An optimised synthesis method for designing an extreme sparse array with the minimum set of elements is proposed. The method is based on a cross-array configuration and a multi-frequency beamforming algorithm. The experimental results show that the extreme sparse array achieves a 98.9% element thinning compared with the fully sampled planar array and the generated beam pattern satisfies the presupposed constraints. This is much better than the results obtained in the previous literature.

A 1 × 4 double-sided dipole antenna array with an associated Butler matrix beamforming network was designed and implemented at 60 GHz using glass-based integrated passive device (IPD) technology. Owing to the chip area limitation, the spacing between the antenna elements is ∼0.32λ ₀. Experimental results show that beams are successfully generated in the −62°, −23°, 22° and 50° directions, with total array gains of 2.5, 3.8, 4.3 and 3.0 dBi, respectively, which agree with simulation predictions. This successful demonstration provides a feasible solution for 60 GHz radio in heterogeneous system-in-package (SiP) integration.

A novel dual-broadband dielectric resonator antenna (DRA) is presented. The proposed antenna has realised both dual-band and wideband features by applying the modified Sierpinski structure to the antenna design of the proposed DRA. The measured impedance bandwidths for │S ₁₁ │ < −10 dB are 2.25–2.6 GHz (14.46%) and 3.1–4.1 GHz (27.78%), which can cover the wireless local area network (WLAN, 2.4–2.484 GHz) and the worldwide interoperability for microwave access (WiMAX, 3.4–3.69 GHz) bands. Meanwhile, stable radiation patterns and gains of about 5 and 3.8 dBi at 2.4 and 3.5 GHz, respectively, have been observed.

A compact broadband circularly polarised slot antenna is designed for universal ultra-high-frequency (UHF) radio-frequency identification (RFID) readers. The antenna consists of an L-shaped metal strip and a square-slot-loaded ground plane with four tuning stubs. The total size is 100 × 100 × 1.6 mm³. The measured –10 dB impedance bandwidth is 40.7% (772–1166 MHz) and the measured 3 dB axial ratio (AR) bandwidth is 13.9% (840–965 MHz). Both the impedance and the AR bandwidth cover the worldwide UHF RFID band.

To explain the variations in field strength measurements seen when measuring radio-frequency (RF) propagation in jet turbines, a model based on helical propagating waves is presented. The model uses a simplified model of the jet turbine based on a cylindrical structure and is compared with both electromagnetic (EM) simulations and measured values. Measurements and simulated values show good correspondence and show that a sum of helical propagating waves could be a useful tool to model the expected field variations.

Utilising an array that is constructed by combining short-ended stubs and microstrip lines, a planar-choke structure is presented. By locating the proposed chock structure on the bottom of the substrate-integrated waveguide slot array antenna, undesired spillover current and edge diffractions are removed. Measurement result show that in the operational bandwidth the backward radiation is reduced by more than 20 dB and the side-lobe level is improved by 5 dB without degrading of the antenna's electrical performance.

Rechargeable neurostimulators make it possible to research and treat brain disorders for a long period of time. However, metal objects such as device cases and inner copper layers of the printed circuit board (PCB) lower the energy transfer efficiency and can even present safety risks due to the eddy currents in these metals. The use of a fractal pattern slot in the metal to suppress the eddy currents is proposed and a rechargeable neurostimulator with deformed H-shape fractal slots in the PCB inner copper layers is described. The results show that the use of an H-shaped fractal pattern slot is effective over a relatively wide frequency range and the maximum temperature of the neurostimulator is in the range of 34.5–39.5°C, which indicates that the device can be used safely for long-term animal studies and even in the clinical treatment of brain disorders.

A sub-1-V bandgap used for passive radio-frequency identification (RFID) tags is presented. The bandgap circuit needs to work under a low supply voltage in the power starving application environment. In the literature, there are lots of low-voltage structures with large current to realise high performance. However, they are not suitable for low-cost RFID tags, so a low-power sub-1-V bandgap is realised. First, the basic structure of the proposed compact low-voltage supply low-power bandgap reference is shown. Secondly, a circuit analysis is presented and some detail considerations in the design processing are given. Finally, the chip is fabricated in a 0.13 μm mixed signal CMOS process. This low-power sub-1-V bandgap can work well at 0.85 V and at only needs 2.5 μA current at the 1.2 V supply voltage.

