Showing papers in "Electronics Letters in 2017"

Multi-Watt high-power THz frequency quantum cascade lasers

Abstract: Multi-Watt high-power terahertz (THz) frequency quantum cascade lasers are demonstrated, based on a single, epitaxially grown, 24-μm-thick active region embedded into a surface-plasmon waveguide. The devices emit in pulsed mode at a frequency of ~4.4 THz and have a maximum operating temperature of 132 K. The maximum measurable emitted powers from a single facet are ~2.4 W at 10 K and ~1.8 W at 77 K, with no correction being made for the optical collection efficiency of the apparatus, or absorption by the cryostat polyethylene window.

Compact four-element SRR-loaded dual-band MIMO antenna for WLAN/WiMAX/WiFi/4G-LTE and 5G applications

Abstract: A four-element dual-band MIMO configuration consisting of split-ring resonator (SRR)-loaded inverted L-monopole antenna elements is realised. In the proposed antenna, the lower-frequency mode of the unloaded MIMO configuration merges with one SRR-induced antenna resonance. This leads to antenna operation around 2.93 GHz with wide impedance bandwidth (IBW) of 35.21%, encompassing the lower WLAN, worldwide interoperability for microwave access, wireless fidelity, fourth generation (4G)-long-term evolution and sub-6 GHz 5G bands. Furthermore, due to SRR loading, the proposed MIMO antenna exhibits a resonance at 5.68 GHz (IBW 6.86%), covering the upper WLAN band. Minimum inter-element isolation of 14 dB is achieved, in spite of the compact total area ( 0.103 λ 0 2 , λ 0 = highest operating wavelength) and the presence of inter-connected ground plane. Both the working bands exhibit directional radiation patterns with average gain ≈ 4 dBi . Experiments on the fabricated antenna prototype confirm that the simulated and measured S-parameters, radiation patterns (envelope-correlation coefficient, channel capacity loss and total active reflection coefficient) are in good agreement.

Facial expression recognition with FRR-CNN

Abstract: Feature redundancy-reduced convolutional neural network (FRR-CNN) is proposed to address the problem of facial expression recognition. Different from traditional CNN, convolutional kernels of FRR-CNN is induced to be divergent by presenting a more discriminative mutual difference among feature maps of the same layer, which results in generating less redundant features and yields a more compact representation of an image. Furthermore, the transformation-invariant pooling strategy is used to extract representative features cross-transformations. Extensive experiments are conducted on two public facial expression databases and the obtained results demonstrate the efficiency of FRR-CNN comparing with the state-of-the-art expression recognition methods.

Mu-negative metamaterial filter-based isolation technique for MIMO antennas

Abstract: In this Letter, a mu-negative metamaterial (MTM) filter-based novel decoupling technique is presented for multiple input multiple output (MIMO) antennas. The design process has been described in a systematic manner, starting with the basic two port monopole antenna and then adding cancellation network and finally the proposed MIMO antenna by adding the matching network. Since the presented decoupling network is developed using MTM structure, good isolation between the antennas is achieved by maintaining compactness. The presented isolation technique can be used in different applications like in developing circularly polarized and multi-band MIMO antennas. As an example, two port circularly polarised MIMO antenna design is also presented. The proposed designs have been fabricated and the simulation results are experimentally verified.

Improved DOA estimation algorithm for co-prime linear arrays using root-MUSIC algorithm

Abstract: The problem of direction of arrival (DOA) estimation with co-prime linear arrays is researched. An improved DOA estimation algorithm based on root-multiple signal classification (MUSIC) is proposed. The method can solve the matching error problem in Sun's algorithm. In addition, it can make full use of signal space and noise space to improve the estimation accuracy with low complexity. Experimental results verify the validity of the proposed algorithm.

Chaotic bursting in memristive diode bridge-coupled Sallen-Key lowpass filter

Abstract: This Letter reports the finding of a point-cycle chaotic bursting phenomenon in a simple third-order memristive diode bridge-coupled Sallen-Key lowpass filter (LPF). By parallel coupling a generalised memristor composed of a diode bridge and an inductor into a Sallen-Key LPF a simple third-order memristive chaotic oscillator is established. With the modelling of this oscillator, stability analyses, numerical simulations and hardware experiments are performed, upon which the striking point-cycle chaotic bursting phenomenon is well demonstrated and effectively validated.

