Development of Polymer-Ceramic-Metal Graded Acoustic Matching Layers via Cold Sintering

Medical ultrasound transducers require acoustic matching layers to optimize sound transmission. Traditional materials often struggle to balance impedance and attenuation. Prior research has shown that high acoustic impedance can lead to poor signal transmission if not matched properly. It was already known that polymer-based composites offer flexibility but lack sufficient conductivity. No prior work had resolved the challenge of achieving low attenuation while maintaining electrical conductivity in such materials. This gap motivated the exploration of multi-phase composites. That uncertainty drove the need for a method that could control acoustic velocity and impedance simultaneously. A cold sintering approach had not been fully explored for this application. The need for scalable fabrication methods also remained unmet in existing literature.

The study aimed to develop a new class of electrically conducting composites for acoustic matching layers in medical ultrasound. The specific problem addressed was the need for materials that combine low acoustic attenuation with high impedance. The motivation stemmed from the limitations of traditional materials in achieving both properties. The researchers sought to use cold sintering to avoid high-temperature degradation of polymer components. They also aimed to control the acoustic properties through phase composition. The goal was to achieve impedance values between 5 and 19 MRayl with minimal signal loss. The study aimed to validate a theoretical model for acoustic impedance prediction. Ultimately, the work aimed to demonstrate scalable fabrication of these composites.

The researchers used cold sintering to fabricate polymer-ceramic-metal composites. They selected zinc oxide, silver, and thermoplastic polymers as primary components. The composites were sintered at pressures below 50 MPa and temperatures of 150 °C. Tape casting was employed to create graded layers with varying impedance. The acoustic impedance was measured at 10 MHz to assess performance. Resistivity and density were evaluated to confirm material properties. A logarithmic model was used to predict impedance based on phase volume fractions. The fabrication process was scaled up to demonstrate practical application.

The composites achieved acoustic impedance values between 5 and 19 MRayl with low attenuation. Acoustic velocities exceeded 2000 m/s in most formulations. Densities above 95% and resistivities below 1 Ω-cm were observed. The measured impedance matched theoretical predictions closely. A three-layer transducer achieved a -6 dB bandwidth of over 85%. Hydrozincite-based composites reached 5 MRayl with velocities above 2000 m/s. Graded prototypes with three distinct impedance levels were successfully fabricated. The cold sintering process allowed consistent material distribution across layers.

The study demonstrated that cold sintering enables the fabrication of polymer-ceramic-metal composites with controllable acoustic properties. The acoustic impedance and velocity matched theoretical predictions closely. The materials achieved low attenuation while maintaining electrical conductivity. The graded prototypes showed potential for use in multi-layer transducers. The cold sintering process allowed scaling to larger dimensions without compromising performance. The results suggest that these composites can replace traditional materials in medical ultrasound. The approach provides a scalable and predictable method for matching layer fabrication. The findings support the feasibility of using this method in commercial transducer design.