Sławomir Hausman

Field-Based Optimal Placement of Antennas for Body-Worn Wireless Sensors

We investigate a case of automated energy-budget-aware optimization of the physical position of nodes (sensors) in a Wireless Body Area Network (WBAN). This problem has not been presented in the literature yet, as opposed to antenna and routing optimization, which are relatively well-addressed. In our research, which was inspired by a safety-critical application for firefighters, the sensor network consists of three nodes located on the human body. The nodes communicate over a radio link operating in the 2.4 GHz or 5.8 GHz ISM frequency band. Two sensors have a fixed location: one on the head (earlobe pulse oximetry) and one on the arm (with accelerometers, temperature and humidity sensors, and a GPS receiver), while the position of the third sensor can be adjusted within a predefined region on the wearer’s chest. The path loss between each node pair strongly depends on the location of the nodes and is difficult to predict without performing a full-wave electromagnetic simulation. Our optimization scheme employs evolutionary computing. The novelty of our approach lies not only in the formulation of the problem but also in linking a fully automated optimization procedure with an electromagnetic simulator and a simplified human body model. This combination turns out to be a computationally effective solution, which, depending on the initial placement, has a potential to improve performance of our example sensor network setup by up to about 20 dB with respect to the path loss between selected nodes.

Simplified human phantoms for narrowband and ultra-wideband body area network modelling

Purpose – The purpose of this paper is to compare the properties of simplified physical and corresponding numerical human body models (phantoms) and verify their applicability to path loss modeling in narrowband and ultra-wideband on-body wireless body area networks (WBANs). One of the models has been proposed by the authors. Design/methodology/approach – Two simplified numerical and two physical phantoms for body area network on-body channel computer simulation and field measurement results are presented and compared. Findings – Computer simulations and measurements which were carried out for the proposed simplified six-cylinder model with various antenna locations lead to the general conclusion that the proposed phantom can be successfully used for experimental investigation and testing of on-body WBANs both in ISM and UWB IEEE 802.15.6 frequency bands. Research limitations/implications – Usage of the proposed phantoms for the simulation/measurement of the specific absorption rate and for off-body chann...

Impact of Indoor Environment on Path Loss in Body Area Networks

In this paper the influence of an example indoor environment on narrowband radio channel path loss for body area networks operating around 2.4 GHz is investigated using computer simulations and on-site measurements. In contrast to other similar studies, the simulation model included both a numerical human body phantom and its environment—room walls, floor and ceiling. As an example, radio signal attenuation between two different configurations of transceivers with dipole antennas placed in a direct vicinity of a human body (on-body scenario) is analyzed by computer simulations for several types of reflecting environments. In the analyzed case the propagation environments comprised a human body and office room walls. As a reference environment for comparison, free space with only a conducting ground plane, modelling a steel mesh reinforced concrete floor, was chosen. The transmitting and receiving antennas were placed in two on-body configurations chest–back and chest–arm. Path loss vs. frequency simulation results obtained using Finite Difference Time Domain (FDTD) method and a multi-tissue anthropomorphic phantom were compared to results of measurements taken with a vector network analyzer with a human subject located in an average-size empty cuboidal office room. A comparison of path loss values in different environments variants gives some qualitative and quantitative insight into the adequacy of simplified indoor environment model for the indoor body area network channel representation.

Combined spiral-discone broadband antenna for indoor applications

A novel design of a broadband omnidirectional antenna is presented. It combines advantages of both the spiral and discone designs. An antenna of this type can find application in indoor radio communication systems. The designed antenna frequency band is suitable for the radio communication services in the indoor environment (GSM 900, GSM 1800, DECT, WLAN). The other advantage of this design is its good impedance match to 50 ohm coaxial transmission lines and undirectional radiation pattern. Two prototypes were made which cover the frequency bands of 650-3000 MHz and 1270-3000 MHz with VSWR<2. The method of moments was applied to calculate radiation characteristics of the antennas. The results of impedance matching and radiation pattern measurements are presented.

Many-Objective Automated Optimization of a Four-Band Antenna for Multiband Wireless Sensor Networks

This paper describes a new design and an optimization framework for a four-band antenna to be used in wireless sensor networks. The antenna is designed to operate effectively in two open frequency bands (ISM—Industrial, Scientific, Medical), 2.4 GHz and 5.8 GHz, as well as in two bands allocated for the fifth-generation (5G) cellular networks, 0.7 GHz and 3.5 GHz. Our initial design was developed using the trial and error approach, modifying a circular disc monopole antenna widely used in ultra wideband (UWB) systems. This initial design covered the three upper bands, but impedance matching within the 700 MHz band was unsatisfactory. The antenna performance was then improved significantly using an optimization algorithm that applies a bi-objective fully-Paretian approach to its nine-parameter geometry. The optimization criteria were impedance matching and radiation efficiency. The final design exhibits good impedance matching in all four desired bands with the Voltage Standing Wave Ratio (VSWR) value below 2 and radiation efficiency of 88%. The simulated antenna performance was verified experimentally.

