Antenna array synthesis based on the back propagation neural network is proposed in this Letter. The synthesis process is divided into three steps: pre-processing, training, and post-processing. In the pre-processing, the interference directions and desired signal direction are coded so as to synthesise an arbitrary number of interferences. The back propagation neural network is unified to emulate the convex array synthesis model. To verify the performance of the network, the nine-element and 11-element linear array synthesis based on the neural network is realised and tested. Synthesis results show that the proposed method gives accurate approximation and have the good generalisation ability.

A compact substrate integrated waveguide (SIW) cavity slot antenna with enhanced bandwidth and quasi-elliptic filtering response is proposed. Served as radiating elements, two slots are etched on the top plane of a square SIW cavity. Quality factors of two original modes are greatly reduced and a new resonant mode is introduced by etching an additional slot on the bottom plane. By merging these three modes within a single passband, the bandwidth can be enhanced. In addition, a radiation null is generated in the lower and upper stopband, respectively. Therefore, a quasi-elliptic filtering response is achieved with three resonant modes in the passband and two radiation nulls in the stopband. A fabricated prototype with the size of 0.48λ ₀ × 0.48λ ₀ × 0.02λ ₀ has been measured. The measured 10 dB bandwidth is 11.5% (3.28–3.68 GHz). The measured efficiency is about 77% in the passband but it sharply drops to 5.6% at 3.26 GHz and 10.5% at 3.76 GHz.

A lossy-to-lossless compression framework for electrocardiogram (ECG) signals is proposed for wearable monitoring devices. In this framework, the tail bits of the coefficients generated by the lifting discrete wavelet transform of the ECG sequences are truncated at different levels configured according to the tolerance of the information loss, while no truncation for lossless compression. These processed coefficients are then encoded with the modified run length code. The algorithm is evaluated by the MIT-BIH arrhythmia database, where the experimental results show that the proposed framework achieves a better comprehensive performance than existing state-of-the-art lossy-to-lossless compression approaches. The authors further demonstrate a three-stage pipeline very large scale integration (VLSI) implementation of the compression framework, which can be used as an intellectual property core with a core area of 0.4 mm² and achieves power consumption of 1.524 μW at 360 Hz in a 0.18 μm CMOS technology.

A low-power, high-linearity, high-charge handling capability two-stage ADC-based 384 × 288 size digital readout integrated circuits (ROIC) for infrared focal plane arrays are presented. A novel high-speed, low-power-consumption comparator structure is proposed in this work. Moreover, the two-stage ADC combines the pulse frequency modulation (PFM)-based pixel-level ADC and fine quantify module, improving the charge handling capability and the linearity of the readout circuit. The ROIC with 25 μm pixel pitch has been realised in 0.18 μm 1P6M CMOS process. The power consumption of the two-stage ADC is 50 μW. The charge handling capability of the pixel is 2.3 Ge⁻ and the non-linearity of the proposed circuit is 0.09%.

The authors present a novel Bayesian approach to adaptively select frequency samples to obtain a rational macromodel of device responses over a broad frequency range while performing as few electromagnetic simulations as possible. The method leverages a Bayesian approach to vector fitting to construct a data-driven uncertainty measure. The presented technique is demonstrated by application to a double semi-circular patch antenna and is shown to accurately and efficiently construct a rational macromodel over the frequency range of interest.

Dynamic RAM (DRAM) is mainly used as the main memory. As the DRAM density increases, the address bus width required for a DRAM device is also increased. However, in a high-speed DRAM interface, as the address bus becomes wider, not only the routing area and power consumption increase but also the timing margin to maintain signal integrity also decreases. Furthermore, without increasing the address bus pins, row addressing may need multiple cycles, which will lead to significant performance degradation. In this Letter, the authors propose a novel row addressing scheme to issue single-cycle row addressing without extra address bus pins for high-density DRAM devices. The proposed scheme prefetches a part of the target row address for the next activate command using unused address bus of a precharge command. The proposed scheme also enables an auto-activate operation which activates automatically after precharge without explicitly issuing an activate command. As a result, the proposed row addressing scheme reduces the performance degradation due to multi-cycle row addressing and the power consumption on the memory bus due to explicit activate command.

A novel intelligent control scheme is presented for accurate position tracking of electrohydraulic servo actuators. The proposed control law is designed by means of a non-linear control approach and includes an adaptive neural network to provide the basic intelligent features. Online learning, instead of off-line supervised training, is proposed to update the weight vector of the neural network. Moreover, the adoption of a composite error signal as the only input to the neural network allows a significant reduction in the computational complexity of the algorithm. Rigorous proofs for the boundedness and convergence properties of the closed-loop signals are provided. Experimental results obtained with an electrohydraulic system demonstrate the efficacy of the proposed controller, even considering the highly non-linear and uncertain plant dynamics.

This Letter demonstrates the capability of long short term memory (LSTM) network in capturing the complex hysteretic dynamics in piezoelectric actuators (PEAs). A LSTM network is constructed to model the PEAs' complex dynamics, which includes static hysteresis, creep, high-order dynamics. The network is trained and evaluated by data sets of input–output pairs with different frequencies and amplitudes. Preliminary results show that, even for the simplest topology, namely one layer with one cell, the LSTM network provides a satisfactory precision in a wide frequency range. Thus, LSTM networks may provide a new approach to approximate the dynamics in complex engineering systems.

