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Acoustical Materials
Published in Lewis H. Bell, Douglas H. Bell, Industrial Noise Control, 2017
Lewis H. Bell, Douglas H. Bell
In the tube method, a sample of the material is placed at the end of the tube, as illustrated in Fig. 6.1. Discrete frequency sound waves generated by the loudspeaker propagate down the tube, impinge upon the sample, and are reflected. A standing wave interference pattern results due to the superposition of the incident and reflected wave. The following parameters are then measured with the movable microphone or probe: L = difference in decibels between the maximum and minimum sound pressure levels in the standing wave pattern in the tubeD1 = distance from the face of the specimen to the nearest minimum in standing wave pattern, measured in any convenient unitsD2 = distance from the first to the second minimum in standing wave pattern, measured in the same unit as D1
Introduction
Published in Marek Pawelczyk, Stanislaw Wrona, Noise-Controlling Casings, 2023
Marek Pawelczyk, Stanislaw Wrona
With the development of microelectronics and signal processing techniques in the last 30 years, active noise reduction methods are gaining popularity. Their hallmark is the introduction of external energy into the process. There are different physical justifications associated with different active control methods. The most common justification is based on the Young's principle of destructive wave interference – the superposition of two acoustic waves with the same amplitudes but opposite phases causes their mutual elimination. Starting from these premises, therefore, it is necessary to generate an additional acoustic wave, which will destructively interfere with the acoustic wave associated with noise. Such a wave should be generated using an additional secondary sound source, such as a loudspeaker or other vibrating structure, based on measurements made in the acoustic field, or by estimating appropriate quantities using mathematical models. Unfortunately, while the general form of the method seems to be very simple, its effective application in practice encounters many limitations. First of all, the acoustic field is complex in nature, and even if one could ensure that the above amplitude-phase condition could be satisfied at a single point in space, it is much more difficult to satisfy it over a larger area. In practice, this can produce so-called local quiet zones, the size of which depends largely on the frequencies dominating the noise. Enlarging these sizes requires suitably favourable geometrical conditions or the use of many or very many secondary sound sources. This involves considerable complexity of the algorithm, of the entire system, including the electronics, requiring multi-channel high-speed processing, and thus considerable and usually unacceptable cost. This complexity increases, in the case when the reduction of the sound pressure level is not the only goal, but it is also necessary to provide a rapid response to changes in the parameters of the sound field caused, for example, by non-stationary of noise, changes in the room itself, movement of users, temperature changes, etc.
A non-uniform strip-array decoupling structure of the MIMO antenna-arrays for the DSRC application
Published in International Journal of Electronics Letters, 2023
In order to further verify the effectiveness of the proposed non-uniform SADS, the radiation and decoupling performances of the MIMO array are analysed and discussed. Figure 3(a) shows the S-parameters of the three arrays with no-strip, the uniform and non-uniform SADS. It is noticed that the of the MIMO array with no-strip and the uniform SADS under −10 dB cover 5.780 GHz~5.825 GHz and 5.75 GHz~5.825 GHz, respectively. The of the array with the proposed SADS contains 5.73 GHz~5.825 GHz, which is occurred to completely cover the required DSRC frequency ranges. It is also seen that the by the proposed non-uniform SADS is less than −32 dB at the required bandwidth. Compared with no-strip and the uniform SADS, the mutual coupling between the elements of the non-uniform SADS is effectively suppressed by 23 dB and 13 dB, respectively. It is proved that the proposed non-uniform SADS can significantly restrain the surface wave interference of coupled field. In Figure 3(b), the simulated and measured results of S-parameters validate the effectiveness of the proposed non-uniform SADS. It is observed that the S-parameters differences between the simulated and measured results are caused by the manufacturing and measurement errors of the array, and the manufacturing and measurement accuracy will cause great changes in the antenna radiation performances.
Research on electrostatic shielding characteristics of electrostatic precipitator
Published in Journal of the Air & Waste Management Association, 2022
Bing Chen, Shiqing Li, Yongheng Guo, Hongjiao Li, Wenning Zhou, Baiqian Liu
In recent years, the problem of environmental pollution has become increasingly serious, which has already affected people’s normal lives and threatened human life and health. The presence of PM10 and PM2.5 in the atmosphere can cause great harm to the human body. Inhalation of these carcinogenic particles by the human body increases the risk of cancer (Yi, Yin, and Huang 2013; Zeng, Yu, and Xia 2006). Therefore, how to reduce the pollutants in the atmosphere and how to control the discharge of pollutants has become a social issue that has attracted wide public attention (Wu, Yu, and Xia 2014). ESP is a device that collects dust in flue gas by electrostatic purification method, and is an ideal equipment for purifying industrial waste gas. The internal high voltage of ESP will cause radio wave interference to most of the instruments, and there are also great safety risks. Therefore, it is difficult to test the space charge density distribution and the movement characteristics of ESP. With the continuous development of computer simulation technology and methods, problems that cannot be solved by testing methods can be solved through numerical simulation.
Matter-wave interferometry with atoms in high Rydberg states
Published in Molecular Physics, 2019
To confirm the attribution of the oscillations in the data in Figure 8 to effects of matter-wave interference, and that they are not a consequence of resonances or fluctuations introduced by the pulsed electric fields, several further tests were performed. The results of these are displayed in Figure 10. For all of the measurements in this figure ns and ns. The data in Figure 10(a) represents a reference measurement which corresponds to that in Figure 8(c). To check that the oscillations in the ratio of the circular state populations upon application of the complete interferometry sequence of microwave and electric field gradient pulses relied on the preparation and coherent manipulation of the superpositions of Rydberg states the data in Figure 10(b–d) were recorded with the first , the and all three microwave pulses omitted, respectively. No oscillations are seen with the periodicity of those observed in Figure 10(a) in any of these data sets. The data in Figure 10(d), in which no microwave pulses were applied and the normalised signal gradually reduces as is increased, confirms that the loss in the circular state populations for larger values of is a result of non-adiabatic internal Rydberg-state dynamics and is not caused by decoherence of the superposition of momentum states.