## 2 Main Blocks for Wirelessly-Powered Cage System
### Scalability for Wireless Coverage  
The animal experimental arena can be either a square standard cage or a specific shape with a larger area depending on the experimental purposes. Some wirelessly-powered cages are dedicated to the standard cage [13; 16], which have an advantage in terms of compatibility with the standard racks of rodent cages in the animal facilities compared to the modular design for a specific shape. This compatibility is beneficial for longitudinal studies on multiple animals in separate standard cages resulting in the simultaneous and massive data collection from many animal subjects [15]. The modular designs can be easily extended for large area or specific shape [11; 17; 18] while the optimized wireless cages dedicated to the standard cage are hard to modify the wireless coverage. One of the important considerations for the scalability using the modular coil design is to choose the suitable method for tracking the Rx coil position because the modular coil design needs to select the nearest Tx coil to the Rx coil. If the modular system does not equip the tracking method, all the Tx coils in the array will be driven simultaneously, resulting in significant power loss. In [11], a small permanent magnet is attached to the mobile device, and the wirelessly-powered cage detects the mobile device using three-axis magnetic sensors to select the nearest Tx coil to the freely moving animal subject. The permanent magnet is also utilized in [18] for the Rx coil tracking, where a single Tx coil moves mechanically on XY-rails located at the bottom of the cage. However, in the WPT system, the performance of magnetic sensors might be degraded due to the strong magnetic fields inside the cage, resulting in not sufficient tracking resolution and quality.  
The optical animal tracking techniques are studied in [16; 19] using an infrared range camera or a Microsoft Kinect(r). The Microsoft Kinect includes infrared depth (IR-3D) and red-green-blue (RGB-2D) cameras allowing animal tracking in both bright and dark conditions. Since the optical tracking method can obtain the information about both the Rx coil position and the animal subject behavior at a time, it is more beneficial than the permanent magnet sensing in terms of the additional analysis of animal locomotion and behavior. However, the optical cameras should be installed on the top of the cage with a few tens of centimeters. As such, the lid of the cage should not be closed during the experiment. As an alternative, the resonator-based cage design, which allows for automatic magnetic field localization, obviating the need for a tracking system or switching the coils, are introduced in [13; 14; 15; 17]. In these  
Figure 9: (**a**) Block diagram of CLPC in the two-coil inductive link, and (**b**) the experimental CLPC waveforms in the wirelessly-powered cage to compensate for the distance variation between Tx and Rx in transient caused by the animal movement [16].  
systems, the multi-resonator coil arrangement around the cage, simply driven by a single LC-tank located at the bottom of the cage, can dynamically focus the magnetic field at the position of Rx coil. However, the parasitic resistance in multi-resonator coils still dissipates power all the time regardless of the Rx coil position, resulting in the additional power loss compared to the switchable modular Tx coil design.