Microelectromechanical Systems Vibration Research Articles

High-Performance Piezoelectric-Type MEMS Vibration Sensor Based on LiNbO3 Single-Crystal Cantilever Beams.

It is a great challenge to detect in-situ high-frequency vibration signals for extreme environment applications. A highly sensitive and robust vibration sensor is desired. Among the many piezoelectric materials, single-crystal lithium niobate (LiNbO3) could be a good candidate to meet the demand. In this work, a novel type of micro-electro-mechanical system (MEMS) vibration sensor based on a single crystalline LiNbO3 thin film is demonstrated. Firstly, the four-cantilever-beam MEMS vibration sensor was designed and optimized with the parametric method. The structural dependence on the intrinsic frequency and maximum stress was obtained. Then, the vibration sensor was fabricated using standard MEMS processes. The practical intrinsic frequency of the as-presented vibration sensor was 5.175 kHz, which was close to the calculated and simulated frequency. The dynamic performance of the vibration sensor was tested on a vibration platform after the packaging of the printed circuit board. The effect of acceleration was investigated, and it was observed that the output charge was proportional to the amplitude of the acceleration. As the loading acceleration amplitude is 10 g and the frequency is in the range of 20 to 2400 Hz, the output charge amplitude basically remains stable for the frequency range from 100 Hz to 1400 Hz, but there is a dramatic decrease around 1400 to 2200 Hz, and then it increases significantly. This should be attributed to the significant variation of the damping coefficient near 1800 Hz. Meanwhile, the effect of the temperature on the output was studied. The results show the nearly linear dependence of the output charge on the temperature. The presented MEMS vibration sensors were endowed with a high output performance, linear dependence and stable sensitivity, and could find potential applications for the detection of wide-band high-frequency vibration.

Effect of -ray irradiation on performance of LiNbO3-based piezoelectric vibration sensors

LiNbO3 (LN)-based micro-electro-mechanical systems (MEMS) vibration sensors exhibit giant perspectives in extreme environments, where a great amount of irradiation exists. However, to the best of our knowledge, it is still unknown whether the irradiation affects the performance of LN-based piezoelectric MEMS sensors. Based on this consideration, it is necessary to model the irradiation environment to investigate the effect of high-dosage irradiation on LN-based vibration sensors. Firstly, the theoretical work is done to study the Compton effect on the gamma-ray irradiation with a 60Co source. After irradiation, X-ray diffraction (XRD) characterization is performed to verify the effect of irradiation on the crystalline of LN thin film. Meanwhile, the performances of output voltages on the five MEMS devices under various dosage of irradiation are compared. As a result, a neglected shift of 0.02 degrees is observed from the XRD image only under maximum irradiation dosage of 100 Mrad(Si). Moreover, the output voltages of cantilever beam vibration sensors decrease by 3.1%. Therefore, it is verified that the γ-ray irradiation has very little influence on the LN-based MEMS vibration sensors, which have great attraction on the materials and sensors under high-dose irradiation.

T-Shaped Piezoelectric Structure for High-Performance MEMS Vibration Energy Harvesting

In the recent decades energy harvesting from ambient vibration by the micro-electromechanical systems (MEMS) has been recognized as a promising solution to boosting lifespan of low-power electronic devices. Apparently, highly efficient MEMS vibration harvesters with lower operational frequencies are advantageous. In this paper we propose a new mechanical structure to aim for energy conversion efficiency enhancement and operational frequency reduction for the piezoelectric MEMS vibration energy harvesters. The proposed structure has a T-shaped geometry with integration of two identical proof masses at the T-segment. Thanks to two degrees-of-freedom, in this structure both bending and torsional mode frequencies can be located close to each other. Its analytic model of frequency response is derived and then validated by finite element modeling (FEM) simulations and prototype measurements. Compared to the conventional straight cantilever configuration, our proposed T-shaped piezoelectric cantilever structure can help distribute mechanical strain in broader areas with higher magnitude and lower resonant frequency. Our analytical, numerical, and experimental studies show that the normalized power density of the proposed T-shaped harvester is 4.8 times higher than that of the conventional one, in addition to 36% resonant frequency reduction. [2019-0146]

