Measurements In Hostile Environments Research Articles

Fiber Bragg Grating Sensor Networks Enhance the In Situ Real-Time Monitoring Capabilities of MLI Thermal Blankets for Space Applications.

The utilization of Fiber Bragg Grating (FBG) sensors in innovative optical sensor networks has displayed remarkable potential in providing precise and dependable thermal measurements in hostile environments on Earth. Multi-Layer Insulation (MLI) blankets serve as critical components of spacecraft and are employed to regulate the temperature of sensitive components by reflecting or absorbing thermal radiation. To enable accurate and continuous monitoring of temperature along the length of the insulative barrier without compromising its flexibility and low weight, FBG sensors can be embedded within the thermal blanket, thereby enabling distributed temperature sensing. This capability can aid in optimizing the thermal regulation of the spacecraft and ensuring the reliable and safe operation of vital components. Furthermore, FBG sensors offer sev eral advantages over traditional temperature sensors, including high sensitivity, immunity to electromagnetic interference, and the ability to operate in harsh environments. These properties make FBG sensors an excellent option for thermal blankets in space applications, where precise temperature regulation is crucial for mission success. Nevertheless, the calibration of temperature sensors in vacuum conditions poses a significant challenge due to the lack of an appropriate calibration reference. Therefore, this paper aimed to investigate innovative solutions for calibrating temperature sensors in vacuum conditions. The proposed solutions have the potential to enhance the accuracy and reliability of temperature measurements in space applications, which can enable engineers to develop more resilient and dependable spacecraft systems.

A coefficient searching based vibration correction method

Absolute gravimeter has played an important role in geophysics, metrology, geological exploration, etc. It is an instrument applying laser interferometry or atom interferometry to the measurement of gravitational acceleration <i>g</i> (approximately 9.8 m/s<sup>2</sup>). To achieve a high accuracy, a vibration correction method is often employed to reduce the influence of the vibration of the reference object (a retro-reflector or a mirror) on the measurement result of absolute gravimeter. Specifically, in an atomic-interferometry absolute gravimeter, the phase noise caused by the vibration of the reference mirror, namely the vibration phase, can be calculated from the output signal of a sensor, either a seismometer or an accelerometer, placed below or next to the mirror. Considering this vibration phase, the fringe signal of the atomic interferometer as a function of the phase shift set by the control system of the gravimeter can be corrected to approach to an ideal sinusoidal curve, thus reducing the fitting residual. Currently, the parameters in the algorithm of most vibration correction methods used in atomic-interferometry absolute gravimeters are set to be constant. As a result, the performances of these methods may be limited when the practical transfer function between the real vibration of the reference mirror and the signal of the sensor has a variation due to the change of measurement environments. In this paper, based on a simplified model of the practical transfer function previously proposed in an algorithm used in laser-interferometry absolute gravimeter, a new vibration correction method for atomic-interferometry absolute gravimeter is presented. Firstly, a detailed description of its principle is introduced. With a searching algorithm, the time delay and the proportional element in the simplified model can be obtained from the fringe signal of the atomic interferometer and the output of the vibration sensor. In this way, the parameters used to calculate the vibration phase can be adjusted to approach to their true values in different environments, causing the fitting residual of the corrected fringe to decrease as much as possible. Then the measurement results of the homemade NIM-AGRb-1 atomic-interferometry absolute gravimeters using this method is analyzed. It is indicated that with the vibration correction algorithm, the standard deviation of the fitting residual of the measured fringe signal can be reduced by 58% at the best level in a quiet environment. In the future, the performance of this vibration correction algorithm will be further improved in other atomic-interferometry absolute gravimeters during their measurements in hostile environments.

High temperature ultrasonic sensor for fission gas characterization in MTR harsh environment

In the contemporary world, the measurements in hostile environment is one of the predominant necessity for automotive, aerospace, metallurgy and nuclear plant. The measurement of different parameters in experimental reactors is an important point in nuclear power strategy. In the near past, IES (Institut d’Électronique et des Systèmes) on collaboration with CEA (Commissariat à l’Energie Atomique et aux Energies Alternatives) have developed the first ultrasonic sensor for the application of gas quantity determination that has been tested in a Materials Testing Reactor (MTR). Modern requirements state to labor with the materials that possess stability on its parameters around 350°C in operation temperature. Previous work on PZT components elaboration by screen printing method established the new basis in thick film fabrication and characterization in our laboratory. Our trials on Bismuth Titanate ceramics showed the difficulties related to high electrical conductivity of fabricated samples that postponed further research on this material. Among piezoceramics, the requirements on finding an alternative solution on ceramics that might be easily polarized and fabricated by screen printing approach were resolved by the fabrication of thick film from Sodium Bismuth Titanate (NBT) piezoelectric powder. This material exhibits high Curie temperature, relatively good piezoelectric and coupling coefficients, and it stands to be a good solution for the anticipated application. In this paper, we present NBT thick film fabrication by screen printing, characterization of piezoelectric, dielectric properties and material parameters studies in dependence of temperature. Relatively high resistivity in the range of 1.1013 Ohm.cm for fabricated thick film is explained by Aurivillius structure in which a-and b-layers form perovskite structure between oxides of c-layer. Main results of this study are presented and discussed in terms of feasibility for an application to a new sensor device operating at high temperature level (400°). Piezoelectric parameters enhancement and loss reduction at elevated temperatures are envisaged to be optimized. Further sensor development and test in MTR are expected to be realized in the near future.

