Showing papers on "Gauge factor published in 2007"

Nanoparticle films as sensitive strain gauges

Abstract: We demonstrate that thin films consisting of cross-linked nanoparticle aggregates function as highly sensitive strain gauges. The sensors exploit the exponential dependence of the interparticle tunnel resistance on the particle separation. Their sensitivity (gauge factor) is two orders of magnitude higher than that of conventional metal foil gauges and rivals that of state-of-the-art semiconductor gauges. We describe the strain gauge behavior in a tunneling model that predicts the dependence of the gauge factor on several parameters, in particular, the nanoparticle size, the interparticle separation gap, and the conductance of the linker molecules.

Piezoresistivity-Based Strain Sensing in Carbon Fiber-Reinforced Cement

Abstract: For piezoresistivity -based strain sensing using carbon fiber-reinforced cement (152 mm [6 in.] specimens under compression) in the elastic regime, the four-probe method of electrical resistance measurement is more effective than the two-probe method in that it provides gauge factor (fractional change in resistance per unit strain) that is higher and that varies less with the strain amplitude. The two-probe method also suffers from the resistance increasing irreversibly in the first few loading cycles due to minor degradation of the electrical contacts. The use of embedded stainless steel electrical contacts gives more effective strain sensing and slightly lower resistivity than the use of silver paint surface electrical contacts, whether the four-probe method or the two-probe method is used. In case of the four-probe method, the use of embedded steel contacts compared with the use of surface silver paint contacts results in greater linearity and lower noise in the variation of the resistance with strain. In case of the two-probe method, the use of embedded steel contacts compared with the use of surface silver paint contacts results in lower variability of the gauge factor and smaller fractional contribution of the contact resistance to the measured resistance.

Study of piezoresistance effect of carbon nanotube-PDMS composite materials for nanosensors

Abstract: Samples of novel nanocomposites of multiwalled carbon nanotube and poly (dimethylsiloxane), i.e., CNT-PDMS, at different filler concentrations are prepared. The mechanical/electrical and piezoresistance properties of these nanomaterials are studied in detail. The gauge factor (GF) of this nanocomposite, dependent on the content of CNT, ranges from 1.38 to 12.4. Since the CNT-PDMS can be easily used as a novel piezoresistor using low-cost MEMS technology, this nanomaterial has decent potential in nanosensors and PDMS-based microfluidic systems.

Piezoresistivity-based strain sensing in carbon fiber-reinforced cement

Abstract: For piezoresistivity -based strain sensing using carbon fiber-reinforced cement (152 mm [6 in.] specimens under compression) in the elastic regime, the four-probe method of electrical resistance measurement is more effective than the two-probe method in that it provides gauge factor (fractional change in resistance per unit strain) that is higher and that varies less with the strain amplitude. The two-probe method also suffers from the resistance increasing irreversibly in the first few loading cycles due to minor degradation of the electrical contacts. The use of embedded stainless steel electrical contacts gives more effective strain sensing and slightly lower resistivity than the use of silver paint surface electrical contacts, whether the four-probe method or the two-probe method is used. In case of the four-probe method, the use of embedded steel contacts compared with the use of surface silver paint contacts results in greater linearity and lower noise in the variation of the resistance with strain. In case of the two-probe method, the use of embedded steel contacts compared with the use of surface silver paint contacts results in lower variability of the gauge factor and smaller fractional contribution of the contact resistance to the measured resistance.

Interdigital capacitive strain gauges fabricated by direct-write thermal spray and ultrafast laser micromachining

Abstract: There is a growing demand for in situ monitoring of strain in high-temperature, harsh environment systems. Resistive strain gauges, while popular and easy to implement, have several disadvantages when used at high-temperatures. This work presents the design, fabrication, and initial testing of capacitive strain gauges for use in high-temperature, harsh environments. The gauges are fabricated using a direct-write thermal spray technology in which a computer-controlled deposition system is used to fabricate silver gauge patterns onto polymer, composite, and alumina substrates to form the strain gauges. Gauges were also fabricated using ultrafast laser micromachining of blanket NiCr coatings thermal sprayed onto an alumina substrate. The typical gauge capacitance was 4–25 pF. Mechanical measurements performed included gauge factor, linearity, and zero shift. Temperature-based measurements include the temperature coefficient of capacitance (TCC) and thermal cycling tests. The devices show promise for use in harsh environments and in wireless strain monitoring applications.

