George Palikaras

Experimental Characterization of UWB On-Body Radio Channel in Indoor Environment Considering Different Antennas

An experimental investigation to characterize the transient and spectral behavior of the ultrawideband (UWB) on-body radio propagation channel for body-centric wireless communications is presented. The measurements were performed considering over thirty on-body links in the front of human body in the anechoic chamber, and in indoor environment. Two different pairs of planar antennas have been used, namely, CPW-fed planar inverted cone antennas (PICA), and miniaturized CPW-fed tapered slot antennas (TSA). A path loss model is extracted from measured data, and a statistical study is performed on the time delay parameters. The goodness of different statistical models in fitting the root mean square (RMS) delay has been evaluated. Results demonstrate that the TSA, due to its more directive radiation behavior is less affected from the reflections from body parts and surrounding environment. The antenna shows significant size reduction and improved time delay behavior, and hence is an ideal candidate for UWB body area networks (BAN).

Experimental demonstration of multiwire endoscopes capable of manipulating near-fields with subwavelength resolution

Endoscopes formed by arrays of metallic wires can transmit, magnify, and demagnify near-field distributions with subwavelength resolution. Our experiments demonstrate that despite their small apertures, the parallel multiwire endoscopes can be used to transmit near-field distributions with a resolution of five thousandths of a wavelength to a distance of a half-wavelength in the microwave frequency range, and tapered multiwire endoscopes with flat input and output interfaces provide threefold image magnification and demagnification.

Magnification of subwavelength field distributions using a tapered array of metallic wires with planar interfaces and an embedded dielectric phase compensator

We report the magnification of subwavelength field distributions using a tapered array of metallic wires with planar front and back interfaces through numerical simulations and experiments. It is demonstrated that subwavelength images with a resolution of one-fifteenth of a wavelength can be transferred to a distance of three wavelengths with a threefold magnification. We also propose embedding a dielectric phase compensator in the tapered array to compensate the phase differences introduced by the different lengths of wires and significantly improve the operational bandwidth of the image transmission and magnification device.

Detection of glucose variability in saline solutions from transmission and reflection measurements using V-band waveguides

This paper presents experimental results that demonstrate the correlation of glucose concentration in water and saline solutions with transmitted electromagnetic (EM) energy in the frequency range of 50–75 GHz. The system is based on placing the aqueous solutions in acrylic holding tanks sandwiched between two open V-band waveguides. The measured samples have clinically relevant range of glucose concentrations, as low as 0.025 wt%. Our measurements show for the first time that it is possible to establish an approximately linear relationship between the signals transmitted through this simple waveguide-based system and the glucose content in the samples. Accurate full-wave EM simulations confirm this linear correlation. The results suggest the possibility of developing a miniaturized non-invasive glucose sensing device based on the transmission of radio waves in this frequency range.

Near-Field Antenna Radome Based on Extremely Anisotropic Metamaterial

We demonstrate experimentally that a block of extremely anisotropic metamaterial formed by an array of metallic wires embedded into a dielectric material is a near-field radome. The radome is intrinsically multiband and can operate, for instance, in both GSM frequency bands. The structure both hides an antenna from external mechanical and environmental influence and transmits its near-field onto an outer interface in contrast to conventional radomes that alter antenna characteristics and have to be taken into account during design process.

Study of a small printed quasi-self-complementary ultra wideband antenna for on-body applications

In this paper, the performance parameters of a small printed quasi-self-complementary ultra wideband (UWB) antenna in close proximity to the human body is investigated. The return loss response, impedance, radiation pattern and gain are investigated. The antenna shows good on-body performance, and therefore it will be suitable for on-body applications in UWB wireless body area networks.

Glucose sensing in saline solutions using V-band waveguides

We present results from an experimental system employed to study the impact of glucose content on measured transmission data. The measurements have been performed at frequencies between 50 GHz and 75 GHz using V-Band waveguides, and the measured samples consisted of saline solutions with glucose concentrations down to 0.025 wt%. The performed transmission measurements show that it is possible to establish an approximately linear relationship between the transmission coefficient and the glucose content in the samples. This linear dependence is also verified via simulations. The results are of interest for developing a miniaturized mobile glucose sensing system.

A Glucose Sensing System Based on Transmission Measurements at Millimetre Waves using Micro strip Patch Antennas

We present a sensing system operating at millimetre (mm) waves in transmission mode that can measure glucose level changes based on the complex permittivity changes across the signal path. The permittivity of a sample can change significantly as the concentration of one of its substances varies: for example, blood permittivity depends on the blood glucose levels. The proposed sensing system uses two facing microstrip patch antennas operating at 60 GHz, which are placed across interrogated samples. The measured transmission coefficient depends on the permittivity change along the signal path, which can be correlated to the change in concentration of a substance. Along with theoretical estimations, we experimentally demonstrate the sensing performance of the system using controlled laboratory samples, such as water-based glucose-loaded liquid samples. We also present results of successful glucose spike detection in humans during an in-vivo Intravenous Glucose Tolerance Test (IVGTT). The system could eventually be developed into a non-invasive glucose monitor for continuous monitoring of glucose levels for people living with diabetes, as it can detect as small as 1.33 mmol/l (0.025 wt%) glucose concentrations in the controlled water-based samples satisfactorily, which is well below the typical human glucose levels of 4 mmol/l.

Balanced antipodal Vivaldi antenna array for microwave tomography

This paper presents simulation studies for an array comprised of twelve balanced antipodal Vivaldi antennas for microwave tomography in the presence of a simple numerical breast phantom. This type of antennas bas been proposed previously in UWB breast imaging, but their use is a microwave tomographic setup is studied for the first time. The coupling effect of array elements and the electric field patterns are investigated with and without the phantom in the frequency range of interest between 0.5 and 5 GHz.

Design and Experimental Validation of a Multiple-Frequency Microwave Tomography System Employing the DBIM-TwIST Algorithm

We present a first prototype of a wideband microwave tomography system with potential application to medical imaging. The system relies on a compact and robust printed monopole antenna which can operate in the 1.0–3.0 GHz range when fully immersed in commonly used coupling liquids, such as glycerine–water solutions. By simulating the proposed imaging setup in CST Microwave Studio, we study the signal transmission levels and array sensitivity for different target and coupling liquid media. We then present the experimental prototype design and data acquisition process, and show good agreement between experimentally measured data and results from the CST simulations. We assess imaging performance by applying our previously proposed two-dimensional (2-D) DBIM TwIST-algorithm to both simulated and experimental datasets, and demonstrate that the system can reconstruct simple cylindrical targets at multiple frequencies.