High sensitivity gravimetric sensor made of unidirectional carbon fiber epoxy composite on (1 - X)Pb(Zn_1/3Nb_2/3)O₃-xPbTiO₃ single crystal substrate

We have derived a general formula for sensitivity optimization of gravimetric sensors and have used it to design a high sensitivity gravimetric sensor using unidirectional carbon fiber epoxy composite (CFEC) waveguide layer on (1 - x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 (PZN-xPT) single crystal substrate with the carbon fibers parallel to the x1 and x2 axes, respectively. The normalized maximum sensitivity (Sm^fλ)max exhibits an increasing tendency with the decrease of (h/λ)opt and the maximum sensitivity (Sm^fλ)max increases with the elastic constant c66^E of the piezoelectric substrate material. For the CFEC/[011]c poled PZN-7%PT single crystal sensor configuration, with the carbon fibers parallel to the x1 axis at λ = 24 μm, the maximum sensitivity (Sm^fλ)max can reach as high as 1156 cm²/g, which is about three times that of a traditional SiO2/ST quartz structure gravimetric sensor. The better design selection is to have the carbon fibers parallel to the direction of propagation of Love wave in order to obtain the best sensitivity.