Input Acceleration Research Articles

A Low 1/f Noise Tunnel Magnetoresistance Accelerometer

Aiming at minimizing 1/f noise of tunnel magnetoresistance (TMR) accelerometers, a new principle incorporated acceleration sensing and 1/f noise suppression is demonstrated both theoretically and experimentally. The elasto-magneto-electric conversion theory is analyzed and a linear relationship between input acceleration and output voltage is derived. A new modulation methodology based on periodically biased magnetic field is proposed and validated to effectively minimize 1/f noise of TMR accelerometers, by integrating a high-frequency resonator with a soft magnetic modulation film. A prototype is used to experimentally demonstrate that a sensitivity of 8.2 mV/g can be realized for acceleration sensing and 1/f noise can be minimized by at least 80 times. This work clarifies a universally applicable low noise sensing principle not only for TMR accelerometers but also for all of the elasto-magneto-electric coupling sensors like MR/ME displacement sensors or strain sensors.

Piezoelectric energy harvesting from rail track vibration using frequency up-conversion mechanism

Piezoelectric energy harvesting has great powering potential in railway applications, but current piezoelectric literature for rail track vibration mainly focuses on a single piezoelectric element or piezoelectric cantilever, whose output power is usually at the level of µW. In this work, a piezo stack energy harvester using the frequency up-conversion method with attractive magnetic force is proposed and experimentally validated for harvesting energy from rail track vibration. It consists of two parts, an inertial mass system and a piezo stack system. The frequency up-conversion mechanism is realised by allowing the inertial mass to attach and detach the piezo stack transducer periodically with the help of the attractive magnetic force. The attractive magnetic force contributes to the collision between the two systems, especially when the excitation frequency is near the resonant frequency. A theoretical model of the proposed energy harvester considering the colliding motion and magnetic force is established. A prototype is fabricated and can generate a peak power of 96.69 mW and average power of 2.59 mW at an input acceleration of 1 g applied at 9 Hz with an optimum load impedance of 200 Ω.

Fundamental study on failure probability assessment method during vibration

The various vibration tests have been conducted, depending on the specification and shape of the structure. However, the data, which was obtained from these vibration tests, are underutilized in the failure evaluation caused by vibration. In this study, the failure probability evaluation method of the similar structure is investigated based on these test data. In previous studies, cabinets and underfloor equipment on railroad vehicles were investigated based on the PRA (Probabilistic Risk Assessment) method used in nuclear facilities. As a result, the failure probability could be evaluated at classifying these sample appropriately before the vibration test. Furthermore, in order to adapt this method to more structures and equipment, an evaluation indicator, which can be evaluated regardless of differences in input waves, is necessary. Accordingly, in this report, the vibration tests with the simple examination specimens were carried out in order to investigate the vibration energy which input to the equipment and accumulated. The natural frequency of the simple examination specimen is 112Hz. The sine wave test was carried out at the resonant frequency. The accumulated energy to failure, was investigated for each vibration test. As a result, the accumulated energy increased with increasing input acceleration, furthermore, the average value of the accumulated energy to failure was approximately 3750 [J] on this test condition.

Liquid cargo effect on load transfer under orthogonal accelerations

A methodology is proposed for the experimental analysis of the liquid cargo effect under combined orthogonal accelerations. To simultaneously subject the vehicle-cargo system to longitudinal and lateral accelerations, the vehicle is set obliquely on a tilt table. The experimental outputs suggest that there is a significant effect of the liquid cargo on the lateral load transfer ratio (LTR), on the order of 20%, which is attributable to the resulting shifting of the liquid cargo's centre of gravity. That is, the peak LTR values due exclusively to sloshing were not significant, in such a way that the liquid cargo would only pose a safety risk under a steady acceleration input. Also, the inverse of the product of the magnitude of the acceleration times the free surface length, correlates with the liquid cargo effect. That is, the magnitude of the input acceleration is not fully determinant for greater load transfers.

Calibration Method of Accelerometer Based on Rotation Principle Using Double Turntable Centrifuge.

