Design, modeling, and performance analysis of novel mechanically adaptive 2-1-2-type piezoelectric composite structures

Flexible ultrasonic transducers are important for wearable medical imaging and therapeutic applications, yet combining high electromechanical performance with structural conformity and array uniformity remains difficult. Here, a 2-1-2-type piezoelectric composite consisting of PZT-4, epoxy resin, and silicone rubber is prepared through a monolithic dice-fill technique. A series-parallel equivalent model is employed to guide the structural optimization of the composite. Based on the theoretical analysis, representative samples with ceramic volume fractions of v_c = 50 % and 60 % and a substrate volume fraction of v_p = 20 % are selected for fabrication and experimental validation. These composites exhibit high-purity thickness vibration, a thickness electromechanical coupling coefficient (k_t) of 0.62, and an acoustic impedance (Z) of 9.41 MRayl, indicating efficient energy conversion and favorable acoustic matching. The composite sustains a maximum tensile load close to 20 N and endures 400 cycles under a 5 N cyclic load without performance degradation. Resonance characteristics remain stable from 20°C to 60°C, showing strong fatigue and thermal stability for long-term wearable use. The fabricated arrays display high inter-element uniformity, with relative mean deviation (RMD) below 1 % and maximum deviation ratio (MDR) below 3 %. These results confirm the 2-1-2 composite as a promising material platform for conformal ultrasonic imaging and wearable therapeutic ultrasound systems.