A circular dense dielectric (DD) patch antenna realised by stacking an upper DD patch on the lower DD patch is proposed to achieve high efficiency and frequency selectivity. The high efficiency is attributed to the non-metallic radiators and the radiations of both lower and upper DD patches operating at TM₁₁ mode. To achieve higher frequency selectivity than that of the reported DD patch antennas, the opposite E-field distribution inside the upper DD patch and the quarter-wavelength open-circuit stub produce two radiation nulls near the lower band-edge, while the opposite E-field distribution inside the lower DD patch and the opposite E-field distribution at the edges of the two DD patches produce two radiation nulls near the upper band-edge. For demonstration, a prototype covering the fifth generation (5G) band (3.4–3.6 GHz) achieves the simulated radiation efficiency of 96%, the measured peak gain of 9.2 dBi, 10 dB impedance bandwidth of 12.3%, four radiation nulls, and the cross-polarisation rejection larger than 22 dB within the 3-dB beam range at the centre frequency. The results show the features of high efficiency, multiple radiation nulls, wide bandwidth and high gain simultaneously while the reported DD patch antennas just have part of the features.

A novel wideband circularly polarised (CP) magnetoelectric dipole antenna, which is excited by microstrip line aperture-coupled feeding structure, is proposed and investigated. The wide impedance bandwidth and broadband CP characteristic are achieved based on the simple feeding structure. An antenna prototype is fabricated and exemplified to validate the proposed concept. Measured results show that the proposed antenna achieves an impedance bandwidth of 65% for voltage standing wave ratio <2 from 2.97 to 5.85 GHz, the broadside maximum gain is up to 10.2 dBi. Moreover, the 3 dB axial ratio bandwidth is about 75%, ranging from 2.7 to 5.8 GHz. Stable and symmetric unidirectional radiation patterns with low backward radiations are obtained over the operating band.

The feasibility of measuring heart rate using radar echoes from a human head is demonstrated. Non-contact measurement of vital signs using radar has been attracting much attention because such technologies can breakthrough benefits for monitoring health conditions without electrodes or wearable devices. Most existing studies have measured echoes from the torso, particularly the chest wall. However, this is difficult because of multiple interfering reflections from the complex shape of the torso and other body parts, such as limbs. The current study is the first demonstration that non-contact heart rate measurement can be easily achieved using echoes from the human head. There are two important advantages of measurement from the human head: (i) the simple shape of the head makes an ideal radar target with only a single reflection, and (ii) the other undesired echoes can be removed using time-gating when an ultra-wideband radar is used. Nonetheless, because the displacement of the human head due to heart rate is small, a millimetre-wave ultra-wideband array radar system is developed, which is installed on the ceiling and used in the proposed measurements with participants.

Electroencephalography (EEG) recordings are often contaminated by muscle artefacts. To address the problem, various methods have been proposed to suppress muscle artefacts from either multichannel or single-channel EEG recordings. However, there exist few studies for muscle artefact removal from few-channel EEG recordings. An effective solution for the few-channel situation by combining multivariate empirical mode decomposition (MEMD) with independent vector analysis (IVA), termed as MEMD-IVA, is proposed. The proposed method consists of two steps. MEMD is first utilised to decompose a few-channel EEG recording into intrinsic mode functions (IMFs) and then IVA is applied on the IMFs to separate sources related to muscle activity. The performance of the proposed method on simulated and real-life data is evaluated. The results demonstrated that MEMD-IVA outperforms other possible existing methods in a few-channel situation.

A novel N-type MOS (NMOS) only Schmitt trigger with voltage booster (NST-VB) circuit is presented. The proposed NST-VB circuit uses NMOS transistors in both pull-up and pull-down networks to reduce the effect of negative bias temperature instability (NBTI) on the circuit. The proposed circuit is less affected by both inter-die and intra-die process variations in consequence of NMOS only structure. Owing to NBTI, the increase in delay for the proposed NST-VB circuit is only 0.47% as compared with 7.2% for conventional Schmitt trigger after the stress time of three years. For the viability of the proposed circuit figure of merit (FOM) is used as a performance metric and it is found that the proposed circuit has and improved FOM as compared with the conventional Schmitt trigger and NMOS inverter, respectively.

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.

An improved disturbance rejection control based on the combination of an extended-state observer (ESO) and Q-filter is presented for piezoelectric actuators. Analysis using the standard disturbance observer framework is performed to verify that the new method can improve the accuracy of disturbance estimation even under measurement noise. An advantage of the proposed method is that the bandwidth of the ESO can be reduced without the degradation of disturbance rejection performance. An experiment is performed to validate the effectiveness of the proposed method.

