Proof Mass Research Articles

A micro-electro-mechanical accelerometer based on gallium nitride on silicon

We report on an accelerometer micro-sensor based on epitaxial gallium nitride and silicon. The device is a vibrating beam accelerometer fabricated with a micro-electro-mechanical-system technology starting from an AlGaN/GaN heterostructure grown on silicon. The vibrating GaN beam has integrated high electron mobility transducers, whereas a high aspect ratio proof mass is engineered in the silicon substrate. The sensor response was investigated for several modes and features a scale factor up to 160 Hz/g, with unconventional dependence vs the mode number. To account for this, we propose an analytical model of the accelerometer scale factor that takes into account the built-in stress during epitaxy. This proof-of-concept device opens perspectives for inertial sensors taking advantage of GaN properties.

Experimental and theoretical studies of effective piezoelectric coefficients of 2-2 connectivity AlN/AlScN composite piezoelectric films

Aluminum nitride (AlN) and Sc-doped AlN have become the most popular piezoelectric thin-film materials in the fields of RF and smart sensing. AlN/AlScN composite films based on 2-2 connectivity exhibit stronger interaction and better lattice matching between AlN and AlScN, resulting in improved nucleation, growth kinetics, crystal quality, piezoelectric response, and surface morphology. In this work, a method for predicting the effective coefficients of AlN/AlScN composite piezoelectric thin films is proposed and validated. This prediction method is based on first-principles calculations, the Reuss model theory, and the Mori-Tanaka (MT) method. It also conforms to the mean strain and stress theory of the micromechanical approach. The precise compliance, dielectric and piezoelectric properties (Sij, ε, dij) of AlN/Al0.8Sc0.2N composite film with different thickness ratios are calculated. Through the deflection measurement of piezoelectric cantilever with proof mass based on AlN/Al0.8Sc0.2N composite film, the experimental piezoelectric stress coefficient (d31) is calculated. The correctness of the prediction method is verified by comparing the theoretical calculation (d31* = −3.1pC/N) and experimental data (d31 = −3.4pC/N), showing excellent agreement within experimental error. Meanwhile, the voltage sensitivity of the accelerometer is significantly enhanced by the AlN/AlScN composite piezoelectric film. It is believed that this work will broaden the theoretical study and application of the AlN/AlScN composite piezoelectric film.

Resilient electret film‐based vibrational energy harvesters with a V‐shaped counter electrode

AbstractVibrational energy harvesters, which can convert mechanical energy distributed widely in the surrounding environment to electrical energy in a convenient, eco‐friendly and sustainable way, have attracted great attention in both academia and industry. In this study, a resilient electret film‐based vibrational energy harvester with a V‐shaped counter electrode is introduced, simulated and constructed. A negatively charged fluorinated polyethylene propylene (FEP) electret film with a wavy shape was adopted in the devices, achieving simultaneously a stable embedded biased voltage and a large tensile deformation during vibration. The influences of the factors on the performance of the device, including the initial stretching state of the resilient electret film, seismic mass and depth of the V‐shape counter electrode, were analyzed comprehensively with finite element simulation and compared to experiments. Further, the structure of the device was optimised for generating a high output power, and a good agreement between the simulation and experimental data was achieved. Additionally, the resonant frequency of the device can be easily tuned between 28 and 68 Hz by merely adjusting the initial stretching state of the wavy FEP electret film, guaranteeing great superiority for broad bandwidth energy harvesting applications. For an optimised energy harvester with a volume of only 15 × 5 × 1.7 mm3 and a tiny seismic mass of 25 mg, and a normalized output power referring to 1 × g (g is the gravity of the Earth) up to 547 μW was obtained at its resonant frequency of 28 Hz. These results demonstrate that such a miniaturised vibrational energy harvester is a promising electrical energy supplier for low‐power‐consumption electronic devices, in particular in wireless sensor networks.

