Piezoresistive Accelerometer Research Articles

Improvement of Method Queues by Progress of the Piezoresistive Accelerometer Parameters

In this paper the queues are used as a method to improve maintenance performance. The information collected by vibration analysis is used to check the system status and see whether a maintenance operation is to be organized. Thus, for a precise decision, the improvement of accelerometer parameters is required. In order to solve this issue, the piezoresistive accelerometer step and impulse responses are enhanced by using appropriate parameters (damping rate and frequency range). Computer simulation tests were conducted to confirm this approach. The obtained results have shown the difference between the accelerometer with the proposed parameters and the accelerometer used in the experiment. It can be concluded that the proposed parameters provide stable and accurate accelerometer.

Miniature accelerometers for sensing middle ear motion

Acceleration sensors are prevalent in handheld electronics, navigation systems, and physical activity monitors as well as for vibration measurement. There are many measurement applications, such as sensing human middle ear motion, that require miniature, low-noise sensors to detect low-amplitude vibration. Both capacitive and piezoresistive MEMS accelerometers have been used for vibration sensing of the middle ear. Recent capacitive designs are large (base area of 2.5 mm x 6.2 mm) and have a limited bandwidth of 6.44 kHz. Low-noise piezoresistive devices power requirements are high for hearing instruments, greater than 1 mW. Commercial piezoelectric accelerometers are a viable means for vibration detection; while small, they are still large and lacking proper electronic connections for middle ear sensing applications. The aforementioned problems motivate the design of a small, passive, broadband accelerometer with low input referred noise (IRN). In this work, we design a micromachined, piezoelectric bimorph cantilever accelerometer for broadband, low-amplitude vibration sensing. An analytic model is developed to minimize the IRN. The analytic expression allows for rapid design of many system parameters that are verified through finite element analysis.

A Simple Analytical Model for MEMS Cantilever Beam Piezoelectric Accelerometer and High Sensitivity Design for SHM (structural health monitoring) Applications

Cantilever beam MEMS piezoelectric accelerometers are the simplest and most widely used accelerometer structure. This paper discusses the design of a piezoelectric accelerometer exclusively for SHM applications. While such accelerometers need to operate at a lower frequency range, they also need to possess high sensitivity and low noise floor. The availability of a simple model for deflection, charge, and voltage sensitivities will make the accelerometer design procedure less cumbersome. However, a review of the open literature suggests that such a model has not yet been proposed. In addition, previous works either depended on FEM analysis or only reported on the fabrication and characterization of piezoelectric accelerometers. Hence, this paper presents, for the first time, a simple analytical model developed for the deflection, induced voltage, and charge sensitivity of a cantilever beam piezoelectric accelerometer.The model is then verified using FEM analysis for a range of different cases. Further, the model was validated by comparing the induced voltages of an accelerometer estimated using this model with experimental voltages measured in the accelerometer after fabrication. Subsequently, the design of an accelerometer is demonstrated for SHM applications using the analytical model developed in this work. The designed accelerometer has 60 mV/g voltage sensitivity and 2.4 pC/g charge sensitivity, which are relatively high values compared to those of the piezoresistive and capacitive accelerometers for SHM applications reported earlier.

Study and analysis of the piezoresistive accelerometer stability and improvement of their performances

With the springing up of the MEMS industry, research on accelerometers is focused on miniaturization, integration, high reliability, and high resolution, and shares extensive application prospects in military and civil fields. The piezoresistive accelerometer is the first element of measurement which converts the vibratory movement into time domain electrical signal and this signal is converted to a frequency domain electrical signal. In this work, the piezoresistive accelerometer step and impulse responses are enhanced by using appropriate parameters (damping rate and frequency range). The proposed parameters provide stable and accurate accelerometer. Therefore, tests were conducted by computer simulation and the obtained results have showed the difference between the accelerometer with the proposed parameters and the accelerometer used in the experiment.

New Formula for the Piezoresistive Accelerometer Motion Acceleration and Experimental Validation

A piezoresistive accelerometer is the first element of a vibration measurement chain, and its improvement can enhance measurement quality. In this paper, we have developed a new formula that links the movement acceleration as a function of the natural frequency and the damping rate of the piezoresistive accelerometer in first time, and movement acceleration as a function of the measurement error in second time. This model allows the decrease of the acceleration measurement error and increases the accelerometer accuracy by choosing the right damping rate and frequency range. Finally, this new formula allows proposing new parameters for more accurate and reliable piezoresistive accelerometer.

