Papers by Author: Li Kun Wang

Abstract: This paper presents a prototype of a new flextensional transducer with PVDF (Polyvinylidene Fluoride) piezoelectric film instead of metallic shell. Resonance frequency, bandwidth, transmitting voltage response, and horizontal directivity of the flextensional transducer with PVDF piezoelectric film were respectively measured by using laser-scanning vibrometer, and underwater acoustic measurement system. Experimental results showed that the new transducer features effectively conversion from longitudinal vibration of piezoelectric stack into radial vibration of PVDF piezoelectric film.

Abstract: Transducer with large directivity and high transmitting sensitivity is designed and fabricated. It is a sandwich transducer with composite horn and it has a finite baffle. A novel model considering the dimension of baffle is deduced, the directivity of transducers are calculated under different conditions. The computations of models agree with the experimental data well. The maximum transmitting voltage response level of the sandwich transducer is 143dB (1V/μPa) and the directivity is up to 99°(-3dB) at the resonance frequency of 75.6kHz.

Abstract: PZT672/epoxy 1-3 piezoelectric composites were fabricated by the cut-filling method. The parameters of PZT672/epoxy 1-3 piezoelectric composites varying with different PZT volume fractions have been measured and compared with theoretical values. The results show a good match between theoretical values and measurements. The authors conclude the regular of the properties of composites varying with PZT volume fraction.

Abstract: The flat transducer is composed of 1-3-2 piezoelectric composite and copper shell. The structure of transducer was determined according to design requirement and finite element analysis by ANSYS. The transducer was prepared by using a 25mm×25mm×4.8mm 1-3-2 composite chip, rigid foam backing, copper shell, polyurethane layer and acoaxial cable. The voltage response, source level, receiving voltage sensitivity and other performance were measured. The resonant frequency of transducer is 294kHz, the maximum transmitting voltage response is 159.6dB, 3dB bandwidth is 32kHz, source level is 208dB, receiving voltage sensitivity of the transducer is -203 ± 3dB in the frequency range of 50-250kHz frequency, the beam width of -3dB is 11º in the directivity.

Abstract: This paper is concerned with the design of a new wideband 1-3-2 piezoelectric composite with multi-mode. The equivalent parameters of 1-3-2 piezoelectric composite with multi-mode are derived from series-parallel theory and uniform field theory. By using numerical calculation, the law of bandwidth varying with the cutting depth is obtained and compared with experiments. The computations show agreement with the experimental results. The results prove that the new wideband 1-3-2 piezoelectric composite with multi-mode can expand bandwidth efficiently, which can be expanded to 28.728 kHz that is 5 times the bandwidth of traditional 1-3-2 piezoelectric composite.

Abstract: According to the simulation by Finite Element Analysis (FEA) for rings with different sizes, how thickness vibration resonance frequency varying as piezoelectric ring structure changing is studied. The relation between thickness vibration mode and height, thickness and radius is obtained. The bandwidth of single circle being narrow has been obtained at the same time, so the method that two high frequency piezoelectric ring oscillators are stacked in axis direction and their structure are optimized to get two times as much as the monocyclic bandwidth is researched, according to the trend of single ring.

Abstract: A novel three-phase (ceramic, epoxy resin and decoupling material) piezoelectric composite with multi-element in parallel connection has been developed by using dice-fill technology. This kind of composite consists of a large number of elements which can be seen as a single-sound radiation source. The space between elements is determined via a precise method of calculation. The ceramic elements are then cut using precision machinery to achieve exact results. A kind of decoupling material has been developed to decrease the cross coupling effect between elements. The vibration velocity curves of active elements and close elements were measured using a Scanning Laser Vibrometer (Polytec PSV-400). The results indicated that the decoupling materials induced in multi-element composites have a good decoupling effect. Vibration attenuations between adjacent elements are larger than 31 dB at resonance frequency.

Abstract: Novel piezoelectric shell stack in radial direction had been developed. The shell stack was composed of inner and outer shells which are bonded with each other by epoxy resin. The vibration and electromechanical characteristics of the piezoelectric shell stack were modeled and simulated by Finite Element Analysis (FEA). The send voltage response (SV) of both single and double shells under water were computed. Particularly the analytical results of shell stack presented in resonance frequency varying with the radius and thickness had been compared with experiments. The computations show agreement with the experimental results, and the errors are less than 1.28%.

Abstract: A new type of piezoelectric composite ultrasonic transducer with high frequency in radial vibration is studied. A high-frequency acoustic transducer has been designed and prepared with pzt-5-type piezoelectric ceramic cylinder. When the piezoelectric ceramic cylinder vibrates along the direction of its radial direction, the working frequency is high. It is composed of a piezoelectric ceramic tube and a steel bracket which is inserted in the inner of the ceramic tube. Use the finite element method by ANSYS for analyzing the radial vibration of a piezoelectric tube. On that basis, through managing ANSYS simulation the vibration mode of transducer system is obtained, and analyzed the working frequency of transducer. According to the simulation, the high-frequency cylindrical acoustic transducer has been produced. Comparing the products and the traditional cylindrical transducers, the products haven’t only a good all-round circle directional, but it also has a high working frequency (300 kHz).

Abstract: Lead magnesium niobate-lead titannate single crystal (abbreviated as PMNT) was used to fabricate PMNT/polymer 1-3-2 piezoelectric composite with different volume fractions of PMNT, by dicing single crystal PMNT along mutually perpendicular two directions on the surface and then filling polymer into grooves. The piezoelectric, dielectric and electromechanical properties of the novel composite were determined. It was demonstrated that a thickness electromechanical coupling coefficient of the composites could reach as high as 0.75 and acoustic impendence decreased to 14.9 Mrayls (lower than 30 Mrayls of PMNT). The pulse-echo waveforms of the composites without backing were also measured. It showed a -6dB bandwidth of 88% at the center frequency of 0.95MHz.