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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic element for emitting ultrasonic waves and a method for driving the ultrasonic element
((prior art and its problems) Conventionally, in the field of monitoring and ranging Measurement
of the propagation time of sound waves by elements has been widely used. FIG. 9 is a diagram
showing a propagation time measurement method using a single ultrasonic element. In FIG. 9,
101 is the ultrasonic element, 102 is a drive circuit, 103 is a detection circuit, 104 is a switch,
105 is a switch. A target object, 106 is a distance fiL between 101 and 105, G. FIG. 10 is a
diagram showing the operation of FIG. In the figure, 11O is a radiation waveform of the
ultrasonic wave emitted from the ultrasonic element 101, and the temporal change of the sound
pressure generated in the propagation medium (for example, air) on the target object side of the
ultrasonic element is conceptual. Is shown. The radiation waveform 110 is generated by the drive
circuit 102. That is, it was basically generated by the drive circuit 102 within a period in which
the switch 104 is in the illustrated position. A voltage or current waveform similar to 110
(described later) is applied for 101 K, and the waveform 110 is emitted. The ultrasonic waves
emitted by this operation pass through the medium. It propagates toward the target object 105
at the speed of sound determined by the medium and its temperature etc., and is reflected on the
surface etc. of the object 105. The reflection is achieved with a reflectance that depends on the
acoustic impedance of the medium, the acoustic impedance of the object 105, the surface shape
of the object 105, the surface roughness, and the like. Due to such reflection, the emitted
ultrasonic wave propagates in the medium in the opposite direction toward the ultrasonic
element. 111 conceptually shows a change in sound pressure of the ultrasonic wave reaching the
ultrasonic element 101. This sound pressure change is a detected waveform detected by the
ultrasonic element 101. For example, if a known piezoelectric effect is used, an electrical signal
similar to the detection waveform 111 is detected. Of course, at the time of such detection, the
switch 104 is set to a position opposite to that shown in the drawing, and the electrical signal is
led to the detection circuit 103. The propagation time t (shown by 112) from the generation of
the radiation waveform 110 to the generation of the detection waveform 111 depends on the
distance between the ultrasonic element 101 and the target object 105. That is, it is known that
the relationship of t = 2 L / v is established, where V is the velocity of sound in the medium. As
FIG. 11 shortens the distance t by 1 hour as the distance becomes shorter, FIG. 11 is a diagram
for more clearly explaining the generation of the radiation waveform 110. In FIG. In the figure,
reference numeral 113 denotes a waveform generated by the drive circuit 102, that is, an
excitation waveform of a voltage or current supplied to the ultrasonic element 101 through the
switch 104.
???????? It is a radiation waveform which made the radiation waveform mentioned
above correspond to the excitation waveform 113 in detail. In general, an ultrasonic element is
governed by mechanical characteristics and electrical characteristics of an electro-mechanical
transducer during ultrasonic radiation. That is, it is known that mechanical vibration can not
follow the excitation waveform due to the constituent material of the ultrasonic element, the
configuration method 9, and the like. It does not coincide with the radiation waveform 114
corresponding to the dynamic vibration. The individual pulse amplitudes constituting the
radiation waveform 114 gradually increase, and after time T0 when the excitation waveform
becomes zero, the radiation waveform In gradually decays to 0, that is, immediately after T0, the
switch 104 is turned to the detection side. Even if it is switched, because of the residual vibration
of the ultrasonic element 101, the radiation of the ultrasonic wave continues to 0. If the distance
is small, reflected ultrasonic waves from the target object arrive during the period in which the
ultrasonic radiation continues, and the detection waveform by the ultrasonic waves is not
detected in the distance detection. It becomes possible. Such an operation determines the
distance detection limit on the near side in the propagation time measurement method using the
conventional ultrasonic element. Although the case where a single ultrasonic element is used as
transmission and reception is exemplified in the above description, two ultrasonic elements are
used, one for ultrasonic wave radiation. In the other case, even in the case of detection of
ultrasonic waves, a similar distance detection limit at the near distance side is determined due to
residual vibration immediately after excitation in an element emitting ultrasonic waves. As
mentioned above, the distance jll on the short distance side! In order to improve the detection
limit, it has been an important task to reduce the residual vibration of the above-mentioned
ultrasonic element O (object of the invention) The object of the present invention is to eliminate
such drawbacks of the prior art and It is an object of the present invention to provide an
ultrasonic element with improved distance detection capability and a method for driving the
ultrasonic element. The ultrasonic element of the present invention is an ultrasonic element
having an element capable of mechanical vibration and a means for mechanically vibrating the
