## 3 Designs of Wirelessly-Powered Cage Systems
### Wirelessly-Powered Cage Systems with Slanted Tx Resonators  
The wirelessly-powered cage systems introduced in this section have multiple slanted Tx resonators wrapping around the cage [13; 16; 32; 33]. The slanted Tx resonators help bend and direct the magnetic flux towards the Rx coil. Such a configuration can improve the system tolerance to angular misalignments. Additionally, the geometry of the Tx and Rx coils are optimized and matched, which is beneficial to improve PTE. The wirelessly-powered cage system, shown in Figure 17a, is built based on a resonance-based inductive link whose configuration is adjustable [16]. The stationary unit includes one square-shaped central Tx coil at the bottom of the cage and four triangular-shaped slanted Tx resonators on the corners of the cage. The Tx coil can directly form a three-coil inductive link with the coils in the mobile device when the animal moves to the center of the cage, or form a four-coil inductive link with one Tx resonator when the mobile device is at a corner of the cage. The position of the mobile device is tracked in real-time by a Microsoft Kinect installed above the cage. Depending on the recorded position information, the stationary unit will either deactivate all Tx resonators or activate the Tx resonator closest to the mobile device by shorting this Tx resonator with a resonant capacitor for forming an LC-tank with a high quality-factor. However, installing the Microsoft Kinect will enlarge the experimental volume needed for the entire system setup, making the system not compatible to the racks of standard-sized rodent cages. Figure 17: _Cont._ \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Publications** & [31] & [11] & [17] \\ \hline Inductive link & 2-coil & 3/4-coil & 4-coil \\ Frequency & 1.5 MHz & 13.56 MHz & 13.56 MHz \\ WPT coverage, & & & \\ length \(\times\) width \(\times\) height & 42 \(\times\) 18 \(\times\) (8–11) cm\({}^{3}\) & 3538 \(\times\) 12 cm\({}^{3}\) & 27 \(\times\) 27 \(\times\) 16 cm\({}^{3}\) \\ Mobile device size, length \(\times\) width \(\times\) height & 40 \(\times\) 40 mm\({}^{2}\) & \(\pi\times\) 20\({}^{2}\)\(\times\) 20 mm\({}^{3}\) & 42 mm diameter \\ PTE & 13–39\% & 5.6–12.6\% & 59\% \\ PDL & 21–225 mW & 20 mW & 100 mW \\ CLPC & \(\times\) & \(\surd\) & \(\times\) \\ Tx control simplicity & \(\times\) & \(\times\) & \(\surd\) \\ Compatible to racks & \(\surd\) & \(\times\) & \(\surd\) \\ Angular misalignment resilience & \(\times\) & \(\times\) & \(\surd\) \\ No view-blocking & \(\surd\) & \(\surd\) & \(\times\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Benchmarking of the wirelessly-powered cage systems with scalable Tx coil array configuration. In Figure 8a, the wirelessly-powered cage system, named EnerCage-HC, includes four-coil inductive link built around a standard-sized rodent cage [13]. The inductive link has a square-shaped Tx coil attached at the center and bottom of the cage and four Tx resonators wrapping around the cage at different heights/orientations, and planar Rx resonator and Rx coil in the mobile device. The slanted Tx resonators, which direct the magnetic field to the mobile device, together with the CLPC can support sufficient and constant PDL up to 80-degree rotation. In Figure 17b,c, two similar wireless cage designs are presented [32; 33]. In the wirelessly-powered cage system, shown in Figure 17b, two more Tx resonators, wrapping around the bottom and top rim of the cage, are added to enhance the homogenous distribution of the transmitted power in the z-direction [32]. The Tx coil consists of multiple identical spiral coils connected in series. However, the Tx coil located at the top of the cage may block the line of view of the camera. The wireless cage design, shown in Figure 17c, has a similar Tx resonator configuration [33]. The Tx coil is formed by three identical coils connected in parallel and tiled at the bottom of the cage to make the transmitted power more evenly distributed in 3D.