Currently, surface nuclear magnetic resonance （SNMR） method is the only geophysical method that detects groundwater directly. In this paper, we investigate the effect of elliptical polarization in the perpendicular ...Currently, surface nuclear magnetic resonance （SNMR） method is the only geophysical method that detects groundwater directly. In this paper, we investigate the effect of elliptical polarization in the perpendicular excitation magnetic field. The effect of elliptical polarization is clearly visible in our ellipticity calculation and it can cause strong distortion to the excitation field in the presence of high subsurface conductivities. By examining the co-rotating and counter-rotating components of the field, we show that elliptical polarization affects transmitting and receiving processes differently and that a clear phase lag exists between transmitter loop and receiver loop. Finally, we derive the response function of coincident loops and calculate proton tip angles, the kernel function and SNMR response curves of a 1D aquifer model. Based on the simulations, we conclude that the elliptical polarization and phase lag can significantly affect SNMR response and it is essential to include elliptical polarization in SNMR modeling and data interpretation.展开更多
Optical-phase-retardation elements are widely used in many fields.Accurate measurement of their phase retardation is crucial to the practical effect of the element's processing and application.The development and ...Optical-phase-retardation elements are widely used in many fields.Accurate measurement of their phase retardation is crucial to the practical effect of the element's processing and application.The development and present situation of the methods for optical phase retardation measurement are reviewed,with the wave plate,the most typical phase-retardation element,as an example.The latest research progress in this field is introduced;the principles and characteristics of individual measurement method are summarized and discussed.Three new methods based on laser frequency splitting or laser feedback are presented in detail,in which the laser is not only regarded as a light source but also plays a role of sensor.Moreover,no standard wave plates are needed and arbitrary phase retardation can be measured.Traceability,high precision and high repeatability are achieved as well.展开更多
基金supported by the National Natural Science Foundation of China(No.40974040)the SinoProbe Projects(No. SinoProbe-01-03-02)
文摘Currently, surface nuclear magnetic resonance （SNMR） method is the only geophysical method that detects groundwater directly. In this paper, we investigate the effect of elliptical polarization in the perpendicular excitation magnetic field. The effect of elliptical polarization is clearly visible in our ellipticity calculation and it can cause strong distortion to the excitation field in the presence of high subsurface conductivities. By examining the co-rotating and counter-rotating components of the field, we show that elliptical polarization affects transmitting and receiving processes differently and that a clear phase lag exists between transmitter loop and receiver loop. Finally, we derive the response function of coincident loops and calculate proton tip angles, the kernel function and SNMR response curves of a 1D aquifer model. Based on the simulations, we conclude that the elliptical polarization and phase lag can significantly affect SNMR response and it is essential to include elliptical polarization in SNMR modeling and data interpretation.
基金supported by the Key Program of National Natural Science Foundation of China(Grant No.61036016)
文摘Optical-phase-retardation elements are widely used in many fields.Accurate measurement of their phase retardation is crucial to the practical effect of the element's processing and application.The development and present situation of the methods for optical phase retardation measurement are reviewed,with the wave plate,the most typical phase-retardation element,as an example.The latest research progress in this field is introduced;the principles and characteristics of individual measurement method are summarized and discussed.Three new methods based on laser frequency splitting or laser feedback are presented in detail,in which the laser is not only regarded as a light source but also plays a role of sensor.Moreover,no standard wave plates are needed and arbitrary phase retardation can be measured.Traceability,high precision and high repeatability are achieved as well.
