Passive acoustic monitoring records large amounts of acoustic data, and thus an efficient detection method is essential to analyse these data. A novel approach is proposed to automatically detect odontocete echolocation clicks. A time–frequency filter detects echolocation clicks in the time–frequency domain, and then the Teager–Kaiser energy operator and Gabor curve-fitting method determine the start and end points of each echolocation click precisely. Detector performance is assessed by using synthetic data. The experimental results showed that the recall rates were higher than 90% when the signal-to-noise ratio was above 10 dB.

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.

The fabrication of a patch antenna using low-cost 3D printing equipment is presented. The circular polarised patch antenna is manufactured by combining inkjet printing and stereolithography technology. The substrate has been fabricated by curing photosensitive resin while the patch element of the antenna has been inkjet printed using silver ink. The printed antenna satisfies the required reflection coefficient, axial ratio and radiation pattern at 1575 MHz. The aim is to demonstrate an inexpensive technology that could be used for the fabrication of antennas on customised 3D printed substrates. The performance of the antenna is summarised through simulations and experimental results.

A novel smooth horn with tanh/linear dual profile is proposed and the low sidelobe level is achieved. Measured results demonstrate that sidelobes <−37 dB can be achieved on the principal cuts of designed radiation pattern at 92–97 GHz. Also, the measurements are in accordance with the simulated results. It is shown that low sidelobe level can be obtained by the proposed horn geometry without tremendous amounts of time and money designing and manufacturing.

To create an active phase-gradient metasurface relying on variable inductance, an impedance converter is used to realise positive inductance values. By varying the inversion coefficient, a variation of the inductance can be achieved electronically. A prototype of the circuit is fabricated and tested. Different inductance values are obtained with respect to the inversion coefficient used. Such circuit can be readily applied to an LC resonant cell to control the phase responses. A potential application for beam steering is further numerically verified.

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.

A method for wideband transmit beamforming using integer-time-delayed and phase-shifted waveforms is proposed. Unlike traditional true-time-delayed digital methods, which employ variable fractional delay filters or discrete Fourier transforms to create fractional time delays, the proposed method uses only integer-time-delayed waveforms with phase shifts corresponding to fractional time delays. Furthermore, the shifted phase can be directly generated; this generation can be simply achieved by controlling the parameters of a direct digital synthesiser. A beam pattern simulation confirms that the integer-time-delayed and phase-shifted waveforms are capable of synthesising wideband transmitting beam patterns. Finally, a power synthesis efficiency analysis demonstrates that the synthesis loss caused by phase shifting is negligible.

To study acute emotional stress, a linear approach may not correspond to the non-deterministic variation due to aetiology of the stress phenomenon itself. Besides that, assuming a linear model such as classic heart rate variability analysis usually has high computational cost and high artefact dependency. A nonlinear approach based on Chaos theory using Higuchi fractal dimension (HFD) is presented to define a measurement methodology for acute emotional stress. HFD was computed for a set of electrophysiological signals recorded during relax and stress states of an ad hoc experiment. Results show that for most of the signals HFD is able to differentiate among relax and stress states. This approach applied to electrocardiogram signals is not affected by the sample rate and does not need pre-process filtering. Photo-plethysmography data is only significant in the highest stress state. So, it can be used to evaluate stress levels higher than those had in this experiment.

In this Letter, a highly reconfigurable crossbar transmission line switch matrix for magnetic resonance imaging (MRI) system is proposed. Unlike the conventional M × N crossbar switch configuration, the proposed structure can manipulate 2M × N matrix without doubling the area occupancy. Also, the proposed structure includes the signal loss-compensation circuitry based on inductor banks to enhance signal-to-noise ratio (SNR). Thus, for any required numbers of input and output channels, the proposed structure can reduce the overall size, the number of required component, and even increase the quality of MR images by SNR enhancement. The proposed structure was implemented and verified at 4-Tesla (170 MHz) MR system through the comparison of RF path loss, SNR and phantom test image qualities.

