Thermal wave technique

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... 

Bias-induced reverse piezoelectric response Broadband dielectric spectroscopy (BDS) Dielectric permittivity spectrum Dielectric resonance spectroscopy Elastic modulus Ferroelectrets Electrical breakdown Acoustic method Characterization Dynamic coefficient Interferometric method Pressure and frequency dependence of piezoelectric coefficient Profilometer Quasistatic piezoelectric coefficient Stress-strain curves Thermal stability of piezoelectricity Ferroelectric hysteresis Impedance spectroscopy Laser-induced pressure pulse Layer-structure model of ferroelectret Low-field dielectric spectroscopy Nonlinear dielectric spectroscopy Piezoelectrically generated pressure step technique (PPS) Pyroelectric current spectrum Pyroelectric microscopy Pyroelectricity Quasistatic method Scale transform method Scanning pyroelectric microscopy (SPEM) Thermal step teehnique Thermal wave technique Thermal-pulse method Weibull distribution... 

In contrast to the thermal wave technique, which operates in the frequency domain, the thermal-pulse method represents a transient technique operating in the time domain. This method was first described in 1975 (Collins 1975) and uses short light pulses of 10-100 ps duration as excitation signal. 

Fig. 17 Three common thermal excitation schemes H (f) or T t) used in thermal wave techniques for the profiling of space charges (a) thermal wave method (LIMM), (b) heat pulse method, and (c) thermal step technique...

From Eq. 21, it is clear that the determination of the distribution function G x) requires the deconvolution of the integral equation knowing both the current response /(/) or 7(time derivative of the temperature profile 7 x, t). Various approaches to solve the deconvolution problem have been discussed (Sessler 1997). 

If this stress gives rise to acoustic emission, this emission can be detected and an image of the discontinuity can be made. The thermal wave technique can be used to detect subsurface flaws in the material. The SLAM is an analytical technique based on this effect. 

The incident and reflected shock-wave technique was employed for a kinetic study of the thermal decomposition of /-butyl bromide110. The substrate dehydrobrominated even at the highest temperature of 1050 K via a unimolecular four-membered cyclic transition state. The A factor and the activation energy obtained in different investigations were compared and, because of the small temperature range in each individual study, these data were combined in order to estimate more reliable Arrhenius parameters between 500 K and 1050 K. Thus ... 

Several other examples for potential application of reverse-flow operated catalytic reactors are described in Ref. 9. Also, other potential techniques of forced unsteady-state operation which allow for combining chemical reaction and heat exchange in a fixed catalyst bed are discussed. One such technique is sequential switching between inlet and outlet ports of the reaction gas between two or more packed beds (Fig. 2(c)). In this case, the thermal wave travels continuously through a series of packed beds in one direction, as if along a closed ring. However, this operation is more complex and requires more catalyst than the reverse-flow operation. 

Ignition by near adiabatic compression or shock wave techniques creates explosions that are most likely chain carrier, rather than thermal, initiated. This aspect of the subject will be treated at the end of this chapter. The main concentration in this section will be on ignition by sparks based on a thermal approach by Zeldovich [13]. This approach, which gives insights not only into the parameters... 

This paper deals with thermal wave behavior during frmisient heat conduction in a film (solid plate) subjected to a laser heat source with various time characteristics from botii side surfaces. Emphasis is placed on the effect of the time characteristics of the laser heat source (constant, pulsed and periodic) on tiiermal wave propagation. Analytical solutions are obtained by memis of a numerical technique based on MacCormack s predictor-corrector scheme to solve the non-Fourier, hyperbolic heat conduction equation. 

Heat waves have been theoretically studied in a very thin film subjected to a laser heat source and a sudden symmetric temperature change at two side walls. The non-Fourier, hyperbolic heat conduction equation is solved using a numerical technique based on MacCormak s predictor-corrector scheme. Results have been obtained for ftie propagation process, magnitude and shape of thermal waves and the range of film ftiickness Mid duration time wiftiin which heat propagates as wave. 

There have been some initial studies of thermal-wave detection using the techniques described above. Ash and his colleagues have performed some imaging experiments with the laser interferometric technique, (8-11) while Amer and his colleagues have used both the laser interferometric and a laser deflection (surface deformation) technique for spectroscopic studies on amorphous silicon. (12-13) These various investigations were all performed at low to moderate modulation frequencies (<100 kHz) only. 

Correlations with EBIC and XRT. Thermal features that arise either from mechanical defects or from metallic grains and grain boundaries are usually easy to recognize. However, thermal features arising from more subtle crystalline disruptions and variations, such as those described above are more difficult to identify. Before thermal-wave microscopy can be accepted as a routine, standard analytical technique, one needs to establish a direct correlation of some of these less obvious thermal-wave images with those obtained with other more widely accepted techniques. Below, we discuss two such correlations, one with electron beam Induced current (EBIC) and the other with x-ray topography (XRT). 

Thermal-wave imaging thus appears to be as powerful a technique as x-ray topograhy for imaging dislocations in GaAs materials, but is much faster and simpler. 

Fig. 5.10.5 Three-omega technique the calculated normalized slope (d(AT)/d (log /)) of the thermal oscillation amplitude AT as a function of frequency/for a 100 nm thick aluminum heater element on a 500 nm thick Si02 layer and a 1 mm thick silicon substrate is shown as a function of thermal oscillation frequency/ With increasing frequency, the thermal wave penetrates deeper, allowing different sections of a (multilayered) sample to be scanned...

The technique of infrared thermography relies upon the detection of infrared radiation emitted from the surface of a structure. An infrared scanning unit converts electromagnetic thermal energy radiated from an object into electronic video signals and produces color-coded maps of isotherms (64). Differences in thermal waves on the surface of a material can be detected that will make certain flaws visible and allow detection of flaws with low-temperature differentials with respect to the surrounding area within... 

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