Circulators are often used in RF systems; however, their size, cost, and weight increase greatly at lower frequencies (<300 MHz). The development of a load-insensitive active quasi-circulator is presented as an alternative for the traditional circulators to be used in low-frequency systems such as Doppler ultrasound. Major challenges to these active devices are limited power and low isolation between non-consecutive ports. The use of current-feedback operational amplifiers allowed higher-power delivery to the load. Simulations using Monte Carlo method showed an isolation >19 dB for 20% of variation of the load impedance. The circuit was implemented and tested with an ultrasound probe in a water tank. The results show that the circuit was able to send and receive signals simultaneously from a single ultrasound transducer element.

A low-profile broadband capacitive circuit absorber has been demonstrated both numerically and experimentally. The design consists of square loop resonators and lumped resistors periodically arranged on the top of grounded dielectric substrate. The novelty of the design lies in its capacitive reactance due to square loop geometry, which reduces the electrical thickness of the structure compared with the earlier broadband absorbers. The simulated results show that the structure exhibits reflectance below −10 dB from 1.91 to 5.75 GHz with the thickness of only 0.07λ_l at the lowest operating frequency. Furthermore, the proposed structure is polarisation insensitive as well as angularly stable. The structure has also been fabricated, whose measured result is in good agreement with the simulated response.

A ground radiation antenna with tunable metal loads is proposed to improve the performance of a normal antenna at 900 MHz for Z-wave applications. The proposed design is comprised of a 5 mm × 5 mm ground radiation antenna and inductor-connected metal loads in a 30 × 50 mm ground plane. The metal loads can take the form of rims, a frame, strips, or wires at the ends of the ground plane and are connected with lumped elements to allow easy adjustment. The proposed antenna was simulated to tune the metal loads, and was then fabricated and measured to verify its improved performance in the Z-wave band.

A wideband low-profile planar square segmented loop antenna for unmanned aerial vehicle (UAV) applications is proposed. The antenna consists of a square segmented loop, a patch element, and a shorting strip. The antenna operates at 956 MHz because the eight segments of the loop are electrically connected by capacitive coupling. By adding the patch element and shorting strip, the antenna has a wideband covering GPS L1, GSM1800, GSM1900, UMTS, LTE2300, LTE2500, and 2400 MHz ISM bands due to improved impedance matching. The antenna has omnidirectional radiation at 956 MHz and quasi-omnidirectional radiation over the broad bandwidth.

A 10 Mbps OQPSK transceiver working in the 400–450 MHz frequency range is designed for medical telemetry applications requiring wireless communication with both high data rate and low power consumption. An inverter based phase-switching transmitter has been proposed to lower the transmitter power consumption. Moreover, a digital-assisted DC offset calibration (DCOC) technique that combines the PGA-gain-uncorrelated DCOC method and a lookup table is adopted to enable an zero-IF receiver architecture. Fabricated in 65 nm CMOS process, both the transmitter and the receiver consumes ∼3 mW from 1 V supply at 10 Mbps data rate. The transceiver energy efficiency is ∼0.3 nJ/bit, which outperforms the similar designs in recent literature.

In biomedical applications, the similarity between a signal measured from an injured subject and a reference signal measured from a normal subject can be used to quantify the injury severity. A generalisation of the adaptive signed correlation index (ASCI) is proposed to account for specific signal features of interest and the trichotomisation of conventional ASCI extended to an arbitrary number of levels. In the context of spinal cord injury assessment, a computational example is presented to illustrate the enhanced resolution of the proposed measure and its ability to offer a more refined measure of the level of injury.

An ambient electromagnetic energy harvesting system for on-body sensors is presented. Specifically, a smart contact lens that monitors the glucose level in the tear fluid of a user is demonstrated. The energy harvesting system rectifies a portion of a cell phone/smartphone-emitted uplink signal into DC power for the operations of on-lens sensors and components. An actual cow eye is used to assist in various measurements of the proposed energy harvester. Ultimately, a power of 1 mW at about 1 V is harvested and delivered to a resistive load of 2 KΩ when a cell phone is held in a typical reading position. This harvested power level is more than adequate to enable numerous possible on-body sensors.

