Известия ВУЗов.Радиофизика

We consider the problem of passive acoustic direction finding with a linear microphone array in the presence of intense interference. It is assumed that a useful signal, as well as interference, is broadband and has an arbitrary time shape. It is also assumed that interference at various microphones differs only by the delay and amplitude. Such a scenario is realized when detecting a weak acoustic source against the background of intense local source (interference). The former and the latter can be represented by a small unmanned aerial vehicle and, e.g., a helicopter, respectively. For the considered scenario, we propose an algorithm, which is based on the maximum-likelihood method in the frequency domain. The proposed algorithm is studied on the basis of numerical models using the spectra of the experimentally obtained useful signal and interference. The achievable accuracies of the noise direction finding for various parameters of the problem are obtained.

In recent years, significant progress has been made in generating ultrashort electromagnetic pulses of single-cycle and subcycle duration. Unipolar pulses contain one half-cycle of the field and have a nonzero electric area. The conventional concepts of interaction of electromagnetic radiation with matter (in particular, interference) used in the case of multicycle pulses are not applicable to unipolar ones. This minireview discusses the latest results on the effects of extremely short low-amplitude pulses (when the perturbation theory is valid) on resonant media and individual quantum systems (atoms, molecules, and nanostructures) from the viewpoint of the recently introduced concept of “interference” of the areas of short light pulses (electric and envelope areas). We provide a simple relation showing that in order to compare the effects of multicycle bipolar and subcycle unipolar pulses on micro-objects, one should compare their areas, not energies. By numerically solving the Maxwell–Bloch equations, we study the features of area interference are studied beyond the limits of perturbation theory. It is shown that, after the collision of a pair of π-like ultrashort pulses, polarization structures and population difference gratings with non-harmonic multipeak structures are formed inside the medium. The possibility of experimentally determining the electric area of unipolar pulses through interference of their areas is discussed for the first time.