Showing papers in "Sensors and Actuators A-physical in 2014"
TL;DR: In this paper, a review of the pull-in phenomenon in electrostatically actuated MEMS and NEMS devices is presented, along with physical principles that have enabled fundamental insights into the pullin instability as well as pullin induced failures.
Abstract: Pull-in instability as an inherently nonlinear and crucial effect continues to become increasingly important for the design of electrostatic MEMS and NEMS devices and ever more interesting scientifically. This review reports not only the overview of the pull-in phenomenon in electrostatically actuated MEMS and NEMS devices, but also the physical principles that have enabled fundamental insights into the pull-in instability as well as pull-in induced failures. Pull-in governing equations and conditions to characterize and predict the static, dynamic and resonant pull-in behaviors are summarized. Specifically, we have described and discussed on various state-of-the-art approaches for extending the travel range, controlling the pull-in instability and further enhancing the performance of MEMS and NEMS devices with electrostatic actuation and sensing. A number of recent activities and achievements methods for control of torsional electrostatic micromirrors are introduced. The on-going development in pull-in applications that are being used to develop a fundamental understanding of pull-in instability from negative to positive influences is included and highlighted. Future research trends and challenges are further outlined.
442 citations
TL;DR: In this article, an inertial device that combines the frequency up-conversion principle with a rotating proof mass was presented for energy harvesting from human motion, in the form of piezoelectric beam plucking through magnetic coupling.
Abstract: Energy harvesting from human motion faces the challenges of low frequency and random excitation. One strategy that has been successful in the past is frequency up-conversion. This paper introduces an inertial device that combines this principle, in the form of piezoelectric beam plucking through magnetic coupling with a rotating proof mass. The advantages rotational systems can have for body movements are discussed. The prototype is described and tested in a real world environment during a running race and later on in a laboratory environment on a custom built linear excitation table. Throughout these tests it is confirmed that such a device can operate over a broad range of frequencies and under varying orientations, making it suitable for this intended application. Across frequencies between 0.5 and 4 Hz and accelerations between 1 and 20 m/s2 power outputs in the range of tens of microwatts were achieved, with a peak value of 43 μW at 2 Hz and 20 m/s2 when the rotor went into a continuous rotation.
276 citations
TL;DR: In this article, the authors proposed a two-dimensional alignment and displacement sensor based on movable broadside- coupled split ring resonators (BC-SRRs), which can be modified and extended by adding a second element to create a high-dynamic range 2D sensor.
Abstract: a b s t r a c t This paper proposes a two-dimensional alignment and displacement sensor based on movable broadside- coupled split ring resonators (BC-SRRs). As a basis for this sensor, a one-dimensional displacement sensor based on a microstrip line loaded with BC-SRRs is presented firstly. It is shown that compared to previously published displacement sensors, based on SRR-loaded coplanar waveguides, the proposed one-dimensional sensor benefits from a much wider dynamic range. Secondly, it is shown that with modifications in the geometry of the BC-SRRs, the proposed one-dimensional sensor can be modified and extended by adding a second element to create a high-dynamic range two-dimensional displace- ment sensor. Since the proposed sensors operate based on a split in the resonance frequency, rather than the resonance depth, they benefit from a high immunity to environmental noise. Furthermore, since the sensors' principle of operation is based on the deviation from symmetry, they are more robust to ambient conditions such as changes in the temperature, and thus they can be used as alignment sensors as well. A prototype of the proposed two-dimensional sensor is fabricated and the concept and simulation results are validated through experiment.
137 citations
TL;DR: In this article, an all-fiber sensor for simultaneous measurement of refractive index and temperature in solutions is proposed and demonstrated, which contains a core-offered Mach-Zehnder interferometer and a fiber Bragg grating (FBG).
Abstract: An all-fiber sensor for simultaneous measurement of refractive index and temperature in solutions is proposed and demonstrated. The sensing head contains a core-offset Mach–Zehnder interferometer (MZI) and a fiber Bragg grating (FBG). The interference fringe of the MZI and the Bragg wavelength of the FBG would shift with the variation of the ambient refractive index (RI) and/or temperature. The experimental results show that the RI sensitivity and the temperature sensitivity for the sensor are 13.7592 nm/RI and 0.0462 nm/°C, respectively. Its low fabrication cost, simple configuration and high sensitivity will have attractive potential applications in chemical and biological sensing.
