external acoustic field
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Proceedings ◽  
2020 ◽  
Vol 60 (1) ◽  
pp. 57
Author(s):  
Vladislav Lemozerskii ◽  
Tatiana Zimina ◽  
Alena Gagarina

The microacoustic methods of biomedical analysis, implemented on piezoelectric crystals and ceramics, are becoming increasingly popular due to the fact of their potential for integration into laboratories-on-a-chip, biochips, and biosensors as functional elements of biosensors. An important stage in diagnostics of infectious diseases is the identification of pathogens. One possible applications of such a sensor is an alternative to the time- and labor-consuming Gram method of discriminating bacteria according to the composition of their cell walls. Thus, bacteria, which in a Gram staining procedure do not decolor after application of the dye solution, are classified as Gram-positive (G(+)). They are surrounded with a thick peptidoglycan layer that is pulpy and dampens acoustic waves. While Gram-negative (G(–)) bacteria, which acquire a red color in a Gram procedure, are covered with a thin and springy layer, demonstrating resonance effects when interacting with acoustic fields. Thus, G(+) and G(–), which are differently colored in Gram procedures, also react differently to an external acoustic field: for G(–) bacteria, this was a sharp decrease in the Q-factor of the “resonator–suspension” system and a shift of the resonance curve to lower frequencies. While for G(+) bacteria, although a certain shift of the resonance curve was also observed, the bandwidth of the resonance curve practically did not change. This effect was studied for L. acidophilus (G(+)) and Escherichia coli (G(–)) bacilli with quarts resonators of 4 MHz, 5 MHz, and 10 MHz. The biosensor was tested using Lactobacillus fermentum, E. coli M-17, Bifidobacterium bifidum, Burkholderia cepacian, and Staphylococcus aureus. At this stage, it has been demonstrated that the method is particularly effective for discriminating bacteria of a similar shape, such as, for example, cocci. The discrimination of the Gram factor for cocci and bacilli was less accurate and needs further studies for selection of precise resonance frequencies.


Author(s):  
Б.П. Шарфарец ◽  
Ф.Ф. Легуша

Рассматривается возможность акустоэлектрического преобразования с использованием явления потенциала течения, обратного к другому электрокинетическому явлению - электроосмосу. Обратимость двух этих явлений позволяет использовать один преобразователь, содержащий заполненную жидкостью мембрану, к торцам которой подведены электроды, либо в режиме излучателя, либо в режиме приемника акустической энергии. В первом случае к электродам подается электрическое поле, во втором случае преобразователь находится в стороннем акустическом поле, а с электродов снимается напряжение, отвечающее стороннему акустическому полю. Работа состоит из двух частей. В настоящей части рассматриваются электрохимические аспекты, а именно получается дифференциальное уравнение, связывающее градиенты потенциала течения и акустического давления в теле преобразователя. Из этого уравнения следует выражение для объемной силы в двойном электрическом слое на границе раздела фаз в пористой структуре. Сила вызывается вектором электрической напряженности, возникающей вследствие образования в пористой структуре потенциала течения. Вывод зависимости потенциала течения от перепада давления приводится с помощью аппарата неравновесной термодинамики. Согласно этому подходу электроосмос и потенциал течения описываются уравнениями термодинамики неравновесных процессов, кинетические коэффициенты которых удовлетворяют соотношениям Онзагера, а вся система является линейной, в том числе и относительно перепада давления и потенциала течения. Полученное выражение для объемной силы в жидких порах мембраны позволит в следующей части статьи изучить акустические аспекты процесса акустоэлектрического преобразования на основе использования явления потенциала течения. Предлагаемый подход к созданию приемной антенны на явлении потенциала течения является новым по причине того, что для увеличения эффективности акустоэлектрического преобразования предполагается применение постоянного напряжения накачки на электродах преобразователя. Результаты работы могут быть использованы при теоретической разработке и практическом конструировании обратимых электроакустических преобразователей нового типа, построенных на использовании электрокинетических явлений. The possibility of acoustoelectric conversion using the phenomenon of the potential of the flow, the inverse of another electrokinetic phenomenon - electroosmosis. The reversibility of these two phenomena makes it possible to use a single transducer containing a liquid-filled membrane, to the ends of which electrodes are connected, either in the emitter mode or in the receiver mode of acoustic energy. In the first case, an electric field is supplied to the electrodes, in the second case, the transducer is located in an external acoustic field, and the voltage corresponding to the external acoustic field is removed from the electrodes. The work consists of two parts. In this part, electrochemical aspects are considered, namely, a differential equation is obtained that relates the gradients of the flow potential and acoustic pressure in the transducer body. From this equation follows the expression for the volumetric force in a double electric layer at the phase boundary in a porous structure. The force is caused by the vector of electric tension arising from the formation of the flow potential in the porous structure. The derivation of the dependence of the flow potential on the pressure drop is given using the apparatus of nonequilibrium thermodynamics. According to this approach, electroosmosis and the flow potential are described by the equations of thermodynamics of nonequilibrium processes. The kinetic coefficients of this system satisfy the Onsager relations, and the entire system is linear, including with respect to the pressure drop and flow potential. The obtained expression for the volumetric force in the liquid pores of the membrane will allow us to study the acoustic aspects of the acoustoelectric conversion process based on the use of the phenomenon of flow potential in the next part of the article. The proposed approach to creating a receiving antenna on the phenomenon of flow potential is new due to the fact that in order to increase the efficiency of acoustoelectric conversion, it is proposed to use a constant pump voltage at the electrodes The results of the work can be used in the theoretical development and practical construction of a new type of reversible electroacoustic transducers based on the use of electrokinetic phenomena.


