Sound emission of solid surfaces through bubble layer

The analysis of the influence of a thin homogeneous bubble layer on sound emission from a solid surface is carried out. Sound pulses and monochromatic wave packets with a carrier frequency equal to the resonant frequency of the bubbles forming the bubble layer are considered. It is shown that the bubble layer transforms short sound pulses into wave sound packets and significantly reduces the amplitude of the emitted sound. The structure of a sinusoidal wave packet is transformed similarly. A long sound pulse is stored in the form of a pulse, its shape changes significantly. A homogeneous bubble layer near a solid radiating surface is an open resonator. The layer generates far-field radiation with spectral lines depending on the method of layer excitation and the internal properties of the bubble layer. The resonant frequency of the bubble is the limiting frequency in the spectrum, but it is not distinguished by a separate line.

Measuring the Continuity of a Gas-Liquid Flow in a Pipeline

The principles of building a meter for the continuity of gas-liquid flows in pipelines have been proposed, based on the polarized electromagnetic wave characteristics. A two-component flow in a pipeline has been analyzed considering the cross-sectional area of the flow in the pipeline. The judgment about the flow continuity by the phase difference between the electromagnetic fields polarized parallel and perpendicular to the wave propagation direction has been justified. The naturally and artificially anisotropic flow continuity measuring study results are given. A polarization technique of electromagnetic wave birefringence in the isotropic medium has been considered, based on placing an isotropic medium in an electric field formed by two capacitor electrodes. The possibility of eliminating the parameter measuring errors induced by temperature impact on the electromagnetic wave refractive index in controlled media is shown based on two electrodes of a capacitor creating an electric field in the dielectric pipeline measuring section as an option for implementing flat reflectors of an open resonator. The study results can be used in the instrument-making industry in the development and implementation of smart contactless measuring instruments in the gas-liquid flow analysis and control.

Summation of Powers in Open Resonator with Slotted Coupling Elements

The paper analyzes the summation of the powers of two sources in a hemispherical open resonator (OR) during its tuning. The first higher axially asymmetric TEM10q oscillation mode is excited in the resonator. A circuit with an E- tee waveguide is proposed, which makes it possible to research the summation of the powers using a Gunn diode. Studies of the conducting part of the millimeter range have been undertaken. It is shown that the coefficient of powers summation of two sources in the OR using slot coupling elements does not exceed 72%. The use of one H- polarized diffraction grating, which is in the resonator, does not lead to a significant increase in the summation coefficient when moving it. This is due to the excitation of the first type of TEM10q oscillations in the resonator.

Sound trapping in an open resonator

The ability of sound energy confinement with high-quality factor resonance is of vital importance for acoustic devices requiring high intensity and hypersensitivity in biological ultrasonics, enhanced collimated sound emission (i.e. sound laser) and high-resolution sensing. However, structures reported so far have been experimentally demonstrated with a limited quality factor of acoustic resonances, up to several tens in an open resonator. The emergence of bound states in the continuum makes it possible to realize high quality factor acoustic modes. Here, we report the theoretical design and experimental demonstration of acoustic bound states in the continuum supported by a single open resonator. We predicted that such an open acoustic resonator could simultaneously support three types of bound states in the continuum, including symmetry protected bound states in the continuum, Friedrich-Wintgen bound states in the continuum induced by mode interference, as well as a new type-mirror symmetry induced bound states in the continuum. We also experimentally demonstrated their existence with quality factor up to one order of magnitude greater than the highest quality factor reported in an open resonator.

DISSIPATIVE INSTABILITIES AND SUPERRADIATION REGIMES (CLASSIC MODELS)

The generation of an electromagnetic field by oscillators in an open resonator is discussed in a one-dimensional approximation. In this case, the development of the so-called dissipative instability  the dissipative generation regime. Such an instability with the generation of electromagnetic oscillations arises when the decrement of oscillations in an open resonator in the absence of oscillators turns out to be greater than the increment of the resulting instability of the system of oscillators placed in this resonator. It is assumed that the oscillators do not interact with each other, and only the resonator field affects their behavior. If the resonator field is absent or small, the superradiance regime is possible, when the radiation of each oscillator is essential and the field in the system is the sum of all the eigenfields of the oscillators. In the dissipative regime of instability generation, the system of oscillators is synchronized by the induced resonator field. The synchronization of the oscillators in the superradiance mode owes its existence to the integral field of the entire system of oscillators. With a weak nonlinearity of the oscillators, a small initiating external field is required to excite the generation regime. It is noteworthy that the maximum value of the superradiance field is approximately two times less than the maximum field that the same particles could generate if they were at the same point. In all cases, for a given open resonator, the superradiance field turned out to be somewhat larger than the resonator field. Nevertheless, for the same resonator, the increments and attainable field amplitudes in both cases are of the same order of magnitude.

QUASIOPTICAL SOLID-STATE GENERATOR WITH OPEN QUASI-FREQUENCY SPHEREOSELETAL OSCILLATING SYSTEM

The results of research related to the development of an effective high-Q open oscillatory system of quasi-optical solid-state generators of millimeter and submillimeter wavelength ranges are presented. It is shown that for the stable operation of solid-state generators based on Gunn diodes and avalanche-transit diodes (ATDs) located inside an open resonator (OR), a significant rarefaction of the resonance frequency spectrum is required, which excludes jumps of the generation frequency. Taking this requirement into account, a spheroechelett open resonator (SE OR) is proposed as an open oscillatory system of solid-state generators, one of the mirrors of which is a reflective lattice of the “echelette” type. The paper presents the results of “cold” measurements of the spectrum of resonance frequencies of the SE OP, which indicate that the SE OP indeed has a significantly rarefied spectrum both in transverse and, which is very important, in longitudinal modes of oscillations. The conditions necessary for the excitation of high-quality stable oscillations with high energy efficiency in a solid-state generator based on an SE OR are discussed and implemented. The results of an experimental study of a quasi-optical generator based on an 8-mm ATD wavelength range are presented. The analysis of the obtained characteristics and their qualitative explanation on the basis of the proposed model of the processes occurring in the investigated generator are presented. It is shown that the SE OR can be used as a resonant system in the entire EHF range of not only solid-state, but also electronic-vacuum devices. Finally, a way is outlined in the direction of further rarefaction of the spectrum of the SE OR in order to create a really single-frequency open oscillatory system.