A dual-mode relative humidity (RH) sensor is fabricated based on a surface acoustic wave (SAW) resonator with anti-corrosive gold electrodes. The reflectors of the SAW resonator consist of two interdigital capacitors with loaded polyvinyl-alcohol (PVA) films as sensitive layers, which further form a LC resonator operating below the SAW resonance frequency. With this sensor configuration, two sensing mechanisms are realised. The SAW resonator senses the mass loading of the PVA film with an average sensitivity of 0.38 × 10⁻⁴/%RH and a minimum electrical quality factor Q of 267 from 14.2% to its cutoff RH of 72.4%. The LC resonator senses the permittivity of the PVA film, which extends the operation range of the sensor to 89.3%RH with an average sensitivity of 4.79 × 10⁻⁴/%RH and a minimum Q factor of 8.7. Furthermore, a figure of merit (FoM) is defined and extracted from measurements to evaluate both the sensitivity and the Q factor. Below the cutoff RH, the sensor is preferable for use for the SAW resonator for RH sensing because of its better FoM. Above the cutoff RH, the SAW resonator is out of function, and the LC resonator is used instead with a good FoM.

As wireless networking becomes more ubiquitous there is an increasing demand for less obtrusive antennas. Optically transparent antennas increase the locations at which antennas can be installed. Prior work on optically transparent antennas has shown their feasibility using materials such as transparent conductive oxides and conductive polymers. An optically transparent antenna using highly conductive thin mesh wires designed to operate in the 5–6 GHz band is presented. This antenna was compared with a solid copper antenna of the same dimensions. The peak gain of the optically transparent antenna was measured to be 5.7 dBi as opposed to 7.6 dBi for the solid copper patch. Further more, the challenges that occur when realising a mesh wire antenna design are addressed.

A compact antenna is proposed using planar-patterned metamaterial structures for ultra-wideband applications. This antenna consists of four metamaterial unit cells that simultaneously show both negative permeability and negative permittivity on the triangular patch and three rectangular slots on the partial ground plane fed with a microstrip line. It has a wide bandwidth from 3.07 to 19.91 GHz for voltage standing wave ratio (VSWR) <2 and an average gain of 5.62 dBi with a peak of 8.57 dBi because of using planar-patterned metamaterial structures. Good agreement between computations and experiments is realised convincing that the antenna can operate over a wide bandwidth with planar-patterned metamaterial structures and compact size (0.28λ × 0.19λ × 0.02λ).

A slot helix antenna with a simple and efficient feeding network for satellite communications and global positioning system (GPS) applications is presented. Rectangular slotted openings, ended with fan-shaped slots, are designed for the helix-shaped slot radiating arms so as to obtain excitation from the circular microstrip feeding line. By adjusting the coupling, the four or more slot radiating elements can obtain appropriate excitation, which leads to the good circular polarisation properties of the antenna.

A novel design of a circular ring microstrip antenna using dual-reconfigurable perturbation to obtain polarisation agility and diversity is reported. The proposed antenna employs two couples of slots and stubs at a diagonal corner for generating and alternating right-/left-handed circular polarisations, respectively. By switching the anti-parallel bridged pin diodes of the implemented antenna, polarisation agility and diversity are successfully demonstrated.

A novel electrically small uniplanar antenna with pattern-agile performance is reported. It consists of a split semi-loop connected to the ground strips of a coplanar waveguide-fed semi-loop antenna. The angle of its maximum directivity can be controlled simply by changing the position of the gap in the ground-connected semi-loop. The measured results of this behaviour are in good agreement with the simulated values. A peak realised gain of 1.93 dBi is achieved experimentally. The radiation efficiency is observed to be higher than 95% for every angle selected.

A technique for designing a parasitic patch antenna array whose beam can be steered dynamically using a fluidic tuning mechanism is presented. Using this technique, a three-element patch antenna array operating at 5 GHz is designed and fabricated using 3D printing. Two oil-filled channels are placed in the substrate of the antenna along the radiating edges of the patches and filled with movable metal cylinders and glass balls. The parasitic elements are mutually coupled to the centre element in the H-plane. As the train of metal cylinders and glass balls are moved from the left or right with respect to the centre-driven patch element, the beam is steered towards the opposite direction. The proposed parasitic patch array is able to steer the beam ±22.5° with maintained impedance matching.

