This communication presents the performance of a vibrating intrinsic reverberation chamber (VIRC) prototype, which is proven to cancel the presence of unstirred paths inside. To do so, the chamber ...made of metallized textile is suspended above the ground. Therefore, each point of the canvas can move under the effect of the stirring process. To highlight this fundamental result, we have introduced an original metric called the "minimum achievable <inline-formula> <tex-math notation="LaTeX">K </tex-math></inline-formula>-factor" derived from the <inline-formula> <tex-math notation="LaTeX">K </tex-math></inline-formula>-factor, the one which assesses the ratio between the stirred and the unstirred energy within a reverberation chamber (RC). When comparing with the results obtained in a classic RC, it is shown that the amount of unstirred energy is significantly reduced in our VIRC, which can benefit to numerous RC applications. Moreover, the presence of unstirred paths is shown to be fully canceled above 7 GHz; the <inline-formula> <tex-math notation="LaTeX">K </tex-math></inline-formula>-factor being similar to the minimum achievable <inline-formula> <tex-math notation="LaTeX">K </tex-math></inline-formula>-factor. It is, therefore, possible to consider that our prototype works as a perfectly chaotic RC above this frequency.
A reverberation chamber is capable of generating and measuring electromagnetic fields and is used for electromagnetic compatibility test evaluations of electrical and electronic equipment and ...systems. While the mechanical stirring type is generally the mainstream, a vibrating intrinsic reverberation chamber (VIRC), which is based on an electromagnetic shielding tent made of flexible conductive fabric, is attracting more interest because it is less expensive and is able to perform in-situ tests. In this article, we presented a VIRC configuration and measured its basic characteristics, i.e., the number of independent samples, the goodness of fit to the Rayleigh distribution and the field uniformity, depending on the wall shaking amplitude as a stirring condition. The measurement results contribute to derive a guideline for the VIRC design, i.e., the wall shaking amplitude should be more than one-eighth of the wavelength at the test frequency.
In recent years, promising results have been reported with the vibrating intrinsic reverberation chamber (VIRC) combining performance and cost-efficiency for electromagnetic compatibility (EMC) ...measurements. This also makes it a potentially attractive solution for over-the-air (OTA) testing, which is yet to be investigated. Therefore, this article proposes the first systematic and thorough methodology to characterize the VIRC for use in EMC and OTA testing of wireless baseband algorithms of narrow-band single-input single-output channels. This methodology has been developed to measure and estimate the channel first- and second-order temporal and spectral characteristics taking into consideration the effect of different carrier frequencies, rotational speeds of VIRC motors, and loading conditions. It is then applied to a channel setup inside a VIRC for a preliminary investigation before the VIRC itself is fully characterized. It is shown that mounting an absorber in a specific location on the hatch significantly improves the rejection rate of the chi-squared goodness-of-fit test for Rician distribution without increasing the <inline-formula><tex-math notation="LaTeX">K</tex-math></inline-formula>-factor above <inline-formula><tex-math notation="LaTeX">-</tex-math></inline-formula>10 dB over the frequency range 755-2740 MHz in the VIRC under investigation. However, the proposed methodology has been devised to be universal to any reverberation chamber, and the obtained results can be used to improve EMC testing due to the better understanding of the unique VIRC environment.
Green roof systems can contribute to sustainable urban planning in terms of acoustics by absorbing sound energy and thereby reducing sound levels. However, these positive contributions may vary ...depending on the substrate's nature, the characteristics of the plants, and the extent of vegetation coverage.
In this work, experimental measurements were carried out in both a reverberation chamber and in an anechoic chamber to assess the effect of two different substrates (an engineered substrate specifically prepared for green roof systems and an ordinary soil), three plant species (Thymus pulegioides, Festuca glauca, and Sedum sediforme), and three levels of vegetation coverage (0 %, 50 %, and 100 %) on the acoustic behaviour of a typical green roof system.
Initially, the experimental setups and the characteristics of plants and substrates used are fully described. Subsequently, the results are analysed to inspect the individual and collective influence of the different variables on the sound absorption, scattering, and diffusion properties.
The results confirmed the expected good sound absorption behaviour and the relatively lesser important scattering properties of the combined effect of substrate and plants. The substrate was found to have a significant impact on the acoustic absorption. Additionally, the scattering results suggest that plant morphology can also influence such systems’ acoustic behaviour.
•Acoustic behaviour of a typical green roof system accessed in laboratory conditions.•Experimental tests carried out in reverberation and anechoic chambers.•Individual and combined role of substrate, plant species and vegetation coverage.•Good sound absorption behaviour provided by the green roof system.•Plant morphology may influence the acoustic scattering behaviour.