High-precision analogue circuits suffer from the finite gain and non-linearity of operational amplifiers (opamps). Correlated level shifting is one efficient technique that provides gain and swing enhancement for switched-capacitor circuits. Charge-compensated correlated level shifting is proposed, a modification for the correlated level shifting technique, that improves the efficiency of gain enhancement for single-stage opamps.

An original circuit-level model of two-terminal vanadium dioxide electron devices exhibiting electronic hysteresis is presented. Such devices allow realisation of very compact relaxation nano-oscillators that potentially can be used in bio-inspired neurocomputing. The proposed model is exploited to determine the parameters, values that ensure stable periodic oscillations.

Geometric errors are the main source of the positioning inaccuracy of robotic manipulators. A novel robot calibration approach is proposed based on compressed sensing to compensate the geometric errors. Simulation results validate that the proposed method improves the accuracy as well as reduces the calibration time.

An energy-efficient and highly accurate change detection method for a vehicular black box system by utilising information in a compressed domain is presented. Studies have shown that most automobiles spend a substantial percentage of time parked rather than driven. Thus, minimising energy consumption in a parked mode is crucial for vehicular black box systems design to prevent the battery being fully discharged. To meet a low energy requirement in parked mode, a hybrid video encoding engine with JPEG for parked and H.264 for driving mode is used. A change detection method is devised for parked mode using the JPEG encoder. The proposed change detection method detects events by utilising discrete cosine transform (DCT) coefficients that are readily available from the JPEG encoder at no extra computing cost. By using the ratio AC coefficients to a DC coefficient in each DCT block, illumination-resistant change detection has been successfully achieved. The illumination-invariant detection reduced the false positives while maintaining a very low false negative ratio. Experimental results demonstrate that the proposed method achieves 25.6–24.2% lower energy consumption and 25.4–1.2% better accuracy in illumination-varying circumstances compared with existing illumination-independent change detection algorithms.

The problem related to energy conservation in a resource-constrained wireless visual sensor network applied for habitat monitoring, border patrol, battlefield surveillance and so on, where images have to be transmitted over a wireless medium with limited bandwidth, is addressed. The proposed approximation band transform algorithm is unique and novel since it extracts and encodes only approximations of the image using fixed-point arithmetic without applying highpass analysis filters. This low bit rate image compression algorithm is specifically designed for resource-constrained low-power sensors. Its performance is analysed in terms of bit rate (bits per pixel), image quality, processing time and its energy consumption in an Atmel Atmega128 processor. It is shown that this algorithm consumes only 12% of energy needed by joint photographic experts group (JPEG) [independent JPEG group (IJG)] version and gives better results than JPEG at very low bit rates and thus the proposed scheme can significantly enhance the lifetime of low-power sensors.

A system design and new method for recognising a flower's species in a natural environment are proposed. An experimental analysis is conducted to improve the optimal method of feature extraction that is developed for the colour, texture and shape. These results showed that the colour (HS, CbCrCg and RGB), texture (grey level co-occurrence matrix) and shape (zero crossing rate) features for pictures of flowers were the most effective. The study develops flower image recognition technology that can be utilised in a mobile environment.

A sub-pixel multiplexing algorithm for generating multi-view images on an autostereoscopic three-dimensional (3D) display at high speed is proposed. Generally, sub-pixel multiplexing in an autostereoscopic 3DTV system is to assign R, G, B colour sub-pixels of multiple view images at the proper position on the display such that a proper view image can be seen in accordance with the viewer's position. The upscaled sub-pixel multiplexing algorithm proposed is composed of bilinear upscaling and a weighted view overlay. Even though upscaling multiple view images requires too much resources and increases system complexity, the proposed algorithm can significantly reduce complexity from an implementation point of view while providing high-quality 3D views. Specifically, the advantage of the proposed weighted view-overlay technique is that several overlaid view images decide the colour value of the sub-pixel, which results in increasing the subjective quality of view images. Through an experiment, it is confirmed that the image quality of generated multi-views with the proposed algorithms is notably better than the existing simple techniques.

