The Study On The Acousitic Impedance Gradient Matching Layer Of Ultransonic Transducer

Ultrasonic transducer, a kind of energy converter, which has been widely used in many fields, can transform electrical signals into acoustic signals according to the piezoelectric effect. The transducer’s matching layer is a transition layer between the transistor and human bodies. It can achieve acoustic impedance matching or transition, thus greatly improve the acoustic transmission rate and sensitivity of ultrasonic transducer.The traditional matching layer is usually single, and the transmission efficiency of ultrasonic is not high. In this paper, we try to prepare a single layer of matching layer by centrifugal method. Then, the matching layer is set into a gradient matching layer to increase the transmission rate of the traditional matching layer. In this paper, alumina powder with particle size of about 5 μm and tungsten powder with particle size of about 2 μm tungsten powder are selected as particle filler. E51 epoxy resin is selected as matrix. The curing agent is amine curing agent W93. We tested the density, sound velocity, acoustic attenuation and acoustic impedance of different matching layers, and compared its result with the conventional casting method.From the results of the test, the density and acoustic impedance of the matched layer increases linearly with the volume ratio of the filler, while the change of the acoustic attenuation is not linear.When alumina was used as filler, the impedance of the matched layer changed from 3.3 MRayl to 6.6 MRayl. With tungsten powder as filler, the impedance changed from 5.9 MRayl to 15.6MRayl. The acoustic impedance of matching layer in normal transducer is 3-15 MRayl, and the monolayer matching layer prepared by centrifugal gradient method can meet the requirements of these ultrasonic transducers.The samples prepared by centrifugal gradient method have bigger impedance range than the ca sting method, and the data points are denser and the operation reliability is higher, and the preparation is more convenient and quick. It can be said that the centrifugal gradient method is better than the traditional casting method for the preparation of single-layer matching layer.Theoretical calculation shows that the matched layer with suitable impedance gradient can improve the performance of the transducer better than the single-layer matching layer. Starting from the transmission and reflection formula, we derived the optimum transmission conditions of the gradient matching layer, and the result was compared with the FDTD method. Both two methods show that matching layer whose impedance is of the exponential decay has excellent performance. This result has laid the foundation for the gradient matching layer experimental work in the future.