Abstract
We present the design, analysis and measurements of a polarization-insensitive tunable metamaterial absorber with varactor diodes embedded between metamaterial units. The basic unit shows excellent absorptivity in the designed frequency band over a wide range of incident angles. By regulating the reverse bias voltage on the varactor diode, the absorption frequency of the designed unit can be controlled continuously. The absorption mechanism is interpreted using the electromagnetic-wave interference theory. When the metamaterial units are placed along two orthogonal directions, the absorber is insensitive to the polarization of incident waves. The tunability of the absorber has been verified by experimental results with the measured bandwidth of 1.5 GHz (or relative bandwidth of 30%).
Highlights
Design of the basic unitThe basic unit of the designed tunable MMA is illustrated in figure 1
There are two identical electric-field coupled-LC (ELC) resonators with the same orientation on the top of the dielectric substrate, which are connected by a microwave varactor diode
The equivalent circuit of the basic unit is two ELC circuits connected by a microwave varactor diode, where the LC resonance is driven by the electric field parallel to the gap of the ELC unit; the resonant frequency of the above-mentioned circuit is determined by its lumped parameters
Summary
The basic unit of the designed tunable MMA is illustrated in figure 1. Since the capacitance of the varactor diode changes under different reverse bias voltages, the absorption frequency of the basic unit will experience a red or blue shift correspondingly, which could be utilized to adjust the designed absorption frequency. The final geometry dimensions are given as: a = 16.84 mm, w = 5.55 mm, w1 = 0.60 mm, w2 = 0.40 mm, w3 = 0.70 mm, φ = 0.25 mm, d = 2.87 mm, d1 = 1.20 mm, d2 = 1.0 mm and d3 = 0.60 mm In this design, a commercial varactor diode SMV2019-079LF from Skyworks Solutions, Inc. The accurate effective circuit parameters of this varactor diode are shown, which are extracted from its spice model using the commercial software Advanced Design System 2008, as demonstrated in figure 2. In the following full wave simulations, the varactor diode will be replaced by the corresponding spice model for simplicity
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