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.     

Injection moulded plastic optical systems for harsh environments

Abstract

The general problems involved in the production of precision optical components are discussed with reference to plastics. The methods available for the manufacture of plastic optical parts are reviewed with particular reference to injection moulding. The design and manufacture of injection moulds are considered, and ways in which dimensional and surface finish requirements may be achieved are given. The criteria for producing optimum quality mouldings are listed, and the role of modern microprocessor controlled machines in producing quality moulded parts is emphasized. Methods for improving surface abrasion resistance and minimizing reflections are described. The optical, mechanical, physical, and processing properties of the plastics most favoured for optical components are given.

MST/375     

Behaviour of semiconductor low temperature sensors in electromagnetic environments

The effect of an electromagnetic field, with frequencies in the 30 – 300 MHz range, on semiconductor cryogenic thermometers, eg silicon diode temperature sensors as well as silicon and germanium resistance thermometers, has been investigated at temperatures from 70 to 300 K.The changes in voltage drop or resistance versus temperature characteristics of the tested thermometers for various fixed frequencies of external electromagnetic field have been found. The frequency dependent electromagnetic field behaviour of the thermometers was studied and a resonance character of the ‘error’ ΔT has been evaluated.It has been shown that the semiconductor low temperature sensors may only be used for accurate recalibration in the presence of a well-known, low-intensity EM field at a constantly held frequency not corresponding with the maximum values of ΔT.     

Knowledge-based qualification tests for electronic components in harsh environments

The objectives of this paper are to propose a practical procedure for knowledge-based reliability qualification, and provide a checklist of required information for qualification analysis and testing. The paper investigates the common failure mechanisms of electronic components in automotive environments, and addresses the role of physics-of-failure approach in component reliability qualification.     

Lithium-drifted,silicon radiation detectors for harsh radiation environments

A model describing the passivation by Li atoms of acceptors arising from radiation damage in Si detectors has been developed. Our studies indicate that it is possible to produce a protocol that will allow the in situ recovery of Lithium-drifted Si particle detectors under irradiation by high-energy particles. Our model for particle damage recovery is supported by preliminary results obtained on the recovery of old, degraded detectors.     

Photoelectrochemical etching to fabricate single-crystal SiC MEMS for harsh environments

In this paper, we report on a novel surface micromachining process technology for the fabrication of microelectromechanical systems in SiC. Single-crystal SiC suspended microstructures were fabricated using a dopant-selective photoelectrochemical etching process, which allows for undercutting the p-SiC layer by rapid lateral etching of the underlying n-SiC substrate. The selective etching was achieved by applying a bias which employs the different flat-band potentials of n-SiC and p-SiC in the KOH solution. Single-crystal SiC MEMS developed in this study fully exploits the superior mechanical and biocompatible properties of SiC and has the capability of monolithic integration with electron devices and circuits, and therefore, is promising for sensing and actuating operations in biomedical, high-temperature and harsh environments.     

Single-crystal sapphire tubes as economical probes for optical pyrometry in harsh environments

One-end-sealed single-crystal sapphire tubes are presented as a simple, robust, and economical alternative for bulky lightpipe probes. Thermal radiation from a blackbody cavity created at the inner surface of the sealed end is gathered by a simple lens-based collecting system and transmitted via optical fiber to the remote detection unit. Simplicity and applicability of the concept are demonstrated by the combination of commercially available sapphire tubes with a common optical pyrometer. Radiation thermometers with sapphire tubes as invasive probes can be useful for applications requiring immunity to electromagnetic interference, resistance to harsh environments, simple replacement in the case of failure, and enhanced mechanical firmness, enabling wider range probe positioning inside the medium of interest.     

Ceramic electrolytes and electrochemical sensors

The electrochemical method involving solid electrolytes has been known as a selective and an accurate way of sensing chemical species in the environment and even in liquid metal for some time. The most successful among the electrochemical sensors are the emission control sensor (-sensor) for the automobile engine and the oxygen sensor used in steelmaking, both made of stabilized zirconia. This article presents an overview of basic principles of various types of electrochemical sensors including active (potentiometric) and passive (amperometric) sensors. Recent advances in oxygen (O₂), carbon dioxide (CO₂) and hydrogen (H₂) sensors are also presented.     

Efficient power-consumption-based load-sharing topology control protocol for harsh environments in wireless sensor networks

Energy conservation and network performance are critical issues in wireless sensor networks.The authors present a novel efficient communication topology control protocol, called quorum-based load-sharing control protocol (QLSCP). QLSCP is a quorum-based communication protocol, which chooses appropriate communication nodes, adjusts the service loads of critical nodes and performs adaptive sleep management. QLSCP is suitable for harsh environments without a central control server calculating the locations of sensors, using the factor of the remaining power to build the system topology. The proposed protocol divides the topology operation into topology formation, adjustment and execution phases. The topology formation phase builds the backbone of an enhanced tree. In the topology adjustment phase, the enhanced tree is adjusted by an optimal balance of critical nodes in the backbone. In the topology execution phase, the efficient surplus-energy consuming (ESC) mechanism is proposed to efficiently exhaust the energy of each node. The ESC mechanism is designed to efficiently exhaust the latest remaining electronic power of sensor nodes. Simulation results of QLSCP demonstrate that it efficiently achieves to prolong system lifetime in harsh environments.     

