The design of miniaturised linear arrays by using isotropic lenses with reduced complexity is addressed. The problem at hand is formulated as a global optimisation one, then solved by means of a computationally-efficient customisation of the system-by-design (SbD) paradigm suitably integrated with the quasi-conformal transformation optics method. To yield arbitrary transformation geometries with a limited set of degrees-of-freedom and to reduce the lens complexity, while guaranteeing the same radiation performance of a larger reference aperture, a spline-based description of the lens shape is adopted. Representative numerical results are reported to assess the effectiveness as well as the computational efficiency of the proposed SbD-based approach.

A slim dual-polarised antenna with omnidirectional patterns is proposed for wireless local area network (WLAN) applications. The antenna is a composition of a modified J-type antenna for vertical polarisation and two crossed-loop antennas for horizontal polarisation. For improving the isolation between the two polarisations, a rectangular loop is partially added in the middle of one of the loop antenna, connecting the end of the J-type antenna. The rectangular loop also acts as tuning the impedance of the antenna. For achieving omnidirectional patterns of the horizontal polarisation, a series circular feeding network is designed to excite the loop antennas. The antenna is fabricated by copper and the circular network is printed on a substrate. Measurement results show the 10 dB return losses of the two ports are covering the whole 2.4 GHz WLAN band, with the isolation better than 20 dB. The gains vary <2.2 dB in the horizontal plane for both the polarisations. With the advantages of slim structure, lightweight, and easy fabrication, the proposed antenna is convenient to use in the WLAN routers.

In this Letter, a novel subwavelength and low-profile element is proposed for the reflected antenna array applications. By using the metallic hole, the proposed element achieves a smaller dimension with the period of 0.1125 wavelength and the profile of 0.036 wavelength at the centre frequency of 13.5 GHz. The element obtains a wide reflected phase shifting range of 337.2° in such a small dimension. The reflected magnitude and phase are less sensitive to the incidence angle over a large range from +60° to −60°. To verify the function of the proposed element with a metallic hole, a reflected antenna array with 2724 elements is designed, fabricated, and measured. The array achieves a maximum peak gain of 23.30 dBi at 13.25 GHz with a high aperture efficiency of 61.05%.

This Letter presents a fully integrated bio-system with the property of high sensitivity for electrochemical detection, which can intrinsically measure electrochemical characteristics with cyclic voltammetry. In normal circumstances, ultra-low electrolytes exist in tissue solution, which is difficult to accurately detect the oxidation/reduction signals, limited by the innate circuit and liquid noise. Hence, the conventional topology of the potentiostat circuit is improved and proposed in this Letter to remove the required analogue-to-digital converter (ADC). The overall operational mechanism of the potentiostat behaves like a single-slope ADC, which achieves a compact, easily implemented, and low-noise design. Additionally, the effective capacitance of potentiostat and liquid resistance make an RC integration to further suppress out-of-band noise, thereby enabling the low-electrolyte detection and improving detecting sensitivity. To simulate the low-electrolyte environment, only 0.01 M (M = mol/l) phosphate buffered saline background solution is used and required to demonstrate its feasibility of the concept. The measured results show the sensor chip with high sensitivity to sense resistive variation of electrochemical action in low electrolytes.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that causes brain regions to undergo structural changes. Shape descriptors are useful in reflecting the morphological alterations of brain structures in AD conditions compared to volume based measures. In this work, moment based shape descriptors are used to classify control, mild cognitive impairment (MCI) and AD subjects. Lattice Boltzmann criterion-based hybrid level set method (LSM) is used to delineate lateral ventricles. Legendre and United moments are extracted from the segmented binary images and are statistically analysed using Statistical Package for Social Science (SPSS). The performance of significant moments in the shape analysis is validated using machine learning algorithm. Results demonstrate that, level set is able to delineate ventricles and found to have high similarity index with ground truth. The area under curve (AUC) values for Legendre moment is found to be 1.0, 0.75 and 1.0 for Control-MCI, MCI-AD and Control-AD subjects. Rather, the AUC for United moment is found to be 0.98, 0.76 and 0.98 for Control-MCI, MCI-AD and Control-AD subjects respectively. Further, machine learning algorithm could classify Control from AD subjects with high accuracy of 99.25% using Legendre moments and hence the study seems to be clinically significant.