Multi-walled Carbon Nanotubes/Poly(L-lactide) Nanocomposite Strain Sensor for Biomechanical Implants

Abstract: Many biomedical applications require high sensitivity for measuring strain induced in biomechanical structures. Although current metallic foil strain gauges are capable of measuring strain deformations, their low sensitivity and relatively large size render them unsuitable for implantable and wearable application. In this paper, we present a novel nanocomposites strain sensor using poly(L- lactide) (PLLA) as a host polymer matrix and multi-walled carbon nanotubes (MWNTs) as filler. The PLLA matrix improves load transfer across the nanotubes by means of better interfacial bonding between polymer and carbon nanotubes filler, thus endowing the nanocomposites material with excellent piezoresistive property. Experimental results using a fabricated nanocomposites strain sensor is presented demonstrating its linear response and high gauge factor. Due to biocompatibility and biodegradability of PLLA, the proposed sensor is attractive for many biomedical and wearable applications.

Characteristics of tantalum nitride thin film strain gauges for harsh environments

Abstract: This paper presents the characteristics of Ta–N thin film strain gauges that are suitable for harsh environments, which were deposited on thermally oxidized Si substrates by dc reactive magnetron sputtering in an argon–nitrogen atmosphere (Ar–N 2 (4–16%)). These films were annealed for 1 h in 2 × 10 −6 Torr in a vacuum furnace with temperatures that ranged from 500 to 1000 °C. The optimized deposition and annealing conditions of the Ta–N thin film strain gauges were determined using 8% N 2 gas flow ratio and annealing at 900 °C for 1 h. Under optimum formation conditions, the Ta–N thin film strain gauges obtained a high electrical resistivity, ρ = 768.93 μΩ cm, a low temperature coefficient of resistance, TCR = −84 ppm/°C and a high temporal stability with a good longitudinal gauge factor, GF = 4.12. The fabricated Ta–N thin film strain gauges are expected to be used in micromachined pressure sensors and load cells that are operable under harsh environments.

Piezoresistive sensors for smart textiles

Abstract: We have used inkjet printing to deposit silver conducting lines and small PEDOT (conducting polymer) sensors onto fabrics. The printed conductors penetrate into the fabric and can be shown to coat the individual fibers within the yarn, through the full thickness of the cloth. The PEDOT sensor has a resistance in the region of a few kilo-ohms and is connected to measuring equipment by printed silver lines with a resistance of a few ohms. In this way, local strains can be measured at different sites on a fabric. The PEDOT responds to a tensile strain by a reduction in resistance with a gauge factor (change in resistance/strain) from -5 to -20. This compares with conventional strain gauges where the gauge factor is normally +2. These sensors cycle to strains of over 10%. We have measured gauge factors as a function of the orientation of the sensing line to the fabric axes, to the strain axes for different fabric structures. We can correlate the gauge factor with the extent to which the twisted multifilament yarns are expected to become laterally compressed. In preliminary tests we have shown that these printed sensors can be used to monitor knee and wrist motions and so could be used to provide information in applications such as rehabilitation from joint damage.

Development of capacitive pure bending strain sensor for wireless spinal fusion monitoring

Abstract: A MEMS (microelectromechanical system) capacitive-based pure bending strain sensor is presented for use in spinal fusion monitoring. The sensor is designed to interface with a telemetry system that does not require a battery and contained in a housing that is attached to spinal fusion rods. The cantilever structure of the sensor is composed of two parallel plates with a narrow gap and a conjoint end. Nine permutations of the design with different metal coverage areas (14 mm 2 , 9.3 mm 2 and 4.7 mm 2 ) and gaps (3m, 6m and 7.4m) were examined. The nominal capacitance ranges from 7.6 pF to 42 pF. The capacitance changes 31.4–65.1% for a strain range of 0–1000 depending on the design parameters. An analytical model is developed for the sensor mounted to a cantilever test bar and compared to experimental results of actual devices. The model and experimental results show an average difference of 5% for all nine designs investigated. The final sensor design achieved a linear gauge factor of 252 and was fabricated for the spinal fusion application. Published by Elsevier B.V.

The piezoresistive effect in diamond-like carbon films

Abstract: Diamond-like carbon (DLC) film was deposited using plasma-assisted chemical vapour deposition (PACVD) at −350 V and −800 V. DLC strain gauges were integrated in bulk micromachined silicon. Optical bandgaps were found to be 1.2 eV and 1.03 eV at −350 V and −800 V, respectively. Films deposited at −350 V have a higher hydrogen percentage, hardness, sp3 content, resistivity and gauge factor compared to films deposited at −800 V. Piezoresistive gauge factors were measured under longitudinal and transversal strain configurations and in vertical and lateral current injection directions. It was found that the gauge factor was independent of the current injection direction and strain configurations. A model to explain the origin of the piezoresistive effect in DLC films along with parameters which can further enhance the gauge factor value of the films is discussed, which is confirmed experimentally.

