Characteristic Research On Terahertz Radar And Cloak Design

In recent years,Terahertz(THz)technology has gained worldwide attraction,related research and applications are now in vigorous development.Among all applications with great potential,Terahertz Radar scattering measurement and electromagnetic invisible cloak are of great importance in military field.Radar detection in THz range can obtain higher resolution,wider signal bandwidth and stronger anti-stealth ability.In scale model measurement,Radar cross-section measurement at THz band has bigger scaling factor,which makes the measurement system much simpler and with less cost.Moreover,some large-scale military objects like aircraft carrier can also be measured and analyzed in scale model measurement.With development of THz electromagnetic detection and THz radar system,THz invisible cloak has been more and more important for researchers.Meanwhile research about THz cloak provides a great boost to THz metamaterials and functional devices.In this dissertation we combined THz technology and radar system,investigated on both THz radar and THz cloak.Main content are listed below: 1.At present,the optical structure and mechanism of this system-showing the radar detection principle and imaging mechanism has attracted a lot of interest in the terahertz research field.Based on 4-f terahertz time-domain spectroscopy(THz-TDS)technology,a broad-band time domain terahertz radar system was built to do research on scattering characteristics of objects,which is the first broad band terahertz radar system based on femtosecond Ti: sapphire osillators pumped terahertz time-domain spectroscopy system in our country.The RCS distribution of three military scale models was measured by this Radar system.This terahertz radar would make great contribution to scale model measurement and military shape optimization.2.Using our improved back projection algorithm,the shapes of the models can be retrieved based on time domain scattering signal.The theoretical resolution of our imaging result can reach sub-millimeter accuracy.Moreover,the strong scattering points on object can be performed by color strength in imaging result,providing a reference tool for military shape design.3.THz invisible cloak is a important topic for THz radar detection.In this thesisa quasi three-dimensional macroscopic cloak functioning in the terahertz regime was demonstrated.The cloak design was based on transformation optics theory.To optimize the cloak design,finite-element software COMSOL Multiphysics was used for simulation.The cloak device was made by crystal sapphire and measured by fiber-coupled TDS.The experimental result is in good agreement with the simulation prediction,which demonstrates the effectiveness of our design.4.Apart from cloak based on transformation optics,absorbing metamaterial is another significant cloak method.Plasmon induced transparency(PIT)metamaterial has great slow light and high transparency feature.Novel absorbing cloak metamaterial can be achieved based on PIT metamaterial.Here we propose a novel PIT metamaterial scheme based on three vertically placed split ring resonators(SRRs)working at terahertz frequencies.This stereo structure couples to both the electric and magnetic fields of the normally incident wave.With higher design freedom of the stereo metamaterials,this work provides a promising way for further absorbing cloak design.