The performance of an optically transparent and frequency-agile antenna operating from 8.8 to 9.8 GHz is reported. The transparent square-loop coplanar antenna is made of a mesh silver film printed onto a glass substrate. A high level of transparency (T > 80%) and low sheet resistance (Rs < 0.2 Ω/sq) are achieved from such a material. Antenna tunability is provided by a surface mounted beam-lead varactor which is invisible to the naked eye. The microwave performance of such an antenna is reported, discussed and compared with that of a reference counterpart made of a continuous silver layer (and thus totally opaque). The optically transparent frequency-agile antenna exhibits gain values ranging from 1 to 3.5 dBi with 10.8% of frequency tunability.

Substrate-integrated-waveguide (SIW) horn antennas built on thin substrates (substrate thickness smaller than λ ₀/10) are not widely used owing to their low front-to-back ratio and the impedance mismatch between the aperture and the free space. A SIW horn antenna with metalised via holes in front of the aperture is proposed to deal with the issue of impedance mismatch. The metalised via holes introduce shunt inductance between the top and bottom metal planes of the SIW, which increases the impedance of the SIW and improves the impedance matching. Two prototypes working at the Ku band with via holes positioned differently are designed, manufactured and measured. The simulated and measured S- parameters, antenna gain and radiation patterns are presented.

A novel on-body antenna targeted for 2.45 GHz customised in-the-ear hearing instrument applications is designed, implemented, and measured. The antenna is designed to use the maximum volume available in the user's ear canal and to provide isolation from the user's body. The polarisation is primarily normal to the surface of the head to ensure the best on-body path gain. Efficiency and S-parameters from measurements in free space and on a specific anthropomorphic mannequin head endowed with ears are presented.

A discrete-time charge-domain filter is proposed, which can realise complex conjugate poles in the transfer function of the filter. By employing a second transconductance in the feedback path of a second-order infinite impulse response charge-domain filter, it is proved that the filter topology is capable of implementing complex poles. This method makes charge-sampling filters more efficient in designing frequency-domain filters where they can be used to synthesise any type of filter structures such as Butterworth, Chebyshev and so on.

In this reported work, firstly, the artificial neural network (ANN) is taken as a target recognition algorithm and then jointly, the computational accuracy and an algorithm parameter (i.e. the number of hidden nodes) are optimised to minimise the overall energy consumption of ANN evaluations. This joint optimisation is motivated by the observation that both the computational accuracy and the algorithm parameter affect recognition accuracy and energy consumption. The evaluation shows that the jointly optimised computational accuracy and the algorithm parameter reduces the energy consumption of ANN evaluations by 79% at the same recognition target, compared with optimising only the algorithm parameter with precise computations. Furthermore, it is demonstrated that to evaluating ANNs with reduced computational accuracy, recognition accuracy is further improved by training the ANNs with reduced computational accuracy. This allows reduction of energy consumption by 86%.

A new strategy is presented that gives near-time-optimal control of a higher-order system that has a constrained input. It is simple enough that it can be embedded in a common microcontroller. It determines the plant input by logical decisions alone, unlike the method today termed model predictive control that requires the computation of cost functions. With such an implementation, very fast systems can be controlled in real time.

A high-speed field-programmable gate array (FPGA) design is proposed to calculate angles and distances for biped robots in real time. A low-complexity and high-accuracy hardware-oriented algorithm based on CORDIC was developed. To reduce hardware cost, a hardware sharing technique was used to realise a CORDIC scaling factor generator and three hardware sharing machines. Moreover, the multipliers and dividers were replaced by cost-efficiency components, such as adders and shifters to further reduce hardware cost. In addition, the proposed design was implemented with a fully pipelined architecture, which achieved improved operating frequency and throughput efficiency. The proposed design was realised and verified by an FPGA device with a maximum operating frequency of 127 MHz, which achieved the calculation of angles and distances for biped robots in real time. Compared with the previous design, this work not only reduced hardware cost by at least 49.6% and average errors by at least 67.2%, but also improved the average executing performance by 62.7% when calculating ten angles for the biped robots.