Toward Carbon Nanotube-Based AFM Cantilevers

Abstract: The mechanical properties of carbon nanotubes have been widely employed to enhance the performance of atomic force microscopy (AFM) cantilever tips Utilizing the electromechanical properties of carbon nanotubes, this paper investigates the potential of using carbon nanotubes as active strain sensing elements on AFM cantilevers A batch microfabrication process was developed to construct silicon microcantilevers Multiwalled carbon nanotubes were dielectrophoretically assembled between electrodes Based on the characterization results of 12 devices, the CNT-based cantilevers demonstrated a linear relationship between resistance changes and externally applied strain The gauge factor ranged from 7884 to 13440 for four different device configurations

Fabrication technology of piezoresistive conductive PDMS for micro fingerprint sensors

Abstract: This paper reports the characterization of piezoresistivity of Conductive Polydimethylsiloxane (CPDMS) and the corresponding fabricating process for a parylene-coated, CPDMS Micro Fingerprint Sensor (MFS) with mushroom-shaped electrodes. Gauge factor of about 7.4 was demonstrated, and the piezoresistive sensitivity was about 3x10-6 Pa-1 in the tensile test setup. The packaged MFS sensors were characterized by a pneumatic test and a nanoindentation test. We demonstrate that the fabricated device can detect pressure and force levels bellow 10 kPa and 50 muN, respectively. The use of the material and process presented in this paper offers the opportunity to realize a robust micro fingerprint sensor with low cost, low temperature process on different substrates.

Optimising of strain sensitivity and electric characteristics of Ni-Cr thin film fabricated by magnetron sputtering

Abstract: By controlling the sputtering power, rotational speed of substrate and sputtering time, Ni–Cr thin films with appropriate composition were fabricated by double target magnetron cosputtering techniques. The homogeneity and oxidation of Ni–Cr film has been studied by Auger electron spectroscopy. The structures of films were determined by an X-ray diffractometer and a transmission electron microscope respectively. Gauge factor (GF) has been determined by the cantilever method. The relations between GF, temperature coefficient of resistance and compositions of films were discussed. The dependence of resistivity and Cr concentration in Ni–Cr thin film follows an exponential function. The optimal resistance stability of nanoscale Ni–Cr thin film is achieved by a rapid thermal process combined with a conventional thermal annealing technique. As a strain sensitive material, Ni–Cr thin films with optimal composition, desire GF and reliable electrical properties have been attained.

High Performance Piezoresistive Micro Strain Sensors

Abstract: This paper presents results of studies on the high performance silicon piezoresistive bridge strain sensors. The microfabricated, boron diffused, piezoresistive strain sensors constructed in Wheatstone bridge structure were used in this work. The temperature stability and time drift problems were studied and improvements were made. Experimental results showed heavily doped sensors are less sensitive to temperature variation but with lower gauge factor as compared with lower doped sensors. In order to solve time drift problem in packaged sensor modules, the stiffness of sensors has to be reduced. The thickness of sensors was reduced from 500 mum to 30 mum by using MEMS structure with novel processes. The drift problem was improved from 7.6% for 500 mum-thick devices to 0.2 % for 30 mum-thick devices.

A method to measure reference strain in FBG strain sensor interrogation system involving actuators

Abstract: A method for reference strain measurement for FBG strain sensor in the testing stage while applying strain using actuators like piezo translators or micro screw is introduced. Unlike conventional methods of surface mounting, in our method the strain gauge is affixed directly to the optical fibre, which allows it to use with systems where the strain is applied directly using actuators while testing the FBG sensing system. Different bonding techniques were tested and a comparison with the results from calculated values are presented. Since the contact area between the fibre and strain gauge is very small, a corrected gauge factor is calculated and is used to measure the strain transfer. As a demonstration of the developed method, the strain gauge is used as a reference in an edge filter based FBG sensors interrogation system, where the strain was applied using a micro screw. The measured strain using foil strain gauge affixed to the optical fibre and FBG sensor interrogation system are in close agreement. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2658–2661, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22817

Measurement and simulation of carbon nanotube's piezoresistance property by a micro/nano combined structure

Abstract: In this paper, the present status of carbon nanotube's electromechanical properties was reviewed. The relationships among the carbon nanotube's resistance, gauge factor and the rates of change of the band gaps with strain (dE g /de) were analyzed and simulated. Then, a micro/nano combined device and method for measuring the piezoresistance property of carbon nanotube were proposed. The device is consisted of a silicon chip and a printed circuit board which is used for loading and leading wire. The microelectrodes were fabricated on the silicon chip by FIB and a CVD-growth single-wall carbon nanotube was connected with the microelectrodes. The voltage-current characteristic of the carbon nanotube was measured using the proposed device. The relationship between the current and the voltage is basically linear, which demonstrates that the carbon nanotube is metallic. The experimental results show that the micro/nano combined device can be used for measuring the piezoresistance of carbon nanotube in our future work.

