Rapid scan Fourier transform detection of a frequency encoded quartz crystal microbalance array

A detection method for thickness shear mode (TSM) or quartz crystal microbalance (QCM) sensor arrays is described. Each element of the sensor array is frequency encoded so that it has a unique resonant frequency and can be identified under any operating condition. Frequency encoding of TSM sensors can be realized (1) by creating individual sensors with different thicknesses of piezoelectric base material or (2) preferably by electroplating sensors of identical piezoelectric base material thickness with predetermined thicknesses of metal films. Frequency changes can be detected by use of pulsed Fourier transform method or rapid scan Fourier transform method with a heterodyne configuration in which frequency reference is generated by a local oscillator based on a device modified according to the frequency encoding procedure. The detection method allows high analysis speed and low cost in hardware construction. A four-sensor chemical vapor detection system is designed and constructed to demonstrate the principle of frequency encoding and rapid scan Fourier transform detection for QCM arrays.