A Nondestructive Liquid-Level Sensor Based on Spoof Surface Plasmon Polaritons Controlled by Liquid Metal Switches

This article proposes a nondestructive multichannel sensor for liquid-level detection based on spoof surface plasmon polaritons (SSPPs). A mathematical model for liquid-level sensing is established by leveraging the dispersion relationship between the permittivity and the phase shift constant. Then, liquid metal switches are integrated into the SSPP channels to dynamically control signal propagation, thereby enabling selective activation of each channel for level detection. The proposed detection theory and dynamic control method are validated through simulations. Subsequently, the designed sensors are fabricated and measured. The results demonstrate a linear relationship between the liquid level and the phase offset. The sensor is capable of penetrating nonmetallic containers for liquid-level detection, with a measurement range determined solely by the length of the component. It achieves a resolution of 0.01 mm and a detection accuracy of less than 1.28 mm. Moreover, the multichannel SSPP design enables the acquisition of more detailed level information, supporting dynamic liquid-level monitoring.