For linear accelerometers, calibration with a precision centrifuge is a key technology, and the input acceleration imposed on the accelerometer should be accurately obtained in the calibration. However, there are often errors in the installation of sample that make the calibration inaccurate. To solve installation errors and obtain the input acceleration in the calibration of the accelerometer, a calibration method based on the rotation principle using a double turntable centrifuge is proposed in this work. The key operation is that the sub-turntable is rotated to make the input axis of the accelerometer perpendicular to the direction of the centripetal acceleration vector. Models of installation errors of angle and radius were built. Based on these models, the static radius and input acceleration can be obtained accurately, and the calibration of the scale factor, nonlinearity and asymmetry can be implemented. Using this method, measurements of the MEMS accelerometer with a range of ±30 g were carried out. The results show that the discrepancy of performance obtained from different installation positions was smaller than 100 ppm after calibrating the input acceleration. Moreover, the results using this method were consistent with those using the back-calculation method. These results demonstrate that the effectiveness of our proposed method was confirmed. This method can measure the static radius directly eliminating the installation errors of angle and radius, and it simplifies the accelerometer calibration procedure.

Determination of Notched Input for Equipment Under Random Vibrations

Equipment that is mounted on a spacecraft is subjected to random vibration tests to verify whether they can withstand the specified random loads. These tests are generally carried out by using shaker systems during which equipment experiences very high responses at the natural frequencies of the equipment. To reduce such over-testing, notching of the input is done. Notching of the input is normally carried out by considering the force generated at the base and limiting it to a specified value. To accomplish the notching, the force spectrum to be limited and measurement of base force during the tests are needed. This work shows that the acceleration input at the interface of equipment gets reduced at its resonance frequency and this feature can be utilized in arriving at the notched input. An expression to determine the depth of notching is derived and the results are compared with those obtained using numerical simulations. The depth of the notch increases with the response of the oscillator and it is sensitive to the stiffness ratios rather than the mass ratios of the oscillator and the mounting panel. This behavior and the expressions derived can be effectively used in arriving at the notched input for an equipment without the need for measuring the base force, especially for random vibration testing, which is demonstrated with an example.

Development of repairability index for steel moment frames with post-tensioned self-centering connections

With regard to the effects of self-centering structural performance in reducing damages in the event of an earthquake, in this study an attempt is made at developing a repairability index for post-tensioned self-centering steel moment connections. Based on the 18 structural models studied, a building in which the maximum connection rotation does not exceed the allowable rotation of the immediate occupancy level is considered repairable. Accordingly, the output data of Incremental Dynamic Analyses have been depicted in OpenSees under 22 sets of near and far-field strong ground motion accelerograms based on connection relative rotation and spectral acceleration the Repairability Index of Self-Centering Frame (RISCF) will be obtained. For input of spectral acceleration of the first mode of the structure in the repairability equation, if this amount is smaller than 1, the aim of repairability is met. In order to qualitatively evaluate angle damages, the Angle Failure Probability of Self-centering Frame (AFPSCF) will be depicted with regard to the fragility curve, if the number is less than 1, the building can return to its previous performance level with angle replacement after the event of an earthquake.

Discussion On Failure Behavior of Piping Systems Under Extremely Large Seismic Loads in BDBE

Abstract To investigate the failure behavior of piping systems under severe seismic loads considering beyond design basis event (BDBE), an experimental approach to use pipes made of simulation materials was applied. "Simulation material" means the substitute material for steel to realize the structural experiment by the existing testing facilities. The simulation materials adopted in this study were pure lead (Pb) or lead-antimony (Pb-Sb) alloy. Using pipe elbows made of simulation materials, static loading tests on elbows and shaking table tests on simple piping system models composed of one or two elbows and an additional mass were conducted. From the static loading tests, the load-deflection relationship of an elbow under monotonic loading was obtained as well as the fatigue failure modes under cyclic loading depending on the several cyclic displacement levels. From the shaking table tests, several failure modes were obtained, namely, "Collapse by self-weight", "Collapse by a few cycles of input", "Ratchet and subsequent collapse", "Overall deformation", and "No failure". It was considered that the occurrence of these failure modes was affected by the ratio of the input frequency to the specimen's natural frequency, the ratio of additional mass weight to the limit mass weight, the configuration of the specimen, and the input acceleration level. The experimental results indicated that it was crucial to understand the structure's ultimate behavior when treating BDBE, and that the research approach using simulation material is effective to investigate the ultimate behavior of piping systems.

