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The Internet of Things (IoT) is increasingly being utilized, by both businesses and individuals, for many\ud applications. This utilization means increases in the smart devices that are connected to the Internet of Things, which\ud will significantly increase the challenges related to devices' interconnectivity and management, data and user privacy,\ud and network, data, and device security. At the same time, blockchain approaches provide a decentralized, immutable,\ud and peer-to-peer ledger technology that could be the right answer to these challenges. Significant challenges, however,\ud accompany the integration of blockchain into the Internet of Things, since IoT smart devices may suffer from resource\ud and power constraints and blockchain is associated with scalability and delay issues. In this paper, a practical\ud incorporation of blockchain into the Internet of Things is demonstrated using Ethereum Proof of Authority (PoA). This\ud provides performance analyses, which include measurement of the transaction arrival time, the system end-to-end\ud latency for different network implementations over cellular and Wi-Fi, and the average power consumption. This includes\ud the study of the effect of network bandwidth on the stability and synchronization of all nodes on the blockchain network.

An Active Artificial Magnetic Conductor (AAMC) is presented to steer the radiation pattern of a printed dipole working at 2 GHz. The elements that generates the phase shift are a set of Varactor Diodes, which are characterized using its spice model in order to obtain a phase shift - capacitance mapping. Overall beam steering of +/40° with a step size of 10° is achieved. A circuit model that describes any multilayer substrate AAMC unit cell, which uses fist form of Foster's theorem along with transmission line theory, is proposed. Our work is suitable to be used as low profile antenna; for example, street furniture antennas, which are located on the facades of houses or buildings, so that they can be visually mixed up with signs or advertisements. Simulations have been validated using a prototype consisting of an array of 22 × 14 AAMC elements; the overall structure measures 1.9λ0 × 1.21λ0. This reflector will generate a phase gradient in its columns, which will modify the reflection angle of an incident electromagnetic wave in the H-Plane. Beam switching control has been achieved using suitably amplified LPF PWM signals generated by two Arduino modules. A printed dipole with a Fractional Bandwidth of 17% is designed and manufactured to illuminate the structure at a distance λ0/4 above the surface. Far-field radiation patterns and reflection coefficients have been measured in an anechoic chamber using a spherical system. These compare favorably with simulations performed using the Time Domain solver in CST Microwave Studio.

An Inductive Frequency Selective Surface (IFSS) self-standing dichroic sub-reflector is presented, which allows the transmission of two frequency bands and reflection of a third band. The operating frequency of the sub-reflector is designed to work at Ku, K and Ka frequency bands, intended for earth to space and space to earth satellite communications. The proposed unit cell is a Jerusalem cross intertwined with an Brigid's cross. The IFSS is investigated using transmission line theory, along with equivalent-circuit model technique. It has been designed, and simulated using CST Microwave Studio and Advance Design Simulator (ADS). The cascade configuration of the IFSS is also investigated to improve frequency roll-off and bandwidth of the reflection and transmission coefficients. The IFSS has been manufactured using two-sided Photo Chemical Machining (PCM) technique, and has been experimentally characterized using an optical configuration, comprising two double ridged horn antennas connected to a VNA and a rotation system. Measured results are in good agreement with theoretical and simulation data, which validates the reliability of the design and manufacturing process.

This paper introduces a transmission line model analysis for dielectric-loaded self-resonant structures (SRSs). Equivalent circuit models, besides their fast computational time, usually offer some insights into the underlying physics of the electromagnetic structures, hence simplifying and improving the design and optimization criteria of these structures. A systematic approach for deriving impedance expressions of SRS on and within multi-layer dielectric media is presented. The process of extracting equivalent circuit parameters from impedance expressions is explained. The trends of equivalent circuit parameters are studied with different dielectric medium properties and various angles of incidence for an SRS with multiple resonant states highlighting the effect of changing the physical and electrical dimensions on the equivalent circuit parameters. The transmission line model responses are compared to full-wave simulation results, and model accuracy is assessed using the mean absolute error criteria. Furthermore, a new simplified method for calculating the forward transmission coefficient of an SRS within multi-layer media is proposed. This expression offers fundamental insights into the factors contributing to the $S_{21}$ response. Finally, experimental measurements for SRS embedded in a multi-layer dielectric media inside a waveguide is conducted and compared to the equivalent model with very good agreement.

