We present a highly sensitive Hall device fabricated in a standard CMOS technology and combined with integrated flux concentrators acting as magnetic amplifiers. The active area of the Hall plate is in a buried n-well with a shape optimized by removing the parts less sensitive to the magnetic field. The effect of the shape of the concentrators is studied. This results in the design of elliptical shape integrated concentrators for the optimization of the sensitivity, and of the measurement range, as well as for the decrease of the overall chip size. The CMOS sensor combined with the optimized concentrators has a sensitivity of 2.1 V/T with a 4 V bias, the lowest detectable field is 0.2 μT in a frequency range of 10−3–10 Hz and the linearity is better than 1% in a ±16 mT measurement range.
DOI : 10.1016/s0924-4247(99)00329-5 Anahtar Kelimeler :
Hall sensor, CMOS compatible, Ferromagnetic flux concentrators, High sensitivity, Low noise
ISSN: 0924-4247 Sayı: 1-3 Cilt: 82 Sayfa: 144-148
Layer manufacturing is generally utilized for the development of micro electromechanical systems (MEMS) and micro total analysis systems (μTAS). However, the preparation of multiple masks and repetitive exposure procedure prevents the rapid fabrication of 3D microstructures. An active mask fabrication by using a liquid crystal display (LCD) as an electrically controllable photomask can simplify the layer manufacturing process. In addition, the gray-tone photolithography is available by using LCD lithography system, since the exposure distribution is easily controlled by an LCD. We have developed the LCD mask exposure system by using UV light source. Firstly, the patterning characteristics of the UV photoresist by exposing line and space patterns are evaluated, and then, a fundamental step shape is produced in order to verify the feasibility of gray-tone UV photolithography by using LCD. A shape with a different height can be fabricated without any repetitive exposure and development procedures. Finally, we confirmed the high patterning resolution such as 11 μm using check patterns and fabricated 3D step shapes by using the LCD as a gray-scale photomask.
This paper discusses the relationships between the deposition parameters and properties of thick (e.g., 5 μm) tetraethylorthosilicate (TEOS) silicon dioxide films deposited on silicon wafers using a dual-frequency plasma-enhanced chemical vapor deposition (PECVD) system. The deposition parameters, including the ratio of low frequency (LF) power to high frequency (HF) power and the TEOS flow rate, were varied to investigate their effect on the residual stress, the deposition rate, and the etch rate of TEOS silicon dioxide film. Analysis of variance (ANOVA) statistical technique was used to verify that the experimental data are valid rather than coincidences of random sampling. The calculated P-values of the deposition parameters verify that the ratio of LF/HF power and the TEOS flow rate significantly affect the residual stress and the etch rate of the films. For the deposition rate, only the TEOS flow rate has a significant effect. The difference in the intrinsic and thermal stresses of TEOS silicon dioxide films co-deposited on the silicon and stainless steel wafers are presented and discussed. TEOS silicon dioxide films are electrically characterized at elevated temperatures (up to 300 °C) using metal-insulator-metal (MIM) capacitors. The characterizations show that capacitance decreases with increasing temperature, as well as with the process thermal budget (temperature × time).
The electrochemical properties of microporous poly(3,4-ethylenedioxythiophene) (PEDOT) and polypyrrole (PPy) films deposited on microfabricated neural electrodes were investigated by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Microporous conducting polymer films were electrochemically deposited on neural microelectrodes in galvanostatic mode from aqueous solutions containing 3,4-ethylenedioxythiophene (EDOT) and pyrrole (Py) monomer with lithium perchlorate (LiClO4) as the counter ion. Impedance spectroscopy was obtained for microporous conducting polymer coated microelectrodes over a frequency range from 1 Hz to 100 kHz. Impedance spectroscopy of neural microelectrodes with microporous films of different thickness and different pore sizes was investigated in buffer solution (pH 7.0). The EIS results show that the microporous coatings decrease the impedance modulus by almost two-orders of magnitude at a frequency of 1 kHz. The EIS data were fitted to an equivalent electric circuit model. The results show that the diffusion capacitance and resistance of the films both increase with deposition charge. The significant drop in impedance magnitude and phase angle is consistent with an increase of the surface area due to the open, roughened morphology. In comparison with microporous PPy/LiClO4, microporous PEDOT/LiClO4 demonstrated much better electrochemical stability, losing only 5% of its original charge capacity after 120 cycles of CV measurement, while microporous PPy/PSS lost 30% under the same conditions.
