Usually, in photothermal experiments using pyroelectric sensors, the instrumental transfer function is cancelled by normalization to reference measurements, regardless of current (C) or voltage (V) mode processing of signals. Nevertheless, there are several advantages when using a current preamplifier, instead of a high-impedance voltage preamplifier. Due to the low input impedance of the former, the capacitance of the sensor (and its temperature dependence), the capacitance of the connection cable, and the loss resistance of the pyroelectric crystal do not influence the signal. Moreover, the whole input circuitry is less prone to electromagnetic pick up through stray capacitances. In (C) mode, the frequency characteristic is linear (with −180° constant phase) up to a rather high frequency, instead of having (in V mode) a 1/f dependence above a certain frequency and a variable phase shift from 0° to −90°.
Whole blood is an inhomogeneous, thermally fragile liquid suspension. It was shown that photothermal radiometry yields meaningful results, but required irradiation level might disturb the sedimentation process. Despite the necessity for direct contact, photopyroelectric method is more sensitive and also easier and cheaper to implement for routine measurements. All the experimental results are in a good agreement with developed theoretical models.
This study aims to assess the in situ spatial distribution of glass-transition temperatures (T g ) of the main lignocellulosic biopolymers of plant cell walls. Studies are conducted using scanning thermal expansion microscopy to analyze the crosssection of the cell wall of poplar. The surface topography is mapped over a range of probe-tip temperatures to capture the change of thermal expansion on the sample surface versus temperature. For different temperature values chosen between 20 • C and 250 • C, several quantitative mappings were made to show the spatial variation of the thermal expansion. As the glass transition affects the thermal expansion coefficient and elastic modulus considerably, the same data line of each topography image was extracted to identify specific thermal events in their topographic evolution as a function of temperature. In particular, it is shown that the thermal expansion of the contact surface is not uniform across the cell wall and a profile of the glass-transition temperature could thus be evidenced and quantified corresponding to the mobility of lignocellulosic polymers having a role in the organization of the cell wall structures.
Using complementary thermal wave methods, the irradiation damaged region of zirconium carbide (ZrC) is characterized by quantifiably profiling the thermophysical property degradation. The ZrC sample was irradiated by a 2.6 MeV proton beam at 600 C to a dose of 1.75 displacements per atom. Spatial scanning techniques including scanning thermal microscopy (SThM), lock-in infrared thermography (lock-in IRT), and photothermal radiometry (PTR) were used to directly map the in-depth profile of thermal conductivity on a cross section of the ZrC sample. The advantages and limitations of each system are discussed and compared, finding consistent results from all techniques. SThM provides the best resolution finding a very uniform thermal conductivity envelope in the damaged region measuring $52 6 2 lm deep. Frequency-based scanning PTR provides quantification of the thermal parameters of the sample using the SThM measured profile to provide validation of a heating model. Measured irradiated and virgin thermal conductivities are found to be 11.9 6 0.5 W m À1 K À1 and 26.7 61 W m À1 K À1 , respectively. A thermal resistance evidenced in the frequency spectra of the PTR results was calculated to be (1.58 6 0.1) Â 10 À6 m 2 K W À1. The measured thermal conductivity values compare well with the thermal conductivity extracted from the SThM calibrated signal and the spatially scanned PTR. Combined spatial and frequency scanning techniques are shown to provide a valuable, complementary combination for thermal property characterization of proton-irradiated ZrC. Such methodology could be useful for other studies of ionirradiated materials. V
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