Near-field measurement has been adopted in the prediction of emission levels for electromagnetic compatibility diagnosis and design purposes. A novel approach for effective reconstruction of the equivalent current source based on the near-field measurement data is presented, for the prediction of magnetic field emissions elsewhere. The approach consists of two steps: first, the distribution of the magnetic field component normal to the entire measurement plane is acquired by interpolation of the discrete measurement data using a radial basis function network; secondly, the magnetic emissions elsewhere are evaluated from the equivalent current source derived from the acquired magnetic field distribution. This approach requires the measurement of only one single magnetic field component. The accuracy of the proposed approach has been demonstrated by comparing the predicted field to that of the full-wave simulation; the robustness of the approach against measurement noise has also been verified.

A new bilateral frame rate upconversion algorithm using the image texture complexity characteristic is proposed. In the proposed algorithm, as the cost function is adjusted according to the image texture complexity, the accuracy of motion estimation (ME) is improved. In the experimental results, the proposed algorithm outperforms the conventional bilateral ME process by 0.32 dB.

Trivial quantisation is widely used in cancellable biometrics and bio-cryptosystems for error tolerance. This method segments the feature domain into several non-overlapping intervals of equal size, whereas all features in the same interval will be considered matched. Although it is intuitive that trivial quantisation brings about the boundary issue, similar features near interval boundaries may be mapped into different intervals and lead to matching failure. Previous works do not provide specific theoretical analysis on how trivial quantisation impacts discrimination power (DP), an important performance index in biometric systems. Assuming genuine features and imposter features follow Gaussian distributions, the DP provided by the conventional matching method and trivial quantisation-based matching method from a theoretical perspective is discussed and compared. Also, formulas are developed for calculating the error tolerance parameter that maximises the DP in each method and the discrimination loss caused by trivial quantisation.

The bilateral filter (BF) has showed great effectiveness for a variety of problems. However, its brute-force implementation is time consuming. One way of accelerating a BF is to approximate the nonlinear range kernel of the BF by a set of linear time shiftable kernels. To achieve this goal, only finite values of the kernel of the BF have been used to perform smoothing due to the quantisation of digital images. Thus, the filtering results are not changed by substituting the range kernel with the function having the same values at finite discrete points. The Lagrange interpolation polynomial can exactly pass through predefined points and therefore can be employed to replace original kernels for accurate by accelerating the BF. To speed up the BF at the cost of small approximation error, two approximation methods are proposed to obtain the optimal fitting polynomial. The performance of the proposed method is validated by extensive experiments.

Pedestrian tracking is a key building block in many emerging technologies, and there are many applications that require a very accurate and reliable pedestrian tracking. Two problems, namely the abrupt changes in motion and the delay in the tracking process are addressed in the reported work. The approach seeks to simulate the uncertainty of the position of electrons around the nucleus by propagating particles in areas where the person is more likely to be, depending on the person's possible motions and taking into account various sources of uncertainty. A novel feature of the presented approach is that it can track abrupt motions accurately with a low delay. The robustness of this approach for abrupt motion situations is demonstrated.

In many traffic-related applications, such as traffic management and structural health monitoring for roads, an accurate estimation of a moving vehicle's size and shape is needed before proceeding further. However, due to the presence of cast shadows, these properties cannot be obtained accurately using common object detection systems. To deal with the problem of misclassifying shadows as foreground, various methods have been introduced. Most of these methods often fail to distinguish shadow points from the foreground object when the boundary between the umbra and the object is unclear due to camouflage. A novel method for detecting moving shadows of vehicles in real-time applications is presented. The method is based on two measurements, namely, the illumination direction and the intensity measurements in the neighbouring pixels in a scanned line. A major advantage of using image lines for classification is the ability to solve the problem associated with camouflages. Experimental results show that the proposed method is efficient in real-time performances and has achieved higher detection rate and discrimination rate when compared with two well-known methods.

