JPH0449593Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a pulse generation circuit that transmits ultrasonic pulses from a piezoelectric vibrator, for example, and particularly relates to an improvement in the waveform of an ultrasonic pulse signal.

[Prior Art] FIG. 4 is a circuit diagram showing an example of a conventional pulse generation circuit. In the figure, 1 is a first semiconductor that controls the transmission of ultrasonic pulses, 2 is a piezoelectric vibrator that performs acoustic-electrical conversion, 3 is a diode, 5 is a capacitor that performs charging and discharging functions, 6 is a coaxial cable that transmits an excitation signal to the piezoelectric vibrator 2, 7 is an input terminal to which a timing signal to operate the pulse generation circuit is given, 8 is a receiving circuit, C ₁ , _C2 are capacitors, _R1 , _R2 , _R3 , _R4
is a resistor.

The conventional pulse generation circuit is configured as described above, and when a positive pulse signal is applied from the input terminal 7 to the first semiconductor 1, the first semiconductor 1 becomes conductive and the electric charge charged in the capacitor 5 is transferred to the first semiconductor 1. , cable 6, piezoelectric vibrator 2, diode 3, resistor
The piezoelectric vibrator 2 discharged through R ₄ is excited and exhibits a unique vibration phenomenon due to the piezoelectric effect.

Figure 5 shows the operating waveform of a conventional piezoelectric vibrator.
The piezoelectric vibrator 2 generates an ultrasonic pulse of amplitude A, performs damped vibration after half a period of the natural vibration frequency, and transmits the ultrasonic pulse from the piezoelectric vibrator 2 to the material to be inspected. The reflected pulse reflected from the test material is received by the piezoelectric vibrator 2 and supplied to the receiving circuit ₈ via the capacitor C2.

In order to increase the output of ultrasonic pulses, when the charging potential of the capacitor 5 is increased, or when the Q of the piezoelectric vibrator 2 at resonance and the peripheral circuit impedance of the piezoelectric vibrator 2 are increased, the amplitude of the damped vibration also increases at the same time, and the amplitude of the damped vibration increases at the same time. The decay time to reach the level also increases.

[Problem to be solved by the invention] In the conventional pulse generation circuit as described above, the damped vibration generated by the piezoelectric vibrator 2 is caused by acoustic losses such as the back plate constituting the piezoelectric vibrator 2 and the piezoelectric vibrator 2.
It is determined by the electrical circuit impedance of the load, and the amplitude and damping time of the damped vibration increase in proportion to the transmission amplitude of the ultrasonic pulse.

Therefore, when measuring the thickness using the ultrasonic pulses transmitted from the piezoelectric vibrator 2, the reflected pulses from the bottom of the thin specimen material and the reflected pulses from near the surface of the specimen material are not transmitted. This overlaps with the attenuation region of the ultrasonic pulse, making it difficult to identify the reflected pulse and making measurements in that region impossible.

When used in a measuring instrument that transmits and receives ultrasonic pulses using one probe, the dead band of measurement becomes large.

Furthermore, during transmission, the power is shunted to the resistor _R4 connected in parallel to the piezoelectric vibrator 2, so the transmitted energy is reduced, and during reception, the level of the received signal is lowered due to the resistor _R4 .

This invention was made to solve this problem, and the purpose is to obtain a pulse generation circuit that can reduce the amplitude and decay time of damped vibration even if the amplitude of the transmitted ultrasonic pulse is increased. .

[Means for Solving the Problems] The pulse generation circuit according to the invention has a collector and an emitter connected in parallel with a piezoelectric vibrator that transmits ultrasonic pulses by conduction of a first semiconductor, and a resistor between the collector and the base. A diode is provided between the base and the emitter at a polarity where the discharge current of the capacitor is conducted, and a second semiconductor is provided which becomes conductive after a half cycle of the natural resonant frequency of the piezoelectric vibrator.

[Function] In this device, most of the discharge current from the capacitor C due to conduction of the first semiconductor is supplied to the piezoelectric vibrator, so that efficient ultrasonic pulse transmission is possible, and after half a period of the ultrasonic pulse, Since the second semiconductor conducts and absorbs the damped vibration of the piezoelectric vibrator, the damped vibration can be rapidly reduced.

Further, since the second semiconductor is in a cut-off state when receiving a reception signal, it exhibits high impedance and the piezoelectric vibrator has high sensitivity, so that an efficient reception circuit can be obtained.

[Example] An example of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a circuit diagram showing an embodiment of this invention. In the figure, numerals 1 to 3 and 5 to 8 are the same as the conventional circuit described above. 4 is a second semiconductor provided in parallel to the piezoelectric vibrator 2 and conductive in one direction; in this example,
Uses an NPN transistor.

In the pulse generation circuit configured as described above, when an input pulse is applied, the first semiconductor becomes conductive, and the charge of the capacitor 5 charged to the same potential as the power supply voltage +VCC is transferred to the first semiconductor 1, the piezoelectric vibrator 2 , a coaxial cable 6, and an impedance circuit consisting of a diode 3. At this time, the base of the second semiconductor 4 of the NPN transistor is at a negative potential and has a high impedance, so that the influence on the operation is small.

