Search

This paper reports a low-g MEMS acceleration switch with threshold acceleration below 10 g. The proposed switch is made of single-crystalline silicon for high thermal stability and stress-free structure. A vertical operation type is adopted to enable fine control of the contact surface during the fabrication process. The switch contains displacement-restricting structures in all directions for impact resistance and is packaged with anodic bonding process. The fabricated switches had an average proof mass, initial gap, and spring constant of 307.38 µg, 6.39 µm, and 3.29 N m−1, respectively. Height profile of the free-hanging proof mass was measured to show that the switch does not suffer from stress problems. In the electrostatic operation test, the contact resistance of the switch was varied with contact force and the minimum value was estimated to be 8.5 Ω. The response time of the switch was measured to be shorter than 1.2 ms. The fabricated switch operated more than 10 000 cycles without failure. For the thermal stability test, the switch was heated at 80 °C for 6 h and the switch operated successfully over 200 times. In the rotation-table experiment, the switch operated at 6.61 g and error analysis was carried out in the consideration of tangential force generated during the rotation-table experiment. From the experimental values, the tangential force was calculated as 2.375 µN and the resulting reduction in the initial switching gap was simulated as 0.32 µm. The reduced threshold acceleration thus was estimated to be 6.62 g, which agrees very well with the measured threshold acceleration value of 6.61 g. [ABSTRACT FROM AUTHOR]

A horizontal sensitive inertial micro-switch with low g value is proposed in this paper. It was simulated using ANSYS software and fabricated by MEMS micromachining technology. It consists of three parts: a suspended thick proof mass as a movable electrode, two novel elastic fixed beams as stationary electrodes to prolong the contact time and a barrier system, which constrains non-sensitive direction movement and eliminates reverse impact. The relationship between the threshold acceleration ath and the intrinsic frequency ω0 is discussed in a theoretical analysis and finite element simulation. The thickness of the proof mass (H) and the width of the springs (k) were designed to be variable to meet the requirement of the application environment. Two novel elastic stationary electrodes were designed specially to improve the contact effect. The fabricated micro-switch was characterized by a standard dropping test. The work frequency is about 33.3 Hz and the threshold acceleration of the sample is about 38g, which meet the simulation value very well. The response time was about 10−4 s and the contact time about 200 us. [ABSTRACT FROM AUTHOR]

A multidirectional-sensitive inertial microswitch with a polymer-metal composite fixed electrode has been designed and fabricated based on surface micromachining in this work. The microswitch mainly consists of a suspended proof mass as a movable electrode and a T-shaped structure on the substrate with maple leaf-like top and cantilevers around the central cylinder as vertical and lateral fixed electrodes. It can sense the applied shock accelerations from any radial direction in the xoy plane and z-axis. The new vertical composite fixed electrode of the switch is completed by electroplating and electrophoretic deposition, which can realize a flexible contact between the electrodes and reduce the bounces and prolong the contact time. As a result, the stability and reliability of the inertial switch could be greatly improved. The fabricated microswitches have been tested and characterized by a standard dropping hammer system. It is shown that the threshold acceleration of the prototype is generally uniform in different sensitive directions in the xoy plane and z-axis, which is about 70 g. The contact time of the microswitch with the composite fixed electrode is ∼110 µs in the vertical direction, which is longer than that (∼65 µs) without a polymer. The test data are in agreement with dynamic finite-element simulation results. [ABSTRACT FROM AUTHOR]

This paper presents a review of the recent advances on micromachined inertial switches/triggers. The review focuses on their advantages and disadvantages, sensitive directions, mechanisms of contact-enhancement, threshold accuracy, and the tunability of the acceleration threshold. Several applications of these sensors are highlighted including in healthcare, structural health monitoring, internet of things, and military. Recent contemporary research directions are also discussed, such as multi-directions/axis, multi-threshold sensors, and machine learning implementation. The article concludes with discussion on future development trends and performance improvements of inertial switches. [ABSTRACT FROM AUTHOR]

Since the end of the last century, energy harvesting technologies have obtained prominent development as the sustainable power supplies for billions of wireless sensor nodes distributed in both the city and remote areas. Microelectromechanical system (MEMS) energy harvesters based on the energy transferring mechanisms of electrostatic effect, electromagnetic induction, and piezoelectric effect were first proposed to scavenge the vibrational energy from the ambient environment. Thereafter, the piezoelectric nanogenerator and triboelectric nanogenerator emerged as promising techniques to harvest diversified mechanical energy for addressing the energy consumption of flourishing wearable devices. Targeting for a more efficient system, multiple strategies for improving the output performance of individual energy harvesters as well as hybridized energy harvesters are extensively investigated. Merging the well-developed energy harvesters with energy storage, wireless data transmission, and other functional units, self-sustainable systems have been realized. Shortly, with the evolving AI technologies, we can foresee that the AI-assisted self-sustainable systems will also be achieved and play a vital role in the future 5 G era. In this review, we systematically introduce the evolution of energy harvesting techniques in the 5 G and IoT era, with detailed operation principles, structural designs, enhancement strategies, self-sustainable and AI-assisted system development, and our perspectives. [ABSTRACT FROM AUTHOR]

