Control of tungsten-epoxy composite porosity prepared using a high-energy ball milling method: An engineering aspect of backing layer fabrication

Tungsten-epoxy composite is commonly used as a backing layer substrate of piezoelectric-based ultrasonic transducers. The physical properties of this composite, such as porosity, play a significant role in controlling the behavior and specifications of transducer fabrication. Therefore, this study aimed to investigate the effects of tungsten content in epoxy to control porosity and determine the engineering aspects of ultrasonic transducer fabrication. The experiment was conducted using a shaker-type high-energy ball milling method, where non-spherical and faceted tungsten particles with a mean size of 1 μm were composited into epoxy resin as a matrix at various tungsten-epoxy weight ratios of 0:1 to 10:1. The prepared composite surface morphological and elemental, tungsten loading, particles, and epoxy bonding were examined and analyzed. Furthermore, analysis was carried out on the relationship between tungsten content and the parameters corresponding to the composite acoustic characteristics, such as sound velocity, acoustic attenuation, and acoustic impedance. The results showed that composite porosity increased in the range of 12.40–31.87%, corresponding to acoustic impedance from 3.04 to 9.37 Mrayl (below 10 Mrayl for biomedical ultrasonic transducers) when the tungsten-epoxy weight ratio varied from 0:1 to 10:1. This showed the significant influence of tungsten particle loading on controlling porosity of tungsten-epoxy composite by precisely tuning the weight ratio, contributing to engineering process in the fabrication. In conclusion, porosity was adjusted by controlling the tungsten loading content in epoxy.