Stabilization Control of a MEMS Accelerometer With Tuned Quasi-Zero Stiffness

In this paper, a novel MEMS accelerometer with tuned quasi-zero stiffness stabilized and operated in a closed-loop is proposed. By using the electrostatic softening effect of the double-sided comb-finger capacitors and the triangular capacitors, the effective stiffness of the accelerometer can be adjusted to quasi-zero. The variation of the electrostatic stiffness arising from the thermal drift of the proposed quasi-zero stiffness accelerometer can be greatly reduced when utilizing the double-sided comb-finger capacitors. For a high-sensitivity and high-linearity acceleration measurement, a traditional proportional-integral-derivative (PID) controller and a proportional-integral sliding mode (PISM) controller are designed for the stabilization near the border of pull-in. The parameters of the controller are tuned to ensure that the proof mass is stably positioned at the desired position. Both the simulation and experiment validate the feasibility of two controllers, showing distinct transient characteristics and long-term stability performance. Compared to the open-loop accelerometer with untuned stiffness, the sensitivity of the closed-loop accelerometer is increased over 40 times while the long-term stability of the closed-loop accelerometer with quasi-zero stiffness is remarkably improved for both controllers. The PID-controlled accelerometer with quasi-zero stiffness has an Allan bias instability as low as 22.51 ng and narrow bandwidth of 0.36 Hz. The PISM controlled accelerometer with quasi-zero stiffness has a linearly varied Allan bias instability from 37 ng to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.02 ~\mu \text{g}$ </tex-math></inline-formula> depending on the switching gain which determines the acceleration input range. However, the bandwidth of the PISM control system exhibits a nonlinear and wide-range variation with respect to the switching gain.

Comparative Analysis of MacAdam Model and PI Control in a Predictive Driver Model

Autonomous vehicles are the future of automotive engineering and understanding how this systems work is critical. In these vehicles, controller models are usually needed to generate signals that would normally be imposed by the driver e.g., steering angles, acceleration inputs and braking commands. Intuitively, each control method utilized has its peculiarities and presents different behaviours. In such situation, this paper aims to develop an error comparison between a car displacement and its reference path due the use of two different predictive driver controllers: The proportional-integrative and the MacAdam model. For this purpose, a 14 degrees of freedom vehicle model is used with the aid of MATLAB Simulink, whereas simulations were made using the double-lane change manoeuvre, a commonly used manoeuvre to analyse the vehicle dynamics performance. At the end of this paper, lateral acceleration, displacement and steering wheel angle analysis led the conclusion that the vehicle behaviour is smoother with the use of the proportional-integrative control regardless of longitudinal velocity. Nevertheless, the trajectory error is smaller for MacAdam model than PI controller is and therefore it is easier to follow the reference path with this one, although in aggressive maneuverers it can cause more discomfort and increase the risk of rolling when compared to the PI controller in a vehicle with the same body stiffness.

Modelling of Flexible Manipulator System via Ant Colony Optimization for Endpoint Acceleration

The application of flexible manipulators has increased in recent years especially in the fourth industrial revolution. It plays a significant role in a diverse range of fields, such as construction automation, environmental applications, space engineering and many more. Due to the lightweight, lower inertia and high flexibility of flexible manipulators, undesired vibration may occur and affect the precision of operation. Therefore, development of an accurate model of the flexible manipulator was presented prior to establishing active vibration control to suppress the vibration and increase efficiency of the system. In this study, flexible manipulator system was modelled using the input and output experimental data of the endpoint acceleration. The model was developed by utilizing intelligence algorithm via ant colony optimization (ACO), commonly known as a population-based trail-following behaviour of real ants based on autoregressive with exogenous (ARX) model structure. The performance of the algorithm was validated based on three robustness methods known as lowest mean square error (MSE), correlation test within 95% confidence level and pole zero stability. The simulation results indicated that ACO accomplished superior performance by achieving lowest MSE of 2.5171×10−7 for endpoint acceleration. In addition, ACO portrayed correlation tests within 95% confidence level and great pole-zero stability.

