Design Of Single Side NMR Sensor Using Array Coil

Because of its open structure,portability and nondestructive measurement,the single side nuclear magnetic resonance?NMR?has been widely used in the field of engineering field measurement.Compared with the traditional closed type magnet structure,although unilateral nuclear magnetic resonance?UNMR?has the advantage,but also have to sacrifice some signal-to-noise ratio?SNR?at the expense of the main field:the uniformity of the magnetic field B₀ is poor,the magnetic field intensity is small,and the magnetic resonance frequency is relatively low,so the signal to noise ratio of the single side NMR system is low.As the core component of RF excitation and NMR signal reception,the structure of RF coil plays an important role in nuclear magnetic resonance signal.Therefore,it is one of the main directions to improve the SNR of the single side nuclear magnetic resonance system by optimizing the structure of RF coils.In the field of parallel imaging and high field magnetic resonance,the array coil has been applied in a large number of applications.Compared with the single planar coil,the array coil has higher SNR.By signal combination technology,the magnetic resonance signals of different coils can be combined to improve the acquisition speed,which can greatly enhance the efficiency of the unilateral nuclear magnetic resonance system.In this paper,a semi ring unilateral NMR sensor is designed and produced.The sensor is not only small in size and low in cost,but also located outside the magnet,and the magnetic field distribution is arc-shaped:the magnetic field intensity at the center of the arc surface is 172mT,the corresponding NMR frequency is 7.323MHz.In the arc with an arc length of 19.1mm and a height of 20mm,the magnetic field uniformity is 3 per thousand,and the gradient of Z axis is 0.51T/m.In this paper,an optimization method based on the total SNR of the target area is proposed.The two-coil array structure,corresponding to the single side magnetic field,was designed.The optimization results are as follow:The parameters of optimal two-coil array structure are too described.Its wiring area of single coil in two-coil array is12mm x 14mm,line width and spacing is 0.5mm,the number of turns is 5 turns,the center distance between the two coils in two-coil array is 6.2mm and two coils in two-coil array are located on two side of circuit board with thickness of 0.2mm.This paper introduces the circuit structure of three RF coil system in the unilateral NMR experiment,designs and produces three kinds of circuit structure RF coil system and an active switching control circuit.The rise time of the drive output waveform is 300ns,the descending time is 1.5us,and the delay time of input signal and output signal is 500ns,which can realize fast driving active switching circuit.In this paper,we compare the NMR signal to noise ratio of three kinds of circuit structures.It is found that the signal to noise ratio of NMR signal obtained by the transceiver is higher than that of passive switching circuit and active switching circuit,The comparison experiment of signal to noise ratio between the array coil and the single coil is carried out by using the optimal transceiver structure.It is found that the signal to noise ratio of the double channel array coil is improved by 14.8%.It is proved that it is feasible to improve the SNR of the single side NMR system by the array coil.