In this research, the authors propose a self-biased relaxation oscillator that outputs a constant 1.2 MHz clock over a wide temperature range. Excluding any external bias, the proposed oscillator embodies a self-bias circuit that generates a bias current from a precisely trimmed resistor. To minimise the power consumption, a switched-bias technique was applied to the two comparators in the oscillator. The proposed circuit was fabricated in a 180 nm CMOS process. It consumes 17.9 µW from a 1.5 V supply, and its temperature coefficient is 16.8 ppm/°C in the range of −20–80°C.

A 7-bit successive approximation register (SAR) analogue-to-digital converter (ADC) with programmable transfer functions is presented. Building upon prior art, a two-step successive approximation technique is used to implement a piecewise-linear approximation of the desired transfer function. However, unlike previous implementations of SAR-based non-linear ADCs, the proposed work demonstrates programmability of arbitrary non-linear transfer functions, thus making it suitable for a wide range of low-bandwidth applications. Simulation results from a proof-of-concept design in a standard 180 nm CMOS process are presented to validate the proposed idea.

A CMOS cross-coupled RF rectifier that improves power conversion efficiency (PCE) with low reverse leakage current for energy harvesting wireless sensors is proposed. In this Letter, the authors propose a CMOS cross-coupled differential RF rectifier that uses a thick-oxide MOSFET as a rectifying device to improve PCE by reducing reverse leakage current. The proposed rectifier is designed for UHF band application using 0.18 µm CMOS technology. Proposed rectifier achieves a peak PCE of 75.2% and sensitivity of − 17 dBm for 1 V output voltage. Peak PCE is improved by 8.8% compared to the conventional rectifier.

The dependence of the noise performance of a 0.6–1.2 V continuous-time delta-sigma modulator (DSM) on its supply voltage is analysed. The noise performance and benchmark figure of merit (FoM) mainly depend on the power dissipation, thermal noise contributions from the analogue loop filter, and the quantisation noise from the quantisers. Theoretical estimates for the supply dependence of loop noise and quantisation noise, and their respective FoM are derived and verified with simulations for a 2 MHz third-order continuous-time DSM, while operating from a supply between 0.6 and 1.2 V. At a larger supply voltage, the FoM related to the loop filter noise improves, whereas at lower supplies, the FoM related to the quantisation noise improves. As a result, the overall FoM of the DSM reaches an optimum at a particular supply. The supply voltage with the best FoM of the DSM is derived with the supply-scaling FoM of the loop filter and quantisers. For an equal FoM of the loop filter and quantisers at a supply V, the optimal supply voltage is 0.66 V.

This Letter presents a novel problem for discovering similar trajectories based on the field of view of the video data. The problem is important for many societal applications such as grouping moving objects, classifying geo-images, and identifying the interesting trajectory patterns. Prior works consider only either spatial locations or spatial relationship between two line-segments. However, these approaches show a limitation to find similar moving objects with common views. In this Letter, the authors propose a new algorithm that can group both spatial locations and points of view to identify similar trajectories. The authors also propose novel methods that reduce the computational cost for the proposed work. Experimental results using real-world datasets demonstrate that the proposed approach outperforms prior work and reduces the computational cost.

Vision-based vehicle behaviour analysis has drawn increasing research efforts as an interesting and challenging issue in recent years. Although a variety of approaches have been taken to characterise on-road behaviour, there still lacks a general model for interpreting the behaviour of vehicles on the road. In this Letter, the authors propose a new method that effectively predicts the vehicle behaviour based on structured deep forest modelling. Inspired by structured learning, the structure information of vehicle behaviour is extracted from the detected vehicle, and then the corresponding structured label is constructed. Especially, the structured label visually expresses the vehicle behaviour as contrast to the discrete numerical label. With the structured label, a structured deep forest model is proposed to predict the vehicle behaviour. Experimental results illustrate that the proposed method successfully obtains the implication of semantic interpretation of vehicle behaviour by the predicted structured labels, and meanwhile it achieves comparable performance with traditional methods.

