The 50 most-cited articles in Electronics Letters, 2019

In this Letter, a wireless transmitter using the new architecture of programmable metasurface is presented. The proposed transmitter does not require any filter, nor wideband mixer or wideband power amplifier, thereby making it a promising hardware architecture for cost‐effective wireless communications systems in the future. Using experimental results, the authors demonstrate that a programmable metasurface‐based 8‐phase shift‐keying (8PSK) transmitter with 8 × 32 phase adjustable unit cells can achieve 6.144 Mbps data rate over the air at 4.25 GHz with a comparable bit error rate performance as the conventional approach without channel coding, but with less hardware complexity.

Microacoustic resonators made on suspended continuous membranes of LiNbO 3 were recently shown to have very strong coupling and low losses at ≥5 GHz, suitable for high‐performance filter design. Employing these simple resonator structures, the authors have designed, fabricated, and measured a 4.7 GHz bandpass ladder‐type filter having 1 dB mid‐band loss and 600 MHz bandwidth to address the 5G Band n79 requirements. The filter is fabricated on a monolithic substrate using standard i‐line optical lithography and standard semiconductor processing methods for membrane release, starting with commercially available ion‐sliced wafers having 400 nm thickness crystalline LiNbO 3 layers. The filter is well‐matched to a 50 Ω network and does not require external matching elements. Through accurate resonator engineering using our finite element method software filter design environment, the passband is spurious‐free, and the filter provides better‐than 30 dB rejection to the adjacent WiFi frequencies. This filter demonstrates the performance and scalable technology required for high‐volume…

Although traditionally associated with defence and security domains, radar sensing has attracted significant interest in recent years in healthcare applications. These include the monitoring of vital signs such as respiration, heartbeat, and blood pressure, analysis of gait and mobility levels, classification of human activities to promptly detect critical events such as falls, as well as the evaluation of fitness and reactivity levels. The attractiveness of radar against alternative technologies such as wearable sensors or cameras lies in its contactless capabilities, whereby people do not need to wear, carry, or interact with any additional device, and plain images of people and private environments are not recorded. In this letter, we discuss some of the most recent achievements and outstanding research challenges related to radar applications in healthcare and present some results from our work at the University of Glasgow, including a dataset of radar signatures of human activities that are openly shared with the wider community.

Deep learning methods are nowadays considered as state‐of‐the‐art approach in many sophisticated problems, such as computer vision, speech understanding or natural language processing. However, their performance relies on the quality of large annotated datasets. If the data are not well‐annotated and label noise occur, such data‐driven models become less reliable. In this Letter, the authors present very simple way to make the training process robust to noisy labels. Without changing network architecture and learning algorithm, the authors apply modified error measure that improves network generalisation when trained with label noise. Preliminary results obtained for deep convolutional neural networks, trained with novel trimmed categorical cross‐entropy loss function, revealed its improved robustness for several levels of label noise.

A compact four‐element UWB MIMO antenna is proposed and its characteristics are investigated. The proposed antenna has a hexagon molecule‐shaped fractal structure as its radiating element. The antenna elements are placed orthogonally to each other in order to yield good isolation, without any additional decoupling structure. The band rejection in WLAN band is attained by etching a C‐shaped slot on each radiating element. The antenna has a compact size of 40 × 40 × 1.6 mm 3 and exhibits stable omni‐directional radiation pattern. In addition, it shows an acceptable impedance bandwidth ( S 11 < −10 dB) in the range 2.4–10.6 GHz with an isolation better than −20 dB over the UWB range. The performance of the proposed antenna is calculated in terms of antenna characteristics and MIMO parameters. The isolation level in‐between the elements is found to be reasonable for MIMO application. The simulated and measured results are in good accord which makes the antenna a suitable candidate for massive MIMO and high‐density packaging applications.

In a cloud system, a malicious user initiates the side channel attacks to steal the private information of other users that share the computing resources through virtualisation. In this Letter, the authors propose a multi‐objective load balancing framework to minimise the likelihood of these attacks by reducing the number of shared servers along with efficient use of computing resources and power. The proposed framework significantly improves the security by reducing the shared servers up to 55.83% and improves the resource and power usage up to 96.54 and 21.97%, respectively, over best fit, first fit and random heuristic schemes.

