Fractional Change In Resistance Research Articles

Continuous deformation monitoring by polymer-matrix carbon fiber sensitive layer

Composite made of short-cut carbon fiber mat and vinyl ester resin was observed to be an effective sensor for tensile strain up to 6 000 μe. Based on its strain sensitivity, a skin-like sensitive layer which can continuously cover the structural surface to sense strain in large area was developed. The sensitive layer was applied to continuously monitor the deformation of a simply supported beam. The result indicates that the fractional change in electrical resistance of the sensitive layer reversibly reflects the beam deformation in each section and describes the distribution of the average strain of the beam. The effect of temperature change on the monitoring was studied by monitoring tests conducted at different temperatures ranging from 20 to 80 °C, which reveals temperature sensitivity in the sensitive layer and the temperature dependence of the piezoresistive behavior when the temperature exceeds 50 °C. By the application of differential connection principle, a method for temperature compensation was established and the gauge factor for the monitoring was dramatically increased. This method was verified experimentally.

A Tactile Sensor Using Piezoresistive Beams for Detection of the Coefficient of Static Friction

This paper reports on a tactile sensor using piezoresistive beams for detection of the coefficient of static friction merely by pressing the sensor against an object. The sensor chip is composed of three pairs of piezoresistive beams arranged in parallel and embedded in an elastomer; this sensor is able to measure the vertical and lateral strains of the elastomer. The coefficient of static friction is estimated from the ratio of the fractional resistance changes corresponding to the sensing elements of vertical and lateral strains when the sensor is in contact with an object surface. We applied a normal force on the sensor surface through objects with coefficients of static friction ranging from 0.2 to 1.1. The fractional resistance changes corresponding to vertical and lateral strains were proportional to the applied force. Furthermore, the relationship between these responses changed according to the coefficients of static friction. The experimental result indicated the proposed sensor could determine the coefficient of static friction before a global slip occurs.

A Transient Signal Extraction Method of WO3Gas Sensors Array to Identify Polluant Gases

Electronic nose is a system, which can determine the fingerprint of gas sample by a sensor array coupled to pattern recognition system. In this paper, a sensor array based on WO3 gas sensor has been described, and a feature extraction technique, including integral and primary derivative, is reported, which leads to higher classification performance as compared to the classical features: fractional resistance change $\Delta R_{s}$ and $\Delta R_{f}$ . The sensor array has been exposed to ozone, ethanol, acetone, and a mixture of ozone and ethanol while keeping the temperature constant. The data array has been normalized and auto scaled then analyzed with the principal component analysis. Results indicate that successful classifications have been gotten in the discrimination of three kinds of oxidizing and reducing gas with the proposed feature extraction method using support vector machine which shows that 97.5% were correctly discriminated with integral and primary derivate comparing the classical variable with 85%. The results of data analysis implied that coupling the extracted features in the same database would be interesting and more robust then the standards features.

Discrimination Enhancement with Transient Feature Analysis of a Graphene Chemical Sensor.

A graphene chemical sensor is subjected to a set of structurally and chemically similar hydrocarbon compounds consisting of toluene, o-xylene, p-xylene, and mesitylene. The fractional change in resistance of the sensor upon exposure to these compounds exhibits a similar response magnitude among compounds, whereas large variation is observed within repetitions for each compound, causing a response overlap. Therefore, traditional features depending on maximum response change will cause confusion during further discrimination and classification analysis. More robust features that are less sensitive to concentration, sampling, and drift variability would provide higher quality information. In this work, we have explored the advantage of using transient-based exponential fitting coefficients to enhance the discrimination of similar compounds. The advantages of such feature analysis to discriminate each compound is evaluated using principle component analysis (PCA). In addition, machine learning-based classification algorithms were used to compare the prediction accuracies when using fitting coefficients as features. The additional features greatly enhanced the discrimination between compounds while performing PCA and also improved the prediction accuracy by 34% when using linear discrimination analysis.

