Resonant performance of cylindrical piezoelectric transducer(2)

The design of this cylindrical transducer is to realize the electro-acoustic conversion by using the thickness vibration of the 1-3-2 composite material element to obtain the uniform directivity in the horizontal direction. The design frequency of the transducer is 74kHz. In order to analyze and predict the resonant frequency of the piezoelectric transducer, the finite element analysis software is used to simulate the transducer. One-eighth of the cylindrical array of  PZT material piezoceramic is selected, that is, one piece of 1-3-2 composite material strip and backing is modeled. The size of the composite material is exactly the same as the actual size of the sample. The outer diameter of the backing is 60mm, the thickness of the pipe wall is 5mm, and the height is 15mm. The figure shows the thickness vibration mode of one element of the transducer, and its resonance frequency is 73.9kHz.

The resonance performance of the two transducers in the muffler pool was measured experimentally, and the admittance curves of the two transducers were almost the same, so that the production process was feasible and the samples had good consistency. The water admittance curve of one of the cylindrical piezoelectric transducers measured with a precision impedance analyzer is presented. The resonance frequency is 72 kHz. The comparison between the two figures shows that the measurement results in water are very close to the simulation results. This shows that the vibration frequency of the cylindrical transducer sample basically meets the design requirements.

 performance measurement of transducer

The automatic acoustic calibration system was used to measure the performance of two composite cylindrical water acoustic transducers such as the transmission voltage response, reception voltage sensitivity, and directivity. The measurement frequency was from 20 to 100 kHz. The experiment was performed in the silencing pool of the Acoustic Measurement Center of the Great Wall Radio Factory. The performances of the two transducers are similar, and the relative deviations are within 5%. The performance of one of the PZT41material piezoelectric strip is selected for analysis. The transmission voltage response varies with frequency. The maximum value is 139dB, and the 3dB bandwidth is 7kHz. The transducer's receiving sensitivity is measured within a frequency range of 20 to 60kHz, and its receiving voltage sensitivity is -212. (Undulating soil 4dB). The directivity measurement results of the transducer show that the transducer basically has a directivity of horizontal 360, but the fluctuation is large, which is mainly because the interval between the array elements of the transducer is too large. The piezo element radiation area is small. The vertical directivity diagram shows that the 3dB beamwidth in the vertical direction of the transducer is 12 °.

In the piezoelectric composite cylindrical transducer, the composite element is 10 mm thick, and when the diameter of the piezo cylinder is 70 mm, the resonance frequency is about 72 KHz. If the thickness of the composite piezo element is reduced and the diameter of the cylinder is reduced, the resonant frequency of the piezo disc transducer material can be further increased, so that when the diameter of the transducer is larger, a higher resonant frequency can be obtained, thereby improving pure piezoelectricity. When the piezo ceramic cylindrical transducer has a higher resonance frequency, its volume is smaller and it is difficult to process. At the same time, the 1-3-2 composite cylindrical transducer has a larger bandwidth improvement than the piezoelectric ceramic cylindrical transducer of the same frequency, and the emission voltage response is comparable to that of piezo ceramic.

Because the design structure of the piezoelectric transducer is slightly different from the structure after fabrication, and the manufacturing process needs to be improved, the performance of the transducer is slightly lower than the expected calculation result. In addition, the radiation area of the transducer array elements is small, and the vibration energy of each array element is distributed along the circumference, resulting in lower receiving sensitivity. However, by increasing the area of the radiating surface of the array element, reducing the thickness of the array element, and reducing the spacing between the array elements, the receiving sensitivity of the transducer can be improved and the uniformity of the horizontal orientation of the transducer can also be improved.