Microstructured Electrode-Piezopolymer Interface for Ultrasound Transducers with Enhanced Flexibility and Acoustic Performance

Ultrasound transducers made from rigid piezoceramics are difficult to adapt for wearable or conformal applications. Piezopolymer-based transducers offer a practical alternative; however, most existing studies focus on piezoelectric materials, while the influence of electrode material and electrode-polymer interface remains underexplored. This study leverages different interface-engineering strategies to examine the influence of electrode-piezopolymer interface morphology on piezoelectric, dielectric, and acoustic behavior in flexible transducers. Devices were fabricated using silver (Ag), gold (Au), graphene flakes (GF), laser-induced graphene (LIG), and Au-decorated LIG electrodes, enabling comparison across interfacial architectures. LIG-based transducers showed strong acoustic and piezoelectric output due to partial infiltration of the piezopolymer into the porous LIG network, which enhances interfacial contact and stress transfer. Au-based transducers achieved comparable acoustic output. In contrast, dense Ag electrodes and layered GF films provided limited coupling, resulting in reduced electromechanical response. LIG-based transducers exhibited the highest flexibility and durability, retaining stable performance after 10,000 bending cycles and an eight-week aging study, whereas GF, Ag, and Au devices degraded under bending, and Ag electrodes declined over time. These findings demonstrate that engineering the electrode-polymer interface is critical for high-performance flexible ultrasound transducers and identify LIG as a strong candidate for wearable imaging applications.