Analysis of Shaking Table Tests of Underground Structures considering the Influence of the Structure-Soil Interface

To investigate the seismic performance of underground structures under the action of the structure-soil interface, in this study, experiments were performed using plexiglass structures (two pieces) and a concrete structure (one piece) as the research objects. The surface of one plexiglass structure was prepainted with a layer of cement mortar as the contact surface between the structure and soil, and the other plexiglass structure was not treated and used for comparison. A rigid model box measuring 2.25 m × 2.25 m × 1.5 m was placed on a 3 m × 3 m shaking table, and the box was filled with the configured model soil and the underground structure prepared in advance. Input transverse uniform excitation was imparted to the whole system. A shaking table model test was performed on the underground structures to analyse the acceleration response, stress strain, and earth pressure changes in the underground structure, and the influence of the contact surface on the seismic dynamics of the underground structure was evaluated. The test results showed that under uniform excitation, the dynamic characteristics of the underground structures were greatly affected by the intensity and depth of the seismic waves. (1) When the soil-structure contact was considered, the stress and strain of the structures increased significantly, and the stress-strain value was significantly greater than the stress-strain value of the soil-structure interface in a fully bonded state. (2) There were inconsistencies between the acceleration peak curve of the plexiglass structure considering the contact effect and the acceleration peak curve of the plexiglass structure without considering the contact effect. The difference between the two lies mainly in the corresponding maximum peak acceleration and the Fourier spectrum amplitude. With respect to the value and frequency composition, regardless of whether the input acceleration intensity was 0.2 g or 0.5 g, the peak acceleration of the organic structure was greater when the contact surface effect was considered than without the contact surface effect. Therefore, the structure-soil interface needs to be considered in actual engineering. The presence of the contact surface improves the safety of the structure and is helpful for seismic design. The results of this study provide a basis for further research on the influence of soil-pipe contact on the seismic response of underground structures.

Analysis of Dynamic p-y Curve Characteristics According to Mode Shape of Structure Using Shaking Table Tests

In the seismic design of pile foundations, a p-y curve representing the nonlinear behavior of the ground considering the dynamic load of the earthquake is required. Recently, p-y curve analyses reflecting the soil-structure interaction have been conducted, but studies on multilayer structures have not been investigated extensively. In this study, the p-y curve characteristics were analyzed, considering the influence of the ground-structure interaction based on the mode shape of the structure (no structure, single-story structure, and three-story structure) through shake table tests. It was found that (1) the bending moment and pile displacement increased with input acceleration, and (2) the maximum soil resistance and pile displacement occurred at the natural frequencies of each structure were observed. In addition, the bending moment, soil resistance, and p-y curve slope were higher in the single-story structure than in the three-story structure. The findings indicate that the seismic design simulated for a single-story structure is conservative.

Experimental investigation of performance tailoring of the multifunctional sensor using transition metal (Fe) doped ZnO nanorods synthesized via a facile solution-based method

A systematic interpretation of the undoped and Fe doped ZnO based multifunctional sensor developed employing economic and facile low-temperature hydrothermal method is reported. The tailoring of the performance improvement of the sensor was deliberately carried out using varied concentration (1, 3 and 5 Wt%) of Fe dopant in ZnO nanorods. The structural and morphological analysis reveal the undisturbed ZnO hexagonal wurtzite structure formation and 1D morphology grown even when the dopant is added. The optical property study evidences a decreased bandgap (3.10 eV) and decreased defects of 5 Wt% of Fe dopant in ZnO nanorods based sensor compared to the undoped one. The electrical process transpiring in the tailored multifunctional sensor is investigated using photoconductivity and impedance analysis elucidates proper construction of p–n junction between the piezoelectric n-type active layer (undoped and Fe doped ZnO nanorods) and p-type PEDOT:PSS ((poly(3,4-ethylene dioxythiophene) polystyrene sulfonate)) and reduced internal resistance of 5 Wt% of Fe dopant in ZnO nanorods based sensor (131.97 Ω) respectively. The investigation on the experimental piezoelectric acceleration and gas sensing validation and the performance measurement were interpreted using test systems. A revamped output voltage of 3.71 V for 1 g input acceleration and a comprehensive sensitivity of 7.17 V g−1 was achieved for the 5 Wt% of Fe dopant in ZnO nanorods based sensor sensor. Similarly, an upgraded sensitivity of 2.04 and 6.75 for 5 Wt% of Fe dopant in ZnO nanorods based sensor was obtained when exposed to 10 ppm of target gases namely CO and CH4 respectively at room temperature. Appending to this, acceptable stability of the sensor for both the sensing (acceleration and gas) was also attained manifesting its prospective application in multifunctional based systems like sewage systems.

