Traditional security systems which include video cameras continuously recording and transmitting data for surveillance systems require a password to prevent entry by unauthorised persons. Actually, such systems have weaknesses such as blind spots or danger of stealth. This reported work focuses on intruder detection in indoor environments, which is based on acoustic channel characteristics. The basic concept of this study is to compute the coherence bandwidth from the measured room impulse response. The coherence bandwidth is influenced by channel delay profiles. Intruders give rise to changes in room channel impulse response inside the room. This variation causes change in the channel delay profile. Experiments have been performed to validate the effectiveness of the proposed method.

The size and shape of a reconstruction surface is the same as a holography surface in conventional near-field acoustic holography (NAH), which limits the size and shape of the measurement surface. To reduce the measurement points and use any shape of measurement array, the direct extrapolation in NAH based on wave superposition is proposed. According to the transitive relation of the acoustic signal in the sound field, the sound field information on a reconstruction surface could be directly extrapolated by the holography surface. A set of simulations are performed with an 18-channel wheel-type array to obtain more sound pressure data on a grid reconstruction surface. On comparing the reconstruction errors produced by different parameters, which are the source frequency, signal-to-noise ratio, reconstruction distance, point numbers, and grid spacing, the results show that the errors are all very low. Moreover, the experiment verifies the feasibility of the direct extrapolation method.

Multiple Helmholtz resonance apertures are proposed to enhance the output pressure of air-coupled capacitive micromachined ultrasonic transducers (CMUTs) for non-contact ultrasound imaging applications. The methodologies of defining the design parameters of CMUTs and the resonant apertures on the membrane of CMUTs are discussed. In comparing certain configurations of resonant apertures with conventional CMUTs, simulation results show that a prospective improvement of output pressure (up to 32.1%) can be achieved.

A slim planar composite antenna for WLAN router applications is presented. A J-antenna and a dipole antenna are proposed as components antennas for the vertical and the horizontal polarisations, respectively. The arms of the dipole adopt a bent structure for size miniaturisation. For tuning the impedance matching, a matching stub is introduced working as a parallel inductor on the upper part of the dipole. The antenna is made by copper and fed by coaxial lines. The final antenna achieves two orthogonal polarisations with a low cross-polarisation level <−18 dB, a return loss better than 10 dB, and port isolation in excess of 19.3 dB from 2.38 to 2.51 GHz, thus making it suitable for use in 2.45 GHz WLAN router polarisation diversity applications. The slim planar structure with 25.5 mm width and light weight makes it easy to install on WLAN routers.

A novel configuration of a multiple-input multiple-output (MIMO) circularly polarised (CP) antenna array operating in the C-band is presented. The array consists of 2 × 2 antipodal tapered slot antenna elements created in the sides of a rectangular as the rectangular grid that supplies a broadband impedance bandwidth and high gain array. To provide broadband MIMO with polarisation diversity, the antenna uses a dual-port feed network consisting of couplers, a crossover and delay lines which the diversity of polarisation changed by input ports.

A novel and compact decoupling and matching network (DMN) is proposed for two symmetric antennas. The DMN is designed and analysis by the lumped-element circuit and the even/odd mode analysis proved the feasibility of the network for a two-element closely spaced array. Then the network is fulfilled by a microstrip line. The measurement results (both with the advanced design system and the high frequency structure simulator) agree quiet well with the simulation ones. High antenna isolation and good matching are achieved simultaneously. The design concept, formulation and experimental results are introduced.

A practical capacitive circuit absorber with low ohm resistive sheets is presented, which is constructed by multilayer low ohm resistive sheets, polymethacrylimide foam and polyethylene terephthalate. For convenience of manufacture and practical engineering applications, a unique low ohm rectangular resistive sheet with a rotational symmetry pattern is employed, which is used to replace high ohm square resistive sheets. Based on the design of the low ohm sheet pattern and the absorber configuration, a prototype absorber is fabricated. The measured results show that the reflectivity of the absorber with a total thickness of 17.9 mm is −10 dB in 1.5–18 GHz for normal incidence. The absorber is shown to have the characteristics of low density and high intensity.