This Letter proposes a novel method to deblur a blurry image corrupted by noise. The authors estimate a noise-free version of the input blurred image and a corresponding noise-free version of the latent image without damaging the blur information, as well as the latent image and blur kernel in an alternating fashion. To this end, they first propose coupled convolutional sparse coding, which incorporates the coupled dictionary concept into convolutional sparse coding. Then they model the noise-free blurred image to share the sparse coefficients with the noise-free latent image using the coupled dictionaries. By utilising these noise-free images as priors in alternating latent image estimation and blur kernel estimation steps, they can estimate a high-quality latent image and blur kernel in the presence of noise. Experimental results demonstrate that the proposed method outperforms previous methods in handling noisy blurred images.

A new stereo matching algorithm which uses improved matching cost computation and optimisation using the semi-global method (SGM) is proposed. The absolute difference is sensitive to low textured regions and high noise on the stereo images with radiometric distortions. To get over these problems, sum of gradient magnitude differences has been introduced at the first stage. This method is strong against the radiometric differences on the stereo images. Hence, this approach will reduce the error of preliminary data for stereo corresponding process. The SGM is used at the aggregation, and optimisation stage uses 16 different directions of 2D path. Additionally, the iterative guided filter is utilised at the refinement stage which minimises the errors and increases the accuracy. The proposed work produces accurate results and performs much better compared with some established algorithms based on the standard stereo benchmarking evaluation from the Middlebury and KITTI.

The problem of learning to rank is addressed and a novel listwise approach by taking document retrieval as an example is proposed. It first introduces the concept of cross-correntropy into learning to rank and then proposes the listwise loss function based on the cross-correntropy between the ranking list given by the label and the one predicted by training model. The use of the cross-correntropy loss leads to the development of the listwise approach called ListCCE, which employs the gradient descent algorithm to train a neural network model. Experimental results tested on publicly available data sets show that the proposed approach performs better than some existing approaches.

Rate-distortion optimisation (RDO) is the key technology that is used to choose the optimal coding parameters in video coding. As the Lagrangian multiplier plays a vital role in RDO, a model-based Lagrangian multiplier derivation method is proposed for depth map coding. This method is based on the analysis of the relationships among the Lagrangian multiplier, the coding distortion, the coding bitrate and the quantisation step. Experimental results demonstrate that the proposed method can achieve an average 3.42% bitrate saving compared with the method in HTM 16.0 reference software, and an average 0.41% bitrate saving compared with a state-of-art method.

A novel micro-silicon resonant pressure sensor with two mechanically coupled resonators is presented. When pressure acts on the diaphragm, the perturbed stress will cause stiffness perturbation, leading to mode-localisation phenomenon. Therefore, pressure can be sensed by measuring the amplitude ratio shift. This novel structure is achieved by fabrication on silicon-on-insulator wafer. The measured result shows that the relative amplitude ratio shift (86,819.9 ppm/kPA) is 197.5 times higher than the shift in resonance frequency (439.6 ppm/kPA).

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.

A mechanical tuning balanced bandpass filter based on substrate integrated waveguide (SIW) dual-mode resonant cavity is presented. It can be accomplished by placing two metallised via-holes with open-loop slots on the top layer which affect the TE₁₀₂ and TE₂₀₁ modes of the square SIW cavity, respectively. Direct source-load couplings have been utilised to achieve the high selectivity of the differential mode (DM) passband and improve the DM out of band rejection. A planar module of 60 × 60 mm² has been fabricated on RO5880 substrate with a dielectric constant of 2.2 which verify the design concept.

A microring resonator realised by femtosecond laser two-photon photopolymerisation in an epoxy-based negative photoresist (SU-8) is proposed and demonstrated, which is further proved to be capable of temperature and refractive index sensing by monitoring the shift of the resonance wavelength of the interferometric pattern. The experimental results indicate refractive index sensitivity of 12.50 nm/refractive index unit (redshift) and temperature sensitivity of −9.51 × 10⁻² nm/^oC (blueshift), respectively.

In this Letter, an interpolation-free imaging algorithm for a near-field cross MIMO array is presented. This method transforms the measurement data into the wavenumber domain along the receiving direction or the transmitting direction for compensation. Then the imaging result is obtained by 1D inverse Fourier transform and 2D accumulation. This method has the same computational complexity as the backprojection algorithm (BPA) with better imaging quality since interpolation is avoided. The imaging performance of the proposed method, the BPA and the approximate range migration algorithm are compared by experiment.

A novel unsupervised change detection for synthetic aperture radar (SAR) images using robust semi-non-negative matrix factorisation (NMF) with total variation (TV) is proposed. In order to effectively handle the noise and outliers as well as consider spatial contextual information, correntropy induced metric and TV regularisation are simultaneously integrated into semi-NMF to build a robust semi-NMF with TV model. Subsequently, the update solutions of the model are optimised by the Karush–Kuhn–Tucker condition and fast gradient projection algorithm. The experimental results demonstrate the effectiveness of the proposed method both visually and quantitatively.

