The 50 most-cited articles in Electronics Letters, 2018

In a free‐standing 400‐nm‐thick platelet of crystalline ZY‐LiNbO 3 , narrow electrodes (500 nm) placed periodically with a pitch of a few microns can eXcite standing shear‐wave bulk acoustic resonances (XBARs), by utilising lateral electric fields oriented parallel to the crystalline Y ‐axis and parallel to the plane of the platelet. The resonance frequency of ∼4800 MHz is determined mainly by the platelet thickness and only weakly depends on the electrode width and the pitch. Simulations show quality‐factors ( Q ) at resonance and anti‐resonance higher than 1000. Measurements of the first fabricated devices show a resonance Q ‐factor ∼300, strong piezoelectric coupling ∼25%, (indicated by the large Resonance‐antiResonance frequency spacing, ∼11%) and an impedance at resonance of a few ohms. The static capacitance of the devices, corresponds to the imaginary part of the impedance ∼100 Ω. This device opens the possibility for the development of low‐loss, wide band, RF filters in the 3–6 GHz range for 4th and 5th generation (4G/5G) mobile phones. XBARs can be produced using standard…

RF fingerprinting is an emerging technology for identifying hardware‐specific features of wireless transmitters and may find important applications in wireless security. In this study, the authors present a new RF fingerprinting scheme using deep neural networks. In particular, a long short‐term memory based recurrent neural network is proposed and used for automatically identifying hardware‐specific features and classifying transmitters. Experimental studies using identical RF transmitters showed very high detection accuracy in the presence of strong noise (signal‐to‐noise ratio as low as dB) and demonstrated the effectiveness of the proposed scheme.

A four‐port MIMO antenna design focused on the sub‐6 GHz fifth generation wireless communication application is presented. The design does not need any other decoupling structure for achieving isolation between multiple ports. A combination of four single wideband antenna units results in the formation of a circular‐shaped metallic disc in the ground plane of the proposed antenna. This disc acts as a pool of current with 180° phase difference leading to isolation between various ports. Diversity performance of the antenna is shown with the help of an envelope correlation coefficient using both S‐parameter and far‐field data. The radiation pattern of the proposed antenna has four lobes in four quadrants for proper reception of signals from different directions. A prototype of the designed antenna is fabricated and measured successfully.

The authors investigate the application of deep convolutional neural networks (CNNs) to the problem of radiometric identification, i.e. the task of authenticating wireless devices on the basis of their radio frequency (RF) emissions, which contain features directly related to the physical properties of the wireless devices. They collected digitised RF from 12 wireless devices, and used various techniques to transform the time series derived from the RF to images. A deep CNN is then applied to the images. The authors' results show that the identification performance of the combination of deep CNN with an image representation significantly outperforms conventional methods based on dissimilarity on the original time series. Moreover, a specific comparison among RF‐to‐image techniques show that on their datasets the wavelet‐based approach outperforms other approaches, also in the presence of white Gaussian noise.

A new image encryption method based on permutation–diffusion architecture is proposed. Permutation and diffusion operations are performed row‐wise and column‐wise on input image. To permute and diffuse the pixels, Lorenz‐like chaotic system with varying bifurcation parameter is used to generate six random sequences. Initially, three sequences help in change the pixel’s position and next three used to diffuse the pixels. The main benefit of this method is that it is more sensitive to input image. Since input parameters required for secure key generation depend upon the input image.

The achievement of single‐channel 100 Gbit/s transmission, using linear unitravelling carrier photodiodes and QAM‐16 modulation format is reported. The wireless link has been done in the indoor case, considering the recent frequency standardised 300 GHz bands.