136 citations
TL;DR: In this paper, the authors present a high coupling coefficient, k eff 2, for micromechanical resonators based on the propagation of SH0 Lamb waves in thin, suspended plates of single crystal X-cut lithium niobate (LiNbO 3 ).
Abstract: We present a high coupling coefficient, k eff 2 , micromechanical resonator based on the propagation of SH0 Lamb waves in thin, suspended plates of single crystal X-cut lithium niobate (LiNbO 3 ). The thin plates are fabricated using ion implantation of He to create a damaged layer of LiNbO 3 below the wafer surface. This damaged layer is selectively wet etched in a hydrofluoric (HF) acid based chemistry to form thin, suspended plates of LiNbO 3 without the wafer bonding, layer fracturing and chemical mechanical polishing in previously reported LiNbO 3 microfabrication approaches. The highest coupling coefficient is found for resonators with acoustic propagation rotated 170° from the y -axis, where a fundamental mode SH0 Lamb wave resonator with a plate width of 20 μm and a corresponding resonant frequency of 101 MHz achieves a k eff 2 of 12.4%, a quality factor of 1300 and a resonator figure of merit ( M ) of 185. The k eff 2 and M are among the highest reported for micromechanical resonators.
128 citations
TL;DR: A water level measurement using an interdigital capacitive sensor with low-cost, low-energy, good repeatability, high linearity, and ease of installation is proposed with a support of experimental results.
Abstract: A water level measurement using an interdigital capacitive sensor with low-cost, low-energy, good repeatability, high linearity, and ease of installation is proposed with a support of experimental results. This sensor comprises a printed circuit board (PCB) with configuration of two interpenetrating comb electrodes. The comb electrode is 70–80 mm width, 300 mm height with 1–2 mm spacing between each comb. This configuration of electrode causes the capacitance between comb electrodes to vary by the water level. Microcontroller is used to calculate the capacitance between comb electrodes in terms of a discharge time correlated to the water level. A practical water level measurement technique using two comb electrodes designated as level and reference sensors is presented. This technique can directly be applied to water with different conditions without recalibration. This sensor is able to measure absolute levels of water with 0.2 cm resolution over 30 cm range. In addition, it is also sensitive enough to trace the variability of water level. A flood monitoring simulation is carried out in wave flume where this sensor is used to detect the rising wave.
128 citations
TL;DR: In this paper, an electrostatic energy harvester with an out-of-the-plane gap closing scheme is presented. But the performance of the device is limited by the external load resistance of 13.4 MΩ and the external acceleration amplitude of 1 g (∼9.8 m/s2).
Abstract: In this paper, we report on an electrostatic energy harvester with an out-of-the-plane gap closing scheme. Using advanced MEMS technology, energy harvesting devices formed by a four wafer stack are batch fabricated and fully packaged at wafer scale. A spin coated CYTOP polymer is used both as an electret material and an adhesive layer for low temperature wafer bonding. The overall size of the device is about 1.1 cm × 1.3 cm. At an external load resistance of 13.4 MΩ, a power output of 0.15 μW is achieved when vibration at an acceleration amplitude of 1 g (∼9.8 m/s2) is applied at a low frequency of 96 Hz. The frequency response of the device is also measured and a broader bandwidth is observed at higher acceleration amplitude.
122 citations
TL;DR: In this article, a flight controller with disturbance observer (DOB) is proposed for high-performance trajectory tracking of a quadrotor, considering the external disturbances, model mismatches and input delays.
Abstract: In this paper, a flight controller with disturbance observer (DOB) is proposed for high-performance trajectory tracking of a quadrotor. The dynamic model of the quadrotor, considering the external disturbances, model mismatches and input delays, is firstly developed. Subsequently, a DOB-based control strategy is designed with the backstepping (BS) technique. In this control scheme, the DOB serves as a compensator, which can effectively reject model mismatches and external disturbances. In this case, the trajectory tracking controller is designed according to the nominal model. Then, the input-to-state stability (ISS) analyses of the developed controllers are presented, which theoretically guarantees the robustness of the developed controller. Finally, comparative studies are carried out. Three types of disturbances including payloads, rotor failures and wind are chosen to verify the effectiveness of the development. The results from simulations and experiments show that the proposed controller provides better performances than the traditional nonlinear controllers.
