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

Smitha Shetty, Prapassorn Numkiatsakul, Kevin Wickline, Regina Incarnato, Haifeng Wang, Hal Kunkel, Clive A. Randall, Susan Trolier-Mckinstry

Research output: Contribution to journalArticlepeer-review

## Abstract

A family of three phase, polymer-ceramic-metal (Poly-cer-met) electrically conducting composites was developed via cold sintering for acoustic matching application in medical ultrasound transducers. A range of acoustic impedance ( ${Z}$ ) between $5 < {Z} < 21$ MRayl with low attenuation (<3.5 dB/mm, measured at 10 MHz) was achieved in composites of zinc oxide, silver, and in thermoplastic polymers like Ultem polyetherimide (PEI) or polytetrafluoroethylene (PTFE) at sintering pressure less than 50 MPa and temperature of 150 °C. Densities exceeding 95% were achieved, with resistivities less than $1~ \Omega$ -cm. The acoustic velocity was homogeneous across the part (variations <5%). The acoustic velocities exceeded 2500 m/s for ${Z}$ above 12 MRayl. The experimentally measured acoustic impedance of ZnO/Ag/PEI composites was observed to be in close agreement with the theoretical logarithmic model developed for different volume fractions of individual phases at the percolation limit for Ag. Thus, the acoustic properties of this family of matching layers (MLs) can be predicted to a good approximation before experimental realization. Additionally, a non-conducting low ${Z}$ (5 MRayl $< {Z} < 12$ MRayl) with acoustic velocities exceeding 2000 m/s was achieved using hydrozincite as the ceramic component. Scaling of the composites to $2{^\prime}{^\prime}$ diameter was demonstrated. A -6 dB bandwidth greater than 85% was measured for a three ML ultrasound transducer, fabricated using a single cold sintered layer ( ${Z} = 19$ MRayl) and two other commercial layers in the stack. Finally, a co-cold sintered graded prototype consisting of three tape-casted formulations corresponding to ${Z} = 5$ , 9, and 19 MRayl, while still retaining the correct distributions of the components was demonstrated.

Original language English (US) 1413-1427 15 IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 69 4 https://doi.org/10.1109/TUFFC.2022.3148792 Published - Apr 1 2022

## All Science Journal Classification (ASJC) codes

• Instrumentation
• Acoustics and Ultrasonics
• Electrical and Electronic Engineering

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