Shaking Table Test of a Friction Sliding System on a Concrete Member with Variable Curvature Fabricated by a Three-dimensional Printer

ABSTRACT Bridge structures play a crucial role in the recovery process after an earthquake; however, the need to produce a resilient structure requires the implementation of expensive materials that are essentially limited to critical structures. To achieve a low-cost resilient system, a novel friction pendulum sliding system fabricated from only steel and concrete was experimentally evaluated. Simple concave shapes mounted transverse to one other; and spherical shapes with variable curvatures fabricated by a three-dimensional printer were evaluated. Bidirectional shaking table tests were conducted with different acceleration intensities, and the input acceleration was reduced by 50% during sliding. The spherical shapes exhibited stable hysteresis responses even when subjected to strong ground motions. The proposed friction pendulum sliding system for bridge structures provides a low-cost design solution that can ensure post-event operability.

Shaking table test of combination isolation plate-shell integrated concrete liquid-storage structure

To obtain the seismic performance of plate-shell integrated concrete liquid-storage structures (PSICLSS), a scale test model was built for shaking table testing. A combination isolation layer is proposed, and the dynamic responses of non-isolation and combination isolation PSICLSS under unidirectional and bidirectional earthquakes were tested. The results show that the combination isolation layer can change the spectral characteristics of the input acceleration, reducing the acceleration response and displacement of the structure, but it will increase the hydrodynamic pressure and liquid sloshing height. Under earthquake action, the liquid sloshing of combination isolation PSICLSS clearly appears as a nonlinear splash phenomenon. When considering the vertical earthquake, the horizontal acceleration response of PSICLSS and the liquid sloshing height change little, the peak hydrodynamic pressure changes significantly, and the peak position also changes. The maximum displacement of the isolation layer increases, but the residual displacement decreases.

Deep-Learning-Based Optimization for a Low-Frequency Piezoelectric MEMS Energy Harvester

High operational frequency is one of the major limitations of the conventional MEMS vibration energy harvesters. In this work, we present a piezoelectric MEMS energy harvester with the capability of operating at a low resonant frequency (i.e., less than 200 Hz). The proposed harvester has a symmetric serpentine structure with a doubly clamped configuration comprising several proof masses at the junctions. In order to facilitate the design process and determine the optimum physical dimensions, an artificial neural network is used to model the design. In the first step, a dataset with 108 samples is generated by finite element modeling (FEM) to train a deep neural network. The validation results indicate that the trained deep neural network model can achieve around 90% estimation accuracy of device features, such as resonant frequency and harvested voltage. Next, this trained model is integrated with genetic algorithm as a performance estimator to optimize the geometry of the harvester to lower the resonant frequency and improve the harvested voltage. An optimized harvester with a total area of 8.7 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> has been fabricated through a standard micromachining process. Our measurement results confirm that the proposed deep-learning-based method can help reach the balanced summit of both higher power density and lower resonant frequency among the published works. Our prototype device features the first resonant frequency of 121.7 Hz and the harvested power of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.73~\mu \text{W}$ </tex-math></inline-formula> under 0.1g input acceleration.