A novel comparative study of different low-density parity-check (LDPC) coding algorithms and implementation issues through field-programmable gate arrays (FPGAs) technology for wireless vehicular applications is presented. A key development in LDPC codes is the iterative decoding algorithm which uses the belief propagation algorithm. A comprehensive investigation of the performance of different coding schemes was carried out. Four different decoding techniques were tested by computer-based simulations of messages modulated under the binary phase-shift keying modulation scheme and transmitted through a vehicular channel model. Finally, the best performance ratio against complexity algorithm was chosen to be implemented on a Xilinx FPGA platform.

For any row weight L, a novel class of (8, L) quasi-cyclic low-density parity-check (QC-LDPC) codes is deterministically constructed with girth eight. Compared with a similar construction, the proposed (7, L) and (8, L) QC-LDPC codes exist for any circulant permutation matrix of size P ≥ (L − 1)(L ² + 3L/4 + 3/4) + 1 and P ≥ (L − 1)(L ² + 3L/4 + 7/4) +1, which remarkably improve the existing bounds of (L − 1)(L ² + L) +1 and (L − 1)(L ² + L + 1) +1, respectively. Moreover, for any column weight J, any row weight L and any common difference, a construction for (J, L) QC-LDPC codes with girth eight is also proposed. This construction has high flexibility with respect to the design of code rate and code length. Simulation results show that the novel codes with moderate lengths perform well in the additive white Gaussian noise channel.

There exists a way that attackers can identify software defined networks (SDNs). Knowing the vulnerabilities of a SDN, the attackers can mount a saturation attack on the SDN controller with the aim of incapacitating the entire SDN. Therefore, the controller should have an architecture to weather out such an attack while continuing operation. A scheduling-based architecture is proposed for the SDN controller that leads to effective attack confinement and network protection during denial of service (DoS) attacks.

A very simple adaptive scheduling method is introduced to improve the convergence rate of low-density parity-check decoders. Although the standard decoding method does not impose any constraint on the process order of check nodes, the proposed scheme adopts a dynamic scheduling method for check node message updating based on syndrome values. The proposed technique is applied to lower-density parity check (LDPC) codes of the 802.11n and 802.15.3c standards. Compared with sequential scheduling, the proposed approach provides a faster convergence speed from 28 to 51% for a WER of 10⁻⁴ and 10⁻², respectively. Consequently, the introduced adaptive scheduling achieves a target performance with less number of iterations, which leads to reduced power consumption with minimal additional decoding complexity.

To reduce pattern-dependent jitter in four-level pulse-amplitude modulation (PAM-4) signalling, a transition-aware feed-forward equaliser (TFFE) is proposed. By allowing the transition time to vary according to the transition types of the PAM-4 symbols, switching jitter in TFFE-based PAM-4 transmitters can be greatly suppressed, down to the non-return-to-zero (NRZ) level. Simulation results confirm that a PAM-4 transmitter that employs a TFFE can reduce the jitter level by 0.18 unit interval peak-to-peak, and this proposed equaliser can achieve nearly identical eye height as the conventional PAM-4 feed-forward equalisers design without introducing any signal-to-noise ratio penalty.

A novel compact dual-band bandpass filter (BPF) using a hybrid structure of microstrip patch and coplanar waveguide (CPW) is proposed, designed, and implemented. The dual-band response can be realised by embedding two CPW structures in the microstrip square patch, which can not only disturb two fundamental degenerated modes, TM₁₀₀ and TM₀₁₀, but also adjust the resonant frequency of the TM₁₁₀ mode. The two degenerated modes are used to form the first passband while the TM₁₁₀ mode and two CPW resonators are used to generate the second passband. The first and second passbands have two and three poles, respectively. The dual-band BPF has a simple structure and good performance.

