High-order symmetric mode of aluminum nitride-based Lamb wave resonator realizing high-sensitivity strain sensing

Surface acoustic wave resonators have been widely developed for strain detection due to their advantages of miniaturization, portability, potential to be integrated with microelectronics, and passive/wireless capabilities. A Lamb wave resonator, similar to a surface acoustic wave resonator, transforms the acoustic waves from surface to bulk propagation, enhancing its sensitivity to deformation. Recent research has reported that Lamb wave resonators exhibit high strain sensitivity and multi-modal characteristics in strain sensing. Our study aims to investigate the underlying mechanisms for high sensitivity and the differences in sensitivity across various modes. This study began with the coupling mechanism of Lamb waves and employed computational and simulation software to investigate the reasons behind the differences in strain sensitivity among different modes: shear-wave-dominated modes achieve higher strain sensitivity. Subsequently, experimental testing of strain sensitivity for various modes on fabricated resonators was conducted, yielding trends consistent with theoretical and simulation predictions. Ultimately, the Lamb wave resonator achieved a high strain sensitivity of 1.97 ppm/με, a minimum detection limit of 25 με, and a maximum hysteresis of less than 1% within a 1000 με strain detection range through the laterally excited higher-order symmetric mode (S1-5 mode). All results clearly demonstrate the sensor's significant potential for strain monitoring applications.