Integrating blockchain into Internet of Things (IoT) systems can offer many advantages to users and organizations. It provides the IoT network with the capability to distribute computation over many devices and improves the network’s security by enhancing information integrity, ensuring accountability, and providing a way to implement better access control. The consensus mechanism is an essential part of any IoT-blockchain platform. In this paper, a novel consensus mechanism based on Proof-of-Authority (PoA) and Proof-of-Work (PoW) is proposed. The security advantages provided by PoW have been realized, and its long confirmation time can be mitigated by combining it with PoA in a single consensus mechanism called Honesty-based Distributed Proof-of-Authority (HDPoA) via scalable work. The measured results of transaction confirmation time and power consumption, and the analyses of security aspects have shown that HDPoA is a suitable and secure protocol for deployment within blockchain-based IoT applications.

A thin Non-absorptive Radar Cross Section Reducer (NARR) surface capable of redirect the scattered energy to different directions is presented. The NARR surface is composed of interwoven Unit Cells, which have the main characteristic of allowing ultra-miniaturized structures. This feature allows more Unit Cells to be placed in a given area, thus improving frequency response over flat, curved or small areas. To generate the inter-weave, two Brigid’s Cross and two hexagonal cross interwoven structures are used for square and rhombus surfaces, respectively. These structures, disposed in a checkerboard arrangement, are used to generate a destructive phase difference in a bandwidth range of 180 +/- 37°, which allows to obtain a Radar Cross Section (RCS) Reduction below -10 dB. The simulation results for monostatic and bistatic RCS are analyzed and compared with the case of a PEC surface.

This paper presents a distributed and decentralized architecture for the implementation of Distributed Artificial Intelligence (DAI) using hardware platforms provided by the Internet of Things (IoT). A trained DAI system has been implemented over the IoT, where each IoT device acts as one or more of the neurons within the DAI layers. This is accomplished through the utilization of decentralized, self-managed blockchain technologies that allow trusted interactions and information to be exchanged between distributed neurons. The platform was built and customized to be used within the IoT system, and it is capable of handling DAI-related tasks. A new consensus mechanism based on Proof of Authority (PoA) and Proof of Work (PoW) has been designed and implemented, along with bespoke block and transaction formats. The proposed architecture was analyzed, implemented, and tested using a dedicated testbed with low-cost IoT devices. A quantitative measurement and performance evaluation of the system based on a real-world IoT application was conducted. The implemented DAI is found to have an accuracy of 92%-98%, with an energy cost of 0.12 joules (J) when utilizing a Raspberry Pi to run one neuron. The measured hash per joule (h/J) when using a Raspberry Pi for mining is 13.8Kh/J compared to 54Kh/J using an ESP32. The results showed that it is feasible to implement a DAI system utilizing the IoT hardware platform while maintaining the system’s accuracy. The integration of the blockchain has added an element of security and trust to the data and the interaction between system components.

In this work, an ultra-compact, angular stable, wide-band, and low-profile Frequency Selective Surface based on intertwined structures is presented. The unit cell is created by entwining the arms of a hexagonal structure with its neighbor cells until the structure is tessellated. The Fractional Bandwidth of the proposed structure is 92.45%, which is the highest value found in the literature regarding intertwined structures. A further increase in λ r /P, preserving a similar Fractional Bandwidth of the original unit cell, is obtained by extending the unit cell in the 2.5 dimension. Simulations results show that the lowest dimensions of the unit cell are 0.029λ 0 x 0.029λ 0 . The miniaturization capabilities of this design are reflected by the high values of equivalent inductance and capacitance, generated by the geometry of the structure. Two prototypes are manufactured using the photolithography technique, which will be measured and compared with the simulation results. This design is suitable to be used for buildings propagation control and as meta-surface for space limited applications such as RCS reduction for small and irregular objects and ground plane for antennas in mobile terminals.

