JPS61223683A - Ultrasonic device and its driving method - Google Patents

Abstract

PURPOSE:To improve the distance detecting capability for short distance by providing a means which detects the mechanical deformation of an element of an ultrasonic device provided with the element which can be oscillated mechanically and a means which oscillates this element mechanically. CONSTITUTION:When an amplified voltage is applied to electrodes 3 and 5, forces attracting them to each other are generated electrostatically to deflect an element 1. Since the deflection of the element 1 is approximately proportional to the momentary value of this voltage, the element 1 is deflected in accordance with the frequency of an exciting waveform to radiate an ultrasonic wave. When this deformation of the element 1 is induced, the electrostatic capacity value between the second and the third electrodes 4 and 5 is changed. This change value of the capacity is converted to a voltage change value by a capacity-voltage converting circuit 6 in a driving circuit. That is, the second electrode 4 constitutes the means which detects the mechanical deformation of this element. This voltage change value is compared with the exciting waveform in a driving circuit 6, and the voltage momentary value to the first electrode 3 is so changed that the voltage change value is always equal to the exciting waveform. As the result, the detection capability for a short distance is improved.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an ultrasonic element that emits ultrasonic waves and a method for driving the ultrasonic element. In the field of distance measurement, measurement of the propagation time of sound waves using ultrasonic elements has been widely used. FIG. 9 is a diagram showing a propagation time measurement method using a single ultrasonic element, in which 101 is the ultrasonic element, 102 is a drive circuit, 103 is a detection circuit, 104 is a switch, and 105 is a The target object, 106 is the distance fiL between 101 and 105.G FIG. 10 is a diagram showing the operation of FIG. 9. In the figure, 1
1O is the radiation waveform of the ultrasonic wave emitted from the ultrasonic element 101, which conceptually shows the time change of the sound pressure generated in the propagation medium (for example, air) on the target object side of the ultrasonic element. ing. Radiated waveform 110 is generated by drive circuit 102 . That is, essentially the signal generated by the drive circuit 102 during the period when the switch 104 is in the position shown.

A voltage or current waveform similar to 110 (described later) is 10
1 K is applied and waveform 110 is emitted. The ultrasonic waves emitted by such operation travel through the medium.

The sound propagates toward the target object 105 at a sound speed determined by the medium and its temperature, and is reflected by the surface of the object 105. The reflection is caused by the acoustic impedance of the medium, the object 10
This is achieved with an acoustic impedance of 5, a reflectance that depends on the surface shape of the object 105, 2 surface roughness, etc. Such reflection causes the emitted ultrasound waves to propagate in the medium in the opposite direction towards the ultrasound element. Reference numeral 111 conceptually indicates a change in the sound pressure of the ultrasonic wave that reaches the ultrasonic element 101. This sound pressure change is a detection waveform detected by the ultrasonic element 101. For example, if the well-known piezoelectric effect is used, an electrical signal similar to the detection waveform 111 can be detected. Of course, at the time of such detection, the switch 104 is set to a position opposite to that shown, and the electrical signal is guided to the detection circuit 103. Propagation time t from generation of radiation waveform 110 until generation of detection waveform 111
(illustrated at 112) is the ultrasonic element 101 and the target object 1.
It depends on the distance from 05.

That is, it is known that if the speed of sound in the medium is V, then the relationship t=2L/v holds true. As the distance becomes shorter, 1 hour t also becomes shorter.0 Figure 11 shows the radiation waveform 1.
10 is a diagram for explaining the occurrence of No. 10 in more detail. FIG. In the figure, reference numeral 113 indicates a waveform generated by the drive circuit lO2, that is, a waveform generated by the ultrasonic element 1 via the switch 104.
This is the excitation waveform of the voltage or current supplied to 01.

Also, 114 is.

This is a radiation waveform that corresponds to the excitation waveform 113 in detail of the radiation waveform described above. Generally, when an ultrasonic element emits ultrasonic waves, it is governed by the mechanical characteristics and electrical characteristics of the electro-mechanical converter. That is, it is known that mechanical vibrations cannot follow the excitation waveform due to the constituent materials, construction methods, and dimensions of the ultrasonic element. It does not match the radiation waveform 114 corresponding to the target vibration. The amplitude of each pulse constituting the radiation waveform 114 gradually increases, and after time T0 when the excitation waveform becomes zero, the radiation waveform In gradually attenuates to 0, that is, immediately after T0, the switch 104 is set to the detection side. Even if the switch is switched, ultrasonic emission continues due to residual vibration of the ultrasonic element 101.

If the above-mentioned distance is small, the reflected ultrasound from the target object arrives during the period when the ultrasound emission continues, and the detected waveform due to the ultrasound becomes chaotic, resulting in failure to detect the distance. It becomes possible. Such an operation determines the distance detection limit on the short distance side in the conventional propagation time measurement method using an ultrasonic element.

In addition, in the above explanation, the case where a single ultrasonic element is used for both transmission and reception was illustrated, but it is also possible to use two ultrasonic elements, one of which is used for emitting ultrasonic waves.

