Nuri Celik

Microwave stethoscope: development and benchmarking of a vital signs sensor using computer-controlled phantoms and human studies.

This paper describes a new microwave-based method and associated measurement system for monitoring multiple vital signs (VS) as well as the changes in lung water content. The measurement procedure utilizes a single microwave sensor for reflection coefficient measurements, hence the name “microwave stethoscope (MiSt),” as opposed to the two-sensor transmission method previously proposed by the authors. To compensate for the reduced sensitivity due to reflection coefficient measurements, an improved microwave sensor design with enhanced matching to the skin and broadband operation, as well as an advanced digital signal processing algorithm are used in developing the MiSt. Results from phantom experiments and human clinical trials are described. The results clearly demonstrate that MiSt provides reliable monitoring of multiple VS such as the respiration rate, heart rate, and the changes in lung water content through a single microwave measurement. In addition, information such as heart waveforms that correlates well with electrocardiogram is observed from these microwave measurements. Details of the broadband sensor design, experimental procedure, DSP algorithms used for VS extraction, and obtained results are presented and discussed.

Implementation and Experimental Verification of Hybrid Smart-Antenna Beamforming Algorithm

In the literature (Zhang et al., and Rezk et al.), a hybrid beamforming algorithm utilizing a subset of array elements according to receive signal strength is proposed. The algorithm utilizes a smart switch which selects a subset of antennas that receive the signals with higher strength and a beamforming algorithm is performed to calculate the weights for the selected antennas. Since earlier results were based on simulations by Zhang et al., and Rezk et al., in this letter we present experimental results of testing a smart-antenna prototype with an eight-element array. This array is designed and implemented by the authors to verify the accuracy and performance of the proposed hybrid-beamforming algorithm. In general, the experimental results confirmed the simulation data. Specifically, it is shown that the proposed hybrid algorithm using a subset of the array has nearly the same performance as the adaptive system with the full array. Tradeoffs regarding beamwidth and the sidelobe levels are confirmed and additional experimental results illustrating the angle resolution of the developed system are presented

A Noninvasive Microwave Sensor and Signal Processing Technique for Continuous Monitoring of Vital Signs

The use of the noninvasive microwave method for measuring changes in lung water content has been previously reported and validated in animal experiments. The approach is based on measuring the transmission coefficient across the thorax and correlating results with changes in lung water content. In this letter, we extend this technique to the monitoring of multiple vital signs including heart rate and breathing as well as the changes of lung water content from a single transmission coefficient measurement. Using a short-time Fourier transform-based digital signal processing method, it is shown that these vital signs can be accurately detected and extracted from a single microwave transmission coefficient measurement. Experimental measurements were made on a thorax phantom model, and the obtained data confirmed the validity and accuracy of the proposed approach. The radiation bio-safety aspects of this approach were evaluated using a DASY4 near-field scanner, often used for certifying cell phones. Obtained results for a 30-mW input power show that the specific absorption rate (SAR) values are about one third of the FCC safety standard at the operating frequency of 915 MHz. The microwave applicator design together with the experimental procedure and the extracted vital signs results are presented, and avenues for future clinical implementation are discussed.

Implementation and Experimental Verification of a Smart Antenna System Operating at 60 GHz Band

With the introduction of the unlicensed spectrum at the 60 GHz range, the development of communication systems with data rates in Gb/s range has become feasible. However, there are quite significant challenges at this frequency range such as high propagation loss, oxygen absorption, antenna alignment and unavailability of high-gain, high power circuit elements. In this paper we present a novel 2-channel hybrid smart-antenna system operating at 60 GHz band which can be used with an antenna switching system to improve the signal power performance and to serve as an automated alignment system. The critical system parameters for a smart-antenna system at this frequency are the transmitter to receiver distance, element spacing, and antenna beamwidth. As the widely known beamforming assumptions may not hold for some configurations, a more general beamforming formulation is given in the paper to serve as a guideline for system designers. The twist angle of array elements is introduced as a new array design parameter. By selecting the optimal twist angle to help overlap radiation patterns, the fine alignment of the transmit and receive beams is established electronically using beamforming, thus reducing the cost of deployment and maintenance of the 60 GHz indoor communication systems.

Propagation Modeling and Measurement for a Multifloor Stairwell

Reliable wireless communications in stairwells are crucial to law enforcement and firefighting safety. Understanding the radio propagation in stairwells is necessary to successfully design such communications systems. In this letter, we study the radio propagation in a multifloor stairwell using measurements and simulations. Fundamental propagation mechanisms such as reflection from stairwell walls and transmission through the stair steps are investigated. It is found that the stairwell walls in this studied case do not reflect much of the incoming energy and that the transmitted energy through the stairs has significant contributions to the total received power. An image-based ray tracing scheme is used to identify the various propagation mechanisms. The ray-tracing simulation results match the measurements very well. Furthermore, physics-based explanations were provided for the trends and characteristics in the obtained results.

