Effects of square-wave magnetic fields on synchronization of nonlinear spin precession for sensitivity improvement of MX magnetometers

• Published in: Journal of magnetism and magnetic materials 2017-11, Vol.441, p.718-723
• Main Authors: Ranjbaran, M., Tehranchi, M.M., Hamidi, S.M., Khalkhali, S.M.H.
• Format: Article
• Language: English
• Subjects: Biomagnetism; Bloch equations; Gradiometers; Harmonic detection; Higher harmonics; Magnetic fields; Magnetic measurement; Magnetic resonance; Magnetometers; MX optically pumped magnetometers; NMR; Nuclear magnetic resonance; Precession; Sensitivity; Sensitivity analysis; Square wave duty cycle; Studies; Synchronism
• ISSN: 0304-8853; 1873-4766
• DOI: 10.1016/j.jmmm.2017.06.084

•Square wave RF magnetic field substituted for sinusoidal field in MX magnetometers.•Amplitude of magnetic resonance signal reinforced at detection of higher harmonics.•Narrower resonance signals achieved as the number of detection harmonic increased.•Sensitivity of biomagnetic field detection improved respect to classical methods.•The Bloch equations predicted the nonlinear dynamics of transverse spin polarization. Optically pumped atomic magnetometers have found widespread application in biomagnetic studies. Most of the studies utilize MX gradiometers as sensitive and simple arrangements. One the sensitivity improvement methods in the MX configurations is detection of magnetic resonance at higher harmonics due to nonlinear precession of spin polarization. To enhance the harmonic components, we have proposed square wave RF magnetic fields with various duty cycles as substitute for sinusoidal fields. Our results revealed that detection of the 5th harmonic of a 10% duty cycle square wave magnetic field, improved the magnetometer sensitivity by a factor of 4.5 respect to the first harmonic which could be a reliable option to generate high sensitivity MX magnetometers in the MCG applications.