Reliability has become one of the most crucial issues in network-on-chip (NoC). But how to keep low latency and power consumption when achieving reliability is still a curial challenge. A novel scheme for reliable NoCs is proposed. In the scheme, header flit is protected from router to router and data is protected from end to end. To implement the scheme, a new header protection buffer in routers is designed, which can check the timing errors and tolerate the soft errors simultaneously. Instead of checking on each router, data packet is only decoded and checked on receiver's network interface. In this way, the scheme ensures reliable transmission with low latency and power consumption. Experimental results show the feasibility of the proposed scheme in terms of power consumption, latency and area cost.

During the last decade, an emerging branch of computer science (biologically inspired engineering) has been made intensive studies to create an efficient CPU based on spiking neural P systems. Most of these studies have been focused on developing theoretical neural arithmetic circuits that could be integrated into an arithmetic logic unit. However, the memory system has a significant relevance since modern computers demand large memory bandwidth affecting significantly their performance and power consumption. Recently, the use of memory processing units (MPUs) allows to increase their performance by processing and storing the data in the same unit. This work maybe considered as a first step toward the design of a memory system highly inspired by the neural processing of the soma, dendritic behaviour and astrocyte-like control. In addition, the basic neural single neural (SN) P memory cells can compute intrinsically two basic arithmetic operations (addition and subtraction) that potentially allow the development of a neural MPU system without modifying the basic structure of the neural SN P memory cell. High definition video processing is one of the potential applications to apply the proposed neural MPU to increase the processing speed compared with existing approaches.

Model-based control algorithms commonly use joint acceleration as a desired trajectory. As the velocity trajectory in the task space is converted into joint velocity by multiplying using a Jacobian matrix, to derive the acceleration in joint space, Jacobian differentiation is required. Although the numerical method for Jacobian differentiation gives sufficiently accurate approximations, it incurs a high computation cost because this method involves computing the forward kinematics twice and Jacobian derivation for every element of the Jacobian matrix. Consequently, this causes difficulties for real-time control. To resolve this, an analytical differentiation method is proposed. Through recursive computation, differentiation is performed without any approximation, in an acceptably small computational time. Performance of the proposed method was verified by comparison with numerical derivation using a computer simulation.

A non-invasive and automatic control method based on real-time virtual reality and reinforcement learning is reported to modulate insects’ flight behaviour. The online configurable LED display system is proposed to present the visual stimulus within ultra-low latency. State-action-reward-state-action (SARSA) coupled with sequential K-means clustering is applied to generate optimal control sequence automatically to ensure the satisfactory control performance. By evaluating the control results of 15 bumblebees, it shows that the proposed method achieves to modulate the abdominal waving pattern quickly (less than six steps) with small deviation (<0.03).

The speed control problem of a time-delay DC motor system is proposed because the control performance can severely deteriorate under uncertain delay time information. Since most of existing delay compensators require exact system parameters and delay time information, the performance improvement has been limited under delay time uncertainty. The proposed method incorporates a disturbance observer on the slave side of the system with a communication disturbance observer that does not require the delay time information for generating a predicted output signal. The effectiveness of the proposed algorithm is tested through comparative simulations and experiments using a testbed system under large delay time uncertainty.

Recognising places under extreme perceptual changes is a challenging problem. A new dynamic programming method to align sequences of image features extracted from a deep convolutional auto-encoder to efficiently solve this problem is proposed. As this method considers not only environmental variations, but also the motion constraint of the mobile robot, places from changing environment can be successfully recognised by finding the most likely path sequence. Experimental results show improved precision–recall performance compared with other algorithms.

A conditional random field (CRF)-based framework is proposed for depth refinement. It consists of two phases: depth impainting and depth super-resolution (SR). The CRF inference procedure uses depth information enhanced in three different ways to ensure the accurate edge of the final depth output. The experimental results show the effectiveness of the method both numerically and visually. Note that the method produces depth map with better edge than other depth impainting and SR methods do.