117 citations
TL;DR: In this article, the fabrication of zinc oxide (ZnO) nanorods on p-type silicon (p-Si) photodiodes was reported, which exhibited an excellent rectifying ratio of 370 at 10-V and 0.29-A/W up to 300-nm.
Abstract: We report on the fabrication of zinc oxide (ZnO) nanorods on p-type silicon (p-Si) photodiodes. The nanorods are prepared by low-temperature hydrothermal processing. The fabricated photodiodes exhibit an excellent rectifying ratio of 370 at 10 V. The responsivity to ultraviolet (UV) photons is stable at 0.29 A/W up to 300 nm, with a peak value of 0.38 A/W at 360 nm. Furthermore, the prepared photodiodes demonstrate visible blind behavior, indicating that ZnO nanorods grown on p-Si substrates can be used as UV photodiodes with visible blind responses.
113 citations
TL;DR: In this article, a mechanical impact driven and frequency up-converted wide-bandwidth piezoelectric vibration energy harvester has been proposed and demonstrated theoretically and experimentally.
Abstract: Vibration energy harvesters are capable of generating significant amount of power at higher frequencies rather than generating at low frequencies. Moreover, as low frequency vibrations (1–30 Hz) around the ambient environment are discursive in nature, resonance based power generators are limited to use within this low frequency range. In this paper, a mechanical impact driven and frequency up-converted wide-bandwidth piezoelectric vibration energy harvester has been proposed and demonstrated theoretically and experimentally. It converts low frequency environmental vibrations into high frequency vibration by mechanical impact. A low frequency flexible driving beam with horizontally extended tip mass, upon excitation, hits two high frequency rigid piezoelectric generating beams at the same time causing a change in the driving beam's effective stiffness that allows the device to offer approximately 180% increased −3 dB bandwidth and more than 62% of the maximum power generation within the remaining operating frequency range as well. The overall bandwidth is 7.5 Hz within 7–14.5 Hz frequency range generating a minimum peak power of 233 μW. A maximum of 378 μW peak power from one generating beam is achieved under 6 ms −2 acceleration at the resonant frequency of 14.5 Hz. Output of both generating beams connected in series produces 734 μW peak power under the same operating condition with the corresponding power density 38.8 μW cm −3 . The experimental results show some discrepancy with the theoretical results due to mechanical loss during impact and the process variations in the beam formation and assembling. The theoretical and experimental results reveal that the proposed configuration has the potential of powering small portable, handheld wireless smart devices from low frequency, specially human motion related vibrations.
112 citations
TL;DR: In this paper, the design optimization of a mechanically decoupled six-axis force/torque (F/T) sensor by minimization of cross coupling error is presented.
Abstract: This paper presents the design optimization of a mechanically decoupled six-axis force/torque (F/T) sensor by minimization of cross coupling error. The new term ‘principal coupling’ is proposed to define the largest cross coupling error. In the first design step of the F/T sensor, the locations of twenty-four strain gages in a sensor structure are predetermined, and four structural design variables are selected to be optimized. In the second step, an optimization framework that reduces principal coupling is developed. Multiple constraints on good isotropic measurement and safety are considered and formulated using the output strain of each strain gauge circuit. The optimal design utilizes FEM software and MATLAB interactively to perform effective shape optimization. As a result of shape optimization, principal coupling of a six-axis F/T sensor was reduced from 35% to 2.5% with good isotropy. The final design of the F/T sensor was fabricated for experimental verification and there was only 0.7% difference in principal coupling and 5.2% difference in the overall strain output between the numerical and experimental results. The optimal design results in this paper are expected to provide a design guideline for multi-axis F/T sensors with significantly reduced cross coupling error, one of the biggest technical obstacles in developing F/T sensors.
TL;DR: The analysis shows that the combination of NN based ν-SVM with LPP can realize faster training of classifier without sacrificing the classification accuracy.