The repetitive mapping and unmapping operations of shared buffers, which are used for data sharing among applications and devices, incur significant processing overhead. Thus, a significant amount of energy is consumed during video playback, especially when physical address space becomes heavily fragmented after a large number of application instances. A caching scheme that preserves mapping information of the shared buffer for later use of the same buffer mapping is proposed. The evaluation shows that the proposed scheme reduces processor utilisation by ∼64% and energy consumption by ∼17% during video playback compared with that of commercial smartphone systems.

A transformer-based cross-coupled complementary LC voltage-controlled oscillator (VCO) is investigated which is capable of operating at the Ku-band frequency range with low power consumption. The VCO simultaneously achieves low phase noise and low power consumption. The VCO demonstrates a measured tuning range of 12.1–13.1 GHz and a phase noise of −116.4 dBc/Hz at 1 MHz at a centre frequency of 12.4 GHz. The VCO consumes 0.96 mW from a 0.45 V supply voltage with a figure of merit of 198.4. It is implemented in a standard 0.13 µm CMOS process with an area of 0.23 mm².

Design equations for wideband single-layer absorbers based on the condition of zero slope reactance (or susceptance) at a specific centre frequency are presented. Using the design equations, a microwave absorber is realised employing a cross-shaped strip structure as a unit on an FR-4 substrate with a relative permittivity of 4.6 and height of 3.2 mm. At a design centre frequency of 10.93 GHz, the size of each unit is 9.6 × 9.6 × 3.2 mm and the overall size of the fabricated absorber is 336 × 336 × 3.2 mm. The EM-simulated and measured absorptions are close to 100% at the design centre frequency and their 90% bandwidths are about 47% (the limit for the case of the layer with ε_r = 4.6). The absorption characteristics of the proposed absorber are shown to be almost unaffected by the polarisation angles of normally incident TEM waves.

The improvement of the front-to-back ratio (FBR) in low-profile antennas to be used in presence detection devices is explored. The main idea is to use electrically small resonators as radiating elements. This minimises the electric currents in the boundary of the ground plane at the working frequency, thus reducing the backward radiation. The choice of the resonant particle and its electromagnetic properties, along with the antenna structure, are discussed. The simulated results indicate that there is good impedance matching (−18 dB) at the operating frequency (3 GHz) and an excellent FBR of 24 dB. These characteristics are validated experimentally and the FBR is compared with that of a conventional patch antenna.

The design of a modified Wilkinson power divider for wideband applications is presented. Instead of using a T-junction at the input port of the traditional design, the proposed divider uses broadside-coupled microstrip to slotline configuration to extend the impedance matching bandwidth at the input port. Moreover, a coupled structure with two isolation resistors and two open-ended stubs is used to enhance isolation and matching of the output ports across a wide band. The device has an overall dimension of 40 × 70 mm using the substrate Rogers RO4003 (dielectric constant = 3.38 and thickness = 0.508 mm). The simulated and experimental results show more than 100% fractional bandwidth assuming 16 dB of isolation and 10 dB of return loss as the reference. The device has equal power division between the two output ports with <0.2 dB amplitude imbalance and <2° phase imbalance across the band 1–3 GHz.

A vialess E-band Lange coupler is presented. The design combines a novel ‘pseudo-dot’ termination with impedance matching techniques. The multiple stage impedance matching network technique is used to design a 50 Ω Lange coupler. The ‘pseudo-dot’ termination provides a suitable load to the isolation port, avoiding via connection to ground, thus reducing the cost of the fabrication process. The design achieves better than 2 dB insertion losses in the through and coupled paths with <0.8 dB amplitude and ±2° phase errors for the entire E-band.

