D. Dadarlat

The application of the photopyroelectric method for measuring the thermal parameters of pyroelectric materials

The photopyroelectric calorimetry, in the standard (back) configuration, is applied in order to measure the thermal parameters of some pyroelectric materials. It is demonstrated that the method is able to simultaneously measure the thermal diffusivity and effusivity of a pyroelectric material. The information is obtained via a frequency scan of the amplitude or the phase of the pyroelectric signal; the measurements need no calibration. A combined amplitude-phase procedure, at a single frequency, leads to the same results. In the mean time, if the thermal parameters of the pyroelectric sensor are known, one can get the thermal effusivity of a sample acting in the experimental cell as a substrate. Investigations and theoretical simulations were performed on a well known pyroelectric material, LiTaO3, with various liquid substrates.

AN APPLICATION OF THE FRONT PHOTOPYROELECTRIC TECHNIQUE FOR MEASURING THE THERMAL EFFUSIVITY OF SOME FOODS

ABSTRACT Photopyroelectric calorimetry, in the front (inverse) configuration (with thermally thick sensor and sample, and optically opaque sensor), was applied to measure the thermal effusivity of some fats and water-based juice products. The information was obtained via a frequency scan of the phase of the pyroelectric signal; the measurements need no calibration. The main advantages of this configuration above the other two previously proposed front schemes are: (i) it does not require the use of very thin foils or expensive semitransparent sensors; (ii) the information is contained in the phase of the signal (and not in the amplitude as usual), which is independent of the power fluctuations of the radiation source and, consequently, the results are more accurate and reproducible.

Analysis of the photopyroelectric signal for investigating thermal parameters of pyroelectric materials

The photopyroelectric signal is analyzed in order to simultaneously obtain the thermal diffusivity and effusivity of pyroelectric materials. Two different experimental configurations are described and compared in terms of accuracy and sensitivity. The information is obtained via a frequency scan of the amplitude or the phase of the pyroelectric signal. The methods have been used for the measurement of thermophysical properties of a lead–titanate–zirconate ceramic sample.

Study of thermal parameter temperature dependence of pyroelectric materials

A simplified photopyroelectric configuration that allows the determination of the temperature-dependent thermal parameters of pyroelectric materials is described. The procedure is based on a combination of phase and amplitude signal data obtained at a single frequency. Experimental results obtained on the thermal parameters of LiTaO3 single crystal are presented.

The photothermoelectric technique (PTE), an alternative photothermal calorimetry

The recently introduced photothermoelectric (PTE) effect is proposed as an alternative for measuring dynamic thermal parameters of solid samples. The front PTE configuration, together with the thermal-wave resonator cavity method as a scanning procedure, was used to measure the value of thermal effusivity. The back PTE configuration, together with the chopping frequency of incident radiation as a scanning parameter, leads to the direct measurement of thermal diffusivity. A theory based on the above two detection configurations was developed and its application to solids, covering a large range of typical values of thermal parameters (aluminum and copper alloys, glass, teflon, polyethylene, LiTaO3), was described in order to demonstrate the suitability of the method. Experimental support for other well-known techniques (photopyroelectric and infrared lock-in thermography) has validated the results obtained with the novel method.

Improved methods for measuring thermal parameters of liquid samples using photothermal infrared radiometry

High accuracy, non-contact measuring methods for finding thermal properties of liquid samples using photothermal infrared radiometry (PTR) are presented. The use of transparent windows to confine micro volume liquid samples and the implementation of front and/or back signal detection procedures helped the successful implementation of the PTR technique for measuring liquids with high proficiency. We present two configurations, the so-called back?front photothermal infrared radiometry and back photothermal infrared radiometry to find thermal diffusivity and thermal effusivity of liquid samples. Sensitivity studies and error analyses included prove the robustness of each method. As an illustration of the temperature and electric field varying studies, we have included the experimental results on a 5CB (4-cyano-4?-pentylbiphenyl) liquid crystal.

Photopyroelectric (PPE) calorimetry of composite materials

The front photopyroelectric configuration was applied to measure the thermal effusivity of some composite materials, inserted as backing layers in the detection cell. The technique is based on the scanning procedure of the coupling fluid’s thickness (TWRC method). Two particular composite materials were selected for investigation: (i) a liquid one: water based nanofluids with gold nanoparticles and (ii) a solid one: urea—fumaric acid (1:1) cocrystal. The thermal effusivity was found independent on the size and concentration of gold particles. Concerning the urea—fumaric acid cocrystal, the thermal effusivity value of the compound is different from the pure starting materials, indicating the formation of the compound.

Photopyroelectric Study of Thermal and Pyroelectric Parameters Temperature Dependence of Pyroelectric Materials

A simplified photopyroelectric (PPE) configuration that allows the simultaneous determination of the temperature dependent thermal and pyroelectric parameters of pyroelectric materials is described. The thermal parameters (thermal diffusivity, conductivity, effusivity and volumic specific heat) are obtained from the analysis of the phase of the complex photopyroelectric (PPE) signal generated from the pyroelectric sample itself and measured for two different modulation frequencies. The pyroelectric coefficient is obtained from the amplitude of the signal. Experimental results on thermal and pyroelectric parameters of LiTaO 3 single crystal in the 25C-70C temperature range are reported.

Pyroelectric Spectroscopy of the Hydrogen Uranyl Phosphate

Abstract Absorption, transmission and reflection properties of hydrogen uranyl phosphate (HUP) are determined, by using pyroelectric (PE) sensors in thermally-coupled (PPE) and thermally-decoupled (conventional) spectroscopy configurations. Absorption bands at 1.25, 1.5 and 2.0μm, stronger for HUP than for the corresponding ammonium salt, have been observed. This can be correlated with the much higher protonic conductivity of HUP and suggests polaronic effects on the conduction mechanism in this solid electrolyte.