Flexible Ultrasound Transducers Achieve Enhanced Acoustic Performance with Novel Interfaces

The development of flexible ultrasound transducers presents a significant challenge, as traditional rigid materials hinder adaptation for wearable or conformal applications. Spencer Hagen, Dulcce A Valenzuela, Parag V Chitnis, Shirin Movaghgharnezhad, and colleagues at George Mason University address this limitation by investigating the crucial role of the electrode-polymer interface in transducer performance. Their research demonstrates that careful engineering of this interface dramatically improves both the acoustic output and flexibility of these devices, moving beyond a focus solely on piezoelectric materials. By fabricating and testing transducers with different electrode materials, including silver, gold, flakes, and laser-induced graphene, the team reveals that laser-induced graphene electrodes, in particular, offer superior performance and durability, retaining stable function even after extensive bending and aging, and paving the way for advanced wearable imaging technologies.

The core innovation lies in optimizing the interface between the electrode and the piezopolymer. Scientists compared four electrode materials, laser-induced graphene (LIG), graphene flakes, silver, and gold, and discovered that porous LIG significantly enhances performance. The porosity allows partial infiltration of the piezopolymer, creating stronger mechanical and electrical coupling, unlike dense metallic electrodes with weak adhesion. Researchers thoroughly characterized the fabricated transducers using scanning electron microscopy, piezoelectric measurements, impedance spectroscopy, mechanical bending tests, and aging tests.

LIG-based transducers exhibited significantly higher acoustic output, improved interfacial coupling, superior mechanical durability after 10,000 bending cycles, and long-term stability over an eight-week period. Optimized poling conditions further enhanced the piezoelectric properties of the piezopolymer film. This research provides a promising pathway for developing high-performance, durable, and reliable flexible ultrasound transducers with potential applications in wearable medical devices, non-destructive testing, robotics, and biomedical imaging. The supplementary information includes detailed data, analysis, and visual demonstrations supporting these findings, confirming that engineering the electrode-piezopolymer interface with porous laser-induced graphene is a highly effective strategy.

Flexible Ultrasound Transducers, Interface Engineering and Fabrication

Scientists engineered flexible ultrasound transducers by meticulously controlling the electrode-piezopolymer interface, demonstrating that interface morphology significantly impacts device performance and durability. Devices were fabricated on polymer substrates using photothermal laser processing for LIG formation and drop-casting of a piezopolymer ink. Researchers systematically examined the influence of silver, gold, graphene flakes, LIG, and gold-decorated LIG electrodes on piezoelectric response, dielectric behavior, and acoustic output. LIG-based transducers exhibited strong acoustic and piezoelectric output due to partial infiltration of the piezopolymer into the porous LIG network, enhancing interfacial contact and stress transfer.

Gold-based transducers achieved comparable acoustic output, while silver and graphene flakes provided limited coupling, resulting in reduced electromechanical response. Rigorous testing, including 10,000 bending cycles and an eight-week aging study, revealed that LIG-based transducers demonstrated exceptional flexibility and durability, while graphene flake, silver, and gold devices degraded. These findings establish electrode-piezopolymer interface engineering as a critical design consideration for high-performance flexible ultrasound transducers and identify LIG as a promising candidate for wearable imaging applications.

Electrode Interface Dictates Transducer Performance

This research demonstrates a significant advancement in flexible ultrasound transducer technology, focusing on the critical role of the electrode-piezopolymer interface. Scientists fabricated devices using five distinct electrode materials, silver, gold, graphene flakes, laser-induced graphene (LIG), and gold-decorated LIG, to directly compare their impact on transducer performance. Cross-sectional imaging revealed that LIG formed a porous network allowing partial infiltration of the piezopolymer, while silver created a dense layer and graphene flakes exhibited a stacked structure. This infiltration within the LIG structure enhanced mechanical interlocking and increased surface interaction, demonstrably improving strain transfer at the interface.

Researchers optimized the poling process, crucial for aligning piezoelectric dipoles within the piezopolymer. Measurements of the piezoelectric charge coefficient showed a maximum value achieved with LIG electrodes, indicating saturation of dipole alignment. Electrical characterization validated these optimized parameters. Notably, LIG-based transducers exhibited superior durability, retaining stable performance after 10,000 bending cycles and an eight-week aging study, while devices using graphene flakes, silver, and gold degraded. These findings establish electrode-piezopolymer interface engineering as a key design consideration for flexible ultrasound transducers and position LIG-based architectures as a promising route toward high-performance, conformable systems for wearable and diagnostic imaging applications.

LIG Electrodes Enhance Piezoelectric Transducer Performance

This study investigated the impact of electrode material on the performance of flexible ultrasound transducers constructed from piezopolymers. Researchers systematically compared devices fabricated with silver, gold, graphene flakes, laser-induced graphene (LIG), and gold-decorated LIG electrodes, focusing on how each material interacts with the piezopolymer layer. The findings demonstrate that the structure of the electrode-polymer interface significantly influences both the electrical and acoustic properties of the resulting transducer. Notably, LIG electrodes proved most effective, exhibiting strong piezoelectric output and acoustic performance.

The porous nature of LIG allows partial infiltration of the piezopolymer, increasing contact area and improving stress transfer between the materials. Gold electrodes also yielded strong acoustic output, attributed to their uniform surface and efficient charge collection. In contrast, devices utilizing silver and graphene flakes showed weaker responses, likely due to limited interfacial coupling. Mechanical testing revealed that LIG-based transducers maintained stable performance through 10,000 bending cycles and an eight-week aging study, while devices with silver, gold, and graphene flakes exhibited varying degrees of degradation. These results emphasize that achieving durable and high-performing flexible transducers depends on interfacial compliance and bonding, not simply electrode conductivity. LIG, with its combination of mechanical flexibility, strong electromechanical coupling, and robust acoustic output, emerges as a particularly promising material for future wearable and conformal ultrasound systems.