A bend-resistant flexible vector hydrophone for curved surface applications

Purpose This study aims to address the reliability issue of fatigue fracture in internal metal interconnects of flexible vector hydrophones due to strain concentration when deployed on curved surfaces. The core objective is to propose a full semi-circular arc periodic serpentine interconnect structure and to systematically investigate its bending resistance and acoustic sensing performance. The goal is to fill the research gap on serpentine interconnects in the field of flexible hydrophones and to provide theoretical and technical support for complex curved surface applications. Design/methodology/approach This research used a systematic approach combining theoretical modeling, simulation analysis and process optimization. First, a mechanical model for linear and serpentine interconnects was established to theoretically reveal the low-stress mechanism of the serpentine structure. Second, a finite element model coupling solid mechanics and pressure acoustics was built using COMSOL multiphysics to simulate the stress, characteristic frequency, directivity and bending resistance of the flexible hydrophone and its serpentine interconnects. Furthermore, an innovative microfabrication process was developed, using transfer printing to achieve high-performance integration of single-crystal silicon piezoresistors onto the flexible substrate, with process reliability ensured by a multiindex collaborative judgment method. Finally, the piezoresistive effect of the sensitive unit was validated through quasi-static pressure resistance tests. Findings The research yielded the following key findings: regarding mechanical performance, simulations showed that at a bending radius of 8 mm, the maximum von Mises stress of the serpentine interconnect was 688 MPa, which is 31% lower than that of the linear wire, significantly enhancing the fatigue life. Regarding acoustic performance, the flexible hydrophone achieved a sensitivity of −179.75 dB, an 18.75 dB improvement over traditional hydrophones, exhibited good directivity, and had an effective working frequency band of 20–543 Hz. Regarding process and electrical performance, the optimized transfer printing process increased the yield by 35%. The measured piezoresistive coefficient of the sensitive unit reached 3.53 × 10–10 Pa-1, approximately 4.92 times that of traditional bulk silicon, demonstrating that this structure greatly enhances mechanical reliability while maintaining excellent electrical performance. Originality/value The originality and value of this research are reflected in three aspects: first, it proposes a novel full semi-circular arc periodic serpentine interconnect structure without straight segments, specifically addressing the stress concentration problem in high-curvature surface applications. Second, it constructs a dedicated mechanical model for this serpentine interconnect, clarifying the relationship between its stress and geometric parameters, thus providing clear guidance for design. Third, it systematically introduces the serpentine interconnect into the field of flexible vector hydrophones and solves the process challenges of integrating it with the bionic sensitive structure, filling a research gap in this area. This study provides a valuable solution and design basis for developing highly reliable flexible electronic devices suitable for dynamic bending environments.