Resonance Tube Research Articles

Dual-hollow-core anti-resonant fiber with silicon layers and nested resonant tubes for constructing a single-polarization 3 dB coupler

A novel dual-hollow-core anti-resonant fiber (DHC-ARF) with silicon layers and nested resonant tubes is proposed for constructing a 3 dB single-polarization coupler. High-index silicon layers are deposited inside four cladding tubes along the x-direction and then nested resonant tubes are introduced into these cladding tubes, which is beneficial to promote the mode coupling between the x-polarized fundamental mode and the dielectric mode in the silica/silicon tubes so as to achieve single-polarization characteristics of the DHC-ARF. The properties of the DHC-ARF are optimized using finite element method combined with perfectly matched layer as a boundary condition. By using a 1.51 cm long DHC-ARF, a single-polarization 3 dB coupler is constructed with a relatively wide bandwidth of 29 nm covering the wavelength range from 1530 nm to 1559 nm, in which the polarization extinction ratio (PER) is lower than -20 dB and the coupling ratio can be guaranteed within 50 ± 2%. This bandwidth is more than 2.6 times higher than the bandwidth of currently reported single-polarization coupler. At the wavelength of 1550 nm, the lowest PER reaches -74.8 dB and the loss of the coupler is as low as 0.33 dB.

Measuring tiny pressure fluctuations using fast pressure-sensitive paint and phase-lock technology: Uniformity evaluation of resonance tube

The tiny pressure fluctuations across the end wall of the resonance tube at different frequencies were captured using fast pressure-sensitive paint (fast PSP) and the phase-lock method. The high signal-to-noise ratio images of phase-averaged pressure fields (57.85 dB at 9076Hz) were obtained by repeatedly recording the pressure data at specific phases. A method reducing the measurement errors caused by illumination fluctuation and photodegradation of PSP was proposed and demonstrated. Afterward, the pressure distributions at different phases in acoustic fields with different resonance frequencies were measured. The measurement errors were reduced by a newly proposed photodegradation correction. The pressure distributions were further corrected based on the dynamic calibration results, i.e. phase delay and gain attenuation. The pressure fluctuations measured by the PSPs corresponded to those determined by a pressure transducer, and the transient pressure distributions across the cross section within the range of 10 kHz was proven to be uniform.

On the Absorption of γ-Radiation by Absorbers with a Thickness Equal to a Multiple of the Mean Free Path and Analogies with Standing Waves in a Sound Resonance Tube

This article addresses the phenomenon of the decreased absorption of γ-radiation when the thickness of the absorber equals a multiple of the mean free path, as observed in relevant laboratory experiments with various absorbing materials. This phenomenon can be compared with the periodic peaks in intensity in an open-ended sound tube that appear at multiples of half wavelength. This could suggest that there is analogy between the two physical systems that are the γ-ray absorber and the sound wave resonance tube. More similarities between the two systems are also presented.

Spatiotemporal evolution of molar fraction in acoustic-resonance tube filled with He-Ar mixture.

This study proposes a time-evolution method to simulate acoustic gas-mixture separation. The proposed method can calculate the separation process without any arbitrary parameters except for space and time resolutions. The molar-fraction distribution within the system during the separation can be calculated, and the results show that a large molar-fraction gradient occurs in the separation tube, while a distribution also occurs in the resonance tube. Although the simulation results for the case with a high-pressure amplitude diverge from that of the experiment during the process of the separation, the simulation results for the case with a low-pressure amplitude agree well with those of the experiment.

Positional Variations of Ukrainian Back Vowel Formants

The purpose of this paper is to study variations in the location of formants of Ukrainian back vowels caused by different phonetic features. To do so, the oscillograms and two-dimensional spectrograms of recorded sounds in speech flow were analyzed. The corresponding invariant acoustic parameters being the ratios between frequencies of the formants rising due to the tube resonance are determined. It is shown that different phonetic environments cause different formant configurations in vowels which is a case of sound assimilation. The following phonetic features were found to give rise to variations of Ukrainian back vowels: coda, distant assimilation by the next or preceding vowel, and progressive assimilation by the preceding hard or palatalized consonant. In particular, high vowels make the other vowels in the phonetic word move higher, and the front ones make the back ones move forward. Such formant shifts are more pronounced in unstressed positions and especially in a coda.