The design of a novel transparent 0° phase shifter (PS) using a proprietary self-assembling nano-particle technology-based micro-metal mesh (MM) conductive film is presented. The transparent MM conductive film has a sheet resistance of 0.7 Ω/sq and a visible-light transmission of 75%, resulting in high transparency and good conductivity. The proposed transparent PS is placed on a 2 mm-thick glass substrate of dielectric 5.7 and designed to operate at 2.45 GHz. A layer of MM film placed at the back of the glass serves as a ground. The transparent PS delivered a measured phase shift of 2.5°. The transparent PS can be used as a building block for realising a transparent Butler matrix (BM) beam forming network for inter/intra-vehicle wireless communication in the intelligent transport system. Besides being transparent, the proposed PS has a 0.25 mm profile excluding the glass substrate. These advantages greatly enhance the PS's potential to be used also as a BM building component that can be mounted onto the glass surfaces of buildings for future fifth generation (5G) indoor wireless communications.

A phase-shifted tunable long-period fibre grating in which a passband can be tuned over a wide spectral range is presented. This device is operated with an electromagnet in combination with a coil spring that includes a shift ring inserted in the middle. The passband wavelength is changed between 1520 and 1630 nm by actuating the coil spring. The minimum transmittance of the rejection band is controlled down to −15 dB by turning on the electromagnet.

The design, analysis, modelling and measurement of transmission lines with very low characteristic impedance in 28 nm bulk CMOS is presented. The so-called zero-Ohm lines are very well suited for power distribution networks and AC shorts in millimetre-wave circuits because of their accurate modelling up to extremely high frequencies and because they do not require metal–insulator–metal capacitors, which are usually not available in digital CMOS processes. Instead, they rely on simple metal structures, which can optionally be enhanced by integrating MOS capacitors. Applying transmission line theory, the lines can be described with models, which are scalable in length and width. Implemented test structures demonstrate a compact line of 450 μm length, which transforms an open circuit to an impedance close to 0 Ω for frequencies above 1 GHz.

An optical code-division multiple access (OCDMA) scheme based on cyclic shift extension of a base code is proposed to enable asynchronous multi-user optical wireless communications for very populated scenarios. This multiple access method is convenient for low–medium data rate communications of a large number of simultaneous transmitters. An expression to obtain a tight upper bound of the bit-error probability of the new scheme is provided which is also confirmed by experimental results. A variant of the proposed communication method which allows the encoding of several bits per symbol is also presented, although its analysis demonstrates that the first simpler strategy reaches similar performance with a significantly lower receiver complexity.

A uniform, smooth and crack-free multilayer silica aerogel film as thick as 5 µm is successfully coated on top of a silicon wafer. The multilayer spin-coated aerogel film was made possible by using the present authors' recently developed novel state-of-the-art aerogel processing technique. The utilisation of the thick aerogel film for the thermal insulation of a microhotplate (µHP) is studied. The super heat insulator aerogel can replace the micromachined air cavity conventionally created under µHPs for the fabrication of metal oxide gas sensors. The thermal insulation capability of the unique aerogel film was investigated by measuring the temperature of the nichrome heaters built on the aerogel coated silicon wafers at different applied powers. The temperature coefficient of the resistivity of the heaters was measured by monitoring the change in the resistance of the heaters at different temperatures. Simulations were also performed using COMSOL multiphysics software for verification of the experimental results, showing good agreement.

A 1342 nm Nd:YVO₄ microchip laser is reported, Q-switched with a dilute nitride GaInNAs/GaAs saturable absorber mirror. The laser produced optical pulses as short as 204 ps with 2.3 MHz repetition rate and 24 mW average output power. In comparison to conventional InP-based saturable absorber mirrors, the advantage of the proposed approach is the availability of excellent Bragg mirror materials that enable high reflectivity and more flexibility in designing the non-linear parameters owing to the use of lattice matched GaInNAs/GaAs quantum wells.

