A review of high-performance MEMS sensors for resource exploration and geophysical applications

MEMS sensors have the advantages of small volume,lightweight,and low cost,therefore,have been widely used in the fields of consumer electronics,industry,health,defence,and aerospace.With their ever-improving performance,MEMS sensors have also started to be used in resource exploration and geophysical applications.However,the requirements of high-precision MEMS sensors for geophysical applications have not been specified in detail.Therefore,this paper systematically analyzes the requirements of high-performance MEMS sensors for prospecting and geophysical applications,including seismic surveillance,Earth tide,volcanic activity monitoring for natural disasters;seismic,gravity,and magnetic resource prospecting;drilling process monitoring and local gravity measurement for gravity aided navigation.Focusing on the above applications,this paper summarizes the state-of-the-art of research on high-performance MEMS sensors for resource exploration and geophysical applications.Several off-the-shelf MEMS sensors have been used for earthquake monitoring,seismic exploration and drilling process monitoring,and a range of MEMS research prototype sensors have successfully been employed for Earth tides measurement and are promising to be used for gravity exploration.MEMS magnetometers should have a lower noise floor to meet the demand for magnetic exploration.MEMS gravity gradiometers are still under early development and will not be deployable in short-term.Highperformance MEMS sensors hold the advantages of low-cost,high integration,and capability of working in extreme environments;therefore,they are likely to gradually replace some conventional geophysical instruments in some application areas.

Near-zero stiffness accelerometer with buckling of tunable electrothermal microbeams

Pre-shaped microbeams,curved or inclined,are widely used in MEMS for their interesting stiffness properties.These mechanisms allow a wide range of positive and negative stiffness tuning in their direction of motion.A mechanism of pre-shaped beams with opposite curvature,connected in a parallel configuration,can be electrothermally tuned to reach a near-zero or negative stiffness behavior at the as-fabricated position.The simple structure helps incorporate the tunable spring mechanism in different designs for accelerometers,even with different transduction technologies.The sensitivity of the accelerometer can be considerably increased or tuned for different applications by electrothermally changing the stiffness of the spring mechanism.Opposite inclined beams are implemented in a capacitive micromachined accelerometer.The measurements on fabricated prototypes showed more than 55 times gain in sensitivity compared to their initial sensitivity.The experiments showed promising results in enhancing the resolution of acceleration sensing and the potential to reach unprecedent performance in micromachined accelerometers.

Design of a large-range rotary microgripper with freeform geometries using a genetic algorithm

This paper describes a novel electrostatically actuated microgripper with freeform geometries designed by a genetic algorithm.This new semiautomated design methodology is capable of designing near-optimal MEMS devices that are robust to fabrication tolerances.The use of freeform geometries designed by a genetic algorithm significantly improves the performance of the microgripper.An experiment shows that the designed microgripper has a large displacement(91.5μm)with a low actuation voltage(47.5 V),which agrees well with the theory.The microgripper has a large actuation displacement and can handle micro-objects with a size from 10 to 100μm.A grasping experiment on human hair with a diameter of 77μm was performed to prove the functionality of the gripper.The result confirmed the superior performance of the new design methodology enabling freeform geometries.This design method can also be extended to the design of many other MEMS devices.

Investigation of a complete squeeze-film damping model for MEMS devices

Dynamic performance has long been critical for micro-electro-mechanical system(MEMS)devices and is significantly affected by damping.Different structural vibration conditions lead to different damping effects,including border and amplitude effects,which represent the effect of gas flowing around a complicated boundary of a moving plate and the effect of a large vibration amplitude,respectively.Conventional models still lack a complete understanding of damping and cannot offer a reasonably good estimate of the damping coefficient for a case with both effects.Expensive efforts have been undertaken to consider these two effects,yet a complete model has remained elusive.This paper investigates the dynamic performance of vibrated structures via theoretical and numerical methods simultaneously,establishing a complete model in consideration of both effects in which the analytical expression is given,and demonstrates a deviation of at least threefold lower than current studies by simulation and experimental results.This complete model is proven to successfully characterize the squeeze-film damping and dynamic performance of oscillators under comprehensive conditions.Moreover,a series of simulation models with different dimensions and vibration statuses are introduced to obtain a quick-calculating factor of the damping coefficient,thus offering a previously unattainable damping design guide for MEMS devices.