Giant Magneto-Piezoresistance and Internal Friction in a Two-Dimensional Electron System

Abstract: We use a micromechanical cantilever with an integrated two-dimensional electron system to show that an extremely small strain of the order of 10-4 induces a localized–delocalized electronic state transition. This strong strain effect improves the piezoresistive gauge factor by more than two orders of magnitude compared to the conventional Si cantilever. Furthermore, we found that the cantilever mechanical motion is affected considerably by friction exerted by the electron systems.

The influence of doping concentration on piezoresistive temperature characteristics of polysilicon nanofilms

Abstract: Compared with ordinary polysilicon films and monocrystalline silicon, heavy doped polysilicon nanofilms have better piezoresistive properties and better temperature characteristics. Therefore, pressure sensors made of polysilicon nanofilms will have many corresponding advantages, including high sensitivity and complete self-compensation of temperature coefficients. In this paper, the influence of doping concentration on temperature coefficient of resistance (TCR) and temperature coefficient of gauge factor (TCGF) is deeply studied to optimize doping concentration in order to make temperature coefficients lowest. TCR and TCGF of samples with doping concentration of 4.1×10 19 cm -3 , 1.0×10 20 cm -3 , 2.0×10 20 cm -3 , 4.1×10 20 cm -3 , 7.1×10 20 cm -3 are tested at temperature range 23°C to 270°C, respectively, and the microstructures of the samples are also observed by the method of scanning electron microscopy (SEM) and transmission electron microscope (TEM). The experimental results have been explained reasonably based on the tunneling piezoresistive theory proposed before. Based on both experimental results and theoretical analyses, to obtain a zero value of TCR and a low value -0.1%/°C of TCGF, the optimal doping concentration of the films of 80nm thickness should be about 3×10 20 cm -3 .

Magnetoelectronical Sensors for Mechanical Measurements

Abstract: Recently, highly sensitive strain gauges were developed, which are based on TMR (tunnel magnetoresistance) or GMR (giant magnetoresistance) effects combined with the inverse magnetostriction. GMR and TMR structures generally possess a symmetrical characteristic which reflects the switching fields of the soft and hard layers, respectively. This characteristic can be changed by a stress field if the soft layer is replaced by a suitable magnetostrictive layer leading to a stress induced rotation of the magnetostrictive layer with respect to the reference layer. In particular in combination with the TMR effect, this approach illustrates an interesting, highly sensitive mechanism in order to detect mechanical variables with a high spatial resolution as well as an unrivaled high gauge factor. In addition, the feasibility of an integrated fabrication compatible to cost effective fabrication routes using nano-/micro techniques is of great interest e.g. for the automotive industry. In this paper, the basics, the fabrication and the features of magnetoelectronical sensors will be discussed in view of an integrated pressure sensor for automotive applications.

STRAIN SENSITIVITY AND TEMPERATURE INFLUENCE OF NICHROME (80/20 wt.%) THIN FILM FABRICATED BY MAGNETRON SPUTTERING

Abstract: The electromechanical properties of nichrome (Ni–Cr 80/20 wt.%) used as a common material for application in thin film strain gauges have been studied. The surface topography and chemical composition of Ni–Cr thin films grown on the glass substrate by magnetron sputtering have been analyzed by atomic force microscope (AFM) and energy dispersive spectroscopy (EDS), respectively. The temperature coefficient of resistance (TCR) has been determined by a Nano-volt/Micro ohm meter. The gauge factor (FG) has been determined by the cantilever method. Low stable TCR values (22 ppm to 46 ppm in the 50–150°C temperature range) have been obtained. Resistance stability is achieved by rapid thermal annealing (RTA) at 300°C for 10 min combined with a 24 h thermal annealing (TA) at 150°C. The desired 45 Ω/m sheet resistance and a gauge factor of 2.6 have been attained for 40-nm-thickness films. The films have very small roughness of 2.1~4.4 nm.