2020 ◽  
Vol 15 (2) ◽  
pp. 25-49
Author(s):  
Mikhail M. Katasonov ◽  
Genrich R. Grek ◽  
Viktor V. Kozlov ◽  
Vladimir I. Kornilov ◽  
Alexey V. Kryukov ◽  
...  

The results of experimental investigations of the influence of distributed suction through a finely perforated surface on the spatial development of perturbations of the straight wing boundary layer at the nonlinear stage of its evolution are presented in this article. It was found that distributed suction reduces the intensity of integral pulsations for natural disturbances by 90 times. A spectral analysis of disturbances showed a decrease in the intensity of high-frequency fluctuations in a narrow frequency band by two orders of magnitude for natural and forced disturbances generated by an external acoustic field. It was found that the distributed suction affects the average flow, namely, when the suction is on, the turbulent state of the boundary layer is eliminated, its separation near the trailing edge of the wing and the laminar flow is defined in the boundary layer.


2019 ◽  
Vol 880 ◽  
pp. 653-683 ◽  
Author(s):  
Sandip Dighe ◽  
Hrishikesh Gadgil

Atomization of a smooth laminar liquid sheet produced by the oblique impingement of two liquid jets and subjected to transverse acoustic forcing in quiescent ambient is investigated. The acoustic forcing perturbs the liquid sheet perpendicular to its plane, thereby setting up a train of sinuous waves propagating radially outwards from the impingement point. These sheet undulations grow as the wave speed decreases towards the edge of the sheet and the sheet characteristics, like intact length and mean drop size, reduce drastically as compared to the natural breakup. Our observations show that the effect of the acoustic field is perceptible over a continuous range of forcing frequencies. Beyond a certain forcing frequency, called the cutoff frequency, the effect of the external acoustic field ceases. The cutoff frequency is found to be an increasing function of the Weber number. Our measurements of the characteristics of spatially amplifying sinuous waves show that the instabilities responsible for the natural sheet breakup augment in the presence of external forcing. Combining the experimental observations and measurements, we conclude that the linear theory of aerodynamic interaction (Squire’s theory) (Squire, Brit. J. Appl. Phys., vol. 4 (6), 1953, pp. 167–169) predicts the important features of this phenomenon reasonably well.


