Noncontact thermal measurements

The four most commonly stated advantages of noncontact thermal IR measurement over contact measurement are that it is nonintrusive, remote, much faster than conventional methods, and that it measures the temperature (or radiant thermal distribution) at the surface of the object of interest (we will call it the target), not the surrounding air. Any one, or a combination of, the following conditions warrant the consideration of a noncontact IR sensor ... 

The measurement of thermal IR radiation is the basis for noncontact temperature measurement and thermography. Thermal IR radiation leaving a surface (W) is called exitance or radiosity. It can be emitted from the surface, reflected off the surface, or transmitted through the surface. This is illustrated in Fig. 2.4. The total radiosity is equal to the sum of the emitted component (We), the reflected component (Wr) and the transmitted component (Wt). The surface temperature is related to We, the emitted component, only. 

Infrared noncontact thermal sensors are classified as infrared radiation thermometers by the American Society for Test and Measurement (ASTM) even though they don t always read out in temperature. The laws of physics allow us to convert IR radiation measurements to temperature measurements. We do this by measuring the self-emitted radiation in the IR portion of the electromagnetic spectmm from target surfaces and converting these measurements to electrical signals. In making these measurements three sets of characteristics need to be considered, as illustrated in Fig. 2.6 ... 

The measurement range is dependent on the instrument but can cover the range -50 to +500 °C. The accuracy is not as high as the best contact thermometers. One reason for this is that the emissivity of the surface has an effect on the measurement result, and an emissivity correction is necessary for most instruments. The positive features are noncontact measurement and very fast dynamics, which enable a rapid scan of surface temperatures from a distance this is convenient when carrying out, for example, thermal comfort measurements. 

Capability of remote measurements. The small size of the fiber and its electrical, chemical, and thermal inertness allow long-term location of the sensor deep inside complex equipment and thereby provide access to difficult locations where temperature may be of interest. Beyond this, however, certain of the optical techniques allow noncontact or remote sensing of temperature. 

We have developed a method for measuring the thickness of semiconductor thin films that is nondestructive, noncontact and that can make measurements with 2-um spatial resolution on both optically opaque and optically transparent films. This method is based on the use of high-frequency thermal waves. 

This sensitivity is, of course, the precision of the measurement based on signal noise considerations, and it does not reflect the absolute accuracy of the measurement. As with other noncontact, nondestructive methods, the thermal-wave technique provides an indirect measure of the geometric film thickness, and absolute accuracy must rely on either an accurate knowledge of the relevant physical parameters, or, as is common with the other methods, the use of calibration standards. In analyzing the data presented here we have used a rather complete (and complex) theoretical model to explain our experimental data, and thereby... 

Tissues such as skin have also been studied using photothermal methods, especially IR radiometry, which is capable of noncontact measurement, and is robust to alignment instabilities. In addition to the thermal and optical depth profiling of the various layers of the skin, photothermal spectroscopy has been used to study the time-dependent penetration of topically applied cosmetics and sunscreens below the skin surface. Photothermal studies have been used to monitor the time for which a topically applied film exists as a discrete phase on the outer surface of the skin. 

All of the systems described are now available with an incorporated differential thermal analyzer. DTA has been described in Section 16.2, so a few examples of the advantages of combining these systems will be presented. The incorporation of a DTA with one of the optical analyzers described requires the use of two thermocouples to measure the temperature difference between the sample and a reference standard (calcined kaolin or alumina). As noted, the optical noncontact instruments described are particularly useful in the glass and ceramics industries, so examples of evaluating raw materials from these industries will be described (from Paganelli and Venturelli). 

In porous silicon (PS), a is dramatically decreased as suggested from thermal flow measurements (Drost et al. 1995). For characterizing the thermal parameter in nanostructures Uke PS, two major ways have been employed to generate a probing signal of the thermal fluctuation electrical input and noncontact optical incidence. The most useful method in the former case is so called the 3(0 method (Cahill 1990), in which the third-harmonic component of the alternating thermal oscillation with a certain frequency is selectively detected by a phase-sensitive measurement. 

Accurate measurement of the temperature in microwave sintering presents more difficulties than in conventional sintering. Because of interference from the microwave field, thermocouples cannot be relied upon to function properly (51). The presence of thermocouples during microwave heating of low and medium loss ceramics (tan 8 < 0.1) can locally distort the electromagnetic field and can lead to enhanced energy absorption, enhanced heat loss by conduction, and even thermal runaway. To avoid these difficulties as well as serious aror in the temperature measurement, a noncontact sensing system such as an optical pyrometer should be used wheneva- it is possible. 

Electrical conductivity measurements have also been developed as tomography (104). Eddy-current testing (ET) of CFRP laminates is feasible (105). ET is noncontact and NDT, as long as thermal effects fi om resistive heating and energy dissipation are sufficiently small. Superconducting quantum interference devices (SQUID) have been used for ET to detect damage in CFRP (106). However, SQUID... 

Such contact measurements of temperature are appealing because they provide a direct measure of the bulk-cooling element temperature. Furthermore, the extraction of heat from an attached sensor is in itself a demonstration of cooling a thermal load. However, the use of thermocouples becomes difficult because of fluorescent heating and heat conduction through the wires. These drawbacks can be avoided with some of the noncontact thermometry methods reviewed in the following. 

The conductivity of mesoscopic metals can be measured only by noncontact means. For this reason the particles were embedded in an insulating matrix. The manufacture of the (indium) particles was generally achieved by condensation from the gas phase in a rotating oil film [69]. This method yielded metal particles of about 20 nm that were (colloidally) dispersed in the oil matrix. By means of thermal coalescence, panicles with a diameter of up to several hundred nanometers were obtained. Thus the effective dielectric function (DF) of the heterogeneous oil-indium system was measured. At constant volumetric filling ratio it was possible to mea-... 

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