A MEMS capacitive, passively powered heart rate monitor: Design and analysis

A MEMS heart rate monitor has been designed for a three-structural-layer fabrication process such as PolyMUMPs. The device size is just over 400 mum times 400 mum. It uses a movable top plate in order to create a variable capacitance in conjunction with a coil for an inductance in order to create a resonant tank circuit. The circuit resonant frequency changes depending on the deflection of the top plate. The device is powered via the sensor coil by a magnetic field produced by an external coil. The resonant frequency is also monitored using magnetic coupling. The capacitance change has been calculated to be about 70.5% corresponding to a 45.8% change in resonant frequency. The reflected impedance magnitude and phase are monitored on the external coil.