## 2 Design and Implementation
### Antenna Design-I with Performance Evaluation  
A small electrical loop microstrip antenna is one of the excellent choices to fix on contact lens platform for receiving RF image without implant inside the human eye. As per ANSI guidelines, any device implantation has a frequency limit, beyond that it is harmless for human tissues. The Federal Communications Commission (FCC) approved an ultra-wide band (UWB) frequency range from 3.1 GHz to 10.6 GHz. UWB antenna design offers various advantages over narrowband systems,  
Figure 2: Proposed block diagram at the interface between wireless power devices and CMOS neuron IC. such as small size, low power consumption, higher bit rates, and highly integrated systems [22; 23; 24]. Here, one important point is that the designed small loop antenna could be placed on a glass contact lens instead of an implanted one. Meanwhile, this work designed a small loop antenna by following ANSI and FCC medical guidelines. Two major issues are concerned when medical professionals need to adopt technology and advancement for retinal prosthesis. First, the size of device should be at least half of the standard contact lens of the human eye. Second, the device should be biocompatible because it needs to be worn for a longer time. With concern of the first point, antenna design has to be chosen as a slotted loop monopole antenna with operating frequency of 3.5 GHz. The reason for considering the operating frequency of 3.5 GHz is to achieve maximum radiation efficiency at lower band of operation. The antenna is fabricated using on-wafer packaging technology to achieve an adequate size in place of using printed circuit board (PCB) substrate. Silicon-nitride wafer in 5 mm diameter is taken to design the antenna because of biocompatibility. The primary challenge for designing a small antenna relies on achieving sufficient antenna efficiency. However, the efficiency will drop if antenna size is smaller than electromagnetic wave length. Therefore, a high frequency is considered in order to achieve sufficient efficiency from the small loop antenna. The proposed three-dimensional (3D) isometric view of the small electrically antenna is shown in Figure 3a, while its fabrication view is shown in Figure 3b. The antenna design consists of cross shape slot on the loop patch while monopole (or defected) on the ground plane. The antenna design is implemented on the silicon nitride wafer having (dielectric constant \((\epsilon_{o})\) of 5.6, loss tangent \((tan\rho)\) of 0.0028 and thickness of 200 \(\upmu\)m) at 3.5 GHz, respectively. The dimension of the on-wafer antenna is 4 mm \(\times\) 3.7 mm, which is less when compared to PCB-fabricated UWB antennas. The fabrication of antenna uses high-resistivity silicon nitride (HRSiN) substrate based on wafer-level packaging technology (WLP). The proposed antenna consists of 50 mm HRSiN on-chip layer, one solder layer, and one 45 mm HRSiN substrate carrying patch layer and feeding structure with WLP technology. An antenna is excited using microstrip feed whose dimensions are measured from edge of the patch and the ground. The full wave simulation of proposed antenna is carried out on Advanced Design System (ADS) v. 2019 using a microwave momentum electromagnetic field (EM) package. The characterization of the antenna design commences with its wideband performance, which is evaluated on the basis of electromagnetic field (EM) analysis, and can be seen in Figure 4. The simulated and measured return loss variation, with respect to frequency, is shown in Figure 4a where wideband performance is achieved from 3.1 GHz to 10.7 GHz with multi-resonating frequencies. Figure 3: Proposed slotted small loop antenna with its (**a**) isometric view and (**b**) fabricated view. Figure 4: The performance of the proposed antenna with its (**a**) return loss versus frequency, (**b**) antenna received power, (**c**) antenna efficiency, and (**d**) tilt angle of receiver antenna.