Measurement Of Backscattered Electric Field Of Chipless Radio Frequency Identification Tag Based On Rydberg Atoms

High precision measurement is the basis of the development of modern physics.The accurate sensing of electric field intensity plays an important role and necessarily means to explore new materials,new devices and new electromagnetic effects.The principles of microwave electric field measurement include thermocouple effect,diode detector(loading dipole)and electro-optic effect.Due to the limitation of measurement principle and sensor structure,there are two major technical bottlenecks in the electric field measurement methods mentioned above: Unable to achieve high sensitivity,high resolution and high accuracy measurement;Unable to trace values directly and effectively to basic physical constants and SI fundamental quantities.Complex traceability chain directly leads to large uncertainty of measurement.In the traditional microwave measurement methods,the sensor size and working frequency are directly related to each other,which makes it impossible to achieve high resolution measurement,especially in small space.Based on the limitation of traditional measurement methods,we propose a microwave measurement method based on Rydberg atom.Due to the small Rydberg energy level interval,this method can measure a large range of frequency and trace the measured values directly to the basic physical constants.This method uses an atomic cell as the measuring sensor,without the participation of metal in the measurement process,which can greatly improve the accuracy and the accuracy of the measurement results.In our experiment,we excited the Cesium atom into the Rydberg state by using two beams of light to form a stepped EIT system.And then add a microwave field to couple the adjacent Rydberg levels together.At splitting of EIT transmission peak.The intensity of microwave electric field is calculated according to the frequency splitting interval of EIT peak.Two-dimensional high-resolution spatial distribution of the microwave E-field strength was achieved inside a cubic cell and a cylindrical cell.The symmetrical geometry of the cubic cell easily induced an FP effect.We demonstrate the anglediscrimination of a line-shape chipless radio-frequency identification tag via the near-field measurements of scattered electric fields in two orthogonal directions.In this paper,there are four aspects:Part 1:The properties and characteristics of Rydberg are introduced.The advantages and disadvantages of traditional microwave measurement methods and those based on Rydberg atomic microwave measurements are compared in detail.The research status of Rydberg atomic EIT-AT effect is also described.Part 2:The detailed description of the system of Rydberg atom measurement of microwave field,including light beams of laser system and the light path is designed and built.The working principle of atom and the key techniques of laser frequency and power locking are described in detail.Part 3:Based on the Hamiltonian of the four-level system,the main equation and the Bloch equation of the system are obtained by the evolution of the density matrix,and the calculation formula of the microwave electric field intensity is derived.Part 4:We observed the EIT spectrum under microwave electric field and measured the spatial two-dimensional distribution of near-field field intensity of the line-shape chipless RFID tag.The influence of atomic vapor cell with different shapes on microwave electric field measurement is compared theoretically and experimentally.The distribution of microwave field in steam cell with different wall thickness is calculated by finite element analysis software.The innovations of this work are shown by two aspects as follow:1.The effects of two atomic vapor cells of the same material and different shapes on microwave measurement were compared.The results showed that the shape of cesium bubble has a significant influence on the spatial distribution of microwave field due to the existence of FP effect in vapor cell.The distribution of microwave field in steam cell with different wall thickness is calculated by finite element analysis software.2.Based on the effect of electromagnetically induced transparent spectrum of cesium Rydberg atom under microwave electric field,the spatial two-dimensional distribution of backscattering field of scattering unit on a chipless RFID tag is studied.The angular resolution between the linear label and the polarization direction of the microwave field is realized.This experiment provides a new method for measuring microwave electric field in near field.