3D printed 1.1 THz waveguides

Abstract: For the first time, 3D printed metal-pipe rectangular waveguides (MPRWGs) have been demonstrated in the WM-380 (500-750 GHz) and WM-250 (750 GHz-1.1 THz) waveguide bands. The ultra-high spatial resolution offered by the new RECILS additive manufacturing technology enables the precision fabrication of these prototype MPRWGs at such high frequencies. This enabling technology avoids the need for access to expensive microfabrication resources and, thus, opens up the terahertz spectrum to the low-cost manufacture of passive components.

Low mutual coupling antenna array for WLAN application

Abstract: A mutual coupling reduction antenna design for WLAN MIMO application is proposed. The proposed antenna array consists of two rectangular patch antennas, six parallel metal strips, a single substrate layer, and common ground plane. About −42 dB mutual coupling is achieved at the 5.8 GHz resonant frequency. Both simulation and measurement results confirm improvements in mutual coupling at about 30 dB when compared with those without metal strips. The radiation patterns are almost unaffected by adding these metal strips in the proposed antenna.

Compact transmission-type negative group delay circuit with low attenuation

Abstract: A novel circuit is presented for the design of transmission-type negative group delay circuit (NGDC) with low signal attenuation. By loading a lumped resistor at a specific point on the loose-coupling microstrip (MS) resonator, a lossy coupled-line resonator is proposed, the size of which is effectively reduced by employing an open radial patch. A cascaded two-stage NGDC scheme is presented to realise an enhanced negative group delay (NGD) value and better reflection coefficients. The layout of the two-stage NGDC is designed in an anti-symmetrical back-to-back manner. To validate the performance of the proposed circuit scheme, a prototype of the two-stage NGDC has been designed, the working bandwidth of which is 35 MHz with a centre frequency of 1.79 GHz. This circuit is fabricated on Rogers RO4350B substrate with a thickness of 20 mil. A measured maximum NGD of −7.7 ns and a corresponding signal attenuation of as low as 8.6 dB have been obtained. Reflection coefficients are better than −20 dB. This NGDC occupies a compact size of 0.3λ g × 0.18λ g, which is much smaller compared to the previously reported NGDCs with distributed elements.

Robust visual tracking via self-similarity learning

Abstract: Self-similarity is an attractive image property that has been successfully applied to object recognition due to its robustness to severe target appearance variations. However, less attention has been paid to explore self-similarity for visual tracking, mainly because it is difficult to learn self-similarity information between different features suitable for visual tracking. To address this issue, a simple, yet effective approach is presented to learn self-similarity information among the local features extracted from the different regions of the target. The target is first divided into some non-overlapping regions, in which each region is described by the histogram of gradient (HOG) features. Then, an explicit polynomial kernel feature map is constructed, which is capable of characterising the self-similarity information among all the local regions in the targets. Finally, based on the feature maps, a linear support vector machine (SVM) is learnt via an online dual coordinate descent method that offers fast convergence guarantee. Experiments on a large tracking benchmark dataset with 50 sequences demonstrate the superiority of the proposed method over state-of-the-art methods.

Effective software-defined networking controller scheduling method to mitigate DDoS attacks

Abstract: To improve the availability of the software-defined networking (SDN) under distributed denial of service (DDoS) attacks, a multi-queue SDN controller scheduling algorithm based on time slice allocation strategy is proposed. The proposed algorithm can take different time slice allocation strategies according to the intensity of DDoS attacks and use SDN controller to schedule processing flow request from different switches (including the switches suffering from different degrees of attacks and normal switches) to ensure better protection to the normal switch in the network under DDoS attacks. Simulation results are presented to show the effectiveness of the proposed algorithm.

Deep-learning-based license plate detection method using vehicle region extraction

Abstract: A new license plate detection method for challenging environments is proposed. Background clutters are common in road scene images and the detection of license plates (occupying only a small part of an image) is considered as a difficult problem. In order to address this problem, a two-step approach is developed: first vehicle regions are detected and the license plate in each vehicle region is localised. This vehicle region detection based approach provides scale information and limits search ranges in license plate detection, so that one can reliably detect license plate regions. To be precise, the faster region-based convolutional neural network algorithm for the vehicle region detection is adopted and candidates for license plates in each detected region with the hierarchical sampling method are generated. Finally, non-plate candidates are filtered out by training a deep convolutional neural network. The proposed method is evaluated on the Caltech dataset and the method showed a precision of 98.39% and a recall of 96.83%, which outperforms conventional methods.