Experimental Study of Factors on the Conductive Properties of Carbon Fiber Reinforced Concrete

Based on the test results of conductive properties of carbon fiber reinforced concrete, the main influence on content of carbon fiber, content of coarse aggregate, and carbon fiber length are discussed and analyzed. The test results show that when CF content reach the amount of 0.8%~1.2% by mass of cement, the factors have no significant effect on the fractional change in resistance under 0.5% of the significance levels. But when CF content reach the amount of 1.2%~2.0% by mass of cement, the factors show significant effect on the fractional change in resistance under 0.5% of the significance levels. The CFRC resistance can be taken the minimum only when the sand-cement ratio is 1.47, the CF nominal length is equal to 12mm and the CF content is accounted for 2.0% by weight of cement.

Stretchable Conductive Networks of Carbon Nanotubes Using Plasticized Colloidal Templates

We present a study of the behavior of highly ordered, segregated single-wall carbon nanotube networks under applied strain. Polymer latex templates induce self-assembly of carbon nanotubes into hexagonal (2D) and honeycomb (3D) networks within the matrix. Using mechanical and spectroscopic analysis, we have studied the strain transfer mechanisms between the carbon nanotube network and the polymer matrix. Axial deformation of the nanotube network under applied strain is indicated by downshifts in the 2D mode in the Raman spectra, as well as variation in the Radial Breathing modes. The slippage within nanotube bundles at high strain is indicated by a reduction in the 2D mode rate of change. The fractional resistance change of the composites with strain obeys power law dependence. We present a model for the behavior of carbon nanotube bundles under strain informed by these measurements, and potential applications for such composite materials in elastic electronic devices that can tolerate high strain.

Sensory carbon fiber based textile-reinforced concrete for smart structures

This article investigates the feasibility of intelligent textile-reinforced concrete structural elements with sensing capabilities. The concept is based on dual use of glass and carbon fiber textiles as reinforcement and, at the same time, as a sensory agent. Experimental investigation demonstrates the feasibility of the concept in two applications: detecting strains in a mechanically loaded textile-reinforced concrete beam and monitoring the interaction of the structural element with a wet environment. By detecting the changes to the integrative electrical resistance of the carbon tow, the ability of the textile to sense strain and exposure to water is demonstrated. For strain sensing, the hybrid reinforcing textile provides electro-mechanical sensing with a gauge factor of the order of 1 and a detectable correlation with the load, strain, and displacement responses. For the detection of wetting, the implementation of the carbon tow in a Wheatstone bridge detects fractional resistance changes in the order of 10−5, a figure that is effectively detected by monitoring the voltage across the bridge. The response to wetting, which is conditioned by the cracking of the beam and the exposure to ionic conductive solutions, provides a mean to monitor the functionality and the structural health of the textile-reinforced concrete beam.

Smart Cement Composites for Durable and Intelligent Infrastructure

The self-healing and self-sensing performances of Engineered Cementitious Composite (ECC) mixtures developed recently at Heriot-Watt University are presented. In the first series of experiments, fifteen dog-bone shaped ECC samples were preloaded to known strains and then left to heal outdoors under a natural environment. Ultrasonic pulse velocity measurements were then undertaken periodically to determine the rate and extent of healing in these samples. It was found that the samples were able to heal micro-cracks and show a recovery in UPV after two loading events over a six month outdoor exposure. In another series of experiments, the effectiveness of incorporating milled carbon (MC) fibers into an ECC mix, with the aim of enhancing the self-sensing functionality of ECC, is demonstrated for the first time. The MC-ECC mix exhibited equivalent tensile response compared to the control ECC mix and displayed a strong relationship between tensile strain and the fractional change in resistivity. The inclusion of MC fibers at 0.75% by volume was found to exhibit high sensitivity to micro-cracks formation, with gauge factor two orders of magnitude larger than that of an ordinary strain gauge, albeit less than that of the control mix. It is envisaged that the use of ECC can create an intelligent infrastructure able to sense and repair damage and monitor the recovery extent.

