Quantitative Contactless Photothermal Monitoring Of Drying In Foodstuff Materials

The role of a quantitative method, based on contactless photothermal monitoring, in the drying process of food products was described. The influence of moisture content on the effective thermal transport properties of the materials was used in the study. The transperency consideration in the foodstuff provided direct information related to the optical and thermal parameters. The infrared detection formed the basis for analyzing the frequency dependent thermal wave signals at different drying states.741 II744746Delgadillo-Holtfort, I., (2000) Quantitative Infrared Thermograph 5, QIRT 2000, pp. 103-104. , Reims, France, edited by D. Balageas et alDelgadillo-Holtfort, I., (2001) Anal. Sci., 17, p. 507Bein, B.K., (1999) BAM-DGZfP-Berichtsband, BB 69-CD, pp. M1Xiao, P., (2001) Anal. Sci., 17, pp. s349Bolte, J., (1997) High Temp.-High Press., 29, p. 567Bein, B.K., (1986) Can. J. Phys., 64, p. 1208Bein, B.K., (1997) High Temp.-High Press., 29, p. 43

THEORY OF SIGNAL GENERATION IN A PHOTOACOUSTIC CELL

La pression dans une cellule photoacoustique est déduite des équations fondamentales décrivant la dynamique des gaz.Based on the fundamental physical equations governing the dynamical behaviour of a gas, the pressure signal is derived for a gas-filled photoacoustic cell in contact with a radiation-heated solid sample

Analysis of active semiconductor structures by combined SThM and SThEM

In this contribution we present a combined experimental set-up for the simultaneous detection of the thermal and thermoelastic signal of electrically heated semiconductor devices measured by scanning probe techniques. A commercial atomic force microscope has been operated using a wollaston wire thermal tip for temperature oscillations, while simultaneously the oscillations of the cantilever have been measured. This set-up has been applied to semiconductor structures, with the aim of characterizing temperature, heat source and current distribution. In addition, having available a very versatile tool for different thermal scanning application, the simultaneous imaging by scanning thermal microscopy and scanning thermoelastic microscopy can improve contrast and quantitative interpretation. In both cases, the measured signals only give an indirect information on the current and heat source distribution. Therefore, the data has to be interpreted by help of theoretical models based on thermal waves, either by analytical approach or by finite element simulations. Here, the combination of the two techniques, can be helpful to find a more precise set of parameters, that describes both the SThM and SThEM signal. Furthermore, the influence of non-thermal and non-thermoelastic contributions to the SThEM-signal will be analyzed and discussed. When performing simultaneous measurements, especially the influence of the tip expansion, either due to heat diffusion from the sample to the tip or due to the probe current in the tip has to be considered

Emissivity measurements by means of combined photoacoustics and modulated IR radiometry

A new method for the determination of the emissivity $\epsilon$ is presented, which relies on thermal wave excitation by intensity-modulated heating in the visible spectrum and on simultaneous detection of the response in the transmission configuration of thermal waves by means of IR radiometry and photoacoustics (PA)

Effect of moisture take-up on the effusivity and ignition of dry fibrous carbon-based materials

The moisture take-up from the humid atmosphere and its effect on the effective thermal properties of dry fibrous carbon-based material have been measured with the help of modulated IR radiometry. For the measured samples, black graphitized paper, the results are independent of the emissivity, and the observed changes mainly refer to the effective thermal properties. The effects of moisture take-up are analyzed with respect to thermal effusivity, thermal diffusivity, and two specific thermal parameters (surface area heat capacity, thermal conductivity per sample thickness), which are relevant in surface heating processes in cylindrical geometry

Simulation of photothermal measurements on Cu-Carbon interface systems

Although the thermal depth profiles measured for Cu-C interface systems show similarities to the depth profiles of 2-layer systems with the effusivity of the first layer smaller than that of the substrate, large differences between the 2-layer model approximations and measured data are found at higher modulation frequencies. This is due to the fact, that the properties of the Cu films are not well described. If on the other hand, a 2-layer model with additional thermal contact resistance between the thin sputter-deposited Cu film and the C substrate is considered, a large variety of mathematically possible solutions can be found, which depend on parameter triplets consisting of the ratio of the effusivities film-to-substrate, the film’s thermal diffusion time, and the thermal contact resistance

Identification of efficient deposition conditions based on the determination of the effective thermal transport properties of Cu-C interface systems

For the photothermal characterization of Cu-C interface systems modulated IR radiometry has been applied. Based on two-layer model approximations, the measured effective thermal depth profiles are interpreted in the range of the intermediate modulation frequencies. The obtained thermal parameters are correlated with the mechanical adhesion strength between Cu film and C substrate, in order to identify film deposition conditions and substrate cleaning procedures contributing to good mechanical bonding and reduced thermal contact resistances

Laser modulated IR transmission of semiconductors

The influence of the charge carrier density on the IR properties of semiconductors is a well known effect, that can be exploited for the analysis of semiconductor materials. In this work, an experimental arrangement is presented, by which the IR transparency of thin semiconductor samples is modulated with the help of an Ar ion laser beam with photon energies h$\nu$ > E$_{\rm gap}$ and by which the oscillating transmitted IR radiation of an external IR source is measured. The transmittance signal (amplitude and phase) which only depends on the charge carrier density can be used for the characterization of semiconductors independent of thermal parameters

High-temperature thermal wave measurements of Cu-C interface systems

Photothermal measurements on Cu-C interface systems before and after annealing, combined with mechanical measurements of the adhesion strength, have shown that both the depth profile of the effective thermal properties and the adhesion strength change considerably with high-temperature annealing processes. To study these effects in more detail, modulated IR radiometry has been applied as a function of temperature. Two effects are observed between 200°C and 250°C which are interpreted as re-crystallization of the RF sputter-deposited initially amorphous Cu films, accompanied by an increase of the thermal contact resistance between Cu film and carbon substrate. The irreversible strong changes of the effective thermal properties are confirmed by frequency-dependent measurements, run at constant temperatures before, during, and after repeated heating processes

Investigations of the optical and thermal parameters of porous silicon layers with the two wavelength photoacoustic method

This paper presents the results of photoacoustic studies of porous silicon layers formed on silicon substrates with the method of constant current anodisation of c-Si in an aqueous solution of HF (50 wt %):H$_{2}$O = 1:1. The aim of the study was to determine the thermal diffusivity of the porous silicon layers and their optical absorption coefficients with the photoacoustic method using two wavelengths of the exciting light for the generation of thermal waves and measurement of thermal and optical parameters