## 4 Fabrication and Measurement
### PTE Performance Verification  
The built Tx and Rx coils are shown in Figure 7a. An SMA connector was soldered at each end of the coil, and a 56 pF lumped capacitor was loaded, creating resonance at 6.78 MHz. The coils were separated by Styrofoam of height \(d\) values of 10, 15, and 20 cm. The S-parameter was measured using a 2-port Anritsu MS42566B vector network analyzer (VNA). Figure 7b shows the measured PTE, calculated as \(\mid\)S\({}_{21}\mid\)\({}^{2}\times\) 100 (%). The measured results showed a slight frequency shift of 2.95% compared with the simulation, possibly due to the fabrication tolerance and ground effect. Nevertheless, the Tx-Rx coil pair showed acceptable values for verifying the AMC performance. The measured peak PTE values shown in Figure 7b at the distances of 10, 15, 20, and 30 cm are 56.4%, 24.23%, 8.1%, and 2.04%, respectively. For the AMC fabrication, the 5 \(\times\) 5 array of the AMC surface was built. A quarter of the entire surface was built individually and then assembled. Two and a half unit cells  
Figure 6: WPTS with the proposed AMC. (**a**) Simulation setup of SML-based AMC. (**b**) Simulation setup of IML-based AMC. (**c**) Simulation setup: side view. (**d**) Magnetic field distribution. (**e**) PTE. Figure 7: Fabrication and measurement. (**a**) Fabricated Tx–Rx coil prototype. (**b**) PTE. were present in the quarter of the \(5\times 5\) array of the AMC surface. The FSS patches of the unit cell in the quarter surface were connected by 0.43 nF capacitors, as in the simulation. Consequently, each quarter surface was connected by the 0.43 nF capacitors, again, as in the simulation, such that the \(5\times 5\) array of the AMC surface was assembled. This assembly procedure is illustrated in Figure 8. For better visualization, only the fabrication of a single unit cell composed of four FSS patches is shown in the figure. As shown in Figure 8a, the ground plane was prepared using a 528 \(\times\) 528 mm\({}^{2}\) copper sheet and attached to the polystyrene foam board. Next, the ferrites were placed on top of the ground plane. The points of the via pin were marked, as illustrated in Figure 8b. After removing the ferrites, via pins were soldered at the marked points, as shown in Figure 8c. Then, the ferrites were properly arranged with the via pins, as in Figure 8d. Once everything was properly fixed, the printed FSS layer on the FR-4 substrate was reversed and placed on the top of the ferrite, as shown in Figure 8e,f. The gap between the ferrite and the printed FSS layer was achieved using small pieces of Styrofoam. In addition, the via pins were soldered to the dielectric substrate-based FSS layer, as marked by the red circles in Figure 8e. The side view of the built IML-based layers is shown in Figure 8f. The lumped capacitors faced toward the ground plane in the case of the IML-based AMC. Then, the Tx coil was placed on top of the AMC at a distance of 4.5 mm for the PTE and magnetic field leakage measurement. Considering the PTE enhancement from the simulations, the PTE measurement was performed for the proposed IML-based AMC, as shown in Figure 9a. For the PTE measurements, the Tx and Rx coils were connected to ports 1 and 2 of the VNA, and the transfer coefficient \(S_{2l}\) was measured by varying the distance (\(d\)) between the coils. The measured PTE values when the IML-type AMC was placed behind the Tx coil and in the case where only ferrite was placed behind the Tx coil are plotted in Figure 9b,c, respectively. The measured results were generally in good agreement with the simulations, showing the same trends observed in the simulations. The improved PTE values from the IML-based AMC-backed Tx-Rx coil pairs compared with the Tx-Rx coil pair in free space were verified, as it shows measured peak PTE values of 64.45%, 24.1%, 7.48%, and 1.95% at the distances of 10, 15, 20, and 30 cm, respectively.