In this paper we describe two versions of a compact broadband ferrite based induction magnetometer system which span an operating bandwidth from 1 mHz to 1 MHz. In order to produce this compact system it was necessary to consider both the design of the pick up coils and the signal processing electronics. Here, we present an alternative to the traditional analogue integrator technique and conclude that this leads to significant advantages in bandwidth, long term stability and weight of the coils.
This work reports the electrical and piezoresistive responses of thin polymer films made of polysulfone (PSF) modified with 0.05–1% w/w multi-wall carbon nanotubes (MWCNTs). MWCNT/PSF films are fabricated by solution casting and their electric and piezoresistive responses are evaluated. Gage factors are measured for films with 0.2–1% carbon nanotube weight loadings. The films are then bonded to macroscopic aluminum specimens and evaluated as strain sensing elements during quasi-static and cycling tensile loading. Excellent piezoresistive capabilities are found for films with MWCNT loadings as low as 0.5% w/w, which renders them functionality as strain gages.
This paper describes the effects of a process of double step deep reactive ion etch (DRIE) using an inductively coupled plasma (ICP) etch system and nickel–cobalt electroplating for a trench-type cantilever probe for a fine-pitched micro-electro mechanical systems (MEMS) probe card. The cantilever probe tip was formed inside silicon after double step DRIE to make a cantilever beam and pyramid type cantilever probe tip and electroplated in a nickel–cobalt solution to produce compliant and wear resistance structures. The advantage of a trench-type cantilever probe tip is that it can be used for a fine-pitch MEMS probe card. For forming the cantilever beam and pyramid probe tip in a trench, DRIE conditions were developed by varying the flow rate of SF6 and C4F8. For electroplating the tip in a deep trench, use of a seed layer was investigated on the bottom of the tip using electron probe microanalyzers (EPMA) and scanning electron microscopy (SEM) for analysis. To reduce tensile stress and to electroplate uniformly over a 6 in. wafer, a cathode mask was employed. Contact force was measured with varying composition of nickel–cobalt. As the percentage of cobalt increased, contact force was improved without depressions. The wafer was exposed to X-rays to investigate the quality of nickel–cobalt electroplating, such as the presence of seams or voids. There were no broken cantilevers or significant degradation after 1,000,000 touchdowns.
This paper proposes a multi-fingered palpation method which employs pneumatic haptic feedback actuators allowing users to experience haptic sensations at multiple fingers while carrying out remote soft tissue palpation. Pneumatic actuators are used to vary the stress on the user's fingertips in accordance with the tissue stiffness, experienced during manual palpation. The proposed method reduces actuator elements compared to tactile actuators and provides more information than single-point force feedback. The results of our finite element analysis have proven that our pneumatic haptic feedback device can recreate the contact stress between fingertip and soft tissue during palpation. The accuracy (96.8% vs. 93.3%) and time-efficiency (4.6 s vs. 8.3 s) advantages of using three-fingered over single-fingered palpation have been confirmed in our user study results of stiffness levels discrimination. Relatively good tumor detection sensitivities have been demonstrated by the palpation user study which has showed a direct correlation between tumor size and detection sensitivity and has further proven the efficiency of the proposed actuator and multi-fingered palpation method for tumor detection in palpation simulation.
The potential for large deformation of the ionic polymer–metal composite (IPMC) is useful in the developments of biomedical device and miniature robot. The goal of this study is to investigate the feasibility of developing a sensing/actuating IPMC transducer as the head of an active guide-wire for cardiac catheterization. The approach employs an amplitude modulation–demodulation technique to obtain a deformation-sensing signal converted from the variation of electrical resistances in the IPMC electrodes. According to solvents and uptake conditions, three types of IPMC were produced and tested for the sensing and the actuating functions. Besides, a simulation of catheterization procedure was demonstrated with an IPMC guide-wire. From the estimated and the experimental results, the relationship between the sensing signal and the tip-displacement representing the deformation of the IPMC was verified. The sensing signal was proportional to the tip-displacement in the small deformation. The tests of the three types of IPMC showed that the sensitivity of deformation depended on the condition of material processing and solvent in IPMC. In addition, there was a trade-off between the sensing and the actuating functions of the IPMC. In the design of sensing/actuating IPMC, the electric power applied on the IPMC for actuation may interrupt the sensing signal with the migration of solvent in the IPMC. Differentiating the deformation-sensing signals between the deformed IPMC and an undeformed IPMC may alleviate the interference. The demonstration of a simulated catheterization exhibited the potential for sensing/actuating IPMC in checking the bifurcation of blood vessels without integrating a bulky sensor or adjusting the curvature of an IPMC-based active guide wire.