Identification of Pyrotechnic Shock Sources for Shear Type Explosive Bolt

To identify the shock generated sources of shear type explosive bolt, five kinds of explosive bolts with different states, including high preload, low preload, no preload, no piston shear, and only propellant combustion, were designed. The decoupling of four kinds of shock sources, including the collision of propellant combustion, piston shear weak surface, end of piston stroke, and preload release, was realized. Their acceleration responses at 15 cm from the shock source center on 60 cm × 60 cm × 1 cm equivalent aluminum plate were measured by using the piezoresistive accelerometer. On this account, the relative contribution values along with frequency and the mean relative values without regard to frequency of various sources were calculated in high and low preload. Results show that the characteristics of different shock sources are different, and the shock induced by propellant combustion is mainly caused by high frequency, while piston shear and piston impact are concentrated in medium and low frequency. In the high preload condition, the preload release is major contributor to the overall shock response output, accounting for approximately 57.51%, while the contributions of the three shock sources of propellant combustion, piston shear, and piston impact are equivalent, but they are significant contributors in the low preload condition. This study provides design reference to reduce the pyrotechnic shock of shear type explosive bolt.

A piezoresistive micro-accelerometer with high frequency response and low transverse effect

With the purpose of measuring vibration signals in high-speed machinery, this paper developed a piezoresistive micro-accelerometer with multi-beam structure by combining four tiny sensing beams with four suspension beams. The eight-beam (EB) structure was designed to improve the trade-off between the sensitivity and the natural frequency of piezoresistive accelerometer. Besides, the piezoresistor configuration in the sensing beams reduces the cross interference from the undesirable direction significantly. The natural frequency of the structure and the stress on the sensing beams are theoretically calculated, and then verified through finite element method (FEM). The proposed sensor is fabricated on the n-type single crystal silicon wafer and packaged for experiment. The results demonstrate that the developed device possesses a suitable characteristic in sensitivity, natural frequency and transverse effect, which allows its usage in the measuring high frequency vibration signals.

A novel piezoresistive polymer nanocomposite MEMS accelerometer

A novel polymer MEMS (micro electro mechanical systems) accelerometer with photo-patternable polymer nanocomposite as a piezoresistor is presented in this work. Polymer MEMS Accelerometer with beam thicknesses of 3.3 µm and embedded nanocomposite piezoresistive layer having a gauge factor of 90 were fabricated. The photosensitive nanocomposite samples were prepared and characterized for analyzing the mechanical and electrical properties and thereby ensuring proper process parameters for incorporating the piezoresistive layer into the polymer MEMS accelerometer. The microfabrication process flow and unit processes followed are extremely low cost with process temperatures below 100 °C. This also opens up a new possibility for easy integration of such polymer MEMS with CMOS (complementary metal oxide semiconductor) devices and circuits. The fabricated devices were characterized using laser Doppler vibrometer (LDV) and the devices exhibited a resonant frequency of 10.8 kHz and a response sensitivity of 280 nm g−1 at resonance. The main focus of this paper is on the SU-8/CB nanocomposite piezoresistive MEMS accelerometer technology development which covers the material and the fabrication aspects of these devices. CoventorWare FEA analysis performed using the extracted material properties from the experimental characterization which are in close agreement to performance parameters of the fabricated devices is also discussed. The simulated piezoresistive polymer MEMS devices showed an acceleration sensitivity of 126 nm g−1 and 82 ppm of ΔR/R per 1 g of acceleration.

Monolithic-integrated piezoresistive MEMS accelerometer pressure sensor with glass-silicon-glass sandwich structure

A monolithic composite MEMS sensor with sandwich structure is designed, simulated, fabricated and characterized. It consists of a rectangular diaphragm piezoresistive pressure sensor and a double-cantilever-mass piezoresistive accelerometer. The professional MEMS software, Intellisuite 8.5, is used to simulate the performances of the composite sensor. The composite sensor is fabricated on a (100)—silicon wafer by using MEMS bulk-micromachining and anodic bonding technology. One-step wet anisotropic etching process on the backside of the wafer can form the main backside shape of the composite sensor including the mass of accelerometer and the pressure sensing diaphragm. The glass-silicon-glass sandwich structure is formed with α-Si (amorphous silicon)-glass anodic bonding on the top surface of the wafer and Si-glass anodic bonding at the bottom. The fabricated composite sensor is measured, resulting in 33.0 μV/V kPa sensitivity for the 450 kPa-ranged pressure sensor, as well as, 11.2 μV/V g sensitivity for the 125 g-ranged accelerometer. The die size of the composite sensor chip is 2.5 mm × 2.5 mm × 1.4 mm. The measured results show that the composite sensor is appropriate for the application fields such as automobile, aerospace and environment monitoring.

