Spectroscopic Measurement of Water Using an Electrostatic Transducer with Near-infrared Absorber

Abstract

The widespread of near-infrared spectroscopes in the consumer field is expected to create new demand, such as the detections of fruit and vegetable rot and the easy measurement of the amount of water in the skin. Conventional cooled photodiodes using compound semiconductor materials such as InGaAs have problems with cost reduction and miniaturization. Therefore, we proposed an electrostatic Si microresonator device for the realization of a near-infrared optical sensor. This device measures the resonance frequency shift caused by the thermal stress generated in the resonator due to light absorption depending on the light intensity. The purpose of this study is to apply the device to near-infrared spectroscopy of water as a photodetector. We proposed an evaluation method based on a theoretical equation and confirmed that the device could detect the near-infrared absorption spectrum of water. The measurement results of the developed device matched well with that of the commercially available photodiode intensity sensor. In the future, it is expected that a compact near-infrared spectrometer with high sensitivity and low cost will be realized by arranging devices that integrate absorbers with different wavelength dependencies.