A novel method to estimate the object velocity for random stepped frequency radar by the waveform design is proposed. The method utilises a so-called ‘complementary random code’ to modulate the transmitted waveform. Theoretical analyses show that the proposed method achieves a high precision in velocity estimation, which could meet the requirements of motion compensation. Moreover, its computational complexity can be significantly reduced, compared with the classical estimation methods. Finally, the simulations validate the effectiveness of the present method.

We fabricated Pt-functionalised hydrogen gas sensors on AlGaN/GaN heterojunction platform and investigated the influence of GaN-cap layer on the sensing characteristics. Pt-Schottky diodes with GaN-cap layer exhibited a larger change of Schottky barrier height than ones with no GaN-cap layer when hydrogen gas was detected. Technology computer-aided design simulation indicated that the increase of electron concentration at heterojunction can be magnified by a larger change of barrier height. The AlGaN/GaN FET-type sensors with Pt catalyst on the gate area demonstrated significant enhancement of hydrogen gas sensitivity from 16 to 35% at 200°C when GaN cap layer was employed.

Fermi-level depinning in germanium (Ge) through nitrogen (N₂) plasma treatment is demonstrated. The Ge surface was exposed to N₂ plasma for 1 min without heat treatment, resulting in the formation of 2.5 nm-thick GeO _x N _y layer with uniform surface and interface morphologies. Ohmic and Schottky behaviours were obtained for Al contacts to N₂ plasma-treated n- and p-type Ge with barrier heights of 0.09 and 0.40 eV, respectively. Fermi-level depinning could be attributed to the reduction in interface states caused by the passivation of Ge surface by highly uniform GeO _x N _y layer.

A high-current cascode gallium nitride (GaN) switch integrating a silicon-MOSFET (Si-MOSFET) and paralleled GaN depletion-mode high-electron-mobility transistors (DHEMT) is presented. The proposed switch can withstand twice or more the current than existing cascode GaN transistors by using only one Si-MOSFET and requiring a single gate driver, which evidently augments the power density, improves the system efficiency and reduces the cost. The causes and treatments of potential unbalanced current sharing among the paralleled GaN DHEMTs are further discussed and an optimised symmetric configuration and wire bonding of integral package are proposed. An effective solution is also introduced for avoiding an Si-MOSFET avalanche. The validity of proposed cascode GaN switch in the optimised package and the effectiveness of avalanche-suppressed method are both verified by simulations.

In current playback speech detection (PSD) Letter, commonly used features are often extracted from magnitude spectrum while phase spectrum information is not used. In order to extract more discriminative information for PSD, the idea of magnitude–phase spectrum (MPS) is proposed. Then a new feature based on MPS is proposed, namely constant-Q magnitude–phase octave coefficients (CMPOC). The experimental result on ASVspoof 2017 evaluation set using CMPOC indicates that: (i) the performance of CMPOC is better than features extracted not only from magnitude spectrum but also from MPS. (ii) CMPOC performs better than some commonly used features. (iii) Their system gives better performance than some known systems.

An improved and specification-compatible general precoding scheme (GPC) for adjustable peak-to-average power ratio (PAPR) reduction in discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-s-OFDM) is proposed. Through the rearrangement of periodic padding for precoded data symbols in the GPC precoding matrix, the proposed algorithm does not increase any computational complexity compared to the original GPC. The LTE-based simulation shows the proposed algorithm has a better improvement of PAPR reduction especially in low-order modulations and the performances can be scaled to the other transmission bandwidth. These works contribute to the flexibility of DFT-s-OFDM for supporting 5G transmission over miscellaneous power amplifiers.

In this letter, the authors report a beam squint compensation method for hybrid precoding in millimetre-wave communication systems. With the objective to maximise the spectral efficiency, they formulate the hybrid precoding problem considering the beam-squinting analogue precoder and reveal its performance loss compared with the ideal identical analogue precoder. They also design a simple but effective compensation matrix for hybrid precoding to reduce the impact of beam squint. Simulation results confirm the performance loss caused by beam squint and reveal the performance gain of the proposed method.

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.

Radio interferometer arrays are instruments requiring real-time synchronisation of all array elements to capture and align the observed source wavefront prior to further processing such as correlation and/or beamforming. One method is to deliver a frequency, from a common central local oscillator (LO), using a round-trip phase-stable distribution system such that each element has its own phase-stable copy of the clock with required real-time fidelity for down-conversion and digitisation. The method described here involves equipping each array element with its own independent ‘eLO’ and sending a ‘tracer’ of it to a central site, where the difference between the elements’ eLOs and the central ‘cLO’ is measured. The digitised data from each element is corrected at the central site according to the measurement, before correlation/beamforming. The advantage of this method is that only a ‘trace’ of eLO, needed to measure the rate of change of eLO relative to cLO integrated over a measurement interval, needs to be conveyed over this tracer link, rather than the frequency itself, thereby requiring lower link temporal fidelity and bandwidth.