Bioelectromagnetics in Healthcare: Advanced sensing and communication applications is a collection of twelve invited chapters from international experts from the UK, Japan, Switzerland, and the United States of America. The book forms a cohesive architecture that covers the state-of-the-art in terms of sensing and communications with relevance to bioelectromagnetics in healthcare. The book provides a valuable insight into the current and future possibilities where electromagnetics engineers will need to keep improving radiofrequency device performance in terms of better efficiency, greater sensitivity, reduced unintended power absorption by the body, smaller size, and lower power consumption.
Topics covered include dielectric measurements, dosimetry for bioelectromagnetics, phantom recipes for implanted and wearable antenna applications, antennas for implants, electromagnetic coupling in biological media, electromagnetic resonators and metamaterials-based structures for chemical and biological sensing in body-centric wireless applications, bone fracture monitoring using implanted antennas, wearable antennas for sensing, epidermal and conformal electronics, radar for healthcare technology, therapeutic applications of electromagnetic waves, and optoelectronic sensing of physiological monitoring.
The book is aimed at electromagnetics engineers and advanced students in electromagnetics working on healthcare and medical applications.
Inspec keywords: phantoms; biomedical communication; health care; sensors; patient monitoring; biomedical equipment; pneumodynamics; muscle; bone; cancer; wearable antennas
Other keywords: muscle; bone; biological tissues; cancer; wearable antennas; phantoms; pneumodynamics; bioelectromagnetics; communication applications; biomedical equipment; sensing; patient monitoring; health care
Subjects: Haemodynamics, pneumodynamics; Single antennas; Sensing and detecting devices; Sensing devices and transducers; Patient diagnostic methods and instrumentation; Biomedical communication; Microwaves and other electromagnetic waves (medical uses); Textbooks
This book on Bioelectromagnetics in Healthcare is a collection of 12 invited chapters from international experts from UK, Japan, Switzerland, and United States of America. It has been a great pleasure to collate and edit these chapters to form a cohesive architecture that covers the state-of-the-art in terms of sensing and communications with relevance to Bioelectromagnetics in Healthcare. We have endeavoured to write these chapters so that they contain the latest developments but are also accessible to people who do not have a pure specialism in these exact topics. We have strived to include valuable practical advice that other engineers can implement to devise the next generation of healthcare devices.
In its simplest form, a dielectric is a material that can store charge when subjected to an electric field. The electric field should penetrate the material, interact with, and rearrange charged entities within it for this to happen. If all the charges are bound as in a perfect conductor, the effect is a slight charge displacement, giving rise to an element of induced polarisation as in a capacitor. Natural materials with free and bound charges would experience charge polarisation and conduction phenomena. These occur over time scales from seconds to picoseconds and manifest over field frequencies from 1 Hz to 100 s of GHz. The complexity of the interaction is commensurate with the structure and composition of the material. The dielectric properties are a measure of such interactions and help explain a material's electrodynamics and related microscopic properties, as well as highlighting the effects of the field exposure on the material.
Bioelectromagnetic applications rely on the ability to control the interaction between electromagnetic fields and the body. Designing electrical sensors and medical devices therefore requires the ability to determine the fields in the body that are caused by these devices, or to determine how much the body impacts the fields, creating an image or perturbation that can be received by a device, such as an electrical sensor. Dosimetry is the process of determining these fields, and is the topic of this chapter. Dosimetry requires three major components - a sufficiently precise model of the physical structure of the part(s) of the body the fields will traverse, a model of the electrical properties of these structures, and a numerical method to compute the fields within this model. We will cover all of these topics in this chapter, with a focus on the use of the finite-difference time-domain (FDTD) method for bioelectromagnetic simulations.
This chapter has provided details on the most important aspects for consideration when designing antennas that operate inside lossy media and extensively referenced the relevant sources found in literature. Furthermore, a literature overview has been provided on the types of frequency dependent tissue-mimicking phantoms that are currently available. It has been highlighted that multi-material phantoms with broadband behaviour, without the undesirable mixing of their constituting ingredients is necessary for implanted antenna applications. Following this, nine different tissue-mimicking phantom recipes have been developed, each approximating the dielectric properties of bone marrow, bone cortical, blood and muscle at different frequencies constituting of off-the-shelf biocompatible ingredients. It has been shown that four of the proposed phantom recipes exhibited broadband behaviour at the frequency spectrum of 0.5-4 GHz according to the IEEE standards for phantom development [53]. The rest of the recipes are narrowband and can be used in measurements where targeting a specific frequency is required.
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.
This chapter describes and explores the impact of biological environments with low conductivity (human/animal bodies and tissues) on the well-known inductive coupling using magnetic coils. Such systems are used for wireless power transfer (WPT) to implantable medical devices and near-field communications. When using this technique in biological media or in general, non-ideal media, a time varying magnetic field induces eddy currents throughout the medium, which affect the self and mutual inductance between coils. To date, the impacts of excited eddy currents have not been fully quantified. In most current literature, scientists and researchers are using an assumption in which the attenuation of the near fields is similar to that of a plane wave travelling in a conductor. It leads to numerous problems in designing and optimizing biomedical applications. This chapter introduces the problem and presents a number of solutions for power transfer and communications through skin, muscle, and bone. A brief introduction of previous and ongoing researches in the field of magnetic coupling in non-ideal media is given in Section 6.1. Section 6.2 proposes a novel equivalent circuit model for two coupled coils inside infinite biological surroundings with the emergence of two complex Kirchhoff's coefficients. Then, the mathematical method to calculate these two new terms is presented in Section 6.3. The closed-form analytical solutions are justified by comparing them to CST EMS numerical simulations in Section 6.4. Section 6.5 performs the network analysis of a two-coil system in detail, especially impacts of the environment on the resonant frequency, Q-factor, frequency splitting, and electrical current distribution. Finally, Section 6.6 examines an immediate application: WPT using near-field magnetic induction for biomedical devices.