Speech enhancement based on mEMD-VMD method

Abstract: A novel and effective speech enhancement method is proposed for suppressing the white noise as well as non-stationary acoustic noises. The proposed method employs the combination of variational mode decomposition (VMD) and empirical mode decomposition (EMD) methods. In this method, first EMD is used to decompose the noisy speech signal into intrinsic mode functions (IMFs). Further, the VMD is applied on summation of selected IMFs. The main contribution of the proposed method is the selection of IMFs based on Hurst exponent and further applying steps of VMD method. The proposed modified EMD-VMD (mEMD-VMD) method is suitable to reduce the low-frequency noise as well as high-frequency noise. The proposed method gives the better results in terms of speech quality and composite measures. The proposed study is performed on eight speech signals under additive white Gaussian noise, street noise, babble noise, and airport noise taken from NOIZEUS database.

Internet of animals: characterisation of LoRa sub-GHz off-body wireless channel in dairy barns

Abstract: Advances in wireless sensor technologies and MEMS have made it possible to automatically monitor the health status of dairy cows using Internet of things (IoT) and wireless body area networks. Since on-cow measuring devices are energy constrained, a proper characterisation of the off-body wireless channel between the on-cow sensor nodes and the back-end base station is required for an optimised deployment of these networks in barns. In this Letter, the long range (LoRa) off-body wireless channel has been characterised at 868 MHz, a typical IoT frequency. Both path loss and temporal fading were investigated using LoRa motes. Based on this characterisation, network planning and energy consumption optimisation of the on-body nodes could be performed, which enables the deployment of reliable dairy cow monitoring systems.

Compact dual-band microstrip filtering power divider using T-junction structure and quarter-wavelength SIR

Abstract: This Letter presents a design of microstrip filtering power divider for dual-band application. The proposed dual-band filtering power divider is based on the traditional Wilkinson power divider and employs T-junction structures and quarter-wavelength stepped impedance resonators (SIRs) to realise dual-band power allocation and bandpass response simultaneously. The design process is simple and effective. For validation, a dual-band microstrip filtering power divider with centre frequencies of 0.9 and 2.1 GHz for the GSM and WCDMA applications is designed, fabricated and measured. The measured results indicate that the proposed dual-band filtering power divider showcases low-loss characteristics, high isolation as well as good selectivity.

Multi-level deep neural network for efficient segmentation of blood vessels in fundus images

Abstract: The exact blood vessel trees segmented from fundus images provide important information required for screening and following-up of diabetic retinopathy and age-related macular degeneration. The trained deep neural network presents an automated prediction of the blood vessels in retinal fundus camera images in the publicly DRIVE database with accuracy up to 0.9533 and area under the receiver operating characteristic curve up to 0.9752, which is better than manual recognition by expert human eyes. A resizing technique is introduced and applied to the multi-level network combining dropout and spatial-dropout layers to obtain more generalised training. The proposed model has the potential for the classification of other types of images.

Ka-band compact and high performance bandpass filter based on multilayer air-filled SIW

Abstract: A substantial reduction of Substrate Integrated Waveguide (SIW) insertion loss can be achieved through the use of air as dielectric instead of usual dielectric material. However, Air-Filled SIW (AFSIW) circuits exhibit larger footprint compared to their dielectric-filled counterparts. In this letter, a compact multilayer AFSIW bandpass filter is proposed to realize both high performance and small footprint. For demonstration purpose, a Ka-band multilayer 4th order AFSIW bandpass filter has been designed and fabricated. Measured and simulated results are in good agreement. Retro-simulations, taking into account fabrication tolerances, are also presented. Finally, a performance comparison with other multilayer technologies is presented.

Fast transient control for power adjustment in a dual-active-bridge converter

Abstract: A transient control for a dual-active-bridge (DAB) dc/dc converter to realise power adjustment in a fast and smooth way is proposed. The converter is able to transfer power between two dc sources with two phase-shifts as control variables. To eliminate the possible high-current overshoot and non-zero dc-bias current, the adjustments of the two phase-shifts are distributed to the gating signals of different switch arms according to a ratio x, which has an universal expression for any transitions among different operation modes in a DAB converter. Experimental results have proved the validity of the proposed transient control in elimination of current overshoot and dc-bias current.