The increased implementation of Edge Computing technology has provided The Internet of Things (IoT) with the ability of real-time data processing and tasks execution requested by smart devices. To support this processing the integration of Artificial Intelligence (AI) into IoT is considered one of the most promising approach. While AI helps in the analyses of the data, blockchain technology provides a robust environment within which to create a secure, distributed way to share and store data. This paper proposes an architecture that combines the strengths provided by edge computing, AI, and blockchain technologies to provide robust, secure, and intelligent solutions for secure and faster data processing and sharing. The pandemic created by the rapid spread of the novel Coronavirus COVID-19, as well as the tracking of viruses in water sewage to help control the spread of such viruses, were used as our case study for exploring this architecture. To secure the proposed architecture a new concept for consensus mechanism based on Honesty-Based Distributed Proof of Work (DPOW) were devised and tested.

An evaluation of a beam reconfigurable base station transceiver for cellular applications is presented from both systems and antenna design perspective. The proposed technique uses an azimuth beam switching method, which incorporates PIN diodes to provide a fast switching reflecting ground plane for a three sector antenna. Numerical systems analysis has been carried out on a hexagonal homogeneous cellular network to evaluate how the reconfigurable antenna can be used to tradeoff the mean and cell edge capacity by reconfiguring the azimuth beamwidth. The systems analysis shows that a mean cell edge improvement from 15 to 18 Mbit/s is achievable and this improvement is consistent for cell sizes ranging from 500 to 1500 m. The proposed reconfigurable antenna has been designed, manufactured, and characterized, and the measured results are shown to be similar to simulations.

This study describes an experimental investigation into improving the detectability of self-resonant structures. Passive self-resonant structures have been used as an alternative to active devices in many applications including radio-frequency identification (RFID) due to their long lifetime and low manufacturing cost. They can be used to store information in terms of the presence or the absence of resonance peaks at a given frequency window. This work investigates practical validation of gain enhancement techniques, aiming to improve the resonance characteristics of passive RFID tags to increase their read range and allow them to operate in highly lossy mediums. Two passive resonator designs are studied: a uniform cross-shaped resonator and a folded (gammadion) cross having a physical aperture 45% less than that of the uniform cross. Arrays of elements have been used to improve the detectability of the structure. Measurement settings have also been investigated in order to achieve higher levels of detectability.

Blockchain technology is a distributed database ‘distributed ledger’ and offers features such as autonomy, decentralisation and a trustless environment. These features make blockchain suitable to be applied to different applications within the Internet of Things (IoT) realm. This paper provides a practical implementation of Proof of Authority (PoA) Ethereum blockchain on an IoT system in a real-world use case. This implementation was practically accomplished in order to investigate and highlight some of the possible issues that could affect the integration of blockchain with IoT, to lay the ground for future research and possible solutions to these issues.

The concept of a secure electromagnetic building (SEB) which can successfully prohibit wireless communications is presented. Wireless security is achieved using a slow phase-switching technique and can be realized by time-varying the transmission properties of a frequency-selective surface (FSS) to increase the bit error rate (BER) of the unwanted signal. Results are presented which demonstrate that a technique of phase switching at rates much lower than the baseband data rate can be used successfully. The system has been implemented using a reconfigurable dual-polarized dual layer FSS incorporating varactor diodes where over 100° of phase change can be achieved for voltage changes of $\pm 0 - 3V$ . A vector signal analyzer was used to evaluate the BER performance of the system for a GSM signal operating at 2 GHz. BERs are shown to be as high as 36% which are sufficient to successfully prohibit wireless communication. The solution is also shown to be robust over a wide range of incidence angles, which is important for real-world applications where the location of the prohibited wireless source may be unknown or mobile. Furthermore, as the system is reconfigurable, the building can be switched between secure and nonsecure modes.

