The photopyroelectric method has been recognized as a reliable and useful tool for the measurement of the thermal properties of condensed matter samples. Usually the photothermal signal is generated using intensity modulated light beams, whose amplitudes are difficult to maintain stable. In this paper we describe a variant of this technique that uses amplitude modulated electrical current as excitation source, via Joule heating of the metal contact on one side of the pyroelectric sensor. The possibilities of this method, called by us the electropyroelectric technique, for thermal effusivity measurements of liquid samples are shown using test samples of distilled water, ethanol and glycerine. The results obtained for this parameter agree well with the values reported in the literature. Our measurement uncertainties are about 3%, a fact that opens several possible applications.

We start with the fact that the actual consensus on the empirical verification of the standard retardation condition does not take into account the complex structure of the whole electromagnetic field in the near zone. The most rigorous and methodologically consistent way to the empirical test of the causal behavior of the whole EM field should be based on testing causal properties for each component—velocity dependent (bound) and acceleration dependent (radiation)—taken separately. Preliminary discussions on the relative contribution of bound and radiation terms for an idealized magnetic dipole provided us with a methodological approach to causal characteristics of bound fields. In view of practical implementation of this method, we made an analysis of the finite size loop antennas. The use of multisection loop antennas was fully justified by a substantial rise of the ratio of bound-to-radiation field strength. Finally, we effected numerical calculations, taking into account particular experimental settings. Comparison with the experimentally obtained data showed considerable discrepancy with the predictions of the standard electromagnetic theory. A possible interpretation in terms of nonlocal properties of bound fields in near zone is proposed.

In practice, any cluster of light-emitting diodes (LEDs) can be modeled or measured as a directional point source if the detector is far enough away from the cluster. We propose a far-zone condition for measuring or modeling propagation of light from an LED array. An equation gives the far-field distance as a function of the LED radiation pattern, array geometry, and number of LEDs. The far field is shorter for high packaging density clusters, and the far field considerably increases with increasing beam directionality of LEDs. In contrast with the classical rule of thumb (5 times the source size), the near zone of an array with highly directional LEDs can extend to more than 60 times the array size. We also analyze the effect of introducing random variations of light flux among LEDs of the array, which shows that far-field variability is low in high packaging density arrays.

No abstract

In this review, the application of the photoacustic spectroscopy (PAS) is presented as an option to evaluate the quality of food. This technique is a type of spectroscopy based on photothermal phenomena, which allow spectroscopic studies. According to the literature review, it was found that its application is increasing in several countries. Spectroscopic studies carried out by employing PAS in the food industry include, among others, fruit, vegetables, condiments, grains, legumes, flours, “tortillas,” milk, water, eggs, etc. Additionally, this technique has been used to evaluate adulterated, irradiated, and contaminated food and so on. The literature review has shown the applicability of PAS to one of the problems of the real world, i.e., food quality assessment. Therefore, PAS can contribute in the future with a wide potential for new applications in the food agroindustry.