Showing papers on "Gauge factor published in 1996"

Piezoresistive effect in wurtzite n‐type GaN

Abstract: We report on the measurements of the piezoresistive effect in the n‐type wurtzite GaN films. The 3–5 μm thick GaN layers were deposited slightly off axis over basal plane sapphire substrates. The static and dynamic gauge factor (GF) of these structures was measured at room temperature for both longitudinal and transverse configurations. The dynamic effect is related to a strong piezoeffect in GaN. The maximum dynamic GF observed was ∼130 (approximately four times larger than for SiC).

Continuous carbon fibre epoxy-matrix composite as a sensor of its own strain

Abstract: Unidirectional continuous carbon fibre reinforced epoxy was found to be able to sense its own strain in the fibre direction, due to its longitudinal electrical resistance decreasing reversibly and its transverse resistance increasing reversibly upon longitudinal tension. The strain sensitivity (gauge factor) is from -35.7 to -37.6 and from +34.2 to +48.7 for the longitudinal and transverse resistances respectively. Both effects originate from resistivity changes associated with the increase in the degree of fibre alignment upon longitudinal tension. Either effect allows strain sensing. Slight irreversibility is associated with the resistance decreasing after the first strain cycle and stems from the decrease in the degree of neatness of the fibre arrangement.

A laterally driven micromachined resonant pressure sensor

Abstract: A new type of resonant pressure sensor is presented which employs a laterally driven resonant strain gauge. The resonant strain gauge is designed using simple linear elastic theory and the sensor fabricated by a combination of bulk- and surface-micromachining techniques. The strain gauge is driven electrostatically and the resultant vibration sensed capacitively. Its lateral mode of oscillation offers several advantages, such as a Q-factor insensitive to the leakage of cavity gases. The resonator has been designed to have a fundamental frequency of 52 kHz and a gauge factor of 60 Hz μN−1. Preliminary measurements of devices yield a fundamental frequency of 52 ± 15 kHz, a Q-factor in air of 50 and a pressure sensitivity of 8.8 kHz bar−1.

A dual-heater gauge for measuring sap flow with an improved heat-balance method

Abstract: Measurements of sap flow in intact plant stems help quantify biophysical relationships governing water transport in the soil-crop-atmosphere continuum. Research was conducted to develop and test a dual-heater sap low gauge based on an improved heat-balance theory. The dual-heater gauge contains two resistance heaters that, when operated in variable power mode, allow mathematical manipulation of the heat balances, so no empirical calibration or zero set is necessary (i.e., no gauge factor). Prototype dual-heater gauges were fabricated and tested on container-grown corn (Zea mays L.) with stem diameters between 25 and 30 mm. Traditional single-heater heat-balance gauges were also built and tested to compare the two designs. Gauges were tested simultaneously in a greenhouse over a continuous 5-d drying cycle when flows ranged from 0 to 140 g h -1 and daily water use ranged from 137 to 1064 g d -1 . Both gauge types measured hourly sap flow to within ±10% relative to gravimetric estimates of transpiration. The dual- and single-heater gauges measured cumulative sap flow over the 5-d test period to within 4.0 and 9.5%, respectively. The largest errors in daily sap flow, 34%, occurred in the single-heater gauge when the plants were subjected to water stress. The dual-heater approach could measure sap flow without predetermined or empirically derived calibration factors or zero sets. Accurate measurements of sap flow were obtained 15 min after the gauge was attached to the plant stem. Additionally, the dual-heater gauge was easier to build, consumed less power, and caused less stem heating than the single-heater gauge.

Electrical and piezoresistive characterization of boron-doped LPCVD polycrystalline silicon under rapid thermal annealing

Abstract: Rapid thermal annealing (RTA) has been performed on boron-implanted LPCVD polysilicon films for doses ranging from 2 × 1014 to 4 × 1015 cm−2. We have investigated the piezoresistance through gauge-factor measurements in the scope of pressure-sensor applications and the electrical properties using Hall techniques. RTA has been carried out at 1100 °C for 20, 40 and 60 s, respectively. Gauge factors and electrical parameters deduced from Hall-effect measurements (resistivity, mobility, carrier density) are reported. We observe a reduction of the resistivity for longer RTA treatments, which is due to an enhancement of the mobility. Moreover, the carrier concentration does not depend on the heat-treatment duration. The gauge factor does not show a very strong dependence on the annealing duration but rather on the implantation dose. Finally, thermal budgets with shorter duration (1100 °C, 5 s) or lower temperature (1050 °C, 20 s) do not lead to uniform boron concentration throughout the film thickness.

A low-cost on-board vehicle load monitor

Abstract: We propose the use of etched optical fibre strain sensors to provide an economical on-board load indicator for minibuses and heavy vehicles. By improving the fabrication process we produced symmetrically etched fibre strain gauges. Manufactured sensors were evaluated experimentally by straining them on a cantilever beam. For strains smaller than 600 microstrain the output of a ten-segment sensor was linear with a typical gauge factor of -57. Bending losses in the fibre sensor became more pronounced for larger strains. This sensor has only two optical components apart from the sensing element. Strain sensors were mounted on the rear axle and on the front torsion bar of a minibus taxi test vehicle. Proper weighting of the outputs of the front and back sensors on the vehicle ensures a monotonic relationship between the sensor output and load. In addition, the reading of the sensor system is virtually independent of the load distribution in the vehicle. Difference-over-sum processing ensures insensitivity to common-mode perturbations such as temperature and source intensity changes.

ESD Susceptibility of High Gauge Factor Thick Film Piezoresistors

Abstract: CTS began manufacturing pointing devices in 1994 for use as cursor controls, mounted in the keyboards of notebook computers While completed keyboards were robust against ESD, many precautions were required during manufacture and assembly to protect against the effects of ESD While these ESD “protective” controls were effective in controlling ESD, they did not eliminate the ESD susceptibility of the pointing sticks ESD Susceptibility of high gauge factor thick film resistors was investigated The thick film resistor processing and the resistor design parameters were studied Improvements in the thick film resistor paste and strain gauge resistor design have produced pointing sticks capable of withstanding an ESD of 20KV

Application of etched fiber strain gauges to low-cost on-board vehicle load monitoring

Abstract: We investigated the use of wavelength compensated coupler sensors and etched optical fiber strain sensors to provide an economical on-board load indicator for passenger vehicles. Cost considerations favored the etched fiber sensor. Manufactured sensors were evaluated experimentally by straining them on a cantilever beam. For strain smaller than 600 microstrain the output of a 10 segment sensor was linear with a typical gauge factor of minus 57. Bending losses in the fiber sensor became more pronounced for larger strain. Proper weighting of the outputs of the front and back sensors on the vehicle ensures a monotonic relationship between the sensor output and load. Difference-over-sum processing minimizes the effects of sensitivity to common- mode perturbations such as temperature and source intensity changes.