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 Green's 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.

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

Preface Bibliography 1. Interpolation. Introduction The Taylor expansion The finite Taylor series with the remainder term Interpolation by polynomials The remainder of Lagrangian interpolation formula Equidistant interpolation Local and global interpolation Interpolation by central differences Interpolation around the midpoint of the range The Laguerre polynomials Binomial expansions The decisive integral transform Binomial expansions of the hypergeometric type Recurrence relations The Laplace transform The Stirling expansion Operations with the Stirling functions An integral transform of the Fourier type Recurrence relations associated with the Stirling series Interpolation of the Fourier transform The general integral transform associated with the Stirling series Interpolation of the Bessel functions 2. Harmonic Analysis. Introduction The Fourier series for differentiable functions The remainder of the finite Fourier expansion Functions of higher differentiability An alternative method of estimation The Gibbs oscillations of the finite Fourier series The method of the Green's function Non-differentiable functions Dirac's delta function Smoothing of the Gibbs oscillations by Fejer's method The remainder of the arithmetic mean method Differentiation of the Fourier series The method of the sigma factors Local smoothing by integration Smoothing of the Gibbs oscillations by the sigma method Expansion of the delta function The triangular pulse Extension of the class of expandable functions Asymptotic relations for the sigma factors The method of trigonometric interpolation Error bounds for the trigonometric interpolation method Relation between equidistant trigonometric and polynomial interpolations The Fourier series in the curve fitting 3. Matrix Calculus. Introduction Rectangular matrices The basic rules of matrix calculus Principal axis transformation of a symmetric matrix Decomposition of a symmetric matrix Self-adjoint systems Arbitrary n x m systems Solvability of the general n x m system The fundamental decomposition theorem The natural inverse of a matrix General analysis of linear systems Error analysis of linear systems Classification of linear systems Solution of incomplete systems Over-determined systems The method of orthogonalisation The use of over-determined systems The method of successive orthogonalisation The bilinear identity Minimum property of the smallest eigenvalue 4. The Function Space. Introduction The viewpoint of pure and applied mathematics The language of geometry Metrical spaces of infinitely many dimensions The function as a vector The differential operator as a matrix The length of a vector The scalar product of two vectors The closeness of the algebraic approximation The adjoint operator The bilinear identity The extended Green's identity The adjoint boundary conditions Incomplete systems Over-determined systems Compatibility under inhomogeneous boundary conditions Green's identity in the realm of partial differential operators The fundamental field operations of vector analysis Solution of incomplete systems 5. The Green's Function. Introduction The role of the adjoint equation The role of Green's identity The delta function -- The existence of the Green's function Inhomogeneous boundary conditions The Green's vector Self-adjoint systems The calculus of variations The canonical equations of Hamilton The Hamiltonisation of partial operators The reciprocity theorem Self-adjoint problems Symmetry of the Green's function Reciprocity of the Green's vector The superposition principle of linear operators The Green's function in the realm of ordinary differential operators The change of boundary conditions The remainder of the Taylor series The remainder of the Lagrangian interpolation formula

Linear Differential Operators. By C. Lanczos. Pp. 580. 80s. 1961. (Van Nostrand, London)

Therapeutic ultrasound is an emerging field with many medical applications. High intensity focused ultrasound (HIFU) provides the ability to localize the deposition of acoustic energy within the body, which can cause tissue necrosis and hemostasis. Similarly, shock waves from a lithotripter penetrate the body to comminute kidney stones, and transcutaneous ultrasound enhances the transport of chemotherapy agents. New medical applications have required advances in transducer design and advances in numerical and experimental studies of the interaction of sound with biological tissues and fluids. The primary physical mechanism in HIFU is the conversion of acoustic energy into heat, which is often enhanced by nonlinear acoustic propagation and nonlinear scattering from bubbles. Other mechanical effects from ultrasound appear to stimulate an immune response, and bubble dynamics play an important role in lithotripsy and ultrasound-enhanced drug delivery. A dramatic shift to understand and exploit these nonlinear and mechanical mechanisms has occurred over the last few years. Specific challenges remain, such as treatment protocol planning and real-time treatment monitoring. An improved understanding of the physical mechanisms is essential to meet these challenges and to further advance therapeutic ultrasound.

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Physical mechanisms of the therapeutic effect of ultrasound (a review)

Thermal therapy is widely known and electromagnetic (EM) energy, ultrasonic waves, and other thermal-conduction-based devices have been used as heating sources. In particular, advances in EM technology have paved the way for promising trends in thermotherapeutical applications such as oncology, physiotherapy, urology, cardiology, ophthalmology, and in other areas of medicine as well. This series of articles is generally written for oncologists, cancer researchers, medical students, biomedical researchers, clinicians, and others who have an interest in this topic. This article reviews key processes and developments in thermal therapy with emphasis on two techniques, namely, hyperthermia [including long-term low-temperature hyperthermia (40-41 degrees C for 6-72 hr), moderate-temperature hyperthermia (42-45 degrees C for 15-60 min), and thermal ablation, or high-temperature hyperthermia (> 50 degrees C for > 4-6 min)]. The article will also provide an overview of a wide range of possible mechanisms and biological effects of heat. This information will be discussed in light of what is known about the degree of temperature rise that is expected from various sources of energy. The review concludes with an evaluation of human exposure risk to EM energy or the corresponding heat, trends in equipment development, and future research directions.