In this Letter, the design of a 3D printed fully dielectric Gutman lens is presented. The authors demonstrate the feasibility of using highly accessible and cheap additive manufacturing technology to produce a compact and high performing antenna lens. The lens is designed to operate at band and utilises a flat feed surface that approximates the focal sphere. The flat feed surface allows for beam steering that requires only translational movement of the feed. The lens has a measured realised gain of 20 dBi with 3 dB scan loss at . The lens finds applications in systems that require high gain antennas, such as the new generation of satellite and 5G communications and radar technology.

Virtual field‐programmable gate array (FPGA) is an emerging technology to put multiple users in the same FPGA fabric with logical isolation. Security researchers have studied new threats in virtual FPGA and proposed attacks on the logical isolation by exploiting analogue natures of FPGA. These attacks use an oscillator comprising a combinatorial loop to have access to the analogue domain using digital components only. Interestingly, the system in the field prohibits a combinatorial loop by a design rule check. In this Letter, the authors study if prohibiting a combinatorial loop is sufficient to thwart the conventional attacks. They negatively answer the question by showing oscillators without a combinatorial loop. They also show how to detect and reject the proposed oscillators by a design rule check.

Automatic modulation classification (AMC) lies at the core of cognitive radio and spectrum sensing. In this Letter, the authors propose a novel convolutional neural network (CNN)‐based AMC method with multi‐feature fusion. First, the modulation signals are transformed into two image representations of cyclic spectra (CS) and constellation diagram (CD), respectively. Then, a two‐branch CNN model is developed, a gradient decent strategy is adopted and a multi‐feature fusion technique is exploited to integrate the features learned from CS and CD. The proposed method is computationally efficient, benefited from its simple neural network. Experimental results show that the proposed method can achieve identical or better results with much reduced learned parameters and training time, compared with the state‐of‐the‐art deep learning‐based methods.

This Letter demonstrates the design of a two‐element polarisation diversity antenna, applicable for modern small satellite application systems. The intended antenna mainly consists of two monopole radiators loaded with metasurface reflector as a ground plane. The dimensions of the radiator antenna are 40 × 22 × 1.6 mm 3 . The antenna measured results offers a wider S 11 bandwidth of (2.23–2.91 GHz) and wider axial ratio bandwidth (ARBW) of (2.16–2.92 GHz) with a common S 11 and ARBW of 26.45% is obtained. A maximum gain of 7.02 dBic and isolation better than 14.5 dB is observed along with the operating frequency range. The antenna provides an ARBW(< 3 dB) and gain (> 2.38 dBic) for theta = ± 45°, for all phi values along with the complete operating frequency range. Also, the antenna port‐1 provides left‐handed circular polarisation and port‐2 provides right‐handed circular polarisation radiation with directional radiation characteristics.

The accurate prediction for the tropical cyclone (TC) intensity is a recognised challenge. Researchers usually develop dynamical models to address this task. However, since the TC intensity is highly influenced by various factors such as ocean and atmosphere conditions, it is difficult to build the very model which can explicitly describe the mechanism of TC. A new idea is developed, utilising the massive historical observation data by a deep learning approach, to conduct a completely data‐driven TC intensity prediction model. All the TC intensity and track data which have been observed in Western North Pacific since 1949 are collected, and recurrent neural network for TC intensity prediction is constructed. In general, their motivation as well as novelty is to develop a data‐driven approach instead of empirical models. There are very few researches similar to their exploratory work. The proposed method has presented 5.1 m s error in 24 h prediction, which is better than some widely used dynamical models and is close to subjective prediction.

This Letter explains the design and development of a wideband circularly polarised (CP) antenna based on composite metamaterial (MTM) structures which are applicable for use in small satellite applications. The presented antenna is based on a modified co‐planar waveguide feeding technique. The proposed antenna unit cell offers compact size due to its MTM property with dimensions of 0.088λ 0 × 0.19λ 0 at 2.4 GHz. The CP radiation is obtained by placing two composite right/left‐handed transmission line unit cells orthogonally and exciting two orthogonally‐polarised modes simultaneously. A new 4 × 4 unit cell artificial magnetic conductor metasurface is designed with a compact size at the same operating frequency of MTM‐based CP antenna as a ground plane for the proposed antenna, which is found to be increased bandwidth, improved gain, and wider axial ratio bandwidth without altering the antenna compactness. The final antenna obtains an overall dimension of 0.37λ 0 × 0.37λ 0 × 0.18λ 0 at 2.5 GHz. The measured result shows a wider impedance bandwidth of 860 MHz (33.07%), improved axial…