Abstract: Reliable online monitoring of the tool condition is paramount for automatic machining process. C-support vector machine (C-SVM) has got many successful applications in the field of tool wear monitoring. However, the selection of penalty parameter C is usually realized based on optimization process, which increases the training time of the classifier greatly. In this paper, ν support vector machine (ν-SVM) is presented to realize multi categories tool wear classification. In this model, C is replaced by a new parameter ν which represents an upper bound on the fraction of training errors and a lower bound of the fraction of support vectors. At the same time, the nearest neighbor (NN) based rule is proposed to realize the fast selection of ν based on training samples. In addition, to further improve training speed and classification accuracy, locality preserving projection (LPP) method is utilized to reduce the dimension of feature vectors by extracting the lower dimensional manifold characteristics. To testify the effectiveness of the proposed method, milling experiment of Ti6Al4V alloy was carried out and vibration signals corresponding to four kinds of tool wear status were collected. Time domain and frequency domain features are extracted based on wavelet packet decomposition and dimension reduction is realized by using LPP algorithm. Based on the selected features, both C-SVM and ν-SVM are utilized to realize the classification of multi categories tool wear status. The analysis shows that the combination of NN based ν-SVM with LPP can realize faster training of classifier without sacrificing the classification accuracy.
TL;DR: In this paper, a low cost solution for vibrational energy harvesting based on a bistable clamped-clamped polyethylene terephthalate (PET) beam and two piezoelectric transducers is presented.
Abstract: This paper presents a low cost solution for vibrational energy harvesting based on a bistable clamped-clamped polyethylene terephthalate (PET) beam and two piezoelectric transducers. Beam switching (between two stable steady states) is activated by environmental vibrations. The mechanical-to-electrical energy conversion is performed by two piezoelectric transducers laterally installed to experience beam impacts each time the device switches from one stable state to the other one. The main advantage of our approach lies in the wide frequency bandwidth of the device; in turn, this leads to improved efficiency at very low cost.
TL;DR: In this article, a strain sensor with vertically aligned zinc oxide (ZnO) nanowire arrays on polyethylene terephthalate (PET) film was reported, and the conductivity of the device is significantly tuned by the change of ZnO/Au Schottky barrier that reflects the strain-induced piezoelectric potential.
Abstract: In this paper, a highly sensitive strain sensor with vertically aligned zinc oxide (ZnO) nanowire arrays on polyethylene terephthalate (PET) film was reported. The device fabrication includes conventional photolithography, metallization, and ZnO nanowire growth through a hydrothermal method. I–V characteristics of the device were highly nonlinear due to the Schottky contact between the nanowire and the gold (Au) electrode. The conductivity of the device is significantly tuned by the change of ZnO/Au Schottky barrier that reflects the strain-induced piezoelectric potential. A gauge factor up to 1813 was obtained from this strain senor, which is higher than the previously reported device based on a lateral ZnO microwire. Theoretical analysis of the piezotronic effect shows that the working nanowire with the largest conductivity change dominates the performance of the device. The non-working nanowire has limited adverse effect on the performance, which explains the robust performance of this novel strain sensor. The stability and fast response of the sensor were also investigated. The sensitive and robust strain sensor is expected to find applications in civil, medical, and other fields.
TL;DR: In this article, a tactile sensor based on piezoresistive sensing material, constituted by a polymeric composite with nanostructured spiky particles as filler, is presented.
Abstract: We present a robust and flexible tactile sensor based on piezoresistive sensing material, constituted by a polymeric composite with nanostructured spiky particles as filler. The composite is able to exploit tunneling conduction mechanism when subjected to a compressive load. We have here integrated this quantum tunneling composite (QTC) with an ad-hoc electronic read-out circuit. In addition a software interface can monitor and visualize the applied mechanical pressure, thus leading to a complete tactile sensor device. Concerning the sensing material, the piezoresistive composite shows an enhanced tunneling conduction due to the presence of nickel particles with nanostructured sharp tips embedded in a silicone matrix. We registered an increase up to nine orders of magnitude of the composite electrical conduction in response to a mechanical strain. The sensor consisted in a continuous layer of functional composite sandwiched between a matrix of patterned top and bottom electrodes. The planar sensor can thus be modeled as a two-dimensional array of resistors whose value decreases by increasing the applied pressure. We also designed an ad-hoc electronic read-out circuit, able to read and process the resistance variations of the sensor upon a compressive load, thus providing not only the pressure intensity but also the pressure distribution data. A software interface was able to achieve the real-time tridimensional response and lead to the visualization of the compressed regions on the sensor. The present device is an efficient and low-cost prototype of tactile sensing skin, thus readily enabling its use for human robotic applications.