Monolithically integrated triaxial high-performance micro accelerometers with position-independent pure axial stressed piezoresistive beams

With the increasing demand for multidirectional vibration measurements, traditional triaxial accelerometers cannot achieve vibration measurements with high sensitivity, high natural frequency, and low cross-sensitivity simultaneously. Moreover, for piezoresistive accelerometers, achieving pure axial deformation of the piezoresistive beam can greatly improve performance, but it requires the piezoresistive beam to be located in a specific position, which inevitably makes the design more complex and limits the performance improvement. Here, a monolithically integrated triaxial high-performance accelerometer with pure axial stress piezoresistive beams was designed, fabricated, and tested. By controlling synchronous displacements at both piezoresistive beam ends, the pure axial stress states of the piezoresistive beams could be easily achieved with position independence without tedious calculations. The measurement unit for the z-axis acceleration was innovatively designed as an interlocking proof mass structure to ensure a full Wheatstone bridge for sensitivity improvement. The pure axial stress state of the piezoresistive beams and low cross-sensitivity of all three units were verified by the finite element method (FEM). The triaxial accelerometer was fabricated and tested. Results showing extremely high sensitivities (x axis: 2.43 mV/g/5 V; y axis: 2.44 mv/g/5 V; z axis: 2.41 mV/g/5 V (without amplification by signal conditioning circuit)) and high natural frequencies (x/y axes: 11.4 kHz; z-axis: 13.2 kHz) were obtained. The approach of this paper makes it simple to design and obtain high-performance piezoresistive accelerometers.

A three-tier system of seismic rock mass monitoring in the Khibiny apatite-nepheline ore deposits

A three-tier system of seismic rock mass monitoring in the Khibiny apatite-nepheline ore deposits

A Coaxial Wrist-Worn Energy Harvester for Self-Powered Internet of Things Sensors

Energy harvesting from human motion has great potential of sustainably powering Internet of Things (IoT) sensors and satisfying their continuous sensing requirement. In this article, we propose a high-performance wrist-worn energy harvester to efficiently capture the biomechanical energy of arm swinging to self-power wearable sensors. Based on coaxial topology, a planetary gear system serves as frequency-up converter to increase energy conversion capacity, and all the functional units are coaxially installed to achieve a highly compact structure. Thanks to improved energy conversion capacity and structure compactness, the energy harvester can efficiently capture the kinetic energy of arm swinging and achieve high average power. We derive an analytical model to predict the system dynamics and power generation performance using the Lagrangian approach and mirror image method. We fabricate a miniature prototype with different proof mass configurations, which is characterized under bench-top excitations and tested under real walking excitations. The results show that in bench-top testing, the prototype generates maximum average power of 2.73 mW and maximum power density of 535.29 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathbf {\mathrm {\mu }}\text{W}$ </tex-math></inline-formula> /cm3 at the excitation frequency of 1.2 Hz among different configurations. In terms of average power and power density, this energy harvester significantly overperforms its counterparts. In real walking testing, the prototype generates maximum average power of 3.13 mW at a walking frequency of 1.2 Hz among different configurations and achieves higher power output than bench-top testing. Finally, the prototype is used to simultaneously power four sensors and demonstrates great potential in self-powered IoT applications.

Broadband Piezoelectric Energy Harvester Based on Coupling Resonance Frequency Tuning.

The bandwidth of piezoelectric energy harvesters (PEHs) can be broadened by resonance-based frequency tuning approaches, including mechanical tuning and electrical tuning. In this work, a new coupling tuning mechanism for regulating the near-open-circuit resonance frequency by changing the effective electrode coverage (EEC) is presented. A linear model of a bimorph piezoelectric cantilever with segmented electrodes is used to evaluate the power harvesting behavior near the open-circuit resonance frequency when EEC changes from 0 to 100%. According to the theoretical analysis, it is found that the variation of EEC brings about the change in coupling strength, which is positively associated with the near-open-circuit resonance frequency of PEH. Two cantilever PEHs with segmented electrodes based on PZT and PZT-PT are constructed for validation of the coupling tuning mechanism. The analytical and experimental results illustrate remarkable improvements in both bandwidth and average power through the coupling resonance frequency tuning method. In addition, adopting extraordinary piezoelectric single crystals and optimizing the proof mass and piezoelectric layer dimensions were theoretically shown to be effective methods for further improvement of bandwidth.

Design of Piezoelectric Energy Harvesting Structures Based on Proof Mass Analysis-Simulation and Experimental Study

In this work, two types of piezoelectric structures A and B are designed for harvesting maximum amount of energy from motor vibrations. The analysis is conducted under various load conditions with the placement of two different shapes of proof mass (square and rectangular) on the piezoelectric energy harvester. An experimental study is conducted for harvesting energy from motor vibrations using two piezoelectric structures A and B, in which, structure B with the placement of square-proof mass generates maximum power, which is efficient for powering low-power electronic applications.