This Letter presents a new combination of a broadband power amplifier (PA) and an output microstrip hairpin bandpass filter. The filter is designed based on the fifth‐order Chebyshev low‐pass prototype element values. Even–odd mode impedance analysis is used to calculate the filter parameters. Meanwhile, only the fundamental impedance matching is considered for this design. Therefore, a highly selective bandpass response is obtained to provide a spurious‐free fundamental impedance matching. For verification, a broadband PA‐filter component across 1.9–3.1 GHz (48%) is designed and fabricated. Measurements have shown a drain efficiency of 48–56.6% with 39.3–40.5 dBm of maximum output power.

A compact self‐isolated multiple‐input–multiple‐output (MIMO) antenna system is proposed. It is based on a quarter‐mode substrate integrated waveguide (SIW) cavity where two edges are shorted by metallic vias and the other edges are open. A narrow slot with a rotated angle of 45° is utilised to divide the single cavity into two equal eighth‐mode sub‐cavities. These sub‐cavities are fed by two coaxial ports to construct the proposed MIMO antenna system. A self‐isolated mechanism that cavity energy inputted by one port is radiated into free space rather than transmitted to the other port is first observed. High isolation between two antenna elements can be obtained without additional isolating or decoupling networks although they are contacted with each other. A fabricated prototype operating at 3.5 GHz achieves the measured port isolation of higher than 18.5 dB, envelope correlation coefficient (ECC) of less than 0.04, the peak gain of 4.6 dBi, and maximum efficiency of 79.2%. With advantages of compact size, high isolation, low ECC, and good radiation performance, the proposed…

In order to simplify the process of analogue circuit fault diagnosis under the premise of improving the fault diagnosis rate of analogue circuit, and to deeply mine the fault characteristics of the output signal, a fault diagnosis method based on convolutional neural network (CNN) is proposed. The output signals in different fault states are directly input into CNN for fault feature extraction and fault classification. By optimising the CNN model and its parameters, the 100% fault diagnosis rate of Sallen‐Key circuit can be achieved. The experimental results indicate that the CNN‐based analogue circuit fault diagnosis method simplifies the fault diagnosis process and improves the fault diagnosis rate.

A compact substrate‐integrated‐waveguide (SIW) cavity multiple‐input–multiple‐output (MIMO) antenna with enhanced bandwidth and high isolation is proposed. It is based on a triangle half‐mode SIW cavity with one open edge and two edges shorted by metallic vias. By etching three slots, the single cavity can be divided into four eighth‐mode sub‐cavities. Two large sub‐cavities with the same size are excited by two coaxial ports to construct two antenna elements and a wide slot between them is utilised as the de‐coupler. Therefore, high isolation can be obtained. On the other hand, cavity energy can be coupled from the excited sub‐cavities to the unexcited sub‐cavities due to two narrow T‐shaped slots serving as the couplers. Therefore, enhanced bandwidth can be achieved by merging two coupled modes into the required operating band. A fabricated prototype centring at 3.51 GHz has been measured. With a compact size of 0.59λ 0 × 0.59λ 0 , enhanced bandwidth of 160 MHz, high isolation of 19.5 dB, the antenna gain of 4.9 dBi, and radiation efficiency of 72.8%, the proposed design has…

Multi‐functional antennas are very important in modern wireless communication systems. A novel dual‐band frequency‐reconfigurable antenna with pattern diversity is designed. The antenna consists of a composite right/left‐handed transmission line inspired structure, which works at the zeroth‐order mode (0) around 2.5 GHz and at the first‐order mode (1) around 3.5 GHz. The 0 mode results in an omni‐directional pattern and the 1 mode results in a broadside pattern. By adding varactors to continuously reconfigure the structure, the antenna is able to tune its lower resonant frequency from 2.36 to 2.60 GHz, which fully covers the 2.4–2.5 GHz ISM band, and tune its higher resonant frequency from 3.34 to 3.73 GHz, which fully covers the 3.4–3.7 GHz WiMAX band. Simulations and experiments match well, proving the validity of this new concept.