Direct write dispenser printed sound-emitting smart fabrics are reported for creative applications and wearable electronics. Using dispenser printing, sound emission can be easily added to various fabric substrates, from industrial coated architectural fabrics to everyday woven polyester cotton fabrics. Two different types of sound emission have been realised on fabrics: a piezoelectric buzzer and an electromagnetic planar spiral speaker with an external magnet. These two planar sound emitting devices are flexible and simpler than conventional three-dimensional electromagnetic and electrostatic sound emitting devices. Furthermore, the spiral-based planar electromagnetic speakers allow interactive applications by changing the distance between the magnet and the speaker. The theory and the manufacturing technology of the direct write printed fabric buzzer and speaker are reported.

A K-band bandpass filter (BPF) based on the fully micromachined substrate integrated waveguide (SIW) structure has been demonstrated. In the proposed SIW platform, borosilicate glass reflowed into the silicon trench is used as a dielectric substrate, and the vias are formed by filling the glass mould with electroplated copper after removing the embedded silicon part. The BPF's characteristics are realised by introducing dual inductive post structures into the SIW platform. The insertion loss and 3 dB bandwidth of the fabricated BPF were measured to be 2.46 dB at 29 GHz and 7.2%, respectively. The proposed BPF platform has high potential for low-loss, compact SIW-based millimetre-wave tunable filters owing to its mechanical robustness and integrity with MEMS tuning devices.

A designed, fabricated and tested electromagnetic bandgap (EBG) structure is proposed for resolving the problem of the lower cut-off frequency of conventional planar-type EBGs. Bandwidth enhancement is achieved by incorporating edge termination along the edges of the whole EBG-patterned power plane. Measurement results show that the lower cutoff frequency is shifted downwards from 800 to 13 MHz. This structure also improves the upper cutoff frequency of 4.3 GHz for the conventional planar EBG to 5.2 GHz. Using this structure, simultaneous switching noise can be suppressed over the relative bandwidth of 63%, which is higher than the commonly used EBGs. The structure is easily fabricated with the current method of printed circuit board manufacturing processes and commonly used SMD resistors and capacitors.

A photonic-assisted scheme for the phase noise measurement of microwave signal sources is proposed based on the optical delay-line method. In the proposed scheme, all the microwave signal processing is implemented in the optical domain, and the electrical devices that would limit the operation bandwidth and measurement sensitivity are avoided, leading to a large operation bandwidth and a high sensitivity. The feasibility of the proved phase noise measurement system is experimentally verified. A large operation bandwidth of 5–40 GHz is achieved, and a phase noise floor as low as −140 dBc/Hz at 10 kHz offset is obtained.

In past years, a great number of substrate integrated circuits have been developed. Among these new transmission lines, the substrate integrated waveguide (SIW) has received special attention. Although the quality factor and losses of these new integrated lines are better than the planar circuits, these characteristics are worst than in the case of waveguides, mainly due to the presence of dielectric substrate. To improve the performance of the integrated circuits, a new methodology for manufacturing the empty waveguides, without dielectric substrate, but at the same time completely integrated in a planar substrate, has been recently proposed, resulting in the novel empty SIW (ESIW). A low-cost and easy to manufacture thru–reflect–line calibration kit for de-embedding the effect of connectors and transitions when measuring ESIW devices is presented. Results prove the high quality of this calibration kit.

A fast stable normalised least-mean fourth (FSNLMF) algorithm is proposed. The major drawback of the stable normalised least-mean fourth (SNLMF) algorithm is its poor convergence rate, especially in the presence of high signal-to-noise ratios (SNRs). Considering the effect of high SNRs, a corresponding constant is introduced in SNLMF algorithm to offer a fast convergence. Simulations on system identifications demonstrate that the proposed FSNLMF algorithm achieves a faster convergence speed than the SNLMF algorithm.

Deep-ultraviolet lithography is essential for the mass production of silicon devices. To date, restrictions in the process have prevented the realisation of high-Q-factor optical resonators. This reported work demonstrates photonic crystal cavities with Q-factor values of ∼200 000 using an optimised design.

