Since its inception, multiple-input multiple-output (MIMO) has become a magical technology that continues to break new grounds and deliver the needed upgrades in mobile communications. The emerging 5G systems are also being labelled by many as the massive MIMO generation. This somewhat oversimplified view is perhaps a reflection of the great impact MIMO has had on our generation of mobile communication networks. Although the technologies have evolved in the past decades, the principle remains the same—to exploit the diversity of different copies of signals at independent locations for reducing the degree of fading and randomness of wireless channels. Through signal processing and coding, the diversity has been translated successfully into capacity gain and enhancement in other forms of the quality-of-service. This article identifies “fluid” antenna as a trending technology that may succeed MIMO and become a reality to transform wireless communications to a new height. Fluid antenna is a radical approach that advocates software-controlled position-flexible shape-flexible antenna. The concept liberates antennas to unleash massive diversity inherent in the small space of a mobile device and makes possible new opportunities that were previously unthinkable. This article attempts to be imaginative and aims to take readers on a short journey of what fluid antenna might bring in future-generation mobile communications systems and speculate on its impact.

This Letter presents the design of a low-profile and low-cost transmitarray antenna operating at 122 GHz. The transmitarray design is based on unit-cells with 1-bit phase resolution. A single RO4350B substrate layer is used to form the unit-cells resulting in a total thickness of 0.326 mm. A wideband shift in the transmission phase of is generated by rotating one metal layer of the unit-cell by . The simulation of the transmitarray with elements and a feed distance of 35 mm shows a maximum directivity of 28 dBi at 122 GHz. Steering angles of and are investigated. Measurements of the fabricated transmitarrays are performed with an open waveguide and a package antenna as feed showing similar results but slightly different maximum relative gain values of 11.8 and 9.5 dB for the version. The measured main beam directions are in good agreement with the simulations and the design values.

Shipboard platforms have numerous antennas crowding topside space. Consolidating these antennas would require having antennas with multi-frequency capabilities. A Gregorian parabolic stacked antenna provides multi-frequency capabilities on a single pedestal which reduces the number of antennas required on a US Navy shipboard platforms. This Letter depicts the simulated design and radiation pattern results of a 1.9 m Gregorian parabolic stacked antenna that is capable of operating at the X-, K-, Ka- and Q-band frequencies at VSWR values <2:1. These frequency band capabilities allow for satellite communication links where two antennas that are currently fielded are operating within. The dual Gregorian parabolic stacked antenna presented is capable of operating at the same frequencies on a single antenna pedestal which would reduce the number of antennas required on shipboard platforms.

Rapid and accurate detection of COVID-19 is a crucial step to control the virus. For this purpose, the authors designed a web-based COVID-19 detector using efficient dual attention networks, called ‘EDANet’. The EDANet architecture is based on inverted residual structures to reduce the model complexity and dual attention mechanism with position and channel attention blocks to enhance the discriminant features from the different layers of the network. Although the EDANet has only 4.1 million parameters, the experimental results demonstrate that it achieves the state-of-the-art results on the COVIDx data set in terms of accuracy and sensitivity of 96 and . The web application is available at the following link: https://covid19detector-cxr.herokuapp.com/.

This Letter presents a millimetre-wave CMOS oscillator, which achieves 4.9 dBm output power with 16% peak power efficiency. A phase noise of at 1 MHz offset frequency and 26.7% tuning range around 57.5 GHz centre frequency were verified experimentally. To the best knowledge of the authors, the output power, efficiency, and phase noise performance are the best among fundamental CMOS oscillators in the frequency range of interest, while the tuning range is the third highest result reported to date. The circuit occupies a silicon area of without the matching inductors on a 22 nm fully depleted silicon on insulator (FD-SOI) CMOS technology.

Efficiency-enhanced and high-precision input common-mode feedback control (ICMFB) is proposed for a fully differential readout circuit of the MEMS capacitive sensor. This ICMFB improves the efficiency and performance of input common-mode voltage control using a smaller feedback capacitor. The noise performance of the readout circuit is improved as a decrease of a feedback capacitor. The correlated level shift (CLS) technique is used to improve the output swing of the amplifier therefore reduce the value of a feedback capacitor. Also, the oversampling successive approximation (OSA) technique is used to improve the accuracy of input common-mode voltage control using a low-gain op-amp. Simulation results show that the input common-mode voltage error decreases to 0.01% when the value of the feedback capacitor is the same as the MEMS sensor. Also, the noise power spectral density of the readout circuit increases by 10 dB.