Due to the edge-preserving ability, the bilateral filter is considered as the fundamental tool in computer vision and computer graphics. However, its computational complexity has a close connection with the size of the box window. This drawback leads that the bilateral filter is inappropriate for the computational insensitive application. One way to accelerate the bilateral filter is to approximate the Gaussian range kernel by trigonometric functions and synthesise final results from a set of filtering results of fast convolutions. A novel approximation that can be applied to any range kernel is proposed. Specifically, first the Z transformation of the range kernel is obtained, then approximate the Z transformation of the range kernel using the Padé Approximation. Finally, inverse the transformation of the Padé approximation and obtain an exponential sum to approximate original range kernel, where the coefficients of the exponential basis are computed by solving a set of linear equations. Experiments show the method achieves state-of-the-art results in terms of accuracy and speed.

Deep models have recently shown improved performance on numerous benchmark tasks in computer vision and machine learning. The availability of huge amount of digital data, possibility of massively parallel computations on graphics processing units and the development of advance optimisation techniques have pushed the limits of the deep learning framework by superseding the performance of state-of-the-art research, in specific the kernel methods. This research proposes a novel connection between the two paradigms of research and shows empirical evidence to emphasise that the knowledge learnt from one domain could be supplemented with the significant properties of the other domain to achieve the best of both the worlds. The proposed hybrid methodology illustrates the advantages of deep architectures for kernel methods by showing significant improvement in the classification performance on benchmark tasks with kernel methods. It is shown empirically that the results achieved are either better or competitive to the leading benchmarks from support vector machines and deep models.

A novel illumination normalisation (IN) method using a convolutional neural network (CNN) is proposed. The proposed network is composed of the local pattern extraction (LPE) and illumination elimination (IE) layers. The LPE layers model the relationships between the pixels in each local region in order to handle various types of local shadow and shading in the face image. Based on the commonly used assumption about the illumination field, the IE layers generate illumination-insensitive ratio images by calculating the ratio between the output pairs produced from the LPE layers. The final feature map obtained by combining the ratio images can possess an improved discriminative ability for face recognition (FR). For training the proposed network, the results produced by the Weber fraction-based IN methods as ground truths are utilised. The experimental results demonstrate that the proposed network performs better in terms of FR accuracy compared with the conventional non-CNN-based method and it can be combined with any CNN-based face classifier.

Reading back of the instructions acquired by pilots through radiotelephony communication from air traffic controllers plays a very important role for civil aviation safety. Whereas the mistakes of readbacks are difficult to find out when the controller or the pilot is under great pressure, fatigue, tension etc. To solve this problem, the authors propose a novel semantic consistency verification method based on recurrent neural network with long short-term memory structure (LSTM-RNN) for Chinese radiotelephony readbacks. The actual Chinese civil aviation radiotelephony recordings are converted to textual format, and the semantic similarity is studied to verify whether the semantics is the same between the controller instructions and the pilot readbacks. The word-based feature is extracted by one-hot vector, and LSTM-RNN is employed to build up a deep network architecture for producing high-level sentence semantic abstraction of the initial input instructions and readbacks pairs. Cosine similarity is used to quantify the semantic similarity, and different classification methods are adopted to verify consistency in semantics. The experimental results show that the method is effective and provides a new scheme for the intelligent checking of aviation radiotelephony readbacks.

Expectation propagation (EP) has been used for Gaussian approximation of discrete-valued symbols to achieve low-complexity message passing based detection. It has been shown that EP-based Gaussian approximation significantly outperforms the direct Gaussian approximation. A doped EP (DEP) approach to Gaussian approximation is proposed, where the EP message is mixed with the Gaussian message obtained through direct approximation. It is demonstrated that the DEP approach delivers remarkably better performance than the EP one.