The authors designed a randomised overlapping ring metallic mesh and built its evaluation model of electromagnetic interference shielding effectiveness. They simulated and analysed the effects of diameter 2R and period g on electromagnetic shielding effectiveness. The simulation and experiment results show that the electromagnetic shielding effectiveness is better than 23 dB in the 10–18 GHz band while its maximum normalised high-order diffraction optical energy is decreased to 0.00134%. The randomised overlapping ring mesh can realise strong shielding effectiveness and low image-degradation simultaneously.

In this Letter, the authors propose an active contour model based on the fuzzy c-means method. Using fuzzy c-means to calculate the values of two types of cluster centres for all points in the image domain, by which local fitting functions in traditional models are substituted. Since the values are calculated before curve evolution, the proposed model can segment images with intensity inhomogeneity efficiently. Furthermore, it has the good robustness to initial contour. The effectiveness of the proposed model is tested by experiments on some synthetic and real images.

Layer thickness is the major parameter of the 3D printing process that should be investigated for digital forensic purposes. However, despite its importance, there have been no studies yet on this parameter of layer-manufactured models. This Letter focuses on an effective estimation of layer thickness parameters for layer-manufactured models. Based on the analysis results of the scanned 3D model, the proposed method provides a new solution for estimating the layer thickness. Regarding potential applications including multimedia forensics, the proposed estimator would be useful in a variety of fields.

In this Letter, a Siamese adversarial network tracker (SANT) is proposed. Recently, in computer vision field, generative adversarial network (GAN) has been widely used for image and video generation. Using the GAN, the proposed method constructs a Siamese adversarial network (SAN) for object tracking. Unlike existing GANs, the proposed SAN uses similarity learning with SAN discriminator. To show the effectiveness of the proposed SAN, the same structure as the residual long-short-term memory tracker is used. Experimental results show that the proposed SANT achieves the highest performance among existing Siamese trackers.

The authors investigate the application of deep convolutional neural networks (CNNs) to the problem of radiometric identification, i.e. the task of authenticating wireless devices on the basis of their radio frequency (RF) emissions, which contain features directly related to the physical properties of the wireless devices. They collected digitised RF from 12 wireless devices, and used various techniques to transform the time series derived from the RF to images. A deep CNN is then applied to the images. The authors' results show that the identification performance of the combination of deep CNN with an image representation significantly outperforms conventional methods based on dissimilarity on the original time series. Moreover, a specific comparison among RF-to-image techniques show that on their datasets the wavelet-based approach outperforms other approaches, also in the presence of white Gaussian noise.

In this Letter, a novel low complexity sparse channel estimation method based on forward–backward processing is proposed for mm-Wave underground channel incorporating a space-time-block coding filter bank multi-carrier (STBC-FBMC) system, which employs quadrature amplitude modulation. The proposed estimation algorithm relies on the idea of the channel support forward selection and backward removal, which iteratively expands and compresses the support estimate, hence improving the ability to cover up for the errors made in the conventional orthogonal matching pursuit (OMP) algorithm. By contrast to the latter, the most innovative feature of the proposed approach is its capability of effective channel reconstruction without prior information of the sparsity level and its adaptive step size method to approach the true sparsity level. The proposed approach is shown to achieve a higher estimation accuracy than OMP alternative.

Today's data centres need efficient traffic management to improve resource utilisation in their networks. It helps to solve the load imbalance problem of each processor. This Letter presents a ‘dynamic hierarchical load balancing’ approach for higher traffic scalability. The method selects the most favourable host satisfying the multi-dimensional resource constraints in terms of computing capability and its performance. The proposed method achieves significant traffic scalability improvement upto 66% over sequential and random virtual machine placement heuristics.

The authors investigate the secure communication in multigroup multicasting cell-free massive MIMO systems in the presence of an active pilot spoofing attack. With the imperfect estimated local channels at access points, a distributed conjugate beamforming with normalised power constraint policy is exploited for downlink multicasting transmission. Closed-form expressions for the per-user achievable rate and information leakage to eavesdropper are derived, respectively. Numerical results are presented to verify the correctness of their analytical results and quantitatively analyse the impacts of eavesdropper's spoofing pilot power and a number of groups on the secrecy performance of the considered systems.

In a free-standing 400-nm-thick platelet of crystalline ZY-LiNbO₃, narrow electrodes (500 nm) placed periodically with a pitch of a few microns can eXcite standing shear-wave bulk acoustic resonances (XBARs), by utilising lateral electric fields oriented parallel to the crystalline Y-axis and parallel to the plane of the platelet. The resonance frequency of ∼4800 MHz is determined mainly by the platelet thickness and only weakly depends on the electrode width and the pitch. Simulations show quality-factors (Q) at resonance and anti-resonance higher than 1000. Measurements of the first fabricated devices show a resonance Q-factor ∼300, strong piezoelectric coupling ∼25%, (indicated by the large Resonance-antiResonance frequency spacing, ∼11%) and an impedance at resonance of a few ohms. The static capacitance of the devices, corresponds to the imaginary part of the impedance ∼100 Ω. This device opens the possibility for the development of low-loss, wide band, RF filters in the 3–6 GHz range for 4th and 5th generation (4G/5G) mobile phones. XBARs can be produced using standard optical photolithography and MEMS processes. The 3rd, 5th, 7th, and 9th harmonics were observed, up to 38 GHz, and are also promising for high frequency filter design.