Myoelectric prostheses aim to help amputees to experience partial function of the absent organ. The sensors usually used to control the prostheses are surface electromyography (sEMG) electrodes, of which the number tends to increase with the increase of the number of degrees of freedom in the recent prostheses, i.e. dozens of sensors today. However, sEMG requires a high sampling frequency, traditionally about 1000 Hz, which drastically limits the number of sensors that the processors can manage. The objective is to develop a device enabling to measure muscle contractions (MCs) with a sampling frequency compared with the movement frequencies. Strain gauges are known for their accuracy, so using them to detect MCs could help to predict the movement intentions of the amputee. The designed devise includes the integration of four strain gauges in silicone rubber that is similar to human skin. The reliability of the sensor results is demonstrated by a comparison with Ag/AgCl electrodes of an electromyography system. The correlation coefficient is very high (0.89) between the tensions measured by the sEMG and the strain gauges. So the advantage of a low sampling frequency compared with sEMG is the potential development of matrices with many strain gauges.

CT images often have some ring artefacts caused by the inconsistent response of detector pixels and other factors. Removing ring artefacts effectively without impairing the image quality is still a hard problem although some methods have been proposed. Given that total variation minimisation is widely used for image denoising, a unidirectional relative variation model is proposed and performs it on the reconstructed images transformed into polar coordinates to reduce the artefacts. The proposed method is tested on both simulated data and real CT images, and the qualitative and quantitative results show that it is effective.

The development of an active ankle foot orthosis (AFO) to enhance the walking capacity is presented. The proposed device consists of a linear actuator mechanism with supportive brace and is controlled by measuring user's interaction force. Initial experimental characterisation of performance of the control system and system usability tested on healthy individuals are reported. Results indicate a decrease in muscle activation, by a factor of 29 and 26% for plantar flexion and dorsiflexion motion while walking with assistance from the developed AFO. The developed system has potential application in the field of assistive technology for geriatrics or for patient with mobility impairments, muscle weakness or as a performance enhancer.

A novel approach for the unscented transform calculation is detailed, showing a technique that can be used to obtain smoother estimates for probability functions based on Monte Carlo technique substitution. The method is computationally efficient for statistical moment estimation of nonlinear transformations and does not require full knowledge of the probability distribution of the random variables, being completely defined by its moments.

In dynamic random access memory (DRAM)-based main memory, access latency is a key performance metric. Commonly, the access latency is improved by employing row buffers that store the most recently accessed row data. However, if a new request tries to access a different row address from that in the row buffer, which is a row buffer conflict, the access latency is significantly increased. In a heterogeneous multi-core system, row buffer conflicts occur frequently because various types of processors with different access patterns share the main memory. A novel DRAM architecture that hides the latency penalty due to row buffer conflicts is proposed. The key idea is that read or write commands serviced during activate and precharge operations for different rows in the same bank are carried out by splitting the row buffer into two buffers. Experimental results show that the proposed DRAM architecture achieves up to 16% higher system performance for memory-intensive applications compared with a conventional DRAM architecture.

A time-based analogue-to-digital converter (ADC) that can exhibit both low power and high resolution is introduced. By amplifying alternate time residues and successively subtracting the comparator-induced timing offset, both fast conversion speed of 2N cycles for an N-bit converter and very small input-referred timing offset are achieved. For a 12-bit ADC implemented in a 0.18 µm CMOS process, an effective number of bits of 10.8 has been measured at a sampling frequency of 100 kHz, while consuming 30 µW of total power.

A new design method of an all-digital automatic gain control easy to implement is described and tested. The discretisation of the instantaneous gain provides a recursive form that merges the exponential function with the level detection. The first proposed circuit is well adapted for a software implementation. It comprises a simple control loop and two multipliers. It does neither contain digital filter nor divider and its setting only requires a loop gain parameter. Some tests were conducted on real digital audio signals with a dynamic range of 80 dB and they validate this approach. Under some conditions, the second circuit can even be simpler since it requires only one multiplier. It is well adapted to an field programmable gate array (FPGA) implementation for high speed signal processing.

A novel full reference image quality assessment method based on statistical local representation from two complementary sources: log-Gabor wavelet representation and local derivative pattern is presented. The dissimilarity of these extracted features between distorted and reference images is quantified and mapped into an objective quality score. Experimental results on large-scale database show that the proposed method not only outperforms the state-of-the-art methods in terms of high accuracy of image quality prediction, but also is robust across different distortion types with high computation efficient.

A redundancy model with generally distributed repair times, imperfect switchovers, and interrupted repairs is considered. Using supplementary variable method and integro-differential equations, the analytical expression of the availability for the redundancy model is obtained.

