Impedance analysis for the investigation of the behaviors of piezoelectricquartz crystal in the liquid at harmonic resonance

The behaviors of piezoelectric quartz crystal (PQC) at harmonic resonance i n viscous liquid have been studied by using impedance analysis. The theoret ical equations comprising of the harmonic number (h), fundamental frequency (f(0)) and the number of sides in contact with liquid (N) have been derive d. The effects of h, f(0), and N on the change of resonant frequency, Delta f, and the motional resistance, R-1, for PQC in viscous liquid were discus sed. It was shown that the crystal with higher fundamental frequency produc ed smaller response of R-1 at a certain value of (rho(L)eta(L))(1/2). This reason was that R-1 was proportional to f(0)(3/2)L(1), where L-1 was the mo tional inductance in air. It was found that, the responses of Delta f and R -1 both deviated from their respective linearity with (rho(L)eta(L))(1/2) w hen (rho(L)eta(L))(1/2) is higher than 8.7 g (1/2) cm(-3/2) cP(1/2). This d eviation was explained by the difference of the decay length (delta) in dif ferent liquids. The slope of Delta f vs. R-1 has been suggested to be a qua litative indicator of the (rho(L)eta(L)) contribution to the total frequenc y changes. For adsorption of some biological materials on gold, the magnitu de order of this contribution to their respective Delta f can be given by A u-C16SH/DNA > Au/L-cys > Au/BSA. (C) 2000 Elsevier Science S.A. All rights reserved.