This Letter presents a dielectric resonator (DR)‐based multiple‐input‐multiple‐output (MIMO) antenna with bi‐directional pattern diversity. The back‐to‐back arrangement of cylindrical DR antennas DRAs (cDRAs) is one of the unique features of the proposed design. The cDRAs are placed on an FR4 substrate with a common ground plane. Each cDRA element is excited by two ports to establish a four‐port MIMO antenna system. At ports 1 and 2, the top cDRA is excited via co‐planar waveguide (CPW) fed conformal strip lines. In case of ports 3 and 4, the bottom cDRA is excited by microstrip line fed conformal strip lines. Isolation between all ports is improved (better than 18 dB) by generating orthogonal modes in the cDRAs and use of opposite excitations. Measured results confirm that the proposed four‐port MIMO antenna system is useful for the frequency ranges between 5.4 and 6.0 GHz for WLAN applications.

This Letter investigates traffic matrix (TM) prediction that is widely used in various network management tasks. To fastly and accurately attain timely TM estimation in large‐scale networks, the authors propose a deep architecture based on LSTM recurrent neural networks (RNNs) to model the spatio‐temporal features of network traffic and then propose a novel TM prediction approach based on deep LSTM RNNs and a linear regression model. By training and validating it on real‐world data from Abilene network, the authors show that the proposed TM prediction approach can achieve state‐of‐the‐art TM prediction performance.

We demonstrate, for the first time, a single section passively mode‐locked InAs/InGaAs quantum dot laser directly grown on on‐axis (001) GaP/Si substrate. The laser has a continuous‐wave threshold current of 34 mA at 20°C. By forward biasing the laser gain section current at 470 mA, 490 fs pulse generation with 31 GHz repetition rate can be obtained. This simple femtosecond pulse generation structure with CMOS fabrication compatibility makes the laser a promising light source candidate in future large‐scale silicon photonic applications.

This work explains the design and development of a low profile and compact single probe‐fed metamaterial (MTM)‐based circularly polarised (CP) antenna using the modified rectangular patch with two pairs of spiral strips and vias for 5.2/5.8 GHz WLAN applications. The intended CP antenna mainly consists of two pairs of radiators and each radiator is realised by using epsilon negative (ENG) transmission line (TL) to generate zeroth‐order resonance. CP characteristics are achieved by placing two radiators for x ‐polarised wave are orthogonally aligned to the other two radiators for y ‐polarised wave. The antenna radiating element offers a compact size of 0.24λ 0 × 0.22λ 0 with a low profile of 0.04λ 0 at 5.5 GHz. To confirm the characteristics of the intended MTM CP antenna design, the designed antenna is fabricated and measured. Measurement results show that the antenna obtains −10 dB impedance bandwidth of 610 MHz (10.86%) which is 2.3 times larger than the standard microstrip patch antenna and axial ratio bandwidth of 140 MHz (2.54%) is obtained.

With increasing markets for fingerprint authentication, there are also increasing concerns about spoofs or synthetically produced fingerprint identifications that can bypass the authentication process. In this Letter, the authors introduce a new convolutional neural networks (CNNs) architecture for fingerprint liveness detection problem that can provide a more robust framework for network training and detection than previous methods. The proposed method employs squared regression error for each receptive field without the usage of the fully connected layer. Such structure provides following advantages from the previous liveness fingerprint CNN. First, unlike the previous techniques which rely on the pre‐trained features, the proposed CNN can be trained directly from fingerprints as the loss is minimised for each receptive field. Second, in contrast to the cross‐entropy layer, the squared error layer allows them to set up a threshold value that can control the acceptable level of false positives or false negatives. Third, the absence of a fully connected layer allows them to crop the…

Steady‐state visual evoked potential (SSVEP) has been widely used in electroencephalogram (EEG)‐based brain–computer interfaces (BCIs) due to its high information transfer rate (ITR) and short training time. Current methods usually measure SSVEP from electrodes on the scalp, which is an uncomfortable and time‐consuming method. Furthermore, most research relies on expensive and non‐portable EEG devices. To utilise BCIs in daily life, however, these are critical issues to address. Hence, a wearable EEG device for in‐ear SSVEP detection is proposed. The system is 40 × 21 × 10.5 mm 3 and weighs 14.2 g, thus being light weight and wearable. Moreover, the system has a noise level of 0.11 µV rms , which is comparable with commercial EEG systems. Six subjects participated in an offline BCI experiment that consisted of six visual targets using the developed in‐the‐ear EEG system. The results showed a highest ITR of 11.03 ± 4.18 bits/min with an accuracy of 79.9 ± 13.1%, and the experiments demonstrated that the system can be utilised for unobtrusive monitoring of SSVEP in BCI applications.