Electromagnetic radiowave exposure is a major concern in most countries due to possible adverse health effects. Over the last 10 years, many technological changes (digital television, mobile technologies, wireless networks…) have led to variations in the electromagnetic field (EMF) levels.\ud \ud A large number of studies devoted to the analysis of EMF levels with personal dosimeters or computer models of the exposure of mobile stations have been conducted. However, the study of the exposure values, taking into account all the existing sources, and their evolution in a wide area, using measurements, has rarely been performed.\ud \ud In this paper, we provide a comparison of the EMF exposure levels for the city of Alcalá de Henares (Spain) over a ten-year period using a broadband isotropic probe in the range from 100 kHz to 3 GHz. A statistical and spatial analysis of the measurements and their variations are also presented for the study of the global and local variations.\ud \ud The measured values in the period from 2006 to 2015 were ranging from 0.02 to 2.05 V/m. Our global results show a moderate increase from 2006 to 2010 and they are almost invariant from 2010 to 2015. Although the whole dataset does not have relevant statistical difference, we have found marked local differences. In the city areas where the population density has remained unaltered, we have measured lower exposure levels. Conversely, new urban and industrial developments have demanded new resources, which have potentially contributed to the observed increase in the measured electric field levels within these areas.

This work presents an analysis of a reconfigurable self-resonant structure using an equivalent circuit model. Reconfiguring the electrical length of the structure results in uniquely identifiable changes to its forward and reflected frequency response. Equivalent circuit models are known to reduce computational time drastically and to provide an insight into the physics of the electromagnetic problem. Equivalent circuit parameters have been calculated for different states of the self-resonant structure. The responses of these equivalent circuits are compared to a full-wave simulation with very good agreement.

An active antenna capable of changing the beamwidth and pointing direction of its main radiating beam is presented. The design exploits the use of a novel frequency selective surface (FSS) and variable capacitance diodes (varactors) to control the main beam of an antenna. The main beam azimuthal pointing direction can be steered ±18° from boresight and the −3dB beamwidth varied from 100° to 140°. Narrower beamwidths can be achieved by changing the size and shape of the active ground plane. The design is suitable for applications where even small changes to the antenna parameters (gain, beamwidth and pointing direction) can have a positive impact on coverage and performance. Operating within the 2.4GHz ISM band, the proposed antenna design is suitable for adaptive indoor WiFi networks, dynamic wireless sensor networks and the internet of things.

Deploying wireless systems in vehicles is an area of current interest. Often, it is implicitly assumed that the electromagnetic environment in vehicle cavities is analogous to that in reverberation chambers, it is therefore important to assess to what extent this analogy is valid. Specifically, the cavity time constant, electromagnetic isolation and electric field uniformity are investigated for typical vehicle and vehicle-like cavities. It is found that the time constant is a global property of the cavity (i.e., it is the same for all links). This is important, as it means that the root-mean-square delay spread for any link is also a property of the cavity, and thus so is the coherence bandwidth. These properties could be exploited by wireless systems deployed in vehicles. It is also found that the field distribution is not homogeneous (and is therefore not uniform), but can be isotropic. For situations where the field distribution is isotropic, the spatial coherence is well defined, and therefore multiple-input-multiple-output antenna arrays can be used to improve performance of wireless systems. For situations where the field distribution is not isotropic, the angular spread is not uniform, and therefore beamforming can be used to improve performance of wireless systems.

This paper presents a method for controlling scattering from a surface with the use of periodic elements on a metallic ground plate. A comb reflection frequency selective surface (CR-FSS) is compared with a novel pin reflection frequency-selective surface (PR-FSS). The performance of the periodic surfaces are based on their ability to reduce specular scatter and redirect this as backscatter compared with a flat perfectly conducting (PEC) plate. The PR-FSS has comparable scattering performance when compared with the CR-FSS, despite a 90% reduction in fin material. Simulation and experimental results show that the PR-FSS is effective only for TM polarization, whereas the CR-FSS is adequate for both TM and TE polarizations. The effect of changes to the angle of incidence, height, and separation of the pins and fins are investigated. Aluminium prototypes have been manufactured and tested to provide experimental validation of the designs and are compared with simulated results. This includes full radar scattering cross sections, angle-of-incidence performance, and operational frequency bandwidth. Furthermore, suitable engineering applications of the CR-FSS and PR-FSS structures are considered.