Internal resonance between the extensional and flexural modes in micromechanical resonators

Internal resonance between different vibration modes in micromechanical devices has been widely studied due to its promising application prospects in microelectromechanical systems (MEMS) resonators and oscillators. In this paper, we investigated the 2:1 internal resonance between the extensional and flexural modes in a micromechanical cantilever beam resonator using open and closed loop testing methods. In the open loop test, energy transfer from the extensional mode to the flexural mode induced by internal resonance is directly observed. Amplitude saturation and internal resonance bandwidth change in the extensional mode are experimentally studied and theoretically verified with numerical simulation. In the closed loop system, internal resonance produces a bistable self-oscillation frequency. The oscillation frequency of the extensional mode will be locked to one of the two peaks induced by internal resonance. In addition, obvious improvement in short-term frequency stability of the closed loop system is observed with the help of internal resonance. The dynamic characteristics studied in this research can be potentially used to enhance the performance of MEMS vibration devices by internal resonance.

Development of energy harvesting MEMS vibration device sensor with wideband response function in low-frequency domain

An aluminum-nitride (AlN) based microelectromechanical system (MEMS) vibration device sensor with a power-harvesting function is developed. We aimed at realizing a vibration sensor with wideband response in a low-frequency vibration domain, owing to the high-power density of vibration sources energy normally in a particular low frequency with several hertz deviations. A special design was implemented in this work, for the first time, to realize the sensor structure with a wideband response function. The given sensor has a disk-shaped proof mass attached to three sandwiched AlN spring flexures and a supporting beam system. Using MEMS techniques, the sensors were fabricated with the single die size of 7 × 7 mm and observed via scanning electron microscopy comprehensively. The functional feature of the electrical performance of the sensors was evaluated. The results demonstrated that with the given sensor, which has a low center resonant frequency of 57.5 Hz with a response feature of a half-voltage bandwidth of > 10 Hz, an output voltage of 2.4–4 mV at an acceleration of 0.1–0.6 g can be typically achieved. The low-frequency vibration sensor with a wideband response function can be used for many industrial and civilian applications to eliminate the restrictions on power sources.

Non-Linear Vibration Electret-Harvester with Optimized Curved Beam for Low-Frequency Operation

In this study, we report the design and fabrication results of an optimized curved beam structure for low frequency, under one-hundred Hz, and non-linear operation of MEMS (Micro-Electromechanical Systems) vibration energy harvester. The optimization procedure for shape and dimension of the curved beam were established combining a FEM and a numerical analysis. Simulated curved beam with bi-stable motion was evaluated for wide bandwidth operation of a vibration energy harvester and preliminary fabrication process was confirmed.

Electric Power Self-Supply Module for WSN Sensor Node Based on MEMS Vibration Energy Harvester.

This paper proposes an electric power self-supply module for the wireless sensor network (WSN) sensor node. The module includes an electromagnetic vibration energy harvester based on micro-electro-mechanical system (MEMS) technology and a processing circuit. The vibration energy harvester presented in this paper is fabricated by an integrated microfabrication process and consists of four similar and relatively independent beam vibration elements. The main functions of the processing circuit are to convert the output of the harvester from unstable alternating current (AC) to stable direct current (DC), charge the super capacitor, and ensure the stable output of the super capacitor. The preliminary test results of the harvester chip show that the chip can output discontinuous pulse voltage, and the range of the voltage value is from tens to hundreds of millivolts in the vibration frequency range of 10–90 Hz. The maximum value that can be reached is 563 mV (at the vibration frequency of 18 Hz). The results of the test show that the harvester can output a relatively high voltage, which can meet the general electric power demand of a WSN sensor node.

