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(Industrial field of application) The present invention is mounted on a robot or various industrial
devices to measure the distance to a target object at a relatively short distance, or to recognize
the size and shape of the target object. The present invention relates to the structure of a new
ultrasonic transducer. In recent years, inexpensive and high-performance microcomputers have
become widespread, and by using them, automation or robotization is being promoted in various
industrial fields. However, robots or automatic devices that are currently put to practical use can
only lift and carry objects of a certain shape, a certain size, or a certain weight according to a
certain program, such as lifting and carrying objects or processing and assembly. The current
situation is that it can not be done. On the other hand, diversification of the consumer segment
has increased the tendency for high-mix low-volume production, and the development of
automation technology called FMS (Flexible Manufacturing System) has been called for. In such a
flow of automation, it is necessary to equip a robot or an automatic machine with various sensors
that replace human sense organs, and to have them have a judgment function. When the robot
thinks that it lifts an object, it first finds the object with the visual sensor, then approaches the
object with the near-room sensor, and finally when the object's hardness and object are grasped
with the tactile sensor Get information on the repulsive force of. Among these sensors, the nearroom sensor is considered to be suitable for airborne ultrasound, as it obtains near-range
distance information that can not be compensated by the vision sensor. Heretofore, as the air
ultrasonic transducer of this type, one utilizing the resonance of a piezoelectric body such as PZT
or a capacitive transducer has been marketed. The most well-known among capacitance type
transducers are acoustic devices such as condenser speakers and condenser microphones, which
have a low frequency band and are in the acoustic sound wave region, but they are
representative of electroacoustic conversion devices. It is. FIG. 6 is a schematic cross-sectional
view showing the operation principle and structure of the capacitor speaker. A frame made of an
insulator 605 is provided on the periphery of the electrode 603, and a polymer film 602 is
attached thereon. A vapor deposited film of a conductor such as aluminum or gold is formed on
the upper surface of the film 602, and the film surface is made to have an equipotential. The
metal film on the film surface is bonded to the ground electrode 601 to be at the ground
potential. A direct current bias voltage is applied to the metal electrode 603 on the back surface,
the film is attracted to the metal electrode, and by applying an alternating current signal, the film
vibrates and a sound wave is emitted into the air.
In the case of a microphone, the film vibrates due to the sound wave propagating in the air, and
an amplifier may be provided instead of the AC signal application in FIG. 6 in order to detect a
change in the capacitance. Further, although a DC bias circuit is required in FIG. 6, the use of the
electret film subjected to the charging process makes the bias circuit unnecessary. These
speakers and microphones have the advantage that they have low efficiency but good frequency
characteristics. FIG. 7 shows a capacitive ultrasonic transducer used as a distance measuring
sensor for autofocusing of a camera. The cross sectional structure is as shown in FIG. A polymer
film 701 on one side of which is vapor-deposited with gold is covered on an aluminum plate 702
having irregularities on the surface, and is pressed from the back side by a plate spring 703. To
drive this transducer, the gold-deposited polymer film 701 is grounded, a DC voltage of about
300 v is applied to the aluminum plate 702, and an AC signal of ± 150 v is input. As a result, in
response to the input AC signal, the polymer film is pulled to the aluminum plate and ultrasonic
waves are emitted. On the other hand, when receiving ultrasonic waves, the polymer film vibrates
by the ultrasonic waves, and the capacity of the capacitor made of the polymer film and the
aluminum plate changes to detect changes in the charge induced on the electrodes 1 ′ ′ ′
more ultrasonic waves To detect Although the above-described capacitive ultrasonic transducer
has the disadvantage of requiring a large driving voltage, it has a simple structure, good
frequency characteristics, and is excellent. On the other hand, there are also reports on trial
production of ultrasonic transducers using silicon integration technology. Fig. 8 shows the
Journal of the Applied Physics Society of Japan, published in 1984 (Japanese Journal of Applied
Physics, vol. 32. (1984), Supplement 23-1 ° pp, 133-135) is a perspective view showing the
structure of the integrated ultrasonic sensor presented by Daigama et al. As shown in FIG. 8, a
high concentration boron diffusion layer 801 is formed on the surface of a silicon substrate 806,
and a one-side supported beam is formed using the anisotropic etching technique of silicon, and
a platinum electrode 803, titanium oxide is formed on the beam. Lead piezoelectric film 804. The
aluminum electrode 805 is deposited and processed. Driving as an ultrasonic transducer is
performed by inputting an AC signal between platinum and aluminum electrodes, applying
distortion to a lead titanate piezoelectric film, and resonating a beam on one side, while receiving
ultrasonic waves by using ultrasonic waves. The single-sided support beam is resonated to detect
the polarization voltage applied to both ends of the piezoelectric film.
