A circular patch antenna under TM₀₂ mode with improved impedance matching is proposed by adopting 3D architecture. It is known that the TM₀₂ mode of circular patch can generate omnidirectional radiation, but its input resistance reaches maximum at centre point. In this context, impedance matching is difficult to be achieved and the feeding probe is often supposed to be placed a distance away from the centre, inevitably destroying the symmetry of radiation pattern. Without introducing pins or slots, a direct strategy is here employed where the circular patch is folded to form a concave at its centre. It is found that the input resistance can be effectively reduced with increasing depth of concave since the described concave serves as vertical electric wall in cavity and weakens the electric field in the region between centre and ground. By using electroplate technology based on plastics, a 3D antenna prototype is fabricated and measured to validate the proposed methodology.

This Letter presents a grating ridged waveguide V-shaped slot array antenna for satellite communication (SATCOM) receiving antenna applications. A special grating ridged waveguide, V-shaped slots and a matching section are applied in the proposed antenna design, so that the antenna provides an extra filtering response with a high radiation polarisation purity in a compact structure. For demonstration, a referential normal ridged waveguide V-shaped slot array antenna is designed and compared. The simulation results show that the proposed antenna not only operates well in the working frequencies (12.25–12.75 GHz) but also provides the antenna gains of lower than compared with those of the referential antenna in the interference frequencies (14.0–14.5 GHz).

A one-step leapfrog weakly conditionally stable finite-difference time-domain method for modelling drude dispersive models is developed. Numerical results show that its stability condition remains invariant with respect to that in lossless media. The new algorithm is applied to efficiently investigate the transmission properties of a graphene sheet and a graphene-based frequency selective surface.

Low-dose computed tomography has been highly desirable because of the health concern about excessive radiation dose, but also challenging due to insufficient or noisy projection data. Compared with post-processing methods by directly denoising filtered back-projection images, iterative reconstruction achieves excellent performance but consumes a large number of iterations. In this Letter, a two-stage method is proposed by incorporating residual learning-based denoising with iterative reconstruction. First, an intermediate image is reconstructed by compressed sensing iterative reconstruction. Then, the image is denoised by a deep neural network. Specially, a network performing two-level residual learning is designed to strengthen denoising effect. Experimental results show that the proposed method outperforms iterative reconstruction with better numeric results and comparable visual performance while consuming fewer iterations.

In this Letter, a low-power, high-speed output buffer for ultra-large infrared focal plane arrays (IRFPAs) is proposed. This buffer adopts a shared trans-impedance amplifier structure, which reduces parasitic resistance and capacitance of column-level bus. A 1280 × 1024 array readout integrated circuit with 20 MHz output frequency is designed for cooled infrared detector using this novel structure. The chip has been realised with 0.35 μm 1P4M CMOS process and power consumption of the proposed single output buffer is 3.83 mW. Though the presented circuit has been designed for this design, it shows great potential to be employed in most ultra-large readout integrated circuits.

Injection-locking properties of a rotary travelling pulse developed in a system of tunnel-diode (TD) transmission lines are characterised for multiphase oscillation. The system includes a unique TD line loop coupled with evenly spaced straight TD lines. The oscillating voltage edges in straight lines are synchronised to organise the rotary pulse on the closed one. Based on the phase-reduction theory, the authors determine where to connect an external oscillator for sufficient locking frequency range. Inherently, the travelling pulse can rotate on the loop in either clockwise or anti-clockwise fashion. The rotation frequency slightly depends on the rotation direction by the finite fluctuation of device parameter values. By matching the frequency of the external oscillator with one of such frequencies, the rotation direction is specified as required. These injection-locking properties are validated experimentally.

An algorithm for the improvement of the physical optics (PO) and equivalent edge currents (EECs) integral calculating near-field scattering is presented in this work. The solution is obtained by a more accurate representation of the Green function with an expansion centre that lies in the neighbourhood of the sources of interest. Phase and amplitude improvements of the approximate Green function overcome the shortcomings of the conventional PO and EEC for scattering evaluation in near-field regions. The improved algorithm preserves the simplicity and computational efficiency of the classical one and applies directly to near-field scattering. Under the consideration of the antenna radiation pattern, the formula of near-field scattering is derived. The applicability and accuracy of the proposed algorithm is demonstrated by numerical simulations.

A new application-specific approach is proposed to reconstruct the full-resolution grey-scale image from its binary spike series. The noisy observation of each pixel value is first computed by counting the spike pulses of a given event duration. The relationship between the light intensity and the signal-dependent noise is utilised in a linear image formation model to compensate truncated intensity error. Then, the minimum variance estimator for the true intensities is derived from this effective model. This estimation problem is non-iteratively solved by applying the asymptotic results of random matrix theory. Experimental results have demonstrated that the algorithm can reliably infer true pixel intensities and is superior to the simple spike counting in terms of both estimation accuracy and robustness.

