Maximum Resistance Change Research Articles

Design, Construction and Validation of an Electrical Impedance Probe with Contact Force and Temperature Sensors Suitable for in-vivo Measurements

Bioimpedance spectroscopy measurements can be used for tissue characterization. These measurements can be performed in soft tissues by direct contact of a non-invasive probe consisting of two or four electrodes. The amount of force applied by users can be quite different, and the measurements can vary as a result. To compensate for this, we have built an electrical impedance probe (diameter 3.2 mm) with fibre optic contact-force and temperature sensors built in it. The different sensors of the probe were tested individually. The errors in magnitude and phase angle of the probe are <0.9% and <4°, respectively, for a 0.9% NaCl solution. The linear dynamic range of the force sensor was from 0 to 100 grams. An ex-vivo experiment on a section of proximal colon from a guinea-pig was performed. Twenty bioimpedance measurements were taken in a frequency range of 5 kHz to 1 MHz, while simultaneously recording the force applied. For an increase in contact pressure applied to tissue from 0 to 15.4 kPa, the maximum change in resistivity was 33% at 5 kHz and the minimum was 6.6% at 142 kHz. The probe is small enough to be introduced via the instrument port of an endoscope.

Applications of the Kalman Filter to Chemical Sensors for Downstream Machine Learning

Chemical sensors play an important role in a variety of civilian and military domains. In these contexts, the ability to accurately and quickly identify chemical agents is of utmost importance. In practice, constraints on physical footprint, power consumption, ease of use, and time required for accurate detection often restrict the utility of sensors, particularly in remote and isolated regions. One solution to address this problem is the engineering of advanced signal processing techniques, which decrease the time required for accurate detection. This allows software to facilitate the construction of hardware that meet stringent power and concept of operations guidelines. In this paper, we propose the Kalman filter as a preprocessing technique applicable to chemical sensor time series data for downstream machine learning. Using data collected from a sensor array of multiple unique polymer-graphene nanoplatelet coated electrodes, we show accurate and early detection of both organophosphates and interferents is improved when the Kalman filter is used as a preprocessing technique. In particular, within two seconds of analyte exposure to the sensor array, classification using Kalman filtered first derivative estimates achieve an error of less than 10%. By comparison, the non-Kalman filtered data set has a classification error rate above 40% within this time. An advantage of our approach is classification does not depend on a set parameter, such as maximum resistance change, or a pre-determined exposure time, and which allows rapid classification immediately after analyte introduction.

Analysis of the Sensing Properties of a Highly Stable and Reproducible Ozone Gas Sensor Based on Amorphous In-Ga-Zn-O Thin Film.

In this study, the sensing properties of an amorphous indium gallium zinc oxide (a-IGZO) thin film at ozone concentrations from 500 to 5 ppm were investigated. The a-IGZO thin film showed very good reproducibility and stability over three test cycles. The ozone concentration of 60–70 ppb also showed a good response. The resistance change (ΔR) and sensitivity (S) were linearly dependent on the ozone concentration. The response time (T90-res), recovery time (T90-rec), and time constant (τ) showed first-order exponential decay with increasing ozone concentration. The resistance–time curve shows that the maximum resistance change rate (dRg/dt) is proportional to the ozone concentration during the adsorption. The results also show that it is better to sense rapidly and stably at a low ozone concentration using a high light intensity. The ozone concentration can be derived from the resistance change, sensitivity, response time, time constant (τ), and first derivative function of resistance. However, the time of the first derivative function of resistance is shorter than other parameters. The results show that a-IGZO thin films and the first-order differentiation method are promising candidates for use as ozone sensors for practical applications.

Mechanism for detecting NAPL using electrical resistivity imaging

The detection of non-aqueous phase liquid (NAPL) related impacts in freshwater environments by electrical resistivity imaging (ERI) has been clearly demonstrated in field conditions, but the mechanism generating the resistive signature is poorly understood. An electrical barrier mechanism which allows for detecting NAPLs with ERI is tested by developing a theoretical basis for the mechanism, testing the mechanism in a two-dimensional sand tank with ERI, and performing forward modeling of the laboratory experiment. The NAPL barrier theory assumes at low bulk soil NAPL concentrations, thin saturated NAPL barriers can block pore throats and generate a detectable electrically resistive signal. The sand tank experiment utilized a photographic technique to quantify petroleum saturation, and to help determine whether ERI can detect and quantify NAPL across the water table.This experiment demonstrates electrical imaging methods can detect small quantities of NAPL of sufficient thickness in formations. The bulk volume of NAPL is not the controlling variable for the amount of resistivity signal generated. The resistivity signal is primarily due to a zone of high resistivity separate phase liquid blocking current flow through the fully NAPL saturated pores spaces. For the conditions in this tank experiment, NAPL thicknesses of 3.3cm and higher in the formation was the threshold for detectable changes in resistivity of 3% and greater. The maximum change in resistivity due to the presence of NAPL was an increase of 37%. Forward resistivity models of the experiment confirm the barrier mechanism theory for the tank experiment.