This Letter presents a global shutter image sensor based on PIN photodiodes intended to be used for optical coherence tomography (OCT) in the spectral domain, where the light is brought to the photodiodes via optical waveguides monolithically integrated on top of electronics in a photonic layer. Photodiodes are optimised to have the peak responsivity in the wavelength range between 800 and 900 nm, while the main features of electronics are high signal-to-noise ratio, high frame rate, low-power consumption and low noise. The sensor is designed using 0.35 µm high voltage CMOS and employing low doped epitaxial starting material in order to improve the detector efficiency by enabling fully depleted photodiodes and lowering the crosstalk. Image sensor parameters are obtained using the photon-transfer curve method and compared with commercial cameras for OCT.

Camera-based object detection in low-light/night-time conditions is a fundamental problem because of insufficient lighting. So far, a mid-level fusion of RGB and thermal images is done to complement each other's features. In this work, an attention-based bi-modal fusion network is proposed for a better object detection in the thermal domain by integrating a channel-wise attention module. The experimental results show that the proposed framework improves the mAP by 4.13 points on the FLIR dataset.

Convolutional neural networks for image steganalysis demonstrate better performances with employing concepts from high-level vision tasks. The major employed concept is to use data augmentation to avoid overfitting due to limited data. To augment data without damaging the message embedding, only rotating multiples of or horizontally flipping are used in steganalysis, which generates eight fixed results from one sample. To overcome this limitation, the authors propose BitMix, a data augmentation method for spatial image steganalysis. BitMix mixes a cover and stego image pair by swapping the random patch and generates an embedding adaptive label with the ratio of the number of pixels modified in the swapped patch to those in the cover–stego pair. The authors explore optimal hyperparameters, the ratio of applying BitMix in the mini-batch, and the size of the bounding box for swapping patch. The results reveal that using BitMix improves the performance of spatial image steganalysis and better than other data augmentation methods.

Depth-image-based rendering (DIBR), as the most popular view synthesis method, is commonly used in the application of multi-view and free-viewpoint videos. However, the quality evaluation of DIBR-synthesised videos remains largely unexplored, which may hinder the development of more advanced view synthesis technology. With this motivation, this Letter presents a new quality metric for DIBR-synthesised videos. Specifically, the disoccluded regions are first detected based on an adaptive threshold to quantify geometric distortions. An energy-based sequence mapping strategy is proposed to portray spatiotemporal inconsistency by calculating first-order and second-order similarities in the gradient magnitude domain and the Laplace-of-Gaussian domain, respectively. Finally, the overall quality score is generated by pooling the scores of geometric distortion and spatiotemporal inconsistency. Experimental results demonstrate that the proposed metric outperforms the state-of-the-art metrics dedicated to DIBR-synthesised images and videos.

Identification of time delay is a prerequisite for the realisation of control compensation. The existing researches generally assume that the system input should be monotonic, which is unsuitable for online identification due to system saturation. To solve this problem, relaxed input conditions are developed in this Letter. Then a modified least-square algorithm with forgetting factors, which has a strong ability in tracking time-varying delays, is presented. Meanwhile, two extra terms whose design parameters are adjusted online according to the input condition are added into the covariance update law to guarantee the boundedness and robustness of the algorithm. Simulation results demonstrate the superiority of the proposed method and the reasonableness of the developed input conditions.

This Letter introduces an optimisation method that is based on parallelism to simulate the behaviour of foraging ants using spiking neural P (SN P) systems. The proposed method is designed by collaborating several SN P systems to obtain a polynomial time optimal solution. The complexity and reliability of the method have been verified. A theoretical analysis has been performed on the measures of complexity and proved the efficiency of the scheme.

Two screen printing inks were developed for the low-temperature fabrication of printed and flexible thick film negative temperature coefficient thermistors able to operate at room temperature. The first of the two screen printing inks developed utilised cobalt ferrite (CoFe₂O₄) as the temperature sensing material with the second ink incorporating manganese ferrite (MnFe₂O₄). These were then screen printed onto lithographically printed silver interdigitated electrodes with a 200 µm track and gap using a synthetic paper (Teslin) as the substrate. The inks required a 10 min curing step at 80°C. Pre-annealing of the ferrite powders before ink formulation enabled the avoidance of high-temperature processing post-fabrication typically required in industrial thermistor production. The printed thermistors were tested at a controlled constant humidity between 15 and 50°C. Both materials demonstrated typical natural logarithmic responses with high linearity and sensitivity.