Application of Cement-Based Sensor on Compressive Strain Monitoring in Concrete Members

The aim of this research was to implement cement-based sensors in monitoring the change of strain in concrete structures in particular where a compression applies. The experiment was conducted in a laboratory by embedding a cement-based sensor in a 150x150x150 mm normal strength concrete cube. When the sensor-installed concrete cube was loaded, the relation between the fractional change in resistivity (FCR) and strain of the sensors was evaluated. In this study, all cement-based sensors were made of cement paste containing carbon fiber at 2% by volume fraction. They were then varied with the addition of graphite powder at 4% and silica fume at 15% by weight of cement. Thus, there were total four mix proportions. From the experimental results, all sensors provided a good corelation between the FCR and compressive strain. Among them, the carbon fiber plus graphite powder (no silica fume) cement-based sensor yielded the most excellent piezoresistive response.

Quantitative indices of baroreflex-sympathoneural function: application to patients with chronic autonomic failure

Chronic autonomic failure syndromes such as Parkinson disease with orthostatic hypotension (PD+OH), multiple system atrophy (MSA), and pure autonomic failure (PAF) typically feature arterial baroreflex failure. Identifying baroreflex-sympathoneural failure from hemodynamic responses to the maneuver usually has been qualitative. We report quantitative methods for evaluating baroreflex-sympathoneural function, based on beat-to-beat systolic blood pressure (BPs) responses to the Valsalva maneuver. Using the trapezoid rule, we calculated the area under the curve (baroreflex area, BRA) between baseline systolic blood pressure (BPs) and the BPs for each beat in Phase II (BRA-II) and Phase IV (BRA-IV) in 136 autonomic failure patients and 171 controls. The sum of the areas was defined as total BRA (BRA-T). We compared individual values by the BRA approach with those by other measures. Mean values for log BRA-II, BRA-IV, and BRA-T were higher in PD+OH, PAF, and MSA than in controls (p<0.001 each). The log of BRA-T correlated negatively with the fractional orthostatic change in total peripheral resistance (r=-0.41, p<0.001), fractional orthostatic change in plasma norepinephrine (r=-0.27, p<0.001), orthostatic change in BPs (r=-0.62, p<0.001), fall in BPs in Phase II of the Valsalva (r=0.58, p<0.001), and log of baroreflex-cardiovagal slope (r=-0.40, p<0.001). Areas under receiver operating characteristic curves were 0.85 for BRA-T and 0.89 for BRA-IV (p<0.001). The BRA approach provides quantitative measures of baroreflex-sympathoneural function. Chronic autonomic failure syndromes entail deficiencies of both the cardiovagal and sympathoneural limbs of the arterial baroreflex.

Heterogeneous metal-oxide nanowire micro-sensor array for gas sensing

Vanadium oxide, manganese oxide, tungsten oxide, and nickel oxide nanowires were investigated for their applicability as chemiresistive gas sensors. Nanowires have excellent surface-to-volume ratios which yield higher sensitivities than bulk materials. Sensing elements consisting of these materials were assembled in an array to create an electronic nose platform. Dielectrophoresis was used to position the nanomaterials onto a microfabricated array of electrodes, which was subsequently mounted onto a leadless chip carrier and printed circuit board for rapid testing. Samples were tested in an enclosed chamber with vapors of acetone, isopropanol, methanol, and aqueous ammonia. The change in resistance of each assembly was measured. Responses varied between nanowire compositions, each demonstrating unique and repeatable responses to different gases; this enabled direct detection of the gases from the ensemble response. Sensitivities were calculated based on the fractional resistance change in a saturated environment and ranged from 6 × 10−4 to 2 × 10−5%change ppm−1.

