# A Magnetic-Balanced Inductive Link for the Simultaneous Uplink Data and Power Telemetry
For example, these special coil structures cannot be used in our intraocular biomedical sensor device, which will be introduced in the following paragraph, as the figure-eight coil will block the eyesight. Furthermore, this special coil structure is sensitive to coil misalignments. In this paper, to address the aforementioned problems, we propose a magnetic-balanced inductive link for our intraocular biomedical sensor device, as seen in Figure 1. The intraocular biomedical sensor device will be implanted in the patient's eyeball to monitor and regulate the intraocular pressure (IOP) for glaucoma treatment, because lowering IOP is the only evidence-based treatment to prevent the deterioration of glaucoma ([PERSON] _et al._, 2018; [PERSON] _et al._, 2018). The uplink sends out the data of the pressure for monitoring the IOP and the data of the peak voltage of the implant load for adaptive power adjustment. When the measured IOP is above the normal IOP, an actuator (micro-pump) is enabled to regulate the IOP. There are three coils (two external coils and one implant coil) used for the wireless power and data transmissions. The external power coil (\(L_{1}\)) is used for feeding the wireless power, and the external data coil (\(L_{3}\)) is used for the uplink data receiving, while the implant coil (\(L_{2}\)) is used for both the wireless power harvesting and the uplink data transmitting. Dual carriers (i.e., power carrier and uplink data carrier) are used for the power and uplink data transmissions, respectively. The two external coils are designed to be partially overlapped and magnetically balanced; thus, the power carrier interference to the uplink receiving can be minimized. The positions of the two external coils are carefully optimized based on the deduced formula of self-inductance and mutual inductance. We further optimize a key resistor of the inductive link circuits to minimize the impacts of the implant uplink transmitter on the WPT. The effects of coil misalignments are also evaluated. Finally, a prototype was implemented and measured. The magnetic-balanced inductive link achieves significant improvement of the SIR compared with the conventional two-coil inductive link. Benefiting from this substantial SIRimprovement, the prototype achieves reliable uplink data and power transmissions under ultra-weak coupling with negligible interactions. The rest of the paper is organized as follows. Section 2 presents a system overview of the magnetic-balanced inductive link. Section 3 presents the equivalent model and analysis of the magnetic-balanced inductive link circuit. Section 4 discusses the coil parameter optimizations, which aim to minimize the power carrier interference and to enhance the received uplink signal intensity. Section 5 discusses a key resistor optimization, which aims to minimize the impacts of the implant uplink transmitter on the WPT. Section 6 evaluates the effects of coil misalignments. Section 7 presents the prototype implementation and the measured results. Section 8 is the Conclusion. Appendix A presents the modeling of self-inductance and mutual inductance of the coils, which are wound using enameled wires.