Numerical investigation of hydrogen ignition induced by unsteady flow phenomena

The purpose of the present study is to evaluate the possibility of using a gas dynamic heater as an igniter of the combustible gas mixtures. The impacts of some operating and geometrical parameters on average temperature of the gas dynamic heater are investigated by numerical simulation of axisymmetric turbulent flow in the resonance tube. The operating gas of the heater is air which is completely decoupled from the ignition chamber. The combustible mixtures under consideration is stoichiometric hydrogen-oxygen at atmospheric pressure, in which the ignition is studied solving the governing equations for one dimensional reacting flow using detailed chemistry. The finite volume method is used in the presently developed flow solver for numerical simulations. The results show that despite highly fluctuating temperature of the end wall of the resonance tube as a hot surface, it can provide proper condition for gas mixture ignition in the chamber, by adjusting an inlet pressure and geometry of the gas dynamic heater. The end wall average temperature depends on the nozzle inlet pressure and convergence angle of the resonance tube, and the results demonstrate that the characteristics of temperature time history of repeating cycles are so effective on ignition process.

Research on engineering technology of compact thermoacoustic air conditioner for vehicles

Thermoacoustic refrigeration technology presents a promising solution for sustainable and efficient air conditioning in vehicles. However, traditional thermoacoustic systems typically employ rigid resonant tubes, which pose challenges in terms of assembly and spatial layout during experimentation. Additionally, electric heating is predominantly utilized as the heat source in most experimental setups.To address the need for compact thermoacoustic air conditioning systems suitable for vehicle applications, this paper introduces the concept of employing flexible resonant tubes in heat-driven thermoacoustic refrigeration systems. Our study begins by constructing a heat-driven thermoacoustic refrigeration platform designed to simulate real automotive exhaust conditions. The DeltaEC software is employed to optimize the design of each component within the system.Both flexible and rigid resonant tubes are used in experimental research. Our findings reveal that the pressure amplitudes measured from experiments using both types of tubes closely match the simulated sound field. Operating at 8.7 MPa, the cooling capacity of the thermoacoustic system with flexible tube is 3.4 kW at 10 ℃. Using more gentle bending of flexible resonant tubes can reduce small losses caused by bending in rigid resonant tubes. Consequently, under similar working conditions, the cooling capacity generated by the system employing flexible resonant tubes slightly exceeds that of systems employing rigid resonant tubes. Furthermore, our study demonstrates a thermoacoustic conversion efficiency of 20.8 % and a refrigerator refrigeration efficiency of 2.34.These findings provide empirical validation for the use of flexible resonant tubes within vehicle exhaust heat-driven thermoacoustic refrigeration systems. The experimental results clearly demonstrate the ability of vehicle exhaust as a heat source to provide heat for thermoacoustic systems, and the ability of flexible thermoacoustic systems to generate sufficient cooling capacity. Ultimately, this research contributes to the advancement and practical implementation of thermoacoustic air conditioning within vehicles.

Mini Winnies: scaled down and transparent Winogradsky columns for microscopy in microbiology education.

Winogradsky columns were invented by Sergei Winogradsky in the 1880s and have commonly been used as a microbiology classroom learning tool in K-12 and collegiate education. However, they can be challenging to examine with microscopy. We scaled down Winogradsky columns into nuclear magnetic resonance (NMR) tubes and replaced the natural sediment with a transparent soil substitute toward the goal of observing the microbial growth under a bright-field microscope without column disassembly. Using this "Mini Winnie" approach, students can practice their microscopy skills while observing microbial growth inside the column after only days of incubation on the laboratory windowsill. Overall, we believe that the Mini Winnies provide a simple method for maximizing student engagement while giving them a greater understanding of how microorganisms interact in the environment.

