Measurement of the electric permittivity using Bleustein–Gulyaev wave sensor

Abstract

We present a novel compact electric permittivity sensor that exploits Bleustein–Gulyaev waves propagating along the surface of shear-poled piezoelectrics. We formulate the dynamic nonlinear electromechanical partial differential equations of motion governing wave propagation under electromagnetically quasistatic conditions. The permittivity of the medium-under-test was found to influence the sensor eigenvalues, enabling the implementation of a frequency-shift permittivity sensor. Solution of the equations of motion demonstrates resonance of the first and third modes when excited using an interdigitated transducer. We fabricated two sensor prototypes on shear-poled PZT4 and LiNbO3 substrates and used a Vector Network Analyzer to observe the shift in their fundamental natural frequency in the presence of various media-under-test. S 11 measurements show deterministic and repeatable shifts in the resonant frequency of the first mode of the LiNbO3 sensor measured at MHz for ethanol and MHz for deionized water where the bare surface frequency was initially at MHz.