TL;DR: In this article, the development of screen printed networks of electrodes and associated conductive tracks on textiles for medical applications is described, where a polyurethane paste is screen printed on a woven textile to create a smooth, high surface energy interface layer.
Abstract: This paper details the development of screen printed networks of electrodes and associated conductive tracks on textiles for medical applications A polyurethane paste is screen printed on to a woven textile to create a smooth, high surface energy interface layer A silver paste is subsequently printed on top of this interface layer to provide a conductive track The silver track is then encapsulated with another layer of polyurethane paste so that the silver track is protected from abrasion and creasing The resulting screen printed structure has a width of 1 mm per conductive track and a total printed height of 200 μm above the surface of the textile Conductive rubber, with a thickness of 3 mm, is stencil printed on to the terminations of these conductive tracks to form electrodes The electrodes, used in contact with the skin, are demonstrated and evaluated for the biopotential monitoring applications of ambulatory electrocardiography, electrooculography and electromyography It is shown that these textile electrodes are suitable for electromyographic monitoring but the baseline drift must be improved for use in electrocardiographic diagnosis
TL;DR: In this paper, the accelerometer structure consists of inertial mass supported by an L-shaped modified cantilever beam having non-uniform cross section area connected to base by a thin neck element which acts as strain concentrated center.
Abstract: This paper focuses on Fiber Bragg Grating (FBG) based accelerometer design. The accelerometer structure consists of inertial mass supported by an L-shaped modified cantilever beam having non-uniform cross section area connected to base by a thin neck element which acts as strain concentrated centre hence an optimum zone for FBG sensors placement. It has a working bandwidth below the structure's natural frequency and responds linearly to vibrations. The parameters for the structure design have been optimised on SolidWorks 2012 platform. Experimental trials yield sensitivity of 46 pm/g for frequency below 50 Hz and 306 pm/g for frequency above 150 Hz. A mathematical model for the accelerometer structure's natural frequency modes is also presented with detailed analysis for different combinations of inertial mass-frame assembly.
TL;DR: In this paper, a magnetic hydrogel-based microgripper that can be wirelessly manipulated using magnetic fields is presented, which can move freely in liquids when driven by direct current (dc) magnetic fields, and perform a gripping motion by using alternating current magnetic fields.
Abstract: This study presents a magnetic hydrogel-based microgripper that can be wirelessly manipulated using magnetic fields. The proposed device can move freely in liquids when driven by direct current (dc) magnetic fields, and perform a gripping motion by using alternating current (ac) magnetic fields. The device is fabricated from a biocompatible hydrogel material that can be employed for intravascular applications. The actuation mechanism for gripping motions is realized by controlling the exposure dose on the hydrogel composite during the lithography process. The preliminary characterization of the device is also presented. The measurement results show that the gripping motion reached a full stroke at approximately 38 °C. By dispersing multiwall carbon nanotubes (MWCNT) into the material, the overall response time of the gripping motion decreases by approximately 2-fold. Device manipulations such as the gripping motion, translational motion, and rotational motion are also successfully demonstrated on a polyvinyl chloride (PVC) tube and in a polydimethylsiloxane (PDMS) microfluidic channel.
TL;DR: In this paper, the authors demonstrate the fabrication and characterization of printed strain gauges with a gauge factor as high as 19.3 ± 1.4, fast signal response and high reproducibility.
Abstract: A growing area for the electronics industry is the development of flexible components for novel devices. Controlling the flexibility of such devices requires the precise and reliable measurement of strains in a manner compatible with the form and function of the device. In this article, we demonstrate the fabrication and characterization of printed strain gauges with a gauge factor as high as 19.3 ± 1.4, fast signal response and high reproducibility. The device is made of graphite ink deposited by screen printing on a plastic substrate. The flexible printed sensor is capable of precisely measuring repetitive tensile and compressive bending strain changes. An approach for eliminating the temperature-induced errors of strain gauges based on neutral axis engineering is also described.