Many studies have demonstrated the capability of radar micro‐Doppler signature for classifying micro‐drones. However, most existing works on radar classification of drones are based on the assumption that the received signal is only reflected from a single drone. When multiple drones are present simultaneously, the existing methods of drone classification fail due to the superimposition of the micro‐Doppler features of multiple drones. In this Letter, a method for detection of multiple drones is proposed. First the time–frequency spectrogram is converted into the cadence‐velocity diagram (CVD), which expresses how the curves in the time‐frequency‐domain repeat. Then the cadence frequency spectrum (CFS), as the basis vector of the training data from each class, of the CVD is extracted. Finally, the K‐means classifier is used to recognise the component of multiple micro‐drones based on the CFS. The experimental results on real radar data demonstrate that the proposed method is capable of dealing with multiple drones with satisfactory classification accuracy.

The performance of the effective capacity metric under Fisher–Snedecor fading channels is investigated. To this end, a novel exact closed‐form expression for the effective capacity is derived. Furthermore, in order to gain more insight, a simple asymptotic expression at the high signal‐to‐noise ratio regime is also provided. Additionally, expressions for the effective capacity of the Nakagami‐ m and Rayleigh distributions are deduced from the proposed results as special cases. The analytical results are compared to Monte‐Carlo simulations to prove the correctness of the analysis. The results show that fading has a more positive influence on effective capacity performance than shadowing.

A novel low‐profile single‐fed circularly polarised single‐layer metasurface antenna for wideband operation is proposed in this Letter. The metasurface antenna consists of nine unit cells arranged in a 3 × 3 layout. Four slits are incorporated into four of them, respectively, to form two orthogonal currents with 90° phase difference; hence, circularly polarised fields are excited. Moreover, a modified L‐type slot is etched on the middle lattice to improve impedance bandwidth and axial ratio performance. The proposed dielectric‐filled ( ɛ r = 3.5, tan δ = 0.001) antenna with a low profile of 0.038 λ 0 ( λ 0 is the working wavelength at 5.7 GHz in free space) achieves about 18.0% measured −10 dB impedance bandwidth. The measured 3‐dB axial ratio bandwidth of the proposed antenna is about 12.8% (5.35–6.08 GHz) with a broadside gain of more than 6.9 dBi.

A Fermi‐level managed barrier (FMB) diode was used for the heterodyne detection of terahertz waves for the first time. A quasi‐optical module integrating an FMB diode and a broadband trans‐impedance amplifier exhibited an intermediate frequency bandwidth of 11 GHz. A very low noise‐equivalent‐power of 1.1 × 10 −18 W/Hz was achieved at ∼300 GHz with a very low local oscillator power of 6 × 10 −6 W.

Task sequence planning (TSP) is the key factor to the efficiency, stableness, and cost of a complex assembly system. To address the issue, an adaptive quantum genetic algorithm based on artificial potential field and gradient of object function is proposed to optimise the solving process, and to obtain the optimal TSP scheme. The simulation results indicate that the proposed algorithm can perform higher efficiency and stableness than the previously reported methods.

The effective capacity of a communications system using unified models is analysed. To obtain a simple closed‐form mathematically tractable expression, two different unified approximate models have been used. The mixture gamma distribution which is a highly accurate approximation approach has been first employed to represent the signal‐to‐noise ratio of fading channel. In the second approach, the mixture of Gaussian distribution which is another unified representation approach has been utilised. A comparison between the simulated and numerical results using both distributions over composite /gamma fading channels have been provided.