Isolated switched-boost push–pull DC–DC converter for step-up applications

Abstract: A high voltage ratio DC–DC converter is proposed which is comprised of four stages. First, an impedance network along with a switching network have been used to boost the input voltage. The boosted voltage waveform is then followed by an isolation transformer to provide another degree of freedom and obtain higher boost ability. Finally, a voltage multiplier rectifier is utilised to rectify the secondary voltage of the transformer. No switching dead‐time is required, which increases the reliability of the converter. The proposed converter benefits from the continuous input current. Besides, a comparison with the existing step‐up topologies indicates that the number of passive elements and hence the weight and size have been reduced. The operating principles were analysed and the experimental tests on a 260 W prototype reveal that a high efficiency above 91% can be achieved.

Triple band-notched UWB monopole antenna on ultra-thin liquid crystal polymer based on ESCSRR

Abstract: A triple band-notched UWB monopole antennas is presented for flexible electronics. To enhance the flexibility, ultra-thin liquid crystal polymer with 50 μm thickness is used as the substrate. The antennas are constituted by swallow tail radiation patch and trapezoid ground. Moreover, band-notched characteristic is realised by etching different sized elliptic single complementary split-ring resonators on the radiation patch. An improved triple band-notched UWB antenna with notched-frequency bands at 3.7–4.2 GHz, 5.15–5.35 GHz, and 5.725–5.825 GHz are designed by a novel capacitance compensation method. The measured radiation patterns indicate that the antennas are an omni-directional antenna both at flat and bent circumstances. The occupied area of antenna is 27 × 21 mm.

Low RCS and high-gain CP microstrip antenna using SA-MS

Abstract: A shared aperture metasurface (SA-MS) is proposed to achieve the wideband radar cross-section (RCS) reduction and gain enhancement of a circularly polarised (CP) microstrip antenna simultaneously. The SA-MS is composed of a wideband polarisation conversion surface and a partially reflecting surface (PRS). A 180° phase difference can be obtained by the polarisation conversion surface, which results in a wideband RCS reduction in normal incident direction. The Fabry–Perot resonator cavity is constructed by the PRS and the metallic ground of the CP microstrip antenna to enhance the gain. Experimental results show that the gain enhancement reaches 1.15 dB around the operating band and a wideband RCS reduction is obtained in the frequency range of 9–17 GHz, in which the average RCS reduction is 10.9 and 10.68 dB for dual polarisation in the normal incident direction.

Sliding mode control with sigmoid function for the motion tracking control of the piezo-actuated stages

Abstract: A Bouc–Wen model is presented and identified based on the bat-inspired algorithm to describe the hysteresis of the piezo-actuated stage. Based on the established Bouc–Wen model, a sliding mode controller is proposed to suppress the hysteresis non-linearity of the piezo-actuated stages. In order to solve the buffeting problem in the process of control, the sign function is replaced by the sigmoid function. Experiment is performed to validate the effectiveness of the proposed sliding mode controller, and the results show that the maximum error of the motion tracking control of the piezo-actuated stage is 0.3264 μm.

UAV-assisted content-based sensor search in IoTs

Abstract: ‘Internet of things’ (IoT) operates for all-time availability of network components to provide a wide range of service applications to the network users or clients. IoT operates for a large number of applications, and one of these include the sensor deployment for data support to clients. However, these sensors require a large number of queries to be handled by the network components considering the constraints of memory, energy, and delays. These issues can be easily tackled by deploying unmanned aerial vehicles (UAVs), which serve as dynamic nodes to handle clients’ queries by acting as on-demand gateways. However, this UAV-assisted IoT requires efficient localisation to determine the sensor for handling multiple-content queries, which is considered as a problem. A cost function is formed in the proposed approach to generate an optimisation problem which is resolved using a radial basis function kernel support vector machine. The effectiveness of the proposed approach is demonstrated in terms of significant gains attained in terms of error in the cost function, overheads in handling queries, and accuracy in UAV allocation.

Flexible and stretchable 3D printed passive UHF RFID tag

Abstract: The fabrication and analysis of a flexible and stretchable 3D printed passive ultra-high frequency (UHF) radio-frequency identification (RFID) tag are presented. The tag is fabricated on a flexible 3D printed Ninjaflex substrate and the conductive part of the tag consists of stretchable silver conductive paste dispensed with direct write method. The details of the 3D printing of the substrate, the characterisation of the substrate material at the UHF band, the direct write dispensing of the tag antenna, and the simulation and wireless measurement results of the fabricated tag are outlined. Moreover, to verify the flexibility and stretchability of the tag, strain reliability results of the tag are presented. Measurement results show that initially the manufactured tag achieves a 10.6 m read range. After 100 times of harsh stretching, the read range is still 7.4 m. Overall, the performance of the tag is robust and concludes that the fabrication methodology can be used in the manufacturing of RFID tags for future identification and sensing applications.

