Noise control by barriers—Part 1: Noise reduction by a thick barrier

This paper presents a method of estimating the excess attenuation of noise by a thick barrier. In this method, the excess attenuation of noise by a thick barrier is assumed to be composed of two parts, one being the effect of a virtual thin barrier with the same height and the other the effect of thickness. A single chart for estimating this thickness effect is offered under conditions which only permit an error of a few decibels. The validity of the method presented here is verified by comparing the estimated with the measured values. Consequently, this method may be useful for the purpose of estimating the excess attenuation of a band of noise by the barrier whose thickness is larger than half a wavelength.     

Noise attenuation in factories

The cost of reducing noise levels in factories by covering large surfaces with sound absorbents is high. It is therefore important to be able to calculate in advance the effectiveness of absorbents and to determine how absorbents may be chosen and distributed for maximal noise reduction for the invested capital. For this purpose a mathematical model of sound propagation and attenuation in factories has been developed on certain simplifying assumptions. The interrelationship between the different parameters is found to be rather intricate and the mathematical model must be evaluated using a computer program. The influence on the noise levels of sound scattering objects, the shape and size of the factory and absorbents on the room surfaces have been studied. Especially if the ceiling is high, acoustic baffles are found to be more efficient than absorbents on the ceiling in reducing noise levels.     

Noise reduction by various shapes of barrier

This paper shows that noise reduction by various shapes of finite barrier can be achieved by applying the Fresnel-Kirchhoff diffraction theory and primarily follows the ideas of Maekawa.¹ The calculated results for several kinds of small-scale model, obtained by our procedure, are compared with experimental results.     

Noise reduction in tunnels by hard rough surfaces

This paper examines the feasibility of using two-dimensional hard rough surfaces to reduce noise levels in traffic tunnels with perfectly reflecting boundaries. First, the Twersky boss model is used to estimate the acoustic impedance of a hard rough surface. Second, an image source model is then used to compute the propagation of sound in a long rectangular enclosure with finite impedance. The total sound fields are calculated by summing the contributions from all image sources coherently. Two model tunnels are built to validate the proposed model experimentally. Finally, a case study for a realistic geometrical configuration is presented to explore the use of hard rough surfaces for reducing traffic noise in a tunnel which is constructed with hard boundaries.     

Noise control by barriers—Part 2: Noise reduction by an absorptive barrier

This paper presents a method of estimating the excess attenuation of a noise by an absorptive barrier covered with sound-absorbing materials. The approximate theory of diffraction by the absorptive barrier is derived from rigorous theory for a hard barrier. A single chart, which may be very convenient for the rapid estimation of the effect of absorption (the increase of the excess attenuation caused by the absorbing treatment of the barrier) in the practice of noise control, is presented. The validity of the method developed in this paper is confirmed by comparing estimated with measured values.     

Noise barrier optimization using a simulated annealing algorithm

This paper presents a novel method to design a desired noise barrier using the global optimization of a simulated annealing (SA) algorithm. This method focuses on minimizing the barrier dimensions, which are related to material and construction costs, as well as satisfying the target sound pressure levels at receiver points on the condition of traffic noise. Various examples are presented to evaluate the optimized barrier dimensions according to given traffic noise sources, ground topography, surface conditions, and the influence of different receiver positions. As a result, a robust method is found that can determine optimized barrier configurations and dimensions that yield cost reductions.     

Determination of attenuation and phase velocity of hypersound by multiple-beam interferometry in evaporated wedge-shaped metal films

By means of movable beams of coherent pulsed phonons it is possible to record multiple-beam interferences in wedge-shaped evaporated films as a function of thickness. By fitting calculated interferograms to these phonon interferograms the attenuation and phase velocity of longitudinal and transverse hypersound can be determined for these films. Details of the experimental setup used at 1 GHz, 3 GHz, 9 GHz and 24 GHz as well as the preparation of wedge-shaped metals films are described, too.Supported by Deutsche Forschungsgemeinschaft     

Noise correlations of fermions and hard core bosons in a quasi-periodic potential

We use Hanbury-Brown-Twiss interferometry (HBTI) to study various quantum phases of hard core bosons (HCBs) and ideal fermions confined in a one-dimensional quasi-periodic (QP) potential. For HCBs, the QP potential induces a cascade of Mott-like band-insulator phases in the extended regime, in addition to the Mott insulator, Bose glass, and superfluid phases. At critical filling factors, the appearance of these insulating phases is heralded by a peak to dip transition in the interferogram, which reflects the fermionic aspect of HCBs. On the other hand, ideal fermions in the extended phase display various complexities of incommensurate structures such as devil’s staircases and Arnold tongues. In the localized phase, the HCB and the fermion correlations are identical except for the sign of the peaks. Finally, we demonstrate that HBTI provides an effective method to distinguish Mott and glassy phases.     

Acousto-optic interaction in a non-homogeneous acoustic field excited by a wedge-shaped transducer

The article is devoted to theoretical analysis of light diffraction in a non-homogeneous acoustic field created by a wedge-shaped piezoelectric transducer. Relationships describing electrical, acoustic and acousto-optic properties of the acousto-optic cell are derived in the approximation of a small thickness of the piezoelectric plate. Principal characteristics of acousto-optic interaction are examined such as dependences of the light diffraction efficiency on the phase mismatch and the acoustic wave amplitude. It is shown that the acoustic field has a complicated amplitude-phase structure changing with the acoustic frequency. It is demonstrated that the diffraction efficiency in the Bragg regime can approach 100% in spite of a noticeable phase mismatch. The appropriate optimal values of ultrasound power and incidence angles of light are found.     

