Excitation Strategy And System Design Of Electromagnetic Tomography

Based on law of electromagnetic induction, the process of ElectromagneticTomography (EMT) is described as follow: exciting magnetic field is produced byforced AC current which is imposed into coils of electromagnetic sensor array in theboundary of sensing field, and induced magnetic field, which is affected by excitingmagnetic field, is aroused in the conductive or magnetic materials. By measuringsignal of measured coil in the boundary of sensing field, the conductivity orpermeability information can be got and the spatial distribution images can bereconstructedinobjectspace.Electromagnetic Tomography (EMT), which is developing in recent years, is onekindofElectricalTomography(ET).Ithasadvantagesofnon-contact,non-hazardandnon-invasion,andit is sensitivetobothconductiveandmagneticmaterials, so it has alargeapplicablepotentialinprocesscontrolandbiomedicalimaging,etc.Appropriate excitation frequency and excitation strategy can improve the sensorarray sensitivity of the object field distribution, and then improve system sensitivityand accuracy; A high-performance system can guarantee high-precision and highstability of the experimental data. Therefore, it is necessary to do the excitationfrequencyandexcitationstrategyanalysis,andbuildahigh-performanceexperimentalsystem.Themainworkofthispapercanbeconcludedasfollow:Firstly, based on the sensor parameter optimization simulation results of theprocess tomography laboratory of Tianjin University and experimental requirements,a8-electrodeelectromagnetictomographysensorarraywhosecoilturns,coildiameterandthedistancebetweenthecoilandthepipecanbeallchangedisdesigned.Secondly, excitation frequency of electromagnetic tomography sensor array isstudied, and the relationship between measurement and excitation frequency isacquired, and the conclusion for the excitation frequency to 750KHz is obtained.Adjacent excitation, opposite excitation compared with single excitation, theconclusion that excitation strategy can not improve the measurement quality isobtained.Thirdly, based on the characteristics of the sensor array and the selected excitation frequency and excitation strategy, a set of EMT experimental system isbuilt. It is composed of the coil sensor array, excitation and selection module, FPGAcontrolmodule,differentialamplifierandADacquisitionmodule.