Reliability test data are presented, which show that non-oxide all-lithographic vertical-cavity surface-emitting lasers (VCSELs) are more reliable than oxide VCSELs under extreme operating conditions. The test data are compared for lithographic and oxide VCSELs of 3 µm size after operating at a stage temperature of 150°C and an injection current density of 140 kA/cm² for various times. The increased reliability under extreme operating conditions can be largely attributed to the lower junction temperature and the internal stress inside lithographic VCSELs.

Novel fault detection schemes for sequence time-domain reflectometry (STDR) and spread-spectrum time-domain reflectometry (SSTDR) are proposed, which improve, the detection performance of far faults without increasing the computational complexity by positioning a sign detector at the front of the time correlator. Simulation results demonstrate that the detection performances of the proposed schemes for far faults are considerably better than those of the conventional ones regardless of sequence lengths and reference types.

Continuous-wave Doppler radar has attracted a lot of attention for non-contact vital sign detection. In the typical quadrature homotype architecture, the DC offset is a tough issue in that it seriously deteriorates the demodulated results. However, existing methods for DC offset calibration can hardly obtain accurate compensation, especially when the sparsity of measurement outliers is relatively large. Proposed is a novel iteratively reweighed ℓ₁ algorithm-based error correction method. Simulated and experimental results demonstrate the advantages of the method for accurate DC offset calibration.

The concept of an electrically doped dynamically configurable field-effect transistor (FET) is presented, which provides freedom to dynamically switch between a high-performance MOSFET and a low-power tunnel FET that can be ideal for complementary circuit implementation. The charge carrier concentration, polarity and conduction mechanism of the device are precisely controlled by the appropriate application of an external polarity control signal, instead of the conventional ion-implantation process. Two-dimensional TCAD simulation results confirm the dynamic configuration of the proposed device and good functionality agreement with existing devices as well as it having the requisite qualities for low-power and high-performance applications.

In this reported work, high-performance fully transparent bottom-gate-type calcium-doped zinc oxide thin-film transistors (Ca–ZnO TFTs) have been successfully fabricated on glass substrate. The effects of substrate temperature during active layer deposition on the electrical properties of Ca–ZnO TFTs were investigated and an optimum condition (substrate temperature: 100°C) was achieved. The optimised thin-film transistors (TFTs) exhibit excellent electrical properties, with an off-state current (I _off) of 1.31 × 10⁻¹² A, an I _on /I _off current ratio of 3.015 × 10⁸, a saturation mobility (μ _sat) of 25 cm²/Vs and a threshold voltage (V _t) of 4.24 V. The variation trend of V _t, the I _on /I _off current ratio and μ _sat against substrate temperatures is analysed in detail. The experimental results suggest that the performance of Ca–ZnO TFTs can be improved effectively by optimum substrate temperature.

An enhanced covariances sparse representation method for direction-of-arrival (DOA) estimation is proposed. The method can estimate coherent sources with low computation complexity. The cross-Kronecker product terms of the steering vector are introduced as an extra basis to improve the sparse model. Based on the enhanced model and iteration operation, the proposed method has greater precision in multiple coherent sources situations. Compared with several existing DOA estimation methods, simulation experiments have validated the effectiveness of the proposed method.

Energy-efficiency (EE) in antenna selection multi-input–multi-output (MIMO) systems over Nakagami-m fading channels is investigated. An EE metric is defined as the number of successfully received bits per unit of energy consumption, which takes into account several important system parameters such as channel coding and modulation. An optimisation problem that maximises the EE metric subject to an error-performance constraint is formulated. On the basis of an analysis of this problem, the optimal value of the average energy per transmitted data symbol is obtained, such that the EE in the system is maximised. Simulation results are provided to validate the analysis.

A wireless physical layer network coding (WPLNC) technique in a decentralised and distributed relay network where a maliciously behaving relay may be present is studied. Most research has optimistically assumed altruistic cooperation of relays. The malicious node can lead to a significant disorder among the other relays by selecting its own WPLNC mapping. This scenario is described as a static (single-shot) incomplete information game where a node type – either friendly or malicious – of the relay is its private information. The focus is on the existence of particular equilibria given the probability of the presence of a malicious node.