Microwave stethoscope: A new method for measuring human vital signs

A new microwave method for human vital signs measurements is described. The method is based on reflection coefficient measurements, thus realizing the microwave stethoscope vision, and the use of DSP algorithms for extracting vital signs. A unique microwave coupler/sensor with good impedance matching to human skin is designed and the developed measurement procedure is verified experimentally using phantom models. Obtained results demonstrated the ability to extract parameters such as breathing rate, heart rate, and lung water content from a single microwave measurement. Results from this new approach are also compared with a previously described transmission coefficient measurement-based method. It is shown that while the transmission measurements provide more sensitivity, the reflection coefficient based results are also accurate and received signal/noise levels are well within the capabilities of the developed DSP algorithms. Results from the phantom experiment as well as from experimental data from a dog experiment are used in this comparative study. The proposed experimental procedure as well as the experimental and DSP extracted vital signs results will be presented.

Low-Profile Multifrequency HF Antenna Design for Coastal Radar Applications

A novel design for an electrically small high-frequency (HF) antenna suitable for coastal radar applications is presented. The principle design objectives were to develop an HF antenna resonant at multiple frequencies that is also compact and easily transportable for deployment to coastal sites and on floating platforms. The compact antenna achieves practical performance values for radiation resistance, bandwidth, and gain while maintaining small values of ka. The design presented in this letter consists of a meandering line antenna composed of helical elements and switchable folded arms. The value of ka ranges down to 0.16 at 5.7 MHz. The antenna is self-resonant at multiple frequencies including 5.7, 16.1, 20.6, and 28.1 MHz for open-circuit mode and 15.1, 18.5, and 26.1 for the short-circuit mode. In all cases, input impedances were easily matched to 50-Ω coaxial feed lines, and the achieved bandwidths ranged from 1% to 12% within the HF band (3-30 MHz). The antenna is 90 cm high with a small ground disk of 60 cm diameter. Simulation results and prototype experimental measurements are presented.

Noninvasive microwave technique for hemodynamic assessments

Pulmonary edema, accumulation of fluid in the lungs is often measured and analyzed after medical and surgical procedures, since pulmonary edema is commonly linked to cases of congestive heart failure (CHF) and kidney failures. Like pulmonary edema, hemodynamic assessments do not occur until after an acute cardiac episode. Early detection of pulmonary edema and routine monitoring of cardiac functions such as cardiac output (CO) - the product of stroke volume and heart rate, would be beneficial for surgical patients as well as others suffering from acute cardiac and pulmonary illnesses. Available diagnostic tools such as the Pulmonary Artery Catheterization are invasive and diagnostic techniques such as Magnetic Resonance Imaging (MRI) or Computerized Active Tomography (CAT) Scans are expensive, cumbersome, and not suitable for continuous monitoring. In addition, techniques such as the double indicator dilution method, the electrical impedance plethysmography, and the re-breathing method are impractical for clinical use because of limitations on sensitivity, consistency, and simplicity [1]. To overcome difficulties with above conventional techniques, an electromagnetic (EM) method has been investigated for this application. Specifically, an EM energy coupler and the associated measurement method have been developed to simultaneously measure breathing rate in addition to the changes in lung water content [2,3]. Specifically, a two-port EM sensor has been developed for animal and phantom experiments [3–5]. In these phantom and animal experiments it is shown that variation of lung water contents and breathing rate can clearly be monitored by the proposed technique.

Genetic-Algorithm-Based Antenna Array Design for a 60-GHz Hybrid Smart Antenna System

The previously described hybrid smart-antenna system solves the transmitter receiver alignment problem of 60-GHz wireless systems when high gain antennas are used. Utilizing multiple highly directional array elements and coherently combining the outputs of a few elements adaptively, the hybrid smart antenna achieves the desired performance and results in significant hardware cost and computational complexity savings. For optimal alignment, however, the output power of the hybrid smart antenna should stay constant over the scanning range. This minimizes the so-called scalloping effects and necessitates a careful selection of the array elements being used in beamforming. In this letter, a genetic-algorithm solution to optimally adjust the beam pattern overlaps the array elements to minimize the output-power fluctuations in a given scan range. It is shown that while the hybrid algorithm may perform satisfactorily with less than one-third of the total number of the array elements (e.g., two or three elements in an array of ten antennas), there is an optimal number of elements for a given array that provides minimal power fluctuation in a specified scan range. A tradeoff between the acceptable level of power fluctuation and the total received power is identified.

Dual-polarization cylindrical long-slot array antenna integrated with hybrid ground plane

In this paper, a dual-polarization ultra-wideband long-slot antenna arrays (LSA) integrated with hybrid electromagnetic band-gap (EBG)/ferrite ground planes is designed for communication radar applications. The dual-polarization was achieved by combining connected dipole and long slot array concept. Connected dipole mode provides horizontal polarization while long slot mode gives vertical polarization. The developed antenna is a cylindrical shape of the LSA with cylindrical EBG/Ferrite hybrid ground plane, which is designed to cover NTDR, and EPLRS bands. This antenna provides the omni directional pattern from 150 to 500 MHz. The hybrid EBG/Ferrite ground plane, previously developed and experimentally verified by the authors for planar arrays, both eliminating the slot radiation toward the center of the cylinder and was important in enhancing the wideband properties of the array. Antenna characteristics of the developed antennas were analyzed by simulations and the simulation results are presented.