## 3 Magnetic Characterization Instruments
### Fluxgate Magnetometers
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Fluxgate Magnetometer Type** & **Advantages** & **Disadvantages** \\ \hline Simple & & Only nanoparticles located close enough to the \\ Fluxgate & Need for only one magnetometer & fluxgate sensor contribute to the output signal \\ \hline Differential & & SNR increases by a factor of \(\sqrt{2}\) \\ Fluxgate & & More accurate measurements & Need for two complete electronic sets \\ Magnetometer & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison Between Simple and Differential Fluxgate Magnetometers. Figure 5: Schematic diagram of the two different fluxgate setups: (**a**) single fluxgate arrangement, (**b**) differential fluxgate arrangement [42]. used for magnetorelaxometry purposes in an environment without shielding. In [121], the first fluxgate magnetometer that contains an inkjet-printed core is presented. This device is characterized by a wide open-loop linear range, enables the fully automatic manufacture process of the core, and offers the capability to manufacture the magnetometer on a substrate of arbitrary shape. The sensor, however, is characterized by small sensitivity. In [122], a method is proposed to increase the permeability of the sensor core. According to [122], this can be achieved if a static magnetic field is applied while ink jetting the nanoparticles. In [123], iron oxide nanopowders are used as a core that guides the flux in a fluxgate magnetometer. The advantage of this material is that it contains supermagnetic nanoparticles, which are not affected by the hysteresis phenomenon at room temperatures. In [124], a fundamental mode orthogonal fluxgate gradiometer that contains AC magnetizing coils is presented. In [125], a three-axial fluxgate magnetometer is proposed that can find application in autonomous aeromagnetic survey. In [126], a fluxgate magnetometer is used for nanoparticle properties investigation that applies the magnetic field strength method. Figure 6: The schematic diagram of the setup for the measurements [27]. Figure 7: Schematic diagram of the setup with fluxgate scanner for magnetorelaxation imaging [45]. In [127], a measurement setup consisting of three applied field coils and two fluxgate magnetometers for the detection of nanoparticle properties in an economical way is proposed. The schematic diagram of the aforementioned setup is depicted in Figure 8, where both the compensation and drive coils are visible, as well as the fluxgate sensors, which are used for nanoparticle characterization. In [128], a measurement setup is proposed that uses two fluxgate magnetometers to identify the effect of the rotating magnetic field, created by Helmholtz coils, on the nanoparticle characterization procedure. The impact of the rotating magnetic field, when defining the magnetic properties of iron oxide suspension nanoparticles, is compared to the impact of the alternating magnetic field. The used fluxgate magnetometers have been proposed also in [27]. In [129], a fluxgate sensor capable of operating at high temperatures is studied, and the analysis of its characteristics is done for temperatures up to 180 \({}^{\circ}\)C.