To overcome antenna design challenges posed by the increasing number of frequency bands, the use of separate transmit (Tx) and receive (Rx) narrow-band antennas is proposed. In addition, a second Rx antenna is utilised for multiple input–multiple output (MIMO) application. While sufficiently low coupling between two antennas is important so as to gain the benifits of MIMO, this becomes even more challenging when considering coupling between three antennas. In this reported work, this is addressed by utilising a loop antenna as one of the three antennas, where the other two will be conventional inverted-L antennas. The measurements show that low coupling is possible between all three antennas, while having low correlation between the two Rx antennas.

An aperture-coupled patch array antenna with a reduced sidelobe level (SLL) at the 28 GHz frequency band is presented. The feeding line consists of an asymmetric stripline with a stripline-to-waveguide transition. The array antenna is serially fed in the E-plane, the excitation of which is tapered by controlling the aperture sizes, and is fed through a power divider in the H-plane. The experimental results show a SLL of <−20 dB and a gain of ∼20 dBi for a frequency band in the range of 27.5–28.5 GHz.

A cost-effective solution for the performance enhancement of circularly polarised array antennas by using a thin metasurface is proposed. The array is considered as reconfigurable, where an antenna engineer can arbitrarily add the metasurface onto the original array according to application requirements. Once added, the new array forms a subwavelength cavity having a compact form factor of 1.63λ _o × 1.63λ _o × 0.07λ _o at 2.45 GHz. The array antenna is demonstrated to have remarkable enhancement on its performance metrics including boresight gain (12.8 dBic), axial-ratio bandwidth (46.5%) and 10 dBic gain bandwidth (24.4%). More interestingly, a sidelobe suppression level of 4.4 dB is achieved.

A very compact circuit for the head direction cell system is presented, which acts as the neural velocity integrator. This is useful in the implementation of robotic spatial navigation systems in hardware. In addition, the use of the circuit as a central pattern generator is also demonstrated, whose silicon implementation is useful in robotic gait control.

Reducing the size of biosignal data is important because a huge amount of data is made by various experiments. In this reported work excitatory postsynaptic potentials (EPSPs) which are one of the biosignal types are efficiently compressed. To the best of authors’ knowledge, EPSPs compression has not been studied yet. The EPSP signal has a feature that the adjacent signals in a single excitatory postsynaptic potential have similar characteristics. Using this feature, a method is proposed which removes the temporal redundancy and statistical redundancy of EPSPs. The compressed and reconstructed EPSPs are similar to the original signal without the loss of analytic information.

A hardware-oriented lossless electrocardiogram compression algorithm is presented for very large-scale integration (VLSI) circuit design. To achieve high performance and low complexity, a novel prediction method based on the fuzzy decision and particle swarm optimiser (PSO) was developed. The accuracy of prediction was advanced efficiently by using the PSO algorithm to find the optimal parameters, which provided 64 situations for the fuzzy decision. Moreover, a novel low-complexity and high-performance entropy-coding algorithm based on Huffman coding was developed, which used one limited Huffman coding to encode a main region and five-region codes to encode the extending regions. The average compression rate of the whole MIT-BIH Arrhythmia database was up to 2.84 by combing the proposed fuzzy-based PSO prediction and Huffman region entropy-coding techniques. The VLSI architecture contained only a 1.9 K gate count and its core area was 5965 μm² synthesised using a 90 nm CMOS process. It consumed 201 μW when operating at a 200 MHz processing rate. Compared with previous low-complexity designs, the average compression rate is not only improved by more than 6.4% but also reduced the gate count by at least 8.2%.

