Abstract
Pulsed magnetic fields can be used to provide instantaneous localized magnetic field variations. In presence of static fields, pulsed field variations are often used to apply torques and in-effect to measure behavior of magnetic moments in different states. In this work, the design and experimental performance of a pulsed magnetic field generator suited for low static field nuclear magnetic resonance (NMR) applications is presented. One of the challenges of low bias field NMR measurements is low signal to noise ratio due to the comparable nature of the bias field and the pulsed field. Therefore, a circuit is designed to apply pulsed currents through an inductive load, leading to generation of pulsed magnetic fields which can temporarily overpower the effect of the bias field on magnetic moments. The designed circuit will be tuned to operate at the precession frequency of 1H (protons) placed in a bias field produced by permanent magnets. The designed circuit parameters may be tuned to operate under different bias conditions. Therefore, low field NMR measurements can be performed for different bias fields. Circuit simulations were used to determine design parameters, corresponding experimental measurements will be presented in this work.
Highlights
Force-based magnetic field measurements require interacting magnetic fields
In nuclear magnetic resonance (NMR), the magnetic moments associated with the nuclei act as the magnetic dipoles
For unilateral NMR, the magnitude of the pulsed magnetic field needs to be slightly higher than the magnitude of the external magnetic field to achieve temporary magnetic moment reorientation.[4,6]
Summary
Force-based magnetic field measurements require interacting magnetic fields. In such measurements, when a magnetic dipole is placed in a uniform external magnetic field it experiences a torque. The turning force is proportional to the strength of the applied magnetic field and the associated dipole magnetic moment.[1]. When the frequency of the applied pulsed field is equal to the energy difference between quantized nuclear states, nuclear transitions will occur between the energy states This is when nuclear magnetic resonance occurs.[2] Detection of this minute signal is conducted by using detection coils which are placed transverse to the direction of applied static field. A higher current would lead to a higher pulsed field and in actual application, coil parameters would contribute to achieving an overall higher NMR voltage signal. Subsequent signal detection will be implemented using orthogonal inductive coils
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