Fundamentals of Vibrations

We present a MEMS inertial switch with multiple, non-latching acceleration thresholds in two directions, that consumes no power in its inactive state. The design implements a suspended proof mass, with stationary electrodes placed at different positions in its sensitive direction so that different shock-induced displacements of the proof mass will result in contact/actuation at the stationary electrodes corresponding to the applied acceleration levels. This allows for automatic acceleration-based action, as a switch, or categorization for acceleration as a binary sensor. The designs were modeled using a finite-element simulation. The device was fabricated through SOIMUMPS and then tested using a drop-table shock system. The experimental results were close to the performed simulations with acceleration thresholds of 69 g and 121 g.

Design, Modeling, and Testing of a Bidirectional Multi-Threshold MEMS Inertial Switch

In this article, we present an inertial switch with three threshold levels, which can provide quantitative acceleration measurements and detect the acceleration direction in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x–y</i> plane. The designed device has four movable electrodes attached to the proof mass (one at every side of the square proof mass) and 12 flexible stationary electrodes (three on each side). When the device is subjected to an acceleration input, the movable electrode can contact one or more of the 12 stationary electrodes based on the acceleration magnitude and direction. The acceleration direction can be determined by identifying the individual electrical switches that are activated. The designed switch is simulated using a finite-element model under different acceleration signals of various magnitudes and directions. A device prototype has been fabricated using the SOIMUMPs process and has been tested by a drop-table system under various shock accelerations in different directions. The experimental and simulation results show good agreement indicating that the acceleration direction detection accuracy and resolution improve with the increase in the number of used electrical switches. 

/pdf/multi-threshold-inertial-switch-with-acceleration-direction-4jeqlw42.pdf

Multi-Threshold Inertial Switch With Acceleration Direction Detection Capability

As a typical type of MEMS acceleration sensor, the inertial switch can alter its on-off state while the environmental accelerations satisfy threshold value. An exhaustive summary of the design concept, performance aspects, and fabrication methods of the micro electromechanical system (MEMS) inertial switch is provided. Different MEMS inertial switch studies were reviewed that emphasized acceleration directional and threshold sensitivity, contact characteristics, and their superiorities and disadvantages. Furthermore, the specific fabrication methods offer an applicability reference for the preparation process for the designed inertial switch, including non-silicon surface micromachining technology, standard silicon micromachining technology, and the special fabrication method for the liquid inertial switch. At the end, the main conclusions of the current challenges and prospects about MEMS inertial switches are drawn to assist with the development of research in the field of future engineering applications.

https://www.mdpi.com/2072-666X/13/3/359/pdf?version=1645785128

Research Progress of MEMS Inertial Switches

In this article, we present an inertial switch with three threshold levels, which can provide quantitative acceleration measurements and detect the acceleration direction in the x–y plane. The designed device has four movable electrodes attached to the proof mass (one at every side of the square proof mass) and 12 flexible stationary electrodes (three on each side). When the device is subjected to an acceleration input, the movable electrode can contact one or more of the 12 stationary electrodes based on the acceleration magnitude and direction. The acceleration direction can be determined by identifying the individual electrical switches that are activated. The designed switch is simulated using a finite-element model under different acceleration signals of various magnitudes and directions. A device prototype has been fabricated using the SOIMUMPs process and has been tested by a drop-table system under various shock accelerations in different directions. The experimental and simulation results show good agreement indicating that the acceleration direction detection accuracy and resolution improve with the increase in the number of used electrical switches.

Based on a bistable mechanism, a novel low- ${g}$ MEMS inertial switch with dual functions of self-locking and reverse-unlocking is presented, along with its fabrication and verification. This MEMS switch is fabricated on a Silicon-On-Insulator (SOI) wafer by using deep reactive ion etching (DRIE), Bosch processing, and wafer bonding technologies. A two-level system is proposed to realize dual functions of this switch, which mainly consists of a spring-mass-damping system as the first level and a bistable structure as the second level. According to the finite element analysis (FEA), the theoretical formula of the bistable structure has been successfully verified to deduce the static mechanical properties. Under positive and negative acceleration excitations, the dynamic response characteristics of the switch has been systematically simulated further. Furthermore, this inertial switch has been tested by using a centrifugal acceleration turntable, and its self-locking threshold and reverse unlocking threshold are 8 ${g}$ and 105 ${g}$ , respectively. Finally, the contact resistance of this MEMS switch is measured about $0.75~\Omega $ by a probe station. [2020-0302]

Chao Wang

Papers

A Novel Low-g MEMS Bistable Inertial Switch With Self-Locking and Reverse-Unlocking Functions