Metamaterial-based perfect absorbers utilize the intrinsic loss, with the aid of appropriate structural design (completely suppress transmission and reflection), to achieve near unity absorption at a certain frequency. The frequency of the reported absorbers is usually fixed and operates over a limited bandwidth, which greatly hampers their practical applications. Active or dynamic control over their resonance frequency is urgently necessary. Herein, we propose a novel approach for efficient tuning of the frequency of the absorber by shifting the movable part of the composite structure composed of the fixed and movable parts. The concept is rather general and applicable to various absorbers as long as the sandwich structure design is valid. The demonstrated continuous tuning of metamaterial absorber can find practical applications in detection, imaging, spectroscopy and selective thermal emitters.
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