This Letter presents an attention-modulating network for video object segmentation that can well adapt its segmentation model to the annotated frame. Specifically, the authors first develop an efficient visual and spatial attention modulator to fast modulate the segmentation model to focus on the specific object of interest. Then they design a channel and spatial attention module and inject it into the segmentation model to further refine its feature maps. In addition, to fuse multi-scale context information, they construct a feature pyramid attention module to further process the top layer feature maps, achieving better pixel-level attention for the high-level feature maps. Finally, to address the sample imbalance issue in training, they employ focal loss that can distinguish simple samples from the difficult ones to accelerate the convergence of network training. Extensive evaluations on DAVIS2017 dataset show that the proposed approach has achieved state-of-the-art performance, outperforming the baseline OSMN by 3.6 and 5.4% in terms of IoU and F-measure without fine-tuning.

Blind signcryption schemes are the extension of signcryption schemes. They are used to protect the privacy and identity of the sender from other users, especially in electronic voting and electronic cash payment systems. A number of blind signcryption schemes are introduced over the years and some of them are proved to be insecure. In this Letter, the authors analysed a recently proposed blind signcryption scheme based on elliptic curves and proved it is insecure. Their analysis showed that the proposed scheme is unable to provide the claimed security attributes of message integrity, authentication, unforgeability, and signer non-repudiation. After successful cryptanalysis, they introduced a modified version of this scheme to overcome the security flaws and weakness.

In this Letter, the authors propose a novel attention mechanism combined with a classical generative adversarial network (GAN) model to improve the visual quality of generated samples. This novel attention model is named regional attention GAN. The proposed mechanism can build dependencies between the high-level representations extracted from attention regions of real images and corresponding feature maps of the generative network. By modelling these dependencies, the generative network can be facilitated to learn feature mapping and fit the distribution of real data. They conduct extensive experiments on widely used datasets CIFAR-10, STL-10, and CelebA. The quantitative and qualitative performance improvement over state-of-the-art methods demonstrates the validity of the proposed attention mechanism in improving the quality of generated images.

In this Letter, the authors theoretically and experimentally investigate the characteristics of phase delay in capacitive pick-off circuits for micro-electromechanical systems (MEMS) resonators for the first time in history. An analytical model considering the phase delay for capacitive pick-off circuits is built up in theory. Only when they use their proposed novel modified double side-band demodulation configuration for resonators to extract motional amplitude and phase, the phase delay of pick-off circuits can be eliminated and extracted meanwhile in real time. Experiments show that the changing feature of phase delay primarily depends on temperature rather than drive frequency. Experimental results agree well with the theoretical model and reveal the relatively high correlation between the phase delay and temperature. This work provides a new indicator of temperature for resonators, using this phase delay of the pick-off interface, to make temperature compensation.

A novel miniaturised dual-band bandpass filter (BPF) based on defected split-ring resonators (SRRs) and irregular stepped-impedance resonators (SIRs) is proposed. By applying defected SRRs embedded with eight combinations of three whole or broken grooves, which are formerly used for divination, the passband of 2.35–2.52 GHz with wideband harmonic suppression is achieved for WLAN applications. To create one more passband of 5.09–5.3 GHz, the irregular SIRs are etched inside the defected SRRs. Finally, such a prototype is designed and fabricated with the dimension of only 20 × 20 mm² (0.27λ _g × 0.27λ _g). The measured results of this dual-band BPF agree well with the simulations verifying the proposed idea.

For homogeneous microwave heating in a microwave cavity with multiple 2.45 GHz microwave generators, power-controlled phase-shifting mode is proposed in this Letter. The proposed microwave heating system consists of a multimode microwave cavity in which dielectric materials are placed to be heated, four phase-shifting WR-340 waveguides for different phase excitation, four 1 kW magnetrons that produce microwave power at 2.45 GHz, and a power supply with a system controller for the magnetron output power controls. Using the proposed power-controlled phase-shifting mode, uniform heating distribution is achieved by reducing the hot and cold spots in the microwave cavity. The proposed experiments demonstrated that in comparison to a conventional mode with simultaneous multiple inputs, the proposed mode can achieve an improved heating uniformity of 64.4.