Influence of angular acceleration on the dynamic response of the proof mass in the MEMS vibratory gyroscope model

Influence of angular acceleration on the dynamic response of the proof mass in the MEMS vibratory gyroscope model

Design and Simulation Study of an Optical Mode-Localized MEMS Accelerometer.

In this paper, we demonstrate a novel photonic integrated accelerometer based on the optical mode localization sensing mechanism, which is designed on an SOI wafer with a device layer thickness of 220 nm. High sensitivity and large measurement range can be achieved by integrating coupled ring resonators with a suspended directional coupler on a proof mass. With the help of FEA simulation and numerical analysis, the proposed optical mode-localized sensor presents a sensitivity of 10/g (modal power ratio/acceleration) and an inertial displacement of from -8 to 10 microns corresponding to a range from -23.5 to 29.4 g. The free spectral range is 4.05 nm around 1.55 microns. The acceleration resolution limited by thermomechanical noise is 4.874 μg. The comprehensive performance of this design is competitive with existing MEMS mode localized accelerometers. It demonstrates the potential of the optical mode-localized inertial sensors as candidates for state-of-the-art sensors in the future.

Seismic Rock Mass Response to Tunnel Development with Destress Blasting in High-Stress Conditions

Seismic Rock Mass Response to Tunnel Development with Destress Blasting in High-Stress Conditions

Optimization of Structure and Control Technology of Tunnel Magnetoresistive Accelerometer

In this work, an optimized tunnel magnetoresistive (TMR) accelerometer with a closed-loop control system was developed and evaluated. The device first introduces a silicon spring–mass sensing structure lower than 50 Hz into TMR-based accelerometry for enhancing the mechanical sensitivity and subsequent readout sensitivity. Simultaneously, in order to realize the in-plane electrostatic feedback control, the comb structure is designed along with the sensing mechanism, owning combined benefits of integrated processing and large feedback force. The whole sensing structure is a silicon-glass chip, fabricated by the standard micro-electromechanical system (MEMS) process—deep dry silicon on glass (DDSOG) process. A permanent rubber magnet is assembled on the proof mass for conversion from the displacement to variation of the magnetic field intensity, which is further detected by a pair of symmetrically arranged TMR sensors. The voltage signals output from TMR sensors are then sent into an analog circuit via an interface module for force-feedback control. The simulation analysis indicates that the proposed MEMS sensing structure has a low natural frequency of 44.55 Hz, corresponding to a compliant mechanical sensitivity of 125.5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> /g. Meanwhile, a maximum magnetic sensitivity of about 0.1 mT/mm is available in a height of 6 mm above the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3\times 3\times0.3$ </tex-math></inline-formula> mm magnet. Finally, the experiments on the assembled prototype demonstrated that a scale factor of 1.79 V/g and a bias stability of 228 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{g}$ </tex-math></inline-formula> have been achieved in the closed-loop modality, which verifies the effectiveness of the proposed TMR MEMS accelerometer.

Fabrication and Underwater Testing of a Vector Hydrophone Comprising a Triaxial Piezoelectric Accelerometer and Spherical Hydrophone.

A vector hydrophone is an underwater acoustic sensor that can detect the direction of a sound source. Wide-band characteristics and high sensitivity enhance the performance of underwater surveillance systems in complex environments. A vector hydrophone comprising a triaxial piezoelectric accelerometer and spherical hydrophone was fabricated and tested in the air and underwater. The vector hydrophone was designed to exceed the quantitative figures of merit (i.e., receiving voltage sensitivity and bandwidth) of commercially available hydrophones. Accelerometer performance was enhanced by placing a pair of piezoelectric single crystals on each axis and modifying the seismic mass material. The receiving voltage sensitivity of the omnidirectional hydrophone was approximately -160 dB relative to 1&amp;nbsp;V/μPa with the amplifier in water; the sensitivity of the accelerometer exceeded 300 mV/g in air and -215 dB relative to 1&amp;nbsp;V/μPa underwater over the frequency range of interest. The receiving directivity of the vector hydrophone was validated underwater, which confirmed that it could detect the direction of a sound source.

