G.S. Deep

A highly linear single p-n junction temperature sensor

A temperature sensor based on the use of two forward-biased p-n junctions is known to exhibit good linearity. An alternative sensor configuration, based on the same principle, but employing only one p-n junction is presented in this paper. The forward current through the p-n junction is switched alternately between two fixed values, and the difference between the corresponding voltages is shown to vary linearly with temperature. This scheme eliminates the problems associated with close matching required for the two p-n junction sensors. Experimental results obtained with the proposed scheme are presented. A configuration to exploit the temperature dependence of the p-n junction incremental resistance is also presented. >

Thermal dynamics of VO2 films within the metal–insulator transition: Evidence for chaos near percolation threshold

The thermal dynamics of thin vanadium dioxide films at the martensitic metal–insulator phase transition has been evaluated experimentally by thermal excitation spectroscopy. Over the transition region, the device becomes highly nonlinear, and its bolometric performance is affected. At low thermal cycling rates for a temperature around the percolation threshold, the device stochastically switches into an unusual pattern. The originally smooth and monotonic shape of the R(T) curve for minor loops suddenly becomes unstable and unpredictable. By direct observation of at least two strange attractors, the phenomenon clearly has been identified as chaotic. Bolometric performance of VO2 based devices in the transition region may suffer strong degradation for low thermal cycling rates. In this region, sensor responsivity for periodic thermal excitation is significantly reduced. Resistance noise is 1/f-type and self-generated oscillations were observed at frequency <10−2 Hz.

A hysteresis model for a vanadium dioxide transition-edge microbolometer

This paper presents the adaptation of the Preisach model, originally developed for magnetic hysteresis, to describe mathematically the hysteresis in the resistance-temperature characteristics of vanadium-dioxide (VO/sub 2/) thin film radiation sensors. The necessary and sufficient conditions for the applicability of the Preisach model to a VO/sub 2/ film sensor are experimentally verified. Experimentally measured characteristics are compared with those given by the model for minor and major loops.

Modeling of the hysteretic metal-insulator transition in a vanadium dioxide infrared detector

The vanadium dioxide (VO2) thin film, usually employed as an infrared detector, exhibits hysteresis in its resistance-temperature characteristic. Considering a polycrystalline VO2 thin film as a composite medium, containing semiconducting and metallic microcrystals, the well- known effective-medium approximation theory is employed to relate the volume fraction of the semiconducting microcrystals to the effective film resistance. A phenomenological model is first proposed for describing the hysteretic dependence of volume fraction on temperature. From this, a model for hysteresis in the resistance-temperature characteristic is then derived, and a procedure for estimating the model parameters is outlined. The model reproduces the more important hysteretic character- istics such as the major, minor, and nested loops, in good agreement with the experimental characteristics.

Modeling a magnetostrictive transducer using genetic algorithm

Abstract This work reports on the applicability of the genetic algorithm (GA) to the problem of parameter determination of magnetostrictive transducers. A combination of the Jiles–Atherton hysteresis model with a quadratic moment rotation model is simulated using known parameters of a sensor. The simulated sensor data are then used as input data for the GA parameter calculation method. Taking the previously known parameters, the accuracy of the GA parameter calculation method can be evaluated.

Dynamic response of thermoresistive sensors

Electronic circuit configurations for determining the dynamic response of thermoresistive sensors, using pulsed electrical excitation step and radiation step, are presented. Experimental results obtained with these circuits are included. The reduction in the response time of an instrument with these sensors in feedback structures is experimentally demonstrated. >

Limiting loop proximity hysteresis model

This paper introduces a simple algebraic limiting loop proximity ((L/sup 2/P)) model to describe magnetic hysteresis. With only four parameters, it has low computational cost and reduced mathematical complexity, thus permitting a fast numerical implementation and simple parameter estimation procedure. The paper presents simulation results and discusses the model performance in terms of its capacity to represent common nonlinearities of the magnetic hysteresis phenomenon. The model avoids the heavy computational burden that results when magnetic hysteresis is included in computer-aided tools for electromagnetic devices and circuit analysis - for example, when hysteresis is combined with the finite-element method. The model also avoids the need to use repeated numerical approximation steps to adjust traditional models to experimental data.

Stability conditions, nonlinear dynamics, and thermal runaway in microbolometers

The nonlinear dynamic behavior of microbolometers, operating at room temperature (300 K) under conditions of positive electrothermal feedback is investigated. An improved device model, based on the heat balance equation is developed. It takes into account the temperature dependence of the thermophysical parameters, such as thermal coupling coefficient between the sensor and its surroundings, and sensor heat capacity and its thermal resistance coefficient. Operational considerations for thermoresistive microbolometer with positive and negative temperature coefficient of resistance are discussed for both, constant current and constant voltage modes of operation. Analytical expressions are derived for predicting stable and unstable operation. Safety factors L0, establishing the biasing conditions for stable device operation are proposed for the positive temperature coefficient of resistance and negative temperature coefficient of resistance type sensors. Limits for fast catastrophic destruction are provided,...

Designing a programmable analog signal conditioning circuit without loss of measurement range

Programmable analog signal conditioning circuits can be programmed in the field to permit their use in several applications with a variety of sensors with different output signal characteristics. The digital programming of the gain and dc level shift of a conditioning circuit can affect the measurement resolution and cause a reduction in the range of the measuring system in which it is employed. For a specified maximum acceptable loss in the measurement resolution, a procedure for defining and employing the programming values that guarantees the full measurement range is proposed. The proposed methodology takes into account practical implementation considerations and can be employed for designing either discrete or integrated circuits.

A feedback I/sup 2/-controlled constant temperature solar radiation meter

The conventional thermoresistive sensor-based feedback constant temperature circuit have shown some performance limitations due to the input offset voltage of the amplifier. The d.c. analysis of this circuit has been presented to graphically demonstrate these limitations. Alternative feedback measurement scheme without employing the Wheatstone bridge is proposed. PI and predictive controller designs are described. Simulation results for these controllers and a practical configuration are presented.