共查询到20条相似文献,搜索用时 15 毫秒
1.
V. V. Arabadzhi 《Acoustical Physics》2006,52(5):505-512
The problems of suppressing the sound field generated by a vibrating body in a liquid are considered. For solving these problems, an acoustically thin active coating with a real-time thickness control is proposed. The coating should be placed directly on the surface of the body to be protected. Solutions to the problems of suppressing the radiation and scattering of sound by a body are obtained in the general form on the basis of linear operators, which characterize (i) the sound radiation by a vibrating surface, (ii) the scattering of incident waves by a fixed surface, and (iii) the vibroelastic properties of the body in an acoustic vacuum. Conditions ensuring the stability of the active system are formulated. 相似文献
2.
D Guicking K Karcher M Rollwage 《The Journal of the Acoustical Society of America》1985,78(4):1426-1434
An adjustment of reverberation time in rooms is often desired, even for low frequencies where passive absorbers fail. Among the active (electroacoustic) systems, incoherent ones permit lengthening of reverberation time only, whereas coherent active methods will allow sound absorption as well. A coherent-active wall lining consists of loudspeakers with microphones in front and adjustable control electronics. The microphones pick up the incident sound and drive the speakers in such a way that the reflection coefficient takes on prescribed values. An experimental device for the one-dimensional case allows reflection coefficients between almost zero and about 1.5 to be realized below 1000 Hz. The extension to three dimensions presents problems, especially by nearfield effects. Experiments with a 3 X 3 loudspeaker array and computer simulations proved that the amplitude reflection coefficient can be adjusted between 10% and 200% for sinusoidal waves at normal and oblique incidence. Future developments have to make the system work with broadband excitation and in more diffuse sound fields. It is also planned to combine the active reverberation control with active diffusion control. 相似文献
3.
Hurrell AM 《The Journal of the Acoustical Society of America》2008,123(6):4210-4217
The interaction of an incident sound wave with an acoustically impenetrable two-layer barrier is considered. Of particular interest is the presence of several acoustic wave components in the shadow region of this barrier. A finite difference model capable of simulating this geometry is validated by comparison to the analytical solution for an idealized, hard-soft barrier. A panel comprising a high air-content closed cell foam backed with an elastic (metal) back plate is then examined. The insertion loss of this panel was found to exceed the dynamic range of the measurement system and was thus acoustically impenetrable. Experimental results from such a panel are shown to contain artifacts not present in the diffraction solution, when acoustic waves are incident upon the soft surface. A finite difference analysis of this experimental configuration replicates the presence of the additional field components. Furthermore, the simulated results allow the additional components to be identified as arising from the S(0) and A(0) Lamb modes traveling in the elastic plate. These Lamb mode artifacts are not found to be present in the shadow region when the acoustic waves are incident upon the elastic surface. 相似文献
4.
Error analysis of a practical energy density sensor 总被引:1,自引:0,他引:1
Parkins JW Sommerfeldt SD Tichy J 《The Journal of the Acoustical Society of America》2000,108(1):211-222
The investigation of an active control system based on acoustic energy density has led to the analysis and development of an inexpensive three-axes energy density sensor. The energy density sensor comprises six electret microphones mounted on the surface of a 0.025-m (1 in.) radius sphere. The bias errors for the potential, kinetic, and total energy density as well as the magnitude of intensity of a spherical sensor are compared to a sensor comprising six microphones suspended in space. Analytical, computer-modeled, and experimental data are presented for both sensor configurations in the case of traveling and standing wave fields, for an arbitrary incidence angle. It is shown that the energy density measurement is the most nearly accurate measurement of the four for the conditions presented. Experimentally, it is found that the spherical energy density sensor is within +/- 1.75 dB compared to reference measurements in the 110-400 Hz frequency range in a reverberant enclosure. The diffraction effects from the hard sphere enable the sensor to be made more compact by a factor of 3 compared to the sensor with suspended microphones. 相似文献
5.
Nowlin WC Guthart GS Toth GK 《The Journal of the Acoustical Society of America》2000,107(4):2039-2048
This paper presents experimental validation of a class of algorithms designed to enable active noise control (ANC) to function in environments when transfer functions change significantly over time. The experimental results presented are for broadband, local quieting in a diffuse field using a multichannel ANC system. The reverberant enclosure is an ordinary room, measuring approximately 1.4 x 2.4 x 2.4 m3 and containing a seated occupant, with six microphones defining the quiet zone near the occupant's ears. The control system uses a single reference signal and two error channels to drive four secondary sources. Using an ideal reference sensor, reduction in sound pressure level is obtained at the quiet-zone microphones averaged over the frequency range 50 to 1000 Hz with an occupant seated in the room. Two main results are presented: first for an adaptive cancelling algorithm that uses static system models, and second for the same algorithm joined with a noninvasive real-time system identification algorithm. In the first case better than 23 dB of performance is obtained if the occupant remains still through calibration and testing. In the second case, approximately 18 dB is obtained at the error microphones regardless of the motion of the occupant. 相似文献
6.