Quarter-mode circular cavity substrate integrated waveguide filtering power divider with via-holes perturbation

Abstract: A compact filtering power divider composed of two quarter-mode circular cavities based on the substrate integrated waveguide is proposed. Two extra perturbing via-holes added in each side of the quarter-mode circular cavity achieve a selective bandpass filtering response and improve the performance of the upper stopband. The proposed FPD operates at 9.1 GHz with a 3 dB fractional bandwidth of 19.8%. The insertion loss in operating band is <; 1.6 dB and the input return loss is better than 16 dB. The amplitude and phase imbalances between the two outputs are measured better than 0.6 dB and 3.5°, respectively. The measured results exhibit good agreement with the simulated ones.

Spatially mutual coupling reduction between CP-MIMO antennas using FSS superstrate

Abstract: A new approach to suppress mutual coupling of spatial electromagnetic fields between two circularly polarised (CP) antennas using frequency selective surface (FSS) technique around 30 GHz is presented. The transmission-type FSS layer with the CP capability is placed on the top of two closely multiple-input, multiple-output (MIMO) antennas. The study shows that the FSS layer can suppress an average of 10 dB mutual coupling between two adjacent CP-MIMO antennas. The proposed technique does not degrade the impedance and radiation performance of the antenna in comparison with the antenna without FSS layer. The two-port CP antennas are fabricated and measured to validate the simulation results. Good agreement is achieved between simulated and measured results in terms of the reflection coefficient, mutual coupling, and axial ratio.

Coding diffusion metasurface for ultra-wideband RCS reduction

Abstract: A coding diffusion metasurface is designed and fabricated for ultra-wideband radar cross-section (RCS) reduction. Two kinds of unit cells based on square ring patch are employed to generate the `0' and `1' elements of the coding metasurface. By precise design of the unit cells, a 180° ± 37° reflection phase difference between these cells is achieved over 8.01-22.76 GHz, leading to dramatically reduce the scattering field level by more than 10 dB. To obtain the diffusion far-field pattern of the metasurface, the optimisation algorithm is utilised to calculate the optimal layout of the digital elements. Both full-wave simulation and measurement results verify the capability of the proposed metasurface.

Impact of receiver's tilted angle on channel capacity in VLCs

Abstract: The impact of receiver's tilted angle on the channel capacity in visible light communications (VLCs) is investigated. First, the system model is analysed. On the basis of the system model, the lower and upper bounds on the channel capacity for the VLC are presented. An optimisation problem is formulated to improve the channel capacity by tilting the receiver plane. The proposed problem is shown to be a convex optimisation problem, which is efficiently solved by using the CVX toolbox for MATLAB. Numerical results show that the channel capacity can be dramatically improved by tilting the receiver plane properly.

Coverage probability of multiple UAVs supported ground network

Abstract: In disaster recovery, ground network consisting of mobile terminals of rescue vehicles and civilians may be disconnected due to severe environment. In this situation, multiple unmanned aerial vehicles (UAVs) form an aerial network to enhance the connectivity of the ground network. When two nodes in ground network are disconnected, they adopt UAVs as relays to transmit data. Otherwise, they communicate with device-to-device manner. With this framework, the coverage probability of these two kinds of users is analysed. Besides, the optimal altitude of UAVs to maximise the capacity of ground network is achieved. A guideline is provided for the design of multiple UAVs support wireless network.

Broadband dual-circularly polarised SIW cavity antenna using a stacked structure

Abstract: A wideband dual-circularly polarised (CP) substrate integrated waveguide (SIW) cavity-backed patch antenna is designed by using two-layer structure. The realised dual-CP, a cavity-backed square patch lies on the top substrate is excited by two pins, which are symmetrically located at an offset to the diagonal axis of the patch. These pins induce strong loading effect in the cavity and generate additional resonances in the vicinity of the patch resonant that help to achieve a wideband response by adjusting their locations. Thus, generation of dual-CP and wide impedance bandwidth is accomplished by using this new feeding topology. Moreover, the antenna is fabricated and tested for dual-CP. The experimental results show an impedance bandwidth of nearly 28.4% (8.59-11.43 GHz) and an axial-ratio bandwidth of 3.4% under the criterion <;3-dB.