A spring-mass system with elastomeric beams and stretchable interconnects

This paper presents a design construct of a spring-mass system involving a silicon seismic mass, elastomeric beams, and stretchable metallic interconnects which exhibits a mechanical strain-based tunable spring constant and resonance. Serpentine-shaped metallic conductors are encapsulated in polyimide to form the electrical interconnects, which are then integrated on a microfabricated silicon seismic mass with elastomeric beams. The interconnected beam undergoes a nearly 93% elongation with high electrical conductance before failure, which benefits microelectromechanical systems (MEMS) devices requiring large deflection and reliable signal transmission simultaneously. Moreover, the experimental results show that the spring constant of the beams increases by more than a factor of four under 30% axial strain. The tunable resonant frequency of the spring-mass system is also characterized, showing that the resonant frequency changes from 85–155 Hz when a 10% axial strain is applied to the beams. Because of these unique tunable mechanical properties, the presented design construct of the spring-mass system serves as a platform for potential applications including soft MEMS sensors and vibration energy harvesters especially for low frequency and broadband ambient vibration sources.

Design and Optimization of Piezoelectric MEMS Vibration Energy Harvesters Based on Genetic Algorithm

Low-power electronic applications are normally powered by batteries, which have to deal with stringent lifetime and size constraints. To enhance operational autonomy, energy harvesting from ambient vibration by microelectromechanical systems (MEMS) has been identified as a vivid solution to this universal problem. This paper proposes an automated design and optimization methodology with minimum human efforts for MEMS-based piezoelectric energy harvesters. The analytic equations for estimating the harvested voltage by the unimorph piezoelectric energy harvesters are presented with their accuracy validated by using the finite element method (FEM) simulation and prototype measurement. Thanks to their high accuracy, we use these analytic equations as fitness functions of genetic algorithm (GA), an evolutionary computation method for optimization problems by mimicking biological evolution. Our experimental results show that the GA is capable of optimizing multiple physical parameters of piezoelectric energy harvesters to considerably enhance the output voltage. This harvesting efficiency improvement is also desirably coupled with physical size reduction as preferred for the MEMS design process. To demonstrate capability of the proposed optimization method, we have also included a commercial optimization product (i.e., COMSOL optimization module) in our comparison study. The experiments show that our proposed GA-based optimization methodology offers higher effectiveness in the magnitude improvement of harvested voltage along with less runtime compared with the other optimization approaches. Furthermore, the effects of geometry optimization on mechanical and electrical properties (e.g., resonant frequency, stiffness, and internal impedance) are also studied and an effective solution to producing maximum power from unimorph piezoelectric harvesters is proposed.

Shock reliability enhancement for MEMS vibration energy harvesters with nonlinear air damping as a soft stopper

This paper presents a novel application of utilising nonlinear air damping as a soft mechanical stopper to increase the shock reliability for microelectromechanical systems (MEMS) vibration energy harvesters. The theoretical framework for nonlinear air damping is constructed for MEMS vibration energy harvesters operating in different air pressure levels, and characterisation experiments are conducted to establish the relationship between air pressure and nonlinear air damping coefficient for rectangular cantilever MEMS micro cantilevers with different proof masses. Design guidelines on choosing the optimal air pressure level for different MEMS vibration energy harvesters based on the trade-off between harvestable energy and the device robustness are presented, and random excitation experiments are performed to verify the robustness of MEMS vibration energy harvesters with nonlinear air damping as soft stoppers to limit the maximum deflection distance and increase the shock reliability of the device.

Theoretical Comparison of Energy Harvesting Methods for Electret-free Variable-Capacitance Devices

Abstract Electret-free variable-capacitance energy harvesters are micro-electromechanical systems (MEMs) that generate electrical power from mechanical vibrations. In order to effectively harvest energy from these devices, the power electronic circuitry is extremely important, and can be the difference between generating or losing energy during a harvesting cycle. Four methods of harvesting energy from these devices are known: the Constant Voltage Method, the Constant Charge Method, the Charge Pump Method, and the Constant Charge With Parallel Capacitance Method. All four methods have been reported; however, the literature is lacking a formal comparison of these methods. This paper evaluates these four methods and the new Voltage and Charge Constrained Method while considering power electronic circuit efficiency as a key parameter. By including efficiency as a parameter, new fundamental properties of these devices are derived: a threshold efficiency necessary for energy harvesting, analytical solutions for optimal harvesting conditions, and a realistic comparison of the four methods. A case study demonstrates the advantage of using the Charge Pump method for MEMs applications, and illustrates the use of the new fundamental properties in the design of a circuit topology that is practical for MEMs vibration energy harvesting applications.