This Letter presents a method for designing a switchable differential filter with high performance using dual-mode dielectric resonator (DR). It consists of a half-cut dual-mode DR, four feeding probes and a printed circuit board which is embedded in the bottom of the metal cavity to enable the integration of the four PIN diodes. In this case, the dual modes of the DR can be differentially excited well by two pairs of feeding probes for constructing the differential passband. By controlling the probe end as open/short status, the differential external quality factor can be adjusted so that the passband is switchable. To validate the proposed idea, a compact switchable differential filter with good performance is designed, fabricated and measured. The simulated and measured results in two states with the good agreement are presented.

In this Letter, a novel inverter-based trans-impedance amplifier (TIA) with enhanced gain and sensitivity is presented for Gb/s visible light communication (VLC). By employing capacitive feedback with a large negative equivalent capacitance to reduce the TIA input capacitance, the proposed TIA achieves a trans-impedance gain of 89.4 dBΩ with 5.7 dB improvement and an input referred noise current of 0.43 µA_rms with 1.8 dB improvement when compared to a reference TIA without capacitive feedback. Both the proposed TIA and the reference TIA have the same −3 dB bandwidth (BW) of 3 GHz and the same power consumption of 1 mW, and they are designed with a 40 nm CMOS process.

The authors propose a control method based on the downhill simplex (Nelder–Mead) method for adaptive optical filters used for channel equalisation in optical communication systems. The performance of this method is compared to gradient methods in numerical simulations. The results show that the proposed method can adapt the filter to more rapid changes of the transmission channel than the gradient methods.

Being dependent on the analysis of intrinsic correlated characteristic between the quadrature components of the entangled microwave field and the uncertainty of measurement, the authors present a classical expression model of the entangled quantum microwave after the measurement. This model describes two correlated random processes. The time-domain characteristic and quantum characteristic of the expression model are discussed, which indicate the random correlated characteristic. Results are in agreement with the generation experiment of the entangled quantum microwave, which proves the rationality. On one hand, the merit of the classical expression is intuitive, which makes it easier to understand the non-classical characteristics of the entangled quantum microwave. On the other hand, it is more convenient to investigate the performance of free-space propagation and receiver detection by classical expression.

The authors report the polarisation insensitive operation of an arrayed waveguide grating using a polarisation rotator/splitter (PRS) waveguide device which attains identical wavelength characteristics and optical losses for both transverse electric (TE) and transverse magnetic (TM) polarisations. The proposed PRS device is composed of a rib structure waveguide and an asymmetrical directional coupler (ADC). The rib waveguide converts TM fundamental mode to TE first-order mode. The ADC splits TE first-order mode into the TE fundamental mode propagating in the sub-adjacent waveguide. Experimental results confirm that the proposed device operates independently of light polarisations; channel isolation is nearly 20 dB, and no transmission wavelength shift or polarisation dependent loss are observed between TE and TM polarisations.

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

In multistatic passive radar systems, the Cramér–Rao lower bound (CRLB) can be used to select the optimal illuminator of opportunity so that it provides the best estimation accuracy for target parameters. In this Letter, the monostatic and bistatic modified Cramér–Rao lower bound (MCRLB) for the Advanced Television Systems Committee (ATSC) signal, which is the pervasive digital television signal of opportunity for North American passive radar systems, is derived using the relationship between the ambiguity function of a signal and its CRLB. It is shown that the derived bistatic MCRLB for the range and velocity measurements can be used to select the optimal illuminator that exhibits the lowest bounds at each region. Examples are provided in the Columbus, OH area where the Ohio State University passive radar is located.