Low-Cost, High-Performance Piezoelectric Nanocomposite for Mechanical Energy Harvesting

Lack of low-cost, large area deposition methods and photo-patternability of high-performance piezoelectric materials restrict the rapid development of efficient functional devices like sensors and energy harvesters. In this paper, we report an optimized process flow for Zinc Oxide (ZnO)/SU-8 and Barium Titanate (BTO)/SU-8 based nanocomposite thin films for mechanical energy harvesting (MEH) applications. Parametric variation of process variables for these nanocomposites reveals that 15% ZnO/SU-8 and 20% BTO/SU-8 nanocomposites show optimum results with good piezoelectric response and UV transmittance, allowing reliable lithography of the nanocomposites. Furthermore, three different types of energy harvesting devices are fabricated using these nanocomposites as piezoelectric layer. Output powers of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$223~\mu \text{W}$ </tex-math></inline-formula> (ZnO/SU-8) and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$642~\mu \text{W}$ </tex-math></inline-formula> (BTO/SU-8) are produced at resonance for the conventional cantilever type MEH devices at an input acceleration of 0.5g. Using the nanocomposites as flexible nanogenerator, open circuit voltages of 570 mV (ZnO/SU-8) and 780mV (BTO/SU-8) are obtained using regular finger pressing. The hybrid energy harvesters, based on combined piezoelectric-triboelectric transduction mechanisms, generate output voltages of 0.4V, 0.95V, 1.4V (ZnO/SU-8) and 0.7V, 1.1V and 1.9V (BTO/SU-8) in piezoelectric, triboelectric and hybrid operations, respectively.

Turn-key constrained parameter space exploration for particle accelerators using Bayesian active learning

Particle accelerators are invaluable discovery engines in the chemical, biological and physical sciences. Characterization of the accelerated beam response to accelerator input parameters is often the first step when conducting accelerator-based experiments. Currently used techniques for characterization, such as grid-like parameter sampling scans, become impractical when extended to higher dimensional input spaces, when complicated measurement constraints are present, or prior information known about the beam response is scarce. Here in this work, we describe an adaptation of the popular Bayesian optimization algorithm, which enables a turn-key exploration of input parameter spaces. Our algorithm replaces the need for parameter scans while minimizing prior information needed about the measurement’s behavior and associated measurement constraints. We experimentally demonstrate that our algorithm autonomously conducts an adaptive, multi-parameter exploration of input parameter space, potentially orders of magnitude faster than conventional grid-like parameter scans, while making highly constrained, single-shot beam phase-space measurements and accounts for costs associated with changing input parameters. In addition to applications in accelerator-based scientific experiments, this algorithm addresses challenges shared by many scientific disciplines, and is thus applicable to autonomously conducting experiments over a broad range of research topics.

Improving the Event-Based Classification Accuracy in Pit-Drilling Operations: An Application by Neural Networks and Median Filtering of the Acceleration Input Signal Data

Forestry is a complex economic sector which is relying on resource and process monitoring data. Most of the forest operations such as planting and harvesting are supported by the use of tools and machines, and their monitoring has been traditionally done by the use of pen-and-paper time studies. Nevertheless, modern data collection and analysis methods involving different kinds of platforms and machine learning techniques have been studied lately with the aim of easing the data management process. By their outcomes, improvements are still needed to reach a close to 100% activity recognition, which may depend on several factors such as the type of monitored process and the characteristics of the signals used as inputs. In this paper, we test, thought a case study on mechanized pit-drilling operations, the potential of digital signal processing techniques combined with Artificial Neural Networks (ANNs) in improving the event-based classification accuracy in the time domain. Signal processing was implemented by the means of median filtering of triaxial accelerometer data (window sizes of 3, 5, and up to 21 observations collected at 1 Hz) while the ANNs were subjected to the regularization hyperparameter’s tunning. An acceleration signal processed by a median filter with a window size of 3 observations and fed into an ANN set to learn and generalize by a regularization parameter of α = 0.01 has been found to be the best strategy in improving the event-based classification accuracy (improvements of 1% to 8% in classification accuracy depending on the type of event in question). Improvement of classification accuracy by signal filtering and ANN tuning may depend largely on the type of monitored process and its outcomes in terms of event duration; therefore, other monitoring applications may need particular designs of signal processing and ANN tuning.