On the other hand, even when used for ultrasonic detection, the distance detection limit was determined on the short distance side due to the residual vibration immediately after excitation in the element that emits ultrasonic waves. As mentioned above, the distance on the near side is jll! In order to improve the detection limit, it has become an important issue to reduce the residual vibration of the ultrasonic element described above. An object of the present invention is to provide an ultrasonic element with improved distance detection ability and a method for driving the ultrasonic element.

(Structure of the Invention) The ultrasonic element of the present invention has an element that can be mechanically vibrated and a means for mechanically vibrating the element, and includes means for detecting mechanical deformation of the element. It is characterized by:

A method for driving an ultrasonic element according to the present invention includes: (1) an element that can be mechanically vibrated; a means for mechanically vibrating the element; and the i!
When driving an ultrasonic element equipped with means for detecting mechanical deformation of the element using interlocking means, the driving means is controlled by a detection signal obtained from the means for detecting mechanical surface deformation of the element. (Embodiment) Hereinafter, the present invention will be explained in detail by way of an embodiment.0 Figure 1 is a diagram showing a practical example of the present invention. 0 element 1 which is a mechanically vibrating element consisting of a thin film fixed by a spacer 2 consisting of a body
The material of the element 1 is, for example, polyester, polyvinylidene fluoride, etc. The openings 3 and 4 are each made of a conductor provided on the surface of the element 1. This is the second 11L pole. 5 is a conductive third electrode facing the element 1;

Grounded. Moreover, the spacer 2 is connected to the electrode 5 of m3 and m
44 connected. In such a configuration, the first
．． The third electrode group faces each other.

Similarly to 0, which constitutes the capacitive electrode group, the 2nd and 3rd electrodes
The electrode groups also face each other, and the first electrode 3 constituting the capacitance electrolytic group is connected to the output of the drive circuit 6, and the 20th electrode 4 is connected to the drive circuit 6. The second input of the drive circuit 6, which is connected to the first input of the drive circuit 6, is connected to the terminal 7, to which an excitation waveform is applied, which is amplified by the drive circuit 6 to the desired voltage level; Electrodes 3, 5
It is supplied to a group of electrodes with a static 11L capacitance formed between them. That is, the first electrode 3 acts as a drive electrode for the ultrasonic element, and together with the drive circuit constitutes means for mechanically vibrating the element. When the amplified voltage is applied to the electrodes 3 and 5, a mutually attracting force is generated electrostatically,
Let element 184M be O concerned j! ! ! The deflection of element l (i.e.
(mechanical deformation of the element) is roughly proportional to the instantaneous value of the voltage, so 4! Element 1 is deflected according to the frequency of the excitation waveform,
Ultrasonic waves are emitted. On the other hand, when such deformation of the element 1 is induced, the capacitance value between the second and third electrodes 4 and 5 changes.

This capacitance change value is converted into a voltage change value by a capacitance/voltage conversion circuit (not shown) in the drive circuit. That is, the second electrode 4 constitutes means for detecting mechanical deformation of the element. This voltage change value is compared with the excitation waveform inside the drive circuit 6, and the instantaneous voltage value applied to the first electrode 3 is changed so that it is always equal to the excitation waveform. ◎Such an operation is used in the electrical control field. One form of feedback technology that is frequently used is that during the period in which the excitation waveform is applied, a waveform roughly similar to the excitation waveform is supplied to the first electrode 3; In the period after the disappearance, a waveform that forcibly causes the residual vibration of the element l to disappear is generated in the drive circuit 6. As a result of this operation, the harmful residual vibration generated in the element l is removed,
Ultrasonic waves having a radiation waveform equal to the excitation waveform are emitted. ◎Figure 2 is a plan view of the main parts of this embodiment (Figure 1), and the same numbers as in Figure 1 indicate the same components. There is. As is clear from Figure 2, 1. The second electrode group is arranged concentrically. 1st. There are no restrictions on the dimensions of the second electrode, the electrode spacing, etc. Of course, the shape of the second electrode 4 is such that, for example, the signal component obtained from the second electrode has a linear relationship with the mechanical deformation of the element 1, so that the above-mentioned ultrasonic radiation situation is favorable. may be selected as appropriate.

Figure 3 is 1. The figure (,) showing an example in which the shape of the second electrode group is changed shows an example in which the second electrode 4 is placed in the center and the first electrode 3 is placed in the periphery. 0 circle diagram (b) is an example in which the second electrode is divided and arranged in the peripheral part, and the first electrode is arranged from the center to the peripheral part.
Of course, in this embodiment, a plurality of second electrodes may be connected in parallel, or a single electrode may be used. The present invention also includes arranging a shield electrode (not shown) between the second electrodes to reduce input/output coupling of the drive circuit 6.

In the example of FIG. 2.3, the electrode pattern is a circle or a concentric book, but the electrode pattern is not limited to this.

An electrode pattern having a shape other than one circle or concentric circles, for example, a polygon, may be arranged on the polygonal element l including a square. FIG. 4 shows another embodiment of the present invention. In this embodiment, one mechanically vibrating element 11 is made of a piezoelectric material, such as an inorganic piezoelectric material, an organic piezoelectric film, or a composite piezoelectric film. On the whole or a part of the lower surface of the element, a conductive layer 12 (for example, a ground conductor layer 12) is formed (by a well-known method such as vapor deposition).

