Epoxy-cement composite packaging for KNN piezoelectric sensors

Sensors and Actuators A Physical, vol. 398, pp. 117356

Abstract

Durable and high-performance piezoelectric sensors are critical for long-term infrastructure monitoring, especially under harsh mechanical and environmental conditions. The choice of encapsulation materials plays a decisive role in determining their stability, sensitivity, and service life. This study evaluates solvent-based and waterborne epoxy resins, with/without cement, for potassium sodium niobate (KNN)-based sensors. Cement addition in solvent-based epoxy reduced compressive strength and signal stability, yet maintained high sensitivity and good linearity under loading. Waterborne epoxy-cement composites achieved higher strength (≤57.8 MPa) and 2-4 times greater voltage output. However, these composites failed structurally at loads exceeding 600 N, limiting their use in environments with heavy loads. Fatigue tests showed that solvent-based epoxy encapsulation had excellent durability, with only a 4.4% voltage drop after 100,000 loading cycles. This indicates superior robustness for long-term deployment. The results reveal a trade-off between sensitivity and robustness in packaging strategies. Waterborne systems are suitable for low-to-moderate load conditions where sensitivity is prioritized, while solvent-based epoxies offer long-term reliability under repetitive and higher mechanical stresses. These findings provide important material selection guidelines for the development of reliable, lead-free piezoelectric sensors tailored to the specific demands of infrastructure health monitoring applications. • The influence of resin formulation on the performance of KNN-based piezoelectric sensors was comprehensively examined. • Cement-filled solvent epoxy systems offered higher voltage response, at the cost of reduced strength. • Waterborne epoxy–cement systems achieved compressive strengths up to 57.8 MPa with amplified signal output. • Solvent-based encapsulants demonstrated excellent cyclic stability over 100,000 mechanical loadings. • Findings reveal a trade-off between electrical sensitivity and structural endurance, guiding encapsulation design.

Authors 3

1. Kai Zheng Aachen Institute of Highway Engineering

   RWTH Aachen University

   Affiliation as printed

   Institute of Highway Engineering (ISAC), RWTH Aachen University, Mies-van-der-Rohe-Street 1, 52074 Aachen, Germany

2. Ning Xie

   Aston University

   Affiliation as printed

   Aston Institute of Materials Research, School of Engineering and Applied Science, Aston University, Birmingham, B4 7ET, UK

3. Pengfei Liu corresponding Aachen Institute of Highway Engineering

   RWTH Aachen University

   Affiliation as printed

   Institute of Highway Engineering (ISAC), RWTH Aachen University, Mies-van-der-Rohe-Street 1, 52074 Aachen, Germany