7.
V. V. Arabadzhi 《Radiophysics and Quantum Electronics》2000,43(7):593-599
We designed, and studied experimentally, an active system for quenching surface gravity waves in a liquid. This system is
based on the cyclic wave gate (CWG) principle. The thickness of the quenching system was about one-tenth of the length of
the seiche wave but can also be much smaller than that in accordance with the CWG principle. The use of a high spatio-temporal
resolution for parameter control of the waveguiding medium in the active region of the CWG and the opacity of this medium
for high-frequency waves make it unnecessary to measure the wave field and generate a quenching wave.
Institute of Applied Physics of the Russian Academy of Sciences, Nizhny Novgorod, Russia Translated from Izvestiya Vysshikh
Uchebnykh Zavedenii, Radiofizika, Vol. 43, No. 7, pp. 657–664, July, 2000. 相似文献
8.
N. G. Kanev 《Acoustical Physics》2016,62(6):760-763
Absorption of sound waves incident on a plane surface with arbitrary impedance by a planar active resonator array consisting of monopole or dipole resonators and positioned near the surface is considered. Appropriate tuning of active resonators ensures complete absorption of sound waves incident at a fixed angle in a broad frequency band. The effect of tuning errors on the efficiency of sound absorption by the systems under study is investigated. It is shown that, for rigid surfaces, a monopole resonator array yields a higher absorption efficiency, whereas for soft surfaces, a dipole resonator array is the more efficient one. 相似文献
9.
We consider the inverse scattering problem of a perfectly conducting one-dimensional rough surface in the case that the incident field is unnecessary to be time harmonic. Based on our previous investigation of the frequency domain algorithm, a new time domain algorithm is proposed, in which we approximate the incident pulse by a finite sum of time harmonic fields and then apply the frequency domain algorithm for time harmonic waves. Numerical experiments indicate that the time domain algorithm shows great accuracy of reconstruction of the surface profile and yields significant improvement than the frequency domain algorithm. 相似文献
10.
We study the transverse or off-axis localization of electromagnetic waves for several different random dielectric systems which are periodic on average. Unlike previous scalar wave treatments of transverse localization, in the present work we present results based on a full vector treatment of the electromagnetic fields based on Maxwell's equations. In a first system, we consider a random semi-infinite array of slabs with plane waves or finite beams of electromagnetic waves obliquely incident on the slab surfaces. The localization of the fields in a region near the surface of illumination is studied as a function of the oblique angle of incidence. In a second system, an array of semi-infinite slabs with random thickness is considered with an incident finite beam of electromagnetic waves initially directed parallel to the slab surfaces. The spreading of the beam width is computed as it propagates through the array of semi-infinite slabs. In a final system, we consider a semi-infinite array of random dielectric rods (2D system) with obliquely incident plane waves. The localization length of the plane-wave fields is computed as a function of the oblique angle of incidence and as a function of the strength of the disorder of the dielectric medium. All the random media we consider, when averaged over their randomness, are periodic on average. The above systems are studied for both p- and s-polarizations of incident electromagnetic waves, and the difference in the transverse localization of the electromagnetic field for these two polarizations is determined. 相似文献
11.
球形传声器阵列是实现封闭空间三维声场重构的测量前端,传声器在球形阵列面上的分布对三维声场重构的精度有重要影响。针对球面近场声全息方法,结合I.H.Sloan,Spherical t-designs,J.Fliege等球面数值积分法,检验传声器数目、传声器几何位置分布、积分权重、波数、基函数扩展项数、声场重构半径等参数对声场重构精度的影响。结果表明:Spherical t-designs球面数值积分法与其它积分法相比,在声场重构误差接近的情形下,允许传声器的数目和位置布置有更多的选择,并且在传声器数目一定时,各点积分权重相等,使得球面近场声全息中球面数值积分计算相对简单。 相似文献
12.
Yu. I. Bobrovnitskii 《Acoustical Physics》2004,50(6):647-650
The method of active impedance matching is applied to the well-known problem of an acoustically transparent body. Two laws of active force control, by velocity and by pressure, are obtained for solving the problem. 相似文献
13.
