• wireless power transfer
• LDO
• inductive coupling
• capsule endoscopy

With the incessant progress and development of new tools for implantable medical devices (IMDs) as Capsule Endoscopy (CE) for gastro-intestinal diseases, it appears increasingly necessary to provide these devices with a proper power supply, able to overtake the limitations of battery solutions. In particular, non-radiative inductive coupling seems to be the most suitable and promising solution, as claimed by the amount of literature articles proposing cutting-edge architectures.

This project deals with a survey of Capsule Endoscopy solutions, explaining why and how Non-Radiative Inductive Coupling (NRIC) has to be preferred to the other Wireless Power Transfer (WPT) alternatives and giving an overview of the state-of-the-art implementations which are present in the scientific literature, analysing the main design features and their effect on the system. Then, a wireless power transfer system is designed, focusing on the possible dissipations which could dangerously overheat the capsule and the environment around it. In these terms, a parasitic capacitance and a parasitic resistance representing the tissue losses are determined through the Conformal Mapping Technique. To handle the heavy calculations of Conformal Mapping Technique and to elaborate an effective simulation method, python scripts have been implemented to execute LTspice simulations by batch. LTspice responses are sent to python scripts, which collect them, deciding if continuing the simulation or storing the outcomes in an Excel sheet. This simulation approach has been used to find the coil parameters which guarantee the best performance in terms of efficiency and maximum achievable distance between the transmitter and the receiver. The result is a system able to successfully send 102 mW at a distance from Tx and Rx of 14 cm. Furthermore, analyses of variations on crucial components of the design are carried out, such as a study about the behaviour of the system in the presence of misalignment between coils.

Also a new signal modulation on the same coil for power transmission is reported. It is based on the birth of two new resonating frequencies and on the use of an oscillator at the transmitter side. This thesis is limited to just show the main concepts of this modulation and its compatibility with the proposed system.

Another compelling need for wireless power system is to understand if the power effectively delivered from Tx to Rx is sufficient or not. For this reason, a closed loop control based on Load Modulation has been designed and successfully tested, exploiting the same simulation approach.

Finally, an LDO has been added to the architecture to regulate the output voltage. The proposed architecture belongs to capacitor-less LDO category to respond to the request of reducing the space occupation, which is a pivotal requirement in a Capsule Endoscopy. Besides, this LDO implementation ensures an output current up to 50mA, with always an excellent phase margin and an enviable time response. The structure has been designed and tested through Cadence Virtuoso Software, exploiting the UMC 180 nm node.

In the end, a simulation of the power transfer complete with the LDO is conduced at a distance of 14 cm, proving the success of the system.