A new configuration of the flipped voltage follower (FVF) offering class-AB operation is presented. The idea uses a bulk-driven transistor instead of the constant current source of the typical FVF topology. This feature enhances the sourcing capability for class-AB operation and the symmetrical slew rate. The key element is changing the basic structure of the original FVF circuit with no additional devices. A detailed analysis of the circuit and simulations using Spice are presented. The experimental results from a manufactured circuit prototype using CMOS 0.35 μm technology demonstrate the feasibility of the proposal.

On-chip cache memory is one of the largest power consumers in modern microprocessors. A dynamic way prediction scheme utilising a hearing policy is proposed for a low-power level-one cache design that handles power limit issues. The high prediction accuracy of the dynamically electing candidate (DEC)-cache helps to prevent large miss penalties. Owing to the high prediction accuracy, the experimental results show that the DEC-cache structure improves the energy-delay product by 26% compared with the existing buffered dual-mode cache.

A gallium nitride (GaN)-based gate driver circuit for high power and high speed GaN power switches is presented. The principle of the proposed circuit is based upon two normally-on GaN HEMTs and a self-biasing resistance. An integrated pulse width modulation functionality has been implemented using the threshold effect of the presented topology. The gate driver has been built with two CGHV1F006S GaN HEMT devices from Cree, Inc. It has been connected to the gate port of a 45 W CGH40045F GaN power switch operating as a DC/DC boost converter for the purpose of demonstration. Low consumption (≈1 W) and high frequency switching operation up to 60 MHz over the 20–80% duty cycle range is demonstrated. The square waveforms having switching times in the order of nanoseconds have been measured.

Timing parameters of the standard cell library are essential for static timing analysis. An on-chip picosecond resolution timing measurement system is presented. The system measures the rise/fall time of the signal and the setup/hold time of the flip flop. Compared with the SPICE simulation, the on-chip physical measurement considerably improves the resolution of the timing parameters.

Two-dimensional (2D) synthetic fingerprint images have been successfully used for evaluating large-scale automated fingerprint identification systems (AFISs). However, they are limited in assessing the whole process involved in an AFIS, particularly fingerprint image acquisition and fingerprint deformation. Hence, it is desired to develop synthetic 3D fingerprints and 3D fingerprint phantoms. In this reported work, a first attempt to establish a statistical shape model of 3D fingerprints is made by first re-sampling and aligning a set of training 3D fingerprint data and then applying the principal component analysis method. On the basis of the proposed model, synthetic 3D fingerprint shapes can be generated randomly. By further mapping fingerprint textures onto the shapes, synthetic 3D fingerprints can be obtained. Example results are provided demonstrating the effectiveness of the proposed model and method. The model and code will be publicly available for academic purposes.

A novel three-dimensional measurement technique is proposed. The methodology consists in mapping from the screen coordinates reported by the optical camera to the real world, and integrating distance gradients from the beginning to the end point, while also minimising the error through fitting pixel locations to a smooth curve. The results demonstrate accuracy of less than half a centimetre using Microsoft Kinect II.

A fractional-norm constrained blind adaptive algorithm is presented for sparse channel equalisation. In essence, the algorithm improves on the minimisation of the constant modulus criteria by adding a sparsity-inducing ℓ_p-norm penalty (0 < p ≤ 1). The simulation results demonstrate that the proposed equaliser exploits the inherent channel sparsity effectively and exhibits faster convergence compared with its counterparts.

A 280 GHz broadband balanced frequency quadrupler chain is presented. The quadrupler can be used to generate as high as 200 μW over a −3 dB bandwidth of 275–285 GHz, which enables emerging applications in sub-millimetre-wave communications and remote sensing. The circuit is designed and fabricated in a 45 nm silicon on insulator (SOI) CMOS technology and occupies an area of 0.21 mm² including the pads. The chip consumes 85 mA dc current from a 1.1 V supply.

The implementation of fully three-dimensional (3D) substrate integrated waveguide (SIW) components by using an additive manufacturing technique is demonstrated for the first time. In particular, a 3D printing process based on the t-glase filament has been adopted. 3D printing allows for the manufacturing of very complex shapes in a few hours, thus leading to a one-day prototyping time for microwave components. To characterise the electromagnetic properties of the 3D printed material, a microstrip lines technique has been adopted. To fully demonstrate the potential of the proposed fabrication process, a SIW cavity resonator and a 3D SIW interconnect with four E-plane bends have been fabricated and tested.

