Wheatstone Bridge Configuration Research Articles

Neutronic analysis for bolometers in ITER

Neutronic considerations in ITER have such importance that they drive the design of many diagnostics and components of the machine, and bolometers are not an exception. Bolometer cameras will be installed on the vacuum vessel, viewing the plasma through the gaps between blanket modules, divertor, equatorial and upper port plugs. The ITER reference bolometer sensors are of a resistive type. For this study it is assumed that they are composed of a thin silicon nitride carrier film and platinum resistors disposed in a Wheatstone bridge configuration. Their assumed radiation hardness is 0.1dpa.Neutronic calculations were performed with the Monte Carlo program MCNP5, the FENDL 2.1 nuclear data library and the latest B-lite ITER neutronic model with the appropriate modifications using the CAD to MCNP converter MCAM. A complete characterization of the neutron fluxes in all the bolometer locations and the calculation of neutron damage were performed. Values above the failure threshold damage were obtained for some of the bolometers, leading to a complete redesign of some parts of the bolometric system in order to extend its lifetime.

High Sensitivity Microbridge for Molecular Sensing Applications

This paper presents the design and simulation of a SiO2 microbridge which measures the differential surface stress induced by the adsorption of molecules. Materials with smaller Young's modulus would be appropriate to measure the small variation of surface stress on the microbridge and therefore SiO2 is chosen as the material for microbridge. The SiO2 microbridge could be a potential application for the glucose detection if the enzyme glucose oxidase was immobilized on a top surface. The microbridge can be constructed on Silicon on insulator (SOI) substrate using the bulk micromachining technology. The surface stress causes displacement which is measured using the piezoresistors placed on top surface of the microbridge. The piezoresistors are arranged in a Wheatstone bridge configuration to measure the change resistance in terms of voltage. The two piezoresistors are placed at the edges where they experience the maximum stress. The obtained sensitivity, ΔR/R of SiO2 microbridge is 6.15x10-4 which is four times higher than that of existing work [1]. The mechanical behavior of the SiO2 microbridge and the electrical response of the piezoresistors are analyzed using the Finite Element Method (FEM). The dimensions for the microbridge are optimized by considering both the sensitivity and nonlinearity with respect to the deflection. The placement location of the piezoresistors and the effect of geometrical parameters of the piezoresistors on the sensitivity SiO2 microbridge are studied.

Load Cell Application in Rocket Thrust Measurement System

A load cell is an important component in measuring thrust generated by rocket in rocket technology research and development. It aims to test the rocket thrust in achieving the targeted objectives of the project. A load cell is a transducer that is used to convert a force into electrical signal and it usually consists of four strain gauges assembled in Wheatstone bridge configuration. The strain gauge converts the deformation (strain) to electrical signals. This conversion occurs in two stages. First, the strain gauges on the load cell will detect the deformation of load cell structure (tension or compression) and second, the strain gauge will convert the changes in the load cell in terms of voltage readings. Before the load cell can be used as the thrust sensor in rocket testing, it must undergo a calibration process to determine the relation between Load (kg) and Voltage (V). LabVIEW is used as a platform for data logging interface which is connected to the National Instrument hardware. National Instrument hardware acts as a signal conditioning which allow the voltage readings acquired by load cell to be collected and analyzed by LabVIEW. Each load cell has its own equation that links between force and voltage. The equation is used as a reference to convert the voltage reading to thrust.

An adsorption-based mercury sensor with continuous readout

A novel readout procedure for a mercury sensor has been proposed. The sensor is based on the surface adsorption. Mercury vapor is adsorbed at the surface of a thin gold layer patterned into four meanders which are connected into a Wheatstone bridge configuration. Sensing is achieved by the resistivity change of the gold film during mercury adsorption. Direct output from the sensor is electric voltage. It takes an additional procedure to convert voltage to mercury concentration. This type of sensor is improved by introducing continuous readout procedure for the voltage–concentration conversion. By using this readout procedure it is possible to monitor mercury vapor concentration as a function of time. Readout is based on the Langmuir time–dependent adsorption theory. This paper illustrates a practical implementation of the new readout procedure.