Mechanical properties and piezoresistive sensing capabilities of FRP composites incorporating CNT fibers

The present study investigates the mechanical properties and piezoresistive sensing capabilities of glass and carbon fiber-reinforced plastic (GFRP and CFRP) composites incorporating solid state spun-carbon nanotube (CNT) fibers. The FRP composite specimens were fabricated by stacking in layer-by-layer sequence in a resin matrix via vacuum infusion process. The mechanical properties were examined by tensile strength tests, while piezoresistive sensing characteristics were explored by measuring the electrical resistance change during loading. The maximum electrical resistance change rate of CNT fiber-incorporated GFRP composites was 3.15%, corresponding to a value 10 times higher than those obtained in previous studies using wet spinning method for the fabrication of CNT fibers. Moreover, continuous sensing characteristics of the CNT fiber-incorporated GFRP composite subjected to cyclic tensile loadings were verified, thereby assessing the feasibility of CNT fibers in practical applications as a piezoresistive sensor.

Percolation threshold and piezoresistive response of multi-wall carbon nanotube/cement composites

The present work aims to develop piezoresistive sensors of excellent piezoresistive response attributable to change in nanoscale structures of multi-wall carbon nanotube (MWNT) embedded in cement. MWNT was distributed in a cement matrix by means of polymer wrapping method in tandem with the ultrasonication process. DC conductivity of the prepared samples exhibited the electrical percolation behavior and therefore the dispersion method adopted in this study was deemed effective. The integrity of piezoresistive response of the sensors was assessed in terms of stability, the maximum electrical resistance change rate, and sensitivity. A composite sensor with MWNT 0.2 wt.% showed the lowest stability and sensitivity, while the maximum electrical resistance change rate exhibited by this sample was the highest (96 %) among others and even higher than those found in the literature. This observation was presumably attributed by the percolation threshold and the tunneling effect. As a result of the MWNT content (0.2 wt.%) of the sensor being near the percolation threshold (0.25 wt.%), MWNTs were close to each other to trigger tunneling in response of external loading. The sensor with MWNT 0.2 wt.% was able to maintain the repeatable sensing capability while sustaining a vehicular loading on road, demonstrating the feasibility in traffic flow sensing application.

Effect of strain on ferroelectric field effect in strongly correlated oxide Sm0.5Nd0.5NiO3

We report the effect of epitaxial strain on the magnitude and retention of the ferroelectric field effect in high quality PbZr0.3Ti0.7O3 (PZT)/3.8–4.3 nm Sm0.5Nd0.5NiO3 (SNNO) heterostructures grown on (001) LaAlO3 (LAO) and SrTiO3 (STO) substrates. For SNNO on LAO, which exhibits a first-order metal-insulator transition (MIT), switching the polarization of PZT induces a 10 K shift in the transition temperature TMI, with a maximum resistance change between the on and off states of ΔR/Ron ∼75%. In sharp contrast, only up to 5% resistance change has been induced in SNNO on STO, where the MIT is second-order, with the modulation of TMI negligibly small. We also observe thermally activated retention of the off state resistance Roff in both systems, with the activation energy of 22 meV (28 meV) for devices on LAO (STO). The time dynamics and thermal response of the field effect instability points to phonon-assisted interfacial trapping of charged mobile defects, which are attributed to strain induced oxygen vacancies. At room temperature, Roff stabilizes at ∼55% and ∼19% of the initial switching levels for SNNO on LAO and STO, respectively, reflecting the significantly different oxygen vacancy densities in these two systems. Our results reveal the critical role of strain in engineering and modeling the complex oxide composite structures for nanoelectronic and spintronic applications.

Directly correlating the strain-induced electronic property change to the chirality of individual single-walled and few-walled carbon nanotubes.