The first backward diplexer for K-band substrate integrated waveguide (SIW) operation is presented. The advantage of this compact diplexer is having input and two output port interfaces at the same side of the substrate, which advances the applications of SIWs to more complex feed system assemblies. The diplexer has two bands at 20 and 21 GHz. The bandwidth of each band is 0.4 GHz, which gives 2 and 1.9% bandwidth at lower and higher bands, respectively. The diplexer is designed and analysed with the mode-matching technique, and its performance is verified by comparison with simulated and measured data. The in-band measured return and insertion losses are 14.65 dB/2.75 dB in the lower band and 13 dB/3.05 dB in the upper band.

A novel chaos-based selected mapping (SLM) scheme is proposed for physical layer security in OFDM-PONs, where a Hénon chaos map is employed to create a large key space for OFDM data encryption. The transmission performance is significantly improved due to the peak-to-average power ratio reduction in the SLM scheme. High quality 8.9 Gbit/s 16-QAM OFDM encrypted data transmission is demonstrated over a 20 km single-mode fibre.

Multichannel optical add–drop multiplexers (OADMs) based on cascaded Bragg grating/Mach–Zehnder interferometers in silicon-on-insulator are reported. The OADMs are fabricated using electron beam lithography with a single etch. Three add–drop channels at wavelengths of 1542.5, 1557.0, and 1570.4 nm, each with a 3 dB bandwidth (BW) of 4 nm are obtained. All channels exhibit a transmission isolation of >20 dB, an interferometric crosstalk of <−30 dB, and a bandwidth utilisation factor of >0.5.

A novel structure of a CMOS differential pair is presented, which is suitable for low supply voltages and low power consumption as well as a much higher gain than that of a conventional differential pair. This structure is based on the new technique of composite transistors. The need for the design of integrated circuits at low voltage, with low power consumption and how this constraint is reflected in the design of digital and analogue integrated circuits are demonstrated.

Novel results on how to reconstruct gain-guided optical fibres starting from arbitrary modal electric fields are presented. It is known that gain-guided optical fibre refractive index profiles are described in terms of complex numbers. Therefore, to achieve the design of such fibres from a knowledge of modal electric fields one is required to use complex refractive index profile waveguides, where one can determine the required refractive index profile on both real and imaginary parts of the refractive index. The novelty here is that the reconstruction starts by using complex-valued desired electric fields. This inverse problem is solved via modelling the waveguide transversely as a transmission line and working inversely from the electric field. Example reconstructions of refractive index profiles are offered which are useful for high-power lasers, in designing optical fibres for sensors, where one may require specifically shaped electric fields from a waveguide, and also in refractive index profiling instrumentation.

The use of multi-objective optimisation techniques in the field of artificial intelligence for designing photonic crystal (PhC) light-emitting diodes (LEDs) is proposed. The extraction ratio and Purcell factor are first identified and considered as the main objectives when designing such LEDs. These two objectives are then optimised simultaneously even though both are in conflict. The proposed method is developed within a framework and applied to a case study. A comparative study shows that the optimised PhC LEDs completely outperform current works in the literature. These results are obtained by just tuning the PhC structural parameters, which can be considered as a substantial achievement in this field.

InP-based strained-well InGaAs/GaAsSb quantum well photodiodes with non-zero net strain can be used to extend detection wavelengths well into the mid-infrared region. However, excess dark current due to defects in the structure can be a performance limiting factor in photodiodes of this type. In this reported work, both low-frequency noise spectroscopy and deep level transient spectroscopy were used to investigate traps in prototypical strained-well photodiode heterostructures. Two distinct traps were identified and their electrical and physical properties and distributions have been evaluated.