Design-dependent gauge factors of highly doped n-type 4H-SiC piezoresistors

This paper presents the experimentally obtained gauge factor (GF) of 4H-SiC piezoresistors, fabricated out of the n-type epitaxial layer and characterized on millimeter-size SiC cantilever beams at room temperature. It was found that the GF is dependent on the piezoresistor's length and width. Piezoresistors narrower than approximately 30 µm showed a width-dependent GF. The highest GF of 20.8 was obtained with a single element piezoresistor in transverse orientation. In longitudinal orientation, the highest GF was −10, which was obtained with a clustered piezoresistor with plural identical elements. Essential factors to consider for the design of optimum 4H-SiC piezoresistors for a Wheatstone bridge configuration are presented.

Thick film resistors on stainless steel as sensing elements for strain sensor applications

In this paper, thick film resistors (TFRs, R8241, Heraeus) on 430 stainless steel (SS) substrate for strain sensor applications are investigated. TFRs are screen printed and fired on dielectrics-on-430SS substrate by thick film technology. Microstructure analysis shows that no interaction or evidence for new phase can be detected at the interface between TFRs and dielectrics-on-430SS, which indicates the compatibility of the dielectrics and TFRs. Further experiments also show the excellent insulativity and robust bonding between the dielectrics layer and 430SS substrate. Meanwhile, temperature coefficients of resistivity (TCRs), gauge factors (GFs) and noise indices (NI) of TFRs are measured. Finally, thick film technology based steel pressure sensors (SPS) are fabricated by screen printing and firing four TFRs on a machined circular diaphragm and then the TFRs are connected in a Wheatstone bridge configuration. Preliminary tests show that the sensors exhibit a sensitivity of 4.68mV/V full-scale (FS) with 0.1% FS linearity and 0.15% FS hysteresis and 0.15% FS repeatability. Moreover, the thermal zero drifts and thermal sensitivity drifts of the sensors in the whole temperature range (−40°C to +125°C) are less than 2.5% FS.

Piezoresistive Strain Sensors and Multiplexed Arrays Using Assemblies of Single-Crystalline Silicon Nanoribbons on Plastic Substrates

This paper describes the fabrication and properties of flexible strain sensors that use thin ribbons of single-crystalline silicon on plastic substrates. The devices exhibit gauge factors of 43, measured by applying uniaxial tensile strain, with good repeatability and agreement with expectation based on finite-element modeling and literature values for the piezoresistivity of silicon. Using Wheatstone bridge configurations integrated with multiplexing diodes, these devices can be integrated into large-area arrays for strain mapping. High sensitivity and good stability suggest promise for the various sensing applications.

Nanocrystalline Piezoresistive Polysilicon Film by Aluminum-Induced Crystallization for Pressure-Sensing Applications

Nanocrystalline piezoresistive polysilicon films were obtained at low temperatures by aluminum-induced crystallization (AIC). The films exhibited granular structure with good polycrystalline properties. A piezoresistive pressure sensor was fabricated on a polyimide substrate, in a Wheatstone bridge configuration comprising two passive resistors and two active piezoresistors made of polysilicon films obtained by AIC. The resistors showed linear I-V characteristics with typical resistance values between 15 and 30 kΩ . Atomic force microscopy was used in contact mode to study the response of the pressure sensor with applied pressure in the 2-19 kPa range. For the higher range of 450 kPa-2 MPa, a load-cell with a nanopositioner was utilized. The pressure-sensor sensitivity was measured to be 41.12 and 5.02 mV/MPa, respectively, for these ranges, when the Wheatstone bridge was bias at 1 V.

