Asimina Kiourti

A Review of Implantable Patch Antennas for Biomedical Telemetry: Challenges and Solutions [Wireless Corner]

Biomedical telemetry permits the transmission (telemetering) of physiological signals at a distance. One of its latest developments is in the field of implantable medical devices (IMDs). Patch antennas currently are receiving significant scientific interest for integration into the implantable medical devices and radio-frequency (RF)-enabled biotelemetry, because of their high flexibility in design, conformability, and shape. The design of implantable patch antennas has gained considerable attention for dealing with issues related to biocompatibility, miniaturization, patient safety, improved quality of communication with exterior monitoring/control equipment, and insensitivity to detuning. Numerical and experimental investigations for implantable patch antennas are also highly intriguing. The objective of this paper is to provide an overview of these challenges, and discuss the ways in which they have been dealt with so far in the literature.

Miniature Scalp-Implantable Antennas for Telemetry in the MICS and ISM Bands: Design, Safety Considerations and Link Budget Analysis

We study the design and radiation performance of novel miniature antennas for integration in head-implanted medical devices operating in the MICS (402.0-405.0 MHz) and ISM (433.1-434.8, 868.0-868.6 and 902.8-928.0 MHz) bands. A parametric model of a skin-implantable antenna is proposed, and a prototype is fabricated and tested. To speed-up antenna design, a two-step methodology is suggested. This involves approximate antenna design inside a simplified geometry and further Quasi-Newton optimization inside a canonical model of the intended implantation site. Antennas are further analyzed inside an anatomical human head model. Results indicate strong dependence of the exhibited radiation performance (radiation pattern, gain, specific absorption rate and quality of communication with exterior equipment) on design parameters and operation frequency. The study provides valuable insight into the design of implantable antennas, addressing the suitability of canonical against anatomical tissue models for design purposes, and assessing patient safety and link budget at various frequencies. Finite Element and Finite Difference Time Domain numerical solvers are used at different stages of the antenna design and analysis procedures to suit specific needs. The proposed design methodology can be applied to optimize antennas for several implantation scenarios and biotelemetry applications.

Performance of a novel miniature antenna implanted in the human head for wireless biotelemetry

In this study, we present a novel, miniaturized, biocompatible antenna at the medical implant communications service (MICS) band (402–405 MHz) for integration in wireless biotelemetry devices implanted in the human head. To reduce simulation time, the antenna is designed while in the center of a skin tissue simulating box and subsequently implanted inside the skin tissue of an anatomical human head model. The resonance, radiation and specific absorption rate (SAR) performance of the antenna is evaluated and design modifications are suggested to overcome the inherent detuning effect.

Implantable and ingestible medical devices with wireless telemetry functionalities: A review of current status and challenges

Wireless medical telemetry permits the measurement of physiological signals at a distance through wireless technologies. One of the latest applications is in the field of implantable and ingestible medical devices (IIMDs) with integrated antennas for wireless radiofrequency (RF) communication (telemetry) with exterior monitoring/control equipment. Implantable medical devices (MDs) perform an expanding variety of diagnostic and therapeutic functions, while ingestible MDs receive significant attention in gastrointestinal endoscopy. Design of such wireless IIMD telemetry systems is highly intriguing and deals with issues related to: operation frequency selection, electronics and powering, antenna design and performance, and modeling of the wireless channel. In this paper, we attempt to comparatively review the current status and challenges of IIMDs with wireless telemetry functionalities. Full solutions of commercial IIMDs are also recorded. The objective is to provide a comprehensive reference for scientists and developers in the field, while indicating directions for future research.

Miniature Implantable Antennas for Biomedical Telemetry: From Simulation to Realization

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.

A Broadband Implantable and a Dual-Band On-Body Repeater Antenna: Design and Transmission Performance

The design of a new miniature broadband implantable antenna and a dual-band on-body antenna are presented along with the transmission performance between the two. The former and latter antennas are intended for integration into implantable medical devices (IMDs) and on-body repeaters, respectively. The on-body repeater antenna favors the use of very low power IMDs. The on-body repeater receives low power data from an IMD (MedRadio band, 401-406 MHz) and retransmits it to remote devices placed further apart (ISM band, 2400-2480 MHz ). The MedRadio implantable antenna maintains miniature size (399 mm3), and exhibits two close resonances which increase the -10 dB bandwidth inside muscle tissue (87 MHz). The on-body antenna is relatively small (6720 mm3), and exhibits dual resonances in the MedRadio and ISM bands. Assuming a typical arm implantation scenario and an on-body receiver sensitivity of -75 dBm, the proposed configuration is found to enable reduction of the IMD power by a factor of 100. Patient safety and tolerance to electromagnetic interference are, thus, preserved, and lifetime of the IMD is increased. The setup is, finally, shown to be robust to antenna misalignment and polarization rotation.