SIMULATION STUDY OF CONVEX CORNER UNDERCUTTING IN KOH AND TMAH FOR A MEMS PIEZORESISTIVE ACCELEROMETER

Undercutting is a common problem in wet anisotropic etching. This problem in turn, influences the performance and sensitivity of MEMS devices. This paper investigates the use of corner compensation to prevent convex corner undercutting in a MEMS piezoresistive accelerometer. The Intellisuite CAD simulation software was used for designing the mask with corner compensation and for analysing wet anisotropic etching profiles in potassium hydroxide (KOH) and tetra-methyl-ammonium-hydroxide (TMAH) solutions at different concentrations and temperatures. Perfect 90 degrees corners on the proof mass was successfully etched using a corner compensation design at etching temperature of 63 °C for KOH and 67.7 °C for TMAH with 25 wt% and 10.3 wt% concentration levels, respectively. Etching in TMAH required lower concentration level, thus making the etching process safer. However, TMAH required longer time to etch perfect convex corners compared to KOH. Nevertheless, both KOH and TMAH etchants have been successfully used to etch perfect convex corners by using the designed corner compensation mask.

Analysis and design of a novel piezoresistive accelerometer with axially stressed self-supporting sensing beams

A novel piezoresistive accelerometer was developed with high performance in sensitivity, resonant frequency and cross-axis sensitivity. The accelerometer chip with axially stressed self-supporting sensing beams has been designed, fabricated and tested in our study. We derived the expressions for the location of the sensing beams, stresses and resonant frequency, and then these results were verified by the finite element method (FEM) simulation. The fabricated accelerometer was characterized by the static and dynamic experiments. The results showed that the measuring sensitivity was 0.666mV/g/3V and the resonant frequency was 17.1kHz. Meanwhile, the proposed accelerometer provided an available method for the low cross-axis sensitivity design. Compared with other accelerometers in the literatures, the developed accelerometer exhibited an excellent performance concerning a comprehensive figure of merit (FOM). The results demonstrated the feasibility of the novel structure to improve the accelerometer’s performance.

Suggestion for a new design of the piezoresistive accelerometer

ABSTRACTThe piezoresistive accelerometer is an electronic device used to measure the vibration level of rotating machines; we can say that an accelerometer more precise and more sensitive is a more reliable sensor. In our paper, based on the improvement of some parameters of piezoresistive accelerometer for develop their accuracy and their sensitivity. This improvement comes from extracting a suitable mathematical model of the accelerometer; this model allows proposing a new design of piezoresistive accelerometer.

A Novel Piezoresistive Accelerometer with SPBs to Improve the Tradeoff between the Sensitivity and the Resonant Frequency.

For improving the tradeoff between the sensitivity and the resonant frequency of piezoresistive accelerometers, the dependency between the stress of the piezoresistor and the displacement of the structure is taken into consideration in this paper. In order to weaken the dependency, a novel structure with suspended piezoresistive beams (SPBs) is designed, and a theoretical model is established for calculating the location of SPBs, the stress of SPBs and the resonant frequency of the whole structure. Finite element method (FEM) simulations, comparative simulations and experiments are carried out to verify the good agreement with the theoretical model. It is demonstrated that increasing the sensitivity greatly without sacrificing the resonant frequency is possible in the piezoresistive accelerometer design. Therefore, the proposed structure with SPBs is potentially a novel option for improving the tradeoff between the sensitivity and the resonant frequency of piezoresistive accelerometers.

伸縮梁構造を用いたMEMS加速度センサの特性安定化

A high-reliability design method for a MEMS accelerometer using a stretchable beam structure was proposed to prevent sensor property variations due to stresses from device fabrication and packaging. To achieve a compact piezoresistive three-axis accelerometer using a low-cost resin-mold packaging, beam buckling due to compression forces originating from residual stresses of thin films and shrinkage of mold resin must be overcome. The proposed stretchable beam structure, which gives axial flexibility by adding a ring-shape part at the center of the beam, has advantages in which it is effective against not only packaging stress but also inner stress such as thin film stress, and it does not sacrifice compactness. Formulations with a simple accelerometer model revealed that large and nonlinear variations in sensitivity occur due to beam compression. Such large variations have to be avoided to stabilize sensor performances. Besides, it is expected to enhance sensitivity up to about 1.5 times while maintaining linearity by arranging an appropriate compression force using the stretchable beam. The effects of the stretchable beam were verified using simulations and experiments on test samples. The designed stretchable beam, which has two rings connected serially, has five times the axial flexibility compared with a conventional straight beam without significant change in bending stiffness. A preferable increase of about 1.4 times and small deviations in measured sensitivity were achieved with the developed stretchable beam, compared with the straight beam with an unstable increase of about seven times and extremely large deviations. These large deviations seem to come from shape variation due to non-uniformity of dry etching technologies commonly used for MEMS devices. Thus, the effects of the proposed stretchable beam to the MEMS accelerometer design were confirmed to prevent large variations and deviations in sensor properties and to enhance sensitivity.