A novel Fermi-level managed barrier diode has been developed for achieving broadband and low-noise terahertz-wave detection. The fabricated quasi-optical module detected signals at frequencies from 200 GHz to 1 THz. The typical voltage sensitivity was 1020 V/W, and the current sensitivity for a 50 Ω load was 4.5 A/W at 300 GHz for a zero-biased condition. Square-law detection with good linearity was demonstrated at 300 GHz with an output current density exceeding 10³ A/cm².

A two-port microdisk laser connected to two radial waveguides is investigated using two-dimensional finite-difference time-domain methods for realising single transverse mode lasing with a heptagonal mode field distribution. Based on the experimental results, it is found that two-port microdisk lasers at the proper angles are easier to realise single transverse mode lasing compared with the one-port microdisk laser.

Impurity free vacancy disordering induced highly intermixed InAs/GaAs quantum-dot lasers are reported with high internal quantum efficiency (>89%). The lasers are shown to retain the device characteristics after intermixing and emitting in the important wavelength of ∼1070–1190 nm. The non-coated facet Fabry-Pērot post-growth wavelength tuned lasers exhibits high-power (>1.4W) and high-gain (∼50 cm⁻¹), suitable for applications in frequency doubled green–yellow–orange laser realisation, gas sensing, metrology etc.

A novel multi-output pulse-width-modulated control scheme based on time sharing is presented and applied to a two-output forward converter. Unlike the traditional two outputs, the main voltage output and the auxiliary voltage output can be controlled independently via two different switching periods and controllers, by inserting one auxiliary switch into the circuit. Put simply, the main turn-on time is used to control the main switch, the auxiliary turn-on time is used to control the auxiliary switch, and there are several auxiliary turn-on times within one main turn-on time. By this means, two stabilised output voltages are obtained with good cross-regulation. The prototype is verified by a 24 V input, the main voltage output, which has a rated output voltage of 56 V and a rated output power of 50 W, and the auxiliary output, which has a rated output voltage of 44 V and a rated output power of 40 W.

There are two weaknesses in conventional constant off-time controlled buck-type DC–DC converters: which are varied switching frequency and poor output-regulation accuracy. To make the switching frequency immune to the variation of the input voltage and the reference voltage and provide both high output-regulation accuracy and a fast transient response for buck-type DC–DC converters, a new control method, called the quasi-constant-frequency variable off-time control technique, is proposed. Circuit simulation results validate the correctness of the theoretical analysis.

A microgrid including distributed generation sources (DGSs) is generally connected to a bulk power system to provide power to its local loads. The point of common coupling between the bulk power system and microgrid should meet relevant standards. The microgrid becomes a weak system with unbalanced and distorted voltages after it is disconnected from the bulk power system. A synchronisation controller for the DGS considering imbalanced three-phase voltages and harmonic voltages is presented. The proposed method can be implemented without altering the traditional phase-locked loop circuit. No filters and compensators are needed in the proposed method. Simulation results reveal that the proposed method is applicable.

A synthetic aperture radar (SAR) system (RotoSAR) is proposed based on a radar head fixed at a rotating arm with antennas aimed in the direction orthogonal to the plane of rotation. This system is able to provide SAR images and the three components of displacement vectors of the targets in the field of view.

For the first time, the low-frequency kink phenomenon in the S ₁₁-parameter of standard MOSFETs fabricated without any degradation of RF performances that exists in previous works is reported and its dependence on the gate finger number is analysed. The kink phenomenon is notable only for wide total gate width devices that show abrupt increase of a negative phase angle of the S ₁₁-parameter in the low-frequency region, because of a widening space between adjacent resistance circles in the Smith chart. This phase increase originated from a quadratic increase of the low-frequency input capacitance against the gate finger number due to a constant load impedance for the S ₁₁-parameter measurement.

