Miniature implantable antennas for biomedical telemetry: from simulation to realization

WOS:000310154700019 (Nº de Acesso Web of Science)“Prémio Científico ISCTE-IUL 2013”We address numerical versus experimental design and testing of miniature implantable antennas for biomedical telemetry in the medical implant communications service band (402-405 MHz). A model of a novel miniature antenna is initially proposed for skin implantation, which includes varying parameters to deal with fabrication-specific details. An iterative design-and-testing methodology is further suggested to determine the parameter values that minimize deviations between numerical and experimental results. To assist in vitro testing, a low-cost technique is proposed for reliably measuring the electric properties of liquids without requiring commercial equipment. Validation is performed within a specific prototype fabrication/testing approach for miniature antennas. To speed up design while providing an antenna for generic skin implantation, investigations are performed inside a canonical skin-tissue model. Resonance, radiation, and safety performance of the proposed antenna is finally evaluated inside an anatomical head model. This study provides valuable insight into the design of implantable antennas, assessing the significance of fabrication-specific details in numerical simulations and uncertainties in experimental testing for miniature structures. The proposed methodology can be applied to optimize antennas for several fabrication/testing approaches and biotelemetry applications

Novel miniaturized antennas and arrays for implantable, ingestible and body-worn applications

University of Technology Sydney. Faculty of Engineering and Information Technology.Implantable medical devices (IMDs) introduced to monitor and transfer physiological information from inside the human body have superb potentials to provide major contributions to disease diagnosis, prevention and therapy. Moreover, minimally invasive biomedical devices helps to reduce the period of long-term hospitalization, so that enhancing the patients’ quality of life. Understanding and developing biotelemetry devices, recording/transmitting data from inside the body to the external base station, requires a multi-disciplinary approach. Such a challenging task merges applied solutions, concepts and models from various fields, including biology, electronics, electromagnetism and package/system engineering. Among the device components, the transmitter antenna plays a key role. Antenna design for biotelemetry applications is extremely challenging due to the effect of the surroundings on the radiator, the essential requirement to miniaturize the antenna structure size, reduced antenna efficiency and the robust effect of multipath losses. More specifically, in this thesis, I design and fabricate several antennas to be integrated in ingestible and implantable devices useful for remote monitoring as well as data biotelemetry. This work also focuses on arrays of body-worn antennas for both wireless endoscope base stations and cancer treatment nearfield microwave systems. Here, my aim is to reduce the physical size of the implantable antennas at specified operating standards frequency bands, while maintaining the antenna electromagnetic performance satisfactory. To achieve this, I introduce and use valuable miniaturization techniques for implantable patch antennas for biotelemetry applications. Additionally, I design and fabricate compact microwave systems for cancer treatment using electromagnetic (EM) energy. Non-Invasive Local Microwave Hyperthermia (NI-LMH), which is my interest in this thesis, is a heat treatment serves to enhance the effectiveness of chemotherapy or radiation therapy and leads to gain remarkable results. The system may directly apply heat to a fairly small specific area such as tumors to destroy the local cancer cells. To achieve this, the heat effect is developed in the target by the transmission of EM energy, using array of antennas, which is adjusted in frequency, time and strength in order to work together to form a focus in the target. This places high demands on the precision of the system. In this thesis, I present different planar antenna array for non-invasive microwave hyperthermia applications. The new Near Field Focused (NFF) arrays operates at ISM 2.45 GHz band and consists of 5 to 25 miniaturized dual slot PIFAs, depends on the array geometry arrangement. The arrays immersed inside a coupling bolus occupies a very small volume of space results in an easy fitting to contoured patient anatomy. These arrays, which are low profile and lightweight, have both superficial and deep focusing properties. The novel NFF body worn arrays are capable to focus on a single target with a high level of accuracy to concentrate the EM energy only on the target. I employ optimized dual slot PIFAs as array elements to reduce the size of the focusing area so that destroying very small tumors and avoid heating up the surrounding healthy cells. I have also introduced size reduced NFF array to simplify the feeding network of the applicator and reduce the system cost, this array configuration satisfies system requirements and can focus on small targets precisely while keep the penetration depth high enough to heat up the deep seated targets. In addition, the performance of both fabricated narrowband and wideband single antennas and array of antennas verified using experimental tissue mimicking phantoms. To validate the dielectric properties of experimental phantoms, over different frequency bands, dielectric probe kit employed, furthermore, optical fibre thermometers employed to confirm specific absorption rate (SAR) values for implanted radiators

