Simulating Boundary Fields of Arbitrary-shaped Objects in a Reverberation Chamber

For the incompressible Navier–Stokes equations, vorticity-based formulations have many attractive features over primitive-variable velocity–pressure formulations. However, some features interfere with the use of the numerical methods based on the vorticity formulations, one of them being the lack of a boundary conditions on vorticity. In this paper, a novel approach is presented to solve the velocity–vorticity integro-differential formulations. The general numerical method is based on standard finite volume scheme. The velocities needed at the vertexes of each control volume are calculated by a so-called generalized Biot–Savart formula combined with a fast summation algorithm, which makes the velocity boundary conditions implicitly satisfied by maintaining the kinematic compatibility of the velocity and vorticity fields. The well-known fractional step approaches are used to solve the vorticity transport equation. The paper describes in detail how we accurately impose no normal-flow and no tangential-flow boundary conditions. We impose a no-flux boundary condition on solid objects by the introduction of a proper amount of vorticity at wall. The diffusion term in the transport equation is treated implicitly using a conservative finite update. The diffusive fluxes of vorticity into flow domain from solid boundaries are determined by an iterative process in order to satisfy the no tangential-flow boundary condition. As application examples, the impulsively started flows through a flat plate and a circular cylinder are computed using the method. The present results are compared with the analytical solution and other numerical results and show good agreement. Copyright © 2005 John Wiley & Sons, Ltd.

Proposal of numerical models to predict the diffuse field sound absorption of finite sized porous materials – BEM and FEM approaches

Incorporating floating surface objects into a fully dispersive surface wave model

An original method allowing to define a particular frequency called “quasi-ideal reverberation chamber (RC) minimum frequency” is presented. This frequency corresponds to the frequency where an RC is considered as working in a “quasi-ideal regime.” According to the definition of an ideal RC, the method is based on the assessment 1) of the electromagnetic (EM) field distributions obtained in the working volume (in comparison with the distributions obtained in the ideal model defined by Hill [D. A. Hill, “Plane wave integral representation for fields in reverberation chambers,” IEEE Trans. Electromagn. Compat., vol. 40, no. 3, pp. 209--217, Aug. 1998.]) and 2) of the number of uncorrelated samples obtained over one mode stirrer revolution. The method is considered as helpful in order to optimize the functioning of an RC at low frequencies for broadband EM compatibility immunity and emission tests. Indeed, it is shown from experimental and numerical results that the insertion of an optimal loading in the chamber allows to decrease the frequency where the chamber works quasi-ideally. The influence of complexifying the mode stirrer geometry is also discussed.

This study aims to simplify the diversity gain measurement in a reverberation chamber since the conventional method requires two extra antennas: a transmitting antenna and a reference antenna with known radiation efficiency. By incorporating the one- or two-antenna method for the radiation efficiency measurement in a reverberation chamber and taking advantage of the enhanced backscattering effect, the proposed method in this letter does not need extra antennas, and only the antenna under test is enough to complete the measurement. A virtual antenna is introduced to help understand the proposed method. The measurement results obtained from the proposed method show a good match with the results obtained from the conventional method; preconditions and limitations of the proposed method are also identified and discussed.

Use of n-perturbation interval ray tracing method in predicting acoustic field distribution

A modified two-antenna method is proposed to measure the radiation efficiency of antennas in a reverberation chamber. By combining the conventional reference antenna method and the one-antenna method, and introducing a virtual antenna, the proposed method does not need a reference antenna with known efficiency and can be applied to highly lossy antennas, which could be problematic for the existing methods. Measurements are conducted to verify the effectiveness of the proposed method. The proposed method can be regarded as a generalized form of the two-antenna method and is compared to the existing reverberation chamber methods. The advantages and limitations of the proposed approach are also discussed.

This paper presents a general method, experimentally validated, highlighting the influence of the number of stirring configurations used during radiated susceptibility tests performed in reverberation chambers in terms of reliability and confidence of the obtained results. This Monte-Carlo based approach (with routines available on demand) computes the risk to declare compliant from an electromagnetic compatibility (EMC) point of view a faulty equipment under test. This risk is calculated according to the number of stirring configurations chosen for the test and to the uncertainty of the electromagnetic field strength applied on the equipment. The proposed method is shown to be applicable for any equipment independently of its size and directivity (or more precisely its receiving polarization pattern). Overtesting is shown in this context to be a promising solution able to increase the confidence of the users about the EMC compliance of tested equipment. The paper also illustrates the possibility to extract the minimum susceptibility level of a valid EUT as a function of the testing conditions.

