Jaehoon Kim

Implanted antennas inside a human body: simulations, designs, and characterizations

Antennas implanted in a human body are largely applicable to hyperthermia and biotelemetry. To make practical use of antennas inside a human body, resonance characteristics of the implanted antennas and their radiation signature outside the body must be evaluated through numerical analysis and measurement setup. Most importantly, the antenna must be designed with an in-depth consideration given to its surrounding environment. In this paper, the spherical dyadic Greens function (DGF) expansions and finite-difference time-domain (FDTD) code are applied to analyze the electromagnetic characteristics of dipole antennas and low-profile patch antennas implanted in the human head and body. All studies to characterize and design the implanted antennas are performed at the biomedical frequency band of 402-405 MHz. By comparing the results from two numerical methodologies, the accuracy of the spherical DGF application for a dipole antenna at the center of the head is evaluated. We also consider how much impact a shoulder has on the performance of the dipole inside the head using FDTD. For the ease of the design of implanted low-profile antennas, simplified planar geometries based on a real human body are proposed. Two types of low-profile antennas, i.e., a spiral microstrip antenna and a planar inverted-F antenna, with superstrate dielectric layers are initially designed for medical devices implanted in the chest of the human body using FDTD simulations. The radiation performances of the designed low-profile antennas are estimated in terms of radiation patterns, radiation efficiency, and specific absorption rate. Maximum available power calculated to characterize the performance of a communication link between the designed antennas and an exterior antenna show how sensitive receivers are required to build a reliable telemetry link.

Dual-band E-shaped patch wearable textile antenna

Future utilization of smart clothing will necessitate applications of multi-function and multi-frequency wearable antennas. The paper addresses the development of a dual-band E-shaped textile antenna for wearable applications. We have considered felt fabric to design an antenna for 2.2 GHz and 3.0 GHz frequencies. The antenna input matching and radiation characteristics have been determined by FDTD simulations and by measurements. Numerical modeling of specific absorption rate was also performed. The results show clearly that E-shaped textile antennas are suitable for multiband operation.

Implanted Antennas in Medical Wireless Communications

Abstract One of the main objectives of this lecture is to summarize the results of recent research activities of the authors on the subject of implanted antennas for medical wireless communication systems. It is anticipated that ever sophisticated medical devices will be implanted inside the human body for medical telemetry and telemedicine. To establish effective and efficient wireless links with these devices, it is pivotal to give special attention to the antenna designs that are required to be low profile, small, safe and cost effective. In this book, it is demonstrated how advanced electromagnetic numerical techniques can be utilized to design these antennas inside as realistic human body environment as possible. Also it is shown how simplified models can assist the initial designs of these antennas in an efficient manner.

An implanted antenna in the spherical human head: SAR and communication link performance

To characterize the performance of implantable biomedical devices, the interactions between the devices and the human body need to be properly assessed. Specifically, wireless telemetry systems for biomedical applications require a reliable communication link between the interior device and the exterior equipment for exchange of required data and information. This paper mainly deals with the implantable antennas embedded on the head telemeter. To generate parametric data, the electromagnetic scattering analysis is confined to the human head and dipole antennas.

Electromagnetic interactions between biological tissues and implantable biotelemetry systems

Biotelemetry which provides wireless communication links between internal devices and outside equipment is a promising function for future implantable biomedical devices. In order to build reliable wireless links, detailed characterization and performance evaluation of the telemetry links are required. In this work, the finite difference time domain (FDTD) simulations are performed to analyze the radiation performances of small dipole and loop antennas in biological tissues for various biotelemetry links. By comparing the electrical characteristics of vertical and horizontal loop antennas above a perfect electric conductors (PEC) plane, the effects of biomedical devices on biotelemetry links are estimated in terms of radiation efficiency and specific absorption rate (SAR). Finally, it is observed that electromagnetic band-gap (EBG) structures are useful candidates for biotelemetry link design.

SAR reduction of implanted planar inverted F antennas with non-uniform width radiator

In this paper, the radiation mechanism of an implanted planar inverted F antenna (PIFA) is studied to improve radiation performances of PIFA in a human body by changing the width of the planar radiators. The PIFA is designed to operate at the medical implant communications service (MICS) frequency band (402-405 MHz). The numerical computational procedures (Annex E of Std. C95.3-2002) recommended by IEEE are applied to calculate spatial-average specific absorption rate (SAR) for the implanted antennas located in a biological tissue model. An experimental setup is used to measure the impedance matching characteristics of the implanted antenna

Low-profile loop antenna above EBG structure

In this work, a low-profile loop antenna is designed using an electromagnetic bandgap (EBG) structure to achieve better than -10 dB 50/spl Omega/ match for a printed loop antenna. The electrical characteristics of the mushroom-like EBG structure which are estimated from FDTD simulations are utilized to determine the length of the loop antenna. After constructing the loop antenna above the EBG structure, return loss characteristics and far-field patterns of the antenna are measured and compared with the simulation results. The design frequency is 2.2 GHz.

Exterior antennas for wireless medical links: EBG backed dipole and loop antennas

Antennas located at the outside of a human body are studied through FDTD simulations. Low-profile antennas are designed using electromagnetic bandgap (EBG) structure and are positioned to radiate power to the outside and inside of a human body. By changing the distance between the antennas and a biological tissue, the return loss variations of the antennas are observed and the radiation efficiencies and specific absorption ratio (SAR) are calculated.

Low-profile antennas for implantable medical devices: optimized designs for antennas/human interactions

Based on the FDTD simulations and the return loss measurement setup, a spiral-type microstrip antenna and planar inverted F antenna (PIFA) are optimized to operate in a human body at the biomedical frequency band and their electric characteristics are compared in terms of physical dimension and radiation characteristics. Although the radiation patterns are similar to each other, the PIFA has advantages over a microstrip antenna, specifically smaller dimensions and higher radiation efficiency. The SAR calculation of two low profile antennas indicates that the dielectric layer used for the superstrate are useful to protect the skin tissue in front of the antenna and make it possible for the implanted antenna to deliver more than 25 /spl mu/W for short-range biomedical devices.

On the Applicability of Simplified Spherical Human Heads for Implanted Antennas in Biomedical Communications

Abstract The spherical dyadic Greens function (DGF) simulations of the interactions between an implanted antenna and a human head are performed with an emphasis on a biomedical communication link between an antenna implanted in a human head and an exterior antenna. Suitability of the spherical head model for characterization of implanted antennas in a human head is tested using the finite difference time domain (FDTD) simulation based on an anatomical head model. The near-field distributions, the far-field patterns, and the radiation power from dipoles in three different types of spherical heads (homogeneous, three-layered, and six-layered heads) are compared to estimate the dependency of implanted antennas on the head configurations. To analyze the performance of the wireless link and to estimate the minimum sensitivity requirements, the maximum available powers are obtained at various locations on the inside and exterior antennas.