Sema Dumanli

Energy efficient body area networking for mHealth applications

Propelled by the need to reduce the cost of caring for the ageing population, we observe an impetus towards enabling remote patient monitoring (mHealth) via low power medical sensor networks. A practical mHealth network consisting of several sensor modules located on the patients body needs to operate over long periods of time without any intervention. This requires efficient hardware and software design which will enable the battery powered sensor devices to operate efficiently and reliably with minimal energy consumption. This paper combines efficient antenna design with a cross layer energy efficient protocol to realize wireless body area networks (WBANs) where the main aim is to maximise network life time. Towards this goal, we demonstrate a high efficiency system design approach where the performance of WBANs are greatly enhanced.

A Slot Antenna Array With Low Mutual Coupling for Use on Small Mobile Terminals

In order to take full advantage of the benefits to be obtained by using MIMO techniques for mobile communications, it is necessary to use an antenna array which is both compact and also has low mutual coupling between ports. Generally these requirements are conflicting and to achieve them simultaneously is the subject of much research. In this paper a novel design for a two element cavity backed slot (CBS) array is described which has a measured mutual coupling of less than -15 dB despite an element spacing of only λ/6. This is achieved by adding a simple and easily manufactured meandering trombone structure to an existing CBS array which carries a portion of the input signal to the feed of the neighboring element. Measured and simulated results are presented for the behavior of the antenna and predictions are presented for the achievable channel capacity in several realistic scenarios.

Analysis of Coupled Tilted Slot Antennas in FDTD Using a Novel Time Domain Huygens Method With Application to Body Area Networks

Despite the undoubted versatility and effectiveness of the finite-difference time-domain (FDTD) method and its enhancements, there remain some problems which require more computer power than is practical. An example of such a problem is the coupling between two or more tilted antennas in the presence of a scattering environment such as is encountered in a body area network (BAN). The dual challenge of a wide range of scales and complicated structures which are not aligned with a Cartesian mesh are addressed using a novel Time Domain Huygens (TDH) approach. Results and comparisons with measurements are presented showing the effectiveness of the method. In addition, the measured and predicted variations of BAN propagation characteristics with body size are investigated.

On-body antenna with reconfigurable radiation pattern

On body antenna design is a challenging task due to the body being in the near-field of the antenna and the interaction between the two. The antenna should be designed to have a more application dependent gain pattern and to be less sensitive to near field effects of the body. For the case of on-body links, the antenna radiation should be directed along the body with an omni-directional pattern in horizontal plane of the antenna. It should preferably have vertical polarization. For the case of off-body links, the antenna radiation should be directed away from the body while the polarisation is not as critical as the on-body case. This paper presents a novel antenna design tackling the aforementioned challenges by exciting TM00 mode of a shorted rectangular patch antenna for the on-body link and exciting the TM01 mode for the off-body links. By means of a switching mechanism, either the on-body operation or the off-body operation is activated at 2.45 GHz with 64% and 75% efficiency respectively.

Design of a Novel Antenna Array for MIMO Applications

In spite of the good benefits of using MIMO technology with modern wireless systems, a major problem has arisen from using it with small wireless terminals. When antennas are placed with less than half wavelength apart then mutual coupling occurs. Researchers have found that mutual coupling can affect the performance achieved by multiple antennas which results in a large reduction in channel capacity. In this paper a practical hybrid circuit is designed for a 2times2 MIMO system to confirm a recent theory which states that a decorrelation network can be used with mutually coupled MIMO antennas to improve the performance. The hybrid circuit was tested with stacked patch antennas and performance was evaluated using cumulative distribution function curves on channel capacity at 5.2 GHz. Results show that some improvement was achieved with the hybrid and results can be further improved by some other manipulations.

A radiation pattern diversity antenna operating at the 2.4 GHz ISM band

A novel planar antenna operating in the 2.4 GHz ISM band whose radiation pattern can be switched by changing the frequency channels of the operating band is proposed here. This is achieved by merging the different radiation modes of the antenna together within a single operating band, in contrast to the conventional procedure of covering the whole band with a single radiation mode. Using this method a single antenna can provide radiation pattern diversity across the operating band without an external switching mechanism. This proposal improves the connectivity significantly when the link is dynamic. The channel selection algorithm can be modified accordingly where the channels can be pre-mapped for expected Direction of Arrival (DoA) of specific links. Depending on the standards assumed, a certain number of channels are used for directing the maximum radiation at φ = 0°, θ = 8°, while the rest is suitable for directing the main beam at φ = 0°, θ = 72°.

A decorrelated closely spaced array of four slot antennas backed with SIW cavities for MIMO communications

An array of four slot antennas backed with substrate integrated waveguide (SIW) cavities is presented for application to multiple input multiple output (MIMO) systems. Two 0.18λ spaced antennas are decorrelated by the use of a rat race hybrid. An investigation based on simulations and measurements has been carried out. The impedance matching and the radiation characteristics of these structures were studied using the Finite Difference Time Domain (FDTD) technique. The array performance is judged by considering the correlation coefficients between the elements and the MIMO channel capacity.

Off-Body Antenna Wireless Performance Evaluation in a Residential Environment

Modern body-centric communication systems require good link quality. Antenna performance is of primary importance when meeting this requirement. This paper contributes a method suited to the difficult task of quantifying antenna performance in a body-centric communications system. In a case study, a planar wrist wearable antenna, which provides radiation pattern switching across the 2.4 GHz operating band through an innovative technique that does not require an additional switching mechanism, is benchmarked against a monopole and a patch antenna in a residential setting. The performance of the antenna and subsequently the benefits of the pattern-switching technique are successfully quantified. The holistic method includes both antenna measurements and channel simulation with ray tracing. Results are verified against real-world measurements.

Performance of a radiation pattern steering on-body gateway antenna for on-body and off-body propagation

Antennas in Body Area Networks (BAN) should be designed according to the link they are expected to form. In most of the systems, an on-body gateway collects data frames from other on-body sensors and relays them to an off-body gateway, realizing two different modes of operation, on-body and off-body. For such a device, the on-body link and the off-body link have different radiation pattern requirements. Moreover the antenna should be designed taking the effects of human body being in the nearfield of the antenna on the performance into account. A planar antenna operating in the 2.4 GHz ISM band which can satisfy all requirements by radiation pattern steering with frequency is analysed here in terms of its on-body and off-body propagation performance. Analysis were performed through simulations featuring two layered numerical chest phantoms, one being cylindrical and one being flat. The effects of the antenna - body spacing are investigated through the flat phantom while the on-body and off-body propagation are investigated through the cylindrical phantom. The antenna is shown to be performing well upto 5 mm spacing. It has been proved that the antenna provides 9 dB advantage in average for the on-body link compared to the case where its off-body radiation mode is used to connect to the on-body sensor and vice versa.

A wide band MIMO slot antenna for 5G Wi-Fi

The bandwidths of the wireless channels have been extended in IEEE 802.11ac compared to 802.11n and is restricted strictly to the 5 GHz ISM band. It also allows MIMO which makes antenna design challenging especially where the space is restricted. Here a wide band slot antenna in the shape of a modified square with dual ports is proposed. The antenna has two asymmetrical orthogonal micro-strip line feeds. One port covers the 802.11ac band with 13% fractional bandwidth while the other port is matched over a greater 26% fractional bandwidth. The slot is modified with protuberances such that the coupling between the feeds are minimized and the excitation of the modes hence the bandwidth of the feeds are controlled by the protuberances. As a result of this modification the slot size is reduced further by 22% compared to the unaltered square slot design.