This study presents an experimental approach to the analysis of absorption characteristics of a lossy dielectric object in a reverberant environment. The study used a canonically shaped water-filled sphere, convenient for Absorption cross-section ACS calculations (analytical or by simulations), and measured the internal temperature rise when exposed to RF radiation. All measurements were conducted in a reverberation chamber. The internal temperature rise due to EM absorption was used to calculate actual SAR, using the bio-heat equation. This was done at two discrete frequencies: 1 GHz and 1.8 GHz. ACS was derived experimentally from scattering parameters measured for a loaded and unloaded chamber. Measured ACS results were compared to the ones calculated analytically using Mie scattering theory, and to the ones calculated from SAR simulations using SEMCAD X, in the frequency range from 1 GHz to 8 GHz. The results show a good agreement, forming a basis for an experimental procedure that can then be used for other less canonical shapes. The results obtained for actual SAR in the reverberation chamber are indicative and can serve as a reference for further exposure studies.

Event-driven sorting algorithm-based Monte Carlo method with neighbour merging method for solving aerosol dynamics

A novel estimation of the collision response between a virtual object and an arbitrarily-shaped real object is presented. By analysing the collision regions, the boundary of the arbitrarily-shaped object is approximated as a sphere for simplicity, and then the collision responds as a sphere-to-sphere collision. Simulations between segmented hand regions and virtual balls show that the proposed method is more appropriate than other methods for augmented reality and serious games, because the motion of real objects can be directly applied.

A new experimental way of testing MIMO systems is proposed by means of two reverberation chambers coupled through a waveguide. The modularity of this experimental setup is emphasized and some theoretical and experimental results are presented. The effect of the waveguide on the propagation channel is pointed out. I. INTRODUCTION MIMO systems have gained a lot of attention since they promise an increase of the capacity with a very high spectral efficiency. The knowledge of the propagation mechanisms is crucial in order to define reliable, precise and adaptive channel models. Theoretical researches have been carried out in order to obtain such a channel model (1). However, a model must be supported by measurements campaigns. Those measurements are highly environment dependent and it is difficult to reproduce or to control the environment. In this paper, a new measurement system is proposed which allows to control and to reproduce different specific environments. This measurement testbed is composed of two reverberation chambers coupled through a waveguide. First, the theoretical modeling of the chambers is presented. To model accurately the channel we have to deepen the understanding of the propagation in the waveguide. The basics of waveguide modal analysis are presented. Then, the power weight of each mode is computed. From this result, we are able to understand intu- itively the propagation mechanism in waveguide like systems and the notion of independent paths with different amount of power. To fulfill the understanding of the waveguide, the radiation of each mode in the receiving chamber is deduced. Some numerical results are provided. A channel model is then presented in order to take into account all the parameters of our system. Measurement results are finally provided, pointing out the ability to obtain different propagation conditions. A discussion about the benefits and the drawbacks of this system concludes the paper. II. THE COUPLED REVERBERATION CHAMBERS The proposed testbed is composed of two mode stirred reverberation chambers (MSRC) of about 16m 3 each. MSRC have first been developed for susceptibility testing of electronic devices. Since they allow to produce a dense and isotropic multipath environment, they are now also used for testing antenna characteristics (such as correlation between antennas, mutual coupling or embedded element pattern) and wireless communications systems (2), (3). By means of the movement of the mechanical stirrer, the boundary conditions are changed and a new distribution of the propagating plane waves in the chamber is obtained. The originality in this paper is the use of two chambers to model separate environments for the emitter and the receiver. Those chambers are coupled through a waveguide (cf. Fig. 1) whose transverse dimensions can be changed in order to modify the channel characteristics between the emitter and the receiver. The waveguide allows to obtain independent propagation paths, and to control the degrees of freedom of the channel.

Reverberation rooms are often used for measuring the sound power emitted by sources of sound. At medium and high frequencies, where the modal overlap is high, a fairly simple model based on sums of waves from random directions having random phase relations gives good predictions of the ensemble statistics of measurements in such rooms. Below the Schroeder frequency, the relative variance is much larger, particularly if the source emits a pure-tone. The established theory for this frequency range is based on ensemble statistics of modal sums and requires knowledge of mode shapes and the distribution of modal frequencies. This paper extends the far simpler random wave theory to low frequencies. The two theories are compared, and their predictions are found to compare well with experimental and numerical results.

In this letter, a fast energy-based method of antenna efficiency measurement in a reverberation chamber (RC) in time domain (TD) is proposed. The antenna efficiency is determined by comparing the received energy from the antenna under test with that from the reference antenna. The measurement results are compared with that from the conventional reference antenna method in the frequency domain (FD). The proposed method needs no mechanical stirring or only a few mechanical stirrer positions, which could reduce the measurement time significantly.

Low-frequency sound source localization in enclosed space based on time reversal method