivity. That is, the elastic compliance S'22 (reciprocal of Young's modulus E) at that time is determined using the cut angle as a parameter. Figure 4 shows the vibrator and crystal axes X and Y when calculating the elastic compliance S'22.

This shows the relationship with 2. The rod has a length l in the Y-axis direction. At this time, it is assumed that the X-axis is rotated by θ degrees (counterclockwise direction is positive). As a calculation step, first of all,
The elastic compliance S'22 in the longitudinal direction is a function of θ and is expressed as follows. (S'22 = 1/,
) S'22=J+11'J+2S13tTL2□rL22
2S14m: rL2+S33 %2 + S44 m2
n2 −− (γ) However, Qi, = residence θ outside 2 = sin θ S+'+! *SI'31"+41 Sss+
S44 is the elastic compliance constant of lithium tantalate. FIG. 5 shows the relationship between the angle θ and the elastic compliance S'22. From FIG. 5, as the angle θ becomes greater than 0 degrees, S',2 becomes smaller and reaches its minimum at about 40 degrees.

Then, as the angle θ increases, ``'li2 increases,
θ shows a maximum value around 160 degrees. Therefore, by selecting θ within the range of 60 degrees to 60 degrees, minimum force sensitivity can be provided regardless of the transducer shape.

[Effect]

The lithium tantalate vibrator configured as described above, in other words, the vibrator is set on a support pedestal and fixed at both ends of the vibrator with an adhesive or the like. The tensile force or compressive force on the transducer can be minimized by selecting the cutting angle of the vibrator of the present invention.

〔Example〕

Embodiments of the present invention will be described below based on the drawings. Second
Figures (α) and L6) show an embodiment of the bending mode lithium tantalate vibrator of the present invention, with Figure 2 (α) showing a front view and Figure 2 Cb) showing a side view. Cutting angle θ (3
The lithium tantalate vibrator 1 is a bending mode lithium tantalate vibrator with both ends connected, that is, both ends are fixed, and both ends of the lithium tantalate vibrator are placed on the support base 2. It is supported and fixed at part 6 with adhesive 4 or the like. The support base 2 is made of an insulating material such as ceramics. As a result, unlike the cantilever type, it has the advantage of being resistant to external disturbances, especially strong impact forces.

〔Effect of the invention〕

As described above, the present invention was able to obtain the cut angle that provides the minimum force sensitivity regardless of the shape of the vibrator from the vibration equation when force F is applied to the fixed portions at both ends. Therefore, even when the lithium tantalate vibrator was mounted on a support pedestal, a highly reliable tantalate vibrator could be obtained. Furthermore, since it is mounted on a support pedestal, it is resistant to impact.
Since the sensor is a lithium tantalate oscillator, it can be made extremely compact. At the same time, since tanfluridium is used as the material, the electromechanical coupling coefficient as a resonator is larger than that of quartz, and the C,1 value (Cr
This has the effect that it is possible to reduce the ystal ystal ystal efficiency.

[Brief explanation of the drawing]

Fig. 1 is a graph showing the relationship between the degree of vacuum and the O0 value of the lithium tantalate resonator in bending mode vibration of the present invention, and Fig. 2 (α) and (A) are the bending mode crystal resonators of the present invention. Fig. 2 (α) is a plan view,
Figure Cb) is a side view, Figure 3 is a model diagram for vibration analysis of the present invention, Figure 4 is a perspective view showing the relationship between the vibrator and the crystal axis, and Figure 5 is the angle θ and elastic compliance S'. 22 is a graph showing the relationship with No. 22. 1... Lithium tankate oscillator 2...
・Support pedestal 3...Both ends of the vibrator W...Width t...Thickness l...Length or more

Claims (1)

[Claims] In the bending mode lithium tantalate oscillator, the lithium tantalate oscillator has a z-plate with the x-axis as the rotation axis,
A vacuum sensor lithium tantalate vibrator characterized by being cut at an angle of 30 to 60 degrees.