We fabricate carbon nanotube (CNT)-field effect transistors (FETs) with a changeable channel length and investigate the electron transport properties of single-walled, double-walled and triple-walled CNTs under uniaxial strain. In particular, we characterize the atomic structure of the same CNTs in the devices by transmission electron microscopy and correlate the strain-induced electronic property change to the chirality of the CNTs. Both the off-state resistance and on-state resistance are observed to change with the axial strain following an exponential function. The strain-induced band gap change obtained from the maximum resistance change in the transfer curve of the ambipolar FETs is quantitatively compared with the previous theoretical prediction and our DFTB calculation from the chirality of the CNTs. Although following the same trend, the experimentally obtained strain-induced band gap change is obviously larger (57%-170% larger) than the theoretical results for all the six CNTs, indicating that more work is needed to fully understand the strain-induced electronic property change of CNTs.

Correlating Electrical Resistance Change with Mechanical Damage in Woven SiC/SiC Composites: Experiment and Modeling

Silicon carbide (SiC) fiber‐reinforced SiC matrix composites are inherently multifunctional materials. In addition to their primary function as a structural material, the electric properties of the SiC/SiC composites could be used for the sensing and monitoring of in situ damage nucleation and evolution. To detect damage and use that information to further predict the useful life of a particular component, it is necessary to establish the relationship between damage and electrical resistance change. Here, two typical SiC/SiC composites, melt infiltrated (MI), and chemical vapor infiltrated (CVI) woven SiC/SiC composites, were tested to establish the relationship between the electrical response and mechanical damage in unload–reload tensile hysteresis tests. Compared to the 55% resistance increase seen for CVI composites, the MI SiC/SiC composites exhibit a maximum resistance change in 450% in response to mechanical loading (damage), which is the highest sensitivity known among various composites. An analytic model accounting for fiber breakage and matrix cracks was developed to link the electrical resistance to mechanical damage in the composites. The predictions from the models agree well with the experimental data for both composites with high and low conductive matrices. The residual resistance change after unloading is also correlated to the loading history by the analytical relationship. This study demonstrates that resistance change is sensitive to damage in a predictable manner and can be used to improve the reliability of damage assessment of SiC/SiC composites.

Magnetoimpedance effects in a CoNiFe nanowire array

This report describes the growth of CoNiFe nanowires into highly ordered porous anodic alumina oxide (AAO) templates by DC electrodeposition at a pH value of 2.6. Scanning electron microscopy (SEM) observations revealed that the wires have diameters of approximately 270–290nm and a length of 25μm. The energy dispersive X-ray (EDX) analysis indicated that the composition of the nanowires is Co12Ni64Fe24. Electrical contacts were created on both sides of the nanowire array, and their magnetoimpedance (MI) properties were investigated. The impedance value was initially 1.2ohm at low frequency and increased to approximately 1000ohm for a 33-MHz driving current frequency under no applied magnetic field. All the MI curves exhibited single peak behaviour due to the high shape anisotropy. The maximum MI change at the 33-MHz driving current frequency was 2.72%. The maximum resistance change was 5.4% at 33MHz.

Crack prevention of highly bent metal thin films in woven electronic textiles

Recent smart textile fabrication methods that are aimed at increasing the integration of electronics with textiles have involved fabricating micro-electronic components directly at the yarn level. Our approach to creating smart textiles is to fabricate thin-film devices and interconnects on plastic strips to create ‘e-fibers’ and weave them into a textile using a commercial weaving machine. e-Fibers are exposed to bending radii as small as 165 μ m during weaving. If patterned interconnect lines and device layers on the surface of the e-fiber are not designed correctly, they will crack due to the high strain and lose their electronic functionality. Brittle sensor and transistor device layers may be protected locally using rigid encapsulation materials, but cracking remains an issue for long metal interconnect lines which require flexibility. We investigated two strain-control methods to prevent the thin-film interconnect lines from cracking during weaving: (1) patterning the metal interconnect lines with a geometric design to slow propagation and merging of cracks and (2) encapsulation of interconnect lines to shift the deposited films to the neutral plain of the substrate. The mechanical behavior of interconnect lines exposed to tensile bending was studied by measuring the change in interconnect resistance versus bending radii ranging from 5 mm to 50 μ m. The critical bending radius, X C , defined as the radius at which the normalized interconnect resistance changes to 1.1 (indicating the onset of film rupturing) was 150 μ m for standard interconnect lines. Patterned interconnect lines had a radius X C of 115 μ m while encapsulated interconnect lines never reached this critical bending radius and showed a maximum resistance change of 1.02 at 100 μ m. These results show that it is possible to design interconnect lines with reduced cracking behavior when exposed to high strain during commercial weaving.

