JP3536876B2 - Aerial ultrasonic transducer, aerial ultrasonic transducer, and aerial ultrasonic transducer with them - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic method for detecting the presence or absence of an object and the distance to the object by radiating ultrasonic waves into the air and measuring the ultrasonic waves reflected from the object. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aerial ultrasonic transducer used for an object detection device and the like, and particularly to an aerial ultrasonic transducer that can be driven at a low voltage and that transmits and receives ultrasonic waves with one ultrasonic transducer.

[0002]

2. Description of the Related Art FIGS. 5 and 6 are explanatory views showing the principle of construction of a conventional ultrasonic type object detecting device, and FIG.
FIG. 6 is a configuration principle diagram in a case where another ultrasonic vibrator is used for transmitting and receiving one ultrasonic vibrator 53 for one and the receiver 52. FIG. 7 shows an example of the frequency characteristic of the input impedance of a general ultrasonic transducer.
Input impedance at the resonant frequency f _r becomes minimum, the input impedance maximum at the antiresonance frequency f _a.

In conventional airborne ultrasonic transducer, for transmitting, at a low to amplitudes required an oscillator driving voltage driven at the resonant frequency f _r which can be excited, high impedance f _a It is common to receive waves, and as shown in FIG. 5, the resonance frequency f of the ultrasonic transducer used for transmitting waves
or using two ultrasonic transducers equal the antiresonance frequency f _a of the ultrasonic vibrator for use in _r and reception, as shown in FIG. 6, one of the anti-resonance frequency of the ultrasonic vibrator An ultrasonic wave is radiated for _a predetermined time at fa and the same ultrasonic transducer is used as a receiver at the next timing.

[0004]

However, the configuration shown in FIG. 5 requires two ultrasonic transducers for transmitting and receiving waves, and the configuration shown in FIG. In order to drive the vibrator at high f _a , _a high voltage is required as a driving voltage, and a step-up transformer is required.

Accordingly, a first technical problem of the present invention is to eliminate the drawbacks of the conventional airborne ultrasonic transducer, eliminate the need for a step-up transformer, and use a single ultrasonic transducer. It is an object of the present invention to provide an aerial ultrasonic transducer capable of transmitting and receiving ultrasonic waves.

A second technical object of the present invention is to provide an aerial ultrasonic transducer used for the aerial ultrasonic transducer.

Further, a third technical object of the present invention is to provide an aerial ultrasonic transducer used for the aerial ultrasonic transducer.

[0008]

SUMMARY OF THE INVENTION The present invention eliminates the drawbacks of the conventional airborne ultrasonic transducer described above, eliminates the need for a step-up transformer, and uses a single ultrasonic transducer. And an inductance L, a capacitance C, and a resistance R connected in series between a pair of first and second terminals forming input / output terminals. The second terminal of the symmetrical three-terminal type piezoelectric bending oscillator represented by substantially equal capacitances C _d and C _d ′ respectively connected in parallel to the two terminals is opened, and The symmetrical three-terminal type piezoelectric bending oscillator is driven by the resonance frequency viewed from the first terminal for a predetermined time to emit ultrasonic waves in the air, and the symmetrical three-terminal type piezoelectric bending oscillator is driven at the next timing. Ultrasonic wave reflected from the object by short-circuiting the second terminal It is characterized by being configured to reception.

Further, the airborne ultrasonic transmitter according to the present invention comprises an inductance L, a capacitance C, and a resistance R connected in series between a pair of first and second terminals forming input / output terminals. Opening said second terminal of a symmetrical three-terminal piezoelectric bending oscillator represented by substantially equal capacitances C _d and C _d ′ connected in parallel to the first and second terminals, respectively;
At this time, the symmetrical three-terminal type piezoelectric bending vibrator is driven for a predetermined time at a resonance frequency viewed from the first terminal to emit ultrasonic waves into the air.

The aerial ultrasonic receiver according to the present invention further comprises an inductance L, a capacitance C, and a resistance R connected in series between a pair of first and second terminals forming input / output terminals.
A symmetrical three-terminal type piezoelectric bending oscillator represented by substantially equal capacitances C _d and C _d ′ connected in parallel to the first and second terminals, respectively; The second terminal is short-circuited to receive the ultrasonic wave reflected from the object.

