Acoustic impedance of a disc type piezoelectric vibrator transducer

Views: 59 Author: Site Editor Publish Time: 2018-09-28 Origin: Site

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Piezoelectric disc type of transducers discuss the advantages and disadvantages of various forms of ultrasonic transducer. Considering the performance,mounting dimensions and field testing of ultrasonic ranging sensors, piezoelectric ceramic discs are selected radial/ thickness of the vibration mode is the vibrator of the ultrasonic transducer. Disc piezoelectric vibrators operate at frequencies ranging from 20 kHz to 120 kHz. It is known from the acoustic theory that the large-diameter disk-type piezoelectric vibrator is working in the low frequency band is developed to develop a large distance and strong directivity. Firstly, the design method of the disc piezoelectric transduce has the acoustic impedance matching and electromechanical impedance matching technology. The theoretical problem of the radial/thickness vibrating vibration are studied. Then, the design and fabrication of the combined transducer are discussed.

Schematic diagram of axial displacement distribution of a disk-type piezoelectric vibrator is concentrated in the center of the radiating surface of the disc, therefore, for the same structural dimensions, the directional characteristic of the disc-type piezoelectric transducer (radial/thickness vibrating mode) is superior to that of the piston-type piezoelectric transducer (pure directional characteristics of thickness vibration mode). In order to determine the structural size of the disc-type ultrasonic sensor to measure distance, the vibration energy relative displacement R (radius) of the piezoelectric vibrator may be estimated by calculating the beam width formula (3.11b) of the piston-type piezoelectric vibrator to estimate the disc-type piezoelectric vibrator. Assuming that the disk piezoelectric vibrator operates at a frequency of 25 kHz, the wavelength of the ultrasonic wave in the air is about 13.6 mm. If the beam width of the transducer is required to be 3 dB, the radius of the disk type piezoelectric vibrator is R should be at least equal to the piezoelectric ceramic, and a piezoelectric ceramic disk is having a radius of R=0.045 m is actually selected as the transducer vibrator. The larger is radius of the disk, the more advantageous is to improve the directional characteristics of the disk piezoelectric transducer. PZT-5 ceramic material is used as the transducer .

Acoustic impedance matching is when the mismatch of the acoustic impedance ratios of the ultrasonic distance sensor not only reduces the transmission coefficient of the interface, but also makes the piezoelectric vibrator resonate at a high value, that is, the working frequency band is narrow and the waveform residual time is long, thus seriously affecting the probe. Transmiting/receiving sensitivity, axial resolution, and channel capacity is to avoid this phenomenon, it is necessary to use acoustic impedance matching antagonistic technique, and the radiating surface of the piezoelectric vibrator is having a high acoustic impedance ratio does not directly contact the gaseous medium which having a very low acoustic impedance ratio.

In this transducer, three different matching materials are used to gradually transition from the radiating surface of the piezoelectric vibrator with high acoustic impedance to the air medium with low acoustic impedance. This matching technique is based on the provided water sound exchange. Energy matching method. In the table, the acoustic impedance ratios of the backing, piezoelectric element, ith layer matching material and load are respectively recorded as ZB, Zo, Z, ZLo because the acoustic impedance ratio ZL of air is 411 Pa·s/m, which is much smaller than the acoustic impedance of the piezoelectric vibrator is Zo. Therefore, a variety of matching ultrasonic depth sensor should be used for impedance matching, so that the acoustic impedance ratio transitions from a high (piezoelectric disc radiating surface) to a low "smooth" transition to an air medium load. Also considering the acoustic attenuation of the matching layer material. In almost all theoretical analysis and engineering practice, the thickness of the matching layer is taken as (and is the wavelength of the acoustic wave of the matching layer material) and is called the "quarter-wavelength matching layer". Considering the change of the frequency characteristics of the transducer after the matching layer is applied, the thickness of the matching layer should also be multiplied by a thickness coefficient, and the value is taken .

In the ultrasonic ranging process using pulse echo method,the resonant process of the piezoelectric vibrator (tailing phenomenon) directly affects the displacement resolution of the ultrasonic depth acoustic transducer. In order to terminate the resonance process of the piezoelectric vibrator as quickly as possible, the most effective method is to use a damping of a high-impedance, high-attenuation backing material to attach a backing material to the back side of the piezoelectric vibrator. However, since some of the mechanical energy is converted into heat dissipation, the backing brings benefits while also reducing its emission and receiving sensitivity. When actually making the transducer, both factors should be taken into account, and the appropriate backing material should be selected and used.