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Thermal therapy, part 1: an introduction to thermal therapy.

The newly released IEEE Std C95.1™-2019 defines exposure criteria and associated limits for the protection of persons against established adverse health effects from exposures to electric, magnetic, and electromagnetic fields, in the frequency range 0 Hz to 300 GHz. The exposure limits apply to persons permitted in restricted environments and to the general public in unrestricted environments. These limits are not intended to apply to the exposure of patients by or under the direction of physicians and care professionals, as well as to the exposure of informed volunteers in scientific research studies, or to the use of medical devices or implants. IEEE Std C95.1™-2019 can be obtained at no cost from the IEEE Get Program https://ieeexplore.ieee.org/document/8859679.

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Synopsis of IEEE Std C95.1™-2019 “IEEE Standard for Safety Levels With Respect to Human Exposure to Electric, Magnetic, and Electromagnetic Fields, 0 Hz to 300 GHz”

Medical applications of RF/microwaves are highlighted in this paper. The emphasis is placed on newer emerging diagnostic and therapeutic applications, such as microwave breast cancer detection, and treatment with localized high power used in ablation of the heart, and liver, benign prostate hypertrophy, angioplasty, and others. A very brief outline of biological effects of RF/microwaves and associated issues is given as background to the applications.

Applications of RF/microwaves in medicine

A common way of describing antennas in the time domain is by means of their impulse response. When the time-domain antenna equations are expressed in terms of the normalised impulse response (normalised IR), they become very simple to use, because all frequency-dependent antenna characteristics are included in the normalised IR. This paper describes a method for measuring the normalised IR experimentally, using a vector network analyser. The normalised IRs of different air and dielectric-filled TEM horn antennas are compared and discussed. The normalised IR is found to be a powerful tool for simulating antenna behaviour directly in the time domain. Thanks to the introduction of the virtual source, (i.e. an apparent point in the antenna from which the radiated field degrades by a factor 1/r), the time-domain antenna equations can also be used near the TEM horns, although still in the far field of the antenna. Some examples of time-domain simulations and system modelling using the normalised IR are presented. In each example, the simulations are compared with measured data.

Time-domain simulation and characterisation of TEM horns using a normalised impulse response

This paper demonstrates that fully-depleted (FD) silicon-on-insulator (SOI) technology offers unique opportunities in the field of low-voltage, low-power CMOS circuits. Beside the well-known reduction of parasitic capacitances due to dielectric isolation, FD SOI MOSFETs indeed exhibit near-ideal body factor, subthreshold slope and current drive. These assets are both theoretically and experimentally investigated. Original circuit studies then show how a basic FD SOI CMOS process allows for the mixed fabrication and operation under low supply voltage of analog, digital and microwave components with properties significantly superior to those obtained on bulk CMOS. Experimental circuit realizations support the analysis.

Fully-Depleted SOI CMOS Technology for Low-Voltage Low-Power Mixed Digital/Analog/Microwave Circuits

We report on the microwave properties of arrays of parallel magnetic nanowires constituted of nickel, cobalt, or Ni/Fe alloy embedded in nanoporous track-etched polymer membranes. The experiments consist of transmission measurements carried out on microwave stripline structures using a magnetically loaded membrane as the substrate. Measurements were performed at frequencies ranging from 100 MHz to 40 GHz and under static magnetic fields up to 5.6 kOe applied along the wires axis. Resonance phenomena have been observed in the magnitude of the complex transmission coefficient at frequencies which depend on the nature of the material and applied static magnetic field. Results are consistent with those expected for a ferromagnetic resonance (FMR) experiment and the observed behaviors are analyzed in the framework of the classical FMR theory. (C) 1999 American Institute of Physics. [S0003-6951(99)02338-4].

Microwave properties of metallic nanowires

The authors present a novel microstrip structure using a nanoscale porous substrate filled by a ferromagnetic material, forming an array of nanowires perpendicular to the ground plane. When compared with photonic bandgap structures, the stopband behavior is created here by a gyromagnetic resonance phenomenon in the metallic nanowires. This resonance is tuned by means of a DC magnetic field parallel to the nanowires, in a very good agreement with the gyromagnetic theory. Also, tuning can be achieved over more than one octave, because the nanoscale geometry ensures that fields penetrate into the whole wire area up to 40 GHz. Other advantages are detailed in this work.

A. Vander Vorst

Papers

Applications of RF/microwaves in medicine

Time-domain simulation and characterisation of TEM horns using a normalised impulse response

Fully-Depleted SOI CMOS Technology for Low-Voltage Low-Power Mixed Digital/Analog/Microwave Circuits

Microwave properties of metallic nanowires

A novel nanostructured microstrip device for tunable stopband filtering applications at microwaves