Fabrication process for FEP piezoelectrets based on photolithographically structured thermoforming templates

Piezoelectrets fabricated from fluoroethylenepropylene (FEP)-foils have shown drastic increase of their piezoelectric properties during the last decade. This led to the development of FEP-based energy harvesters, which are about to evolve into a technology with a power-generation-capacity of milliwatt per square-centimeter at their resonance frequency. Recent studies focus on piezoelectrets with solely negative charges, as they have a better charge stability and a better suitability for implementation in rising technologies, like the internet of things (IOT) or portable electronics. With these developments heading towards applications of piezoelectrets in the near future, there is an urgent need to also address the fabrication process in terms of scalability, reproducibility and miniaturization. In this study, we firstly present a comprehensive review of the literature for a deep insight into the research that has been done in the field of FEP-based piezoelectrets. For the first time, we propose the employment of microsystem-technology and present a process for the fabrication of thermoformed FEP piezoelectrets based on thermoforming SU-8 templates. Following this process, unipolar piezoelectrets were fabricated with air void dimensions in the range of 300–1000 upmu text {m} in width and approx. 90 upmu text {m} in height. For samples with a void size of 1000 upmu text {m}, a d_{33}-coefficient up to 26,508 pC/N has been achieved, depending on the applied seismic mass. Finally, the properties as energy harvester were characterized. At the best, an electrical power output of 0.51 mW was achieved for an acceleration of 1 times g with a seismic mass of 101 g. Such piezoelectrets with highly defined dimensions show good energy output in relation to volume, with high potential for widespread applications.

A High-Sensitivity Dual-Axis Accelerometer with Two FP Cavities Assembled on Single Optical Fiber.

In this paper, a dual-axis Fabry-Pérot (FP) accelerometer assembled on single optical fiber is proposed. The sensor is equipped with a special beam-splitting prism to split the light into two perpendicular directions (the X- and Y-axes); the prism surface coated with semi-permeable film and the reflective sheet on the corresponding Be-Cu vibration-sensitive spring form two sets of FP cavities of different sizes. When the Be-Cu spring with a proof mass (PM) is subjected to the vibration signal, the cavity length of the corresponding FP cavity is changed and the interference signal returns to the collimator through the original path of the prism. After bandpass filtering and demodulation, the two cavity lengths are obtained, and the acceleration measurement in dual-axis directions is completed. The resonant frequency of the proposed dual-axis fiber optic accelerometer is around 280 Hz. The results of the spectral measurements show 3.93 μm/g (g = 9.8 m/s2: gravity constant) and 4.19 μm/g for the applied acceleration along the X- and Y-axes, respectively, and the cross-axis sensitivity is below 5.1%. Within the angle range of 180°, the maximum error of measured acceleration is less than 3.77%. The proposed fiber optic dual-axis FP accelerometer has high sensitivity and strong immunity to electromagnetic interference. The size of the sensor mainly depends on the size of the prism, which is easy to reduce and mass produce. Moreover, this FP construction method has high flexibility and development potential.

Fabrication of Vertical MEMS Actuator with Hollow Square Electrode for SPR Sensing Applications.

In this study, an electrostatically driven vertical MEMS actuator was designed using a hollow square electrode. To attain vertical actuation, a hollow square-shaped electrode was designed on the glass substrate. The silicon proof mass, containing a step, was utilized to realize analogue actuation without pull-in. The vertical MEMS actuator was fabricated using the SiOG (Silicon on Glass) process and the total actuator size was 8.3 mm × 8.3 mm. The fabricated proof mass was freestanding due to eight serpentine springs with 30 μm width. The vertical movement of the MEMS actuator was successfully controlled electrostatically. The measured vertical movement was 5.6 µm for a voltage of 40 V, applied between the top silicon structure and the hollow square electrode. The results shown here confirm that the proposed MEMS actuator was able to control the vertical displacement using an applied voltage.

