Experimental and numerical analysis of a carousel stirrer for reverberation chambers
The paper analyzes the performance of a reverberation chamber equipped by a “carousel” stirring system. The working volume is positioned inside the stirrer rotating volume. More precisely, the carousel consists of several vertical strips that rotate around a central axis and having a total diameter as large as possible compared to chamber dimensions. An FDTD code, optimized for reverberation chamber simulations and tested with experimental results, is used to analyze the chamber performance as function of strip number and width. The proposed setup increases the working volume and improves the reverberation chamber behavior with respect to a traditional setup. Moreover, it needs just one motor to control the stirrer, and it does not require more complex mechanical part. All simulations are compared to measurements showing a good agreement.
Reliable Finite-Difference Time-Domain Simulations of Reverberation Chambers by Using Equivalent Volumetric Losses
A numerical code based on the finite-difference time-domain technique is adopted to simulate a large reverberation chamber including the stirrers and the actual antenna presence in the frequency range 200-1000 MHz. The power of the code lies in the parallelization that allows the execution on high-performance computers. Chamber losses are accounted for by introducing virtual volumetric losses in the hypothesis of ideal conductor walls. The correction that arises from this choice which allows us to speed up the numerical computation is verified by a comparison with the case of wall losses implemented by assuming a finite conductivity. The analysis of the statistics of the chamber field, stirrer uncorrelated positions, Rician K-factor, backscatter, and field uniformity returns overlapping results for the two techniques. The analysis of the spatial field correlation within a spatial grid shows a correlation greater than 0.5 in the whole frequency range and for all stirrer angles, so confirming the equivalence of the two methods to manage losses.
Measurement and Demonstration of Thermal Expansion Coefficient
There are many classroom demonstrations, such as the ball-and-ring experiment, for showing the existence of thermal expansion of solids. The coefficient of linear expansion α (= increase in length divided by the original length times the change in temperature) may be measured in high school laboratories using a number of methods.1–4 In this paper we describe an especially simple experiment for determining α for a metal rod. It is based on the well-known optical lever method and is suitable for either a laboratory experiment or a classroom exercise.