Here, the airborne ultrasonic transmitter according to the present invention,
In each of the aerial ultrasonic transducer and the aerial ultrasonic transducer, the symmetric three-terminal type piezoelectric bending vibrator is formed on one surface of the piezoelectric ceramic from both ends in the length direction toward the center. It is preferable to include a pair of split electrodes and an entire surface electrode formed on the back surface of the piezoelectric ceramic.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing an aerial ultrasonic transducer according to an embodiment of the present invention. In FIG. 1, a bimorph vibrator 10 is supported by vibrator supports 2 and 3 and housed in a case 7. Bimorph vibrator 10
The electrodes formed on the front and back surfaces are connected to a ground terminal 4, an input terminal 5, and an output terminal 6, respectively. Further, a reflection plate 8 is provided at a position facing the upper surface of the bimorph vibrator 10. The reflecting plate 8 is provided to match the phases of the ultrasonic waves at the central portion and the both side portions of the bimorph vibrator 10.

FIG. 2 is a perspective view showing an example of a bimorph vibrator 10 used in the aerial ultrasonic transducer of FIG. Referring to FIG. 2, the bimorph vibrator 10 includes a piezoelectric ceramic plate 1. One surface of the piezoelectric ceramic plate 1 is provided with electrodes 11 and 12 which are divided into two parts in the longitudinal direction with the central part in the longitudinal direction as a center.
Is given. The piezoelectric ceramic plate 1 is polarized in the thickness direction using these electrodes 11, 12, and 13, and a metal plate 14 is adhered to the lower surface to form a bimorph vibrator.

The bimorph vibrator 10 shown in FIG.
In the case of vibrating in the one-wavelength resonance mode of the bending vibration as shown in FIG. 4, its equivalent circuit is represented as shown in FIG. 4, and it becomes a symmetrical three-terminal type piezoelectric bending vibrator.

Here, the operation principle of the bimorph vibrator according to one embodiment of the present invention will be described with reference to FIG.

Referring to FIG. 4, the bimorph oscillator is
The inductance L, the capacitance C and the resistance R connected in series between the input terminal and the output terminal, and the substantially equal capacitance C _d connected in parallel to each of the input terminal and the output terminal.
And C _d ′.

An ultrasonic transducer represented by such an equivalent circuit is called a symmetrical three-terminal piezoelectric bending transducer.

In such a bimorph oscillator, C _d ′
= Resonance frequency and anti-resonance frequency when the C _d is open and shorted output terminals respectively given by the following equations.

When the output terminal is opened, it is expressed by the following equations (1) and (2).

[0021]

(Equation 1)

(Equation 2)

When the output terminal is short-circuited, it is expressed by the following equations (3) and (4).

[0023]

[Equation 3]

(Equation 4)

As can be seen from the above equations (1) and (2), the resonance frequency f _ro when the output terminal is open and the anti-resonance frequency f _as when the output terminal is short-circuited are equal. Therefore, by driving the ultrasonic vibrator at the resonance frequency at that time with the output terminal open, driving with low impedance becomes possible, and the driving voltage is sufficient with a low voltage that does not require a step-up transformer. On the other hand, when receiving a reflected wave, if the output terminal is short-circuited, the transmitted frequency becomes equal to the anti-resonance frequency at that time, so that it is possible to receive the wave with high impedance. Opening and shorting of the output terminal can be easily performed by using a so-called analog switch or the like, and the driving and detecting circuit does not become particularly complicated.

Although the airborne ultrasonic transducer according to one embodiment of the present invention has been described above, the symmetric three-terminal type piezoelectric bending oscillator used in the present invention is not necessarily limited to the bimorph oscillator shown in FIG. However, it is sufficient if the equivalent circuit is a bending oscillator represented as shown in FIG.

[0026]

As described above, according to the present invention,
An airborne ultrasonic transducer that eliminates the drawbacks of conventional airborne ultrasonic transducers, does not require a step-up transformer, and is capable of transmitting and receiving ultrasonic waves with a single ultrasonic transducer. An aerial ultrasonic wave transmitter and its aerial ultrasonic wave receiver can be provided, and the effect is large practically.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an aerial ultrasonic transducer according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a bimorph transducer used in the airborne ultrasonic transducer of FIG.

