Electromagnetic signal is generated from a vector network analyzer (Agilent N5230C) on one of its two ports (Port 1) and is received on the other (Port 2).
The x-axis is perpendicular to the surface of split-rings and y-axis is parallel to the opening gaps. X-axis, y-axis, and z-axis are defined as the directions of the orthogonal magnetic field, wave vector and electric field, respectively, as illustrated in Fig. Such waveguide has a cross section of 22.86 mm × 10.16 mm and can support TE 10 mode microwave wave propagating inside it. The metamaterial sample is inserted into a rectangular X-band (8~12 GHz) waveguide to obtain scattering parameters. Numerical simulation further validates the experimental results.įull size image Experimental setup and measured results A temperature-dependent hysteresis curve of the metamaterial’s transmission property under microwave frequency bands is also revealed. Scattering parameters are measured and the results clearly indicate a variation of resonant characteristics in correlation to incident power and the resulting heat-induced phase transition of VO 2, confirming its nonlinear property. VO 2 thin film is deposited onto gold split-rings by means of magnetron sputtering. Here we report a power-tunable VO 2 metamaterial under microwave frequency band, based on the concept of combining VO 2 semiconductor-metal phase transition with SRR array. implemented such proposal and measured the power-dependent scattering parameters of varactor-loaded split-ring resonators in microwave frequency bands 32. had foreseen the possibility of enhancing nonlinearity by introducing nonlinear elements into the gap of split-ring resonator where electromagnetic field reaches its maxima 31. It is a non-negligible fact that metamaterials working under microwave frequency range bear broad research and utilization prospects, and as a matter of fact, power-tunable microwave metamaterials have already been on the rise for drawing the very latest academic attention. However, the vast majority of existing studies are carried out in the frequency range of terahertz or far-infrared, leaving microwave VO 2 metamaterials a largely uncharted area for exploration.
Typical focus of attention concentrates on several subfields of research, including tunable or switching metamaterials 12, 13, 14, 15, 16, 17, 18, 19, transmission modulation 20, 21, perfect absorber/emitter 22, 23, 24, 25, 26, hyperbolic metamaterials 27, 28, memory metamaterials 29, 30, etc.
For this reason, the combination of VO 2 thin film or small particles with multifarious metamaterial structures, such as split-ring resonators 11, are regarded as, and often proven to be, an efficient way towards dynamically controlling electromagnetic properties. Such phase transition can be induced thermally 8, electrically 9 and optically 10. When heated above that point, crystal structure changes to rutile, accompanied with a dramatic increment of conductivity by several orders of magnitude, which signifies the occurrence of a metal-like state 4, 5, 6, 7. VO 2 behaves like semiconductor under its phase transition temperature Tc = 68 ☌ with monoclinic crystal structure. Such feature endows vanadium oxide with high potentialities in its application as electromagnetic functional materials, along with a number of possible tuning and modulation applications. Among which, stands out the vanadium dioxide, a material capable of sharply altering its electromagnetic properties through a process known as semiconductor-metal phase transition, which happens at a rather moderate temperature. In the effort to maximize their capabilities, functional materials with intriguing specialities are frequently utilized in the building blocks for metamaterials. Such properties not only involve the famous examples of negative-index materials 1, perfect lens 2 and their use in cloaking devices 3, but also a rich variety of appliances in the field of telecommunication, a critical part of our social infrastructure, built around devices with tuning and modulation capacities. With elaborately designed size, shape and repetitive array of the “meta-atoms”, various exotic electromagnetic responses could be achieved. Owing to the ever-growing advances in the burgeoning field of metamaterials, the world is introduced to a whole spectrum of engineered structures and devices with features so unique that are never observed in nature.
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