Unintentional modulation on pulse (UMOP) is the basis for specific emitter identification and has been studied for decades. However, the isolated distribution of UMOP in frequency domain has not been investigated. This Letter first gives the signal model of UMOP, and then evaluates its frequency-domain distribution based on sinc-function fitting. Experiments on real-world data validate the effectiveness of the proposed method, and further indicate that UMOP mainly distributes in low frequencies with dramatically limited bandwidth. Furthermore, the proposed distribution density can also serve as a practical UMOP feature which exhibits better recognition performance than conventional spectrum features.

The possibilities of a known class of chaos-based coded modulation (CCM) systems are expanded to address the problem of high-power amplifier (HPA) non-linearity. The hypothesis is that the CCM non-linear nature can be exploited to counteract its effects on the system perfomance, avoiding the need of a predistorter. An optimisation method for the design of the CCM to prove this hypothesis is proposed. The results show that, for a given back-off level, a non-linear mapping function for the chaos-based encoder and decoder can be designed to compensate the HPA effect on the error rate.

Self-learning convolutional neural network (self-CNN) for time series stream forecasting is proposed. First, the proposed self-CNN model was trained using the different types of the time series data. With the lapse of the time series stream the self-CNN model was self-trained again and again, which was using the previously predicted correct data as the input. Finally, the model was used to forecast the new time series data. The performance evaluation using the self-CNN method forecast and generate from the financial time series stream shows that the proposed self-CNN method performs better than the traditional Bollinger bands method.

A new phase shifter based on injection-locked ring oscillator is proposed. By using a multi-stage phase generator with voltage-controlled injection locking technique, the proposed phase shifter is able to generate a flexible combination of coarse and fine-tuned phase delays over a wide range of operating frequencies while a small silicon area is maintained. Fabricated in a 0.18 µm RF CMOS process which only occupies 50 × 40 µm, a proposed three-stage phase shifter achieves flexible phase delays and a measured operating frequency up to 2 GHz with a maximum power consumption of 2 mW from a 1.8 V supply.

A compact dual-band bandpass filter (BPF) with wide stopband performance using stub-loaded spiral short-circuit λ/4 stepped-impedance resonator is proposed. Spiral configuration has been used for compactness of filter. Both passbands can be controlled individually by changing the geometric parameters of resonator. Multiple transmission zeros provide high selectivity to both passband and extend stopband up to 3 GHz. The filter has compact size of 0.06λ _g × 0.09λ _g. A dual-band BPF has been designed and fabricated for terrestrial trunked radio (TETRA) band and global system for mobile communication applications.

A dual-band balanced-to-unbalanced filtering power divider by coupled ring resonators is proposed. Two passbands can be easily realised by the two coupled ring resonators. Three transmission zeros near the two passbands are used to improve the selectivity. The common mode can be easily suppressed by the bandstop performance of the open stubs. A fabricated prototype (ε _r = 2.65, h = 1 mm, tanδ = 0.003) with centre frequencies located at 2.82 and 3.22 GHz is designed and measured to prove the proposed methods.

A miniaturised equal/unequal substrate integrated waveguide power divider with bandpass filtering response loaded by complementary split-ring resonators (CSRRs) is proposed. The proposed structure is based on the theory of evanescent mode propagation. The use of the CSRRs enables the filtering function of the power divider and is able to reduce its size. By changing the orientations of the CSRRs, the equal/unequal power dividers are achieved. In the unequal power divider, the power ratio can be arbitrarily controlled by carefully tuning the parameters of the CSRRs and locations of the output ports. Three miniaturised filtering power divider samples with power division ratios of 1:1, 1:4 and 1:8 are fabricated and tested. These designs resonate at the frequency of 5.8 GHz covering WLAN. The sizes of the proposed power dividers (1:1, 1:4 and 1:8) are only 0.37 × 0.21λ _g ², 0.3 × 0.16λ _g ² and 0.3 × 0.15λ _g ², respectively.

An ultra-high bandwidth (BW) and a low V_π InP Mach-Zehnder modulator with an n-i-p-n heterostructure is proposed. The combination of the n-i-p-n heterostructure and the capacitive-loaded travelling-wave electrode provides a modulator with extremely low electrical loss. The device exhibits a 3 dB electro-optic BW of over 67 GHz and a V_π of 2.0 V. A 100 Gb/s non-return-to-zero on–off keying modulation with an extinction ratio of over 10 dB is also realised.

