Y. Nechayev

Antennas and propagation for body centric wireless communications

Research in antennas and propagation for body centric wireless communications continues to grow, in response to increasing demands for body area networks (BANs) for healthcare, defence and personal communications and entertainment. This paper will briefly review recent international work, and then report on advances in three UK BAN research centres, Birmingham, Queen Mary and Queens Belfast. The demand for greater security in BAN links could be met by the use of 60GHz channels, and the likely channel characteristics will be discussed and initial results given. New insights into surface wave excitation on the human body has enabled a novel low profile antenna to be designed that maximises link performance where very thin antennas are necessary. Finally advances in the numerical computation are reported, in which the importance of relating phantoms directly to patients to give subject specific simulations and to allow improved modelling of internal organs.

Statistical Analysis and Performance Evaluation for On-Body Radio Propagation With Microstrip Patch Antennas

On-body propagation channel measurements using two microstrip patch antennas for various links are presented and statistically analyzed. The attenuation attributed to factors such as the body, head and clothing are: 19.2, 13.0, and 1.7 dB, respectively, when measurement performed in the anechoic chamber. Measured cumulative distribution function (CDF) of data in the chamber and lab fits to lognormal distribution with deviation factors comparable in both cases. The results demonstrate that the human body is a major shadowing contributor in body area network (BAN) radio systems. The performance of potential radio systems under the measured channel variations is also investigated. Excellent system performance is achievable with power levels as low as 0.01mW. These results support the significance of channel characterization and modelling in producing suitable wireless systems for ultra low power BANs

On-body path gain variations with changing body posture and antenna position

Variability of an on-body transmission channel at 2.45 GHz is investigated. The propagation path gain was measured for a number of antenna positions and at a number of static human body postures as well as during arbitrary movements. Dependence of the path gain on conformal antenna separation is investigated and probability distributions of the path gain during arbitrary movement are derived

Statistical and deterministic modelling of radio propagation channels in WBAN at 2.45GHz

In this paper the on-body radio channel is statistically analysed at 2.45 GHz and analytically and numerically modelled at the same frequency applying different techniques. The channel exhibits great variability due to body movements with path loss data behaving in different manors depending mainly on the freedom of the communication link between transmitting and receiving antenna. Simple and accurate UTD model was applied for propagation along the body which resulted in good comparison with measurement. For more complicated on-body scenarios, conformal FDTD technique was used to evaluate received signal strength in comparison to measurement

Novel conformal surface wave Yagi antenna for on-body communication channel

Wearable antennas for on-body communication are desired to be low profile and planar [1]. Although, planar antennas do not provide very strong path gain due to the close proximity to the human body, they have high priority to other type of the antennas in practice. Different planar types of antennas have been introduced for on-body communication channels. But most of them are designed in free space. Then, the body influence on the antenna characteristics has been investigated [2]. In other words, the proximity of the body as a dielectric bulk to the antenna is ignored at the antenna design stage. However, this volume of dielectric can contribute to radiation of the antenna on and off the body. Also, it can affect the wave propagation mechanism in the communication channel regarding to the antenna type. Therefore, the antenna should excite the wave modes which are supported by communication channel [3]. In this paper, the proximity of the body is included in the antenna design which leads to propose a novel antenna for on-body communication channel. As the initial stage, the behavior of a dipole parallel to the body surface is investigated. This study provides valuable information which is used in the novel surface wave antenna design. To evaluate the new antenna performance, a pair of antenna is put on two opposite sides of cylinder made of muscle tissue property and the path gain results are compared with a pair of parallel dipole and also monopole.

Parasitic Array Antenna With Enhanced Surface Wave Launching for On-Body Communications

This paper presents a novel planar directive antenna array with enhanced coupling to the surface wave on the human body. Coupling of a small wearable antenna into the Norton surface wave and creeping wave modes on the surface of the human body is first discussed. Based on these observations, the surface wave parasitic array (SWPA) antenna was designed, and parametric studies were performed to optimize the antenna directivity on the body phantom surface. The antenna was fabricated and measured. Its performance was tested by path gain simulations and measurements. The measurements were performed on a liquid phantom inside an anechoic chamber. Comparison of the performance of the new antenna with other antennas is also presented.

Depolarization in On-Body Communication Channels at 2.45 GHz

This paper describes an investigation into the polarization behavior of on-body wireless communication channels at 2.45 GHz. The effect of the polarization of an antenna on the channel path gain has been studied and the channel cross-polarization discrimination (XPD) has been quantified, using both simulation and measurement. In simulation, short dipole antennas, which significantly reduce the simulation time, were used to investigate path gain behavior in different channels for vertically and horizontally polarized antennas. Measurements were taken in an indoor environment using a novel dual-polarized antenna, producing normal and parallel polarizations to the body surface. The measured signals were also analyzed to extract the Rician K-factor which was defined as the ratio of the power in the line of sight (LOS) signal to the scattered power for various polarization combinations.

Antenna Design and Channel Measurements for On-Body Communications at 60 GHz

On-body communication is of increasing interest for a number of applications, such as medical-sensor networks, emergency-service workers, and personal communications. This paper reviews 60 GHz on-body communication and its benefits and challenges. Two novel low profile high gain, end-fire wearable antennas are then described. Measurements with an experimental phantom and real human body are presented. Results show antennas achieve good performance close to a phantom. Shadowing effects and polarisation issues for on-body communications at 60 GHz are discussed.

Surface and creeping waves excitation by body-worn antennas

Surface and creeping waves play an important role on-body communication channels. In this paper, we explore the characteristic of the wave on the body surface relate this to the antenna type. Simple models are used to extract the attenuation exponent and evaluate capability of the practical antennas in lunching the surface wave. Both flat and cylindrical phantoms are used in the simulations and the wave variation versus distance is investigated for each antenna.

Preliminary estimate for observability of 60 GHz wireless body area networks

Observability of 60 GHz wireless body area networks is being investigated, in the context of the maximum outdoor detection range for such a network. An off-body channel within a scattering environment has been characterized. By decomposing the detection channel into a free-space channel and a body-local environment channel, an observability estimation model is proposed based on the measured data.