ZnO thin film piezoelectric MEMS vibration energy harvesters with two piezoelectric elements for higher output performance.

Zinc oxide (ZnO) thin film piezoelectric microelectromechanical systems (MEMS) based vibration energy harvesters with two different designs are presented. These harvesters consist of a silicon cantilever, a silicon proof mass, and a ZnO piezoelectric layer. Design I has a large ZnO piezoelectric element and Design II has two smaller and equally sized ZnO piezoelectric elements; however, the total area of ZnO thin film in two designs is equal. The ZnO thin film is deposited by means of radio-frequency magnetron sputtering method and is characterized by means of XRD and SEM techniques. These ZnO energy harvesters are fabricated by using MEMS micromachining. The natural frequencies of the fabricated ZnO energy harvesters are simulated and tested. The test results show that these two energy harvesters with different designs have almost the same natural frequency. Then, the output performance of different ZnO energy harvesters is tested in detail. The effects of series connection and parallel connection of two ZnO elements on the load voltage and power are also analyzed. The experimental results show that the energy harvester with two ZnO piezoelectric elements in parallel connection in Design II has higher load voltage and higher load power than the fabricated energy harvesters with other designs. Its load voltage is 2.06 V under load resistance of 1 MΩ and its maximal load power is 1.25 μW under load resistance of 0.6 MΩ, when it is excited by an external vibration with frequency of 1300.1 Hz and acceleration of 10 m/s(2). By contrast, the load voltage of the energy harvester of Design I is 1.77 V under 1 MΩ resistance and its maximal load power is 0.98 μW under 0.38 MΩ load resistance when it is excited by the same vibration.

High Voltage Output MEMS Vibration Energy Harvester in $d_{31}$ Mode With PZT Thin Film

The voltage output of PZT thin film microelectromechanical system (MEMS) vibration energy harvester in d 31 mode is usually <;1 V at present. In practical applications, rectifier circuit is often utilized after vibration energy harvester. So the low voltage output will cause most of the power loss in rectifier circuit. To solve this problem while ensuring high power output, a d 31 mode PZT thin film MEMS vibration energy harvester with high voltage output is designed and fabricated. The proposed harvester consists of five cantilevers and one silicon proof mass. The dimensions of each cantilever are 3 mm x 2.4 mm x 0.052 mm and the proof mass dimensions are 8 mm x 12.4 mm x 0.5 mm. Al/PZT/LaNiO3/Pt/Ti/SiO 2 multilayered films are deposited on a SoI wafer and then the cantilevers are patterned and released. The single cantilever of the harvester produces 21.36-μW average power and 8.58-mW cm -3 g -2 power density at 0.5-g acceleration and 228.1-Hz frequency. When the cantilevers are connected in series, the harvester produces 3.94 V rms open circuit voltage with 59.62 μW power for 0.5-g acceleration and 5.72 V rms open circuit voltage with 157.9 μW power for 1-g acceleration at their resonance frequency.

Determination of Parameters With Uncertainties for Quality Control in MEMS Fabrication

A reliable technique for rapid monitoring of critical dimensional and material parameters during the fabrication of microelectromechanical systems (MEMS) is still an open task. Electrical excitation is sometimes simply not possible, or an electrical test does not reveal sufficient information for a complete characterization. In this paper, we present a new approach that employs optical testing of MEMS vibration frequencies. It is not necessary to have electrical connections because we have developed probes with transparent electrodes to excite vibrations electrostatically without contact on the wafer level. Broad-bandwidth excitation is applied to detect all relevant resonances interferometrically through the probes in a single broad-band measurement. Peak detection of the resonances results in a measurement vector containing the resonant frequencies. We demonstrate a new method to estimate system parameters by model identification. The analytical models are derived from a general approach based on finite-element analysis. The parameters with uncertainties are finally determined by guaranteed parameter estimation.