This article presents an original simulation procedure devoted to the simulation of arbitrary-shaped reverberation chambers especially well suited for the analysis of vibrating intrinsic ...reverberation chambers (VIRC). The described method is based upon conformal finite-difference in time-domain (FDTD) modeling in order to model the rough surface geometry of the VIRC walls. On this point, we take full advantage of the performance of our in-house numerical FDTD code called TEMSI-FD and of its associated conformal mesher. First, uncorrelated geometries of the VIRC under study have been generated in order to analyze its performance as a RC from the computed <inline-formula><tex-math notation="LaTeX">S_{11}</tex-math></inline-formula> parameter of a log-periodic antenna. Second, correlated geometries have been generated in order to consider the continuous movement of the VIRC walls with a straightforward algorithm, each geometry being associated to a given instant. In both frequency and time domains, numerical outcomes demonstrate excellent agreement with experimental results available in the literature in similar conditions.
Considering the time-varying movement of the canvas constituting a vibrating intrinsic reverberation chamber (VIRC), the optimization of the stirring process of such facility is not trivial. Indeed, ...this task requires reliable and accurate metrics able to state if a given modification of the stirring process will increase or decrease the VIRC performance. This article presents a fast and accurate relative method based on the K -factor metric. For each stirring configuration to be assessed, the scattering parameter measurements that are required typically last less than a minute. Used in a recently installed VIRC, the method has led us to optimize each implemented stirring process (fans installed outside the VIRC and two motors pushing the canvas) and to greatly increase the VIRC performance when all these processes are combined together.
The paper deals with reverberation chambers for over-the-air (OTA) testing of wireless devices for use in multipath. We present a formulation of the S-parameters of a reverberation chamber in terms ...of the free space S-parameters of the antennas, and the channel matrix in the way this is known from propagation literature. Thereby the physical relations between the chamber and real-life multipath environments are more easily explained. Thereafter we use the formulation to determine the uncertainty by which efficiency-related quantities can be measured in reverberation chamber. The final expression shows that the uncertainty is predominantly determined by the Rician K-factor in the reverberation chamber rather than by the number of excited modes, assumed by previous literature. We introduce an average Rician K-factor that is conveniently expressed in terms of the direct coupling between the transmitting and receiving antennas (corresponding to a line-of-sight contribution) and Hill's transmission formula (corresponding to a multipath or non-line-of-sight contribution). The uncertainty is expressed in terms of this average K-factor and geometrical mode stirring parameters, showing strong reduction by platform and polarization stirring. Finally the formulations are verified by measurements, and the new understanding of uncertainty is used to upgrade an existing reverberation chamber to better uncertainty.
This article presents a complete framework able to characterize the performances in both frequency and time domains of "vibrating intrinsic reverberation chambers" made of a metallized tent of shape ...continuously changing under the action of the stirring process. In the frequency domain, the analysis is based on a method proposed recently in order to assess from which frequency the chamber can be "well-stirred." The method uses <inline-formula><tex-math notation="LaTeX">S_{11}</tex-math></inline-formula> measurements of the emitting antenna in only one position of the VIRC for different stirring conditions, here at different instants. The performances of the VIRC are shown to be similar to the ones obtained in a "classical" parallelepipedic RC of similar volume. In the time domain, a method is proposed in order to measure the decorrelation time defined as the minimum interval of time to wait in order to collect two successive independent samples and to detect any periodical repetition of the stirring process. This time-domain analysis emphasizes that the number of collectable samples is proportional in a VIRC to the measurement time. The use of a VIRC could therefore contribute to severely decrease the uncertainty budget of some RC measurements such as antenna efficiency measurements or over-the-air testing of wireless devices.
New over-the-air (OTA) measurement technology is wanted for quantitative testing of modern wireless devices for use in multipath. We show that the reverberation chamber emulates a rich isotropic ...multipath (RIMP), making it an extreme reference environment for testing of wireless devices. This thereby complements testing in anechoic chambers representing the opposite extreme reference environment: pure line-of-sight (LOS). Antenna diversity gain was defined for RIMP environments based on improved fading performance. This paper finds this RIMP-diversity gain also valid as a metric of the cumulative improvement of the 1% worst users randomly distributed in the RIMP environment. The paper argues that LOS in modern wireless systems is random due to randomness of the orientations of the users and their devices. This leads to the definition of cumulative LOS-diversity gain of the 1% worst users in random LOS. This is generally not equal to the RIMP-diversity gain. The paper overviews the research on reverberation chambers for testing of wireless devices in RIMP environments. Finally, it presents a simple theory that can accurately model measured throughput for a long-term evolution (LTE) system with orthogonal frequency-division multiplexing (OFDM) and multiple-input-multiple-output (MIMO), the effects of which can clearly be seen and depend on the controllable time delay spread in the chamber.
This letter describes the effects of atmospheric attenuation on reverberation-chamber measurements in the mmWave range. It is evaluated using chamber-decay time, as the atmospheric attenuation is ...also defined as the rate of decay. We describe a method to de-embed atmospheric attenuation to evaluate for which cases it has a measurable impact and show results from 50 to 140 GHz, including uncertainty. We report a measurable impact in the used chamber when the attenuation is approximately 2 dB/km. We report this effect to show that the chamber loss can be dominated by atmospheric attenuation at higher frequencies. This can lead to increased measurement uncertainty or can make reverberation-chamber measurements highly impractical in a similar setting. With a climate-controlled environment, this can potentially be overcome.
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