Erdem Topsakal

Design of a Dual-Band Implantable Antenna and Development of Skin Mimicking Gels for Continuous Glucose Monitoring

In this study, we present a small-size dual medical implant communications service (MICS) (402-405 MHz) and industrial, scientific, and medical (ISM) (2.4-2.48 GHz) band implantable antenna for continuous glucose-monitoring applications. The antenna is optimized for dual-band operation by combining an in-house finite-element boundary integral electromagnetic simulation code and particle swarm optimization algorithm. In order to test the designed antenna in vitro, gels mimicking the electrical properties of human skin are also developed. The optimized antenna is fabricated and measured in the gel. The simulated and measured bandwidths are found to be 20.4% MICS, 4.2% ISM, and 35.3% MICS, and 7.1% ISM, respectively. Although we have emphasized continuous glucose monitoring throughout this paper, the antenna and skin mimicking gels presented here can be used for many other wireless telemetry applications.

A Small Antipodal Vivaldi Antenna for Ultrawide-Band Applications

A compact antipodal Vivaldi antenna for ultrawide-band (UWB) applications is proposed. The antenna operates across the entire UWB spectrum from 3.1 to 10.6 GHz, and also has low cross-polarization levels and reasonable gain values over the same frequency band. Two different substrates, Rogers RO3006 and FR4, are considered, and results regarding return loss, far field pattern, phase response, group delay, and gain are presented.

Array decomposition method for the accurate analysis of finite arrays

Presented in this paper is a fast method to accurately model finite arrays of arbitrary three-dimensional elements. The proposed technique, referred to as the array decomposition method (ADM), exploits the repeating features of finite arrays and the free-space Greens function to assemble a nonsymmetric block-Toeplitz matrix system. The Toeplitz property is used to significantly reduce storage requirements and allows the fast Fourier transform (FFT) to be applied in accelerating the matrix-vector product operations of the iterative solution process. Each element of the array is modeled using the finite element-boundary integral (FE-BI) technique for rigorous analysis. Consequently, we demonstrate that the complete LU decomposition of the matrix system from a single array element can be used as a highly effective block-diagonal preconditioner on the larger array matrix system. This rigorous method is compared to the standard FE-BI technique for several tapered-slot antenna (TSA) arrays and is demonstrated to generate the same accuracy with a fraction of the storage and solution time.

Electrical Properties of Rat Skin and Design of Implantable Antennas for Medical Wireless Telemetry

The design and test is described of a small size dual band implantable antenna operating in Medical Implant Communications Service (MICS) (402 MHz-405 MHz) and Industrial, Scientific and Medical (ISM) (2.4 GHz-2.48 GHz) bands to be used in animal studies for medical research. The antenna is intended for wireless medical monitoring of the physiological parameters such as glucose, pressure, temperature, etc. First, the electrical properties (epsivr and sigma) of skin samples from donor rats are measured at Mississippi State Universitys (MSU) College of Veterinary Medicine. A dual band antenna is then designed using an in-house finite element boundary integral solver in conjunction with particle swarm optimization algorithm. Finally, the antenna is tested using both skin-mimicking materials and real skin samples. The development details of the skin-mimicking materials are also given. Results regarding the S11 and gain of the designed antenna are given and discussed in detail.

In Vivo Verification of Implantable Antennas Using Rats as Model Animals

The main objective of this study is to test in vivo a small-size dual-band implantable antenna operating in Medical Implant Communications Service (MICS) (402405 MHz) and Industrial, Scientific, and Medical (ISM) (2.42.48 GHz) bands and to investigate the effects of live tissue on the antenna performance. To do so, we have designed and fabricated three identical antennas that were surgically implanted into rats at Mississippi State Universitys (MSU) College of Veterinary Medicine. X-ray images are also taken to ensure the proper placement of the antenna within the body. Results regarding return loss measurements and the performance change of the antenna are presented. We have also investigated possible candidate materials that can be used for encasing of the antenna for biocompatibility.

A Double-Sided Rounded Bow-Tie Antenna (DSRBA) for UWB Communication

A double-sided rounded bow-tie antenna (DSRBA) for ultrawideband (UWB) communication is proposed. The antenna covers the UWB spectrum from 3.1 to 10.6 GHz, and has return loss below -10 dB throughout the entire band. The antenna has also omnidirectional radiation characteristics and reasonable gain values over the same frequency band. Two different substrates, Rogers RO3006 and Liquid Crystal Polymer (LCP), are considered. Both materials have very low loss tangent. Results regarding return loss, far-field pattern, and gain are presented

Characterization and Testing of a Skin Mimicking Material for Implantable Antennas Operating at ISM Band (2.4 GHz-2.48 GHz)

In this study, we present a simple recipe for a skin mimicking material intended for in vitro testing of implantable antennas operating at Industrial, Scientific, and Medical (ISM) (2.4 GHz2.48 GHz) band. The material is composed of de-ionized water, Triton X-100, and Diethylene Glycol Butyl Ether (DGBE). The relative dielectric constant and conductivity of the proposed material are within 0.5% and 3.4% of the properties of the reference human skin from the literature in the entire ISM band. In order to test the transmission characteristics of the material, in vitro measurements of a dual-band antenna are performed.

A procedure for modeling material junctions in 3-D surface integral equation approaches

Surface integral equations become cumbersome to solve when arbitrary combinations of materials, and complicated arrangements of junctions between those materials, are considered. This paper describes a straightforward approach for generalizing integral equation techniques to handle any combinations of materials with junctions. Particular attention is focused on a unique, easily implemented junction resolution algorithm that maps each basis function coefficient to one or more unknowns. Three examples are presented for validation purposes.

Glucose-dependent dielectric properties of blood plasma

In this study, we show a correlation between electrical properties (relative permittivity-εr and conductivity-σ) of blood plasma and plasma glucose concentration. In order to formulate that correlation, we performed electrical property measurements on blood samples collected from 10 adults between the ages of 18 and 40 at University of Alabama Birmingham (UAB) Childrens hospital. The measurements are conducted between 500 MHz and 20 GHz band. Using the data obtained from measurements, we developed a single-pole Cole-Cole model for εr and σ as a function of plasma blood glucose concentration. To provide an application, we designed a microstrip patch antenna that can be used to predict the glucose concentration within a given plasma sample. Simulation results regarding antenna design and its performance are also presented.

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.