Combined FPPE–PTR Calorimetry Involving TWRC Technique. Theory and Mathematical Simulations

Abstract

Photopyroelectric calorimetry in the front detection configuration (FPPE) was combined with photothermal radiometry (PTR), in order to investigate dynamic thermal parameters of different layers of a detection cell. The layout of the detection cell consists of three layers: directly irradiated pyroelectric sensor, liquid layer, and solid backing material; and the scanning parameter is the thickness of the liquid layer (thermal-wave resonator cavity method). The theory developed for the two techniques indicates that both FPPE and PTR signals can lead, in the thermally thin regime for the sensor and liquid layer, to the direct measurement of the thermal diffusivity or effusivity of the sensor and/or liquid layer, or the thermal effusivity of the backing material. The two methods offer complementary results and/or reciprocally support each other.

Combined FPPE–PTR Calorimetry Involving TWRC Technique II. Experimental: Application to Thermal Effusivity Measurements of Solids

“…The conclusion of the previous theoretical paper [19] was that both normalized FPPE and PTR signals (Eqs. 1, 3, 4) depend on the thermal effusivity of the backing material.…”

“…In fact, for a three-layer detection cell (pyroelectric sensor/liquid layer/semi-infinite solid backing), the theory and mathematical simulations demonstrated that both FPPE and PTR calorimetry give similar information [19].…”

“…In a previous paper [19], we showed theoretically that the PTR technique can be used together with the TWRC method for thermal inspection of a second and/or third layer of a detection cell. In fact, for a three-layer detection cell (pyroelectric sensor/liquid layer/semi-infinite solid backing), the theory and mathematical simulations demonstrated that both FPPE and PTR calorimetry give similar information [19].…”

“…1, in the approximation of one-directional heat propagation and thermally thin limit for the sensor (exp(±σ p L p ) = 1 ± σ p L p ), the normalized complex FPPE signal is given by [13][14][15][16][17]19] …”

“…1 was performed with the signal obtained with a very thick liquid layer (exp(−σ l L l ) = 0). In the same approximation, the PTR signal is given by [19,20] …”