Effect of Carbon Fiber and Graphite Powder on Resistivity of Cement-based Sensor under Compression

Structural health monitoring currently becomes an important part in the maintenance of concrete structures. Thus, using of sensors to monitor the structural behavior is necessary. Cement-based sensors have been developed recently to be embeddable in structures and to be implemented by measuring the change in their resistivity. In this research, the electrical resistivity and compressive strength of the cement-based sensors with the addition of carbon fiber (2% and 4% by volume fraction) and graphite powder (2%, 4%, and 10% by weight of cement) were studied. Three water to binder ratios (w/b) that are 0.3, 0.4 and 0.5 were varied. For 28 days after demolding, the resistivity of the non-load-bearing sensors was monitored to determine the influence of their maturity. At the age of 28 days, their compressive strength was evaluated. Subsequently, the fractional change in resistivity (FCR) of the sensors was measured under a set of compressive loading, which comprised of three cycles of loading; first loading to the strain of 0.0025, then to 0.005 and 0.01. From the test results, it is showed that the carbon fiber was more favorable than the graphite powder. Although the addition of graphite powder could reduce the resistivity, it dropped the compressive strength and highly fluctuated the resistivity results of the cement-based sensors. In term of the piezoresistivity, all of the sensors when loaded provided good responses only when the compressive strain was less than 0.005.

Micro-Experimentation Research on Compression Sensitivity of Carbon Fiber Concrete

The carbon fiber cement has compression sensibility. In this paper, the compression sensitivity of carbon fiber concrete is analyzed by Scanning Electron Microscopy with single fiber pull-out testing. Results show that the resistance of carbon fiber cement increases during the tensile test, the fractional change in resistance per unit strain of The carbon fiber cement is 38.38±0.05. In the meantime, the variation of resistance of single fiber pull-out under cyclic loading was studied. The resistance change caused by the elastic deformation is reversibility.

Implantable electrolyte conductance-based pressure sensing catheter, I. Modeling

Direct measurements of arterial blood pressure most commonly use bulky external instrumentation containing a pressure transducer connected to an ex vivo fluid-filled arterial line, which is subject to several sensing artifacts. In situ blood pressure sensors, typically solid state piezoresistive, capacitive, and interferometric sensors, are unaffected by these artifacts, but can be expensive to produce and miniaturize. We have developed an alternative approach to blood pressure measurement based on deformation of an elastic tube filled with electrolyte solution. We have constructed an analytical model describing the deformation of a fluid-filled tube part of which is exposed to external pressure, with the remaining part unexposed. The model predicts pressure-induced change in dimension of the internal electrolyte-filled volume and a resultant change in its electrical resistance, which can be measured to determine the pressure and is the basis for the sensor operation. We have applied the model to find the pressure sensitivity of fractional change in resistance as a function of device material and dimensional parameters. Construction and testing of a device is described in the following paper.

Through-thickness piezoresistivity in a carbon fiber polymer-matrix structural composite for electrical-resistance-based through-thickness strain sensing

Piezoresistivity (change of the volume electrical resistivity with strain) in continuous carbon fiber polymer-matrix structural composites allows electrical-resistance-based strain/stress sensing. Uniaxial through-thickness compression is encountered in fastening. As shown for a 24-lamina quasi-isotropic epoxy-matrix composite, compression results in (i) strain-induced reversible decreases in through-thickness and longitudinal volume resistivities, due to increase in the degree of through-thickness fiber–fiber contact, and (ii) minor-damage-induced irreversible changes in these resistivities, due to a microstructural change involving an irreversible through-thickness resistivity increase and an irreversible longitudinal resistivity decrease. The Poisson effect plays a minor role. The effects in the longitudinal resistivity are small compared to those in the through-thickness direction, but longitudinal resistance measurement is more practical. The through-thickness gage factor (reversible fractional change in resistance per unit strain) ranges from 2.6 to 5.1 and the reversible fractional change in through-thickness resistivity per unit through-thickness strain ranges from 1.5 to 4.0, both quantities decreasing with increasing strain magnitude from 0.19% to 0.73% due to the increasing irreversible effect. The irreversible fractional change in through-thickness resistivity per unit through-thickness strain ranges from −1.0 to −1.3 and is strain independent. The effects are consistent with the surface resistance changes previously reported for the same material under flexure.

Nano-carbon black and carbon fiber as conductive materials for the diagnosing of the damage of concrete beam

The nano-carbon black (NCB) and carbon fiber (CF) as electric conductive materials were added into the concrete. The effect of the NCB and CF on the mechanical properties and on the fractional change in resistance (FCR) of concrete was investigated. The relationships among the FCR, the strain of initial geometrical neutral axis (IGNA) and the beam damage degree were developed. The results showed that the relationship between the FCR and IGNA strain can be described by the First Order Exponential Decay function, and the internal damage of concrete beam was reflected by the relationship between damage degree and resistance.