Carbon nanotube-based strain sensing cantilevers

Abstract: This paper presents the design, fabrication, and testing results of silicon cantilevers with carbon nanotubes (CNTs) as active strain sensing elements. A batch microfabrication process was developed for device construction and packaging. Multi-walled carbon nanotubes (MWNTs) were dielectrophoretically assembled between electrodes. Based on the characterization results of 12 devices, the CNT-based cantilevers demonstrated a linear relationship between resistance changes and externally applied strain. The gauge factor ranged from 78.84 to 134.40 for four different microelectrode configurations.

Piezoresistive effect in amorphous carbon thin films

Abstract: In this contribution amorphous carbon (a-C) films are integrated as strain gauges in micromachined silicon boss membranes. Sputter deposited a-C films have high hardness and <2 % hydrogen content in it. The tribological properties of the a-C films are comparable with diamond and can be used for hard coatings. The films have very low resistivity which decreases with the temperature. Current voltage characteristics of a-C/oxide Si shows Ohmic behaviour. Variable range hopping mechanism is dominant at low temperatures and is thermally activated at room temperature and at higher temperatures. Piezoresistive gauge factor are measured in the temperature range 23–50°C.

Evaluation of Piezoresistive Effects for Carbon Nanowire using MEMS Actuators

Abstract: This research develops Electrostatic Actuated NAno Tensile testing devices (EANATs) to evaluate mechanical and electrical properties of carbon nanowires fabricated by focus ion beam assisted chemical vapor deposition (FIB-CVD). This research measured I-V characteristics of carbon nanowires, with diameters ranging from 88 nm to 129 nm, under tensile loading in order to evaluate the gauge factor of nanowires. The averaged gauge factor of 0.7 is lower than that of hydrogenated amorphous C films. Discussion of the mechanical and electrical properties of the nanowires is made from scanning electron microscope-energy dispersive X-ray spectrometer (SEM-EDX) and scanning transmission electron microscope (STEM) observations.

Development of Ultra Miniature 1-French Sensors for Wireless Radial Arterial Pressure Monitoring (Non-Refereed)

Abstract: Miniaturized pressure sensors attached to catheters have numerous applications in the biomedical and life science fields including the monitoring of arterial, ventricular, intracranial and intraocular pressures. Recent advances in MEMS (microelectromechanical systems) technology and its associated fabrication processes, such as DRIE (deep reactive ion etching), have allowed for further miniaturization of these devices, expanding the application landscape to include small animal models and new human applications. One such human application is the wireless measurement of radial arterial blood pressure (BP). The goal of this research program is to produce a truly portable wireless radial arterial monitoring system using a custom–designed ultra-miniature pressure sensor appropriately sized to fit within the tip of a 1-French catheter (333 micron), so that convenient in-vivo measurements of BP are possible. The proposed system consists of two assemblies. The sensor, catheter, and wristband containing the battery and telemetry circuit form one assembly and the portable wireless PDA-sized transceiver module forms the other. This paper reports on the custom miniature MEMS pressure sensor developed for this application. The piezoresistive pressure sensor was designed using a combination of SUPREM for the process modeling, LEDIT for the device layout, and Mathcad for the mechanical modeling. Doping concentration is a critical design parameter for the piezoreisistive gauges. A trade-off is required when optimizing this parameter because gauge sensitivity (i.e gauge factor) is inversely proportional to concentration while ohmic contact and TCR (temperature coefficient of resistance) scale directly with concentration. Doping concentration also effects the final sheet resistance of the gauges which directly impacts the size and layout of the elements. Ion implantation was selected as the preferred doping method because it results is shallow junctions, low lateral “diffusion”, and better control. Boron implanted resistors were consequently formed using a dose of 1.8e15 cm -3 and an energy of 35 keV, resulting in a sheet resistance

Piezoresistivity in films of nanocrystalline manganites.

Abstract: Rare earth manganites having perovskite structure are susceptible to lattice strain. So far most investigations have been done with hydrostatic pressure or biaxial strain. We have observed that hole doped rare-earth manganites, which are known to display colossal magnetoresistance (CMR) also show change in its resistance under the influence of uniaxial strain. We report the direct measurement of piezoresistive response of La0.67Ca0.33MnO3 (LCMO) and La0.67Sr0.33MnO3 (LSMO) of this manganite family. The measurements were carried out on nanostructured polycrystalline films of LCMO and LSMO grown on oxidized Si(100) substrates. The piezoresistance was measured by bending the Si cantilevers (on which the film is grown) in flexural mode both with compressive and tensile strain. At room temperature the gauge factor approximately 10-20 and it increases to a large value near metal-insulator transition temperature (Tp) where the resistivity shows a peak.