This paper presents the construction and validation of a novel bistatic measurement system for the purpose of accurately measuring the scattering from a centralised target. Unlike previous systems, this bistatic system is capable of a measurement. Empty chamber calibrations are completed to ensure that any unexpected noise in scattering patterns is understood. Measurements of a flat, perfect electrically conducting plate and more complex frequency-selective surfaces are presented and highlight the effectiveness of the system. Finally, time gating is integrated into the measurement system to allow for noise reduced characterisation. Three-dimensional scattering images are plotted using the measured data, with good agreement to simulated results reported on in previous publications.

Proposed is a passive periodic pin reflection frequency selective surface (PR-FSS) suitable for installation in indoor environments to reduce interference caused by multiple cochannel wireless transmitters. The PR-FSS is developed from a comb reflection FSS and provides comparable performance with the use of less material. © 2014 The Authors. Microwave and Optical Technology Letters Published by Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1424–1427, 2014

This paper investigates microstrip patch antennas designed using aesthetic and asymmetrical logo-based shapes. A range of shapes have been considered and analyzed using electromagnetic simulations and measurements. Particular attention has been given to the radiation patterns of these asymmetric antennas.

The performance of a 2 × 2 microstrip patch array under crumpling conditions is presented. The antenna array was manufactured on textile material, and three cases of crumpling resembling real applications are discussed. The performance of the individual patch elements correlate with the overall performance of the array. Frequency shifts of up to 6% are measured for the array when crumpled, the boresight gain is reduced by up to 6 dB with significant changes in directivity and efficiency, up to 20%. The overall efficiency for the textile array increases for crumpling in one plane but falls in the other.

A compact multiband tunable PIFA system using a varactor as an active tuning component is presented covering 88-2175 MHz. The antenna was designed to cover the mobile telephone bands (GSM850, 900, 1800, 1900, UMTS) by controlling the value of the capacitance across the gap in the slotted PIFA and two broadcast bands, FM radio (76-108 MHz) & mobile television DVB-H (470-702 MHz), were added by designing an appropriate matching circuit into the system. The antenna measured λ/15 × λ/43 × λ/19 at 470 MHz and was easily integrated into a small mobile phone handset. Simulations are verified by measurements.

This paper presents a technique for reducing the average sidelobe level of a random spherical volume array using frequency diversity. The technique combines data obtained at several discrete measurement frequencies over a wide bandwidth. By using appropriate signal processing the measured data can be combined to produce an array response with an average sidelobe level that is significantly lower than that obtained at a single frequency. It is applicable to broadband blind-source location estimation and can be used to enhance holographic imaging. Experimental holographic imaging results are presented to validate the method which provides superior image resolution by reducing noise from unwanted directions. Furthermore, this technique can be used in addition to other sidelobe suppression methods such as amplitude tapers.

An automated, low-field disturbance probe positioning system for measuring 3-D electric field distributions inside vehicles or similar resonant environments is described. Correlations between measured and simulated electric field distributions for a simple rectangular cavity demonstrate that the probe positioner has little impact on the measured field levels. Comparisons between measurements and simulations for a real vehicle indicate that the predicted field population distributions are within the estimated uncertainties of the measurements.

This paper describes an experimental investigation into improving the detect-ability of passive RFID tags. Previous work published by the authors considered a novel passive chip less RFID tag for subcutaneous implant. This work investigates practical validation of gain enhancement techniques, aiming to improve tag detect-ability in the highly attenuating environment of the human body. Two passive tags are considered, a uniform cross shaped resonator, and a folded (Gammadion) cross having a physical aperture 45% less than that of the uniform cross. Arrays of elements have been used to improve the detect-ability of the tag. It has been shown that with the folded cross it was possible to accommodate more elements on the tag without increasing the original physical aperture. Improved tag detect-ability with reduced size is ideal for any implantable medical device.

Due to the ever growing population of mobile device users, there is an increasing demand for improved capacity in wireless cellular networks. Cell densification and 2-tier heterogeneous networks (HetNets) are two solutions which will assist 5G systems in meeting these growing capacity demands. Papers including [1] consider small-cell deployment over existing heterogeneous networks. Additionally, there has been considerable research performed into techniques for determining user location and cell deployment.