A hollow‐waveguide‐output uni‐travelling‐carrier photodiode (UTC‐PD) module operating at frequencies from 400 to 900 GHz has been developed. The module consists of a UTC‐PD, a photodiode‐to‐waveguide coupler, and a metallic package with a waveguide rectangular (WR)‐1.5 rectangular waveguide. The coupler is monolithically integrated with the UTC‐PD chip. The fabricated module exhibits the output power as high as −19 dBm at 500 GHz and the 3 dB bandwidth of 340 GHz, which is the widest among ever‐reported photodiode modules.

In this Letter, the authors present a new analytical method for determining the parameter values for the single‐diode model of photovoltaic (PV) panels. More specifically, the authors propose explicit equations for all the parameters of the model so that their values can be directly extracted from the data provided in the PV panel datasheet. The results show that the proposed method provides smaller errors between the calculated and experimental I–V curves than other analytical approaches.

With the increasingly multiple‐input multiple‐output (MIMO) applications in ultra‐wideband (UWB) communication systems, antenna researchers face big challenges in designing compact operational geometries that meet the essential demand of achieving high isolation among antenna elements over the ultra‐wide operating bandwidth. Disposed antenna elements orthogonally are seen to be the most common methodology to reduce mutual coupling of MIMO antenna by exploiting polarisation diversity performance. In such configuration, the mutual coupling mainly depends on the inter‐element spacing, which it may not be in line with the compact structure. In this Letter, taking the advantages of symmetry of planar UWB antennas, asymmetric feeding scheme miniaturising technique is utilised to improve the inter‐element isolation of a reference MIMO antenna made up of four previously designed slot antenna elements, closely‐disposed orthogonally. Analytical results have validated the design concept and the improved MIMO antenna using the halved‐chopped elements, showing good performance in terms of…

A compact dual‐band filtering power divider (FPD) is presented based on substrate‐integrated waveguide (SIW) triangular cavities (TCs). By exploiting the first two modes in SIW TCs, the FPD is synthesised and designed with centre frequencies of 5.5 and 8.3 GHz and identical absolute bandwidths of 0.8 GHz. Two‐section 50‐Ω transmission lines loaded with two resistors are explored to achieve good isolation at two arbitrary frequency bands of the dual‐band PFD. Good agreements can be observed between the measured and simulated results and better than 20‐dB isolation within the two passbands has been successfully achieved.

A new selected mapping orthogonal frequency division multiplexing modulation (SLM‐OFDM) that generates symbol candidates using U inverse fast Fourier transform is presented. The complementary cumulative distribution function of peak‐to‐average power ratio (PAPR) of the so‐called GreenOFDM is derived and computer simulations show that the proposed method outperforms any other SLM‐OFDM proposed method so far. Also, GreenOFDM is compared with localised single carrier frequency division multiple access as it is a well‐known PAPR reduction technique standardised for long‐term evolution advanced.

Outage events caused by dynamic blockage of a radio signal propagation path are one of the key challenges in 5G millimetre‐wave (mmWave) cellular networks. To mitigate them, Third Generation Partnership Project standardisation has recently ratified multi‐connectivity techniques aiming to enable user connectivity to several base stations simultaneously, while switching between them whenever the currently active connection becomes blocked. A closed‐form upper bound on the probability density function of the respective system capacity in a random field of moving blockers is obtained.

A record output power of 16.1 W with a direct‐bonded dual‐SiC‐heatspreader distributed Bragg reflector (DBR)‐free active region at 10.5°C coolant temperature is reported. A comparison in laser performance confirms the dual‐heatspreader DBR‐free configuration dissipates heat more effectively than the single‐heatspreader geometry.