Fabrication of a Wheatstone-Bridge Integrated SU-8 Cantilever

We describe the design and fabrication of an SU-8 cantilever with an integrated Wheatstone-bridge configuration. A photolithographic process of SU-8 on an anisotropically wet-etched Si substrate is used to produce reliable sharp tips. Changes in the surface stress on the cantilever are detected by an integrated Au piezoresistor. Preliminary results of the measurement are presented for cantilever evaluation. The fabricated SU-8 cantilever has a resonance frequency of about 4.5 kHz, which yields a spring constant of approximately 0.15 N/m. These cantilevers are very suitable for the nondestructive atomic force microscope (AFM) analysis of fragile biological samples, such as cells and body fluids.

A new device for fretting fatigue testing

Fretting fatigue damage occurs in contacting parts when they are subjected to fluctuating loads and sliding movements at the same time. Fretting fatigue can reduce the fatigue life of materials by half or even more. Fretting fatigue tests are usually performed using universal hydraulic testing devices. The contact pressure is produced by a fixture, typically designed and manufactured by researchers. In this investigation, a new device is introduced in which the fluctuating loading is supplied by a variable crank system (VCSD). The device called VCSD for abbreviation is basically a position control machine in which displacements can be imposed with an accuracy of 0.01 mm. The axial and contact loads are measured by load cells. The friction load is also measured by using foil strain gauges using a Wheatstone bridge configuration. The functionality of the device is examined by making a comparison between fretting fatigue lives of a number of Al7075-T6 specimens tested on a universal testing machine and VCSD. The results show a very close agreement between the functionality of the two testing rigs. The main advantages of VCSD are its higher frequency with respect to universal devices, simplicity, and cheapness. It can be developed further for high and low temperature tests in future.

Instrumentation system for improvement of temperature sensor performance

The semiconductor resistances known as thermistors have more advantages compared with all other temperature transducers. Unfortunately, the non-linear characteristics, lower sensitivity for the higher temperature range of measurement and the self-heating effect of thermistors are some of their disadvantages that are limiting their application. As a result of some intensive research on improvement of the measurement and instrumentation techniques with thermistors, an electronic circuit is developed that is reducing considerably the thermistor non-linearity, its self-heating effect and is increasing its sensitivity in a wider temperature range of measurements and control. The circuit involves a set of thermistors, connected in a specific Wheatstone-bridge configuration. Analysis of the circuit and testing it in real environment proves its effectiveness in improvement the performance of this temperature sensor equipment. Keywords: Sensors, Transducers, Thermistors, Characteristics, Stable, Linearity, Self-heating, Sensitivity, Range, Measurement, Wheatstone bridge

Pentacene-Based Low-Voltage Strain Sensors With PVP/$ \hbox{Ta}_{2}\hbox{O}_{5}$ Hybrid Gate Dielectrics

Field-controllable pentacene-semiconductor-based strain sensors were fabricated with hybrid gate dielectrics using polyvinyl phenol (PVP) and high-k inorganic tantalum pentoxide (Ta2O5) onto polyethylene naphthalate films. The Ta2O5 gate-dielectric layer combined with a thin PVP layer to form very smooth and hydrophobic surfaces turns out to improve the molecular structures of pentacene films significantly. The PVP-Ta2O5 hybrid-gate-dielectric films exhibit a high dielectric constant of 19.27 and a leakage-current density of as low as 100 nA/cm2 . The sensors employing a thin-film-transistor-like Wheatstone bridge configuration able to operate at reduced voltage (~ 4 V) show good device characteristics with a field-effect mobility of 1.89 cm2/V · s and a threshold voltage of -0.5 V. The strain sensor characterized with bending at 45° with respect to the bridge bias direction with different bending radii of 50-, 40-, 30-, 20-, and 8-mm displays output signals improved in linearity in a low range of operating voltages.

