Purely first harmonic magentic particle detection: A single frequency spectrometer

The detection of magnetic particles in general is based on the fact, that superparamagnetic particles have a non-linear magnetization curve. If excited with an alternating magnetic field at a certain frequency, this generates detectable signal at higher harmonics. In general, the first harmonic is not used for detection especially of spatial encoded signal, the detection of the non linear bahaviour of particles in a spectrometer or the field-free-point of an imaging apparatus is done by detecting higher harmonics. One of the major challenges for quantification is the absence of a `gold standard´ particle system with well known magnetization behavior, but well known paramagnetic material, only generating signal on the first harmonic, is available. In the presented work, the first harmonic signal for detection and quantitative characterization of magnetic particles. The presented technique reduces the hardware requirements for signal detection dramatically with no demand for broadband detection. It can be used for spectroscopic measurements as well as for the detection of spatial encoded signal, as the imaging is based on the non linear behavior of particles which is only present in the field free area. It is also suggested to be a sensitive method for signal detection based on the fact that the first harmonic signal is substantial higher. Nevertheless, calibration with a well known paramagnetic substance allows quantitative measurements.