Agro-based inexpensive ionic polymer sensors are demanded in wearable sensors, humidity sensors, human-machine interface, actuators, fuel cell, battery, water purifier, and supercapacitor applications. Ionic polymer sensors using polyelectrolytes and ionic liquid have been widely used for sensing skin, strain, and pressure sensor applications. These ionic polymer sensors were fabricated using expensive and toxic materials. Here we develop an inexpensive new agro-based micropore-structured ionic polymer sensor using sugarcane extract (SCN) attached poly (vinyl alcohol) (PVA) membrane. The cost of the PVA/SCN based ionic polymer sensor is around 0.023$ per 78 cm2. The sensing performance of PVA/SCN ionic polymer sensor increased with increasing SCN content, and PVA/SCN (1/2.72 gm) ionic sensor showed 1100 and 1.65 times higher sensing current compared to those of the commercial Nafion ionic polymer and PVDF/PVP/ionic liquid-based ionic sensors. The new agro-based ionic polymer using sugarcane extract showed enhanced ionic conductivity, high dielectric constant, and mechanical properties compared to those of the pure PVA due to the sulphur (S), iron (Fe), and bagasse content. The ionic conductivity and tensile strain of PVA/SCN (1/2.72 gm) increased 43 and 13 times that of the PVA pure polymer, and these mentioned properties enhanced the sensing performance of PVA/SCN strain sensors.
Spectroscopic measurements at infrared and visible wavelengths are widely used as a tool for laboratory analysis. Due to technological improvements, more and more possibilities are opened for making similar methodology feasible for direct on-line process measurements in harsh industrial conditions or small portable equipment. New optoelectronic components together with compact design can even be used to realize integrated sensor-like analyser devices. Array and multiple-wavelength detectors reduce the need for mechanisms for wavelength multiplexing and offer the possibility of simultaneous measurement of several wavelength channels. The use of narrow-band semiconductor sources gives advantages for modulation arrangements. Using array sources, electronic wavelength scanning becomes possible in some applications. The increased real-time signal-processing capability can be used to implement more complex measuring principles and efficiently compensate for disturbing effects. Instead of using only a few wavelengths, a whole spectral band analysis can be employed. As an example, real-time multielement analysis, with complex calibration functions, becomes a feasible industrial methodology. The fields of application for infrared analysers can be found in chemical process industries, food industries, energy production, and environmental protection. Portable and integrated sensor-like analyser components substantially increase application markets.
DOI : 10.1016/0924-4247(93)80030-k
ISSN: 0924-4247 Cilt: 37-38 Sayfa: 173-179
A multi-degree of freedom micro-energy harvester has been designed, fabricated, and tested and sub 100 Hz natural frequencies have been achieved. This design's resonant frequencies at its first three mode shapes are within the low ambient vibration frequency range. The structure is fabricated from a silicon substrate with Aluminum Nitride (AlN) energy harvesting elements on thin silicon beams and uses a chip as a proof mass. The nonlinear stiffness due to stretching strain in the structure provides a wider harvestable frequency bandwidth in each mode. The nonlinear load-deflection equation for the second mode shape of the device, which corresponds to vertical oscillation and maximum harvester deflection, has been modeled using finite element simulation. The first three natural frequencies of 71.8, 84.5, and 188.4 Hz were measured experimentally for the presented harvester. A frequency bandwidth of 10 Hz has been obtained for the second mode shape under a base excitation of 0.2 g. A maximum open circuit voltage of 1 V and power output of 136 nW with a load resistance of 2 MΩ have been measured using this harvester. Using a synchronized switch harvesting on inductor (SSHI) electrical interface and Lead Zirconate Titanate (PZT), simulations estimate that the power output could be improved to ∼3.1 μW.
DOI : 10.1016/j.sna.2015.02.036 Anahtar Kelimeler :
Piezoelectric, Energy harvester, Multi-degree of freedom, Wide bandwidth.
