Bio-inspired MEMS flow and inertial sensors

Abstract

In biology, mechanosensors, equipped with differing hair-like structures for signal pick-up, are sensitive to a variety of physical quantities like: acceleration, flow, rotational rate, balancing and IR-light. As an example, crickets use filiform hairs for sensing of low-frequency flows to obtain information about the environment and avoid, for example, attacks. Their filiform hairs are able to sense airflows with velocity amplitudes down to 30 um/s and operate around the energy levels of thermal noise. Hair-sensor inspired flow-sensors for measurement of (tiny) ac-airflows using capacitive readout, have been designed and fabricated using technology generally denoted as MEMS (microelectromechanical systems). An improvement of the hair-sensors is obtained in both an increase in responsivity for frequencies within the sensor's bandwidth as for lower flow velocity thresholds. It is demonstrated that electromechanical amplitude modulation (EMAM) can improve the measurement performance at low frequencies. Under certain conditions, noise can be used to increase signal-to-noise ratios by exploiting the concept of stochastic resonance. SR is implemented by controlling the strength of position dependent on capacitive wells. Further. First, a biomimetic accelerometer has been realized using surface micromachining and SU-8 lithography, inspired by the clavate hair system of the cricket. Second, inspired by the fly's haltere, a biomimetic gimbal-suspended hair-based gyroscope has been designed, fabricated and partially characterized. Third, an angular accelerometer based on the semicircular channels of the vestibular system, has been developed. In general, cricket flow sensors perform not only better than the MEMS hair sensors, but are also close to operation at their physical limits. The results emphasize the intriguing research on bio-inspired sensors in order to learn from nature.