TL;DR: In this article, a fabrication process is developed that uses accessible PDMS soft lithography techniques to produce compliant pneumatic actuators with a width of 7mm and a thickness of 0.65mm.
Abstract: Compliant pneumatic actuators have recently attracted the interests of the robotics community, especially for soft robotic applications where large strokes are needed in delicate environments. To date, these actuators have demonstrated the ability to generate contracting, expanding and bending strokes. This paper introduces a new actuator design that complements the existing actuators by generating twisting deformations upon pressurization. A fabrication process is developed that uses accessible PDMS soft lithography techniques. With this process, prototype actuators with a width of 7 mm and a thickness of 0.65 mm have been made that achieved a twisting rotation of 6.5°/mm actuator length at a pressure of 178 kPa. This paper also presents the integration of four twisting actuators into a 2 DOF tilting mirror platform which is capable of deflecting a mirror over 25° at a pressure of 231 kPa.
TL;DR: In this paper, a novel peninsula-structured diaphragm with specially designed piezoresistors was proposed to resolve the trade-off between sensitivity and linearity, which could achieve a sensitivity increase by 11.4, nonlinearity reduction of 60% and resonance frequency increase of 41.8%.
Abstract: The trade-off between sensitivity and linearity has been the major problem in designing the piezoresistive pressure sensors for low pressure ranges. To resolve the problem, a novel peninsula-structured diaphragm with specially designed piezoresistors was proposed. Finite element method (FEM) was adopted for analyzing the sensor performance as well as comparisons with other sensor structures. In comparison to flat diaphragm, the proposed sensor design could achieve a sensitivity increase by 11.4%, nonlinearity reduction of 60% and resonance frequency increase of 41.8%. In addition, the modified peninsula-structured diaphragms featuring a center boss have been optimized to achieve ultra-low nonlinearities of 0.018%FFS and 0.07%FFS for the 5 kPa and 3 kPa pressure ranges respectively with higher sensitivities as compared to the CBM (cross beam membrane) and hollow stiffening structures. In accordance with the FEM results, the fabricated pressure sensor with the peninsula-structured diaphragm showed a sensitivity of 18.4 mV/V full-scale output and a nonlinearity error of 0.36%FSS in the pressure range 0–5 kPa. The proposed sensor structure is potentially a better choice for designing low pressure sensors.
TL;DR: A new array of flex sensors was developed for integration into a sensory glove to perform goniometric semi-automated measurements, performing with the lowest Range and Standard Deviation ever obtained.
Abstract: A new array of flex sensors was developed for integration into a sensory glove to perform goniometric semi-automated measurements. With this array, the sensory glove gained in repeatability of the measures, with respect to other gloves previously reported, performing with the lowest Range and Standard Deviation ever obtained. The reliability was notable, insofar the ICC averaged the “state of the art” sensory gloves. Performances and cheapness (tens of dollars) make this array particularly suitable for rehabilitation, when objective measures of the functional capabilities of subject's hand can be mandatory.
TL;DR: In this paper, an oscillator featuring an in-liquid piezoelectric microplate resonator as the frequency-selective element was used for density and viscosity sensing.
Abstract: The resonant characteristics of a mechanical resonator immersed in liquid provide valuable parameters for density and viscosity sensing. In particular, the combination of microresonators with electronic circuits, for tracking their natural frequency and quality factor, has great interest as low cost and size solution. In this work, we focus on an oscillator featuring an in-liquid piezoelectric microplate resonator as the frequency-selective element. Specifically, by selecting the second-order bending mode in the length-direction, a reliable oscillator operation, for a range of liquid properties, was achieved at moderate frequency. Besides, the out-of-plane vibration allowed for both density and viscosity to be deduced separately. The influence of parasitic capacitances in the device response has been identified as the major difficulty for the realization of the oscillator circuit. To minimize this effect, a compensation method based on a non-released reference device and an instrumentation amplifier was implemented, which resulted in a clear resonance with low baseline and high phase step. In a first test with the resonator immersed in isopropanol, the circuit generated a stable wave with an Allan deviation of 2.32·10 −7 , improving by one order of magnitude the only published value, to the authors knowledge, for a comparable device in liquid. An alternative tracking system, based on digital phase-locking benchtop instrumentation, was tested with the same resonator, showing a comparable stability (2.35·10 −7 ) and supporting our approach. Finally, the operation of the system as a sensor was demonstrated. After a calibration process, the density and viscosity of eight test liquids could be compared to measurements with a commercial instrument, showing differences lower than 0.4% in density and 8% in viscosity. The minimum detectable changes were also evaluated, being 4.09·10 −6 g/ml for the density and 2.07·10 −3 mPa s for the viscosity, both for a viscosity of 7.36 mPa s at 10 samples per second.
