Quartz crystal capacitive sensor with inductance-capacitance resonance circuit for vapor sensing

Using a novel capacitive sensor, which we call a quartz crystal capacitive sensor (QCCS), the vapor sensing of acetaldehyde was performed. QCCS consists of a parallel plate capacitor and a quartz crystal oscillator, which has an inductance-capacitance (LC) resonance property. The developed sensor can indirectly convert the perturbation of the permittivity of sampled gas into the deviation of the oscillation frequency of the quartz crystal, and determine the characteristics of chemicals existing between the parallel plate with a high accuracy. The results of an organic vapor sensing test indicated that QCCS had a high sensitivity [6.1 ppm (30 Hz)] to the permittivity of acetaldehyde.