Tommi Tuovinen

Effect of the antenna-human body distance on the antenna matching in UWB WBAN applications

In this paper, the interaction between the ultra wideband (UWB) antenna and human body is considered and demonstrated in the range of 0-30 mm above the body surface, which could be practical operation distance for the on-body antenna. Two different planar UWB antennas (loop and dipole) are used for the examinations. First, the antenna performance in free space (FS) is shown. Then, the effect of the antenna-body distance on the antenna operation is analysed in the terms of the matching, i.e., reflection coefficient S11. Measurements are carried out in the proximity of a real human body while the simulations are run by using the whole body model having a frequency-dependent behaviour. Observations are concluded to commensurate with the antenna field regions and the size of antennas reactive near-field was satisfied to be an important factor in the evaluation of an acceptable on-body operation. No significant differences between different antennas were observed through investigations. Both antennas perform satisfactory when the distance is high enough. The results of this study are helpful to engineers and designers evaluating antennas for the use in UWB wireless body area network (WBAN) applications.

Measurement-based on-body path loss modelling for UWB WBAN communications

This paper presents a path loss model for an ultra wideband (UWB) wireless body area network (WBAN) on-body communication. The modelling is based on the static frequency domain measurements in an anechoic chamber. The studies are done for several on-body radio channels and with two different UWB antennas (dipole and double loop) for the frequency range of 2-8 GHz. A linear least squares (LS) polynomial data fitting is applied to the post processed measurement data resulting parameters for a path loss model. It is shown that the loop antenna outperforms the dipole antenna in respect to the slope of the attenuation. However, the path loss at the reference distance is higher for the loop. It is also shown that the signal propagation delay in the antenna structures causes error in distance measurement and unless the error is compensated significant differences in the parameters of the path loss model may occur in a WBAN case. Finally, it is observed that by using energy detection notable benefit can be obtained if all propagation paths are considered instead of the first arriving path.

Monopole Ultra Wideband antenna for on-body communication in Wireless Body Area Network

The IEEE 802.15.6 is a standard for the Wireless Body Area Network (WBAN), which is covering on-body and in-body communications. The Ultra Wideband (UWB) technology is a one of the possible technology to utilise for the WBAN. In this paper, we will present a monopole UWB antenna having large bandwidth for on-body communication in wireless body area network. The body tissue layers for the simulation model are chosen such that the antenna is meant to be work on the chest area of human body. Based on simulations, corresponding prototype was fabricated and measured. The simulation and measurement results of the S11, Voltage Standing Wave Ratio (VSWR) and maximum gain of the antenna and radiation patterns of the prototype are presented.

Radio channel modelling for pseudo-dynamic WBAN on-body UWB links

In this paper, pseudo-dynamic radio channel models for ultra wideband (UWB) wireless body area network communications are presented. To produce the models, frequency domain on-body measurements were conducted in an anechoic chamber within the frequency band of 2-8 GHz. The study was conducted for two UWB antenna types (dipole and double loop). A walking sequence with five positions was modelled and the antennas were placed on both wrists and the left ankle of a person. At first, the amplitudes of the first arriving paths were solved for all links and positions. In the second phase, the resulting channels were divided into three classes: line-of-sight, (partially) obstructed line-of-sight and non-line-of-sight. Statistical channel models were developed for all classes. As a result, six models were obtained for both antennas to be used, e.g., as time-cyclic channel models in computer simulations. The channel impulse responses were modelled by 7-10 taps, depending on the class and antenna. The amplitude statistics can be modelled with the inverse Gaussian distribution.

Impedance Dependency on Planar Broadband Dipole Dimensions: An Examination with Antenna Equivalent Circuits

The present paper considers the connection between complex input impedance and the physical dimensions for planar ultra wideband (UWB) antennas. The flrst time the efiect of both the actual radiator width and length for impedance behaviour is comprehensively presented. Also the efiect of feed point dimensions on complex impedance is studied. The investigations involve both UWB single-resonant dipoles to cover bandwidth ‚ 500MHz and a multi-resonant dipole for the entire Federal Communications Commissions (FCC) frequency band of 3.1{10.6GHz. Lumped-element equivalent circuits are used identically with 3D antenna simulations in order to observe the corresponding impedance behaviour with the studied antennas. The used equivalent circuits consisting of series- and parallel-resonant stages are widely accepted in the open literature. The series-resonant circuit of equivalent is observed to have the analogue to the antenna feeding area. The physical dipole dimensions in terms of a length and width are connected to parallel-resonant part, which mainly determines the antenna input impedance. The resistance of a parallel-resonant stage behaves as the maximum value of real part of dipole impedance with an in∞uence on bandwidth together with the ratio of parallel capacitance C and inductance L. The increase of the antenna physical width has an efiect on bandwidth, because of the wider the antenna, the higher the capacitance in the antenna feed. Since the traditional dipoles are used for these studies, the results can be extended in several ways for other antenna types or, for instance, to verify the efiect of body tissue, close to a wearable antenna.