2019 ◽  
Vol 29 (2) ◽  
pp. 208-220
Author(s):  
Liming Ying ◽  
Donghui Wang ◽  
Guodong Wang ◽  
Wenyi Wang

Power transformers in substations are common sources of noise in residential areas of neighbourhoods. A quantified and visualized analysis of the power transformer acoustic characteristics is a prerequisite for the suppression of audible noise from the corresponding substation. In this study, based on a combined finite and boundary element method, a full-sized 3D power transformer multiphysics coupling model, which is aimed at realizing high accuracy and improving the computational efficiency, was developed. After validation of the numerical method using comparative tests, profile analyses in the near-field and far-field in the extended planes and three-dimensional areas of a power transformer were conducted to characterize the external acoustic field. The calculation results included the distribution of the spatial sound pressure levels of the power transformer at multiple levels in the frequency domain. These spatial sound pressure levels can be used to guide the efficient measurement of the external acoustic field of a power transformer and the soundscape planning around a substation, and the differentiated design of the sound absorption structure inside a substation.


2019 ◽  
Vol 14 (4) ◽  
pp. 28-54
Author(s):  
G. R. Grek ◽  
M. M. Katasonov ◽  
V. V. Kozlov ◽  
V. I. Kornilov ◽  
A. V. Kryukov ◽  
...  

The results of experimental investigations of the influence of distributed suction through a finely perforated section of a symmetric airfoil on the spatial development of disturbances in the boundary layer are presented. It was found that distributed suction reduces by 10 times the intensity of natural disturbances of the boundary layer and by 20 times the intensity of artificial disturbances generated by an external acoustic field. A spectral analysis of disturbances showed that suction reduces the intensity of high-frequency fluctuations for both natural and forced disturbances. It was found that the distributed suction affects the average flow – when the suction is on, the separation of the boundary layer near the trailing edge of the wing is eliminated. It was found that distributed suction significantly affects the mean flow, up to eliminating the boundary-layer separation near the trailing edge of the wing.


2016 ◽  
Vol 51 (4) ◽  
pp. 386-390 ◽  
Author(s):  
A. R. Mkrtchyan ◽  
A. S. Bagdasaryan ◽  
V. R. Kocharyan ◽  
A. A. Kiziridi ◽  
T. R. Muradyan

2015 ◽  
Vol 10 (4) ◽  
pp. 21-28
Author(s):  
Yuriy Litvinenko ◽  
Anton Balbutsky ◽  
Valentin Vikhorev ◽  
Grigory Kozlov ◽  
Maria Litvinenko

Experimental study of subsonic round micro jets in the diffusion combustion of propane and without combustion at low Reynolds numbers was performed. Development of the jet was as under natural conditions without the acoustic excitation and as acoustic excitation of high intensity (90– 100 dB), frequency of acoustic oscillations was from a few Hz to 6 kHz. The jet flow was realized through the nozzle of round cross-section with a bevel of 45° and a diameter d = 0,45 mm. Blown trough the nozzle mixture of propane-butane previously passed through the evaporator, then through flowmeter (two-channel PR4000B) gas consumption. The studies were performed using Schlieren method based on the IAB-451. The pictures of the shadow visualizations was received, the presence of a developing hydrodynamic instability was found, including the presence of convective forces (by burning). The pictures of diffusion combustion of round propane-butane micro-jet at various modes of combustion – lifted and attached flame were received. It was found that the flame in the diffusion combustion of round microjet at an external acoustic field, exposed to flattening and bifurcation as the air free round microjet, while the source of acoustic oscillations is oriented perpendicular to the jet. The pictures of the diffusion combustion for splitting impact jet by acoustic field were obtained. It was found that in this case on the limits plate two temperature maximum were realized.


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