We propose an all‐optical switch based on a microfibre Mach–Zehnder interferometer (MMZI) in which the MMZI is considered with a microfibre loop resonator (MLR) in one arm of it. The authors numerically demonstrate that the enhanced phase shift of the MLR near its resonance wavelengths can be used for constructive/destructive interference and switching functionality of the MMZI. The calculated switching threshold power of the switch is about 2 mW, which can be further reduced by the use of an MLR with more finesse, and the rising and falling times are computed with 21 and 91 ps, respectively. Natural connection to silica single mode fibres, easy configuration and high speed make it as a suitable choice for all‐optical signal processing and communications applications.

This Letter demonstrates design, simulation, fabrication and performance of a metamaterial (MTM) absorber having wide incident angle insensitivity for conformal applications in X‐band region. The important feature of the proposed structure is achieving more than 90% absorptivity with very low thickness. In this design, an FR4 material having thickness 0.1 mm is used as a substrate. Hence, the overall thickness of the proposed MTM absorber is only 1/81 of the wavelength at the resonance frequency of 9.2 GHz. Also, the presented absorber is offering more than 80% absorptivity up to 50° incident angle which is very much suitable for conformal applications where curved surfaces are involved. Designed MTM absorber has been fabricated and simulation results are experimentally verified.

An optimised power control with extended phase shift (OPC‐EPS) for dual‐active‐bridge (DAB) dc–dc converters is proposed to improve the efficiency and dynamic performance simultaneously. By combining the current stress optimised calculation with direct power control, the smaller current stress and higher efficiency can be achieved compared to the traditional extended phase‐shift scheme, and the dynamic response of DAB converters can be significantly improved under the input voltage fluctuation or load disturbance conditions. Meanwhile, the OPC‐EPS scheme has strong robustness and it has no dependence on the circuit parameters. Finally, experimental results have verified the excellent performance of proposed scheme and the associated analysis in this Letter.

This Letter proposes a low‐cost, single event double‐upset tolerant latch which utilises interlocked nodes to keep data, clock gating (CG) in Muller C‐element (MCE) to turn off the storage cell, a three‐input MCE to block the soft error from the storage cell and a weak keeper to prevent high impedance state. The storage cell in the proposed latch has better reliability than the conventional triple path dual‐interlocked storage cell (TPDICE). Most up‐to‐date single event double‐upset (SEDU) tolerant latches are carried out with too large cost penalties. The proposed one saves up to 93.32% area‐power‐delay product (APDP) compared with one up‐to‐date SEDU tolerant latch and even saves 36.36% APDP compared with only single event upset (SEU) tolerant latch in the referential. Simulation results have verified SEU and SEDU tolerance of the proposed latch.

The letter deals with the methodology for determining the optimal number of phases of a multi‐phase DC to DC buck converter from the point of view of its maximum efficiency. It also analyses the impact of individual parameters of the converter and the used components on the number of these phases.

Folding band sharpening of the cascaded‐integrator‐comb filter results in a high passband droop. In applications requiring low passband deviation, the droop is reduced by connecting a low‐order FIR compensator in cascade with the filter. In this Letter, the authors present a method for optimum design of compensators whose coefficients are expressed as sums of signed‐power‐of‐two terms. The method is based on the minimisation of passband deviation, with specified total number of terms.

A method for horizon detection in maritime scenes using a scene parsing network is proposed. First, each pixel from an input image is segmented into corresponding semantic categories using a scene parsing network, which relies on a deep neural network. Then, the boundary information related to the horizon and the sea is extracted. Scene segmentation allows the proposed method to identify the horizon, regardless of whether the boundary between the sea and sky is smooth or blurry, or whether the image contains many line elements like the horizon. Moreover, least squares and median filtering are iteratively used to retrieve an accurate estimation of the horizon line. Experimental results demonstrate the superior accuracy of the proposed method to identify the horizon when compared to state‐of‐the‐art methods.