Reactive near-field region radiation of planar UWB antennas close to a dispersive tissue model

This paper focuses on the radiation properties of planar Ultra Wideband (UWB) antennas in the vicinity of a dispersive layered tissue model through the range of 0-30 mm above the body model surface. Radiation properties are investigated in terms of the realized maximum gain, total antenna efficiency and radiation patterns (the plots of realized gain) at different antenna-body distances. Two planar UWB antennas are simulated in free space in this study and at multiple distances to the tissue model. Results are analyzed and discussed based on the antenna theory. When the operation distance over the boundary of antennas reactive field can be used, the performance close to free space can be achieved.

Impedance behaviour of planar UWB antennas in the vicinity of a dispersive tissue model

In Ultra Wideband (UWB) Wireless Body Area Network (WBAN) systems, the propagation environment is comprising free space and lossy medium (human body tissues), which have a very strong effect on the antenna operation. This paper investigates the UWB antenna-body tissues interaction in terms of the reflection coefficient and input impedance behavior through the range of 0-30 mm away from the body surface. Planar UWB antennas are exploited in the investigations. A layered tissue model based on the Debyes dispersion model for UWB frequencies is used in simulations. Observations are considered in relation to the antenna near-field regions and the size, i.e., the boundary distance of antennas reactive near-field is noticed to be the important factor in the evaluation of the shortest antenna-body operating distance.

Effect of the antenna-body distance on the on-ext and on-on channel link path gain in UWB WBAN applications

This paper investigates the effect of the operation distance (i.e., practical use) between an antenna and a human body on wireless body area network (WBAN) channel path gain. Different use cases in WBAN on-external (ext) and on-on links with different antenna-body distances for ultra wideband (UWB) technology are considered. These studies are carried out with two types of planar UWB antennas in the vicinity of a real human body. Corresponding scenarios are repeated by computer simulations, and differences between these environs (i.e., challenges in the modelling of the measurement situation) are analysed and discussed.

Analysis of the Impedance Behaviour for Broadband Dipoles in Proximity of a Body Tissue: Approach by Using Antenna Equivalent Circuits

Ultra wideband (UWB) antenna operation close to tissue is examined by using lumped- element equivalent circuits in the present paper. The impact of tissue within the reactive near-fleld of the antenna is introduced in terms of e-ciency, impedance and matching to 50›. The parasitic components for the series- and parallel-resonant stages of the equivalent models are proposed for taking the impact of tissue into account on the antenna design. The flrst time the antenna impedance behaviour is presented in terms of capacitance, inductance and resistance as a function of the radiator distance on the tissue surface for UWB antennas. The capacitance was observed to increase with the distance on the tissue surface by achieving the maximum value close to the reactive near-fleld boundary. The inductance has the maximum on contact the tissue, decreasing strongly with the flrst millimetres and remaining constant with the higher distance. The maximum value of input resistance was seen to clearly increase with the distance, having the maximum value in the flrst third of the studied range, descending close to the value in free space at the boundary at the end. The results are achieved by realising electromagnetic simulations for the antennas and comparing the performance with the operation of the equivalent models.

On the evaluation of biological effects of wearable antennas on contact with dispersive medium in terms of SAR and bio-heat by using FIT technique

Considerations of biological effects, executed as the bio-heat and bio-thermal simulations, in terms of a specific absorption rate (SAR) and temperature rise in human body tissues for ultra wideband (UWB) wireless body area network (WBAN) applications are studied in this paper. 3D-electromagnetic (EM) simulation software, utilizing finite integration technique (FIT), is used in order to obtain temperatures and power losses by thermal stationary and transient solvers (TSS, TTS) in the vicinity of the modelled dispersive medium. Two different UWB antennas having excellent radiation properties are experimented on contact with tissues. The effect of the antenna input power on the temperature and maximum SARs over 1 g and 10 g averaging masses are evaluated. Obtained results are compared with the restrictions set by the institute of Electrical and Electronics Engineers (IEEE) and International Commission on Non-Ionizing Radiation Protection (I CNIRP). This paper investigates generally how much power should be fed to the UWB antenna in order to cross the maximum SAR limits in WBANs or in order the antenna start to heat the tissues significantly, both in the stationary conditions and further as the transient solutions.