On the upper surface of the element 11, a first. Second electrode 8v- (respectively indicated at 13.14)
is formed. Furthermore, the periphery of the element is fixed to a conductor or insulator support 15. In this embodiment, electrodes 13 arranged on both sides of the element 11
When an alternating current voltage (or a direct current voltage may be applied) is applied between element 11 and 12, the well-known piezoelectric inverse effect causes the element 11 to
When the deflection occurs, that is, mechanical deformation occurs, a potential based on the conductive layer 12 is induced in the second electrode 14 due to the piezoelectric effect. The potential is connected to the first input of the drive circuit described above (not shown). In this embodiment, unlike the first embodiment shown in FIG. 1, the mechanical surface deformation is directly detected as a voltage signal, so there is an advantage that a capacitance/voltage conversion circuit is not required. , FIG. 1, and FIG. 4 are combined.

For example, the present invention also includes a configuration in which the element is electrostatically vibrated and the deformation is detected piezoelectrically, or a configuration in which the deformation is detected piezoelectrically. , the element must be composed of piezoelectric material. Furthermore, if we do not consider the complexity of R follow-up,
It should be noted that a piezoelectric material may be provided on one surface of the element (either the upper or lower side) by adhesive or other means.In such a configuration,
It is shown in FIG. 5 in correspondence with FIG. 1. In the figure, 21 is a piezoelectric material provided on the element 1;
Electrical connection means (not shown) are provided. Figure 6 shows another embodiment using silicon technology. This figure corresponds to Figure 1 and only the main parts are illustrated. ), the same numbers as in FIG. 1 indicate the same components. In the figure, 31 is a spacer processed using a well-known silicon processing technology. ◎The two main surfaces of 31 may have exposed silicon, which is a conductive material, or may be made of an insulating film such as an oxide film. It may be covered. By using anisotropic etching, it is possible to penetrate a deep hole (corresponding to a case where the silicon thickness is i) with high accuracy. In this example, silicon processing technology is used, so the configuration shown in Figure 6 is possible. This is advantageous when miniaturizing and forming an array.

Figure 7 shows another embodiment using silicon technology.
In Figure 0, in which only the main parts are shown in correspondence with the figures, the same numbers as in Figure 1 indicate the same components. In the figure, numeral 32 is a holding base made of silicon and also used as a spacer. This example is.

Unlike the example shown in FIG. 6, a hole is drilled from one main surface side of the roux silicon, and a third electrode 5 is placed at the bottom of the hole to insulate the group of electrodes.

The bottom surface of 32 may be covered with an insulating film such as an oxide film, but this is not limited to this. In this embodiment, miniaturization and array formation can be made more easily as in FIG. 6.

Although both FIGS. 6 and 7 are shown in a manner corresponding to FIG. 1, the present invention is not limited to this, and the piezoelectric effect described above may be combined.

FIG. 8 is a configuration example of the drive circuit shown in FIG. 1, and in FIG. 0, 40 is a capacitance/voltage conversion circuit.

41 is an amplification circuit using an operational amplifier, etc. The configuration shown in the figure is well known to those skilled in the art.

Since various specific configurations are publicly known, it is difficult to describe them in detail.
The present invention has been explained in detail by giving examples. (Effects of the invention) As described above, according to the present invention, the distance detection characteristics at short distances are improved. Alternatively, a single ultrasonic radiation waveform can be generated, which has the advantage of improving the accuracy of distance detection not only at short distances.

[Brief explanation of the drawing]

1 to 8 are diagrams for explaining the present invention in detail. 9 to 11 are diagrams showing conventional examples. In fig. 1.11... Element, 2... Spacer, 3.13...
- First electrode, 4.14... Second electrode, 5... Third electrode, 6. 102... Drive circuit S7... Terminal, 12... Conductor layer, 15... Support), 21...
...Piezoelectric material%31゜32...Silicon%40...
Conversion circuit %41...Amplification circuit, 101...Ultrasonic element, 103...Detection circuit, 104...Switch,
105...Target object, 106...Distance, 110°114...Radiation shape, 111...Detection waveform, 1
12... hours. 113... Excitation waveform O l-:＼ Tei 1 Figure half 2 Surface missing 4 Circle half 5 Figure bow b Figure half q Figure m, driven O distance 101. M Sound Liquid Iwao J 廚, Rokkaku Rikiichi Han t
o diagram

Claims (1)

[Claims] 1. An ultrasonic element having an element that can be mechanically vibrated and a means for mechanically vibrating the element, characterized in that it is equipped with means for detecting mechanical deformation of the element. The ultrasonic element. 2. When driving an ultrasonic element equipped with an element that can be mechanically vibrated, a means for mechanically vibrating the element, and a means for detecting mechanical deformation of the element using a driving means, the mechanical vibration of the element is A method for driving an ultrasonic element, characterized in that the driving means is controlled by a detection signal obtained from a means for detecting physical deformation.