The rapid spread of the SARS-CoV-2 coronavirus has led to the global COVID-19 pandemic and a lockdown was introduced in Ukraine in March 2020. This forced universities to urgently transform the traditional system of organisation of the educational process and transfer to distance learning. This study aims to evaluate the distance learning system organised by a technical university in COVID-19 lockdowns from the perspective of the students as the main stakeholders of education. The method of the survey as the most widely used research method of sociological research was used to collect and analyse the data obtained. In this context, a number of surveys involving from 2,721 to 9,000 students of technical and humanitarian specialities were conducted to evaluate the level of their satisfaction with the distance learning system. The results of the study showed that the transformations introduced in the organisation and realisation of the learning process were on the whole positively estimated by students, which means that the elements of distance learning should remain after the end of the lockdown restrictions. However, more research is needed to evaluate the diagnostic tools for preventing academic dishonesty.

The paper considers the features of the formation of an acoustic field by a spherical source with complicated properties in a regular plane-parallel waveguide, which is of practical importance in marine instrumentation and oceanographic research. The calculation algorithm is based on the use of the Helmholtz equation and the Fourier method for each partial region and the conjugation conditions on their boundaries. The presented calculation allows one to get rid of the idealized boundary conditions on the source surface, with the subsequent determination of the excitation coefficients of the waveguide modes within the framework of the Sturm-Liouville problem. In this case, the attraction of the boundary conditions on the surface and the bottom of the sea, as well as the Sommerfeld conditions, makes it possible to obtain the real distribution of the field in the vertical sections of the waveguide. The obtained frequency dependences of the pressure and vibrational velocity components show their amplitude-phase differences, which reach 90 degrees, which partially explains the appearance of singular points in the intensity field in a regular waveguide. It has been determined that multiple reflections of sound waves from the boundaries of the working space and the space of the waveguide cause oscillations of the pressure components with a change in the amplitude level up to 6 dB. It was found that with an increase in the size of the source, a kind of resonance is formed in the working space, the frequency of which depends on the depth of the sea and corresponds to the region kr=x=5.8. It was found that when the acoustic field is formed in the working space, the frequency response of the impedance components is represented as a multiresonant dependence formed on the basis of the frequency characteristics of the lower modes and their combinations. Experimental studies have shown that the results of calculations of the mode composition of the acoustic field of the emitter, obtained in the conditions of the pool, correspond to the spatial characteristics of the mode components of the acoustic field with an error of up to 3 dB

The work considers broadband ultrasonic piezoelectric transducers for medical diagnostic echoscopes, ultrasonic therapeutic devices, which are widely used for the diagnosis and treatment of various diseases in medicine. Such piezoelectric transducers provide a bandwidth that covers almost the entire operating range of single-frequency electroacoustic transducers, specifically 1.4 to 18 MHz for diagnostic devices and 1 to 3 MHz for therapeutic devices. The use of broadband piezoelectric transducers significantly expands the capabilities of ultrasound devices. With the help of a 4.5-18 MHz band scanner, it becomes possible to obtain an image of the spinal canal, the possibility of which has not even been discussed before. Therapeutic devices become more effective, and at the same time, their safety increases by eliminating the possibility of the formation of standing waves in the broadband mode. In this work, a method was chosen for expanding the band of a piezoelectric transducer using acoustic layers and electrical circuits, and the features of their medical application were taken into account: the load of piezoelectric transducers on a medium with low impedance and high attenuation -biological tissue -and operation in the echo mode. In all of the above applications of broadband piezoelectric transducers, the transfer function parameter becomes important, that is, the ratio of the input action to the output one. The purpose of the work is to obtain expressions for the transfer functions of wideband piezoelectric transducers of various designs with one or two transition layers. The calculation of the piezoelectric transducer transfer functions was carried out by two methods: the wave equation method, which is characterized by the need to solve a system consisting of a large number of equations even with a small number of transition layers, and on the basis of A-matrices of the regular line segment. It is shown that these two methods give the same calculated ratios, but the second method is more convenient for calculations.

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