The standard i-vector/Gaussian probabilistic linear discriminant analysis (G-PLDA) system does not compensate for duration mismatch, which is a significant confounding factor in short duration speaker verification. A novel duration compensation technique to normalise the distribution mismatch caused by duration variation in the i-vector space is proposed. The proposed technique involves the use of two factor analysers that are tied together to share latent variables for a given speaker as the underlying generative model of the i-vector space. This leads to a transform which maps the original i-vectors onto a latent subspace that is expected to be duration invariant. The proposed method has the advantages that it normalises distribution mismatch while taking into consideration both inter- and intra-speaker variability. Experiments conducted on NIST SRE 2010 database shows that the proposed method leads to 18.54, 15.48 and 8.77% relative improvements when tested on utterances of 10, 5 and 3 s durations, respectively, compared with the best results obtained by either standard i-vector/G-PLDA or the previously proposed twin model G-PLDA.

Software routers are becoming popular building blocks of software defined networking, due to their low cost and flexibility. Netmap is a platform that allows packet processing with high throughputs using standard computing hardware. The algorithm for energy-efficient network processing based on netmap platform, named energy-efficient netmap (EEN) is proposed and evaluated. EEN saves the energy by minimising the number of active cores needed to handle the given traffic load. Appreciable energy savings that can be achieved by the proposed algorithm is demonstrated.

This Letter presents interference cancellation and signal detection technique for faster-than-Nyquist (FTN) signalling. The proposed scheme uses QR decomposition (QRD)-M algorithm to execute interference cancellation and signal detection. Based on the Toeplitz structure of the inter-symbol interference coefficient matrix, the QRD-M algorithm is adopted to detect the transmitted symbols from an FTN signal. The computational complexity comparisons and numerical results demonstrate that the proposed technique can achieve the complexity <10% of Bahl–Cocke–Jelinek–Raviv (BCJR) algorithm while maintaining BER performance similar to that of BCJR algorithm.

A new parameter is introduced to the method of polarisation which is dual to the Bhattacharyya parameter in some sense. Through this parameter, the authors give an alternative proof on the result about the speed of the entropy polarising to 1.

RF design and implementation of ceramic-filled resin-based 3D printed millimetre-wave bandpass filters (BPFs) using a new class of compact high-quality-factor hemispherical cavity resonators are addressed. Design concept of the hemispherical resonator is discussed for BPF applications in both X and Ka bands. For validation purpose, the Ka-band fourth-order BPF is fabricated with a high-temperature-resistant ceramic-filled resin using a fast and low-cost stereolithography-based 3D printing technique, and its surface metallisation is realised by employing electroless copper/silver plating. The proposed BPF's geometrical configuration contributes to a significantly improved out-of-band rejection. The RF-measured results demonstrate the Ka-band BPF an insertion loss of 0.43−0.9 dB from 31.52 to 32.42 GHz, a passband return loss mostly better than 15 dB, and a small frequency shift of about 0.06%.

An original and integrated solution to provide frequency agility to microstrip circuits using plasma is proposed. A volume DC plasma discharge is implemented inside a microstrip circular resonator to change its dielectric permittivity in order to tune its frequency. Plasma relative permittivity indeed exhibits positive values lower than 1. Experimental measurements confirm the tuning abilities and performances of such a solution for different pressures and types of gas.

In this Letter, the perfectly matched layer (PML) absorbing boundary condition is incorporated into the unconditionally stable radial point interpolation meshless method based on Crank–Nicolson radial point interpolation method scheme. By splitting field variables in the whole computational domain, all variables are defined in the support domain of nodes near PML boundary, and an implicit time-stepping formulation is derived. Numerical experiment is implemented to demonstrate the performance of the implemented PML.

Variable propagation constant directional coupler is proposed and demonstrated. Compared with its conventional counterpart, the proposed coupler uses variable waveguide propagation constants as an extra degree of design freedom to achieve the required signal addition and cancellation. The operation principle is mathematically formulated and a step-by-step design methodology is presented. Two double-layer two-hole substrate integrated waveguide couplers: namely, one forward directional coupler and one backward directional coupler, are fabricated to validate the proposed concept. A coupling of −20 dB is achieved in both couplers and the maximum isolation of −47 and −52 dB are obtained by the forward and backward structures, respectively.

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.