In this work, we report on a novel simple yet robust two-mask metal-on-insulator (MOI) process and illustrate its implementation for the fabrication of a meso scale MEMS inertial switch. The devices were fabricated of a ∼40 µm thick layer of nickel electrodeposited on top of a 4 µm thick thermal field oxide (TOX) covering a single crystal silicon wafer. A 40 µm thick layer of KMPR® resist was used as a mold and allowed the formation of high-aspect-ratio (1:5) metal structures. The devices were released by the sacrificial etching of the TOX layer in hydrofluoric acid. The fabricated devices were mounted in a ceramic enclosure and were characterized using both an electromagnet shaker and a drop tester. The functionality of the switch, aimed to trigger an electrical circuit when subjected to an acceleration pulse with amplitude of 300 g and duration of 200 µs, was demonstrated experimentally and the performance targets were achieved. The experimental results were consistent with the model predictions obtained through finite element simulations. [ABSTRACT FROM AUTHOR]

This paper presents an experimental proof-of-concept of an innovative design of electrostatic vibration energy harvester based on a double bistable curved beam whose mechanical behaviour is significantly modified by additional linear springs. The basic analytical model for a curved beam with dynamical and quasi static behaviour is introduced and validated by finite element modelling. It is shown that the static force offset due to the gravity field can provide an important increase in the sensitivity to external acceleration. The device is fabricated using silicon on glass technology without the need of a wafer bonding technique. Energy harvesting experiments are performed with various orientations of the device relative to the gravity field direction. The electrical power output is derived from the output voltage measured across a storage capacitor. It is shown that the maximum power output of the energy harvester reaches 10 µW under 50 Hz, 10 m s−2 sine excitation, and is sensible at accelerations with amplitudes less than 1 g (down to 3 m s−2) and operating at a very low frequency range (5–100 Hz) with an overall device size of 1 cm  ×  1.5 cm  ×  200 µm. [ABSTRACT FROM AUTHOR]

A micro-vibration energy harvester employing two-stage mutual ferromagnetic interaction is proposed and developed to frequency up-convert sub-g weak-vibration energy into electricity, with high efficiency. The two-stage structure consists of a low-frequency cantilever (stage 1) with a magnet and seismic mass attached at the cantilever end, as well as a magnetized high-frequency nickel cantilever (stage 2) with a piezoelectric thin film bonded for electric generation. Through magnetic repelling between stage 1 and the magnetized nickel stage 2, a magnetic barrier is formed between the two stages. Once ambient vibration reaches a certain acceleration threshold, the stage 1 cantilever can overcome the magnetic barrier to trigger the piezoelectric stage 2 into frequency up-conversion resonance and electricity generation. Otherwise, the harvester remains in an idle state. Thus, this threshold triggered harvester (TTH) can be used directly as a sensor to autonomously monitor vibrational events. Herein, the seismic mass on the stage 1 cantilever is proposed to set and adjust the sub-g vibration threshold; thereby, the developed sub-g TTH with fixed small gap distance can reliably induce strong dual-stage magnetic interaction under sub-g vibration. Using this approach, the threshold-triggered generating efficiency for sub-g vibration is much higher than in traditional TTH, where the threshold is set by the gap distance between two magnets on the two stages. The relation of threshold versus seismic mass is obtained by both theoretical analysis and numerical calculation, and the accuracy of the design model is confirmed by experimentally testing the microfabricated TTH for thresholds of 0.25, 0.5, and 0.75 g. A comparison is made between the sub-g and traditional TTH, and the switch-on triggered generating power and power density under 0.25 g weak-vibration of the sub-g TTH are 0.72 and 0.48 µW cm−2, respectively, four times higher than in the traditional TTH. Therefore, the novel sub-g TTH is promising in various applications such as monitoring for building structure vibration and people movement. [ABSTRACT FROM AUTHOR]

In this paper, an automatic-recovery inertial switch is presented which for the first time adopts gallium–indium (EGaIn) as the switching metal droplet. The device consists of a glass substrate with patterned sensing electrodes, a PDMS microfluidic chip with microchannels and microvalves and a metal droplet. Here, we used EGaIn as the conductive element of the switch because it has several advantages compared with other conductive materials such as water or mercury. Specifically, the proposed device has the ability to automatically recover and can be used repeatedly. In the initial off-state, the droplet is stored in the reservoir. During the working state, the metal droplet passes through the channel and connects the sensing electrodes when the acceleration exceeds the designed threshold level. After that, the EGaIn will return to its original position by a subtle use of its structural characteristics. [ABSTRACT FROM AUTHOR]

