Zlatan Šoškić

Theory of photoacoustic effect in media with thermal memory

This paper presents a model for indirect photoacoustic response that includes thermal memory effects. At low frequencies, the model reduces to the well-known thermal piston model of photoacoustic response given by Rosencweig and Gersho. However, at high frequencies, the presented model predicts resonant behavior of amplitudes and phases of photoacoustic response and determines the respective resonant frequencies. The results of the presented model enable experimental determination of standard thermal properties of solids (thermal diffusivity and thermal conductivity), as well as thermal memory properties, thermal relaxation time, and heat propagation speed.

Thermal memory influence on the thermoconducting component of indirect photoacoustic response

In this paper, a model of the thermoconducting component of the indirect photoacoustic (PA) response is derived that includes thermal memory properties of the examined material and its fluid environment. A comparison is made between the derived model and the classic one, which neglects the influence of thermal memory. It has been shown that, at modulation frequencies lower than a certain boundary frequency of the light source, these models tend to overlap, while at higher frequencies, noticeable differences occur. The boundary frequency depends on heat propagation velocity through the sample and its thickness. This observation limits the validity domain of previous models to a range lower than the boundary frequency, offering, at the same time, the possibility of obtaining thermal memory properties using PA effects at frequencies above it.

On the applicability of the effective medium approximation to the photoacoustic response of multilayered structures

If the model of the photoacoustic (PA) response of an investigated system contains many unknown parameters, as is the case with multilayered samples, then the inverse procedure for the calculation of the parameters is highly sensitive to experimental noise. The problem cannot be solved by developing the experimental setup or by data acquisition methods, but only by an improvement of the theoretical approach. This paper presents an analysis of the applicability of the effective medium approximation to the PA response of multilayered samples. It has been shown that the theory is not applicable to the general case, and explicit expressions for the effective values of thermal diffusivity and heat propagation speed have been derived for some special cases.

Application of Artificial Neural Network to Prediction of Traffic Noise Levels in the City of Niš, Serbia

Road traffic noise is one of the main sources of environmental pollution in urban areas. Since the early 1950s many mathematical models for traffic noise prediction have been developed. Available models are usually based on regression analysis of experimental data. This paper presents the application of multilayer feedforward neural network in prediction of equivalent continuous level of road traffic noise in urban areas of the city of Nis, Serbia. Predictions of developed neural network are compared to data collected by traffic noise monitoring, as well as to predictions of commonly used traffic noise models. Obtained results show that the application of artificial neural network may improve accuracy of traffic noise prediction.

Calculation of Noise Field in an Urban Area close to a Traffic Overpass-Case Study

The paper presents methodology for calculation of a spatial noise field in an urban area where the dominant noise source is road traffic passing over an overpass. The height of the overpass is variable, with one end in the foot, and with the other end at the top of a hill. On one side of the overpass is the hill, covered by vegetation. On the other side of the overpass is residential area with houses and multi-floor buildings. The noise map is obtained by SPM9613 software package, which is based on international standard ISO 9613.

Noise Protection of an Automobile Scrapyard with Car Crushers – A Case Study

The paper presents a procedure for design of an appropriate noise protection system for an automobile scrapyard. The influenced object is a residential area that borders the scrapyard. The noise impact was estimated by measurements of noise levels in the residential area. Since the measurements revealed that the noise level is above the allowed limits in a wide part of the residential area, a noise map was assembled. The noise maps enabled determination of critical points, with the highest noise levels. Based on calculated noise levels in critical points, characteristics of sources of noise and the relevant noise regulations, a sound barrier was designed as a noise protection mean that will provide a sufficient noise protection of the plant.

Influence of Heavy Data Transmission Losses on Spectra of Signals

Measurements of machine vibrations are often influenced by heavy data losses during wireless transmission of signals, which arise because of electromagnetic interference of electric motors. In this paper, authors present an analytic calculation of distortions introduced in spectra of harmonic signals by heavy data transmission losses, which are characterized by the loss ratio and frequency of losses. The results may be used to reduce errors that arise during spectral analysis of signals in conditions of heavy spectral losses.

Photothermal characterization of polymer-based three-layer nanoelectronic structures

The generalized model of surface temperature variations of a three-layer structure irradiated by intensity modulated laser beam was derived, including thermal memory effects. In the specific case of a polymer layer sandwiched between two thin metal foils the model was simplified by electrical analogy. It allowed formulation of unambiguous inverse procedure for estimation of dominating system thermal properties of system from measured photothermal spectra.