Simultaneous detection of particles and airflow with a MEMS piezoresistive cantilever

This paper describes a particle and airflow sensor using a MEMS piezoresistive cantilever with the dimensions of 250 µm × 200 µm × 0.29 µm. The sensor structure is simple and detects both the airflow velocity and particle collisions by measuring the fractional resistance change due to the cantilever bending. The signals of the airflow velocity and particle collisions can be simultaneously detected by distinguishing continuous and pulse responses. The sensitivity to the airflow velocity was 1.2 × 10−3 (m/s)−1 from 0 to 2.5 m s−1. When a particle of 35 µm diameter (Lycopodium) collided with the cantilever surface, the fractional resistance change varied with the collision. After the collision, reverberation occurred at 3 kHz, which was the same as the resonance frequency of the cantilever. The magnitude of the fractional resistance changes due to particle collision was proportional to the airflow velocity. The sensitivity to particle collision was 2.0 × 10−3 (m/s)−1 when the airflow velocity varied between 0 and 2.5 m s−1.

A Flexible Underwater Pressure Sensor Array Using a Conductive Elastomer Strain Gauge

This paper presents a flexible pressure sensor array which is demonstrated to transduce underwater pressure variations produced by moving objects and surface waves. The sensors exhibit a 0.0014 fractional resistance change per 100 Pa, achieving a high 1.5-Pa pressure resolution. The measurement has a repeatability of 22% of the peak amplitude of the pressure waveform, due to creep. Additionally, sensor operation while bent to a 0.5-m radius of curvature is demonstrated. Each sensor consists of a strain-concentrating polydimethylsiloxane (PDMS) diaphragm and a resistive strain gauge made of a conductive carbon-black-PDMS composite. A 1-D array of four sensors with a 15-mm center-to-center spacing is fabricated, and the dynamic response of the sensors is characterized and modeled.

Effect of Compressive Strain on Electrical Resistivity of Carbon Nanotube Cement-Based Composites

Multi-walled carbon nanotube (MWCNT) fiber reinforced cement-based composites (MWFRC) with 0.1 wt.% and 0.5 wt.% weight concentration of MWCNT (wcM)were prepared, associated with the reference. The electrical resistances and compressive strains of these cured nanocomposites under cyclic uploading/unloading were real-time collected, to explore their stress/strain-sensitive properties. Results reveal as follows, there is no self-sensing trait for the reference, but exists good piezoresisitivity and high strain sensitivity (above 110) for MWFRC; the fractional change in resistivity (Δρ) regularly descends or ascends following the compressive stress, or the longitudinal strain of MWFRC; the resistance caused by pore electrolyte polarization has obvious impact on the time-stability of the Δρ trendline of MWFRC with 0.1 wt.% wcM, similar to the reference, but negligible effect on that of MWFRC with 0.5 wt.% wcM.

Piezoresistivity of carbon fiber graphite cement-based composites with CCCW

The electrical conductivity and piezoresistivity of carbon fiber graphite cement-matrix composites(CFGCC) with carbon fiber content(1% by the weight of cement), graphite powder contents (0%–50% by the weight of cement) and CCCW(cementitious capillary crystalline waterproofing materials, 4% by the weight of cement) were studied. The experimental results showed that the relationship between the resistivity of CFGCC and the concentration of graphite powders had typical features of percolation phenomena. The percolation threshold was about 20%. A clear piezoresistive effect was observed in CFGCC with 1wt% of carbon fibers, 20wt% or 30wt% of graphite powders under uniaxial compressive tests, indicating that this type of smart composites was a promising candidate for strain sensing. The measured gage factor (defined as the fractional change in resistance per unit strain) of CFGCC with graphite content of 20wt% and 30wt% were 37 and 22, respectively. With the addition of CCCW, the mechanical properties of CFGCC were improved, which benefited CFGCC piezoresistivity of stability.