This paper proposes a novel laterally-driven inertial micro-switch with multi-directional compact constraint structures for lowering off-axis sensitivity and improving shock-resistibility. The design utilizes constraint sleeve and reverse stop-block structures to limit too much displacement of proof mass in the micro-switch and avoid damage to the device under a high shock load. The dynamic contact simulation indicates that the designed inertial micro-switch can limit the movement of proof mass and lower the off-axis sensitivity by constraint sleeve and reverse block structures. The first collision response time between proof mass and constraint structures in the z-direction has been analyzed theoretically and simulated, which have indicated that the collision response time mainly depends on geometric parameters, applied shock acceleration amplitude and the inherent frequency of the mass-spring inertial system. Simulated dynamic response curves under applied reverse directional shock accelerations show the proposed inertial micro-switch also has a good shock-resistibility. The inertial micro-switch fabricated by surface micromachining technology has been evaluated using a drop hammer system. The test results indicate that spurious triggering is more likely to occur in the inertial micro-switch without constraint structures, and the designed constraint structures can effectively lower the off-axis sensitivity and improve the shock-resistibility. [ABSTRACT FROM AUTHOR]

A novel micro-electro-mechanical systems (MEMS) inertial switch with universal sensitivity was investigated in this paper. Using a single circular mass, the switch was able to detect accelerations in all of the radial directions of a hemisphere. Four suspended springs with 90° symmetry were employed to be compliant in all directions, and flexible stationary electrodes were used to allow for long-duration contact. More than forty switch prototypes were produced using a microfabrication process. Dynamic finite element analysis and shock table experiment were carried out to study the behavior of the proposed switch. The results indicated that universal sensitivity was successfully achieved by the new design. Agreement was achieved between the numerical predictions and actual test results for the acceleration thresholds in the different sensitive directions of a hemisphere. [ABSTRACT FROM AUTHOR]

This paper reports on the dynamic characteristics of a MEMS electrostatic harvester employing interdigitated gap-closing topology. Devices are fabricated using SOIMUMPS technology and are characterized with and without biasing voltages for a broad range of excitation accelerations. At low vibration amplitudes the presence of a dc bias causes the resonant frequency peak to shift to lower frequencies with increasing bias. At higher vibration amplitudes the dynamic response of the devices exhibits the behavior of a Duffing oscillator with spring softening due to nonlinear stiffness attributed to the effect of electrostatic forces. Specifically, the devices exhibit sweep direction hysteresis with jump phenomena due to the multivaluedness of the response curve. Amplitude sweeps at constant frequency and varying bias voltage also show jump phenomena, highlighting how slight differences in operating conditions dramatically affect device performance. Spring hardening effects are reported for devices contaminated with dust particles. The paper also discusses SOIMUMPS limitations, the importance of reducing off-axis vibration during testing, characterization methods, and the effect of grounding on parasitic capacitance. [ABSTRACT FROM AUTHOR]

This paper reports an inertia switch with a flexible carbon nanotubes/copper (CNTs/Cu) composite array layer between movable and fixed electrodes, which achieves a longer contact time compared to the traditional design using rigid-to-rigid impact between electrodes. The CNTs/Cu layer is fabricated using the composite electroplating method, and the whole device is completed by multi-layer metal electroplating based on the micro-electro-mechanical systems (MEMS) process. The dynamic responses of the designed inertia switch and the contact impact between a single CNT and a fixed electrode/another CNT have both been simulated by the ANSYS finite-element-method (FEM). It is shown that the contact time of the designed inertia switch is about 100 µs under the applied 80 g half-sine-shaped acceleration in the sensing direction. Finally, the fabricated MEMS inertia switch with the flexible CNTs/Cu composite array layer between electrodes has been evaluated by a dropping hammer system. The test contact time is about112 µs, which has a good agreement with the simulation and is much longer than that of the traditional design. [ABSTRACT FROM AUTHOR]

A novel micro-electromechanical systems inertial switch based on non-silicon surface micromachining technology has been designed, fabricated and characterized in the present work. Compared with the traditional inertial switch, a compliant cantilever beam as a stationary electrode has been proposed to prolong the contact time, which can realize sufficient elastic deformation during the contact between the electrodes. The dynamic contact process is analyzed theoretically and the corresponding mechanical impact mechanism is also explained. To investigate the contact-enhancing mechanism of the cantilever beam, the switch applied half-sine acceleration with various amplitudes in the sensitive direction is simulated with ANSYS software. The dynamic simulation results confirm the contact-enhancing mechanism described by the theoretical analysis and it is shown that the contact time (i.e., the switch-on time) can be prolonged effectively by utilizing the elastic deformation of the cantilever beam and increased with the applied accelerations. The inertial switch is successfully fabricated by electroplating and sacrificial layer processes technologies. The prototype has been characterized by dropping hammer experiment. The test results indicate that the contact effect is improved significantly and the contact time is ∼80 µs under the 297 g acceleration, and the maximum value is ∼410 µs for the 672 g acceleration amplitude, which is in general accordance with the simulated results. The mechanical contact between the cantilever beam and the proof mass is evaluated following thousands of impacts. The scanning electron micrographs of the contact surfaces indicate that the all-metal switch still keeps a good mechanical property after suffering the hot contact, and the contact resistance is also stable. [ABSTRACT FROM AUTHOR]