Optimisation of surface passivation for highly reliable angular AMR sensors

AbstractFor state‐of‐the‐art angular sensors based on the anisotropic magnetoresistive (AMR) effect in NiFe layers, the angular accuracy over time is limited by a drift of the offset voltage of the Wheatstone bridge configuration. It is shown that the interaction of the passivation layer and the magnetic permalloy is crucial for the drift of the offset voltage. By investigating the time and temperature dependence, the offset drift is attributed to stress relief of the PECVD passivation layer due to microstructural changes. Hydrogen outdiffusion from the passivation layer is involved in the observed stress evolution. It is demonstrated that optimising the passivation layer composition as well as the time of the subsequent annealing is beneficial for stress stabilisation of the permalloy‐passivation layer system. With this optimised passivation layer a significant offset drift reduction of the NiFe Wheatstone bridge has been achieved resulting in highly accurate and long‐term stable angular AMR sensors. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Force sensor clip for orthopedic applications

A force sensor clip for the measurement of forces with orthopedic instruments is presented. The clip can be attached to different orthopedic instruments and be removed after use for sterilization. It consists of an elastically deformable metal body made from titanium alloy and a strain gauge foil. Four strain gauges in a Wheatstone bridge configuration were fabricated on a single polyimide foil and assembled to the clip. In a test setup the sensor shows a linear response with respect to the bending of the clip with good sensitivity.

Phase-preserving amplification near the quantum limit with a Josephson ring modulator

Recent progress in solid-state quantum information processing has stimulated the search for amplifiers and frequency converters with quantum-limited performance in the microwave range. Depending on the gain applied to the quadratures of a single spatial and temporal mode of the electromagnetic field, linear amplifiers can be classified into two categories (phase sensitive and phase preserving) with fundamentally different noise properties. Phase-sensitive amplifiers use squeezing to reduce the quantum noise, but are useful only in cases in which a reference phase is attached to the signal, such as in homodyne detection. A phase-preserving amplifier would be preferable in many applications, but such devices have not been available until now. Here we experimentally realize a proposal for an intrinsically phase-preserving, superconducting parametric amplifier of non-degenerate type. It is based on a Josephson ring modulator, which consists of four Josephson junctions in a Wheatstone bridge configuration. The device symmetry greatly enhances the purity of the amplification process and simplifies both its operation and its analysis. The measured characteristics of the amplifier in terms of gain and bandwidth are in good agreement with analytical predictions. Using a newly developed noise source, we show that the upper bound on the total system noise of our device under real operating conditions is three times the quantum limit. We foresee applications in the area of quantum analog signal processing, such as quantum non-demolition single-shot readout of qubits, quantum feedback and the production of entangled microwave signal pairs.

Sensitivity improvement of a microcantilever based mass sensor

This article describes two approaches for sensitivity improvement of a micromachined silicon T-shaped cantilever resonator for mass sensing applications. In order to increase sensitivity values, higher order resonance mode was used and device dimensions were reduced. The cantilevers proposed are piezoelectrically actuated and the movement detection is done by four piezoresistors in a Wheatstone bridge configuration. Two types of cantilevers were fabricated: for the first cantilever of 400 μm long, 300 μm wide and 15 μm thick, the fundamental and second resonance frequency in air were 100 kHz ± 0.4 and 690 kHz ± 15, respectively, both with a quality factor of ∼800. And for the second cantilever of 200 μm long, 150 μm wide, 15 μm thick, the fundamental resonance frequency in air was 400 kHz ± 5 with a quality factor of ∼900. The devices were characterized attaching microspheres of polystyrene to the cantilever’s surface tip and measuring resonance frequency changes. For the first cantilever sensitivity values of 0.07 and 0.3 Hz/pg for the fundamental and second mode, respectively were achieved and 1.3 Hz/pg for the second cantilever. These results show the great potential for high sensitive mass sensor of this simple device.