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.

Person re-identification aims at searching in a large gallery image database for images of the same identity as probe image, which can also be treated as a retrieval task in which the pairwise affinity is often used to rank the retrieved images. However, most existing methods of person re-identification only consider pairwise affinity but ignore the group affinity information. Some frameworks incorporate group affinity into the testing phase, which is not end-to-end trainable for deep neural networks. In this Letter, a powerful deep learning based framework for person re-identification is presented, which aims at fully utilising group affinity information for more discriminative features. Specifically, hypergraph model for group information mining is novelly proposed in the training phase, which significantly improves the performance of features acquired by the baseline networks. Extensive experiments on two popular benchmarks demonstrate the effectiveness of the authors' model and applicability on different baseline networks.

The emerging versatile video coding (VVC) standard currently adopts 67 intra-prediction modes in order to improve the intra-prediction performance. The most probable mode (MPM) is used in video coding to encode the prediction mode efficiently based on the modes of the neighbouring blocks. Due to an increase in the number of intra-modes and increase in the resolution of the input sequence, it is necessary to efficiently encode the intra-mode of the current block. This Letter proposes an efficient intra-mode coding method extending MPM called most frequent mode (MFM), which exploits the number of occurrences of the modes in the neighbouring blocks. The proposed MFM derives the most frequent intra-mode. Then the derived MFM is signaled by a flag with a higher priority than MPM. Experimental results show that, compared to the test model of VVC (VTM), the proposed method gives up to 0.48% Bjotegaard-Delta-rate savings for the all-intra-configuration.

Multimodal image-to-image translation is a class of vision and graphics problems where the goal is to learn a one-to-many mapping between the source domain and target domain. Given an image in the source domain, the model aims to produce as many diverse results as possible. It is an important and challenging problem in the task of image translation. To this end, recent works utilise Gaussian vectors to produce diverse results but with a small difference. It is because of the special probabilistic nature of Gaussian distribution. In this work, the authors propose linearly distributed latent codes instead of conventional Gaussian vectors, which control the style of generated images. Taking advantage of linear distribution, their model can produce much more diverse results and outperform the state-of-the-art baselines in terms of diversity. Qualitative and quantitative comparisons against baselines demonstrate the effectiveness and superiority of their method.

An inverse problem in which the observed signal is produced by passing the original signal through a filter that is derived from a convex minimisation problem is dealt. The filter is available as a black box. It is shown that the Bregman iteration, which is a tool for convex optimisation, can be used to solve this inverse problem. This novel application of the Bregman iteration is demonstrated through successful restoration of the original image from images filtered by a low-pass filter. Theoretical analysis is conducted to explain the inversion process.

Studies on human visual systems (HVS) recommend that assessing the structural information change can provide a good approximation of the perceived image quality. Moreover, psychovisual studies have suggested that the HVS is more sensitive to the extraction of visual information in the salient regions rather than minor regions. Based on the above observations, this Letter proposes a novel full-reference image quality assessment metric called the visual saliency based structural contrast-quality index by the modification and adjustment of an image signature to incorporate into the structural contrast index (SCI) features, which can well depict the visual quality by considering the local and global visual quality perceptions for different types of structural distortions on the salient regions. The proposed method was tested on four world recognised databases and from the experimental result, it became apparent that the authors proposed method strongly correlates the subjective mean opinion scores and performs better than the existing state-of-the-art image quality assessment methods.

Array-based non-binary (NB) low-density parity-check (LDPC) codes are attractive in practice for their advantages in implementation and performance. However, existing construction of array-based NB LDPC codes is only with the prime number cases. In this Letter, the authors extend the array-based construction to composite numbers to give an explicit construction of structured array-based NB LDPC codes with column weights three, four, and five. The resulting codes have girth at least six. The simulation results show that the proposed structured codes perform as well as the random codes constructed by progressive edge-growth algorithm, when decoded with the Q-ary sum product algorithm and the low-complexity weighted bit-reliability-based decoding algorithm.

One of the major challenges in evolutionary many-objective optimisation is to maintain convergence and diversity among Pareto-optimal solutions. Taking both into consideration, this Letter presents a -NSGA-III algorithm which incorporates minimum-vector-angle principle in association operation of original non-dominated sorting genetic algorithm III (NSGA-III) scheme to solve unconstrained many-objective optimisation problems. Each non-dominated population member close to a reference point is emphasised in optimal solution set using minimum vector-angle penalty parameter with perpendicular distance in association operation. Performance evaluation of -NSGA-III algorithm is done over unconstrained DTLZ test suite by computing delta () and inverted generational distance as quality metrics. The improved performance of the suggested algorithm over NSGA-III, MOEA/D and VaEA could be considered as an alternative tool to handle optimisation problems with more than three conflicting objectives.