Convolutional neural network (CNN) architectures have shown excellent image classification performance on large‐scale visual recognition tasks. If a CNN architecture contains a shorter connection between layers close to the input and those close to the output, the training can be deeper, more accurate and efficient. In this Lette, the authors propose a densely connected CNN architecture for facial expression recognition (FER‐Net), which connects the output of each convolution layer to the inputs of the next convolution layers in the architecture. Experiments conducted on a publicly available dataset show that FER‐Net produces state‐of‐the‐art results in facial expression recognition.

In this Letter, the authors propose a novel convolutional neural network (CNN)‐based estimation of the distance between an ultra‐wideband (UWB) transmitter and receiver for a localisation. By exploiting the UWB signal characteristics, such as high‐resolution in the time domain, the CNN is designed. The proposed CNN‐based method estimates the distance from only the received signals, without signal‐to‐noise ratio information which is used for the conventional time of arrival (TOA)‐based methods. Furthermore, as verified by simulation, the proposed CNN‐based method significantly outperforms the conventional TOA‐based method with respect to the distance estimation accuracy.

In this Letter, a dual‐channel trench‐gate tunnel field‐effect transistor (DCTG‐TFET) is proposed and investigated. The gate of DCTG‐TFET is placed vertically in a trench to create two channels which carry drain current in parallel. The proposed device dimensions are optimised to reduce channel resistance and tunnelling width for an appreciable increase in the ON‐state current ( ). The performance of DCTG‐TFET is analysed using two‐dimensional simulations in the device simulator. The proposed DCTG‐TFET provides one order of magnitude improvement in / current ratio and 17 times reduction in subthreshold swing as compared to recently reported two‐source‐region tunnel field‐effect transistor structure.

The double shadowed Rician model was recently proposed to describe some realistic physical signal propagation phenomena, where a Rician faded signal is impacted by cascaded shadowing processes. In this Letter, the authors study the outage performance of the double shadowed Rician model. More specifically, they investigate the impact of two different shadowing processes on the secrecy performance by deriving novel and exact expressions for secrecy outage performance metrics. The obtained results reveal the following physical implications: (i) when a Rician faded signal undergoes line‐of‐sight shadowing, which is further cascaded by another round of composite shadowing, the latter form of shadowing imposes larger impact on the secrecy performance; (ii) the widely investigated concept of ‘protected zone’ to improve the secrecy performance should not be limited to the legitimate transmitter but also extended to the legitimate receiver due to the adverse shadowing effect caused by objects in its vicinity; and (iii) the rate of outage performance degradation grows larger as the shadowings…

A compact wideband four‐element multiple‐input‐multiple‐output (MIMO) antenna with high isolation is proposed in this Letter. The proposed MIMO antenna consists of a tapered microstrip line fed rectangular monopole antenna arranged in orthogonal symmetric fashion on the interconnected partial ground plane. The overall size of the proposed antenna is 35 × 35 × 0.8 mm 3 with 9.5 mm edge‐to‐edge separation between a pair of radiating elements. The proposed MIMO antenna has a −10 dB fractional impedance bandwidth of 49.57% covering 4.4–7.3 GHz, encompassing sub‐6 GHz 5G (4.5 GHz), WLAN (5/5.2/5.8 GHz), WiMAX (5.5 GHz), HYPERLAN/1, 2, and ISM bands (5.2/5.8 GHz) applications. The proposed MIMO antenna has a minimum isolation value of 21 dB, maximum envelope correlation coefficient (ECC) value of 0.014 between antenna elements throughout the band. The measured results are found in good agreement with the simulated S ‐parameters, radiation patterns, ECC, total active reflection coefficient, and channel capacity loss.

Orthogonal time‐frequency space (OTFS) modulation is a recently proposed waveform for efficient data transfer in high‐speed vehicular scenario. Use of rectangular pulse shape in OTFS results in high out of band (OoB) radiation, which is undesirable for multi‐user scenarios. In this work, the authors present a circular pulse shaped framework for OTFS for reducing the OoB. The authors also design a low complexity transmitter for such a system. They argue in favour of orthogonal transmission for low complexity transceiver structure. The authors establish that frequency‐localised circulant Dirichlet pulse is one of the possible pulses having this desirable unitary property, which can reduce OoB radiation significantly (by around 50 dB) without any loss in BER. They also show that the proposed pulse‐shaped OTFS has a lower peak to average power ratio than conventional OTFS system.