The monolithic integration of four-colour indium gallium nitride (InGaN)-based nanocolumn light-emitting diodes (LEDs) is demonstrated. In the integrated nanocolumn LED unit, blue-, sky-blue-, green- and yellow-emitting micro-LEDs (LEDs 1–4) with a 65 μm diameter circular indium tin oxide emission window were arrayed in a 2 × 2 square lattice with a lattice constant of 190 μm. LEDs 1–4 consisted of nanocolumn arrays arranged in a triangular lattice with a lattice constant of 300 nm and their nanocolumn diameters at the position of the InGaN/gallium nitride (GaN) multiple quantum wells (MQWs) were 119, 145, 188 and 231 nm, respectively. The increase in nanocolumn diameter from LED 1 to LED 4 resulted in increasing emission peak wavelengths, which were 465, 489, 510 and 570 nm for LEDs 1–4, respectively. On the same substrate, a red-emitting micro-LED was prepared, in which the nanocolumn diameter was increased to 260 nm by using a 350 nm-lattice-constant nanocolumn array. A combination of different lattice constants in an integrated LED unit is expected to contribute to the achievement of red–green–blue–yellow (RGBY)-colour-integrated nanocolumn LEDs.

High performance Si-based Ge_0.9Sn_0.1 photoconductive infrared detectors have been demonstrated. The device fabrication is fully compatible with the complementary metal-oxide-semiconductor (CMOS) process. The room temperature responsivity at 1.55 μm is 0.26 A/W and comparable with that of commercially available InGaAs and Ge photovoltaic detectors. Temperature-dependent study shows an increased peak responsivity of 2.85 A/W at 77 K. The spectral response has a longwave cutoff of 2.4 and 2.2 μm at 300 and 77 K, respectively. Specific detectivity (D*) was calculated and compared side by side with D* of market dominating infrared detectors.

A novel method for the generation of the power-on-reset (POR) signal needed by the SOC is described. A POR signal is required for initialisation of the logical state in digital systems. To obtain an accurate trip point for the POR, generally a bandgap voltage reference is used along with additional logic. Such logic tends to limit the lowest possible trip point that can be achieved. The proposed implementation of POR is based on a modified bandgap circuit where a supply-dependent current is injected into the loop. In this case, the reference generation is not explicitly required and thus the trip point can be kept very close to the minimum supply required for the bandgap operation. This implementation also needs very small delay as the required delay is not dependent on supply ramp rates and can be made very small.

Flicker transfer is significantly affected by the dynamic impedance of the three-phase voltage source converter (VSC) in the distribution network. A methodology to determine the flicker transfer coefficient in a distribution system with a VSC is proposed. The formula of VSC dynamic impedance in the phase domain is derived based on the linearisation model of the VSC with the inner-loop current control and outer-loop power control as well as the phase-locked loop block taken into consideration.

A new microelectromechanical systems (MEMS) design of an integrated DC–DC converter electrostatically driven is proposed. The converter has one output based on the tunable capacitor principle. The output voltage has been achieved by designing a capacitor with different gaps. Compared to previous research works, the complete mathematical model of the converter is proposed. To examine the dynamic behaviour of the converter two different methods are used: the differential quadratic method and the Galerkin method. The obtained results show good agreement between the methods. In addition, two mechanical switches are added in the structure to replace the conventional diodes that have the advantage of zero leakage current, low power consumption and synchronous operations. Results show that the converter takes about 22.73 ms to convert a 5 V voltage to a range of voltages that are varied from 10 to 50 V.

A graded dielectric inhomogeneous nosecone radome design with superior electromagnetic (EM) performance characteristics for airborne applications is presented. The radome wall is designed in such a way that the middle layer has the maximum dielectric parameters (dielectric constant and electric loss tangent). On either side of the middle layer, the dielectric parameters of the constituent layers decrease in a graded (or step-wise) manner. This wall configuration facilitates better impedance matching as required for radome applications. The computation of the EM performance parameters of a tangent ogive nosecone radome based on the above-mentioned wall configuration, enclosing an X-band slotted waveguide planar array antenna, is carried out using ‘geometric optics’ based three-dimensional ray tracing along with the ‘aperture integration’ method. EM performance analysis shows that the proposed graded inhomogeneous dielectric radome design is a better choice for streamlined airborne radomes compared with the ‘variable thickness radome’ (VTR) designs based on monolithic half-wave and multilayered radome wall configurations. Furthermore, it excludes the constraints on fabrication that generally occur in the case of streamlined airborne VTRs.