TL;DR: In this article, a surface control technique for preparing mesoporous polyvinylidene fluoride (PVDF) thin films toward high piezoelectric output was introduced. But the morphology of the film could be controlled by varying the solvent evaporation rate.
Abstract: We demonstrate that nanostructured thin films play a significant role in compact energy harvesting polyvinylidene fluoride (PVDF) nanogenerators. In this work, we introduced a surface control technique for preparing mesoporous PVDF thin films toward high piezoelectric output. We demonstrated that the morphology of the film could be controlled by varying the solvent evaporation rate. The material crystallinity was experimentally confirmed by X-ray diffraction (XRD) and differential scanning calorimeter (DSC) measurement. The multilayer PVDF structure with porous surface significantly increased the compressibility and charge collecting area which contributes to the significant output enhancement. The piezoelectric output increased 100% with the modified mesoporous layer. The charging capacity increased 107% compared with the same thickness solid PVDF film.
TL;DR: The screen printed flexible and breathable fabric electrode array (FEA) demonstrates the potential for printable polymer materials to realise comfortable, wearable and cost effective functional systems in healthcare applications.
Abstract: Functional electrical stimulation (FES) activates nerves using electrical currents, and is widely used in medical applications to assist movement of patients with central nervous system lesions. The recent emergence of small electrode arrays enables greater muscle selectivity and reduces fatigue compared to the use of traditional large electrodes; however existing fabrication techniques are expensive and have limited flexibility and comfort which limits patient uptake. This work presents a screen printed flexible and breathable fabric electrode array (FEA) which consists of four printed functional layers. Successful operation has been demonstrated by stimulating an optimised selection of electrodes in order to achieve clinically relevant reference postures (‘pointing’, ‘pinch’ and ‘open hand’). The materials with skin contact used in FEA have been cytotoxicity tested to establish that they are biocompatible. The FEA demonstrates the potential for printable polymer materials to realise comfortable, wearable and cost effective functional systems in healthcare applications.
TL;DR: In this paper, a multilayer PZT-5H stack under axial compressive loading in the off-resonant low-frequency range is considered, where the power spectral density of band-limited stochastic excitation is used to predict the expected value of the power output.
Abstract: Deterministic and band-limited stochastic energy harvesting scenarios using a multilayer piezoelectric stack configuration are investigated for uniaxial dynamic pressure loading. The motivation for exploring this off-resonant energy harvesting problem derives from typical civil infrastructure systems subjected to dynamic compressive forces in deterministic or stochastic forms due to vehicular or human loads, among other examples of compressive loading. Modeling of vibrational energy harvesters in the existing literature has been mostly focused on deterministic forms of mechanical vibration as in the typical case of harmonic excitation, while the efforts on stochastic energy harvesting have thus far considered second-order systems such as piezoelectric cantilevers. In this paper, we present electromechanical modeling, analytical and numerical solutions, and experimental validations of piezoelectric energy harvesting from harmonic, periodic, and band-limited stochastic excitation of a multilayer piezoelectric stack under axial compressive loading in the off-resonant low-frequency range. The deterministic problem employs the voltage output-to-pressure input frequency response function of the harvester for a given electrical load, which is also extended to periodic excitation. The analytical stochastic electromechanical solution employs the power spectral density of band-limited stochastic excitation to predict the expected value of the power output. The first one of the two numerical solution methods uses the Fourier series representation of the excitation history to solve the resulting ordinary differential equation, while the second method employs an Euler–Maruyama scheme to directly solve the governing electromechanical stochastic differential equation. The electromechanical models are validated through several experiments for a multilayer PZT-5H stack under harmonic and band-limited stochastic excitations at different pressure levels. The figure of merit is also extracted for this particular energy harvesting problem to choose the optimal material. Soft piezoelectric ceramics (e.g. PZT-5H and PZT-5A) offer larger power output as compared to hard ceramics (e.g. PZT-8), and likewise, soft single crystals (e.g. PMN-PT and PMN-PZT) produce larger power as compared to their hard counterparts (e.g. PMN-PZT-Mn); and furthermore, single crystals (e.g. PMN-PT and PMN-PZT) generate more power than standard ceramics (e.g. PZT-5H and PZT-5A) for low-frequency, off-resonant excitation of piezoelectric stacks.
