Robert Greenlaw

Sensors for harsh environments by direct-write thermal spray

High-temperature thermocouple sensors for harsh environments have been fabricated using thermal spray technology with excellent performance demonstrated. Concepts for strain sensors fabricated with thermal spray technology are also being developed. This work reports on functional high-temperature thermocouples and strain gauge concepts fabricated using thermal spray processing.

Sensors for harsh environments by direct write thermal spray

Novel temperature sensors for harsh environments have been fabricated using thermal spray technology. Concepts for strain sensors fabricated with thermal spray technology are also being developed. This work reports on functional thermocouples and strain gauge concepts fabricated using this novel application of thermal spray processing.

Direct-Write Thermal Spraying of Multilayer Electronics and Sensor Structures

Direct write methods provide an efficient and environmentally conscious means of additive fabrication of electronic multilayers on conformal substrates. Thermal spraying is a method for additive fabrication of multilayers through direct write approaches. This technique offers promise in the area of direct write conformal electronics, sensors, and sensor array concepts. This chapter reviews preliminary assessment of the technology, materials, and various application concepts. Thermal spray is a directed spray process, in which material, generally in molten form, is accelerated to high velocities, impinging upon a substrate, where a dense and strongly adhered deposit is formed by rapid solidification. Material is injected in the form of a powder, wire, or rod into a high velocity combustion or thermal plasma flame, which imparts thermal and kinetic energy to the particles. Components ranging from insulated substrates, capacitors, conductors, resistors, to inductors and sensors, can be fabricated using a group of established and novel thermal spray processes.

Plasma-sprayed thick-film anisotropic magnetoresistive (AMR) sensors

We report our recent work on thick-film permalloy (NiFe) and NiCo-alloy anisotropic magnetoresistive (AMR) sensors made by thermal spray. Various sensor layouts have been fabricated and characterized. The AMR effect of 2.45% and 2.68% is obtained in as-sprayed permalloy and NiCo-alloy sensors. Resistivity of thermal-sprayed thick film is 40-60 /spl mu//spl Omega/ cm, which is higher than bulk material. A maximum /spl Delta/R/R value of 5.2% is achieved after thermal annealing. A high-/spl Delta/R/R value and low-saturation fields are the important features of thermal spray sensors. The very promising results demonstrate the potential applications of thermal spray sensors.

Plasma sprayed thick film anisotropic magnetoresistive (AMR) sensors

Reports recent work on thick film permalloy (NiFe) and NiCo alloy anisotropic magnetoresistive sensors made by thermal spray. Various sensor layouts have been fabricated and characterized. The AMR effect of 2.45% and 2.68% is obtained in as-sprayed permalloy and NiCo alloy sensors. Resistivity of thermal sprayed thick film is 40-60 /spl mu//spl Omega/-cm, which is higher than bulk material. A maximum /spl Delta/R/R value of 5.2% is achieved after thermal annealing. A high /spl Delta/R/R value and low saturation fields are the important features of thermal spray sensors. The very promising results demonstrate the potential applications of thermal spray sensors.

High-Temperature Calibration of Direct Write Heat Flux Sensors From 25 °C to 860 °C Using the In-Cavity Radiation Method

Heat flux sensors fabricated using Direct Write Thermal Spray are thin, surface-based devices that can operate at high temperatures. In this paper, Direct Write heat flux sensors are calibrated over a temperature range of 25 °C-860 °C. A substitution-based quartz lamp configuration is used to measure the steady-state sensitivity and transient response of Direct Write sensors at ambient temperatures, with repeatability confirmed over a 10-month period and after thermal aging. A matched heat flow approach is used to characterize the sensors at operating temperatures up to 860 °C. The sensitivity is found to increase by a factor of two from 25 °C to 650 °C, after which it plateaus up to the maximum tested temperature of 860 °C. A cubic polynomial calibration function captures the temperature dependence of the sensitivity and provides a good agreement for the measured data.

Thermal sprayed thick-film anisotropic magnetoresistive sensors

Ni/sub 80/Fe/sub 20/ and Ni/sub 80/Co/sub 20/ alloys anisotropic magneto-resistive sensor films were deposited by plasma spray. The resistivity (/spl rho/) of the films is determined to be 40-70 /spl mu//spl Omega//spl middot/cm in the as-sprayed state. The oxygen impurity dissolved in the metal acts as a strong scattering center and results in higher resistivity. The /spl rho/ of sensor film improves significantly with thermal annealing up to 500/spl deg/C and it remains constant for further increase in temperature. The dissolved oxygen precipitates out as oxide phase during heat treatment and that reduces the scattering. The /spl rho/ values are 19 and 22 /spl mu//spl Omega//spl middot/cm for permalloy and NiCo alloy films, respectively, which are close to bulk values. The anisotropic magnetoresistance (AMR) effect is found to be increased by a factor of 2 in both the permalloy and the NiCo sensors. The /spl Delta/R/R values are increased from 2.0% to 4.0% and 2.6% to 5.8%, respectively, for permalloy and NiCo sensors.