(Problems to be Solved by the Invention) The first and second prior art electrostatic transducers
of the prior art described above have the advantage of being simple in structure, but ultrasonic
waves are generated using the 29 In the past, electronic scanning has not been considered at all.
In the case of the third example, it is considered to be an excellent method for arraying or
integration of elements, but since the ultrasonic elements are of a resonant type, it is an
electronic scanning ultrasonic wave that needs to be considered up to the phase. In order to
make a transducer, it is necessary to make a cantilever with high precision so that all element
elements can be driven at the same resonance frequency, and this causes the element to be
poorly dispersed. In addition, since the Q value indicating the sharpness of the resonance of the
element is large, the vibration of the vibrator is difficult to attenuate, and it is not possible to
measure the reflected sound wave at a short distance. The object of the present invention is to
eliminate the above-mentioned conventional drawbacks and to provide a novel structure of an
array type ultrasound transducer suitable for electronic scanning. (Means for Solving the
Problems) In the electrostatic ultrasonic transducer, the present invention divides at least one of
a movable electrode formed on a vibrating film or a fixed electrode facing the movable electrode.
And an array type ultrasonic transducer characterized in that (Operation) The array type
ultrasonic transducer of the present invention is a capacitive ultrasonic transducer in principle,
and therefore has flat frequency characteristics. As a result, it is possible to transmit or receive a
sound wave that is faithful to the source of the signal. Also, in the case of forming such a
capacitive ultrasonic transducer in the prior art, if the film is not completely fixed between the
electrodes, the film vibrated by the signal applied to one electrode is directed in the adjacent
electrode direction Also, ultrasonic waves propagate, and electronic scanning of ultrasonic waves
was considered impossible because of crosstalk between elements. However, it has been found
that ultrasonic waves can be electronically scanned with almost no crosstalk with only a simple
structure of dividing an electrode which the present inventors have found for the first time. The
vibration frequency of the piezoelectric body is usually about 100 kHz to I MHz, and the
ultrasonic wave in the air is strongly attenuated. In this respect, the electrostatic transducer is
advantageous. The present invention will be described based on examples. 1 (a) and 1 (b) are top
and cross-sectional schematic views for explaining the first embodiment. A silicon oxide film 102
is formed to a thickness of 1000 on a silicon substrate 101, and an aluminum film is formed to a
thickness of about 5000 by a vacuum evaporation method, and processed to form a divided
electrode 103.
Although the size, pitch, number, etc. of the width of this electrode are determined by the
required directivity and the scanning angle depending on the frequency to be driven, in the case
of this embodiment, the width of one electrode is 0.63 mm and 20 mm long. I made 32 games
with a pitch of 1 mm. チップサイズは、35mmX25mmである。 Next, the back surface of
the polyester film of aluminum film of about 500 thickness is attached to a silicon substrate with
appropriate tension, and fixed at both ends of the chip. At this time, the film may be bonded at
the exposed portion of the oxide film portion 107 between the separated electrodes, but since it
is attracted by the electrostatic force, it is not necessary to specifically bond, and the arrayed
ultrasonic waves are formed by an extremely simple process. Elements can be configured. Next,
the chip was mounted on a package, the electrode pad 106 and the package pad were connected
by bonding wires, and the connection on the film surface was performed by a conductive tape. As
shown in FIG. 2, programmable delay circuit 203, 200 V DC bias circuit 205, and AC signal
generator 204 are connected to each electrode of the array type ultrasonic transducer thus
obtained, and the amplitude 10 V p − Five 50 kHz sine waves were input at p, and ultrasonic
waves were emitted in a predetermined direction. As shown in FIG. 3, 301 samples were placed
at the center, and the microphone 302 of Pruell & Care (Brnel & Kja = r) was rotated on a 30 cm
radius arc, and the directional characteristics in each direction were measured. . 4 (a) shows that
all elements are transmitted in the same phase, FIG. 4 (b) shows that the phase delay between
adjacent electrodes is every 0.64 psec, and FIG. 4 (C) is 1.59 psec. In each case, super-sounds are
radiated in the direction of O ', 13 ° and 33 ° respectively, which agrees very well with the
calculated value when 82 point sound sources are arranged at intervals of 1 mm. . FIG. 5 (a) is a
second embodiment. The process is almost the same as in the first embodiment. That is, a silicon
oxide film 102 is formed on a silicon substrate, and an aluminum film is deposited to form an
electrode 103. Next, a polyester film 104 with an aluminum vapor deposition film of about 500
thick is fixed at both ends of the tension chip, and the electrodes 105 are processed to form
divided electrodes and arrayed. FIG. 5 (b) is a third embodiment. A silicon oxide film 102 is
formed on a silicon substrate, and an aluminum film is deposited and processed to form divided
electrodes 103. Next, a polyester film 104 with an aluminum vapor deposition film of about 50
OA thick is attached and fixed at both ends of the chip.