V-band waveguide components operating in 57–64 GHz ISM band is presented. Consumer-grade stereolithographic 3D printer is used to print these waveguide components with black-pigmented acrylate-based polymer. Electroless deposition of silver on these microwave components is achieved using an in-house system assembled with off-the-shelf components. This system is driven by a peristaltic pump, circling plating solution between silver bath and waveguide. Metal plated WR-15, 2-inch waveguide section offers average insertion coefficient of −0.35 dB. Trough waveguide section connected to rectangular waveguide through rectangular to trough waveguide transition is metal plated and offers average insertion coefficient of −1 dB. Silver deposited using the pump operated system offers potential of achieving comparable results as conventional dip coating technique.

The implementation of mainstream passive low-pass filters (LPFs) remains a challenge to satisfy the requirements of small size and compatibility with standard CMOS process. Fortunately, the emerging technology of through-silicon via (TSV) offers a possible solution to this issue by developing 3D LPF architecture. A 3D LPF based on coaxial TSV is exploited by fabrication and measurement. The measurement result shows good agreement with that obtained by finite element method.

A novel right-angle coaxial-to-single ridge waveguide transition with capacitive coupling is presented at X band. Contrarily to the state of the art, the coaxial inner conductor is not in DC contact with the ridge, and such a feature can be a considerable mechanical advantage in the manufacturing of high-performance systems. In addition to this, few geometrical parameters need to be optimised, thus simplifying the overall design with respect to traditional counterparts. Nevertheless, the whole X band can be potentially covered with a return loss better than 20 dB. An ultra-compact transition is designed, manufactured with stereolithography technology and tested in a back-to-back configuration. Good agreement between simulated and measured results is observed for a proof-of-concept prototype.

A scheme for simultaneous down-conversion and linearisation of radio-frequency (RF) signals is proposed and demonstrated. Based on carrier-suppressed double-sideband modulation, the input RF signal can be down-converted to any intermediate frequency (IF) tone in the range of 8–12 GHz. Compared with the down-conversion scheme with two cascaded intensity modulators, the proposed scheme has improvement of >21 dB of the suppression ratio of third-order intermodulation distortion and 6.17 dB of spurious-free dynamic range.

A wavelength filter using a pair of one-dimensional photonic crystal (1D-PhC) waveguides incorporating cavity sections for one-directional output is reported. The small number of holes for 1D-PhC is used to attain distinct transmission peaks in the stop band. Two cavity sections are used to obtain peak with steep slope and widened top. The three-dimensional finite difference time domain simulation results agree with the experimental result.

The transient response of the single-phase enhanced PLL (EPLL) under the step change of amplitude, phase angle, and frequency is derived. It is revealed that there are transient periodic ripples in the estimation results of the standard EPLL. Furthermore, a virtual quadrature-coordinate EPLL combining a second-order generalised integrator with a quadrature-coordinate EPLL is proposed and the transient response is derived. The proposed EPLL possesses a better dynamic performance than the standard EPLL. The detailed experimental results are shown and compared with each other to validate the theoretical analysis and the advantages of the proposed EPLL.

The platform of multi-channel synthetic aperture radar/ground moving target indication (MC-SAR/GMTI) system may encounter the problem of curvilinear trajectory due to the existence of acceleration in several applications, e.g. manoeuvring responding, orbital motion, and long-time observing. The curvilinear trajectory changes the attitude of the array, which leads to instantaneous baseline changing during echo reception. Thus, the traditional constant baseline range model is no longer valid since it will introduce severe phase error. In this Letter, a general range model that it applies to both stationary and moving targets for MC-SAR/GMTI is proposed. Simulation results of the point spread functions demonstrate that the proposed model can achieve good performance.

In this Letter, an enhanced bidirectional modified lateral silicon-controlled rectifier (EBMLSCR) is proposed for advanced dual-directional electrostatic discharge (ESD) protection applications. The ESD characteristics of the novel EBMLSCR and conventional bidirectional modified lateral silicon-controlled rectifier (BMLSCR) are measured using the transmission line pulsing tester. Compared with the BMLSCR, the EBMLSCR owns a lower trigger voltage down to 7.7 V, a higher failure current up to 6.5 A, a suitable holding voltage as well as the same superior leakage current. Based on these advantages, the proposed EBMLSCR can provide an effective ESD protection for the advanced 2.5 V/3.3 V input/output circuits, while the traditional BMLSCR becomes invalid for these applications due to its high trigger voltage and low robustness. In addition, the impact of some critical dimensions of the EBMLSCR has also been evaluated to further optimise the device performances.