An adaptive super-resolution imaging algorithm to enhance the performance of airborne single channel forward-looking radar is proposed. Multiple beams data to expand the processing space to enforce the sparsity of scatterers with respect to the antenna pattern was first utilised. Then, the imaging is converted into a problem of signal reconstruction with Lp-norm regularisation, and the regularisation parameter is data driven. Simulations are given to verify the effectiveness of the algorithm.

A first reported complementary metal-oxide semiconductor (CMOS)-integrated acceleration sensor obtained through isotropic inter-metal dielectric (IMD) etching of a back-end-of-line (BEOL) integrated circuit interconnection stack, without any additional substrate etching steps, is presented. The mechanical device composed of a CMOS-process 8 μm-thick metal-via-metal stack of 135 μm diameter and suspended 2.5 μm over a bottom fixed electrode, has a resonance frequency of 20 kHz, a sensing capacitance of 50 fF with sensitivity 14 aF/G and it is integrated on the same substrate with a simple low-noise amplifier reaching 25 mG of RMS noise measured from 0.25 to 100 Hz bandwidth.

The channel process to further improve the performance of bottom gate hafnium-doped zinc oxide (HZO) thin-film transistors (TFTs) is optimised. The effects of channel thickness on the electrical performances of HZO TFTs is studied. The results show that the extracted saturation mobility increases first and then decreases with the increase of HZO film thickness, reaching maximum when the channel thickness is optimum. The dependence of the optimum thickness on channel length is studied and it is found that optimum thickness increases with the increase of channel length.

The average of integer powers of the Gaussian Q-function over fading distributions is commonly found in the evaluation of the average error performance of wireless communication systems over fading channels. Expressions known in the literature for η–μ and κ–μ fading channels only include solutions for the average of one Gaussian Q-function and the product of two Gaussian Q-functions. This limitation has been overcome by providing a general solution for the average of arbitrary powers of the Gaussian Q-function over η–μ and κ–μ fading channels.

An enhanced electrostatic discharge (ESD) power clamp for an antenna switch controller with silicon-on-insulator (SOI) complementary metal-oxide-semiconductor (CMOS) technology is presented. The gate drive voltages of larger n-type metal-oxide-semiconductor transistors in a stacked configuration of a RC-triggered power clamp have been optimised to obtain larger discharging capability and shorter turn-on time compared to the conventional topology. The proposed ESD power clamp circuits are implemented in a double-pole five-throw antenna switch controller and the experimental results confirm the validity of this approach.

A QR decomposition aided belief propagation (QR-BP) detector for multiple-input multiple-output (MIMO) systems is proposed. Before the iterative message passing process, linear transformation is performed by using the unitary matrix obtained from the QR decomposition of the original MIMO channel matrix. Then, the original MIMO channel matrix is replaced by an upper triangular channel matrix after the linear transformation and the proposed QR-BP detector operates over the new bipartite graph from the upper triangular channel matrix. Therefore, the number of cycles in the new bipartite graph is significantly decreased when compared with the fully connected bipartite graph from the original MIMO channel matrix. In addition, since the unitary matrix is utilised for the linear transformation, there is no information loss on the likelihoods estimated from noisy observations. Simulation results verify that the proposed QR-BP detector outperforms existing BP detectors and achieves near-optimum performance close to the maximum-likelihood detector in terms of bit error ratio.

The secrecy outage performance of multiuser multiple-input–multiple-output (MU-MIMO) transmit antenna selection systems is analysed, where some of the users overhear transmissions as long as they are not scheduled currently. A general closed-form expression of secrecy outage probability is derived by ordering the qualities of paths and calculating the joint probability density functions. Numerical results are provided to illustrate the different impacts of multiuser diversity and antenna diversity on the secrecy performance.