The authors present an expanded porous polytetrafluoroethylene terahertz fibre transmission link using resonant tunnelling diodes integrated with photonic‐crystal waveguides as a transmitter and a receiver. The measured coupling efficiency between the terahertz fibre and the photonic‐crystal waveguide integrated with a silicon tapered coupler is ∼30% with a 3 dB bandwidth of 50 GHz at the 0.3 THz band. Error‐free 10 Gbit/s transmission and uncompressed 4 K high‐definition video transmission have been successfully demonstrated using 1 m‐long terahertz fibre.

The usefulness of applying singular value decomposition (SVD) on triaxial accelerometer data for one‐dimensional (1D) convolutional neural network (CNN) based fall and activity recognition is investigated. Three‐dimensional reduction methods, namely, SVD, sparse principal component analysis, and kernel principal component analysis, are compared for their effectiveness in extracting useful features for fall and activity recognition. Experiments conducted on three public falls and activities of daily living datasets show that SVD applied to acceleration data coupled with raw acceleration data or acceleration signal magnitude vector exhibited better 1D CNN fall and activity recognition accuracy than those using other principal component analysis based acceleration features.

A smooth torque control of switched reluctance motor (SRM) is essential to avoid speed fluctuations causing stability problems in vehicular applications. This can be accomplished by an appropriate motor design and/or use of direct control of torque in SRM. It is reported that high RMS current is required to minimise the torque ripple in the conventional direct torque and flux control (DTFC), thereby reducing the torque per ampere ratio. To overcome this issue, a new DTFC technique with improved torque per ampere ratio while minimising torque ripple in an SRM traction drive is presented. Results demonstrated that the proposed DTFC technique reduces torque ripple with enhanced torque per ampere. Finally, the performance of the proposed scheme is compared with conventional DTFC of a four‐phase (8/6) SRM to show the improvement in the traction drive.

A novel high‐selective triple‐mode substrate integrated waveguide (SIW) bandpass filter using higher‐order resonant modes is proposed in this Letter. The new triple‐mode SIW resonator is realised by the second degenerate dual modes TM 210 and one perturbed higher‐order mode TM 020 in a circular SIW cavity. The resonance of TM 020 mode can be independently moved to that of dual modes TM 210 by changing the size of a floating circular patch. The proposed triple‐mode SIW filter can produce three finite‐transmission zeros (FTZs), which can also be controlled well by the angle between two feeding lines. For the demonstration, a triple‐mode SIW filter with the centre frequency of 13.5 GHz was designed, fabricated and measured. The proposed triple‐mode circular SIW filter has the merits of the high‐quality factor, high selectivity and controllable bandwidth as well as FTZs.

By means of the restricted isometry property of order k and the restricted orthogonality property of order ( k,k ), this Letter mainly establishes an improved sufficient condition for a recently emerged ‐minimisation to guarantee the robust signal recovery. The obtained condition is proved to be much better than the state‐of‐the‐art ones for almost all parameters k .

The authors report, for the first time, a novel SiGe/Si n ‐type hetero nanotube (HNT) junctionless field‐effect transistor (JLFET), which leads to a remarkably enhanced performance below the sub‐10 nm gate length. It is shown that valence band discontinuity in the HNT JLFET causes tunnelling width of the channel–drain interface to increase and therefore diminishes the lateral tunnelling of electrons in the OFF state. The impact of high‐ κ spacers and core gate diameter on the dynamic performance of HNT JLFET has also been studied. They show that the inclusion of high‐ κ spacers does not affect the dynamic performance of the HNT JLFET. It is demonstrated using calibrated 2D simulations that the proposed device exhibits a smaller value of DIBL 4 mV/V, sub‐threshold slope almost 60 mV/decade, and an improved I ON / I OFF ratio of ∼10 12 even for sub‐10 nm gate lengths.

A polarisation independent conformal absorber has been proposed for X‐band microwave application. The absorber unit cell consists of three resonators, which generate three absorption bands at 9.1, 11.04 and 11.44 GHz with more than 90% absorption. The full wave at half maximum bandwidth of the absorber is 320 and 720 MHz at lower and upper‐frequency bands. The absorber is conformal as it has a low‐profile flexible substrate with an ultrathin thickness of 0.01 λ o , where λ o is the wavelength at 9.1 GHz. The proposed absorber unit cell has a fourfold symmetry, which makes the absorber polarisation independent and possesses a wide angle stability under oblique incident angle up to 50°. The absorption performance of the absorber on various radii of cylindrically curved surface has been confirmed through the simulated and measured results.

