Abstract
In this letter, we report the unique design, simulation and experimental verification of an electrically tunable THz metamaterial perfect absorber consisting of complementary split ring resonator (CSRR) arrays integrated with liquid crystal as the subwavelength spacer in between. We observe a shift in resonance frequency of about 5.0 GHz at 0.567 THz with a 5 V bias voltage at 1KHz between the CSRR and the metal backplane, while the absorbance and full width at half maximum bandwidth are maintained at 90% and 0.025 THz, respectively. Simulated absorption spectrum by using a uniaxial model of LC matches perfectly the experiment data and demonstrates that the effective refractive index of LC changes between 1.5 and 1.7 by sweeping a 1 kHz bias voltage from 0 V to 5 V. By matching simulation and experiment for different bias voltages, we also estimate the angle of LC molecules versus the bias voltage. Additionally, we study the created THz fields inside the spacer to gain a better insight of the characteristics of tunable response of this device. This structure and associated study can support the design of liquid crystal based tunable terahertz detectors and sensors for various applications.
Highlights
Metamaterials are well-known for their exotic electromagnetic characteristics such as negative refractive index, subwavelength imaging, and invisibility cloak that are impossible to elicit from natural material.[1,2,3,4,5] Perfect metamaterial absorber is one of the metamaterial structures that has been recently the subject of growing interest.[6,7,8,9,10,11] It completely absorbs electromagnetic radiation in a very narrow spectrum which is adjustable by fashioning its configuration and dimensions
Several liquid crystals (LCs) tunable THz metamaterial filters were realized by embedding metamaterials inside LC cells where either two Indium Tin Oxide layers or the metamaterial structure made of noble metal along with a conductive wire were used as two electrodes to apply a bias voltage on LC cell and thereby to align LC molecules in the direction of created bias electric field.[25,26,27,28,29]
We show that while the resonance frequency is tuned by about 5 GHz at 0.567 THz through varying a 1 kHz applied voltage from 0 V to 5 V, the measured absorbance and full width at half maximum (FWHM) bandwidth are preserved at 90% and 0.025 THz, respectively
Summary
Metamaterials are well-known for their exotic electromagnetic characteristics such as negative refractive index, subwavelength imaging, and invisibility cloak that are impossible to elicit from natural material.[1,2,3,4,5] Perfect metamaterial absorber is one of the metamaterial structures that has been recently the subject of growing interest.[6,7,8,9,10,11] It completely absorbs electromagnetic radiation in a very narrow spectrum which is adjustable by fashioning its configuration and dimensions. (Received 7 September 2016; accepted 22 December 2016; published online 4 January 2017)
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