TL;DR: In this article, an air cavity was created by pressing an elastic cap with microstructures onto the piezoresistive cantilevers of a sensor chip to increase the sensitivity of a triaxial tactile sensor.
Abstract: In this paper, we proposed a design to increase the sensitivity of a piezoresistive-type triaxial tactile sensor. Using conventional piezoresistive tactile sensors, in which the piezoresistive elements were completely embedded inside an elastic block, our proposed tactile sensor design features an air cavity underneath the piezoresistive elements. The cavity was created by pressing an elastic cap with microstructures onto the piezoresistive cantilevers of a sensor chip. We confirmed that the proposed design increased the sensitivity of the tactile sensor by approximately 150 times and 100 times in response to normal and lateral forces, respectively.
TL;DR: A multiply arrayed tactile display device with Dielectric Elastomer Actuator with liquid coupling between the touch spot and the actuator as the transmission of force to ensure the comfort of touch and the safety of operation for the users while contacting with the human skin is presented.
Abstract: The tactile display is an important tool to help the human interact with machines by using feels of touch. In this paper, we present a multiply arrayed tactile display device with Dielectric Elastomer Actuator (DEA). The device employs the liquid coupling between the touch spot and the actuator as the transmission of force. It is designed to ensure the comfort of touch and the safety of operation for the users while contacting with the human skin. The operating principle is explained in details, and a systematic design analysis is given. The displacements of tactile display is about 240–120 μm at 3–10 Hz, which satisfies the frequency requirements for simulating the Merkel cells as well as the Meissner corpuscles and the force is over 40 mN to simulate the finger tip. In addition, a dedicated fabrication method and performance measurements are explained.
TL;DR: In this article, an optical fiber magnetic field sensor was proposed by merging the advantages of magnetic fluid and a core-cladding-mode interferometer which was directly fabricated on a standard single-mode fiber by using an arc fusion splicing machine.
Abstract: We report an optical fiber magnetic field sensor by merging the advantages of magnetic fluid and a core–cladding–mode interferometer which is directly fabricated on a standard single-mode fiber by using an arc fusion splicing machine. The sensing performances of the sensors are controllable by designing the parameters of the asymmetric-tapered structure. Experimental results show that the sensor with axial offset of 168 μm and taper waist diameter of 45 μm not only has good optical properties but also a relatively high magnetic-field sensitivity of ∼162.06 pm/mT ranging from 0 to 21.4 mT. The proposed sensors would find potential applications in weak magnetic sensing fields.
TL;DR: The interconnect, a flexible polymer gasket co-printed with, rigid clamps, eliminates adhesives and additional assembly by direct multi-material 3D, printing from a computer-aided design model, and has demonstrated the ability to withstand, pressures exceeding 400 kPa.
Abstract: Lab-on-a-chip (LOC) devices have enabled significant advancements in medical, biological, and chemical analysis. However, widespread adoption of these devices in, clinical settings and academic environments has been impeded by a lack of a reliable, adaptable, and easy-to-use packaging technology. In this work, we introduce a rapid, prototyped modular microfluidic interconnect that addresses these challenges of the, world-to-chip interface. The interconnect, a flexible polymer gasket co-printed with, rigid clamps, eliminates adhesives and additional assembly by direct multi-material 3D, printing from a computer-aided design model. The device represents the first, application of multi-material 3D printing to microfluidic interconnects, and it can be, rapidly re-designed and printed, and has demonstrated the ability to withstand, pressures exceeding 400 kPa.