The article investigates the problems of mine hazard prevention, identification and control. Acoustic emission signals are one of the important signs of the appearance of deformations in rocks that can cause accidents in mines. Acoustic emission signals are quite broadband in nature. The article considers the task of the possibility of using broadband nature of acoustic emission signals to localize areas in which acoustic signals are generated for early warning of an emerging danger. The results of modeling of the process of localization of hazardous areas are presented. The proposed method is based on the frequency dependence of acoustic signal attenuation in rocks. Moving away from the signal source, not only changes its intensity, but also its spectrum. By measuring the intensity of acoustic signals in several spectral bands and knowing the frequency dependence of signal attenuation, it is possible to calculate at what distance from the receiving points the signal source should be located so that its spectral components would be changed as they are observed at the receiving points. This allows to localize the signal source. It is shown that four signal reception points and intensity measurements in two spectral frequency bands are sufficient to apply the method. It is shown that the proposed method allows not only to determine the coordinates of the local area of fracture formation, but also to restore the spectral characteristics of acoustic emission signals in the area of their occurrence, which can provide information about the mechanism of formation and development of processes of rock destruction.

Purpose. To investigate the influence of LOS/NLOS conditions on the radio signal propagation and the possibility of interference mitigation by using multi-frequency method of transmitting and receiving for positioning tasks in enclosed spaces. To check the difference in measurement accuracy when receiving a signal at one frequency from receiving a signal at four frequencies by combining the measurement results of individual frequencies into one reading. To check the influence of various obstacles on the signal passing. Methodology. Design at the laboratory of UHF generator and BLE beacons with the ability to set broadcast frequencies and adjust transmission power. Application of a multi-frequency transmission and reception method. Findings. The possibility of increasing the accuracy of positioning of objects in closed rooms, including mine workings, through the use of multi-frequency radio signals is investigated. It is shown that the influence of re-reflections of radio signals from the walls of structures, from obstacles of various origins, and the associated interference, can be reduced by using averaged values of attenuation at different frequencies. The use of radio emitters with many frequencies as beacons can provide new possibilities in solving the problem of positioning objects in closed rooms. Originality. The work proposes a method for combining measurement results of individual frequencies into one reading, which will reduce interference. Multi-frequency transmission method and multi-frequency reception method are proposed to reduce the influence of interference caused at one frequency on the overall signal level. Practical value. The experimental results obtained can be used at deploying positioning systems in closed rooms, including mine workings.

The combined method for assessing risk factors in underground construction

Purpose. Development of a new approach to improving the accuracy of orientation based on radar reflections from local objects and a digital terrain model. Methodology. The research is based on the theory of radiation, reflection and reception of radar signals. Statistical analysis of a large volume of recorded signals establishes causal relationships between the appearance of “false” reflections formed by the back lobe of the radiation pattern and to develop a computational algorithm for their suppression. Findings. A method and software that allows detecting and suppressing “false” reflections formed by the rear lobe of the antenna pattern without distorting the reflections created by the main lobe. For this purpose, a criterion has been developed, determined by the ratio of the amplitude of the signal received by the front lobe to the amplitude of the signal recorded by the rear lobe. The criterion allows eliminating the “false” signals without having a priori information about the real radiation pattern using a regulator for the reduction of phantom reflections to an average noise level. Originality. For the first time, suppression has been carried out of “false” reflections without having a priori information about the real radiation pattern of the radar station antenna, as well as elimination of the loss of informativeness of the real reflection formed by the main lobe. Practical value. A method is suggested of radar immunity of radar stations is noise immunity due to “false” reflections. The potential of the method and the capabilities of the developed computer program determines the relevance of their capabilities for use by all radar stations at various frequencies, azimuths, ranges and terrain features.

The radio-wave method for monitoring bronchopulmonary function is attractive due to its simplicity of implementation and safety for patients. The achieved results in imaging the lung air-filling process were encouraging; however, they also revealed several limitations that hinder the development of the method as a diagnostic tool. This paper describes an improved setup for radio-wave monitoring of the breathing process, enabling the measurement of not only amplitude but also phase pulmonograms. The setup is based on the USRP device PlutoSDR and the GNU Radio framework. Using the Helmholtz equations, it was possible to separate the contributions to amplitude and phase variations in the pulmonograms into those associated with changes in lung size during breathing and those related to changes in relative permittivity due to lung aeration. The values of relative permittivity at selected measurement points may serve as a basis for developing diagnostic indicators of various bronchopulmonary diseases. The problem of selecting these measurement points is discussed, drawing an analogy with auscultation points, but focusing on locations that provide information about the lung air filling process. The estimated measurement accuracy indicates that a single breathing cycle is sufficient to determine the relative permittivity at each measurement point.

Purpose. Reducing the dispersion of radar reflections from local objects, with multi-frequency sensing, to solve the problem of orientation by radar reflections from objects. Methodology. Reflections from local objects in the entire frequency range of the radar station (RS) at the same radio engineering position were measured by three independent radars of the same type on different days and at different antenna elevations. The deviation of the radar stations in the position did not exceed 500 meters. Coordinates (azimuth, range) of reflections of several separate local objects were allocated for each radar. The average values of reflections from local objects and their dispersion in the frequency range were calculated. Using various algorithms, individual frequencies were sampled and the reflected signals were averaged at these frequencies. The decrease in the dispersion of the reflected signal from the number of frequencies at which reflections were measured and from the algorithm for selecting these frequencies was investigated. Findings. Averaging the values of reflections from local objects for several frequencies leads to a decrease in dispersion and, as a result, to a more accurate correspondence of the reflected signal level to the geometric size of the local object. The variance decreases most rapidly for a small number of frequencies selected for averaging when selecting frequencies located in an interval of at least 1% relative to each other. Originality. To solve the problem of orientation based on radar reflections from local objects, it is necessary to identify the landmarks selected on a digital terrain model. Due to the fact that local objects (hills) are a collection of many reflectors falling into the allowed volume of the radar, with different levels of reflections and random phases, there may not be radar reflection from a local object at a certain frequency, or it may be very small. In order to unambiguously identify all landmarks, measurements must be carried out at several frequencies. The work has established how many frequencies measurements should be performed at and on what principle these frequencies should be selected. Practical value. The advent of digital terrain models made it possible to solve the problem of terrain orientation by comparing radar reflections from local objects with reflection models based on digital terrain maps. Radar reflection models use mathematical expectations of reflection values, unlike real reflections, which have random deviations in signal levels depending on the operating frequency. Reducing the variance of these deviations increases the accuracy of identifying characteristic local objects (landmarks) used to orient the radar in the absence of data from satellite navigation systems.