Radiotehnika i èlektronika

Based on direct and without simplifying assumptions calculation of the Fourier integral, the analysis of the process of the passage of terahertz pulses with Gaussian envelope and amplitude spectrum belonging to the frequency interval occupied by the spectral line, through the layer of resonantly absorbing medium was made. The interaction of the medium and the pulse is described by Drude-Lorenz model. It is shown that with an increase in the optical depth of the medium layer, the current envelope of the radiation field recorded at the receiving end of the path is increasingly affected by the interference effect of harmonics of individual sections of the current pulse spectrum, which leads to its fundamental deformation, but not to its systematic shift towards negative time values. Analysis of the integral characteristics of the received radiation field also does not agree with the conclusions corresponding to the first approximation of the dispersion theory. Methods are proposed for eliminating oscillations of the envelope of the received pulse by shifting the carrier and changing the bandwidth of the receiving device.

The task of improving the speech intelligibility in communication systems is considered. The acute problem of speaker voice recognition when using known methods for solving it is pointed out. To overcome this problem, new method for converting a speech signal is proposed. It based on an autoregressive model of the vocal tract and on the principle of frequency-selective amplification of the main formants. An example of the practical implementation of a new method based on the fast Fourier transform is considered. Estimates of computational costs and its performance are given. A full-scale experiment was set up and carried out. Based on its results, the positive effect achieved by applying the proposed method was established, namely: increasing the intelligibility of the speech of the control speaker while maintaining a sufficiently high degree of recognition of his voice. The results obtained are intended for use in the development of new and modernization of existing voice communication systems, including a mobile communication and VoIP-systems.

The dependence of the Lamb wave attenuation due to radiation into an inviscid nonconducting liquid (radiation losses) on 1) the ratio of the phase velocities of the waves in the plate V_n and the liquid V_L and on 2) the ratio of the vertical component of the surface displacement U₃ to the horizontal U₁ in the wave of the considered number n has been experimentally investigated. It is shown that the dominant value in the formation of radiation losses is U₃/U₁: for small U₃/U₁  1, the emission of Lamb waves into a liquid and the magnitude of radiation losses are small even at V_n  V_L, for large U₃/U₁ ≥ 1, radiation into a liquid and the magnitude of radiation losses are large and can reach values comparable to with those for surface acoustic waves in the same material (~5 dB/mm). The dependence of the Lamb wave attenuation on the ratio of the velocities V_n and V_L is much weaker.