engleski

An Intuitive Experimental Demonstration of Backward-wave Propagation in One-dimensional Metamaterial Structures

In a last few years there has been a great interest in artificially made materials (metamaterials), electromagnetic properties of which cannot be found in Nature. Probably mostly investigated metamaterial is an Double Negative metamaterial (DNG), which real parts of effective permeability and permittivity have negative values. Investigation of this type of material has revealed several new counter-intuitive physical phenomena such as negative refraction, growing evanescent waves and imaging with the subwavelength resolution. All these phenomena rely on the fact that DNG material supports propagation of the backward waves i.e. the waves whose phase velocity vector and Poynting vector point in the opposite directions. Although the backward-wave propagation has been used in microwave technology since fifties of previous century, the literature is sparse of its direct and intuitive demonstration in the metamaterials. This is an important issue because the metamaterials have already been included into several postgraduate courses worldwide and there is a need of simple ‘ in front of class’ experiments for demonstration of backward-wave propagation. This paper reports development of a simple backward-wave propagation line and experimental methodology that clearly shows basic background physics of backward-wave propagation. In the first step, the prototypes of simple ordinary forward-wave transmission line as well as the CL backward-wave line, operating in RF 300 MHz band, were manufactured. The modes of the propagation were demonstrated by scanning of the phase of the magnetic field along the lines with the help of a small loop antenna connected to the network analyzer. This simple method enables clear demonstration of both forward-wave propagation (decreasing phase along the line) and backward-wave propagation (increasing phase along the line). In the next step it was attempted to demonstrate backward-wave propagation by direct measurement in the time domain. To this end, the line was excited by CW RF generator and magnetic field distribution is measured by scanning loop antenna connected to a high-speed digital oscilloscope. It was found possible to directly observe change of the phase along the line and therefore verify the type of the propagation (either forward-wave propagation or backward-wave propagation). Finally, the field distributions along both experimental lines were simulated with the help of commercial electromagnetic simulator (CST Microwave Studio TM) and the results were found to be in good agreement with the simulation. We believe that this experimental methodology complemented with the animations obtained from full-wave simulations can be successfully used in teaching the basic of metamaterials in physics and engineering course, both at undergraduate and postgraduate levels.

backward-wave; education; experiment; metamaterial

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