The focusing of squint beam-steering synthetic aperture radar (SAR) data is a challenging task for the technical difficulty of space-variant range cell migration correction (RCMC). It is more complicated when considering the manoeuver of high-speed platforms. The conventional Doppler domain RCMC method is with low performance and requires a large amount of zero-padding. This Letter proposes a modified RCMC method which removes the space-variant range cell migration (RCM) components by deramp-keystone transform and then compensates the unified RCM terms in the time domain. Compared with the conventional method, the proposed one is with high performance and can avoid zero-padding. This method is validated by the simulated SAR data.

A novel micro-printing process, using anodic bonding to deposit patterned diamond-like carbon (DLC) coatings on glass, is investigated. Various patterns such as squares, triangles and letters are successfully fabricated. The coatings are characterised by Raman spectroscopy, atomic force microscope (AFM) and ultraviolet spectrophotometer. A G-band shift of approximately 1614 cm⁻¹ indicates that the DLC coatings have a relatively high content of sp³ bonds (>20%). The result of the AFM topography shows that the surface roughness of DLC coatings is 1.21 nm. The transmittance of DLC-coated glass wafer is above 85% ranging from 760 to 1100 nm, indicating that the patterned DLC coatings have high optical transparency in the infrared radiation spectral range.

Optimisation problems exist widely in real-life applications. A quantum-inspired optimisation algorithm under the harmonic oscillator well transforms the function optimisation into solving the ground state wave function through the transformation of the Schrödinger equation. A novel approach using energy equipartition for the exchange of energy information is present to construct the candidate solutions. Elitists preservation is utilised to preserve dominant energy information for the improvement of search efficiency. Experiments on benchmark test functions for the 30D problem show that the proposed approaches are more effective than compared algorithms.

A combined coprime and nested array geometry is designed and a corresponding direction of arrival (DOA) method is proposed. The proposed array has three subarrays, where two are prototype coprime subarrays, and both of them are nested to the third one. Then the vectorisations of two covariance matrices yield two virtual coprime subarrays, which show a much larger aperture compared to the physical ones. Thereafter, through Toeplitz matrix reconstruction and root multiple signal classification, two coprime estimations are obtained and they are combined to obtain the final unique DOA estimation. Multiple analysis and simulations verify that the proposed method achieves larger aperture, better DOA estimation accuracy and higher angular resolution compared to other coprime array-based methods.

In this Letter, a compressed channel estimation approach referred to as burst weighted -minimisation is proposed to alleviate the overwhelming pilot overhead in the downlink path of frequency division duplex (FDD) massive MIMO systems. The proposed approach exploits the burst-sparse property of channel as the prior support information (PSI) and sets adaptive weights for the channel coefficients according to the accuracy of PSI values. Furthermore, a novel greedy algorithm is elaborated, which extracts PSI from the massive MIMO channel. Simulation results demonstrate that the proposed algorithm outperforms other solutions in terms of the channel state information (CSI) estimation error.

The finite-impulse-response (FIR) decision feedback equalisers (DFEs) with a large number of taps are used to eliminate the intersymbol interference. In this Letter, a hybrid optimisation approach based on reweighted ℓ ₁-norm minimisation and the greedy algorithm is proposed to get a better estimation of the non-zero taps. First, the authors transform the problem of designing sparse FIR multiple-input multiple-output DFEs into an ℓ ₀-norm minimisation problem, then use the proposed approach, which involves two stages as the preliminary selection of non-zero tap positions and re-optimisation with non-zero taps, to determine the positions and values of the non-zero taps for the FIR DFEs. The simulation results demonstrate the effectiveness of the proposed hybrid optimisation approach.

A downlink non-orthogonal multiple access with QPSK input constellations based on virtual channel optimisation is presented to address the similar channel conditions scenario. The novel idea is to construct a uniquely decodable sum constellation by maximising the minimum Euclidean distance among the points of the superposed constellation. An optimal angle difference is derived to make the proposed scheme easy to implement. With a fixed angle pair setup, a non-orthogonal multiple access system without the knowledge of channel state information is proposed. Simulation results are provided to demonstrate the performance of the proposed scheme.