Substrates for zero temperature coefficient Love wave sensors

Microacoustic Love wave delay lines show high sensitivity to perturbations such as mass depositions on the wave-guide surface. Furthermore, because of their shear polarization, Love waves are ideally suited for liquid sensing applications. Using a Love wave delay line as feedback element in an oscillator allows the realization of viscosity sensors, and, using a chemical interface, chemical sensors, where the output signal is the oscillation frequency. To achieve a high effective sensitivity, the cross-sensitivity to temperature has to be kept low. We outline the proper choice of a material and especially focus on the influence of crystal cut and the major device design parameters (mass sensitivity and coupling coefficient) on the temperature coefficient of the sensor.     

Erbium-doped silica fibers for intrinsic fiber-optic temperature sensors

The variation in the green intensity ratio ((2)H(11/2) and (4)S(3/2) energy levels to the ground state) of Er ions in silica fibers has been studied as a function of temperature. The different processes that are used to determine the population of these levels are investigated, in particular 800-nm excited-state absorption in Er-doped fibers and 980-nm energy transfer, in Yb-Er-codoped fibers. The invariance of the intensity ratio at a fixed temperature with respect to power, wavelength, and doped fiber length has been investigated and shown to permit the realization of a high-dynamic-range (greater than 600 °C), autocalibrated fiber-optic temperature sensor.     

RF sputtered ZnO-ITO films for high temperature CO sensors

In this work is reported the development of ceramic sensors based on ZnO-doped ITO thin films for engine diagnostics able to withstand the harsh environments associated with exhausts. ZnO-ITO films were deposited by RF-sputtering and have been employed in the development of thin films-based carbon monoxide resistive sensors operating at high temperature (500 °C). ZnO-ITO films, with different Zn/In ratio and thickness around 3 µm., have been deposited by changing the power on the targets. The effects of both the working temperature and the ZnO loading on the sensors performances were investigated. Undoped ITO film has shown negligible response to CO, whereas ZnO-ITO films were found to be sensitive at the required working temperatures. The reported results show how the ZnO-ITO devices under study can be promising sensors for CO monitoring in real exhausts of car engines.     

Titanium dioxide thin films for high temperature gas sensors

Titanium dioxide (TiO₂) thin film gas sensors were fabricated via the sol-gel method from a starting solution of titanium isopropoxide dissolved in methoxyethanol. Spin coating was used to deposit the sol on electroded aluminum oxide (Al₂O₃) substrates forming a film 1 μm thick. The influence of crystallization temperature and operating temperature on crystalline phase, grain size, electronic conduction activation energy, and gas sensing response toward carbon monoxide (CO) and methane (CH₄) was studied. Pure anatase phase was found with crystallization temperatures up to 800 °C, however, rutile began to form by 900 °C. Grain size increased with increasing calcination temperature. Activation energy was dependent on crystallite size and phase. Sensing response toward CO and CH₄ was dependent on both calcination and operating temperatures. Films crystallized at 650 °C and operated at 450 °C showed the best selectivity toward CO.     

Effect of chemical environments on palladium phthalocyanine thin film sensors for humidity analysis

Chemiresistors based on palladium phthalocyanine (PdPc) thin films were investigated as humidity sensors. The samples were thermally evaporated onto gold electrodes with a thickness about 100 nm. Optical and electrical characteristics of PdPc thin films were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and electrical measurements. The SEM image demonstrates PdPc (30–60 nm) nanosized particles, and XRD pattern shows that thin films are in α-phase at room temperature. Electrical measurements also confirm that PdPc exhibit semiconducting and photoconducting behaviors, and thermal activation energies of thin films were calculated. After that, the sensitivity and reversibility of devices were investigated on exposure to 20–90% RH in various chemical environments at 293 and 323 K. The response time (35–45 s) and recovery time (75–105 s) of sensors were measured at 293 K with respect to different chemical environments. At last, the stability of devices versus different RH% and chemical environments were tested. The sensors show very good stability on exposure to RH for a period of 2 months but their stability has been reduced in ethanol, acetone, and ammonia environments.     

Lam e-mode miniaturized quartz temperature sensors

Lam e-mode is very useful for realization of a miniaturized quartz crystal resonator because its resonant frequency principally depends only on the contour dimensions. Because the heat capacitance for the miniaturized quartz crystal resonator is small and the frequency response versus temperature is very rapid, the quartz crystal resonator is useful for application in temperature sensors. In addition, because a Lam e-mode quartz crystal resonator has zero temperature coefficients, designated LQ(1) cut and LQ(2) cut, and, particularly, the resonator for LQ(1) cut has a comparatively large value of the second-order temperature coefficient beta, a Lam e-mode quartz crystal resonator can be obtained with the large first-order temperature coefficient or when beta=0. In this paper, when cut angles phi=45 degrees and theta=45 degrees , alpha has a value of 44.6x10(-6)/ degrees C in the calculation and 39.9x10(-6)/ degrees C in the experiments with beta=0; when phi=51.5 degrees and theta=45 degrees , alpha=68.1x10(-6)/ degrees C in the calculation and 62.0x10(-6)/ degrees C in the experiments with a value of beta larger than that of phi=45 degrees and theta=45 degrees . For both cut angles, the calculated frequency change vs. temperature is found to be sufficiently large and slightly larger than the measured one.     

Fiber Bragg grating cryogenic temperature sensors

Temperature sensing to as low as 80 K was demonstrated with 1.55-μm fiber Bragg gratings. The gratings were bonded on substrates to increase sensitivity, and a shift of the reflection wavelength was measured. The temperature sensitivity was 0.02 nm/K at 100 K when an aluminum substrate was used and 0.04 nm/K at 100 K when a poly(methyl methacrylate) substrate was used. These values are smaller than those at room temperature because of the nonlinearity of both the thermal expansion and the thermo-optic effect. Extension to the liquid helium temperature is also discussed.