This Letter presents a new real-time and compact current-mode temperature sensor for system-on-chip thermal monitoring. The proposed temperature sensor provides a low-cost readout scheme that utilises a current switching comparator and dual-control bucket searching algorithm. It does not require an ADC or charged capacitor with large area and power dissipation. The dynamic element matching and threshold-setting techniques are employed to further increase the accuracy of the proposed sensor. It is fabricated with a standard 55 nm CMOS process, achieves an accuracy of while occupying a silicon area of , and consumes with a conversion time.

An anti-parallel (AP) diode pair based on a Fermi-level managed barrier (FMB) diode was developed for the sub-harmonic mixing of terahertz waves. A quasi-optical module integrating an AP–FMB diode pair and a trans-impedance amplifier exhibited a very low noise-equivalent-power of 9 × 10⁻¹⁹ W/Hz at an input signal frequency of 304 GHz with a very low local oscillator power of 30 μW.

This Letter presents a miniaturised multi-channel millimetre-wave filter bank implemented by stripline and substrate integrated waveguide (SIW). Since the orthogonal transverse electric mode and transverse electromagnetic mode can coexist in the same hybrid structure cavity and be transmitted almost without mutual interference, embedding stripline into SIW to miniaturise the size of the filter bank is achievable. A prototype composed of four bandpass filter units working at X-band is designed, fabricated and tested. Measurement results show that the proposed device has four independent channels with a good quality of bandpass filtering and the isolation among ports of different filter units are relatively high. The proposed prototype has 39.5% volume reduction than traditional stacking structure as well as good scalability, which has broad prospects in the application of next-generation wireless communication system.

Photonics-based radar enables a large operation bandwidth that is particularly favourable for high-resolution synthetic aperture imaging. However, how to implement fast and high-accuracy imaging with photonics-based broadband radar is still an open question. In this Letter, the performance of photonics-based inverse synthetic aperture radar imaging with frequency-domain and time-domain algorithms are experimentally investigated and compared. The results show that, frequency-domain range–Doppler algorithm has fast imaging capability, but the image suffers from defocusing and distortions. Although migration compensation techniques can be applied to improve the imaging accuracy, the imaging speed is significantly reduced. On the other hand, using time-domain back-projection (BP) algorithm can achieve well-focused images, and the imaging speed can be enhanced with fast BP methods. Therefore, the time-domain imaging method is found to be the best choice for fast and high-accuracy synthetic aperture imaging with photonics-based broadband radars.

Owing to the existence of non-line-of-sight (NLOS) signals in global navigation satellite system (GNSS) challenged environment, the real-time kinematic (RTK) position precision is seriously damaged. In order to improve the position accuracy, the authors propose a robust positioning method which tackles this problem by detecting the NLOS through a decision tree and estimating the double-differenced multipath errors in real time. The NLOS detection performance of the proposed method is 95.64%. The field experiment shows that the ambiguity fixing rate has improved by 43% in the instantaneous mode, and the 3D position accuracy is about 81.77% higher better than that of normal RTK method which is implemented by using RTKLIB software.

In this Letter, the authors report a flexible CMOS chip converted by a novel chip transformation process. To realise a truly flexible CMOS chip, a two-step etching process was employed in the transformation process: (i) vapour etching to remove inter-dielectric layers followed by polymer encapsulation and (ii) plasma etching to remove the substrate of the chip. The I–V results measured after the chip transformation process show a voltage variance of <0.8% compared to the rigid chip. The bending test also revealed very small changes (0.6%) under strain conditions. Their results offer a viable route to use the foundry-fabricated CMOS chip for flexible chips; thus, a high-performance flexible chip can be realised. This technology will enable us to utilise various foundry-processed chips for future flexible applications such as health and environment monitoring, advanced mobile communication systems, and wearable electronics via a simple post-transformation process.