The Dispersivity of Multi-Walled Carbon Nanotubes (NMWTs) and Pressure-Sensitive Property of NMWTs Reinforced Cement Composite

The individual and/or combinatory impacts of two surfactants (polyoxyethylene nonyl phenyl ether 10 (Tx-100), Arabic gum powder (AG)) on the dispersivity of multi-wall carbon nanotubes (NMWTs) were firstly investigated and evaluated through naked and microstructures observation; hereafter, NMWTs with 1.0% loading were firstly dispersed in aqueous solution with surfactant ultrasonic dispersion process, and cast-mixed into cement matrix to fabricate 2 groups NMWTs reinforced cement composites (NMTRCs), associated with the plain reference. Wheatstone bridge configurations were simultaneously employed to obtain the resistances and the monoaxial stresses, to investigate the pressure-sensitive properties of these nanocomposites. Results with naked observation reveal that either Tx-100 or AG at some concentration has good dispersion effect on NMWTs, the blackness homogeneity and stability of NMWTs suspended solution could retain more than 15 d; yet microstructures results show that NMTRC with AG has more homogeneous dispersion impact and more compatible with cement hydration than that with Tx-100. Results related on the pressure-sensitive properties of NMTRCs demonstrate that, the fractional change in resistivity of NMTRC with AG linearly falls down by increment of applied pressure within elastic range, this good pressure-sensitive traits mainly contribute to the increasing chance of physical contacts, the denser of current chargers between NMWTs, and the shortened trend of the potential barrier widths between NMWTs and matrix by increment of pressure, after efficient dispersion with AG. Yet that of NMTRC with Tx-100 has not good linearity descending trend, but some exaggerate fluctuations, and that of the reference has also no any regular descending trend.

Symmetrical PolyMUMPs-Based Piezoresistive Microcantilever Sensors With On-Chip Temperature Compensation for Microfluidics Applications

Microelectromechanical systems (MEMS)-based cantilever beam sensors for microfluidics applications with on-chip temperature sensors for temperature drift compensation were developed. The stress induced on gold surface with polysilicon piezoresistive sensing is demonstrated. In principle, adsorption of biochemical species on a functionalized surface of the microfabricated cantilever will cause surface stress and, consequently, cantilever bending. The sensing mechanism relies on the piezoresistive properties of the doped polysilicon wire encapsulated in the beam. The beam is constructed through multiusers MEMS Process (PolyMUMPs) foundry with postprocessing silicon etching. Bending analysis is performed so that the beam tip deflection can be predicted. The piezoresistor designs on the beams were varied, within certain constraints, so that the sensitivity of the sensing technique could be measured by external read-out circuit. The mass detection of 0.0058-0.0110 g is measured by the beam resistor series as a balanced Wheatstone bridge configuration. The voltage output of the bridge is directly proportional to the amount of bending in the MEMS cantilever. The temperature dependency and sensor performance have been characterized in experiments. Compensation by resisters on the substrate significantly reduces the temperature dependence.

Angular magnetic field sensor for automotive applications based on magnetic tunnel junctions using a current loop layout configuration

An angular magnetic field sensor for automotive applications based on magnetic tunnel junctions has been designed. Using magnetic tunnel junctions, the power consumption has been reduced by a factor of 1000 with respect to the one based on Hall sensors and the working distance has been increased. The standard Wheatstone bridge configuration is replaced by an electrical circuit based on a current loop layout. Using this configuration, the balancing of resistance is not necessary as for a Wheatstone bridge that can be a bottleneck when using magnetic tunnel junctions. The field to be measured is produced by a multipolar magnetic seal integrated in a wheel bearing. To obtain an angular sensor, four blocks of tunnel junctions in series have been used and with an appropriate sensor design, the two signals with a 90° phase shift required for an high accuracy angular measurement have been obtained.

Fabrication and evaluation of a thermal sensor formed on a thin photosensitive epoxy membrane with low thermal conductivity

This article present the fabrication and development of a thin metal film bolometer IR detector connected in a Wheatstone bridge configuration. The bolometer is constructed on a 4 μm thin self-supported SU-8 2002 membrane. A polymer material such as SU-8 has low thermal conductivity and is applied using standard photolithographic processing step, and this could increase detector sensitivity and lower the production cost. Thermal simulation results are presented, which verifies SU-8 as a better choice of materials compared to common membrane materials such as Si and Silicon nitride. Measurements on the fabricated nickel resistance bolometer on SU-8 2002 membrane show a sensitivity of 9.3 V/W when radiated by an IR laser with a wavelength of 1.56 μm.