Metal composite as backing for ultrasonic transducers dedicated to non-destructive measurements in hostile

Our team is specialized in ultrasonic measurements in hostile environment especially under high temperatures. There is a need for acoustic transducers capable of continuous measurement at temperatures up to 700°C. To improve the performances of acoustic sensors we focus our works on the realisation and characterisation of transducer backings able to operate under very high temperature. Commercially, they are produced by the incorporation of tungsten powder in a plastic matrix, which limits the working temperature. The realisation of ultrasonic transducers for non-destructive measures at high temperatures requires adequate materials, manufacturing and assembly processes. To produce the backings, composites were made using very ductile metals such as tin and tungsten. These composites are manufactured by uniaxial hot pressing. First, we studied the influence of temperature and pressure on the densification of tin pellets. Then, several specimens made of tin/W were made and characterised by measuring the specific weight, speed and attenuation of sound. The acoustic measures were realised by ultrasonic spectroscopy. This test-bench was designed and tested on control samples of PMMA and on standard backings (epoxy / tungsten).

A tribometer for measurements in hostile environments

A tribometer at the National Institute of Standards and Technology in Boulder, Colorado is used to measure the coefficient of friction and the wear rate for various specimens in a controlled atmosphere of oxygen or non-corrosive gas. The wide range of demonstrated operating temperature of 80 to 1030 K is presently unavailable in any commercial apparatus. The machine uses ball-on-flat or ring-on-flat specimen geometries for comparison of conforming and non-conforming contacts. The tribometer can be loaded to produce a hertzian contact stress in excess of 12 GPa (1.7×10 6 Ibf in −2) and surface velocities from 0.06 m s −1 to 4.0 m s −1. A range of environmental conditions this wide is unusual, especially the temperature range. The apparatus is described and some test results are compared with known values.

A miniaturized semiconductor fibre optic phase-Doppler anemometer (DFPDA) with applications to liquid sprays

For many particle size measurements in industrial applications conventional phase-Doppler systems are unsuitable due to their large size. For such purposes a PDA probe has been developed which consists of miniaturized transmitting and receiving optics and fibre optic coupling to the laser source and photodetector. A laser diode and avalanche photo diode have been used to reduce size and power consumption and this makes the PDA probe very mobile and flexible. The receiving optics is designed for easy alignment and is therefore suitable for field measurement and measurements in hostile environments. Design and performance specifications of the PDA probe are given in detail and example measurements, including comparisons with conventional PDA systems, are presented.

A remote pressure sensing technique by using the photothermal bending effect

Photothermal technique for sensing pressure in a cell is reported. The pressure is monitored from the frequency change of the vibration of the cell itself. The vibration is generated by the photothermal bending effect caused by the chopped laser irradiation, and it is sensed by the deflection of the probe laser beam. The proposed technique is noncontact, and thus it will be useful for remote pressure measurements in hostile environments.

Cars Diagnostics for Combustion and Plasma Processes

AbstractCoherent anti-Stokes Raman spectroscopy (CARS) is a powerful analysis approach for nonintrusive temperature and species measurements in hostile environments. Widely utilized in combustion, it may be able to significantly impact materials processing research. CARS is described and its applications to combustion and plasma process environments are reviewed and contrasted.

Laser diagnostics of materials and chemistry

Several examples are given of the ability of laser-based diagnostic techniques to make noninvasive measurements in hostile environments. Using coherent anti-Stokes Raman scattering both majority and minority species concentrations, as well as temperature, have been measured in the hot, high-pressure, particle-laden stream of a coal gasifier. In addition, numerous toxic and corrosive elements in the gasifier stream have been identified, but not yet quantified. In addition to providing the capability for making analytical determinations, laser techniques have been extensively employed to measure the rates of elementary chemical reactions. Recently, the temperature regime over which such meaurements are possible has been expanded. Although much of the laser diagnostic activity to date has involved investigations of the gas phase, significant information concerning heterogeneous phenomena can still be inferred. For instance, gas-solid reactions can manifest themselves as changes in vapor phase composition. Furthermore, in the future we expect expanded studies involving reactions of refractory metals (both atoms and clusters) and additional investigations of processes occurring at interfaces and on surfaces.

Photoacoustic generations and applications

A wide variety of acoustic pulses (different magnitudes and temporal/frequency profiles) can be produced in a sample by optical absorption of various light beams, i.e., photoacoustic (PA) pulse generation. Various generation mechanisms are possible: thermal expansion, gas evolution, chemical changes, dielectric breakdown, electrostriction, etc. PA pulse generation has found several important applications, including ultrasensitive spectroscopic detections of linear and nonlinear optical absorptions, noncontact ultrasonic measurements in hostile environments, PA imaging techniques, PA operation of mechanical devices, and so on. This paper presents some basic understanding of a PA generation process, and examples of important recent applications.

Making measurements in hostile environments

The types of hostile environments are examined together with a few specific problems that have arisen in particular fields. These include the use of transducers in steel-making, instrumentation used in electricity generation, and measurements in offshore engineering