ISSN: 0924-4247 Cilt: 228 Sayfa: 104-111
The development and calibration to experimental data of a nonlinear stochastic dynamics model for a Micro-Electro-Mechanical System (MEMS) inertial switch is discussed. The MEMS switch is modeled as a classical vibro-impact dynamic system: a single degree-of-freedom oscillator subject to impact with a single rigid barrier. An applied load, modeled as a stationary Gaussian stochastic process with prescribed power spectral density (PSD), excites the device and causes repetitive impacts with the barrier. A subset of the model parameters are described as correlated random variables to represent the significant unit-to-unit variability observed during testing of a collection of the switches. Experimental measurements from linear modal and nonlinear transient tests on multiple nominally-identical units are used to calibrate the probabilistic model. The calibrated model for the MEMS inertial switch is then used for probabilistic design studies, where the metric of performance is the amount of time the switch remains closed when subject to the applied stochastic load.
DOI : 10.1016/j.sna.2006.04.033 Anahtar Kelimeler :
Probability, Random vibration, Nonlinear dynamics, Vibro-impact system
ISSN: 0924-4247 Sayı: 1 Cilt: 134 Sayfa: 109-118
A pair of one-way passive microvalves is fabricated by using the p+ etch-stop method. The two valves have a simple structure and are easy to fabricate. Each valve consists of several p+ silicon diaphragms and is designed to open and close depending on the pressure difference. The fabrication process of the valves consists of a boron diffusion and simple anisotropic etch processes. According to the experimental results, the water flow rate is 1.6 ml min−1 at 4 kPa of forward pressure and −0.05 ml min−1 at 4 kPa of backward pressure.
An attempt has been made to develop an optical power-feed system capable of supplying power to sensors and interfacing circuits. Laser light is transmitted to solar cells, where the optical energy is converted into electrical energy. A continuous-wave laser diode (wavelength 813 nm, maximum optical power 800 mW) is used as the light source. A laser diode with graded-index fiber coupling (400 μm core diameter, numerical aperture 0.2) is connected to eight solar cells assembled in series around the fiber end. The active area of each solar cell is 0.5 cm × 0.27 cm. The open-circuit voltage and the short-circuit current are found to be about 4.5 V and about 8.5 mA, respectively, with a laser diode optical power of 650 mW. Upon temperature measurement using this power-feed system, the modulated signal can be transmitted by a light-link diode via a step-index fiber. The results indicate that the system can be used as a power supply for conventional sensor elements.
DOI : 10.1016/0924-4247(92)80186-7 Anahtar Kelimeler :
optical power-feed, laser diode, fiber-optic communication, solar cell, temperature measurement.
ISSN: 0924-4247 Sayı: 2 Cilt: 34 Sayfa: 155-159
A novel neural network based method for modeling of rate-dependent hysteresis in piezoelectric actuators is proposed. In order to approximate the behavior of rate-dependent hysteresis which is a kind of nonsmooth dynamic nonlinearity with multi-valued mapping, a diagonal recurrent neural network (DRNN) with modified backlash operators (MBOs) is developed. In the proposed neural architecture, the MBOs are used as the activation functions of the hidden layer. Then, the corresponding Levenberg–Marquardt (L-M) algorithm for the DRNN with MBOs is proposed. Taking into account the nonsmooth characteristic of the MBO, the proximal bundle (PB) method is applied to search the appropriate subgradients at the nonsmooth vertexes of the MBOs. Finally, the experimental result on rate-dependent hysteresis in piezoelectric actuators is presented.
This study presents a shoe-mounted piezoelectric energy harvester (PEH) to harvest energy from human walking. The PEH realizes frequency up-conversion technology through the impact between ratchet and piezoelectric beam in the gait cycle. A piecewise force-electric coupling model of the PEH is established based on the different motion states of the piezoelectric beam. Three motion states of piezoelectric beam are named as “plucking”, “vibration” and “impact” and analyzed through dynamic simulation. An experimental prototype of the proposed PEH is manufactured and its performance is tested at different gait frequencies. When the gait frequency increases from 1.5 Hz to 4 Hz, the output voltage varies weakly, and the output power varies differently in the upward phase and downward phase of a gait cycle. In the upward phase, when the walking frequency varies from 1.5 Hz to 4 Hz, the peak output power and average output power increased from 9.17 mW and 0.11 mW–13.88 mW and 0.98 mW, respectively. In the downward phase, the peak output power slightly fluctuates around 8 mW, and the average output power slightly increases from 0.12 mW to 0.18 mW. The experimental results show that the proposed PEH has 8 high-power peaks in a gait cycle and provides effective energy output within the frequency range of human walking, which has the potential in the application of driving wearable devices.
