## 3 Results and Discussion
### Evolution of the Microwave Scattering Properties in Co-Based MWs Linear Arrays
This is why \(\Delta S_{21}\) vs. thickness (Figure 6c) has been determined tuning the fixed microwave frequency in the domain time measurement at the\(f_{\text{min}}\) of each thickness. When no polymer slab is used, the amplitude value of \(\Delta S_{21}\) is close to \(\sim\)\(-\)5.9 dB. In contrast, the \(\Delta S_{21}\) increases considerably up to \(\sim\)\(-\)24.2 dB, with an almost linear trend up to thickness (\(t\)) \(\sim\)3100 \(\upmu\)m. Beyond that, it reaches  
Figure 6: AC magnetic field studies performed in the sensor array platform configuration 2: (**a**) Illustration of the influence of the magnetization switch from MWs with a circumferential magnetization (\(S_{21,\text{minimum}}\)) to one with an axial magnetization (\(S_{21,\text{plateau}}\)) produced by a saturating AC magnetic field (\(H_{\text{AC}}\)). The frequency of the modulation (\(\hat{f}_{\text{modulation}}\)) is twice the frequency of \(H_{\text{AC}}\) (\(\hat{f}_{\text{HAC}}\)). (**b**) Layout of the configuration 2 with overlapping polymer slabs (\(t\)). (**c**) The \(\Delta S_{21}\) and \(f_{\text{min}}\) parameters as a function of the total thickness of polymer slabs (\(t\)). a stabilization level of \(\sim\)\(-\)25.1 dB that could be considered as a broad system's matching thickness [55; 56]. The example presented shows the high versatility of the designed systems to obtain adjustable time-resolved variations up to \(\sim\)\(-\)25.1 dB for the configuration 2. Surprisingly, the system has a high sensitivity to the progressive addition of polymer slabs with a thickness below 3100 \(\upmu\)m (Figure 6c), indirectly obtaining the added thicknesses by knowing the AC applied magnetic field with a resolution of \(\sim\)5.10\({}^{-3}\) dB/\(\upmu\)m. For sensor applications, it is important to widen the spectral effectiveness of the electromagnetic frequency near the antenna resonance exhibited. In this line, the time-resolved modulation is also investigated for frequencies that are located in the vicinity of the \(f_{\mathrm{min}}\) (2.40 GHz). Figure 7a displays the effect of the polymeric slab thickness (\(t\)) on the \(\Delta S_{21}\) modulation for five selected frequencies, varying from 2.00 GHz to 2.40 GHz (within the dipole scattering). It can be observed that the \(\Delta S_{21}\) difference shows a maximum for each frequency and it corresponds to the matching thickness under the experiment conditions. For 2.40 GHz, it is \(\sim\)0 \(\upmu\)m, coinciding with the minimum scattering (Figure 4b2). The rest of the chosen frequencies are as follows \(\sim\)200 \(\upmu\)m (2.30 GHz), \(\sim\)1000 \(\upmu\)m (2.20 GHz), and \(\sim\)4000 \(\upmu\)m (2.10 GHz). Concerning the fixed frequency of 2.00 GHz the matching thickness is located beyond 6500 \(\upmu\)m. In the time-domain representation, the \(\Delta S_{21}\) pulses are represented as an example at a fixed frequency of 2.10 GHz for six different thicknesses that ranged from 0 to 6000 \(\upmu\)m (Figure 7b). This modulation exhibits a maximum amplitude of \(\sim\)\(-\)18.1 dB for a thickness of 4000 \(\upmu\)m, according to the results that are displayed in Figure 7a. Hence, the influence of remarkable magneto-impedance effects on the \(\Delta S_{21}\) coefficient displayed by the configuration 2 is also confirmed for frequencies that are close to the \(f_{\mathrm{min}}\) as a function of the thickness. Therefore, these kinds of measurements are, in fact, a way to experimentally obtain the matching thickness for a specific microwave absorber system at a fixed frequency located in the close environment of the dipole resonance. Accordingly, the resonant frequencies of a specific array configuration can be modified by fine-tuning the overlapping thickness. Microwave Scattering Experiments Performed in Cu and Co-Based MWs Sensing Array Platforms by Applying DC Magnetic Fields  
In an electromagnetic wave scattering that is produced by dipole antenna effects, it is well known that the energy that is scattered by the MW depends on its electrical conductivity [40; 57].