A novel transmission scheme called fully generalised spatial modulation (FGSM) is proposed for underwater communication, where any subset of available transmitting antennas ( N t ) is activated at a time instant to transmit the data constellation symbol and the index of the active antenna is also harnessed to carry information. The FGSM offers better energy efficiency (EE) than previous spatial modulation (SM) and generalised SM systems. The proposed FGSM system is tested in an acoustic underwater multipath channel. Simulation results show that it can significantly improve the average bit error rate (ABER) as well as EE.

To date, the authors are not aware of an in‐depth investigation about embedded applications of the convolutional neural network (CNN) algorithm on small, lightweight, and low‐cost hardware (e.g. microcontroller, FPGA, DSP, and Raspberry Pi) applied to detect faults in structural health monitoring (SHM) systems. In this Letter, the authors implement and evaluate both feasibility and performance of an embedded application of the CNN algorithm on the Raspberry Pi 3. The CNN‐embedded algorithm quantifies and classifies dissimilarities between the frames representing healthy and damaged structural conditions. In a case study, the CNN‐embedded application was experimentally evaluated using three piezoelectric patches glued onto an aluminium plate. The results reveal an impressively effective 100% hit rate. This performance may significantly impact the design and analysis of CNN‐based SHM systems where embedded applications are required for identifying structural damage such as those encountered by aerospace structures, rotating machineries, and wind turbines.

A miniaturised coplanar waveguide‐fed multiple notched monopole antenna for ultra‐wide bandwidth (UWB) application is presented. By introducing multiple inverted L‐shaped stubs embedded within a polygonal shaped monopole antenna, multiple notches can be achieved. A prototype antenna with triple band‐notched at WiMAX, WLAN, and X‐band is designed and fabricated. The proposed antenna has an impedance bandwidth of 3–12 GHz with a voltage standing wave ratio of <2 except for the selected notched bands. The main advantage of the antenna is its miniaturised size (21 × 14 mm 2 ), as well as the straightforward design. The antenna has a unipolar configuration and good omnidirectional radiation pattern with negligible distortion which is suitable for UWB applications.

The quest continues for microelectronic implementations with higher throughput and reduced power consumption, particularly for digital signal processing, graphic processing unit and CPU portable applications. This Letter focuses on the digital multiplier circuit, which is a key component in determining the power‐delay‐product for numerous battery powered applications. A proposed radix‐4 8 × 8 Booth multiplier is implemented using four stages with a unique optimised stage‐1 architecture. Instead of using adder/subtractor in stage‐1, it is replaced with a novel binary‐to‐2's complement converter and a 2:1 MUX to reduce the delay and power consumption by 7.08 and 49.46%, respectively, compared to the other stages. The proposed design is implemented using CMOS 90 nm technology with 1.2 V supply to demonstrate performance.

A new step‐up DC–DC converter is presented, based on quasi‐Z‐source network intended for photovoltaic applications. The proposed converter combines voltage multiplier cells to the secondary winding of the coupled inductor which is included in the second inductor of the quasi‐Z‐source network. In the output of the quasi‐Z‐source network, a switched capacitor is connected. This converter shows attractive characteristics such as high voltage gain, low voltage stresses on their components, continuous input current. A detailed description of the operating principles of the proposed converter is presented and experimental results on a 250 W prototype show that a high efficiency above 91.4% can be achieved.

Systems for counting vehicles should be fast enough to be implemented in real‐time situations. Most of the related work uses two stages for vehicle counting, vehicle detection and tracking, which increase the computational complexity. In this Letter, a fast and efficient approach for vehicle counting is proposed, where there is no need for the vehicle tracking step. A background model is created only for a narrow region, a line, in the video frames. The moving vehicles are detected as foreground objects while passing this narrow region. Morphological processes are applied to the extracted objects to enhance them and decrease the effects of vehicle occlusions. Finally, an efficient counting vehicles method is introduced employing only the extracted detection information. The experimental results performed on diverse videos show that the proposed method is fast and accurate. The average execution time per frame is 7.78 ms.