Inkjet-printed stretchable silver electrode on wave structured elastomeric substrate

We report high performance and stable inkjet-printed stretchable silver electrodes on wave structured elastomeric substrates. Highly conductive silver electrodes were deposited directly on a ultraviolet ozone treated polydimethylsiloxane (PDMS) substrates having vertical wavy structures. Adhesion between printed silver lines and PDMS surface has been enhanced by intentionally roughened PDMS surface with wire-electro discharge machined aluminum mold. During slow (16.7 μm/s) stretching test, resistance of the printed silver electrode was increased only by three times at 30% tensile strain. Inkjet-printed silver electrodes also showed good mechanical stability during 1000-time fast (1 mm/s) cycling test with 10% tensile strain, showing maximum resistance change of less than three times.

Vapor sensing properties of thermoplastic polyurethane multifilament covered with carbon nanotube networks

The volatile organic compound (VOC) vapor sensing properties of a novel kind of thermoplastic polyurethane multifilament – carbon nanotubes (TPU–CNTs) composites is studied. And the sensing is based on changes in the electrical resistance of the composites due to vapor contact. The composites were readily obtained by adhering CNTs on the surface layer of TPU by means of simply immersing pure TPU multifilament into CNT dispersion. The uniformly formed nanotube networks on the outer layer of composite multifilament are favorable for providing efficient conductive pathways. The resulting TPU–CNTs composites show good reproducibility and fast response (within seconds) of electrical resistance change in cyclic exposure to diluted VOC and pure dry air. The vapor sensing behaviors of the composites are related to CNT content, vapor concentration, and polar solubility parameters of the target vapors. A relatively low vapor concentration of 0.5% is detectable, and a maximum relative resistance change of 900% is obtained for the composite with 0.8 wt.% CNT loading when sensing 7.0% chloroform. It is proposed that both the disconnection of CNT networks caused by swelling effects of the TPU matrix and the adsorption of VOC molecules on the CNTs are responsible for the vapor sensing behavior of TPU–CNTs composite, while the former effect plays the major role.

Design and Characterization of Microelectromechanical System Flow Sensors Using Silicon Nanowires

Cantilever structures were reported to be used for flow sensing purposes. Herein, we present silicon nanowire (SiNW) based cantilever flow sensor. Five cantilever flow sensors with different depths are modeled and simulated (fluid-structure) with water flow velocity from 50 cm/s to 200 cm/s. SiNW is embedded in the cantilever as piezoresistive transducer at the anchor, and a maximum resistance change of 11.2% is obtained. Based on the results, increasing depth will not only contributes to lager cantilever deformation at fixed flow velocity, but also improves its sensitivity. However when the depth become larger to certain degree, this effect tends to saturate.

Photoinduced resistivity change of electron-doped La0.8Te0.2MnO3 film

In this paper, electron-doped La0.8Te0.2MnO3 film has been prepared on SrTiO3 (100) substrate by pulsed laser deposition method, and the photoinduced resistivity change and colossal magnetoresistance effect have been investigated. The results show that the film has a high metal-insulator transition temperature TMI of ∼283 K and the maximum magnetoresistance ratio is ∼24% at 0.7 T. Under laser irradiation, TMI varies from 283 to 243 K and resistivity increases below TMI, while it decreases above TMI. The maximum photoinduced resistivity change in resistivity (LR%) is 134.8%. The photoinduced relaxation character of the film indicates that the relaxation of photoinduced character relates to the excitation of small polarons.

A piezoresistive cantilever integrating an InAs-based semiconductor–superconductor junction

Targeting highly sensitive displacement and force sensors, we fabricated a piezoresistive cantilever that integrates a superconductor–semiconductor–superconductor (S–Sm–S) junction based on an InAs/AlGaSb heterostructure. The S–Sm–S junction is composed of a submicron Nb gap patterned on the InAs thin film, and a deflection of the cantilever is detected as a resistance change at the junction. We confirmed that the resistance change caused by induced strain (i.e., piezoresistance) has a strong dependence on bias current. When the maximum Josephson current ( I c ) is biased to the junction, the resistance change is significantly enhanced by more than a factor of 10 compared to that at the bias current above I c (the resistive state). The resulting maximum resistance change is 3.9 m Ω , which is three orders of magnitude larger than that obtained for our preliminary sample. This large piezoresistance at the S–Sm–S junction will lead to highly sensitive self-detective sensors.

