Wireless communication with an implanted sensor represents a huge challenge due to the large losses in the link. A key element in such a system is the implanted antenna, which has an important impact on the global efficiency of the communication link. The design of implantable antennas presents two main challenges: first, the miniaturization, as the available space in an implantable capsule is usually much smaller than the wavelength. Second, the antenna radiates into a lossy environment, which is very different from the lossless free space environment we know from classic antenna theory. This has a deep impact not only on the link performance but also more fundamentally on the way antenna radiation performance is described and on the bounds on the performance of these antennas. In this chapter, we will gain insight into the main fundamental differences between classic electrically small antennas and implantable antennas. We will then study some canonical cases to understand the loss mechanisms and propose certain physical bounds on the efficiency of implantable antennas. Based on these results, we will propose design rules, illustrated by realistic examples. Finally, we will discuss issues linked to the measurement of implantable antennas.

Chapter Contents:

• 5.1 Introduction
• 5.2 Key performance indicators: implantable antennas versus classic electrically small antennas
• 5.3 Loss mechanisms and efficiency in implanted antennas
• 5.3.1 A spherical multishell model for the lossy host medium
• 5.3.2 Bounds on power density reaching the surface of the lossy phantom
• 5.3.3 Design rules of thumb
• 5.4 Examples
• 5.5 Measurements
• 5.6 Conclusion
• References

Inspec keywords: antenna theory; antenna radiation patterns

Other keywords: antenna radiates; implanted antenna; wireless communication; implanted sensor; implantable capsule; classic antenna theory; implantable antennas

Subjects: Antenna theory