This chapter has illustrated the potential and importance of EM antennas, resonators, and MTM structures in the field of chemical sensing and healthcare applications. EM resonators and MTM structures provide an appealing solution for microfluidic applications with sensors having high sensitivity for concentration estimation and detection of various chemicals and biochemicals. Comprehensive review has been provided on applications of EMs in field of healthcare applications like wireless endoscopy, cancer detection and curative treatment using hyperthermia, Wireless drug delivery, glucose sensing and cardiovascular healthcare. Remarkable amount of research has been done in field of wireless wearable sensors and implantable devices for early diagnostics and curative treatment of chronic diseases, and for real-time monitoring of crucial parameters for instance, breathing, heart rate, blood pressure, body weight, body movements, and numerous chemical variables like hydration, glucose, and various other essential nutrients in case of patients susceptible to serious health conditions. Progression in this field will facilitate implementations of more reliable sensors in future, hence, providing an extensive solution for non-invasive and contactless measurements in chemical and healthcare applications.
In this chapter, the development and testing of two geometrical human body phantoms based on the recipes that were investigated in Chapter 4 is presented. The first is a two-material phantom consisting of bone cortical and muscle layers simulated in Section 8.1 and measured in Section 8.2. The second is a three-material geometrical phantom consisting of bone marrow, bone cortical and muscle layers simulated and measured in Sections 8.3 and 8.4 accordingly. The specific absorption rate (SAR) evaluation of the test-bed according to the USA, Canada, and European Union standards is conducted in Section 8.5. Two radiofrequency (RF) monopoles were implanted in a multi material phantom, and the condition of a bone fracture representative was replicated. The bone fracture was modelled as a cylinder residing in the mid distance between the implanted monopoles for the simulations. The technique was tested in the measurement section using three multi-material geometric phantoms. The results between simulation and measurements showed good agreement. In this section, the two-monopole system that is used for the simulations and measurements of this chapter is presented.
The term "wearable antennas" refers to antennas that are placed upon the human body by embedding them into fabrics and other accessories (e.g., belts, shoes). Typically, the purpose of such antennas is to serve as the wireless interface of a wearable device that has the antenna embedded in it. For example, wearable antennas may enable data transfer from wearable sensors to a personal digital assistant (such as a smart phone or laptop), they may collect information from an underlying ingestible device, or they may send wireless power to remotely charge a patient's implant. As would be expected, extensive research work has been pursued in terms of designing wearable antennas, optimizing their performance to account for loss associated with biological tissues, miniaturizing their size for seamless operation, and enabling flexible and robust implementations. This above has already been extensively reviewed.
This chapter has discussed two aspects of low power epidermally or conformally mounted UHF RFID sensing tag applications. First, colonising infections on voice prostheses can be detected using an entirely passive system by exploiting the thickening biofilm which decouples a saliva layer from the sensor tag antenna aperture fields. Obtaining passive backscattered UHF communications is challenging, though this voice prosthesis application benefits from both the relative stability in throat tissue electrical parameters in association with the low bulk density of the neck.
Second, for systems such as skin mounted accelerometry or ECG measuring tags, a microcontroller-based system can achieve streaming data at rates of 5.2 kB per second using RAM rather than EEPROM and avoiding clashes between the microcontroller and the RFID transponder chip. This technique has the potential for enabling low cost, compact and body conformal electronics in areas such as rapid diagnostics, where low overhead and instant response sensors are vital. Future investigations into this technique will aim to focus on optimised read/write cycles to improve read range and data throughput to the extent that more advanced multicombination sensor suites might be achievable.
Radar systems can detect vital signs from a distance by sensing the chest displacement. The later comes from the heartbeat and respiration. This chapter presents the theoretical background of this application along with the main characteristics of such a system. Limitations and challenges are presented. An implementation of a CW radar-based system in order to detect the heartbeat of a person is presented and demonstrated. Radar technology has the potential to replace traditional methods to monitor vital signs.
This chapter focuses on therapeutic applications of electromagnetic waves. Thermal therapy and surgical devices utilize temperature elevation in the human tissue caused by electromagnetic energy. On the contrary, brain/nerve stimulators and a few types of cancer treatment are based on non-thermal effects. These topics have been actively studied and discussed within some scientific organizations such as International Union of Radio Science (URSI) Commission K [1] and COST (European Cooperation in Science and Technology) MyWAVE [2].
Opto-physiological monitoring (OPM) considers biological tissue as a set of optical media, and studies how light interacts within biological tissue, where the optical properties of the latter reflect the mechanical, physical, and biochemical functions of the living organism. This kind of physiological monitoring includes optoelectronic sensor-based contact monitoring and image sensor-based remote monitoring.