The influence of temperature and dielectric materials on stress induced voiding in Cu dual damascene interconnects

In this work, package level stress migration test of Cu dual-damascene interconnects in via-line structures was performed. The effects of stressing temperature and dielectric materials on SIV behavior were investigated. The via-line structures were studied at temperatures ranging from 150 to 250 °C, with highest failure rate being detected at 200 °C. In comparing stress migration data on carbon doped oxide (CDO) with undoped silica glass (USG), a difference of two orders of magnitude was detected in the rate of change of resistance. About 40% of the CDO samples showed open circuit failures after a 1344-h test, whereas the maximum resistance change in the USG samples was only 10%. Failure analysis indicated that failures in both CDO and USG were very similar in nature. In both cases, voids formed symmetrically at the bottom of the via, showing that the integrity of the Ta barrier in the via bottom area was of significant influence to stress induced voiding. Finite element analysis (FEA) indicated that the driving force for void growth, the gradient of hydrostatic stress, at via bottom in CDO structure is 30% higher than the one in USG. Besides the stress gradient, other factors that could affect SIV behaviour are the back stress and interface adhesion. Similar to the case of electromigration, back stress might be generated during stress migration, provided that the interface between the Cu line and the surrounding dielectric material is strong. Back stress reverses the trend of migration of atoms. Discussion and comparison of all these factors are made between the two types of dielectrics in order to explain the observed higher failure rate of stress-induced-voiding in CDO structures.

Simulation of SiO 2-based piezoresistive microcantilevers

This article uses finite element design for optimization of piezoresistive Si covered SiO 2 microcantilevers. The maximum resistance changes were systematically investigated by varying piezoresistor geometries and doping concentration. Our simulation results show that both cantilever deflection displacement and Δ R/ R change decrease when the thickness of piezoresistors increases; the highest sensitivity can be obtained when the piezoresistor length is approximately 2/5 of the SiO 2 cantilever length; increase of both Si width and leg width result in decrease in cantilever deflection and sensitivity; the sensitivity of cantilevers with lower doping concentrations is more significant than those with higher doping concentrations. Temperature control is critical for thin piezoresistor in lowering the S/N ratio and increasing the sensitivity.

Mixed-ligand nanoparticles of chlorobenzenemethanethiol and n-octanethiol as chemical sensors

A series of mixed-ligand gold nanoparticles were synthesized, characterized and used to form transducer films to investigate and enhance vapor-sensing properties. Chlorobenzenemethanethiol (CBMT) nanoparticle, prepared using a two-phase method, was used for place-exchange reactions with a varying amount of n-octanethiol (OT) to produce a series of mixed-ligand gold nanoparticles (Au_CBMT-OT-1, Au_CBMT-OT-2, and Au_CBMT-OT-3). The nanoclusters were characterized by 1 H NMR spectroscopy, thermal gravimetric analysis (TGA), and transmission electron microscopy (TEM). Thin film transducers of the monolayer-protected nanoparticles were formed through a dip-coating procedure on glass substrates mounted with interdigitated gold electrodes. SEM analysis indicated that mostly the surfaces of the sensors films were smooth. Nanoparticle sensors experienced repeated cycles of analyte vapors and blank air gas as the analyte concentrations were varied. Mostly the nanoparticle sensors produced rapid and reversible responses toward the vapors of 1-propanol, acetone and cyclohexane. Linear relationship between maximum resistance changes and vapor concentrations were observed. Above all the variations in compositions of the ligand molecules (CBMT and OT) resulted in differences in signal amplitudes.

Electrical Conductivity and Vapor-Sensing Properties of ω-(3-Thienyl)alkanethiol-Protected Gold Nanoparticle Films

Gold nanoparticles protected with thiophene-terminated alkanethiols having different alkane chain lengths have been synthesized, and vapor-sensing properties of their spin-coated films have been investigated. Transmission electron microscopy and measurement of the sulfur and gold peak areas of the films by X-ray photoelectron spectroscopy indicate gold core diameters in the 3−5-nm range. Exposure of the films to chloroform, toluene, hexane, and ethanol vapors results in significant and selective increases in electrical resistance, with the response to the vapors having the following order: toluene > chloroform > hexane ≫ ethanol. The magnitude of the maximum resistance change correlates well with solubility properties of the protected gold nanoparticles, as determined by optical absorbance spectroscopy and the energy of the gold plasmon. The detection sensitivity of the films increases with increasing alkanethiol chain length. These data are consistent with a sensing mechanism in which organic vapors cau...