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Magnetization Response Spectroscopy of Superparamagnetic Nanoparticles Under Mixing Frequency Fields

In this paper, we report a mixing frequency method (MFM) that has two driving fields, in which one is a high frequency of fH = 300 kHz and the other is a low frequency field with fL = 500 Hz. Two traditional magnetic particle imaging technologies are compared with an MFM, one with driving field frequency of fM = 25 kHz and the other at 10 kHz. An assumed iron-cobalt magnetic nanoparticle (MNP) suspension of which the sizes follow normal distribution is modeled and their magnetic response is modeled by Langevin function. Odd harmonics induced from the nonlinear magnetic response of MNPs under driving fields are extracted from the magnetization response spectroscopy. The signal-to-noise ratio, harmonic strengths at field-free points (FFPs) over strengths at non-FFPs, is defined as an evaluation standard to assess which technology is better for imaging spatial distribution of MNPs.