Design, fabrication, and experimental demonstration of a piezoelectric cantilever for a low resonant frequency microelectromechanical system vibration energy harvester

Moonkeun KimBeomseok HwangYong-Hyun HamJaehwa JeongNam Ki MinKwang-Ho KwonKorea UniversityDepartment of Control and InstrumentationEngineeringChungnam 339-700, Republic of KoreaE-mail: kwonkh@korea.ac.krAbstract. Wecompare the performances of vibration-powered microelec-tromechanical system (MEMS) electrical generators using a PbðZr;TiÞO

MEMS in-plane motion/vibration measurement system based CCD camera

We report on the development of a vibrometer for in-plane motion which is particularly suitable for Micro Electro Mechanical System (MEMS) samples. The system combines a conventional microscope, coherent electronics and a Full Frame CCD camera. Stroboscope lighting allows the system to freeze the motion. The obtained images correspond to different phases of the sample motion. Different subpixel motion measurement algorithms are compared in terms of precision and computation time. An algorithm that we specially design for this application proved to be the best. It is based on the shift Fourier theorem and uses first harmonics, where most energy is present. Thus the system allows computing the phase and magnitude of the sample displacement. With the system we can obtain a measurement resolution of 100 pm demonstrated on the AFM cantilever vibrations measurement. The effect of the edge roughness was studied. It decreases the performance of the algorithm but roughness is very low on most MEMS applications. This method based on a CCD camera, is very well suited for measuring in-plane MEMS vibration since it does not require surface roughness for scattering the light as with the speckle methods (for example). It can quickly obtain full field motion, with a high precision. Furthermore, the used algorithm is simple, fast and very noise insensitive.

Design and analysis of a low frequency MEMS vibration sensor for automotive fault detection

The modern automobile requires the use of many DC motor and solenoid-actuated systems that are susceptible to wear and sudden failure. Real-time monitoring of the vibration signature of these components could provide early detection of mechanical faults and lead to timely repairs, thereby preventing unexpected failures. This paper presents the theoretical analysis and experimental results of two Micro Electro Mechanical Systems (MEMS)-based sensors designed for low frequency vibration detection. One sensor was designed utilising lateral capacitive sensing, and provided an order of magnitude higher mechanical sensitivity than the design employing transverse capacitive sensing. Experimental results confirm the theoretical analysis.

Microelectromechanical systems motion measurement and modal analysis based on Doppler interferometry

Microelectromechanical systems (MEMSs) have been growing rapidly over recent years. However, measurement of their motions is a difficult problem. A laser Doppler interferometric system for measuring the instantaneous velocity and displacement of the periodic and nonperiodical in-plane and out-of-plane motions of the vibrating combs simultaneously has been developed. The working principle and optical diagram of the system are explained. The instantaneous velocity and displacement of vibrating combs are acquired by demodulating the frequency modulated Doppler signal by using a phase-locked loop. The developed laser Doppler interferometer provides a powerful means in studying the performance of the MEMS devices, particularly in studying their vibration modals. Modal analyses of the vibrating combs are carried out theoretically and experimentally. Due to the nonrigid structure of the MEMS resonator besides the basic modal there are also high order modals in the MEMS vibration. The basic modal is the desired in-plane lateral vibration. The second order vibration is a torsion vibration about the axis perpendicular to the fingers of the movable combs. Both third and fourth order vibrations are lateral bending of the supporting beams. The measured experimental data are presented. The accuracy of the developed interferometer has been checked by an acceleration calibrator.

A micromachined scanning grating interferometer for the out-of-plane vibration measurement of MEMS

A micromachined scanning grating interferometer (µSGI) is presented for use in measuring the out-of-plane vibration of microelectromechanical systems (MEMS). The µSGI uses a phase sensitive deformable diffraction grating to achieve interferometric axial resolution and a microfabricated lens to improve lateral resolution of the measurement. The grating is intended to be actuated to control diffraction patterns while measuring the MEMS vibration to increase measurement sensitivity. The deformable grating and the microlens are fabricated by surface micromachining techniques on separate wafers which are then precisely aligned and assembled. The fabricated deformable grating shows an actuation range of 0.54 µm and an operating voltage of under 31 V. An assembled grating and lens chip are successfully integrated with a silicon photodiode in less than 2 cm3. The integrated µSGI has been demonstrated by measuring 4.4 nm, 900 kHz vibration of a MEMS device while actuating the deformable grating in the measurement.