element, provided with means for detecting mechanical deformation of the element. It is
characterized by The method of driving an ultrasonic element according to the present invention
comprises: (1) an element that can be mechanically vibrated, a means for mechanically vibrating
the element, and the i! When driving an ultrasonic element provided with means for detecting
mechanical deformation of element using interlocking means, the driving means is controlled by
a detection signal obtained from means for detecting mechanical surface deformation of the
element In the following, the embodiment of the present invention will be described in more
detail by reference to the drawings. FIG. 1 is a view showing an embodiment of the present
invention. In FIG. The material of element 0, which is a mechanically vibrating element made of a
thin film fixed by a spacer 2 made of a body, is 1, for example, polyester, polyvinylidene fluoride,
etc. A port 3.4 is provided on the surface of the element 1 Each of the first conductors 1
It is the second 11 L pole. Reference numeral 5 denotes a conductive third electrode facing the
element 1. It is grounded. The spacer 2 is coupled to the m3 electrode 5 in a manner m44. In
such a configuration, the first one. The third electrode group faces each other. Similar to 0, which
constitutes an electrostatically charged electrode group, the second and third electrode groups
face each other, and the first electrode 3 constituting an electrolytic group of electrostatic
capacity is driven. The second input of the mouth drive circuit 6 is connected to the output of the
circuit 6 and the 20 'pole 4 is connected to the first input of the drive circuit 6 is connected to
the terminal 7, and the excitation waveform is applied The excitation modification is amplified to
a desired voltage level by the drive circuit 6 and supplied to the electrode group of the static 11
L capacity formed between the electrodes 3 and 5. That is, the first electrode 3 acts as a drive
electrode of 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, mutually attractive forces are electrostatically generated to cause the element 184 M to be
released. ! ! The deflection of the element l (ie the mechanical deformation of the element) is
roughly proportional to the instantaneous value of the voltage, so 4! The element 1 is bent
according to the frequency of the excitation waveform, and an ultrasonic wave is emitted. On the
other hand, when the deformation of the element 1 is induced, the capacitance value between the
second and third electrodes 4 and 5 changes. The variation value of the capacitance is converted
to a voltage variation 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 voltage instantaneous value to the first electrode 3 changes so as to always be
equal to the excitation waveform. In a period in which the excitation waveform is applied, which
is one form of a feedback technique frequently used, a waveform substantially similar to the
excitation waveform is supplied to the first electrode 3 but the excitation waveform is In the
cycle after the extinction, as a result of such an operation that a waveform that forcibly cancels
the residual vibration of the element l is generated in the drive circuit 6, the harmful residual
vibration generated in the element is removed, An ultrasonic wave having a radiation waveform
equal to the excitation waveform is emitted ? FIG. 2 is a plan view of the main part of this
embodiment (FIG. 1)), the same reference numerals as in FIG. There is. As evident in FIG. The
second electrode group is arranged concentrically. 1st. There is no limitation on the dimensions
of the second electrode, the distance between the electrodes, and the like.
Of course, the shape of the second electrode 4 such that 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 condition is good 1 May be selected as
appropriate. FIG. 3 shows FIG. In the figure (()) showing an embodiment in which the shape of the
second electrode group is changed, the second electrode 4 is disposed at the central portion and
the first electrode 3 is disposed at the peripheral portion. In the 0 circle diagram (b), the second
electrode is divided and arranged in the peripheral portion, and the first electrode is arranged
from the center to the peripheral portion. 0 Of course, in the present embodiment, a plurality of
Two electrodes may be connected in parallel, or only one electrode may be used. It is also within
the scope of the present invention to place a shield electrode (not shown) between the second
electrodes to reduce the input / output coupling of the drive circuit 6. In the example of FIG. 2.3,
although the electrode pattern illustrated the circle and the concentric book shape, it does not
restrict to this. An electrode pattern of one circle or a shape other than a concentric circle, for
example, a polygon may be arranged on the element 1 of a polygon including a square. FIG. 4
shows another embodiment of the present invention. In this embodiment, the element 11 capable
of mechanical vibration is made of a piezoelectric material, such as an inorganic piezoelectric, an
organic piezoelectric film or a composite piezoelectric film. For example, 1) an adjacent
conductor layer 12 is formed on all or part of the lower surface of the element by a well-known
method such as vapor deposition. The upper surface of the element 11 corresponds to the first
one corresponding to the third and fourth. A second electrode 8v-(each shown as 13.14) is
formed. Further, the periphery of the element is fixed to a support 15 of a conductor or insulator.
