A novel monolithic piezoelectric sensor

A novel monolithic piezoelectric sensor (MPS) is presented for the detection of physical, chemical and biochemical measurands. This new sensor overcomes specific deficiencies associated with the quartz crystal microbalance (QCM) while still employing a well-characterized, temperature-stable thickness-shear mode (TSM). The sensor is applicable to both gaseous and liquid phase measurements; however, the principal benefit of the MPS is in liquid phase measurements. In these applications, it offers the ability to operate simple, yet stable, oscillator circuits in relatively viscous media. The proposed sensor structure is based on a two-pole coupled resonator, in which mechanical coupling between the electrical input and output determines the electrical properties. This structure offers approximately 180/spl deg/ of phase shift over its 3dB bandwidth with nominally 180/spl deg/ of insertion phase at the symmetric resonant frequency and approximately 0/spl deg/ of insertion phase at the antisymmetric resonant frequency. Simple oscillator circuits may be implemented which measure the symmetric frequency (f/sub s/), the antisymmetric frequency (f/sub a/) or the nominal center frequency (f/sub s/). Suitable switching allows combinations of these frequencies to be sequentially measured, expanding the capabilities of the MPS versus the QCM. This novel MPS sensor structure should accelerate the commercialization of piezoelectric sensor technology, particularly in such areas as chemical, biochemical and environmental testing.