Wireless sensor networks are being deployed for engine health monitoring on marine vessels, which enables longer periods of time between engine servicing while reducing the risk of component failure. Due to the nature construction of such vessels this type of wireless sensor network must be able to operate within a highly resonant environment. To ensure reliability of suitable communication systems electromagnetic modelling can be performed. Several techniques are available for such modelling including ray tracing, finite element method, method of moments, and FDTD based methods. Each has its own relative merits and disadvantages including, material characterisation, computational time and required memory.

Previous work published by the authors has considered a passive bio-degradable implant as a novel method to monitor the healing of soft tissue trauma. By implanting a passive tag inside the wound area during the final stages of surgery can allow early stage diagnosis of infection. The tag is passive so an off-body receiver uses backscattering waves to communicate with the implanted tag. As the tag degrades, its electrical length changes. This change can be monitored from outside the body by measuring its forward transmission coefficients. Infection results in an increase in the rate of degradation due to local changes in temperature and acidity. Therefore, monitoring the rate of change in degradation allows us to infer the onset of infection.

In a ZigBee network, low-cost, low-power sensor nodes are deployed to carry out specific tasks like environment sensing, home automation, human and animal condition monitoring, and robot navigation monitoring etc. Normally the network comprises of numerous sensor nodes deployed in different locations and a coordinator node where the sensor nodes report back the sensed data for possible analysis and further action. For certain applications it is desirable to be able to locate the sensor node within the network. Currently localisation can be achieved using time dependent methods (TOA and TDOA) or received signal strength (RSS). Time dependent approaches require time synchronisation at all times which can be difficult to achieve. RSS based method is simple and cost effective but require at least three anchor nodes for a nodes location to be calculated via triangulation. Such a method can increase the complexity and cost of a network deployment. This paper presents a single anchor based location system which utilizes a differential two-element antenna array to perform node localization. An experimental system is introduced and results demonstrate the effectiveness of the proposed system. The anchor node, which can also be the network gateway, is connected to two dipole antennas separated by ⋋/2. The relative phase of each antenna can be varied using a phase shifter. The combined output of the two antennas can be used to create sum and difference radiation patterns, and to steer the antenna radiation pattern. Experimental validation was performed using seven XBee sensor nodes. Accurate azimuthal localization (relative to the anchor node) can be achieved and range estimation can be made with minimal errors. Adaptive path-loss model estimation can further improve range estimation. Overall, this cost effective localisation system performs well for ZigBee based wireless sensor networks.

Frequency selective surfaces have been widely used to control radio propagation within buildings. In this paper we consider the application of a sparse FSS for improved coverage of radio signals between two isolated adjacent rooms. The scattering lobes which will occur from a sparse FSS design can therefore be exploited to alter the coverage pattern within the second room.

Understanding radio channel path characteristics is a very important factor for ensuring quality of service and high data rates for indoor wireless communication systems. Obstacles such as human occupants, doors, walls, windows, etc. all have a significant impact on received signals strengths and will contribute to fading, multipath and shadowing effects. This paper studies the effects of changes within a building, such as opening and closing doors, and the movement and number of human occupants, on indoor signal propagation at 5.8 GHz. The effects of different obstacles inside the rooms are compared and highlight which has the most significant effect on the received electric field strength.

A challenge faced by the information and communications technology (ICT) industry is the growing data volume and associated energy consumption. How to both meet a dynamic tra-c demand at a consistently low energy consumption level is of importance from both commercial and climate change perspectives. This paper proposes a dynamic basestation concept that allows the number of active sectors to be adjusted in accordance with the tra-c load. This is achieved through a novel switchable antenna design that can adjust the azimuth beam-width by using a tuneable re∞ector. Simulation and theoretical results show that the dynamic basestation can reduce the total operational energy of a cellular network by a peak of 75% and a mean of 38%.

The possibility is explored for exploiting the properties of AMC surfaces for controlling the radiation pattern of simple dipole antennas for mobile phone street furniture applications, where the main lobe of radiation is significantly off boresight. Predictions are shown for a halfwave dipole above a square patch AMC, which illustrate the technique operating in the GSM 880-960 MHz frequency band. It will be shown that a profile reduction of 37.4% can be achieved.