This Letter proposes a novel 3-hot-wire acoustic particle velocity sensor with high sensitivity and low self-noise for the first time. Three parallel wires, covered with platinum film, are suspended on silicon substrate by MEMS process. The middle wire works as a heater and the left and right ones work as both heaters and temperature sensors. Compared with the 1-hot-wire and 2-hot-wire counterparts, this sensor has higher sensitivity and lower self-noise, showing its potential for sound source localisation, acoustic camera and so on. The self-noise of the sensor is about at 1 kHz and the relative direction sensitivity is as high as 42 dB.

Every year, different areas of knowledge are becoming more interested in 3D-printing technology. Recently, this technology was also proved to be feasible for creating sensitive materials such as piezoelectrets. This Letter extends the concept of a 3D printed piezoelectret to produce a pressure sensitive film that can be employed as an ultrasonic transducer for underwater applications, such as hydrophones. In order to achieve this, a two-layer polypropylene film was printed using a filament-based 3D printer. Afterwards, adhesive electrodes were attached on both sides of the film and electrical charging was applied. Later, the 3D printed film was mounted in a metal housing specially designed to keep the film in direct contact with the water and to isolate the electronic amplification. The validation was performed using a piezoelectric ceramic made of lead zirconate titanate (PZT), immersed in a water tank, to produce ultrasonic sweeps to be sensed by the 3D printed transducer. These tests revealed sensor sensitivities up to 600 mV and promote a precise detection of the acoustic resonance frequency of the PZT at 43.7 kHz.

Electrode-less integrated optics lithium niobate (LiNbO₃) asymmetric Mach–Zehnder interferometers (AMZIs) can be used as electric field (e-field) sensors. Electrode-less sensors are attractive for practical use as such devices do not perturb the sensed variable. A critical issue when using electrode-less sensors is to ensure a linear sensing process. This requires the electro-optic transfer function (EOTF) to be adjusted at its quadrature point. For this purpose, an electrode-less sensor can be optically biased. However, an accurate optical bias is strongly limited by the fabrication tolerances of the AMZIs. Hence a linear sensing-detection process is not actually ensured. To explore a linear e-field sensing-detection process, a simple linearising scheme is proposed in this Letter. The scheme is configured by cascading two optically matched AMZIs. The first AMZI is an electrode-less sensor; the second one, which is provided of electrodes performs simultaneously as an optical demodulator and an EOTF tuner. The EOTF of the demodulating AMZI can be tuned to its quadrature point by a DC voltage on its associated electrodes. The sensing-detection scheme is modelled and experimentally tested when illuminated either by coherent and incoherent light. The sensed e-field is linearly recuperated only when incoherent light is used.

A type of lossy transversal-signal-interference planar bandpass filter (BPF) with a flattened passband is reported in this Letter. The authors exploit in-series-cascaded transversal filtering sections composed of two in-parallel transmission-line segments and series-type lossy hybrid resonators connected at their inputoutput accesses. The resistors of these lossy resonators by dissipating part of the RF-input-signal energy in the BPF passband region following a complementary frequency-variation profile with regard to the one associated with conventional substrate filter loss allow obtaining an overall flattened transmission band. To experimentally validate the proposed approach, a 2 GHz microstrip prototype of a sharp-rejection lossy signal-interference BPF with a flattened passband is developed and characterised.

This Letter proposes a balanced dual-mode substrate integrated waveguide (SIW) filter for the first time. Based on dual-mode square SIW cavities, perturbation vias, and balanced ports, the quasi-elliptic differential mode response with improved selectivity as well as high-performance common mode suppression can be obtained conveniently. Resonator number decrease and compact size can also be available.

Compact dual-mode dual-band bandpass filters (BPFs) with multiple transmission zeros (TZs) using over-mode half-mode substrate integrated waveguide (HMSIW) resonators are presented. Each passband built by TE₀₀₁ or TE₂₀₁ has three TZs introduced by source–load coupling and low-/high-order mode cross-coupling between TE₀₀₁ and TE₂₀₁ to improve the frequency-selectivity. The equations that determined the TZs are built. Perturbation slots realise the independent-control of frequency ratio. Dual-mode dual-band BPFs are designed, fabricated and measured, and the simulated results agree with the measured results well.