Effect of Electroplated Gold Film on the Performance of a Piezoresistive Accelerometer with Stress Concentrated Tiny Beams

Background/Objective: In the recent times, piezoresistive accelerometers have been extensively explored with the primary focus on the optimization of its sensitivity and measurement bandwidth. In this paper, the design of an in-plane deflection mode accelerometer sensor has been devised with selective deposition of gold metal on the top and both the sides of the proof mass. Methods/Statistical Analysis: The micromachined silicon accelerometer constitutes of stress concentrated tiny piezoresistor beams and a central cantilever beam to support the proof mass. In order to improve the electromechanical response of the sensor, selective deposition of the gold metal layer was performed on the top and both the sides of the proof mass. The design and modeling of the sensor has been performed utilizing a Finite Element Model (FEM) software simulation tool IntelliSuite®. Findings: Compared to the conventional designs reported in the literature, accelerometer sensors with stress concentrated tiny beams and gold layer selectively deposited on the proof mass have shown an improvement in the electrical sensitivity and the FOM (product of the sensitivity and square of the resonant frequency). Simulation results demonstrate that the accelerometer structure with gold layer atop of the proof mass has a better sensitivity and FOM than the conventional design without gold by 28.26% and 27.43% respectively. Similarly, the accelerometer structure with gold on both sides of the proof mass has shown an improvement in the sensitivity by 57.82% and the Figure Of Merit (FOM) by 29.70% compared to the structure without gold layer. Conclusion/Improvements: It has been demonstrated that the performance metrics of piezoresistive accelerometer sensors with stress concentrated tiny beams can further be improved by selective deposition of metal gold layer on the proof mass of the accelerometer structure.

Design Issues of Piezoresistive MEMS Accelerometer for an Application Specific Medical Diagnostic System

ABSTRACTThis paper reports the design and simulation of finite element method (FEM)-based micro-electro-mechanical-systems (MEMS) piezoresistive accelerometer used in a strapdown medical diagnostic system. A square proofmass with four flexures is used in this design. Here, p-doped single-crystal silicon are used as eight piezoresistors implanted on the flexures for sensing the maximum stress; and they are connected in the form of a wheatstone bridge with each arm containing two piezoresistors. Basically, here two different geometric configuration but of same material have been designed and simulated using FEM-based tool for dynamic range (±)2g. To assure better performance characteristics, different analysis for both the configurations are done. Configuration 1 is found to have better performance with respect to load withstanding capability, eigen value analysis, better response characteristic, and low cross-axis sensitivity. Furthermore, the measurement scheme adopted is the wheatstone bridge, which gives better performance as offset is almost nullified.

High performance MEMS accelerometers for concrete SHM applications and comparison with COTS accelerometers

Accelerometers used for civil and huge mechanical structural health monitoring intend to measure the shift in the natural frequency of the monitored structures (<100Hz) and such sensors should have large sensitivity and extremely low noise floor. Sensitivity of accelerometers is inversely proportional to the frequency squared. Commercial MEMS (Micro Electro-Mechanical System) accelerometers that are generally designed for large bandwidth (e.g 25kHz in ADXL150) have poor sensor level sensitivity and therefore uses complex signal conditioning electronics to achieve large sensitivity and low noise floor which in turn results in higher cost. In this work, an attempt has been made to design MEMS capacitive and piezoresistive accelerometers for smaller bandwidth using IntelliSuite and CoventorWare MEMS tools respectively. The various performance metrics have been obtained using simulation experiments and the results show that these sensors have excellent voltage sensitivity, noise performance and high resolution at sensor level and are even superior to commercial MEMS accelerometers.

Performance enhancement for piezoresistive microaccelerometer by geometrical design: a focused review

Purpose – This paper aims to provide a focused review on the geometrical designs for performance enhancement of piezoresistive microaccelerometers. Design/methodology/approach – By analyzing working principle and conventional geometries, the improved research proposals are sorted into three groups in terms of their anticipated objectives, including sensitivity, resonant frequency and cross-axis sensitivity. Accessible methods are outlined and their merits and demerits are described. Findings – Novel geometries obviously enhance the performance of accelerometers, and the efficacy can be further elevated by newer materials and fabrication processes. Research limitations/implications – This paper mainly focused on the improved geometrical designs for sensitivity, resonant frequency and cross-axis sensitivity. Other performance parameters or design schemes are not included in this paper. Originality/value – This paper generalizes the available geometries and methods for the enhancement of sensitivity, resonant frequency and cross-axis sensitivity in piezoresistive accelerometers design.

