Impedance characteristics of piezoelectric ultrasonic transducers

Publish Time: 2018-09-28 Origin: Site

A physical picture of a piezoelectric disc-type transducer designed and fabricated. In order to reduce the influence of multipath noise, using the aforementioned sound field Fresnel zone, the ultrasonic transducer is slightly higher than the radiating surface (or acoustic window) of the piezoelectric transducer to block the surrounding from the target. The clutter reflected back from the object. Experiments have shown that this measurement can reduce the clutter interference reflected from objects around the target. The measuring characteristics of the ultrasonic transducers has he test procedure is as follows: the transducer is intermittently excited by a high-voltage pulse driving power supply, and the peak voltage across the transducer at different frequency points is observed and recorded by an oscilloscope; at the same time, the transducer is intermittently observed and recorded as an echo signal. The resulting voltage peak (not amplified). The ratio of the peak value of the output voltage of the transducer to the peak value of the excitation voltage of the transducer under the action of the excitation signals of different frequencies approximately reflects the quality factor or the operating frequency band of the transducer. Here, the echo is an ultrasonic signal reflected back from the wall at 1 meter from the transducer.

Electromechanical impedance matching of ultrasonic transducer for depth is very important to understand the impedance characteristics of piezoelectric transducers. Otherwise, it is impossible to apply electromechanical impedance matching technology to design ultrasonic transmitting circuits and receiving circuits, which will seriously affect the performance of ultrasonic sensors. In addition, considering the simplicity of the implementation of the ultrasonic transmitting circuit, the pulse transformer is usually used to directly amplify the low-frequency ultrasonic pulse signal. For such ultrasonic transmitting circuits, due to the high frequency of ultrasound.

The equivalent circuit of the piezoelectric vibrator determines the series resonance frequency f of the piezoelectric vibrator from the series inductance L and the series capacitance C in a relatively narrow frequency range, that is, at the frequency point, the capacitive reactance Xc of the equivalent capacitance C and the like The inductive reactance XL of the underwater acoustic transducer has the same magnitude and opposite phase. Therefore, the impedance of the piezoelectric vibrator}Z{ reaches a minimum value whose magnitude is determined by the equivalent resistance R. In the vicinity of fr, piezoelectric transducers are the most efficient as ultrasonic transmitters. The equivalent parallel capacitance Co and the inductance L and the capacitance C together determine another resonant frequency of the piezoelectric vibrator, which is called the anti-resonance frequency fa, which is slightly higher than the ratio. The anti-resonant frequency is not ok. At this frequency, the piezoelectric oscillator's impedance}Z reaches its maximum value; near the child, the transducer is the most efficient as a receiver. External equivalent parallel capacitances such as external cables, sockets, and transceiver circuits of the piezoelectric vibrator will shift the anti-resonant frequency of the piezoelectric vibrator, but will not affect the series resonant frequency. In addition, the parallel capacitance Co as the AC load will reduce the amplitude of the echo signal; at the same time, the resonant impedance of the piezoelectric oscillator will be reduced, so that the ultrasonic transmitting circuit needs to provide a larger current value to ensure that it is applied to both ends of the piezoelectric vibrator. The voltage amplitude meets the design requirements.

The impedance of the piezoelectric vibrator is at a certain frequency point (except the resonant frequency). The impedance characteristics of the ultrasonic depth measurement transducer can be expressed as series, parallel capacitive or inductive equivalent circuits R is the series resistance, and Xs is the series impedance. ; Rp represents the parallel resistance, and Xp represents the parallel impedance. Piezoelectric oscillator resonance impedance value R (R=RS=Rp) is one of the important parameters of piezoelectric transducers. The following steps can be used to determine the value of R: Wiring method of test instrument and piezoelectric vibrator ,which the initial value of the potentiometer is 1kS2o. Adjusting the frequency of the sine wave signal generator until the amplitude of the sinusoidal signal displayed by the oscilloscope shows a minimum value. At this time, the frequency of the signal generator is close to that of the piezoelectric transducer. working frequency. Disconnect the terminal of the piezoelectric vibrator and adjust the resistance of the potentiometer to 0 (short circuit) to record the amplitude of the signal displayed by the oscilloscope. Reconnecting the piezoelectric vibrator to the test circuit and adjust the resistance of the potentiometer until the amplitude of the signal displayed by the oscilloscope is exactly half of that when the piezoelectric vibrator is open. Removing the potentiometer from the test circuit and measuring the resistance of the potentiometer with a multimeter. The resonant impedance of the piezoelectric vibrator is equal to the sum of the internal resistance of the signal generator and the resistance of the potentiometer. The piezoelectric disk transducer was tested. The resonant frequency of the transducer was 24. 5 kHz and the resonance resistance was about 475 SZo. The impedance matching of the receiving ultrasonic ech sounde depth transducer is in the receiving circuit. It is intended to use a high-impedance preamplifier whose impedance is much larger than the resonant impedance R of the transducer. Therefore, the preamplifier can be directly transduced

Impedance characteristics of piezoelectric ultrasonic transducers

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