The electromagnetic field solution for a spherical invisibility cloak with an active device inside is established. Extraordinary electric and magnetic surface voltages are induced at the inner boundary of a spherical cloak, which prevent electromagnetic waves from going out. The phase and handness of polarized waves obliquely incident on such boundaries are kept in the reflected waves. The surface voltages due to an electric dipole inside the concealed region are found equal to the auxiliary scalar potentials at the inner boundary, which consequently gain physical counterparts in this case. 相似文献
14.
This paper focuses on an active noise cancellation system for a home window using a transparent acoustic transducer. In a traditional active noise cancellation system, direct microphone measurements are used for reference and error signals. In the case of the window application, both external and internal sound would be picked up by such microphones. This leads to adverse effects on the performance of the active noise cancellation system and also to distortion of the internal sound. To address this problem, a wave separation technique is proposed to separate the internal and external components of sound. The wave separation algorithm is based on the use of two microphones and an algorithm that separates components based on their direction of travel. An active noise cancellation system is implemented using wave separation for both the error and reference signal measurements. The performance of the resulting ANC system is experimentally tested in a cabin equipped with a window and results are presented. Experimental results show that the new system is able to accurately preserve desired internal sound while cancelling uncorrelated external noise. 相似文献
15.
Fang Xue-Qian Zhang Le-Le Liu Jin-Xi 《Applied Physics A: Materials Science & Processing》2012,106(3):625-633
Taking into account the size of the nanostructure, the effect of surface/interface stiffness on the dynamic stress around
a cylindrical nano-inhomogeneity embedded in an elastic half-plane subjected to anti-plane shear waves is investigated. The
boundary condition at the straight edge of the half-plane is traction free, which is satisfied by the image method. The analytical
solutions of displacement fields are expressed by employing a wave function expansion method. The addition theorem for a cylindrical
wave function is applied to accomplish the superposition of wave fields in the two half-planes. Analyses show that the effect
of the interface properties on the dynamic stress is significantly related to the nano-scale distance between the straight
edge and the center of the cylindrical nano-inhomogeneity. The frequency and incident angle of incident waves and the shear
modulus ratio of the nano-inhomogeneity to matrix also show different effect on the dynamic stress distribution when the inhomogeneity
shrinks to nano-scale. Comparison with the existing results is also given. 相似文献
16.
A solution of the problem of parametric interaction between a plane monochromatic shear wave and a uniformly moving 180°-domain wall of a garnet-ferrite crystal is obtained in the exchangeless magnetostatic approximation by using the perturbation method under the conditions of a nonlinear response of the spin subsystem. It is shown that in a ferromagnetic resonance with magnetostatic oscillation of stray fields, the nonlinearity of the spin subsystem leads to the excitation of shear waves of triple frequency, which may have amplitudes comparable with that of the incident wave for oscillations doubly localized by a domain wall. 相似文献
17.
Yusuf Z. Umul 《Optik》2012,123(7):624-628
A theory of scattering, based on the non-perturbation of the incident field, is developed for the black bodies. The method is applied to the diffraction problem of plane waves by an interface between the black and soft/hard half-planes. The solutions are obtained in terms of infinite series and then transformed into Fresnel integrals. The scattered fields are investigated numerically. 相似文献
18.
Wiederhold CP Gee KL Blotter JD Sommerfeldt SD 《The Journal of the Acoustical Society of America》2012,131(4):2841-2852
One design for three-dimensional multimicrophone probes is the four-microphone orthogonal design consisting of one microphone at an origin position with the other three microphones equally spaced along the three coordinate axes. Several distinct processing methods have been suggested for the estimation of active acoustic intensity with the orthogonal probe; however, the relative merits of each method have not been thoroughly studied. This comparative study is an investigation of the errors associated with each method. Considered are orthogonal probes consisting of matched point sensor microphones both freely suspended and embedded on the surface of a rigid sphere. Results are given for propagating plane-wave fields for all angles of incidence. It is shown that the lowest error for intensity magnitude results from having the microphones in a sphere and using just one microphone for the pressure estimate. For intensity direction, the lowest error results from having the microphones in a sphere and using Taylor approximations to estimate the particle velocity and pressure. 相似文献
19.
The propagation of transverse surface waves in a piezoelectric layer/metal substrate system with one or multiple hard metal interlayer(s) is investigated analytically. The general dispersion equations for the existence of the waves are obtained in a simple mathematic form for class 6 mm piezoelectric materials. The presence of a hard metal interlayer can not only get rid of the undesired mode appearing in the case without an interlayer but shorten the existence range of the phase velocity within which a nonleaky but dispersive mode exists. The effects of the hard interlayer on the phase velocity can be used to manipulate the behavior of the waves and has implications in acoustic wave devices. 相似文献
20.