A compact microstrip balanced bandpass filter (BPF) with a pair of adjustable transmission zeros (TZs) and a common mode suppression of over 20 dB in a frequency range of >2.42f ₀ by using the mixed electromagnetic coupling technology has been developed. The filter TZs in differential-mode are attributed to the mixed electromagnetic coupling, and can be adjusted by the electric/magnetic coupling individually. The filter bandwidth can also be controlled by the electromagnetic coupling. The proposed balanced BPF has been fabricated and measured, and the prediction has been demonstrated.

A novel bi-functional ground plane is presented based on frequency selective surface (FSS) and switchable PIN diodes. The proposed FSS can not only be used as a conventional ground plane but it can also be used for spatial filtering purpose. Moreover, the structure is reconfigurable, which means it does not suffer from post fabrication design inflexibilities and can be tuned into any of its two modes of operation by simply changing the bias voltage of the PIN diodes. Unlike the traditional FSSs where transmission band remains no longer under the user's control after fabrication of the structure, the authors have demonstrated here the full control over transmission band of the FSS with the help of a PIN diode and thereby providing two modes of operation of the proposed FSS, i.e. as a spatial filter or as a ground plane.

4H-SiC ultraviolet p-i-n photodiodes with four different epitaxial structures were fabricated. The experimental results prove that both a thin P⁺-type Ohmic contact layer and a thick intrinsic layer were indispensible for a high-performance ultraviolet p-i-n photodiode. A 4H-SiC p-i-n photodiode with responsivity as high as 0.139 A/W at 278 nm incident wavelength was achieved. Meanwhile, within a certain wavelength range, the peak response wavelength of an ultraviolet p-i-n photodiode would be modulated by properly varying the thicknesses of P⁺-type layer and the intrinsic layer. Moreover, the theoretical calculation was carried out to further authorise the experimental results.

Motivated by the need for robust frequency estimation for both balanced and unbalanced power system conditions and the fact that most of the existing techniques perform poorly in the presence of external interferences, a more noise-resilient widely linear least mean kurtosis (WL-LMK) algorithm is proposed that uses both the magnitude and phase angle errors for online estimation of three-phase power system frequency. The proposed method makes use of the full second-order information within the complex-valued system voltage through Clarke's transformation and the concept of augmented complex statistics and WL modelling. The effectiveness of the proposed scheme is verified through simulation studies of synthetic signals and experimental data.

This Letter proposes a simple realisation of a circuit (referred to as electronic capacitor) capable of emulating large capacitance of controllable value while utilising a much smaller capacitor and a DC–DC converter. The circuit may be used in a plug-and-play fashion instead of any real large capacitor within the control bandwidth. The proposed control algorithm forces the terminal voltage of the DC–DC converter to follow the well-known capacitance equation by sensing the terminal current and simultaneously compensates conversion losses by an auxiliary control loop. The proposed algorithm is successfully verified by emulating bulk DC-link capacitance of a commercial power factor correction front end.

A path planning approach is proposed that is in accordance with Collision Regulations (COLREGS) for avoidance of a potential collision and considers the time-varying trajectory uncertainties of an autonomous surface vehicle (ASV) and an obstacle. Unfortunately, as the motion information for each object includes various uncertainties caused by characteristics of the navigation and perception systems, the trajectory uncertainties increase linearly during the pre-specified time in a trajectory prediction process. This trajectory uncertainty is preferentially modelled using the error covariance of a tracking filter designed for estimating motion information. Subsequently, collision risk is computed using a probabilistic method, and a collision risk zone (CRZ) is configured on the predicted trajectory. Finally, a COLREGS-compliant path is planned with consideration of the dynamic characteristics of the ASV to avoid the CRZ. Simulation results that demonstrate the feasibility of the proposed approach with marine traffic examples are presented and discussed.

The analytical approximation of the Ricean channel (non-central Wishart) matrix is often analysed with the central Wishart matrix. This method falls short of exploiting the non-zero Ricean channel mean to calculate the average zero-forcing (ZF) massive multiple-input and multiple-output(MIMO) ergodic rate. In this Letter, the authors develop a new approach to accurately approximate the inverse Ricean channel, and determine the main diagonal. After which, optimal power allocation is used to maximise the ergodic rate. Numerical results validate the accuracy of the proposed approximation with the ideal channel.

In this Letter, the author proposes a low complex sub-optimal algorithm for resource allocation in spatial spectrum usage of a cognitive radio network by minimising the bandwidth power product while satisfying secondary user's quality of service and interference constraints of primary users. The author has proposed an approach to solve the problem by using linear programming techniques. The author compares the proposed method with the optimal solution to show its effectiveness.