Atom-Based Near-Field Measurement Of Scattering Fields Of Radio Frequency Identification Tag

Measurement is an indispensable mean for human beings to understand and transform the objective world.Without measurement,there would be no science.The technical level of measurement has been regarded as one of the important symbols of a country’s science and technology and modernization level.As an electromagnetic wave with wavelength between 1 mm and 1 m and frequency range between 300 MHz and 300 GHz,microwave has important applications in communication,remote sensing mapping,radar velocity measurement and ranging and cosmic observation.In recent years,with the rapid development of information technology,miniaturized integrated microwave devices play an increasingly important role in the national economy and national defense construction.Especially for the on-chip nearfield measurement technology of integrated circuits,it is very important to research and develop microwave sensors with sub wavelength,high spatial resolution and low disturbance.At present,the principle of microwave electric field measurement mainly includes thermocouple effect,diode detection(loaded dipole)and photoelectric effect.The measuring probe is mostly dipole antenna.Its basic structure is a diode in the two arms of the dipole antenna.The diode is connected to the DC voltmeter through a high impedance line(1000kΩ/m).The diode induces the electric field strength through the induced current and is connected to the DC voltmeter.The change of electric field intensity is recorded by over-dc voltmeter.However,for the measurement of microwave electric field based on electric dipole antenna,the antenna of metal conductor will cause the disturbance of microwave electric field,especially in the nearfield measurement,which will bring great measurement uncertainty.The geometric size of the antenna is relatively large,which can not achieve the spatial resolution of microwave electric field of sub wavelength,and the dipole antenna needs to be calibrated.All these problems limit the high spatial resolution of electric dipole antenna applications in the field of resolution measurement.Based on the limitation of traditional microwave measurement methods,we propose a new method of microwave electric field measurement based on Rydberg atom.In this method,the atomic vapor cell is used as the measurement sensor,and the traceable and spatial high-resolution measurement of microwave electric field is realized through the quantum coherence effect between Rydberg atom and microwave electric field.In recent years,quantum precision measurement based on atomic time,frequency,length and magnetic field has attracted more and more attention,and has achieved great success in the field of atomic clock and magnetic field measurement.However,the application of quantum system in microwave electric field measurement is still in continuous development.In this paper,using cesium Rydberg atomic sensor at room temperature,high resolution measurement of microwave electric field vector space is realized based on the spectral characteristics analysis of Rydberg atom electromagnetically induced transparency.The finite element analysis software is used to model the atomic gas chamber,and the space vector field distribution in the gas chamber is simulated.The microwave direction calibration technology based on Rydberg atom electromagnetically induced transparency(EIT)spectrum is developed.The vector measurement of near-field scattering field of RFID tag is realized.The effective resolution of RFID tag angle is obtained,and the angle resolution reaches 1.64 °.The main contents of this paper are as follows:1.In the first chapter,RFID tags are introduced briefly,and then the development of microwave electric field measurement is described in detail.Finally,the basic characteristics of Rydberg atom and the research status of microwave electric field measurement based on Rydberg atom are introduced.2.The second chapter introduces the setup of the whole experiment.The laser system,the optical path diagram,the experimental device and the specific experimental process(divided into three parts)are introduced in detail.3.The third chapter introduces the measurement theory of microwave electric field based on the eit-at effect of Rydberg atom,including two parts:the measurement theory of microwave electric field strength based on atom and the measurement theory of polarization direction.Then the finite element analysis software is used to model the atomic gas chamber,and the space vector field distribution in the gas chamber is simulated.4.In Chapter 4,the experimental results are analyzed and discussed.The calibration measurement of the polarization direction of the microwave electric field is realized in the experiment,and the vector measurement of the nearfield scattering field of the RFID tag is realized based on the Rydberg atom.Through the analysis of the spectral characteristics of the three peaks,we can realize the effective resolution of the complementary angle of the tag,and realize the angle recognition of the RFID tag,with the angle resolution of 1.64°.5.The fifth chapter summarizes the work of this paper and prospects the future work.The innovation of this paper is as follows:1.A new measurement method of polarization direction of microwave electric field based on Rydberg atom is proposed,which solves the problem that the complementary angle cannot be identified in the measurement of polarization direction of microwave electric field.2.Through the vector measurement of near-field scattering field of RFID tag and the characteristic analysis of electromagnetically induced transparency spectrum,the effective resolution of tag angle is achieved,and the angle resolution reaches 1.64 degrees.This paper has important reference value for microwave electric field space high resolution imaging,RFID tag design and identification,electromagnetic compatibility testing and so on.