Dual-band implantable antennas for medical telemetry: a fast design methodology and validation for intra-cranial pressure monitoring

WOS:000323538100010 (Nº de Acesso Web of Science)In this study, we suggest and experimentally validate a methodology for fast and optimized design of dual-band implantable antennas for medical telemetry (MICS, 402-405 MHz, and ISM, 2400-2480 MHz). The methodology aims to adjust the design of a parametric dual-band antenna model towards optimally satisfying the requirements imposed by the antenna-fabrication procedure and medical application in hand. Design is performed in a systematic, fast, and accurate way. To demonstrate its effectiveness, the proposed methodology is applied to optimize the parametric antenna model for intra-cranial pressure (ICP) monitoring given a specific antenna-fabrication procedure. For validation purposes, a prototype of the optimized antenna is fabricated and experimentally tested. The proposed antenna is further evaluated within a 13-tissue anatomical head model in terms of resonance, radiation, and safety performance for ICP monitoring. Extensive parametric studies of the optimized antenna are, finally, performed. Feasibility of the proposed parametric antenna model to be optimally re-adjusted for various scenarios is demonstrated, and generic guidelines are provided for implantable antenna design. Dual-band operation is targeted to ensure energy autonomy for the implant. Finite Element (FE) and Finite Difference Time Domain (FDTD) simulations are carried out in homogeneous rectangular and anatomical head tissue models, respectively

Antenna Development in Brain-Implantable Biotelemetric Systems for Next-Generation of Human Healthcare

In the growing efforts of promoting patients’ life quality through health technology solutions, implantable wireless medical devices (IMDs) have been identified as one of the frontrunners. They are bringing compelling wireless solutions for medical diagnosis and treatment through bio-telemetric systems that deliver real-time transmission of in-body physiological data to an external monitoring/control unit. To set up this bidirectional wireless biomedical communication link for the long- term, the IMDs need small and efficient antennas. Designing antenna-enabled biomedical telemetry is a challenging aim, which must fulfill demanding issues and criteria including miniaturization, appropriate radiation performance, bandwidth enhancement, good impedance matching, and biocompatibility. Overcoming the size restriction mainly depends on the resonant frequency of the required applications. Defined frequency bands for biomedical telemetry systems contain the Medical Implant Communication Service (MICS) operating at the frequency band of 402– 405 MHz, Medical Device Radiocommunication Service (MedRadio) resonating at the frequency ranges of 401– 406 MHz, 413 – 419 MHz, 426 – 432 MHz, 438 – 444 MHz, and 451 – 457 MHz, Wireless Medical Telemetry Service (WMTS) operating at frequency specturms of 1395 to 1400 MHz and 1427 to 1432 MHz, and Industrial, Scientific, and Medical (ISM) bands of 433.1–434.8 MHz, 868–868.6 MHz, 902.8–928.0 MHz, and 2.4–2.48 GHz. On the other hand, a single band antenna may not fulfill all requirements of a bio-telemetry system in either MedRadio, WMTS, or ISM bands. As a result, analyzing dual/multi-band implantable antenna supporting wireless power, data transmission, and control signaling can meet the demand for multitasking biotelemetry systems. In addition, among different antenna structures, PIFA has been found a promising type in terms of size-performance balance in lossy human tissues. To overcome the above-mentioned challenges, this thesis, first, starts with a discussion of antenna radiation in a lossy medium, the requirements of implantable antenna development, and numerical modeling of the human head tissues. In the following discussion, we concentrate on approaching a new design for far-field small antennas integrated into brain-implantable biotelemetric systems that provide attractive features for versatile functions in modern medical applications. To this end, we introduce three different implantable antenna structures including a compact dual-band PIFA, a miniature triple-band PIFA and a small quad-band PIFA for brain care applications. The compelling performance of the proposed antennas is analyzed and discussed with simulation results and the triple-band PIFA is evaluated using simulation outcomes compared with the measurement results of the fabricated prototype. Finally, the first concept and platform of in-body and off-body units are proposed for wireless dopamine monitoring as a brain care application. In addition to the main focus of this thesis, in the second stage, we focus on introducing an equivalent circuit model to the electrical connector-line transition. We present a data fitting technique for two transmission lines characterization independent of the dielectric properties of the substrate materials at the ultra-high frequency band (UHF). This approach is a promising solution for the development of wearable and off-body antennas employing textile materials in biomedical telemetry systems. The approach method is assessed with measurement results of several fabricated transmission lines on different substrate materials

