Debye-Based Frequency-Domain Magnetization Model for Magnetic Nanoparticles in Magnetic Particle Spectroscopy

Signal generation in magnetic particle imaging and magnetic particle spectroscopy is generally described via the Langevin function of superparamagnetism. To include the magnetization dynamics, the Langevin function is augmented with a frequency-dependent term derived from the linear Debye model. Here, we extend that expression to cover the dynamics of higher harmonics, where each harmonic is multiplied with a complex-valued weighting factor, obtaining a frequency-domain model for application in the context of viscosity-/binding-dependent magnetic particle spectroscopy measurements.