Speaker
Description
To emit short broadband pulses, piezoelectric transducers require a high acoustic impedance, highly attenuating backing material that reduces backside reflections. The current generation of Transducer Array Systems (TAS 3.0) for the KIT 3D USCT III device uses a polyurethane-tungsten composite backing. Although this backing exhibits significant acoustic attenuation, some drawbacks are its relatively low acoustic impedance (Z ~ 5.5 MRayl) and processing difficulties. Compared to polyurethane, epoxy resins are much easier to process, but have lower sound attenuation. However, improved attenuation can be achieved by mixing epoxy with large-grain tungsten powder. This allows epoxy to be used in the backing material, taking advantage of its favorable properties.
Samples of epoxy-tungsten composite backing were prepared by mixing large-grain tungsten powder with epoxy. To avoid precipitation, the epoxy was pre-cured prior to mixing. After final curing, the samples were ground flat to the desired thickness and polished.
This method enabled the production of tungsten-epoxy composites with a tungsten volume concentration of up to 40%, resulting in a high acoustic impedance (Z > 10 MRayl).
The acoustic characterization of the samples was performed in an ultrasonic through-transmission setup. A broadband chirp (0.5 MHz < f < 5 MHz) was used as the excitation signal. The sound velocity of the material was calculated to determine the acoustic impedance of the samples. To calculate the attenuation, the signals were corrected for reflection losses at the media boundaries.
The epoxy-tungsten backing formulation was applied to the next generation TAS 3.1. The frequency and angle-dependent acoustic field of the TAS was measured using a hydrophone. We present results of the characterization of the backing composites as well as initial results of the improved acoustic performance of the new TAS showing an increase in the -10 dB bandwidth of more than 15 %.