The application of memristor in non‐linear diffusive network is introduced. A charged‐controlled memristor model is used in the quantitative study of pixel‐to‐pixel communication via a memristor. To quantitatively understand the behaviour of the system, the authors emphasised on two cells: master and slave. Information is launched from the master cell to the slave cell through a memristor and the dynamics, as well as, the saturation of the system is observed.

Pulse‐agile radar systems are becoming more prevalent as the demand for adaptive and cognitive systems increases. This focus is motivated by the need for interference avoidance and spectrum sharing. Pulse agility within a coherent processing interval (CPI) or intra‐CPI adaption has been shown to cause distortion, which will negatively impact the radar's performance. This problem can be framed in the context of image processing such that an ideal range–Doppler image is corrupted by some point spread function. Deconvolution is then applied to remove this distortion and improve radar performance while maintaining the ability to use computationally efficient fast Fourier transform‐based processing.

Subject Editor Paolo Crovetti spotlight on future information processing

The authors introduce a novel approach for swarm reinforcement learning that extends the standard Q‐learning to multi‐agent systems. State‐of‐the‐art methods implement a knowledge sharing mechanism between the agents that is triggered by the episodes succession. This causes an intrinsic limit in the convergence speed of the algorithms. They overcame this issue by developing a Q‐learning real‐time swarm algorithm (Q‐RTS), which is iteration‐based and suitable for real‐time systems. Q‐RTS was tested in different environments and compared to other related methods in the literature. They obtained positive results in terms of learning time and scalability, i.e. achieving a speed‐up factor of at least 1.49 with respect to standard Q‐learning. Moreover, Q‐RTS shows enhanced learning performance as the environments complexity increases.

In this Letter, a new construction of aperiodic Z‐complementary sequence sets (ZCSSs) is proposed. The constituent sequences of ZCSSs have odd‐length of the form (where , and are non‐negative integers). The resultant ZCSSs are optimal with respect to the Welch bound.

A new cascaded multilevel topology is proposed in this study. It is denominated single DC source quasi‐Z‐source cascaded multilevel inverter (SS qZS‐CMI). The SS qZS‐CMI performs at maximum power point tracking of the photovoltaic (PV) array with a single inverter module and each of the inverter modules shares an equal amount of the power of the whole system. The SS qZS‐CMI has the capacity to equally regulate the peak voltage on each inverter module by means of the dual control loop of the main inverter module and the shoot‐trough state of the auxiliary inverter modules, ensuring the symmetry of the cascaded multilevel inverter. Experimental results verify the proposed topology.

Non‐orthogonal multiple access (NOMA) and ambient backscatter communication are two promising techniques recommended for the fifth generation wireless network. This work combines these approaches to propose a backscatter NOMA system, which incorporates a backscatter device together with a downlink NOMA. Such NOMA employs the base station equipped with multiple antennas. To evaluate the performance of backscatter NOMA, the expressions of the outage probabilities are derived. Finally, the numerical results are provided to verify the theoretical analysis.

At present, palmprint recognition based on deep learning has been more and more widely used in identity recognition due to its many advantages. However, these algorithms often require a large amount of labelled data for training. In fact, it is difficult and expensive to get enough data that meets the requirements. In this Letter, based on a small amount of labelled images, the authors proposed a method for few‐shot palmprint recognition using Graph Neural Networks (GNNs). The palmprint features extracted by the convolutional neural network are processed into nodes in the GNN. The edges in the GNN are used to represent similarities between image nodes. The parameters in the network are continuously optimised, and finally, the category to which each image belongs is obtained. Further, they adopted a mobile phone to create a palmprint database in an unconstrained way. Adequate experiments were performed on the benchmark database and the authors’ self‐built database. The experimental results show that their proposed GNN‐based few‐shot palmprint recognition can obtain state‐of‐the‐art…

Recently an extremely linear voltage‐controlled ring‐oscillator for use in VCO‐ADCs was proposed by Babaie‐Fishani and Rombouts. In this current Letter, a circuit‐level technique to improve the bandwidth and noise performance of such a linear VCO is proposed. The key element is the modified delay cell, where the traditional cross‐coupled inverters are modified into ‘feed‐forward’ coupling inverters that pre‐charge the subsequent elements in the ring. The resulting circuit maintains the excellent linearity, but has greatly enhanced bandwidth (up to 3 times higher) and considerably reduced power for the same circuit noise level (up to 2.5 times lower).