A Brillouin grating-based optical low coherence reflectometer (OLCR) using a broadband light source is constructed. The reflection distributions of Brillouin gratings generated at mated fibre connectors are measured. The measured reflectograms agreed with theoretical curves calculated from the coherence function of the OLCR, showing that the OLCR technique made it possible to measure Brillouin gratings with a spatial resolution of the order of 100 μm.

Neutral-point-clamped (NPC) three-level converter has been widely used in wind power generation systems. However, traditional NPC three-level converter often suffers excessive voltage fluctuation at the neutral point of DC-link capacitors. This problem may leads to switching devices damage and increases additional harmonics in output voltage of the converter. To solve this problem, a compensating scheme based on a current compensation method is proposed. The results show that the proposed scheme can alleviate considerably voltage fluctuation. Consequently, it is effective and can also enhance the reliability of the converter.

Forward scatter radar (FSR) is actively studied in the field of radars, as it has many advantages such as robust to radar absorbing material and possibility in target recognition. In many radar systems, micro-Doppler signature is one of the most distinguished information used for target recognition. Yet, there is lacking in established work on investigating the feasibility of using FSR to detect and analyse micro-Doppler signature generated from micro-motions of moving targets. Hence, a theoretical and experimental investigation of using the FSR to detect micro-Doppler signatures is presented. The preliminary results for both theoretical and experiment investigations verified that the FSR system is capable to detect the micro-Doppler signature for a swinging pendulum attached to the moving trolley.

The current spaceborne synthetic aperture radar systems are operated to illuminate the scene along the satellite flying direction. However, in many cases, the interested areas are not parallel to the flying direction, so an innovative smart imaging mode is acquired, which can be employed for illuminating scene along a given direction. A novel three-axis attitude steering method is proposed for smart imaging mode. First, mathematical model of the attitude steering is built by considering the restrictive conditions of zero-Doppler centroid requirement and the position of interested area. Then, an iterative optimisation algorithm is designed to calculate the three-axis steering angles. Finally, experiment results using the satellite tool kit tool validate the proposed methods well, especially in the case of coastline imaging.

A single source bins (SSBs) detection based multiple source localisation scheme is proposed. This scheme is based on detecting the SSBs in mixture signals that are only derived from one source. Specifically, after proposing a ‘DOA convergence’ assumption, K-means clustering algorithm is used for SSBs detecting. Thus, the multiple source localisation is converted to a single source one among these SSBs. Moreover, the proposed SSBs detection is applicable to other localisation methods and not limited to specific microphone topology. Experimental results demonstrate the localisation accuracy of the proposed method outperforms the localisation approaches which are based on single source zone detection.

A cognitive cross network where both primary and secondary users’ receivers are closer to the transmitter of the other user; however, the distances to their own transmitters are too large that a relay is required for a reliable communication, is considered. To this end, the secondary user shares its relay with the primary user (PU) by means of physical-layer network coding in exchange for access to PU's licensed band. It is assumed that both transmitters and the relay adopt the emerging spatial modulation concept to improve the error performance. Bit error probability of the proposed scheme is analytically derived and supported via computer simulation results.

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.

A joint power splitting ratio optimisation and power allocation scheme is proposed to maximise the energy efficiency in amplify-and-forward two-way relay networks with the simultaneous wireless information and power transfer scheme. Both the locally optimal solution and simplified equal power allocation scheme with closed-form expressions are derived. Simulation results show the effectiveness of the proposed schemes.

In this Letter, a combined algorithm known as receiver-assisted slow start (RASS) and feedback-assisted recovery (FAR) proposed to address the joint optimisation problems of transmission control protocol (TCP) such as non-optimal initial window (IW) size, slower window growth and spurious window deflation under multi-hop wireless (MHW) networks. The RASS fix the sender's optimum IW size from the receiver's advertised value and replaces the conventional exponential window growth with enhanced window increment mechanism that significantly accelerates the transmission rate. The FAR uses relay router's feedback information to regulate false transmission rate reduction during packet drops. The simulation result reveals that the proposed algorithms had a substantial improvement in throughput and reduction in packet latency over the existing standard New Jersey and non-congestion events algorithms under MHW environment.