A method to achieve realistic values for the thermal expansion coefficient in atomistic simulations of III–V materials using empirical Tersoff potentials is reported. The acceptance criterion of the Metropolis Monte Carlo algorithm that is used to relax the structures is modified to suppress exceedingly high thermal expansion, which has previously been observed for Tersoff potentials of III–V materials. Compared with earlier works, the error is reduced from more than 200% to ∼3% for GaAs. Similar behaviour is found for other binary III–V compounds with errors typically around 10% with respect to the experimental data.

The quantised kernel least mean square (QKLMS) is a simple yet efficient online learning algorithm, which reduces the computational cost significantly by quantising the input space to constrain the growth of network size. The QKLMS considers only the input space compression and assumes that the desired outputs of the quantised data are equal to those of the closest centres. In many cases, however, the outputs in a neighbourhood may have big differences, especially when the underlying system is disturbed by impulsive noises. Such fluctuation in desired outputs may seriously deteriorate the learning performance. To address this issue, a simple online method is proposed to smooth the desired signal within a neighbourhood corresponding to a quantisation region. The resulting algorithm is referred to as the QKLMS with desired signal smoothing. The desirable performance of the new algorithm is confirmed by Monte Carlo simulations.

Noisy condition is an important extrinsic degradation affecting speaker verification system performance. A feature-recovery approach is proposed to eliminate noise-dependent variability in feature space. A frame of the noisy feature vector is recovered using the information of itself and the neighbour feature vectors. Experiments are conducted on noisy test sets for text-dependent speaker verification tasks and the results indicate that the system can achieve significant performance improvement by using recovered feature vectors.

A 60 GHz low-noise amplifier (LNA) using standard 65 nm CMOS technology is presented. A gain of the 60 GHz amplifier was boosted by using a transformer feedbacked capacitor neutraliser. To stabilise the process variations caused by the positive feedback system, the body node of the triple well was adjusted to tune the capacitor value. The theory, simulation and measurements are presented. An implementation prototype is evaluated using on-wafer proving. The LNA showed a measured peak gain of 30 dB and a measured noise of 4.6 dB under 8.9 mW power consumption with a 1 V supply voltage. The measured IIP3 was −26 dBm. This is believed to be the first CMOS 60 GHz LNA to compensate the overlap capacitor with a single-ended structure.

An interleave-division multiple-access (IDMA) system supports the presence of multiple users in a cell by resorting to a different interleaver per user. Therefore the choice of the interleaver critically impinges on system performance. A new interleaver structure is proposed for the so-called STBC–OFDM–IDMA [space-time block coding (STBC), orthogonal frequency division multiplexing (OFDM) and IDMA] architecture, combining the viable features of the STBC, the OFDM and the IDMA techniques. This interleaver is based on the new idea of adopting permutation control keys generated using two cryptography elliptic curves in which the degree of randomness of the interleaved sequence is scalable by using several rounds and a different subkey in each round. In addition to offering a certain degree of data security, it is shows through simulation results that the resulting architecture incorporating the proposed interleaver yields a viable bit error rate performance.

A 94 GHz CMOS resistive mixer is presented using the 65 nm CMOS process. Parasitic losses which are serious at high frequencies are minimised by adopting the optimised transistor size and symmetric transistor layouts as well as a scaled-down 65 nm CMOS technology, which contribute to reducing the conversion loss at 94 GHz by 2–3 dB, the conversion loss being 8.8–9.2 dB from 87 to 94 GHz of RF frequencies with an LO power of <7.6 dBm. To the best of the authors' knowledge, this is the best performance of CMOS resistive mixers operating in the frequency band of more than 90 GHz. The results also are competitive when compared with GaAs-based resistive mixers having moderate LO power requirements and a reasonable noise figure.

A system that achieves compression using artificial DNA packaging with the support of two algebraic curves is presented, whereby the Hermitian channel code algorithm introduces gain and safety. Additionally, performance results are presented with a gain of 7 dB against uncoded quadrature phase shift keying and 1 dB against McEliece, for a bit error rate of 10⁻³. The results of the security levels compared with the McEliece system are also presented.