DOI : 10.1016/j.sna.2020.112530 Anahtar Kelimeler :
Energy harvester, Up-conversion, Piezoelectric, Wearable, Vibration
ISSN: 0924-4247 Cilt: 318 Sayfa: 112530
This work reports the impact of junction area on the device performance parameters of Graphene/n-Silicon (Gr/n-Si) based Schottky photodiodes. Herein, three batches of Gr/n-Si photodiode samples were produced based on various sized CVD grown monolayer graphene layers transferred on individual n-Si substrates. The fabricated devices exhibited strong Schottky diode character and had high spectral sensitivity at 905 nm peak wavelength. The optoelectronic measurements showed that the spectral response of Gr/n-Si Schottky photodiodes has a linear dependence on the active junction area. The sample with 20 mm2 junction area reached a spectral response of 0.76 AW−1, which is the highest value reported in the literature for self-powered Gr/n-Si Schottky photodiodes without the modification of graphene electrode. In contrast to their spectral responsivities, the response speed of the samples were found to be lowered as a function of the junction area. The experimental results demonstrated that the device performance of Gr/n-Si Schottky photodiodes can be modified simply by changing the size of the graphene electrode on n-Si without need of external doping of graphene layer or engineering Gr/n-Si interface. This study may serve towards the standardization of junction area for the development of high performance Gr/Si based optoelectronic devices such as solar cells and photodetectors operating in between the ultraviolet and near-infrared spectral region.
The dynamic properties of membranes have been object of many researches since they can be used as sensor heads in different devices. Some methods have been proposed to solve the problem of determining the resonance frequencies and their dependence on the stress caused by forces applied on the membrane surface. The problem of the vibrating rectangular membrane under a stress caused by a uniform in-plane force is well known. However, the resonance frequency behaviour when the force is out-of-plane instead of in-plane, is not so well understood and documented. A gradiometer which uses a silicon square membrane with a magnet fixed on it as a sensor head has been developed in a previous work. This device reports a quadratic dependence of the frequency on the out-of-plane magnetic force. In this work, simulations to obtain the dependence of the frequency of the fundamental flexural mode on the stress have been performed. It has been studied the influence of in-plane and out-of-plane forces applied to the membrane. As expected, a square root dependence has been found for in-plane forces. Nevertheless, the problem is more complex when out-of-plane forces are considered. Out-of-plane forces give rise to an initial quadratic dependence which turns into a square root dependence from a certain stress value. The quadratic range increases and the rate of change of the frequency decreases as the surface of the magnet fixed on the membrane increases. The study has addressed these problems and both, experimental and simulated results have been compared and a good agreement between experimental and simulated results has been found.
DOI : 10.1016/j.sna.2010.07.012 Anahtar Kelimeler :
46.70.Hg, 46.15.−x, 46.40.Ff, Silicon, Resonance frequency, Finite Element Method, Magnetic field gradiometer
ISSN: 0924-4247 Sayı: 1 Cilt: 163 Sayfa: 75-81
The low actuating voltage and quick bending responses of ion-exchange polymer metal composite (IPMC) are considered very attractive for the construction of various types of actuators and sensors. The principle of IPMC actuation under electric field has been believed to be the ion cluster flux and electro-osmotic drag of water from the anode to cathode direction through the hydrophilic channels in the perfluorinated sulfonic acid polymer chains. In this study, the effect of water content residing in the perfluorinated polymer was investigated by electrochemical and thermal experiments as well as hydraulic mechanical modeling. The water residing in the IPMC actuator seemed to exist as free water and bound water, each corresponding to interstitial and hydrogen-bonded water molecules. Using the classical lamination theory (CLT), a modeling methodology was developed to predict the deformation, bending moment, and residual stress distribution of the anisotropic IPMC thin-plate actuators. In this modeling methodology, the internal stress evolved by the unsymmetric distribution of water in the IPMC was quantitatively calculated and subsequently the bending moment and the curvature were estimated for the IPMC actuator.