The authors demonstrate a broadband, heterogeneous terahertz frequency quantum cascade laser by exploiting an active region design based on longitudinal optical‐phonon‐assisted interminiband transitions. They obtain continuous wave laser emission with a threshold current density of ∼120 A/cm 2 , a dynamic range of ∼3.1, and an emission spectrum spanning from 2.4 to 3.4 THz at 15 K.

Broadband circularly polarised square slot antenna excited by a coplanar waveguide feed with enhanced axial ratio bandwidth (ARBW) is proposed, designed and experimentally studied. Larger than 21% 3 dB ARBW can be attained by using asymmetric feed and implementing a T‐shaped grounded stub from the left side of the square slot in orthogonal direction towards the slot centre. To further enhance the 3 dB ARBW of the proposed slot antenna, a pair of equal grounded L‐shaped strips with different sizes is embedded at the top right corner of the square slot. Small L‐shaped grounded strip plays an important role for merging two closely spaced multi‐resonant modes, generated by the combined effect of asymmetric feed with T‐shaped grounded stub and with large L‐shaped strip. Overall size of the proposed antenna is 40 × 40 × 1.6 mm 3 . Measured value shows that the impedance bandwidth and 3 dB ARBW of the designed antenna are 73.39% (5.02–10.84 GHz) and 58.08% (5.07–9.22 GHz), respectively. Good agreement is achieved between simulated and measured results.

Three types of commercially available conductive three‐dimensional (3D) printing filament are electrically characterised for use in 3D‐printed functional devices. The three plastics were carbon dispersed acrylonitrile butadiene styrene, carbon dispersed polylactic acid (PLA) and graphene dispersed PLA. The method of 3D printing used was material extrusion and prints were made in both single and dual extrusion modes. The plastics were found to be piezoresistive, enabling them to be characterised as strain sensors. The electrical characteristics of these materials enabled the measurement of strain using low cost, readily available prototyping equipment and minimising the requirement for dedicated instrumentation components (e.g. Wheatstone bridges). Increasing the thickness of the plastics improved conductivity. However, this also decreased the reliability and reproducibility of strain sensor data due to a complex internal 3D structure. The recommendation for reliable use in prototyping and manufacturing is to print tracking under 0.8 mm thickness, thus producing resistance…

Wireless multimedia sensor networks (WMSNs) have been proposed for use in many challenging applications, such as military surveillance, wildlife tracking, and security monitoring. Reducing energy and storage space consumption are challenging in WMSNs. To address this issue, the authors propose a novel low‐duty‐cycle WMSN (LWMSN) based on Wi‐Fi. This special WMSN is especially suitable for security monitoring, which involves long invalid times in which humans do not appear in the target area. The LWMSN can be intelligently switched on and off by human detection based on channel state information provided by Wi‐Fi products. The authors evaluated their design with a simulation and an experiment. Results show that the accuracy of human detection can be >97% on average. In addition, energy and storage space consumption are reduced by 53 and 40%, respectively.

The Gini index is a statistical dispersion metric widely used in economic and social sciences to measure inequalities. In this Letter, it is used to build the novel Gini index detector (GID) for cooperative spectrum sensing. The GID is blind, is robust under unequal and dynamical noise and signal powers, suits to line‐of‐sight channels with mild dominant component (the need for dominance is relaxed if the number of primary transmitters increases), has the constant false alarm rate property, outperforms state‐of‐the‐art robust detectors, and is one of the simplest detectors devised so far.