Harmonic series experiments: end-correction factor of the Indonesian Angklung

In this study, we employed the harmonic series experiment to determine the end correction factor of the Indonesian Angklung. Indonesian Angklung are categorized as one-closed-end resonance tubes and consist of different lengths that represent different musical notes. The end correction factor of the Indonesian Angklung is determined from the L-intercept of Lres versus 1f graph. The findings indicate that the experimental values of the end correction factor are less than 6.00% compared to theoretical values. Hence, the harmonic series experiment can be utilized to determine the end correction factor of the Indonesian Angklung.

Influence of length of resonance tubes on multi-stage looped thermoacoustic electric generator

Resonance tubes are often used to connect multi-stage looped thermoacoustic heat engine and linear alternators to form a multi-stage looped thermoacoustic electric generator. In this paper, we experimentally investigate the performance of a multi-stage looped thermoacoustic electric generator with two sets of resonance tubes of different lengths. With the increase of the length of resonance tubes from 1.5 m to 2 m, the system frequency decreases from 70 Hz to 62 Hz. The maximum output acoustic power increases from 6.97 kW to 8.16 kW, and the maximum output electric power increases from 5.09 kW to 6.24 kW. Meanwhile, the maximum thermoacoustic efficiency increases from 23.08 % to 23.94 %, the maximum acoustic-to-electric efficiency increases from 78.03 % to 82.06 % and the maximum thermal-to-electric efficiency increases from 17.79 % to 19.64 %. Numerical simulation is also conducted based on a 3-step coupling method and validates the experimental results. This study demonstrates that adjusting the length of resonance tubes in a multi-stage looped thermoacoustic electric generator is an effective way to tune the frequency as well as to improve the coupling between the multi-stage looped thermoacoustic heat engine and linear alternators.

Evolution of Acoustic Streaming Inside and Around the Open Tube Resonator

Evolution of Acoustic Streaming Inside and Around the Open Tube Resonator

Signal Enhancement of a Differential Photoacoustic Cell by Connecting the Microphones via Capillaries.

Differential photoacoustic spectroscopy (DPAS) cells are usually excited on the first longitudinal ring mode, with a microphone situated in the middle of each of the two resonator tubes. However, it is known from other photoacoustic spectroscopy cell designs that connecting the microphones via a capillary can lead to signal enhancement. By means of finite element method (FEM) simulations, we compared such a photoacoustic spectroscopy (PAS) cell with a capillary to a DPAS cell with a capillary attached to each of the two resonators and showed that the behavior of both systems is qualitatively the same: In both the PAS and the DPAS cell, in-phase and anti-phase oscillations of the coupled system (resonator-capillary) can be excited. In the DPAS cell, capillaries of suitable length also increase the pressure signal at the microphones according to the FEM simulations. For different capillary diameters (1.2 mm/1.7 mm/2.2 mm), the respective optimal capillary length (36-37.5 mm) and signal amplification was determined (94%, 70%, 53%). According to the results of these FEM simulations, a significant increase in sensitivity can, therefore, also be achieved in DPAS cells by expanding them with thin tubes leading to the microphones.

Rapid Photoacoustic Exhaust Gas Analyzer for Simultaneous Measurement of Nitrogen Dioxide and Sulfur Dioxide.