Multi-antenna systems for wireless capsule endoscopy

With the advent of new medical diagnostic techniques, the wireless capsule endoscopy has been emerged as more convenient than traditional endoscopy for the digestive tract monitoring. The typical use of wireless capsule endoscopy is to diagnose intricate areas of the small intestine. However, the current wireless capsule endoscopy systems suffer from low data rate which cannot meet the requirement for transmitting high resolution images. The poor quality of received images can bring ambiguities during the diagnosis. In this master thesis, the MIMO antennas employing polarization diversity is proposed for a wireless capsule endoscopy system at 433 MHz ISM band. The polarization diversity between in-body capsule and on-body receiver is considered to be main responsible for increasing the data rate. Two conformal dual polarized loop antennas are designed for the in-body capsule transmitter, while two planar dual polarized printed monopole antennas are designed for the on-body receiver. The on-body receiving antennas are designed using the flat and flexible substrates to study their impacts on the size, bandwidth and efficiency. The simulated refection coefficients of proposed in-body MIMO antennas are less than -10 dB over the required bandwidth (400-500 MHz). The mutual coupling between them is found to be less than -20 dB over a wide range of frequencies. The on-body MIMO antennas are measured on the liquid phantom to validate the simulated results. The simulated and measured results showed good agreement of matching in terms of reflection coefficients and mutual coupling. Moreover, the size of on-body antennas found to be compact by using the high permittivity substrate. The on-body MIMO antennas are also measured on the human body. It is observed that the lossy properties of skin significantly reduce the mutual coupling between the MIMO antennas

Compact Antenna with Artificial Magnetic Conductor for Noninvasive Continuous Blood Glucose Monitoring

A non-invasive technique for real-time continuous monitoring of blood glucose has been under development by Venkataraman’s research group in the ETA lab at RIT [16]-[18]. The methodology involves placing an antenna on the arm and monitoring changes in the resonant frequency, which is attributed to changes in the blood glucose level. This is because the blood’s permittivity depends on the glucose levels, and in turn, affects the antenna’s resonant frequency. In order to correlate the antenna’s resonant frequency shift with the real-time blood glucose change, glucose estimation was also modeled using the antenna’s input impedance. The antennas designed could successfully track the rise and fall of blood glucose using the glucose estimation model for both diabetic and non-diabetic patients. However, the antennas being used in this research are too large in size and not flexible. Additionally, the antenna’s radiation pattern was omnidirectional as it is a monopole antenna where the radiation is into the arm as well as away from the arm (back radiation). As a result, during the test procedure, the arm must be in a steady position throughout the time of the resonant frequency measurement. While it worked very well to prove the feasibility of continuous glucose monitoring, a better antenna is required for the next phase of research that involves clinical testing in a hospital environment. My goal in this thesis is to take the research further by designing antennas that are unidirectional, flexible and small in size. The unidirectional property can be achieved by using PEC (Perfect Electric Conductors) or PMC (Perfect Magnetic Conductors) over the antenna that can suppress the back radiation. Unlike the presence of infinite electric charges on an electric conductor, magnetic charges don’t exist. Therefore magnetic conductors are modeled artificially to achieve magnetic properties commonly known as Artificial Magnetic Conductors (AMC). The antenna used in this thesis is a monopole antenna with AMC as a ground plane. The advantage of using AMC over a perfect metal conductor as a ground plane to the antenna is that the AMC reflects the incident wave in phase and not out of phase like a regular metal conductor. Moreover, AMC layers not only suppresses the back radiation but also enhances the gain of the antenna into the arm. Using the AMC layer as the ground plane has also helped in miniaturizing the antenna. The different artificial magnetic conductors designed in this thesis are Rectangular Patch, Rectangular Ring, I-shaped, and Jerusalem Cross. The antennas were fabricated and tested in the unlicensed ISM band (2.4GHz – 2.5GHz) and are within the SAR standards laid out by FCC. The fabricated antenna was strapped to the arm and measurements of resonant frequency similar to those made previously were conducted with respect to time [16]-[18]. Two types of measurements were compared, that is, when the arm was held steady and when the arm had some movement. No significant change or fluctuations in the resonant frequency was observed with arm movement. Whereas the same type of measurements conducted on the monopole antenna in [18] showed significant fluctuations in the resonant frequency with arm movement. This experiment shows the significant advantage of the antenna with AMC layer as compared to the monopole antenna. Also demonstrated in the present work, is the ability of the designed antenna in tracking the increase and decrease of glucose level with changes in the resonant frequency, similar to [16]. This has been demonstrated with two non-diabetic subjects. Further, no back radiation was noted, when a hand above the setup is moved. Additionally, the effect of creeping waves was negligible. The antenna designed in this work will conform well to clinical studies of the ETA Lab research