This paper presents simulation and measurement results of a corrugated comb reflection frequency selective surface (CR-FSS). Surface parameters are altered to investigate the effect of sloping the comb elements to produce a corrugated structure. It is proposed that the strength of such elements can therefore be increased, however the effect on the reduction in specular scatter is unknown. CST simulations and measurement results on foam and foil prototypes provide evidence that increasing the slope angle can alter scattering performance. Furthermore, issues with manufacture and the application of such surfaces are discussed.

Limiting mobile phone usage while maintaining a viable communication link for the emergency services can be crucial for secure facilities such as prisons. This paper presents the design of an inductive frequency selective surface (FSS) with a pass-band operating from 380 to 420 MHz covering the TETRA frequency band used by emergency services in Europe. The FSS is designed to attenuate signals in the mobile cellular frequency bands aiming to inhibit the operation of contraband mobile phones. The paper considers how the optical impact of the design can be reduced, thereby enabling its usage as a window covering, and the subsequent effect on the surface's band-pass and band-stop performance.

Numerical techniques for calculating electromagnetic fields within three-dimensional surfaces are computationally intensive. Therefore, this paper presents the application of a mode-matching technique developed for analyzing electromagnetic scattering from periodic comb surfaces illuminated by a plane wave. A set of linear equations has been developed to calculate mode coefficients of the field distribution for both E- and H-polarized incident waves. Analysis is performed for two cases where the comb thickness is either infinitely thin or of a finite thickness. The technique is shown to accurately predict both field intensities within the near-field of the periodic surface and far-field scattering patterns. Results are compared to those obtained using the finite integration techniques (FIT) implemented in CST Microwave Studio. Furthermore, numerical results are compared to measurements of an aluminum prototype. Additional far-field scattering measurements using a bi-static system provide additional confidence in CST simulations and the mode-matching methods presented here.

In-body medical devices can play an important role in clinical monitoring and diagnosis of diseases. Wireless devices implanted within a patient have to be physically small, and must overcome the challenges of having a little or no onboard electrical power and the highly attenuating electromagnetic propagation environment which is the human body. In this paper, we investigate the use of biodegradable implant to monitor the healing of soft-tissue trauma and to allow early stage diagnosis of infection. The implantable tag is designed to degrade in a predetermined and controlled method, the stage of which can be measured from outside the body without the need for further surgical intervention. The speed of degradation of the tag depends on the temperature and acidity of the subcutaneous tissue in which the tag is implanted. We show that as the electrical length of the tag pattern increases due to degradation, the resonant frequency changes significantly, and this change in resonant frequency can be detected from outside the patient. Results are presented showing the tag's performance at normal and oblique incidence, and techniques for miniaturizing and enhancing the tag's response sensitivity are given. As the entire tag is biodegradable, there is no need for further postoperative surgery to remove it from the patient at the end of its useful life.

A method is described for producing images of acoustic sources using a volumetric array. Theoretical results are presented and compared to those obtained experimentally from an acoustic 64 element random spherical volumetric array. Application areas for such a system include auditorium characterisation, recording studio optimisation and covert surveillance operations.

This article presents a broadband tunable band-pass filter which operates between 380 and 960 MHz covering the trans-European trunked radio, AMPS, GSM900, and long-term evolution “whitespace” bands. The design has an increased operational tuning range when compared to existing designs and is suitable for low-cost wireless spectrum bandwidth expansion analysis and spectral efficiency analysis. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2847–2849, 2013

Practical measurements of a reconfigurable frequency selective surface (FSS) designed to stop the transmission of the GSM network protocol are shown. The method uses the time-varying transmission phase of the FSS to impair a GSM signal transmitted into a building or room, such that the receiver cannot detect the incoming signal. Measurements of the FSS response are shown for varying reconfigurable states and the FSS has been tested against a GSM signal to observe the level of impairment offered by the FSS. It is shown that the FSS can provide up to 35% bit error rate.