Implantable Antennas: A Tutorial on Design, Fabrication, and In Vitro\/In Vivo Testing

Implantable medical devices (IMDs) are medical devices that are implanted inside the patients body by means of a surgical operation and can be used for a number of diagnostic, monitoring, and therapeutic applications. Typical examples include implantable pacemakers, defibrillators, glucose monitors, cochlear implants, drug infusion pumps, intracranial pressure monitors, neurostimulators, etc. [1]. To be truly beneficial while preserving patient comfort, IMDs need to wirelessly exchange data with exterior monitoring/control equipment. Low-frequency inductive links have traditionally been used for wireless telemetry of IMDs [2], [3]. However, in an attempt to overcome their inherent limitations related to low data rate, restricted communication range, and sensitivity to inter-coil misalignment, recent focus is on antenna-enabled medical telemetry for IMDs. Wireless transmission is most commonly performed in the 402-405 MHz frequency band, which has been exclusively allocated for medical implant communications systems (MICSs), is internationally available and feasible with low-power circuits, falls within a relatively low-noise portion of the spectrum, and allows for acceptable propagation through human tissue [4]. Nevertheless, other radio-frequency (RF) bands might also be used, such as those defined in the recent IEEE 802.15.6 standard [5].

Pulmonary Edema Monitoring Sensor With Integrated Body-Area Network for Remote Medical Sensing

A wearable health monitoring sensor integrated with a body-area network is presented for the diagnosis of pulmonary edema. This sensor is composed of 17 electrodes with 16 ports in-between and is intended to be placed on the human chest to detect lung irregularities by measuring the lungs average dielectric permittivity in a non-invasive way. Specifically, the sensors active port is fed by a 40 MHz RF signal and its passive ports measure the corresponding amplitudes of the scattering parameters (S-parameters). The dielectric constant of the lung is then post-processed and expressed as a weighted sum of the S-parameters measured from each port. An important aspect of the sensor is the use of multiple electrodes which mitigates the effect of the outer layers (skin, fat and muscle) on the lungs permittivity. This allows for the characterization of deeper tissue layers. To validate the sensor, tissue-emulating gels were employed to mimic in-vivo tissues. Measurements of the lungs permittivity in both healthy and pulmonary edema states are carried out to validate the sensors efficacy. Using the proposed post processing technique, the calculated permittivity of the lung from the measured S-parameters demonstrated error less than 11% compared to the direct measured value. Concurrently, a medical sensing body-area network (MS-BAN) is also employed to provide for remote data transfer. Measured results via the MS-BAN are well matched to those obtained by direct measurement. Thus, the MS-BAN enables the proposed sensor with continuous and robust remote sensing capability.

High-Geometrical-Accuracy Embroidery Process for Textile Antennas With Fine Details

An embroidery process with high geometrical accuracy is presented for antennas with fine details. Previous embroidery processes employed thicker threads, leading to resolution not better than 1 mm. Therefore, fine details (e.g., sharp corners) could not be realized, and geometrical accuracy was low, viz. > 1 mm. To overcome these limitations, in this letter we: 1) employ much thinner E-fibers to enable the “printing” of sharp corners, and 2) increase embroidery density to boost surface conductivity. Two Liberator E-fibers were tested: 1) 40-strand ( diameter = 0.27 mm), and 2) 20-strand ( diameter = 0.22 mm). Embroidery density was optimized using double-layer stitching of 7 threads/mm. To validate our embroidery approach, we fabricated and tested a dipole antenna with intricate details operating at 2.4 GHz. This design could not be formerly “printed” on textiles. Both E-fiber (40/20-strand) prototypes exhibited excellent performance, comparable to that of copper antennas. The achieved geometrical accuracy was ~ 0.3 mm (viz. 3 times better).

Accelerated Design of Optimized Implantable Antennas for Medical Telemetry

We modify our latest reported methodology for implantable antenna design in an attempt to further accelerate the design while achieving optimized resonance characteristics. Design is performed inside a small-sized single- or multilayer tissue box for the single-layer tissue model (SLTM) and the multilayer tissue model (MLTM) variations, respectively. Given a specific medical application scenario, the idea is to take into account the dielectric loading of the surrounding tissues and exterior air on the antenna while using an adequately small tissue model to speed up simulations. Effectiveness of the methodology is assessed for antenna design aimed at intracranial pressure (ICP) monitoring and cardiac pacemaker applications. The MLTM variation provides more accurate results than the SLTM at the expense of being slightly more complex and slow.