Non-contact sensor for measurement of liquid concentration based on quartz oscillator

In this paper, a noncontact sensor for the measurement of liquid concentration using a quartz oscillator is reported. An out-of-plane electric field with a planer sensing capacitor (SC) is used for sensing a liquid on a spacer. This sensor measures the changes in the capacitance of the SC as the changes in the frequency of the quartz oscillator. The capacitance is dependent on the relative permittivity and the conductivity of the liquid sample on the spacer. Therefore, it is possible to measure the concentration of the sample. The response is very stable because in this sensor, the SC is incorporated into the quartz oscillator. Because the quartz crystal resonator is not contact with liquid, the proposed sensor has a high quality factor (approximately 30,000). Moreover, this sensor can be used with a general IC and an electronic component, with a low cost. The proposed sensor can be expected to be used for various kinds of liquid sensing applications.