Mobile edge computing (MEC) has been deemed as one of the key technologies for pushing powerful computing ability to the radio access network. Different scenarios require different services, and tasks usually require computing in a specific runtime environment. However, few studies have taken this into consideration. To this end, the authors propose a novel model of service‐dependent task offloading for the multiuser MEC system with resource constraints. Through determining which services should be deployed at the network edge and how many tasks should be offloaded, a revenue maximisation problem is constructed. Accordingly, they propose an iterative optimisation algorithm with high performance for the service deploying and task offloading problem. Finally, numerical simulations reveal that their proposed algorithm outperforms other schemes.

Conventional pseudo‐random number generator (PRNG) is vulnerable to machine learning (ML) attacks since algorithms are used to generate the random number. Physical unclonable function (PUF) is a kind of hardware security primitive that can also be cracked by ML attacks. However, the main security difference between a regular PRNG and a PUF is that training the output data of a regular PRNG is sufficient to break the PRNG while the challenge‐to‐response pairs of a PUF must be available for a successful training. In order to design a ML‐resistant PRNG, in this Letter, the output data of a regular PRNG is fed into a PUF to generate the encrypted data first. Then the encrypted data is added to the output data of the other regular PRNG to create the output data for the ML‐resistant PRNG. Since the input challenge of the PUF is concealed, the adversary is unable to model the PUF with ML techniques. The result shows that the training accuracy of a single output bit of the ML‐resistant PRNG is only about 52.6% even if 200,000 data are sampled for training. In contrast, only 50,000 data are…

A generic nano‐power voltage and current reference topology, which takes advantage of the unequal threshold voltage ( ) of two MOSFETs in subthreshold region, is developed to provide reliable bias and reference signals for the analogue integrated blocks used in the Internet‐of‐Things applications. The new architecture is a self‐powered four‐transistor topology with a single temperature‐insensitive resistor, generating both temperature‐independent voltage and current without any operational amplifier or bias network. Instead, the resistor defines the absolute value of the current reference ( ) which supplies the core devices. The circuit is designed and simulated for a target current reference of 7.50 nA in 0.18 µm CMOS process, and achieves a worst‐case temperature coefficient (TC) of 59.47 ppm/°C over a temperature range from −40 to 125°C and 1.8 V voltage supply. The average voltage reference ( ) is 346 mV, and the worst‐case TC of different corners is 21.98 ppm/°C. The nominal current consumption is twice the (15 nA) regardless of the supply and temperature, and can be scaled…

The authors report a waveform‐selective metasurface that operates at 2.4 GHz band, i.e. one of ISM (Industrial, Scientific and Medical) bands. This structure gives us an additional degree of freedom to control electromagnetic waves and absorbs a particular waveform or pulse width of an incident wave at the same frequency band, while transmitting others. This unique capability is demonstrated using either ideal sinusoidal waves or Wi‐Fi signals as a more practical waveform in wireless communications. Especially, this Letter shows how the waveform‐selective metasurface interacts with realistic wireless communication signals from the viewpoint of communication characteristics, such as error vector magnitude, bit error rate, and phase error. Thus, the authors’ Letter paves the way for extending the concept of waveform selectivity from a fundamental electromagnetic research field to a more realistic wireless communication field to, for instance mitigate electromagnetic interference occurring at the same frequency band without significantly degrading communication characteristics.

Intrusion detection is a prevailing area of research for several years, and numerous intrusion detection systems have been proposed for industrial control systems (ICS). In recent ages, the attacks like seismic net , duqu and flame against ICS infrastructures have instigated great harm to nuclear infrastructures and precarious facilities in several nations. The authors outline an approach to detect intrusions/anomalies in ICS. A method is presented to detect intrusions in real‐time and automatically. The existing techniques are normally designed for open systems and protocols, that lacks adequate generalisation and resistance to acclimate to other networks, and they have either short detection rate or tall rate of false positive. This Letter presents a network packet contents behaviour and bidirectional Gated Recurrent Units‐based method to detect intrusions in a timely and efficient manner. The method has proven a robust method of classifying intrusions/anomalies in a proficient way. Through extensive evaluation on an actual huge scale dataset spawned from SCADA‐based gas pipeline…