A Reusable Pseudo-Liquid-to-Solid Inertial Switch Based on Hetero-Coated Galinstan Droplets

Compared to solid-to-solid inertial switches, the devices based on liquid-to-solid contact can avoid the signal bouncing and contact wear caused by the rigid contact between the proof mass and the stationary electrode. However, most of the current liquid-to-solid inertial switches can only support one-time use. To resolve this issue, we, for the first time, present a pseudo-liquid-to-solid inertial switch that not only has a soft electronic contact but also is reusable. We utilize one graphene-coated galinstan droplet (GGD) with high conductivity as the proof mass and two polytetrafluoroethylene (PTFE)-coated galinstan droplets (PGDs) with excellent elasticity and mechanical robustness as springs to restrain the GGD. Moreover, the coated powder shell can prevent galinstan droplets from being oxidized thus enables superior performance in terms of nonstick property and high mobility. As a result, a pseudo-liquid-to-solid inertial switch with a threshold of 20 g is designed and fabricated, and it exhibits high reliability, reusability and stability with a contact time of 1 ms. In summary, this novel type of inertial switch combines the advantages and overcomes the limitations of both liquid-to-solid type and solid-to-solid type, therefore is of great potential for practical applications. [2022-0151]

Investigation of temperature sensitivity of a MEMS gravimeter based on geometric anti-spring.

This paper describes a technique for temperature sensitivity or thermal sag measurements of a geometric anti-spring based microelectromechanical system (MEMS) gravimeter (Wee-g). The Wee-g MEMS gravimeter is currently fabricated on a (100) silicon wafer using standard micro-nano fabrication techniques. The thermal behavior of silicon indicates that the Young's modulus of silicon decreases with increase in temperature (∼64 ppm/K). This leads to a softening of the silicon material, resulting in the proof mass displacing (or sagging) under the influence of increasing temperature. It results in a change in the measured gravity, which is expressed as temperature sensitivity in terms of change in gravity per degree temperature. The temperature sensitivity for the silicon based MEMS gravimeter is found to be 60.14-64.87, 61.76, and 62.76 µGal/mK for experimental, finite element analysis (FEA) simulation, and analytical calculations, respectively. It suggests that the gravimeter's temperature sensitivity is dependent on the material properties used to fabricate the MEMS devices. In this paper, the experimental measurements of thermal sag are presented along with analytical calculations and simulations of the effect using FEA. The bespoke optical measurement system to quantify the thermal sag is also described. The results presented are an essential step toward the development of temperature insensitive MEMS gravimeters.

Developing Ball Pulse Generator in Piezoelectric Transduction Designed on Wireless Sensing Devices

Progressing Ball pulse generator through piezoelectric transduction is designated in this paper directed on wireless recognizing procedures. A silver rolling ball is stimulated popular the original through method of an inertial proof mass motivated finished outside waves at random low frequency. Winning development of the metallic resistant mass, magnetic construction can be extended near motivate the piezoelectric cantilever finished awarding tip magnets near the acceptable completion. Prevalent accretion, self-synchronous switching is achieved via relating electrodes toward the path of the developing ball. An unique passive prebiasing instrument is familiar toward advance the presentation of the pulse producer. Together simulation also new results continued showed near determine the expansion. Experimental results rally supplementary energy container remains impassive through the prebias instrument associated near the impartial occasion. A announcement circuit founded decided a Colpitts oscillator stayed constructed toward examination the presentation of the capacitor-powered oscillator which remains calculated in way of the load of the pulse generator. Through addition a voltage regulator element, the transmission circuit is accomplished of software design an instrument signal via frequency intonation which controls the possibility of affecting a developing ball wireless sensing original founded decided the piezoelectric pulse generator.

An Inertial Uni-Axial Interferometer-Based Accelerometer for Harsh Environments

For high-impact devices, subsequent vibrations have as much influence on the deterioration of the mechanical structure as the impact itself. To mitigate the consequences of both impacts and resulting vibrations, it is crucial to accurately understand the peak acceleration and vibration frequencies that originate in the structure. In this article, a radiation tolerant opto-mechanical sensor based on an absolute measurement inertial accelerometer is presented. This method of measurement is chosen due to the viability of placing the readout electronics far from the highly radioactive environment that the sensor may be installed in. The designed accelerometer consists of a fixed aluminum frame with a built-in membrane that acts as a leaf spring. In the same membrane, a retro-reflector is attached which acts as a seismic mass. The retro-reflector reflects the light beam coming from the collimator lens placed on the frame. To prove its viability, the device has been tested under different conditions. First, the device is calibrated and validated using a high-frequency exciter. Second, a high-acceleration testbench is used to compare its output signal with a commercial accelerometer and verify its proper operation as well as its expected lifetime. The experimental results showed an average sensitivity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${9} \times {10}^{-{4}}$ </tex-math></inline-formula> g/pm with reading measurements of up to 5000 g and a working bandwidth located between 50 and 800 Hz.