Design Of Adjustable Terahertz Metamaterial Structures Based On Pneumatic Actuation

Metamaterials are a kind of periodically arranged composite materials that are artificially manufactured.Through structure design,many excellent properties can be obtained that are not available in nature materials.In recent years,the emergence of terahertz wave sources has surged a new tide of the research on terahertz waves.At the same time,considering the fact that terahertz waves possess numerous disctinct characteristics,the design and development of terahertz functional devices have become one of the current research hot spots.However,due to limitation of the inherent properties of traditional materials,it is difficult to provide accurate electromagnetic responses to terahertz waves.Owing to the artificial maneuverability,metamaterials can ensure that the responses between the structure and the electromagnetic wave can be well controlled within the terahertz band through structural design and parameter optimization,and achieve the modulation of the amplitude,phase and polarization of the terahertz wave.However,most current terahertz metamaterial designs lack dynamic modulation capability.Once the structure is processed,its modulation function will be fixed.In addition,for some existing tunable metamaterial designs,the modulation processes are complicated and the integration and miniaturization are difficult,preventing their widespread application.Aiming to solve these issues,a novel pneumatic actuation strategy is proposed in this thesis,demonstrating easy integration and convenient control characteristics.Based on this design concept,two types of tunable terahertz metamaterial structure are designed to realize dynamic modulation for the phase and polarization of the terahertz wave,respectively.The design concept is based on the pneumatic actuator formed by the bonding of the PDMS substrate with air cavity and the PDMS suspending membrane.By increasing or decreasing the air pressure in the cavity,the suspended membrane will be raised or depressed correspondingly,thus changing the structural parameters of the metal array sitting on it and realizing the dynamic modulation of the phase or polarization of the terahertz wave.The COMSOL software is used to simulate the modulation process mentioned above,in which the solid mechanics module and electromagnetic module are combined together for multiphysics analysis.The reflective phase-tunable terahertz metamaterial designed in this thesis possesses continuous dynamic phase modulation capability.Through the combined arrangement of the structural units,the dynamic reconstruction of the wavefront profile can be realized,and two types of devices,namely phase gradient metamaterial and reflective superlens,are reported accordingly.In addition,the resonance states of the proposed structures are analyzed by constructing an equivalent circuit model,and the internal mechanism of phase modulation is analyzed using the multi-beam interference theory.As for the multi-functional polarization conversion terahertz metamaterial designed in this thesis,three working states can be achieved,each of which can realize different polarization conversion functions respectively.In the meanwhile,the dynamic switching of the three working states can be realized by pneumatic actuation.Then the theoretical verification of the polarization functions is performed by using the Jones matrix analysis method.Finally,the internal mechanism of polarization conversion provided by the structure is discussed through analyzing the electric field and current distributions at the resonance frequencies.