A rapid photoacoustic (PA) exhaust gas analyzer is presented for simultaneous measurements of nitrogen dioxide (NO2) and sulfur dioxide (SO2). A laser diode (LD) emitting at 450 nm and a light-emitting diode (LED) with a peak wavelength of 275 nm operated simultaneously, producing PA signals of NO2 and SO2, respectively. The LD and LED were modulated at different frequencies of 2568 and 2570 Hz, and their emission light beams were transmitted through two resonant tubes in a differential PA cell (DPAC), respectively. A self-made dual-channel digital lock-in amplifier was used to realize the simultaneous detection of dual-frequency PA signals. Cross interference between the PA signals at the two different frequencies was reduced to 0.02% by using a lock-in amplifier. In order to achieve a rapid dynamic measurement, gas sampling was accelerated by an air pump. The use of mufflers and the differential PA detection technique significantly reduced the gas sampling noise. When the gas flow rate was 1000 sccm, the response time of the PA dual-gas analyzer was 8 and 17 s for NO2 and SO2, respectively. The minimum detection limits of NO2 and SO2 were 1.7 and 26.1 ppb when the averaging time of the system was 10 s, respectively. Due to the wide spectral bandwidth of the LED, NO2 produced an interference to the detection of SO2. The interference was reduced by the precise detection of NO2. Since the radiations of the LD and LED passed through two different PA tubes, the impact of NO2 photochemical dissociation caused by UV LED luminescence on NO2 gas detection was negligible. The sharing of the PA cell, the gas lines, and the signal processing modules significantly reduced the size and cost of the PA dual-gas analyzer.

Research on the effects of resonance tube bending in loop thermoacoustic refrigeration system

A high-power-density heat-driven loop thermoacoustic refrigeration system has the potential to meet miniaturization requirements of vehicle waste heat recovery systems. Given the strict space constraints in vehicle power compartments and the need to reduce equipment footprint, the resonance tubes need to be bent and coiled. However, the introduction of curvature may increase losses in resonance tubes. In order to evaluate the minor losses caused by bending on resonance tubes, a double-acoustic-source driven acoustic field modulation platform was constructed to experimentally investigate bent resonance tubes with different arc lengths under two common bending angles (90° and 180°) under high working pressure. Through the acoustic field reconstruction method, the acoustic field distributions of each resonance tube were obtained, and the effects of changes in bending angle and arc length on acoustic field and acoustic power dissipation were analyzed. The results indicated that the introduction of curvature leads to an increase in traveling-standing wave ratio, acoustic power, and acoustic power dissipation, with the degree of increase influenced by both curvature and arc length. Under the same bending angle, the minor loss is directly proportional to curvature, and there is an ExpAssoc function relationship between minor loss coefficient and curvature. Under the same curvature, the minor loss is not proportional to arc length, and minor loss coefficient slightly increases with the arc length doubles. The findings fill the research gap in resonance tube bending in loop thermoacoustic systems and provide guidance for the selection of resonance tube bending parameters.

Spatiotemporal theory of a gyrotron based on a three-mirror cavity

We present the quasi-analytical spatiotemporal theory of the resonant traveling-wave tube scheme of a gyrotron based on the transverse amplifications of the operating wave and on the use of a remote delayed feedback. The main idea is to implement a system with a dense spectrum of eigenmodes, which makes it possible to smoothly adjust the generation frequency by switching from mode to mode when the operating magnetic field changes. On the basis of a simple 2D three-mirror model, we show the possibility of achieving the stable single-frequency generation regime in this system if the excess of the operating current above the starting threshold is not too high. The mechanism of loss of stability of the single-frequency generation with an increase in operating current is also described.

Low-frequency broadband sound absorption of the metastructure with extended tube resonators and porous materials

A composite acoustic metastructure consisting of double porous materials and resonators with extended tubes is proposed to seek low-frequency broadband sound absorption, considering the low-frequency absorption of resonators and medium–high frequency absorption of porous materials. Based on the double porosity theory and finite element simulation, the sound absorption performance of the composite metastructure is investigated, and the numerical results are verified by experiments. It has been demonstrated that the metastructure with porous materials arranged vertically or horizontally can exhibit a sound absorption coefficient greater than 0.5 at 265–2000 Hz and greater than 0.8 at 760–2000 Hz, which is significantly superior to the existing sound absorption structure with resonator and porous material with the same thickness. The dependence of the sound absorption performance on the geometric parameters of the extended tubes and the porous materials is revealed. On the premise of keeping the cross-section shape of the extended tube and the arrangement of the porous material unchanged, sound absorption performance at low frequencies depends on the diameter, length, and porosity of the extended tubes, whereas sound absorption performance at medium–high frequencies is primarily determined by the percentage of porous materials. Finally, an improved multiple population genetic algorithm (IMPGA), improved by introducing a weight factor function, is used to optimize the parameters of the composite metastructure in a finite space with a thickness of 50 mm, and the sound absorption coefficient was greater than 0.5 in even lower and broader frequency range of [225,2000] Hz. Additionally, the IMPGA can be adjusted to achieve broadband sound absorption within the target frequency range. It provides a new exploration for acoustic material design for low-frequency broadband sound absorption.