Design, Simulation and Fabrication of Triaxial MEMS High Shock Accelerometer.

On the basis of analyzing the disadvantage of other structural accelerometer, three-axis high g MEMS piezoresistive accelerometer was put forward in order to apply to the high-shock test field. The accelerometer's structure and working principle were discussed in details. The simulation results show that three-axis high shock MEMS accelerometer can bear high shock. After bearing high shock impact in high-shock shooting test, three-axis high shock MEMS accelerometer can obtain the intact metrical information of the penetration process and still guarantee the accurate precision of measurement in high shock load range, so we can not only analyze the law of stress wave spreading and the penetration rule of the penetration process of the body of the missile, but also furnish the testing technology of the burst point controlling. The accelerometer has far-ranging application in recording the typical data that projectile penetrating hard target and furnish both technology guarantees for penetration rule and defend engineering.

Application of Artificial Neural Network Model to Human Body Vibrations in Large Haul Trucks

The working conditions in oil sand mines in Northern Alberta, Canada, are greatly affected by the climate and geology. The ground is very hard and competent in winter but very soft during summer [1]. This changing behaviour of the ground has a great impact on the truck’s frame and the health of the operator because he is exposed to large Whole Body Vibrations (WBV). When the human body is exposed to large WBV for prolonged periods, it begins to have chronic back problems resulting in diseases of the lumbar spine, disc degeneration and other pathological effects to the spine and skeletal structure [2]. Many of these health effects are irreversible and people suffering from WBV disorders can experience pains for the rest of their lives. Studies carried out to correlate WBV to health problems have resulted in the setting of standards with the help of various government agencies, physiologists and industry experts. The main WBV standards that the mining industry has to observe are those of International Standards Organization (ISO) and the British Standards Institute [2]. ISO 2631-1 uses a three dimensional coordinate system where the axes are orthogonal to each other as shown in Figure 1 [3]. The standards require that the measuring device (accelerometer) should be placed at a point where vibrations are entering the body. In this study the data was collected for the seat accelerations in X, Y and Z directions by installing the accelerometer on the seat pan of a CAT 797 haul truck. An Artificial Neural Network (ANN) model was developed to predict the seat vibrations in very large capacity haul trucks in the X and Y directions. The study was done to find if the vibrations in the truck and their effects on the operator can be correlated to the truck’s operational parameters like speed, payload and strut pressures. There is a need for an onboard monitoring system on large haul trucks to alert the driver when he exceeds specified speed limits at certain locations along the haul road which are unsafe for him. Caterpillar 797 trucks use Vital Information Management System (VIMS) to track the truck’s behaviour when driven along a haul road. It includes onboard truck measuring equipment and off-board VIMS software which enables data logging and downloading into a computer. A record of real time parameters gives a detailed view of what happens to the truck body while performing the various functions [4]. The disadvantage of using a piezo-resistive accelerometer to collect the data collection is that it has a limited high frequency response [5]. Thus, it is necessary that the data be collected at higher frequencies to obtain a better model that can give more accurate predictions. In this work the accelerometer was replaced with an ANN model. The ANN model is developed for the dump truck such that it models the seat vibrations in the truck in response to the truck’s speed, payload, changing ground stiffness and profile. These truck parameters can be estimated from the strut pressure responses measured in terms of machine rack, machine roll and machine pitch. The machine’s roll, rack and pitch give an idea of the truck’s response to the changing ground conditions and operator’s driving skills. These values are calculated using the changing pressures of the four struts on which the whole truck frame is resting. These parameters were used as input variables during the development of the ANN model. This study focused only on the seat accelerations in the X-direction and Y-direction as output variables, as these are more important than the accelerations in the Z-direction. The ANN model is very efficient for non-linear processes and tends to improve its performance as it learns more and more about the system. Thus when the ANN model is used, very accurate acceleration values can be predicted. This is important for the health of the operator and also for the lifespan of the truck as the high amplitude vibrations are detrimental to truck’s structural components. Using the NeuroShell® 2 software, a multilayer perceptron ANN was trained with the back propagation algorithm. The model’s performance was optimized following the systematic approach developed by [6,7]. This is done by looking for the simplest network architecture that can converge. During the development of the ANN model for Seat X acceleration, the number of hidden layer neurons was increased from 10 to 70 while keeping the number of learning epochs constant at 50. The number of neurons which gave the best value for R 2 (Validation)