Frequency-Tunable and Magnitude-Tunable Microwave Metasurface Absorbers Enabled by Shape Memory Polymers

In this article, we demonstrate a new strategy for achieving a kind of shape-controlled tunable microwave absorbers based on shape memory polymers (SMPs). Using the heat-driven shape memory effect of SMPs, a frequency-tunable absorber and a magnitude-tunable absorber are designed. Both of the designs consist of a periodic metallic array printed on both sides of the FR4 substrate, SMPs' substrate (VeroWhitePlus) in the middle layer, and a metallic ground at the bottom. The equivalent circuit models are introduced to analyze the operational principles of the two absorbers. Furthermore, the functionalities of the designed shape-controlled tunable absorbers are investigated by full-wave simulations. For the frequency-tunable absorber design, the simulated results indicate that the resonant frequency can be tuned from 11.3 to 13.5 GHz with a frequency shift of 2.2 GHz. For the other design, the simulated results show that the reflection coefficient can be tuned from −17.00 to −1.34 dB. The proposed frequency shift responses and magnitude modulation responses are experimentally demonstrated by fabricating two prototypes containing 33 $\times33$ units. The above designs overcome the limitation of the traditional electrically adjustable wave absorber requiring an external power supply, providing a new paradigm for the design of tunable devices.