A CHF₃ inductively coupled plasma (ICP) based dry etching method is proposed for accurate etching of Ge waveguides. CHF₃ ICP based dry etching produces excellent anisotropy along with good selectivity with regards to regular polymeric photoresist, which leads to the elimination of under-cut. As a result, an almost vertical sidewall angle of 85° with an etching rate of 190 nm/min was realised with a relatively high selectivity ratio of 5:1 against regular photoresist.

Extremely scaled down tri-gate RF metal-oxide-semiconductor field-effect transistors (MOSFETs) utilising lateral nanowires as the channel, with gate length and nanowire width both of 20 nm are reported. These devices exhibit simultaneous extrapolated f _t and f _max of 275 and 400 GHz at V _DS = 0.5 V, which is the largest combined f _t and f _max, as well as the largest f _max reported for all III–V MOSFETs.

Hereby a novel thin film-based configuration of redox resistive switching memory (ReRAM) based on cheap and abundant copper sulphide (CuS) is reported. The devices working mechanism is based on the junction of two layers of CuS stacked nanocrystal with different stoichiometry (CuS and Cu_2−x S). CuS thin films were deposited using a fast, easy and low-temperature drop-casting technique. The devices shown memresistive characteristics, with well-defined ON and OFF resistance states, inducible by voltage pulses. A polynomial model has been proposed to characterise the devices considering both space-charge-limited current and ionic diffusion.

Resonant optical strain sensors, obtained by closing in loop coupled π-shifted Bragg gratings (π-FBGs), are reported. Despite of a conventional π-FBG, showing a transmission Lorentzian resonance in the reflection band, the coupled π-shifted Bragg grating structure is characterised by a spectral response formed by a split doublet of the primary transmission Lorentzian mode of π-FBG. By closing in loop this structure, the coupled π-shifted Bragg grating ring resonators show better performance than π-shifted Bragg grating ring resonators in terms of strain sensitivity (i.e. 2.86 pm/με) is demonstrated. Thus, the coupled π-FBGRR is suitable for enhanced sensitivity strain sensing applications.

Highly efficient interface-dominated electrical injection lasers in the near-infrared regime based on the type-II band alignment in (GaIn)As/Ga(AsSb)/(GaIn)As single ‘W’-quantum wells are realised. The structure is designed by applying a fully microscopic theory, grown by metal organic vapour phase epitaxy, and characterised using electroluminescence measurements and broad-area laser studies. A characteristic blue shift of 93 meV/(kA/cm²) with increasing charge carrier density is observed and compared with theoretical investigations. Low threshold current densities of 0.4 kA/cm², high differential efficiencies of 66%, optical output powers of 1.4 W per facet, and internal losses of only 1.9 cm⁻¹ are observed at a wavelength of 1164 nm for a cavity length of 930 µm. For a cavity length of 2070 µm, the threshold current density is reduced to 0.1 kA/cm². No indication for type-I related transitions for current densities up to 4.6 kA/cm² is observed.

The wireless power transfer (WPT) system based on dual-coupled transmitters has been proved to be a good alternative for high-power applications. However, the efficiency of the WPT system is various with different loads. An active rectifier (H-bridge) is equipped in the secondary side to replace the passive rectifier (diode rectifier). By controlling the conduction angle and the output voltage of the active rectifier, the equivalent optimal load of the secondary side can be achieved. Owing to the equivalent optimal load, the WPT system with dual-coupled transmitters can achieve optimising power efficiency. The experimental results agree well with the theoretical analysis. The results show the proposed efficiency optimising strategy is a good candidate for a WPT system with dual-coupled transmitters.

For an energy harvesting relay network, an optimal secure transmission scheme is proposed. In the case of limited harvesting energy and total power, destination-based jamming technique is applied to protect the confidential information from relay's jamming and eavesdropping. Moreover, the penalty function algorithm is utilised to obtain the optimal power allocation factor to maximise secure rate. The impacts of power allocation factor and energy transformation efficiency on the system secure rate are analysed. Simulation results validate the correctness and efficiency of the proposed scheme.

Energy harvesting using the human body as an antenna is presented. Low-frequency interference, mainly in the 40–60 kHz range, was generated from electronic ballast of a fluorescent light. Radiated electromagnetic energy was induced in a human body and a rectifier circuit converted induced energy into DC power. An input matching network of the diode rectifier was designed based on an equivalent source model of interference. A wristband-type harvesting module comprising a metal electrode designed to be in contact with the human skin was implemented. A power of −8.5 dBm was harvested from the body of a person with a height of 180 cm made to stand 60 cm below a fluorescent light with two 32 W lamps in a hemi-anechoic chamber. The proposed system can supply energy to the sensors used in body area networks.