DOI : 10.1016/j.sna.2004.07.001 Anahtar Kelimeler :
Ion-exchange polymer metal composite (IPMC), Water migration, Actuator, Classical lamination theory
ISSN: 0924-4247 Sayı: 1 Cilt: 118 Sayfa: 98-106
This paper presents the results of our ongoing investigation of using Nafion solution to construct micron scale actuators as grippers to operate under aqueous environment. Thus far, we have demonstrated that MEMS-based fabrication of cantilever structures composed of Au/Nafion/Au tri-layers on silicon substrates is possible using Nafion solution. The smallest actuators fabricated were 30 μm wide, 300 μm long and 0.4 μm thick. We have shown that two-finger actuators (each 100 μm wide, 1200 μm long and 0.4 μm thick) can be fully actuated in water at ∼7 V DC. In addition, with a special sacrificial release process, micro ICPF structures can be made to curl whenever they come in contact with water, and can be de-curled instantaneously when they are immersed in acid, suggesting that they can be used in sensing pH level changes.
Macroporous silicon photonic crystals show a great potential for a range of applications such as optical sensing or signal processing. These applications require tight fabrication tolerances. In particular, the effect of process variability in 3-d photonic crystals and out of plane propagation has been seldom studied in literature. In this paper we report the effect fabrication imperfections on the spectral response of macroporous silicon photonic crystals. To quantify fabrication disorder and its influence, several 3-d macroporous silicon structures were fabricated consisting of modulated pores arranged in a square lattice. The pore modulation is similar to a stretched sinusoidal waveform. Lattice pitch is 700 nm, pore diameter is in the range from 250 nm to 520 nm, and modulation period is 1.2 μm. The samples were characterized by SEM inspection and the actual etched pore profiles extracted. The statistical analysis of the profiles reveals two main sources of randomness: radius variability and modulation period irregularity. Surface roughness and asymmetry do not seem to play a major role. Several FDTD simulations have been performed based on the statistical parameters extracted, and the results are compared to actual FT-IR measurements of the fabricated samples. The obtained results show that, in general, the dispersion in z period has the most severe effect in the structure’s optical response.
Introduction Impedance curves, equivalent circuit parameters in Tb1−xDyxFe2−y/Pb(Tix,Zr1−x)O3 laminate vibrator have been characterized as a function of external DC magnetic field. Clearly, the equivalent circuit parameters are function of external DC magnetic field due to the field-dependent properties of magnetostrictive material. Conclusion Based on these researches, the magneto-impedance (MI) effect is observed in the laminate vibrator, i.e., the impedance across the electrodes of the piezoelectric layer strongly depends on DC magnetic field. Analysis shows that the MI effect is primarily attributed to the field dependence of magneto-mechanical damping in Tb1−xDyxFe2−y. The experimental results show that the maximum MI ratios up to 280% and 222.4% along with the sensitivities correspondent to DC magnetic field up to 1.71% Oe−1 and 0.8% Oe−1 are obtained at the selected operating frequencies around the frequencies of maximum and minimum impedances. The results open up possibilities for a new type of MI devices, magnetic field sensors, or multi-functional ferromagnetic/piezoelectric composite devices.
In this paper we investigated the possibility to conduct a non-invasive identification process of liquid samples packed in glass and polypropylene containers. Interdigital capacitor (IDC) structures were designed as solid (build using standard PCB fabrication procedure) and flexible (paper based) structure. Testing was performed using benzene, olive oil, acetone, alcohol, methanol, purified water and formaldehyde. Sample volume and container influence was examined. Information about the sample is available on a 2 × 16 character and through RS232 connection on PC. Experiments showed promising in building a portable and cost-effective sensing unit for on-field application where it is necessary to discriminate between several packed liquid samples.
An active stick which has variable force-feel characteristics is developed. A combined position and force control strategy is mechanized by using a 2-axis built-in force sensor and LVDT. The 2-axis force sensor, which measures the stick force felt by the operator, is developed by using strain gages and appropriate instrumental amplifiers. A mathematical model of the active stick dynamics is derived, and compared with the experimental results. The frictional torque of the stick due to the mechanical contact of several parts causes the experimental frequency responses to be dependent on the magnitude of the excitation signal and the precision closed loop control to be difficult. A friction observer which estimates the frictional torque of the active stick in real time is designed, and applied to the closed loop control. The benefit of using the friction observer is verified through numerical simulation and experiments.