The piezoelectric vibrator 2 has a natural resonant frequency and exhibits electrical characteristics similar to those of a dielectric capacitor, and also functions as a mechanically moving body and a power generating body.
When an electric field is applied to the piezoelectric vibrator 2, the piezoelectric vibrator 2
generates strain (coupling force) and transmits ultrasonic waves, and at the same time electric polarization occurs that generates a charge on its surface.

Due to the discharge of the capacitor 5, the piezoelectric vibrator 2 transmits an ultrasonic pulse having a natural resonance frequency, and the electric charge polarized on the surface of the piezoelectric vibrator 2 has the polarity as shown in the figure. Damped vibration occurs after half a period of the natural resonance frequency of the piezoelectric vibrator 2.

At this time, the collector of the NPN type transistor of the second semiconductor 4 has a positive potential with respect to the emitter, and the second semiconductor 4 becomes conductive due to base-emitter current conduction, and the collector impedance becomes small, and the polarized charges on the surface of the piezoelectric vibrator 2 are transferred to the second semiconductor 4. 2 is discharged as a collector current of the semiconductor 4 in a short time. Therefore, the generation of strain in the piezoelectric vibrator 2 is reduced, and along with this, the electrical polarization is also reduced, and the damped vibration is rapidly attenuated.

As mentioned above, when the ultrasonic pulse is transmitted due to the discharge of the capacitor 5, the second semiconductor is non-conductive, the electric circuit serving as the load of the piezoelectric vibrator 2 exhibits high impedance, and the ultrasonic pulse of a predetermined level is transmitted from the piezoelectric vibrator 2. After half a period of ultrasonic pulse transmission, the second semiconductor provided in parallel to the piezoelectric vibrator 2 conducts and its collector impedance decreases, so the amplitude of the damped vibration rapidly decreases and is attenuated to a predetermined level. The decay time can also be made very small.

FIG. 2 is a circuit diagram showing another embodiment of this invention. In the figure, 1 to 8 are the same as those in the above embodiment, but when a PNP transistor is used as the second semiconductor 4, the first semiconductor - of negative voltage on the collector of
VCC power is applied to reverse the polarity of the diode 3 provided between the base and emitter of the second semiconductor 4.

Therefore, the polarity of the ultrasonic pulse transmitted from the piezoelectric vibrator 2 is reversed. Other operations are the same as when an NPN transistor is used as the second semiconductor 4.

FIG. 3 shows the operating waveform of the piezoelectric vibrator, and the damped vibration amplitude is significantly smaller than the ultrasonic pulse amplitude A.

As described above, the decay time of the damped oscillation of the ultrasonic pulse is shortened, the interference with reflected pulses from a short distance is improved, and the reflected pulses can be easily identified.

When used as an ultrasonic thickness gauge, it can measure thin objects such as paint films and thin plates, and detect defects near the surface of the test material with high resolution in ultrasonic flaw detection, and can also emit ultrasonic waves into the air. When used with an ultrasonic rangefinder, measurements can be taken from short distances.

The second semiconductor 4 can perform the same function with either an NPN type or a PNP type transistor, and the second semiconductor 4 is not limited to the above-mentioned semiconductors. It is possible to control the impedance of the electric circuit that becomes the load of the piezoelectric vibrator 2 after the transmission.

[Effects of the invention] As explained above, this invention has a simple structure in which a second semiconductor is provided in parallel with the piezoelectric vibrator, which reduces the impedance after transmitting ultrasonic pulses. The second semiconductor exhibits a high impedance when the first semiconductor conducts and transmits an ultrasonic pulse due to discharge of the charge in the capacitor, and becomes conductive and has a low impedance after half a period of the natural resonance frequency of the piezoelectric vibrator. , the polarization voltage of the piezoelectric vibrator decreases rapidly, the generation of distortion becomes small, the damped vibration decreases significantly, the decay time can be shortened, and the reflected pulse from a position close to the piezoelectric vibrator can be easily identified. It can accurately measure the thickness of paint films and thin plates, detect defects near the surface of test materials, and measure short distances in the air.

Further, since the second semiconductor exhibits high impedance at necessary timings during transmission and reception, there is an effect that loss is reduced and efficient transmission and reception can be performed.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing one embodiment of this invention, Figure 2 is a circuit diagram showing another embodiment of this invention, and Figure 3 is a circuit diagram showing another embodiment of this invention.
The figure shows operating waveforms of a piezoelectric vibrator, FIG. 4 is a circuit diagram of a conventional pulse generation circuit, and FIG. 5 shows operating waveforms of a conventional piezoelectric vibrator. In the figure, 1 is a first semiconductor, 2 is a piezoelectric vibrator, 3 is a diode, 4 is a second semiconductor, 5 is a capacitor, 6 is a coaxial cable, 7 is an input terminal, 8 is a receiving circuit, C ₁ and C ₂ are The capacitors R ₁ , R ₂ and R ₃ are resistors. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims for Utility Model Registration] In a pulse generation circuit that transmits ultrasonic pulses from a piezoelectric vibrator that is excited via a diode by discharging the charge in a capacitor due to conduction of a first semiconductor, in parallel with the piezoelectric vibrator. The collector and emitter are connected, a resistor is connected between the collector and the base, and the diode is provided between the base and the emitter with a polarity that conducts the discharge current of the capacitor, so that the discharge of the capacitor causes the natural resonance of the piezoelectric vibrator. A pulse generation circuit comprising a second semiconductor that becomes conductive after a half cycle of the frequency.