Behaviour of a series piezoelectric sensor in electrolyte solution: Part I. Theory

Abstract The theory, methodology and behaviour of a piezoelectric and conductivity sensor in electrolyte solution are reported. The sensor was constructed by connecting an AT-cut piezoelectric quartz crystal and a conductivity electrode in series. It has a sensitive and selective frequency response to the change in solution conductivity and permittivity. The relationship between frequency and solution conductivity was derived according to the oscillating theory and supported by the experiments. The effects of the solution conductivity, permittivity, temperature, density and viscosity, cell constant of the conductivity electrode, foreign electrolytes and the operating voltage of the integrated circuit-TTL oscillator on the behaviour of the series piezoelectric sensor were investigated. The sensor possesses high sensitivity to the solution conductivity and a low frequency-temperature coefficient, and its frequency depends very little on the operating voltage and density and viscosity of the solution. Its sensitivity and accuracy were improved in the presence of foreign electrolytes.