DOI : 10.1016/j.sna.2004.06.018 Anahtar Kelimeler :
Active stick, Friction observer, Hysteresis, 2-Axis force sensor, Variable force-feel characteristics
ISSN: 0924-4247 Sayı: 2 Cilt: 117 Sayfa: 194-202
The optical and electrical properties of hydrogenated amorphous silicon (a-Si:H) thin films, prepared by plasma deposition, were studied as a function of r.f. power in the range from 12.5 to 200 mW/cm2. Film analysis performed included spectroellipsometry, FT-IR absorption spectroscopy, photothermal deflection spectroscopy, and dark and photoelectrical conductivity measurements. The initial effect of increasing r.f. power is characterized by a decrease in material density and an increase in film microstructure and structural disorder, resulting in a deterioration of a-Si:H optoelectronic properties. In contrast, at higher r.f. power, film density is hardly affected and microstructure is reduced, as well as the structural disorder. As a consequence, a-Si:H films were obtained at high deposition rate (1 nm/s) with optoelectronic properties comparable with that obtained at low r.f. power ( < 0.4 nm/s). These results are discussed in terms of plasma polymerization and ion bombardment mechanics induced by r.f. power.
DOI : 10.1016/0924-4247(93)80124-y
ISSN: 0924-4247 Cilt: 37-38 Sayfa: 733-736
Described is a novel fabrication process of manufacturing ionic polymer–metal composites (IPMCs) equipped with physically loaded electrodes as biomimetic sensors, actuators and artificial muscles. The underlying principle of processing this novel IPMCs is to first physically load a conductive primary powder layer into the polymer (ionomeric) network forming a dispersed particulate layer. This primary layer functions as a major conductive medium in the composite. Subsequently, this primary layer of dispersed particles of a conductive material is further secured within the polymer network with smaller secondary particles via chemical plating, which uses reducing agents to load another phase of conductive particles within the first layer. In turn, both primary and secondary particles can be secured within the polymer network and reduce the potential intrinsic contact resistance between large primary particles. Furthermore, electroplating can be applied to integrate the entire primary and secondary conductive phases and serve as another effective electrode. In this paper, we describe the details of this newly developed technique to efficiently produce an IPMC loaded with spherical silver particles (D10<0.8 μm, D50<1.5 μm, D90<2.5 μm; Asur<6 m2/g) and subsequently secured by palladium (Dp∼50 nm, via a chemical reducing process). It has been established that such an IPMC is quite comparable in force and displacement performance with the traditional platinum loaded and gold electroplated IPMCs but can be manufactured at about 1/10th of the cost. Yet it produces a low surface resistivity (less than 1 Ω per square), which is highly desirable in creating more uniform deformation.
This work proposes a highly novel centrifugally spun lanthanide doped nonwoven fibrous mat as a non-contact optical pressure sensor with a wide linear dynamic range and good pressure sensitivity. The sensor properties are based on the spectral shift, broadening and intensity enhancement of Ce3+ ion in Ce doped PVDF fiber upto significantly high pressure. Two different systems: Ce(NO3)3·6H2O and (NH4)4Ce(SO4)4·2H2O doped PVDF flexible fibers (CeN-PF and CeS-PF) were produced using the Forcespinning® technique. Both CeN-PF and CeS-PF fibers displayed violet-blue emission under UV irradiation due to a 5d-4f transition of Ce3+ ions. Our emission results show that both CeN-PF and CeS-PF spectral characteristics are influenced by high pressures, inducing significant spectral ref shift in 5d-4f. The pressure-induced monotonous changes in bandwidth and emission intensity enhancement along with red shift suggesting the potential application of these fibers for pressure sensing applications. The CeN-PF fiber exhibits a high-pressure sensitivity (dλ/dP ≈ 0.28 nm/GPa) under a comprehensive linear dynamic range (0–64 GPa) with no pressure-induced luminescence quenching. The changes in CeS-PF is less pronounced with a lower pressure sensitivity of 0.10 nm/GPa compared to CeN-PF due to large crystal field splitting energy of nitrate ion compared to sulphate ion. This work presents a highly efficient, cost effective, scalable lanthanide doped flexible fibrous based system with negligible high pressure quenching and a wider linear dynamic range for optical pressure sensing applications.
DOI : 10.1016/j.sna.2019.111595 Anahtar Kelimeler :
Cerium, High pressure, Sensor, Photoluminescence, Fiber, Forcespinning
ISSN: 0924-4247 Cilt: 298 Sayfa: 111595