Multi-Objective Optimization of a Wireless Body Area Network for Varying Body Positions

The purpose of this research was to improve the performance of a wireless body area sensor network, operating on a person in the seated and standing positions. Optimization-focused on both the on-body transmission channel and off-body link performance. The system consists of three nodes. One node (on the user’s head) is fixed, while the positions of the other two (one on the user’s trunk and the other on one leg) with respect to the body (local coordinates) are design variables. The objective function used in the design process is characterized by two components: the first controls the wireless channel for on-body data transmission between the three sensor nodes, while the second controls the off-body transmission between the nodes and a remote transceiver. The optimal design procedure exploits a low-cost Estra, which is an evolutionary strategy optimization algorithm linked with Remcom XFdtd, a full-wave Finite-Difference Time-Domain (FDTD) electromagnetic field analysis package. The Pareto-like approach applied in this study searches for a non-dominated solution that gives the best compromise between on-body and off-body performance.

Optimization of wearable microwave antenna with simplified electromagnetic model of the human body

Abstract In this paper the problem of optimization design of a microwave wearable antenna is investigated. Reference is made to a specific antenna design that is a wideband Vee antenna the geometry of which is characterized by 6 parameters. These parameters were automatically adjusted with an evolution strategy based algorithm EStra to obtain the impedance matching of the antenna located in the proximity of the human body. The antenna was designed to operate in the ISM (industrial, scientific, medical) band which covers the frequency range of 2.4 GHz up to 2.5 GHz. The optimization procedure used the finite-difference time-domain method based full-wave simulator with a simplified human body model. In the optimization procedure small movements of antenna towards or away of the human body that are likely to happen during real use were considered. The stability of the antenna parameters irrespective of the movements of the user’s body is an important factor in wearable antenna design. The optimization procedure allowed obtaining good impedance matching for a given range of antenna distances with respect to the human body.

Cost-effective design optimization of a wearable wideband microwave antenna

In this paper the problem of design optimization of a microwave wearable antenna is investigated. Reference is made to a specific antenna design that is wideband vee antenna which is characterized by 6 geometrical parameters. Those parameters were automatically adjusted with an evolution strategy based algorithm to obtain the impedance matching of antenna located in the proximity of the human body. Antenna was designed to operate in the ISM band that covers the frequency range of 2.4–2.5 GHz. The optimization procedure used finite difference time domain method based full wave simulator with a simplified human body model. In the optimization procedure small movements of antenna towards the human body that are likely to happen in real applications were considered. This is an important factor in wearable antenna design. The optimization procedure allowed obtaining the good impedance matching even if antenna is located close to the human body.

Objective-alternance optimization of wireless body area sensor network

In this paper the optimization process of a wireless body area network is presented. The optimization goal is to improve the performance of the body area sensor network with respect to the on-body transmission channel and off-body link performance. The sensor network consists of one node with fixed position (1) towards the ear and two sensor nodes that are located on the chest (2) and the back (3), respectively. The position coordinates of the nodes on the trunk are the design variables. The objective function in the design process includes two components: one that controls on-body data transmission between the 3 sensor nodes and another one controlling off-body transmission between the nodes and the remote receiver. The on-body component of the objective function is the maximum value of the path loss while the off-body component controls the gain of two antennas located in nodes 2 and 3 that are used for transmitting the data to the remote receiver. The optimization procedure utilizes EStra that is an evolutionary strategy optimization algorithm linked with finite-difference time-domain method based full-wave XFdtd simulator for obtaining the objective function value. Considering the two on-body and off-body components, the objective-alternance approach applied in this research yields a solution of the problem that is a compromise between on-body and off-body optimal solution.

Hierarchical multiparameter optimization of dual-band wearable antenna

In this paper an optimization method of a dual-band wearable antenna is presented. The antenna geometry is described with 8 geometrical parameters that are automatically adjusted with the use of a evolutionary algorithm to obtain the impedance matching of antenna located in the proximity of a human body. The antenna has been designed to operate in the ISM band which covers the frequency range of 2.4–2.5 GHz and 5.7–5.9 GHz. Within the optimization procedure the direct problem is solved by full wave finite-difference time-domain method to calculate the antenna impedance matching used in the objective function. As the first approach the optimization algorithm was firstly executed in an 8-dimensional parameter space. Subsequently the optimization algorithm was modified so it could start from the reduced set of parameters and then dynamically increase the dimension of the design variable space following the prescribed hierarchy of the parameters. The latter variant of the optimization procedure gave a better solution of the design problem with less computational effort.