In the present embodiment, when an AC voltage (a DC voltage may be weighted) is applied
between the electrodes 13 and 12 disposed on both sides of the element 11, the element 11 is
formed by the known piezoelectric reverse effect. When such a deflection, ie mechanical
deformation, occurs so that the radiation of the deflection ultrasonic waves is achieved, the
piezoelectric effect induces a potential in the second electrode 14 with respect to the conductor
layer 12. The potential is connected to the first input of the drive circuit (not shown). In this
embodiment, unlike the first embodiment shown in FIG. 1, since the mechanical deformation is
directly detected as a voltage signal, there is an advantage that the capacitance-voltage
conversion circuit becomes unnecessary. , FIG. 1 and FIG. 4 are combined. For example, a
configuration in which the element is electrostatically vibrated and the deformation is detected
piezoelectrically or the reverse configuration is included in the present invention. Of course, in
the configuration in which either vibration or detection is piezoelectrically performed. The
element must be made of piezoelectric material.
It should be noted that if the complexity in addition to R is not considered, a piezoelectric
material may be provided on one surface of the element (both upper and lower vh) by means of
adhesion or the like. It corresponds to the figure and is shown in FIG. In the figure, 21 is a
piezoelectric material provided on the element 1, and an electrical connection means (not shown)
is applied. FIG. 6 is another embodiment using silicon technology. 0 corresponds to FIG. 1 and
illustrates only the main part), and the same reference numerals as in FIG. 1 indicate the same
components. In the figure, 31 is a spacer processed using a well-known silicon processing
technique. Two main surfaces of ? 31 may have exposed silicon which is a conductive material,
and an insulating film such as an oxide film. It may be coated. With anisotropic etching, deep
holes (silicon corresponding to thickness i) can be accurately penetrated. ? In this embodiment,
since silicon processing technology is used, the configuration shown in FIG. 6 is used. 9), which is
advantageous when arrayed. FIG. 7 is another embodiment using silicon technology, and in FIG. 0
corresponding to FIG. 1 and only the main part is shown, the same reference numerals as in FIG.
1 indicate the same components. In the figure, reference numeral 32 denotes a holding stand
which also functions as a spacer using silicon. This example is. Unlike the example of FIG. 6, a
hole is formed from one principal surface side of rutile silicon, and the third electrode 5 is
disposed at the bottom of the hole. The bottom surface 32 may be coated with an insulating film
such as an oxide film, but this is not a limitation. In the present embodiment, as in FIG. 6,
miniaturization and array formation can be simplified. FIGS. 6 and 7 are illustrated in
correspondence with FIG. 1, but the present invention is not limited to this, and the abovedescribed piezoelectric effect and the like may be combined. FIG. 8 is an example of the
configuration of the drive circuit shown in FIG. 1. In FIG. 8, 40 is a capacitance-voltage
conversion circuit. 41 is an amplifier circuit using an operational amplifier etc. 0 The
configuration shown in the drawing is well known to the person skilled in the art. Since various
specific configurations are known, the detailed description may be zero or more, and the present
invention will be described in detail by way of examples. O (Effects of the Invention) Thus,
according to the present invention, at a short distance The distance detection characteristics are
improved. Also, it is possible to generate a sharp pulse waveform or a single ultrasonic radiation
waveform without being stupid, and it is possible to improve the accuracy of distance detection
as well as near distance.
Brief description of the drawings
1 to 8 are diagrams for explaining the present invention in detail.
9 to 11 are diagrams showing a conventional example. In the figure. 1.11 ... element, 2 ... spacer,
3.13 ... 1st electrode, 4.14 ... 2nd electrode, 5 ... 3rd electrode, 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 inside, 111 ... detected waveform, 112 ...
time. 113 иии Excitation waveform Ol?: \ 1 1 half of the figure half 5 half of the figure 5 figure b b
half of figure q figure m, driven O distance 101. M sound liquid J J ?, Liaohe strength city half to
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