— Smart meters utilizing wireless technology could help to improve building energy efficiency. Wireless smart meters have to be carefully deployed in the building to ensure reliable communication and optimize signal strength. This simulation study considers how changing the configuration within a Victorian terraced house affects the electric field strength. Ten scenarios are presented to investigate the effect of doors and human occupancy on RF signal propagation. Keywords—Smart meter, propagation, RF, wireless. I. I NTRODUCTION The European Community has committed to save energy among most of European Union (EU) nations [1]. Currently, power consumers in the UK are given the estimated reading of electricity, gas and water every three months. In most cases they are not fully aware of the total power consumption and may consume more than they expect. The UK government aims to let most customers get a real indication of their consumption by 2020. To achieve this a smart meter will be installed in every home, with the aim of raising consumer awareness of energy consumption and thereby reducing overall domestic energy consumption [2]. Smart wireless meters are used to record and display the energy consumption of a household for the purpose of optimal power management. They offer consumers the potential for lower energy bills by making them more aware of their energy usage and can benefit energy suppliers by providing higher resolution data on customer demand. Smart wireless meters therefore have to effectively communicate with each other. A variety of commercial standards are available for wireless sensor networks (WSN) communication, such as Bluetooth, 6lowpan, Wireless HART, Z-wave and ZigBee. The latter has proven to be an appropriate solution for the smart meters [3]. Improving the performance of wireless systems is becoming a very important element especially inside buildings. For a wireless friendly building, improving the signal coverage is one of the main issues studied in the literature [4]. There are many parameters that can affect the radio frequency (RF) signal's propagation inside the buildings. Among them are the structure of building, the type of materials and the incident angle of wave into the wall, windows or any other obstacles [5]. Researchers have investigated the effects of various building dielectric parameters and structures of internal wall on the performance of wideband channels [6, 7]. The results have shown that the path loss increases if one of the permittivity, loss tangent or thickness of the wall is increased. A door state (open or closed) and presence of people on indoor environment have a big impact on propagation of the signal. In [8] the author has studied the affect of the doors when they are open or closed on the propagation for the cases of line of sight (LOS) and non line of sight (NLOS) using finite element method (FEM) simulations at 2.4GHz. It was clear that the door status has a more significant effect on the signal strength in the LOS scenario, whereas the door status has a small effect on the signal propagation in the NLOS scenario. The effect of human body on wireless signals in an indoor environment has been investigated. It has been reported that the strength of the electric field distribution through a wall obstacle is higher than when it passes through people [9]. Also, the influence of human movement on wireless sensor networks in indoor radio propagation has been studied in [10 -12] and it was concluded that the electric field is significantly affected by the number of people and their mobility in the rooms. The signal level is decreased in case of slow speed movement but the trend at slow and medium speeds have the same effect as the number of people is increased. In this paper, the electric field (E-field) strength of a dipole antenna transmitter operating at 2.4 GHz in different locations within a Victorian terraced house has been investigated. Simulations were performed using the electromagnetic simulation tool FEKO [13]. Several scenarios were investigated to address the critical factors in the positioning of smart meters. E-field distributions of the ground floor, comprising a kitchen and front room have been analyzed for different occupancy scenarios. II. S

An inductive dichroic surface is presented for use as a sub-reflector in a tri-band reflect antenna. Such antennas are often used for satellite communications systems. The surface is designed to be reflective in the frequency range 10.7-12.75 GHz, situated in the Ku band, and minimal transmission loss at the two Ka sub-bands 17.3-20.2 GHz and 28.295-30 GHz. The large bandwidths of operation in the transmission bands and the requirement of fast roll-off characteristics constitute the challenging aspects of the design of this frequency selective surface (FSS). Simulated results for the preferred design are given, fulfilling the reflectivity and transmission specifications required in the different frequency bands.

This paper considers the problems associated with cellular network coverage for mobile phone users within energy efficient buildings. As energy efficient building materials can significantly attenuate radio frequency (RF) signals, a two story energy efficient building is considered having external wall attenuation of 20 dB, and an internal floor attenuation of 3 dB. Results are presented showing how external signals propagate within the building and how a passive antenna system can be utilized to increase the internal signal coverage by up to 30 dBm.

This paper presents a low profile multiband antenna suitable for future wireless communication systems. The design comprises a co-planar fed patch antenna and a planar inverted-F antenna (PIFA). Active switching enables the antenna to resonant in different lower frequency bands while maintaining fixed operational performance in the upper bands.