Stark effect in a wedge-shaped quantum box

The effect of an external applied electric field on the electronic ground-state energy of a quantum box with a geometry defined by a wedge is studied by carrying out a variational calculation. This geometry could be used as an approximation for a tip of a cantilever of an atomic force microscope. We study theoretically the Stark effect as function of the parameters of the wedge: its diameter, angular aperture and thickness; as well as function of the intensity of the external electric field applied along the axis of the wedge in both directions; pushing the carrier towards the wider or the narrower parts. A confining electronic effect, which is sharper as the wedge dimensions are smaller, is clearly observed for the first case. Besides, the sign of the Stark shift changes when the angular aperture is changed from small angles to angles θ>π. For the opposite field, the electronic confinement for large diameters is very small and it is also observed that the Stark shift is almost independent with respect to the angular aperture.     

高功率楔形介质填充天线设计

 针对高功率超宽带天线应用中的绝缘性及方向性等关键问题,设计了一种基于TEM喇叭天线形式的楔形介质填充天线,并利用时域有限差分数值方法分析了这种新型介质填充天线的辐射性能。数值模拟与测试结果表明,所设计的这种楔形介质填充天线不仅可以满足高功率天线的绝缘性要求,而且在主轴方向上具有较强的辐射场。     

Nonuniform elastic stagnant wave in a wedge-shaped plate

An acoustic field near the edge of an elastic wedge-shaped plate is studied. The field is represented in the form of two counterpropagating nonuniform waves. The standing vibration profiles varying with distance to the edge are constructed. A specific acoustic effect arising when the wave moves away from the wedge is revealed. Theoretical results are confirmed by measuring the standing wave amplitudes with a proprietary setup.     

Noise annoyance and activity disturbance before and after the erection of a roadside noise barrier

Questionnaire studies were conducted in a residential area before and after the erection of a 2.25 m high noise barrier of conventional type along a heavily traveled road (19,600 vehicles/24 h). The interval between studies was two years. Houses closest to the barrier received a sound-level reduction from -70.0 to 62.5 dB Lden at the most exposed facade. The sound-level reduction decreased with distance to the road, and was negligible for houses at more than 100 m distance. Up to this distance, the noise barrier reduced residents' noise annoyance outdoors and indoors as well as improved speech communication outdoors. Indoors, speech communication and sleep disturbance were slightly but nonsignificantly improved. Predictions of the number of annoyed persons from published exposure-response curves (in Lden) agreed with the percentage of residents being annoyed when indoors, before and after the barrier. Conversely, the percentage of residents being annoyed when outdoors clearly exceeded the predictions. These results suggest that these exposure-response curves may be used in predicting indoor situations, but they should not be applied in situations where outdoor annoyance is at focus.     

Large negative Goos-Hainchen shift from a wedge-shaped thin film

The analytical expression for the complex amplitude of light reflected from a wedge-shaped thin film is derived. For plane wave incidence, a simple ray tracing approach is used to calculate Goos-Hanchen （GH） shifts; and for non-plane wave incidence, for example, a Gaussian beam, the angular spectrum approach of plane wave is used in simulation. The two approaches predict that a wedge-shaped thin film can produce large negative longitudinal GH shifts. Although the reflectivity is small near the condition of resonance, the large negative GH shifts can be more easily detected in comparison with the shift from a plane-parallel film in vacuum.     

Transitions in a Logistic Growth Model Induced by Noise Coupling and Noise Color

With unified colored noise approximation, the logistic growth model is used to analyze cancer cell population when colored noise is included. It is found that both the coupling between noise terms and the noise color can induce continuous first-order-like and re-entrance-like phase transitions in the system. The coupling and the noise color can also increase tumor cell growth for small number of cell mass and repress tumor cell growth for large number of cell mass. It is shown that the approximate analytic expressions are consistent with the numerical simulations.     

Transitions in a Logistic Growth Model Induced by Noise Coupling and Noise Color

With unified colored noise approximation, the logistic growth model is used to analyze cancer cell population when colored noise is included. It is found that both the coupling between noise terms and the noise color can induce continuous first-order-like and re-entrance-like phase transitions in the system. The coupling and the noise color can also increase tumor cell growth for small number of cell mass and repress tumor cell growth for large number of cell mass. It is shown that the approximate analytic expressions are consistent with the numerical simulations.     

Sound diffraction by a barrier with a fan-shaped headpiece

With respect to a noise barrier, sound diffraction by a half-plane with a fan-shaped headpiece is calculated. The fan consists of a set of rigid strips of different widths, which form narrow wedge-shaped channels of different lengths. The channels are connected to each other through the inner cylindrical cavity into which the inner open ends of the channels face. The curves representing the degree of sound suppression as a function of the frequency and the angle of incidence of sound waves are calculated. These curves demonstrate the high efficiency of the proposed barrier.