Increasing the birefringence splitting in single‐mode vertical‐cavity surface‐emitting lasers (VCSELs) enables high‐speed polarisation dynamics which can be the basis to overcome the current bandwidth limitations in short‐haul data transmission. The authors observe large birefringence splittings of up to 98 GHz in an oxide‐confined AlGaAs‐based VCSEL with a tailored integrated surface grating. Since surface gratings are routinely used in VCSEL production, there is a great potential of this technique to realise spin‐VCSELs for ultrafast optical communication.

The inclusion of organic light emitting diodes (OLEDs) in high‐end devices, such as TVs and smart‐phones, along with the insertion of cameras embedded in daily use devices, provides the opportunity to establish optical camera communication (OCC) systems based on OLED emitters for Internet of Things (IoT). This Letter presents an experimental demonstration of this OLED‐based OCC system for IoT. The results suggest that despite the low emitted power of OLED devices, long range links can be established based on OCC. One outdoor and two indoor scenarios are tested, validating BER below for short range and give just for long range links.

In this letter, to overcome the drawbacks in reconfigurable antennas and maintain all the advantages in planar antennas, a compact 12 port integrated UWB and narrow band (NB)/wideband antennas for cognitive radio MIMO applications with polarisation diversity is presented. The proposed system has one pair of UWB antennas for sensing the spectrum and five pairs of NB/wideband antennas for communication. Each pair has two identical antennas, which are orthogonal to each other for polarisation diversity. Sensing antennas linked with ports (P1 and P7) have operating bandwidth of 3–11 GHz, whereas the antennas linked with ports (P2 and P8), (P3 and P9), (P4 and P10), (P5 and P11), and (P6 and P12) have operating bandwidths of 3.5–5.8 GHz, 2.8–3.5 GHz and 5.6–8 GHz (dual band), 8–8.4 GHz and 9–9.8 GHz (dual band), 8.4–9 GHz, and 9.8–11 GHz, respectively. Moreover, the overall volume of the antenna is 58mm × 50mm × 1.6 mm and the entire UWB spectrum is covered by NB/wideband antennas. Also, without any decoupling network, isolation of better than 20 and 15 dB is achieved between every two…

A band‐stop filter based on spoof surface plasmon polaritons for microwave applications is proposed, which can realise high‐efficiency band rejections by etching gradient semi‐circular grooves on both sides of the middle stripline of coplanar waveguide. The operating bandwidth and frequency of band‐stop can be controlled by changing the radii of semi‐circular holes and the length of unit cell, respectively. The operating principle of the designed band‐stop filter is explained by the dispersion curves and electric field distributions. Parametric studies are also conducted to analyse the effects of key parameters on the performance of the band‐stop filter, which is useful for practical designs. A prototype of the band‐stop filter is fabricated and measured. The good agreements between the simulated and measured results validate the proposed design, which indicate that the presented band‐stop filter can be potentially useful in many microwave applications.

Ring oscillator physical unclonable functions (RO PUF) promise cheap, efficient, and secure identification and authentication of the chip. However, RO PUF typically has high hardware overhead, and it is difficult to guarantee its stability due to the complex operating environment. In this Letter, the programmable delay lines were utilised to configure the ring oscillator to improve the performance of PUF on FPGA. The proposed structure generates a 16‐bit reliable PUF response using only two slices. Experimental results show that the proposed PUF has low hardware overhead, and multiple measurements under a wide range of operating environments demonstrate that it is highly stable.

A commercial graphene nanoplatelets‐based tunable attenuator is proposed. The attenuator comprises of a couple of microstrip lines connected through a gap where the commercial graphene nanoplatelets are drop casted. The transmitted signal through the microstrip line can be varied by an applied DC bias voltage that alters the graphene resistance. The DC resistance of commercially acquired graphene is higher than lab‐grown graphene and so is the resulting minimum attenuation of the transmitted signal. The proposed structure is designed to reduce both the minimum graphene resistance and the transmission. The resultant dynamic range of attenuation is more than twice as compared to other series attenuators designed with lab grown graphene nanoplatelets. The operating frequency of the attenuator is from 1 to 5 GHz with maximum dynamic range of attenuation almost 10 dB.