Doctor of Philosophy

dissertationAntenna design and reduction of losses in antenna systems are critical for modern communications systems. Two categories of antennas suffer from limited power supply and difficult operating environments: implantable antennas and antennas for spacecraft applications. Minimizing and controlling losses in these two antenna types is critical for developing next-generation implantable devices, spacecraft, and satellites. Research suggests that future tattoo antennas will be made from low-conductivity ink utilizing the natural insulating property of the body's fat and lossy ground plane of muscle. This paper supports tattoo antenna work by: (1) demonstrating the insulating properties of fat and conductivity of muscle with various antenna systems, (2) showing the effect of biological materials on the current distribution of subdermal antennas, and (3) validating the use of lower-conductivity materials in subdermal antenna design including a novel gold nanoparticle material. Simulations and measurements are used to evaluate current distributions shared between solid, segmented, and meshed strip dipole antennas and surrounding body tissues. Fat insulates the antenna similar to a thin layer of plastic wrap. Muscle acts as a conductive ground plane. Dipole antennas with mesh or gap structures are more strongly coupled to body tissues than solid antennas. A minimum acceptable conductivity benchmark of 105 S/m is established for dipole antennas and Radio-Frequency Identification (RFID) antennas. This work also provides novel information on the design of low-cost, circularly polarized (CP), Ka-band (26 GHz), millimeter-wave, 50 Ω edge-fed, corners truncated patch antennas on RT/duroid 5880 (εr = 2.2, ½ oz. copper cladding). Microstrip feed width, axial ratio (AR) bandwidth, and best AR at 26 GHz are optimized by the use of 10 mil substrate. The effects of corner truncation are further investigated, showing that increasing corner truncation increases AR bandwidth, increases percent offset between best S11 and AR frequencies, and worsens the best AR. A truncation of 0.57 mm is a good compromise between these effects with AR bandwidth of 6.17 % (measured) and 1.37 % (simulated). Increasing ratio of substrate thickness to design frequency, t / λd, improves AR bandwidth. For t / λd below a certain threshold a corners truncated patch antenna will not produce CP. A new nearly-square, corners truncated patch antenna is measured and simulated as a method of increasing circular polarization bandwidth (CPBW)

Implanted Antennas for Biomedical Applications

Body-Centric Wireless Communication (BCWC) is a central topic in the development of healthcare and biomedical technologies. Increasing healthcare quality, in addition to the continuous miniaturisation of sensors and the advancement in wearable electronics, embedded software, digital signal processing and biomedical technologies, has led to a new era of biomedical devices and increases possibility of continuous monitoring, diagnostic and/or treatment of many diseases. However, the major difference between BCWC, particularly implantable devices, and conventional wireless systems is the radio channel over which the communication takes place. The human body is a hostile environment from a radio propagation perspective. This environment is a highly lossy and has a high effect on the antenna elements, the radio channel parameters and, hence a dramatic drop in the implanted antenna performance. This thesis focuses on how to improve the gain of implanted antennas. In order to improve the gain and performance of implanted antennas, this thesis uses a combination of experimental and electromagnetic numerical investigations. Extensive simulation and experimental investigations are carried out to study the effects of various external elements on the performance improvement of implanted antennas. The thesis also shows the design, characterisation, simulation and measurements of four different antennas to work at ISM band and seventeen different scenarios for body wireless communication. A 3- layer (skin, fat and muscle) and a liquid homogenise phantom were used for human body modelling in both simulation and measurements. The results shows that a length of printed line and a grid can be used on top of the human skin in order enhance the performance of the implanted antennas. Moreover, a ring and a hemispherical lens can be used externally in order to enhance the performance of the implanted antenna. This approach yields a significant improvement in the antenna gain and reduces the specific absorption rate (SAR) in most cases and the obtained gain varies between 2 dB and 8 dB