The Study Of High-frequency Broad-band Piezocomposite Transducers

The 21st century is the century that humanity focuse on developing the ocean field. And to China, there will be a long way to go on exploring ocean if it wants to become a powerful nation in the world. As a result, sonar research increasingly highlights the importance and urgency. As a core component of high-resolution sonar, research in high-frequency wide-band transducer field has great significance.Broadband transducers have much advantage in signal transmission, such as reducing of signal distortion, widening the secureity about information transmission, reducing the ratio of false codes. But there are some difficulties to make high-frequency transducer as the broadband transducer. Because the mechanical size of transducer is usually inversely proportional to the resonance frequency (that is the resonant frequency of transducer is higher, the mechanical size of transducer is smaller), and the expanding bandwidth method of middle or low frequency transducer is difficult to apply to the high-frequency transducer.As a typical high-frequency projector, the bandwidth expansion of 1-3 piezocomposite transducer becomes an urgent problem. But when it works in the thickness mode, the bandwidth itself is not wide. It is difficult to apply in practical. The usual way to widen the bandwidth of high-frequency transducer is adding the matching layer in front of the piezocomposite material. But as time passes, the performance of matching layer will change, this change may cause performance instability of the transducer. In view of this, in order to overcome limitations of high-frequency matching layer transducer, this paper focuses on the use of multi-modal coupling method, to make a study on high-frequency broad-band piezocomposite transducers.First, the computing time of the entire 1-3 piezocomposite transducer finite element model will be very long.1-3 piezocomposite material has a two-dimensional periodic feature, so 1-3 piezocomposite broad-band transducer performance can be analyzed by analyzing the performance of one cycle of 1-3 piezocomposite material. Also cycle model method is given to simulate the response characteristic of 1-3 piezocomposite broad-band transducers in water.Then, the paper proposes two broadband transmission methods of 1-3 piezocomposite transducer:lateral mode 1-3 piezocomposite broadband transducer and single-ended excitation 1-1-3 piezocomposite broadband transducer.Lateral mode 1-3 piezocomposite broadband transducer is the use of the thickness mode and lateral mode coupling to expand the piezocomposite transducer bandwidth. The mode of 1-3 piezocomposite material and the effect of piezoelectric phase volume fraction and piezoelectric pillar aspect ratio on piezocomposite material are studied. On this basis, two broadband transmission methods of 1-3 piezocomposite transducer are proposed:one is the two-mode coupled transducer, using the thickness mode and the first symmetric lateral mode coupling to broaden the 1-3 piezocomposite transducer bandwidth; the other is the three-mode coupled transducer, using the first thickness mode, the first symmetric lateral mode and the third thickness mode coupling to broaden the 1-3 piezocomposite transducer bandwidth.Single-ended excitation 1-1-3 piezocomposite broadband transducer is applying the concept of single-ended excitation to the 1-3 piezocomposite material, and a new piezocomposite structure, that is 1-1-3 piezocomposite material, has been achieved. The mode of 1-1-3 piezocomposite material and the effect of 1-1-3 piezocomposite micro-structure parameters on piezocomposite resonance frequency are analyzed. On this basis, the bandwidth of piezocomposite transducers can be expanded by the first thickness mode, the second thickness mode and the third thickness mode of 1-1-3 piezocomposite material.Finally, lateral mode 1-3 piezocomposite broadband transducer and single-ended excitation 1-1-3 piezocomposite broadband transducer had been manufactured; and they had been prepared measurements about their impedance and transmitting voltage response. The working bandwidth of two-mode coupled 1-3 piezocomposite broadband transducer is 190kHz-390kHz, its band fluctuations do not exceed±2dB, and its maximum of transmitting voltage response is 158dB. The working bandwidth of single-ended excitation 1-1-3 piezocomposite broadband transducer is 112kHz-450kHz, its maximum of transmitting voltage response is 174dB. Experimental results coincide well with ANSYS software calculated conclusions.