Optical micro-electro-mechanical-system pressure sensor based on light intensity modulation

An optical micro-electro-mechanical-system pressure sensor based on light intensity modulation is described. The idea is to use light for signal transmission to replace electrical signal, which isolates the sensor from electrical signals, so that it is quite suitable in flammable and combustible areas such as petrochemical and oil well. The sensor is composed of silicon diaphragm and optical system. The silicon diaphragm is fabricated from bulk micromachining technology and Si₃N₄ film is deposited on diaphragm for reflecting light. In the optical cable, one fibre conducts source light to the diaphragm and the other fibres conduct the reflected light back to photoelectric detection circuit. When pressure is applied on the sensor, the diaphragm will deform causing the intensity shift of reflected light. Photoelectric detection circuit converts the intensity of reflected light to voltage. The voltage is proportional to reflected light intensity and, in turn, to the deformation of silicon diaphragm, so that pressure can be measured. Deformation of silicon diaphragm is acquired by finite element method. Sensor's optical features are also analysed. Sensor prototype has been fabricated and encapsulated. The measurement range is 0-20 MPa and experimental sensitivity is -7.2 mV/MPa.