Next, according to the lower electrode pattern, the electrode 105 on the film is processed to form
divided electrodes. At this time, if the aluminum film is thick, the lower pattern can not be
processed without being visible (it can not be processed without being visible, but in this device,
it is sufficient to have an equal potential, so that the aluminum electrode on the film works well
even if thin). Above 2nd. When an array type ultrasonic transducer obtained in the third
embodiment was subjected to an ultrasonic scanning experiment by providing a delay circuit in
the same manner as in the first embodiment, the second embodiment corresponds to the first
embodiment and the first embodiment. Almost the same characteristics were obtained. In the
third embodiment, electrical and loss-talk are further reduced and directivity characteristics are
improved. (Effects of the Invention) As described above, the array-type ultrasonic transducer
according to the structure of the present invention can be manufactured by an extremely simple
process, and the yield is improved. Moreover, the ultrasonic scan by the electronic scan in the air
was able to be performed. In this embodiment, transmission experiments of ultrasonic waves
have been shown, but it goes without saying that ultrasonic waves from oblique directions can
also be received by providing a receiving amplifier instead of an AC signal generator. It is also
possible to obtain a secondary brother by electronic scanning of ultrasonic waves by performing
transmission and reception while shifting the phase in time. Further, although a DC bias voltage
is applied in the embodiment of the present element, the DC bias circuit can be eliminated and
self-bias can be achieved by using an electret film which has been subjected to a preliminary
charging process.
Brief description of the drawings
FIG. 1 is a view showing a first embodiment of the present invention, FIG. 1 (a) is a top view, and
FIG. 1 (b) is a schematic sectional view taken along AB of FIG. 1 (a). .
2 is a peripheral circuit connection diagram in an embodiment in which a delay circuit or the like
is connected to the array type ultrasonic transducer obtained in FIG. 1 and ultrasonic scanning is
performed. FIG. 3 is a layout view of the sample and microphone of the ultrasonic scanning
experiment, and FIG. 4 shows the directivity of the ultrasonic wave obtained thereby. Fig. 4 (a)
shows the case where ultrasonic waves are transmitted with the same phase in all the elements,
and Fig. 4 (b) shows the case where the delay time of 0.64 psec is given to the adjacent
electrodes respectively. Is a case where a delay time of 1.59 psec is given. FIGS. 5 (a) and 5 (b)
show the second embodiment of the present invention. It is an element sectional view in a 3rd
example. Fig.6, Fig.7, and Fig.8 are schematic diagrams of the prior art, respectively. Fig.6 is a
diagram of a capacitor speaker, and Fig.7 is a cross section of an electrostatic transducer for auto
7-ocus of a camera FIG. 8 is a perspective view of a resonant ultrasonic sensor using a
piezoelectric body. In the figure, reference numeral 101: silicon substrate, 102: silicon oxide film
103, 105 = aluminum electrode 104: polymer film. Director of Industrial Technology Technology
jlfl (b) bee 2 Figure Father 2 3θ2. Mike 01 von 3θ /, 4 Formulas 2 Doon 5 Figure (a) (b) Half 7
Figure 8 8 Figure
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