## 3 Results
### Tunable Sensor
It is important to underline that the measurement results given in Figure 12 show a good agreement with the simulation data presented in Figure 3. A direct comparison in a common figure was not appropriate because the model (Figure 3) did not include the exact physical geometry of the WPT power loop location, but the capacitance of the discrete capacitor was set here directly using the discrete element parameters in the simulator. In contrast, in the measurement case, the actual geometry was considered, including the change in varactor capacitance via the voltage induced across the power loop and rectified. Taking these differences into account, the shape similarity of the waveforms in Figures 3 and 12 together with the corresponding resonant dip shift was considered a good agreement between the simulations and measurements. The curve \(P_{\mathrm{g}}=-10\) dBm represented the highest resonance frequency. This corresponded to the maximum voltage at which we had a minimum capacitance. Figure 3 also shows that for the lowest capacitance, we obtained the maximum resonance frequency. As a result, the same continuous tuning range of 200 MHz from 3.2 to 3.4 GHz was achieved. Changing the varactor capacitance depending on DC bias would slightly change the Q-factor of the resonator, which may have affected the detection tolerance. This change was very small in a given voltage range, as can be seen in Figure 12. The repeatability of the sensor was also an important issue. Verification of these effects was not the focus of this manuscript; we only aimed to present a proof of concept. This issue will need to be thoroughly verified before any real deployment of such a sensor. However, considering the relatively small frequency variations, the need for individual calibration can be assumed. Table 6 compares the properties of the concept presented here with relevant published acetone sensors operating in the microwave frequency band [22; 23; 24; 25]. Although the relative sensitivity of the presented solution was lower than some results published by other authors, these structures were mostly detected by direct measurements over a cable or, in a few cases, wirelessly over a short distance. In fact, the remote sensing structure proposed in our paper showed a better RCS response that outperformed the referenced competitors. This, together with the possibility of baseband detuning, can be considered as the main contribution of this paper. Future research will address the issue of further improving the performance of the sensitive phthalocyanine layer. The presented solution was similar in principle to the previously published solution [14]; however, the benefit of the approach presented here lies in the ability to realign the fundamental resonant frequency using WPT. The advantage of our solution compared to that in [23] is the possibility of the independent design of the WPT and the reading part. The WPT loop must be placed relatively close to the tag due to sufficient efficiency; however, the actual reading of the RCS response (and hence the information) can be performed at a substantially larger distance. This can be achieved by using the structure with increased RCS response. Figure 12: Measured RCS for different values of input power \(P_{\mathrm{g}}\).