Influence of Coaxial Resonance Tube on Gain Performance of QEPAS

Influence of Coaxial Resonance Tube on Gain Performance of QEPAS

Impact of stack length on performance of standing wave thermoacoustic refrigerator

The low coefficient of performance of thermoacoustic refrigerators has limited their development. The goal of this paper is to investigate the effect of different stack lengths on standing wave thermoacoustic refrigerator (TAR) performance. The stack is essential in TAR because it expands the gas-solid interface, allowing for a greater temperature difference between the warm and cold regions. Hence literature studies on stack length, geometry, plate spacing, and material have been investigated. A quantitative analysis was performed to determine an effective TAR design by numerically modelling three geometries using COMSOL Multiphysics 6.0. A quarter wavelength resonator tube was designed using a 2D axisymmetric model. The acoustic wave and energy fields in solids were studied using conjugate heat transfer, with the fluid flow considered laminar and helium as the working gas. The optimal TAR design was chosen based on the lowest temperature difference between the three simulated geometries. Seven numerical models were simulated for stack lengths ranging from 15 mm to 45 mm, revealing that COP increased as stack length decreased, while the temperature difference decreased.

Eigenfrequency Shift of Piezoelectric Backplate in Vibro-Acoustic Energy Harvesting

Noise is increasingly recognised as a serious, worldwide public health concern. Noise is a type of occupational hazard that can cause damage to hearing and other health effects in workers who are exposed to high levels of noise in their work environment. Traditionally, noise can be controlled and suppressed but recently, noise can be useful and converted into electrical energy. The process of converting noise or acoustic waves into electrical energy by using a quarter wavelength resonator tube embedded with a flexible piezoelectric backplate was used in this study. The results show the maximum output voltage of 1.41 V/Pa at 112 Hz and 0.44 V/Pa at 225 Hz in the experiment, and 1.44 V/Pa at 106 Hz and 0.41 V/Pa at 226.5 Hz with incident sound waves at 90 dB. A parametric study was then performed by adjusting the lumped pointed mass at the piezoelectric backplate to tune the resonant frequencies of the system and the optimal power output. The point mass has given significant change in the acoustic properties. The maximum output power increased from 20.4 at 112 Hz using a flexible back plate to 711 at 119.75 Hz. Various small power applications can benefit from the approach by reducing and absorbing specific low-frequency bandwidths of continuous noise in the environment.

Study of Quality and Damping Factor at First and Second Resonance of Closed Organ Pipe

The quality factor is a dimensionless physical quantity related to the damping factor present in the medium. The sound is recorded from the resonance tube experiment at the first and second resonating lengths. It is analyzed by PRAAT software to calculate the quality and damping factor. The quality factor varies from 12.50 to 146.70 and 6.32 to 130.95 at first and second resonant length respectively. In case of damping factor, it varies from 3.50x10−3 to 40.00x10−3 and 3.82 x10−3 to 79.11x10−3 at respective first and second resonating length. The ratio of the quality factor of the second resonance to that first resonance varies from 0.49 to 0.97 and for the damping factor that ratio varies from 1.02 to 2.02. The quality factor is higher at the first resonating length than at the second resonating length. The damping factor is lower in the first resonating length than in the second resonating length. From the experiment on the closed organ pipe, it was found that the system is under-damped due to the damping factor of less than one. At the first and second resonating lengths the relation between quality and damping factor is inversely nature.