A reverse conducting (RC) insulated gate bipolar transistor (IGBT) with p-float and n-ring surrounding trench-collector is proposed. The p-floats surrounding sidewalls of trench-collectors suppress snapback and also avoid snapback when there are semiconductor/trench-collector interface charges (Q _f). The n-rings surrounding the top of the trench-collectors speed up the forward recovery and ensure a high breakdown voltage. Technology computer aided design (TCAD) simulations are carried out to compare the proposed RC-IGBT and the RC-IGBT with p-poly trench-collector (PTC RC-IGBT). With Q _f = 1 × 10¹¹ cm⁻², the proposed RC-IGBT is snapback-free while the PTC RC-IGBT has a snapback voltage of 4.43 V. The peak forward recovery voltage of the proposed RC-IGBT (12 V) is much lower than that of the PTC RC-IGBT (246 V). Besides, the reverse recovery charge of the two RC-IGBTs is 48% lower than that of the PiN diode.

Active noise control is an expanding field that requires a suitable synthesis of secondary perturbations. Unfortunately, most schemes for noise cancelling do not take into account that the input signal that drives the adaptive filter can be noisy. In this Letter, it is theoretically shown that noise perturbations in the excitation data degrade the performance of the standard filtered-x least mean squares (FX-LMS) algorithm. Furthermore, a method that compensates such an issue is devised, and a first-order stochastic analysis of the resulting algorithm is performed. The results reveal that the proposed scheme outperforms the standard FX-LMS algorithm, even when the variance of the additive noise in the input is not accurately estimated.

A new, direct and practical scheme is proposed for determining the model orders of a system, its signal and disturbance using key properties of Kalman filter (KF). Unlike conventional methods, it enjoys the unique property of being both necessary and sufficient. The system is described by the Box–Jenkins model, whose accessible input and output are corrupted by unknown zero-mean white Gaussian-distributed disturbances and measurement noise. The signal and disturbance are outputs of asymptotically-stable linear time-invariant systems driven by an inaccessible input and a zero-mean white Gaussian noise process, respectively. Predictive analytics is used to estimate the input by exploiting its smoothness and the randomness of the noisy input. The system, signal, and disturbance models and their associated KFs are identified for various selected model orders by minimising the KF residuals so that these become zero-mean white noise processes. The selected model-order corresponds to the minimum-variance residual. Equivalently, the minimum order is selected when the number of poles or the output estimates of the identified models are all identical for all orders equal to, or exceeding the minimal order. The scheme is successfully evaluated and shown to outperform the commonly-used but only sufficient Akaike Information Criterion.

In this Letter, based on certain binary Golay complementary pairs and deletion function, a new construction of binary near complementary sequences with low peak-to-average power ratio is proposed. The length of these sequences takes the form (where a, b and c are non-negative integers) and has not been reported before.

In this Letter, a new beamforming technique called sliding beamforming is proposed for target detection when a strong jamming signal is present. The basic philosophy of the sliding beamforming is to repeat an antenna-pair beamformer in a sliding manner across the array to completely eliminate the jamming signal while preserving the gain of the array. For uniform linear antenna arrays, only a single beamformer weight is required so that the sliding beamforming has very low implementation complexity. Moreover, the sliding beamforming is also effective to handle the case that the jamming is in the array mainlobe. Output signal-to-interference-plus-noise ratio of the sliding beamformer is studied. A radar target detection example using the sliding beamforming is presented as well.

The third generation partnership project has recommended π/2-binary phase-shift keying (BPSK) in discrete-Fourier-transform-spread orthogonal frequency division multiplexing (DFT-s-OFDM) for low peak-to-average power ratio (PAPR) uplink transmission. Recently, the rotation angle of 7π/6 for rotated BPSK has been proposed by J. Kim et al. to achieve optimal PAPR performance. However, the authors discovered that this angle might negate the contribution to PAPR reduction in most number of allocated subcarriers owing to the discrete-Fourier-transform (DFT) boundary-matching problem. To solve this issue, they propose a novel scheme to fine-tune the rotation angle to approximately 7π/6 in a manner compatible with the long-term evolution/new radio specification, while ensuring that the data phase matches the periodicity. Simulations show that the proposed scheme can stably improve the PAPR by ∼0.2 dB compared to π/2-BPSK for any DFT spacing, thereby benefiting user equipment by providing better power efficiency and wider signal coverage without additional computational complexity.