FIG. 3 is a sectional view showing a vibration mode of the bimorph vibrator of FIG. 2;

FIG. 4 is a diagram showing an equivalent circuit of the bimorph vibrator shown in FIG. 2;

FIG. 5 is an explanatory diagram showing an example of a configuration principle of a conventional ultrasonic object detection device.

FIG. 6 is an explanatory diagram showing another example of the configuration principle of the conventional ultrasonic object detection device.

FIG. 7 is an example of a frequency characteristic of an input impedance of an ultrasonic transducer.

[Explanation of symbols]

1. Piezoelectric ceramic plate 2,3 support 4 Ground terminal 5 Input terminal 6 Output terminal 7 cases 8 Reflector 10 bimorph oscillator 11 split electrode (input electrode) 12 split electrode (output electrode) 13 Full surface electrode (earth electrode) 14 Metal plate 51 Transmitter 52 receiver 53 Transmitter / receiver

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-7-270261 (JP, A) JP-A-58-47318 (JP, A) JP-A-57-124398 (JP, A) JP-A-60-1985 165565 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01S 7/521 H04R 17/00 330

Claims (6)

(57) [Claims] 1. An inductance L and a capacitance C connected in series between a pair of first and second terminals forming an input / output terminal.
And resistance R, and substantially equal capacitances C _d and C _d ′ connected in parallel to the first and second terminals, respectively.
The second terminal of the symmetrical three-terminal type piezoelectric bending oscillator represented by the following formula is opened, and the symmetrical three-terminal type piezoelectric bending oscillator for a predetermined time at a resonance frequency viewed from the first terminal at this time. Is driven to emit ultrasonic waves into the air, and the second terminal of the symmetrical three-terminal type piezoelectric bending oscillator is short-circuited at the next timing to receive the ultrasonic waves reflected from the object. An aerial ultrasonic transducer which is characterized in that: 2. The aerial ultrasonic transducer according to claim 1, wherein the symmetric three-terminal type piezoelectric bending vibrator includes a pair of piezoelectric ceramic vibrators formed on one surface of the piezoelectric ceramic from both ends in the length direction to the center. An aerial ultrasonic transducer comprising: a divided electrode; and a full-surface electrode formed on a back surface of the piezoelectric ceramic. 3. An inductance L and a capacitance C connected in series between a pair of first and second terminals forming an input / output terminal.
And resistance R, and substantially equal capacitances C _d and C _d ′ connected in parallel to the first and second terminals, respectively.
The second terminal of the symmetrical three-terminal type piezoelectric bending oscillator represented by the following formula is opened, and the symmetrical three-terminal type piezoelectric bending oscillator for a predetermined time at a resonance frequency viewed from the first terminal at this time. Aerial ultrasonic wave transmitter which emits ultrasonic waves into the air by driving the air. 4. The airborne ultrasonic transmitter according to claim 3, wherein the symmetric three-terminal type piezoelectric bending vibrator includes a pair of piezoelectric ceramic vibrators formed on one surface of the piezoelectric ceramic from both ends in the length direction toward the center. An aerial ultrasonic transmitter comprising: a divided electrode; and a full-surface electrode formed on a back surface of the piezoelectric ceramic. 5. An inductance L and a capacitance C connected in series between a pair of first and second terminals forming an input / output terminal.
And resistance R, and substantially equal capacitances C _d and C _d ′ connected in parallel to the first and second terminals, respectively.
Wherein the second terminal of the symmetrical three-terminal type piezoelectric bending oscillator represented by the following formula is short-circuited to receive the ultrasonic wave reflected from the object. Aerial ultrasonic receiver with special features. 6. The aerial ultrasonic receiver according to claim 5, wherein the symmetric three-terminal type piezoelectric bending vibrator includes a pair of piezoelectric ceramic vibrators formed on one surface of the piezoelectric ceramic from both ends in the longitudinal direction toward the center. An aerial ultrasonic receiver comprising: a divided electrode; and a full-surface electrode formed on a back surface of the piezoelectric ceramic.