# Design and Analysis of an Inductive Coupling System for the Early Detection of Heart Failure
## 4 Experimental Measurements  
In accordance with the optimum specifications derived from the simulation environment, the fabrication procedure was executed. The coils, \(Rx_{1}\) and \(Rx_{2}\), with finalized dimensions from the simulation environment, were printed out and stuck on a plastic bowl in order to trace the copper coil exactly on the surface precisely, as shown in the Figure 7a. The receiver coils were then tuned with capacitance in order to match the resonant frequency. The \(Tx\) coil was soldered onto a dotted PCB with a similar procedure (Figure 7b). This \(Tx\) coil was then tuned to the resonant frequency. Figure 7c represents the \(Rx_{1}\) and \(Rx_{2}\) placed at a distance of 20 mm in the air medium to compare the changes in \(S_{11}\), \(S_{22}\), \(S_{33}\), and \(S_{21}\) between the air and tissue mediums. The entire experimental setup is displayed in Figure 7d in which the \(Rx_{1}\) and \(Rx_{2}\) were dipped into the minced pork, which has similar properties to that of a human heart. The minced pork was refrigated and placed at room temperature for a few hours before conducting the experiment. The transceiver \(Tx\) was placed at exactly 50 mm perpendicular to the receiver coils \(Rx_{1}\) and \(Rx_{2}\). The results were measured using the specified apparatus (Rohde Schwartz, ZVH4, Seoul, Republic of Korea). Figure 6: Average specific absorption rate (SAR) at the maximum simulated average. To determine the \(S_{11}\), \(S_{22}\), and \(S_{33}\), the \(Rx_{1}\), \(Rx_{2}\), and \(Tx\) were driven by port 1, which were tuned by the capacitances \(C_{1}\), \(C_{2}\), and \(C_{3}\), respectively. The obtained \(S_{11}\), \(S_{22}\), and \(S_{33}\) values were \(-20.8\) dB, \(-25.4\) dB, and \(-16.6\) dB, respectively. Variations in \(S_{33}\) in the tissue medium imply that the transceiver coil placed outside the minced pork could be used to monitor changes in the distance between the implanted receiver coils, hence predicting the shift in the distance, as shown in Figure 8. Similarly, for the real-time application, the same procedures will be carried out. The coils, on the other hand, will be made of flexible PCB instead of the copper coils that were used in the experiments. This is because flexible PCB is very light and gives the patient a greater degree of comfort. In addition, when the system is used in the real world, a nanoVNA will be attached to the transceiver/external coil so that the entire system is small and it is easy to use and gauge changes in the receiver coils. Comparison between Simulated and Measured Results  
\(S_{11}\), \(S_{22}\), and \(S_{12}\) were also evaluated in both the measured and simulated results in order to compare the effectiveness of the implanted coils in all aspects. Measuring the changes in \(S_{33}\) is the most important factor for monitoring the size of the ventricular chamber as it can be operated without any physical contact with the human body since it is placed above the chest connected to a nanoVNA. Comparing the results revealed that both the simulated and measured data exhibited a similar trend. Interestingly, In Figure 9c, the \(S_{33}\) in the simulated result followed a similar pattern to \(S_{33}\) in the measured result with a difference of about \(-0.4\) dB. As previously indicated, although \(S_{11}\) and \(S_{22}\) (Figure 9a,b) displayed a substantial divergence between the simulated and measured  
Figure 7: (**a**) The spherical receivers, \(Rx_{1}\) and \(Rx_{2}\), with diameters of 34 mm; (**b**) Planar \(Tx\) with a diameter of 61 mm; (**c**) \(Rx_{1}\) and \(Rx_{2}\) placed in the air medium with \(D_{12}\) at 20 mm; (**d**) the experimental setup for measuring \(S_{33}\) under different conditions. values, both \(S_{11}\) and \(S_{22}\) grew linearly with increasing distance and exhibited a dramatic drift in the reflection coefficients at 20 mm and 30 mm.