Electrostatic Micro-Hydraulic Hair Sensors and Actuators.

Abstract

A novel, optimally-designed micro-hydraulic structure is introduced to significantly improve performance of many MEMS devices for sensing and actuation. The micro-hydraulic system in conjunction with application-specific appendages can realize high performance sensors and actuators. For instance, biomimetic hair-like structures can provide external air flow sensing with high accuracy and high resolution that can replace bulky, high power and fairly low-resolution hotwire anemometers or other conventional sensors in most applications. Moreover, 3D hairs with small footprints enable dense array fabrication to provide redundancy, fault tolerance and directional sensitivity. Previous works using hairs with piezo-resistive or capacitive transduction have very fragile structures that limit the use of the air flow sensors in outside environments. Additionally, the high accuracy of these sensors is achieved at the expense of full-scale range. Using a micro-hydraulic structure a new type of low-power, accurate and robust flow sensor has been fabricated and tested in which a hair-like appendage is used to translate flow into hydraulic pressure. This pressure is sensed with an integrated capacitor within the micro-hydraulic system by which the sensitivity is amplified. The air flow sensor detects flow speeds ranging from about 2 mm/s to over 15 m/s with a resolution of 1.7 mm/s. This corresponds to about 78.9 dB of range to minimum detection ratio, which is the highest range over resolution ratio to the best of our knowledge. An array of sensors allows 2D directional sensing with minimum 13° angular resolution. This enables utilization of the hair sensors for state estimation and wind gust rejection when integrated with micro-air-vehicles. The micro-hydraulic structure can also be used as a platform to realize many cross-disciplinary high performance devices. This platform has been used to make tactile sensors that are needed in humanoid robotics, providing performance similar to human skin. Additionally, these structures have been tested in actuation mode to form micro-valves for micro-fluidic circuits and have the ability to provide hexa-pedal locomotion for micro-scale robotic applications. With use of proper appendages, devices such as shear stress sensors, 3D accelerometers, 2D gyroscopes, active flow controllers or tri-gait locomotion actuators can be realized.