Planar quasi-Yagi antenna gain enhancement using zero-index metamaterials

In this letter we have applied a new anisotropic zero index metamaterial (ZIM) structure to the quasi-Yagi antenna to achieve a high-directivity quasi-Yagi antenna. Simulation results show that the antenna gain increases for a frequency range over which the proposed metamaterial structure exhibits ZIM properties (10.3-11.7 GHz)

Improving multiple broadcasting of multimedia traffic in wireless ad-hoc networks

The increasing use of multimedia streaming applications in addition with advent of internet television and radio, demands from today's wireless networks to handle with reliability multiple broadcasting and multicasting sources. However, the way that 802.11 standard, which is the primary technology in wireless networking, handle this type of traffic raises a series of problems mainly related to the lack of an effective feedback mechanism. This lack in turn, limits the capability of random backoff process to eliminate collisions and reduce reliability and fairness. This inherited drawback of the standard is affecting the way broadcast and multicast traffic is transmitted as well as the overall performance of the network. In this paper initially we are highlighting the drawback of the IEEE 802.11 MAC algorithm in handling multiple stations “media type” data broadcasting in an ad-hoc wireless network. Then, we propose two different approaches in alleviating these problems. The first approach is the simple linear increase of the contention window (CW) while the second propose a linear increase of the CW implementing an exclusive backoff number allocation (EBNA) algorithm. In addition we are modifying the 802.11 medium access control (MAC) algorithm to use the clear to send to self (CTS-to-Self) protection mechanism prior to every transmission. Both the above techniques are simulated and compared with the classic 802.11 MAC. The results show that the overall performance of the network can be improved using these alternative MAC methods

Modelling metallic discontinuities with the non-orthogonal finite difference time domain method

Numerical electromagnetic models, such as the finite difference time domain (FDTD) method, have many applications. The authors focus on the non-orthogonal FDTD method, which offers an improved geometric flexibility compared to other standard techniques. Results from numerical electromagnetic analysis methods, such as the FDTD method, are often degraded by an error known as numerical dispersion. For metallic structures this dispersion error is often higher than expected from theoretical considerations. The source of this additional error is due to the reciprocal field interpolation scheme used in the non-orthogonal FDTD algorithm. The error is illustrated by means of a microstrip waveguide and a microstrip antenna. Techniques for reducing this error are evaluated; careful construction of the mesh at the metallic boundary being the most reliable solution

Enhancement of IEEE 802.11 in handling multiple broadcasting audio data in wireless ad-hoc networks

This article is made available through the Brunel Open Access Publishing fund and can be downloaded from the publisher’s website at the link below. Copyright @ 2013 Audio Engineering Society.Audio networking is a growing field, introducing new and exiting possibilities in the professional audio industry [1]; but it also drastically changes the way audio systems will be designed, built, and used. Today’s networks have enough bandwidth to transport hundreds of high quality audio channels, replacing hundreds of kilograms of cabling in conventional analog audio systems [2]. Currently there are many systems on the market that distribute audio over Ethernet but the majority of sound engineers are not using them yet. There are mainly two reasons that audio networks are not as popular as expected. First, many of the systems are based on a proprietary implementation that does not allow interoperability between different vendors. Second, wired networks, like the conventional analog audio networks, also need a cable installation. It is therefore understood that the development of a wireless digital audio distribution system would be a significant contribution in this sector. IEEE 802.11 (Wi-Fi) as the primary wireless technology in computer networking has made wireless networks widely available and inexpensive. With its most recent amendments, as well as the use of the 5-GHz ISM band, it can facilitate many high quality audio channels. However, the use of this technology has not been the choice for the audio industry so far. It is obvious that a sequence of problems related with the nature of this technology impede the use of Wi-Fi in professional live sound and studio applications [3]. Apart from the well-known drawbacks of interference and security, encountered in all wireless data transmission systems, the way that Wi-Fi arbitrates the wireless channel access is what causes the majority of the problems. In this paper we highlight the drawbacks of the IEEE 802.11 MAC algorithm in handling multiple stations broadcasting of audio data. We simulate a live audio data wireless network and test the limits of the protocol for this type of traffic. Moreover, we modify the 802.11 MAC algorithm to address the above problems. We test the amended protocol using simulation and analyze the results. We also give the directions for the future research in order for this widely accepted technology to be used in the professional audio industry

A FDTD model for the post-reception synthetic focusing surface penetrating radar with mine detecting applications

Surface penetrating radar (SPR) is extensively used in military, civil, geophysical and archaeological applications. There has been an increasing emphasis on the use of SPR in the identification of buried unexploded ordnance, such as anti-tank mines, antipersonnel mines etc., which can be metallic or plastic in nature. Mine detection methods can be classified as destructive or non-destructive. Non-destructive mine detection methods employ metal detectors, magnetometers, infrared sensors and SPR. However, neither the metal detector nor the magnetometer can differentiate a mine from metallic debris and the infrared sensor merely notes a difference in thermal conductivity. In most battle fields the soil is contaminated by large quantity of shrapnel, metal scraps and cartridge cases which will give a high false alarm rate in the identification process. In this scenario the SPR is a promising technique for identification of both metallic and plastic mines. The use of finite difference time domain (FDTD) model to analyse the SPR, which makes use of post-reception synthetic focusing (PRSF) techniques, is presented

Wideband printed bowtie antenna element development for post reception synthetic focusing surface penetrating radar

A printed bowtie antenna for a Post Reception Synthetic Focussing Surface Penetrating Radar (PRSF-SPR) has been developed with the aid of FDTD analysis. Antenna free space characteristics were compared against practical measurements and its performance was analysed when soil is present

Study on the performance deterioration of flexible UWB antenna

A flexible transparent film uwb antenna for curved surfaces has been designed and developed for wireless communications. The antenna has demonstrated good performance over the entire UWB bandwidth. It can be mounted on any conformal shape by virtue of the film properties of both the antenna as well as the substrate. The radiator and ground are both designed using AgHT-8 while the substrate is of a polymer. The antenna is shown to be able to maintain its performance below the 10dB level throughout the entire UWB bandwidth of 7.5GHz i.e from 3.1 GHz to 10.6 GHz as it is flexed through various radius of curvature thus providing an insight into how to overcome performance deterioration in wearable antennas

A novel technique to enhance throughput and fairness over wireless mesh networks

This extended abstract was submitted to and published in the ReSCon '12 Book of Abstracts. The fifth SED Research Student Conference (ReSCon2012) was hosted over three days, 18-20 June 2012, in the Hamilton Centre at Brunel University

Depth of penetration effects in eddy current testing

The simple depth of penetration equation used for most eddy current calculations does not take into account the effect of the size of the coil or the effect of flaw morphology. The work described in this paper describes use of the CIVA eddy current model to investigate this effect and some experimental investigations. Knowledge of this effect is important in examination of thin sections with eddy currents. Two examples of this are the small sections required to be inspected in laser metal deposition, and welds in thin sections joining dissimilar metals such as copper and aluminium for electrical connections