A new alternative to achieve fast transient response while inherently managing the in-rush current during DC/DC switching converter start-up is proposed. An AC coupled feedback (ACCF) is introduced using a capacitor multiplier from the output of the converter to the output of the error amplifier. With this additional feedback, the transient response, which used to be limited by the compensator mid-band gain has been significantly improved. Meanwhile, the ACCF circuit can help to control the converter output ramping speed during power-up, thus eliminating the bulky soft-start circuit. The simplified circuit design means the new controller can be realised by a tiny on-chip circuit, thereby minimising the footprint and the cost. A buck converter with the proposed technique is designed using 0.18 μm CMOS process and simulated across different process corners. Simulation shows that the output voltage increases linearly with the designed slope despite the variations of the input voltage, inductor or output capacitor values. An excellent load transient response of 0.021 mV/mA is achieved for a load current variation from 50 μA to 1 A in 1 μs.

A single electrode based triboelectric nanogenerator (TENG) utilising a human skin as an active triboelectric layer for self-powered wearable devices and electronics applications is presented. The proposed flexible TENG was fabricated by sandwiching a conductive elastomer and fabric films with polydimethylsiloxane through a simple and cost effective process. The fabricated device exhibited an average open-circuit voltage and short-circuit current of 107.2 V/0.32 μA/cm² and 132 V/0.5 μA/cm², respectively. With the integration of rectifier circuit, 4.7 μF capacitor was charged using the proposed TENG up to 6.6 V.

A hybrid soft-switching converter including two resonant circuits and an un-regulated dc–dc pulse-width modulation (PWM) circuit is presented. Two split capacitors with four active switches are used at primary side to limit power switches at V _in/2. The variable frequency operation is adopted to regulate output voltage. Two flying capacitors are also adopted at the primary side to automatically balance two input split voltages. One un-regulated PWM converter shared the same power switches of two resonant circuits is used to reduce the output current ripple. Therefore, the power rating of power semiconductors and passive components are reduced. The operation principles, performance and effectiveness are illustrated and verified on a 1.44 kW (48 V/30 A) prototype circuit.

The loop-handover (LHO) technique is proposed to overcome the problem of close-loop performance in digitally controlled single-inductor multiple-output dc–dc boost converters during start-up. The presented technique utilises an existing clock source and requires only a small number of blocks. It also occupies a smaller silicon area, thus consuming low power and increasing efficiency. The presented technique is validated with proposed on-chip digital controller with multiple-output boost converter architecture using segmented delay line digital pulse width modulation. Experimental results show a successful close loop with reduced transients by using the simpler LHO technique.

An initial demonstration is reported in terms of maximising performance of photovoltaic modules. Experimental results of a triple junction solar cell covered with a 3 mm red-emitting luminous glass which can be efficiently excited by ultraviolet light indicate that this combination exhibits significantly enhanced efficiency of 36.5% under one-sun of AM1.5G. Integrating a luminescent (LSC) glass onto modules without converting any fabrication process at the device level is considered to be one of the predominant advantages of this device. Additionally, in order to achieve strong visible emission, it is mandatory to determine a thickness of LSC coverglass due to the edge reflection.

Shadowing determination is a crucial step in methods based on the physical optics approximation, which are widely used for electromagnetic scattering analysis of electrically large, conducting bodies. When the surface current is represented by basis functions on a mesh of triangle elements, this involves determining for each mesh edge and/or elemental face whether it is visible to the source or obscured by another mesh element. A field-of-view buffer-based shadowing determination algorithm for plane wave illumination of triangle-element meshes is presented, with special provision to maintain efficiency in case of grazing incidence. For homogeneous meshes, the computational costs in runtime and memory are both directly proportional to the number of mesh elements.

A fast algorithm is presented to dramatically reduce the complexity of the multiple signal classification (MUSIC) algorithm with centro-symmetrical arrays. The proposed method requires only real-valued computations with a limited spectral search over half of the angular field-of-view, and the dimension of the noise subspace and that of the search vector are reduced, leading to about 96.875% complexity reduction as compared with MUSIC. Simulations show the new estimator performs well at low signal-to-noise ratio and with a small number of snapshots.

A resonant-tunnelling-diode terahertz oscillator capable of wide-band direct modulation was fabricated, and wireless data transmission at a 500-GHz range was demonstrated. An error-free transmission up to the data rate of 22 Gbit/s and a transmission with a bit error rate less than the forward error correction limit up to 34 Gbit/s were achieved.