A novel substrate integrated waveguide (SIW) cavity‐backed self‐triplexing slot antenna, consisting of a hybrid SIW cavity resonator is proposed for tri‐frequency operation. The hybrid cavity resonator is an amalgamation of a half‐mode circular and half‐mode rectangular SIW cavity resonator. A radiating slot is etched on its top surface, which produces three distinct resonant frequencies (5.57, 7.17 and 7.65 GHz) when it is excited by three microstrip lines. The lower band around 5.57 GHz is achieved due to a half‐mode circular cavity resonator, when the corresponding microstrip line is excited. On the other hand, remaining two bands around 7.17 and 7.65 GHz are achieved due to half‐mode rectangular cavity resonator when excited by the corresponding microstrip lines. The experimental isolation level between any two feed lines is better than 20 dB, which helps to introduce the self‐triplexing phenomenon. Moreover, the proposed design is realised on a single‐layered copper‐laminated dielectric substrate, maintaining planar configuration.

A quasi‐elliptic bandpass filter has been designated based on substrate integrated waveguide cavity and parallel‐coupled microstrip line (PCML). Two PCMLs are utilised to provide cross‐coupling at both sides of the investigated filter. Electrical coupling intensity in the filter can be controlled by the proposed PCMLs which generate transmission zeros at sides of pass‐band. Sharp sideband and significant out‐of‐band rejection are achieved.

Flexible electronics combined with new materials and fabrication processes offer unique characteristics such as mechanical flexibility, thin‐form factor, large area scaling feasibility, and adaptability to irregular surfaces. In this work, a smart electronic skin adopting the hybrid system‐in‐foil concept is designed to monitor the uniaxial bending of a robotic gripper. The newly designed smart skin contains an array of printed strain gauges, organic thin‐film transistor (TFT) addressing circuits and a 20 μm ultra‐thin silicon readout chip, all integrated on the same polymeric foil. The silver‐ink printed strain gauges achieve a relative resistance sensitivity Δ R / R of 2% and a gauge factor of 2. In addition, the organic TFT multiplexer containing a three‐stage shift register and analogue switches operate at a frequency of 100 Hz and a supply voltage of 3 V. The ultra‐thin silicon chip provides the functions of system control, strain gauge readout, analogue‐to‐digital conversion and serial communication.

A novel residual‐error prediction method based on deep learning with application in lossless image compression is introduced. The proposed method employs machine learning tools to minimise the residual error of the employed prediction tools. Experimental results demonstrate average bitrate savings of 32% over the state‐of‐the‐art in lossless image compression. To the best of the authors’ knowledge, this Letter is the first to propose a deep‐learning based method for residual‐error prediction.

In this letter, a quintuple‐mode bandpass filter for a UWB system with improved performance is presented. The presented filter is implemented with asymmetric parallel‐coupled lines loaded open stub and short stub connected at the symmetrical plane of the filter to increase its frequency selectivity. Five resonant frequencies within the UWB band and two transmission zeros at the lower and upper passband/stopband edges are observed. A filter prototype is fabricated for verification and the experimental data are corresponding well with the simulated results. The proposed filter achieves a bandwidth that can exactly cover the whole UWB frequency band. Moreover, this filter has a compact size (0.645 λ g × 0.318 λ g ) and low insertion loss.

A 28 GHz 5‐bit switch‐type phase shifter (STPS) using 0.18 μm CMOS technology is presented for 5G mobile communication applications. Utilising a process variation insensitive transmission line‐based bridged T‐type topology for 11.25°, 22.5°, 45°, 90° 1‐bit phase shifters and high‐pass/low‐pass network switched‐path‐type topology for 180° 1‐bit phase shifter, the 5‐bit STPS achieves ultra‐low root mean square (RMS) phase error of 1.7° and low RMS amplitude error of 0.59 dB at 28 GHz with intrinsic digital phase‐control mechanism. The measured insertion loss of all 32 states is 15 ± 1.5 dB at 28 GHz with zero dc consumption.

A method to reduce the mutual coupling in wide‐band multilayer patch array operating in C band is presented. The proposed device use conveniently sized meander line parasites printed on the same substrate of the upper patch. Measurements on a prototype shows a measured bandwidth of about 19.6% centred at 5.1 GHz, therefore adequate to cover the whole WLAN frequency range. The meander lines allow to reduce the patch mutual coupling by about 2.4 dB.