In this paper, we report the non-contact sensor for measurement of liquid concentration based on quartz oscillator. The non-contact sensing can be realized by using a leaked electric field of a planer sensing capacitor for sensing liquid on a spacer. This sensor measures capacitance changes of the sensing capacitor (SC) as frequency changes of the quartz oscillator. Since the capacitance is dependent on relative permittivity or conductivity of liquid on the spacer, it is possible to measure the concentration of them. The response is very stable because this sensor is incorporated the SC into the quartz oscillator. Because the SC is in contact with the sensing liquid instead of the quartz crystal resonator, the proposed sensor has a high quality factor (about 30,000). Moreover, this sensor can be used with general IC and electronic component, which takes low cost. The proposed sensor is expected to use for non-contact measurements of liquid concentration.
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