Fabrication And Properties Of Matching Layers For High-frequency Ultrasonic Transducer

High frequency ultrasonic transducers can provide high resolution in medical imaging, providing better conditions for the diagnosing ,treating and monitoring of many medical diseases. Researchers always pay great attention to the research on matching layers for high frequency ultrasonic transducers. Matching layers can solve the problem of mismatch of acoustic impedance at the interface between the piezoelectric ceramics of the transducers and human bodies, which can improve the utilization rate of the ultrasound energy and performance of the transducers. In order to meet the requirement of acoustic impedance matching, most of the matching layers are made of composite materials. Powder in the composite usually has higher acoustic impedance while polymer has lower acoustic impedance so that one can simply adjust the acoustic impedance of the matching layers by changing the volume fraction of the constituents to meet the acoustic impedance requirements.In this paper, we report the fabrication of matching layers for high frequency ultrasonic transducers which are made of tungsten powder and epoxy resin. The particle size of the powder used in the preparation is in nanoscale. Ultrasonic spectroscopy method is used to measure the phase velocity of the samples, and we also get the results of the acoustic impedance measurements. It is found that as the volume fraction of tungsten increases, the density of the samples goes up linearly while the phase velocity gradually drops. The acoustic impedance of the samples also increases linearly with the growth of the volume fraction of tungsten. When the volume fraction of tungsten grows from 0% to 15%, the acoustic impedance of the samples increases from 3.065MRayl to 5.609MRayl. The acoustic impedance of the samples can be further increased by annealing the composite at higher temperatures. The acoustic impedance can reach as high as 6.693MRayl after annealing the samples. In this work, we also use Z6040 as the coupling agent to disperse the tungsten powder in the composite. Both the doctor-blade technique and spin-coating process is adopt to accomplish the fabrication of the matching layers.