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Third generation perovskite solar panel technology is one of the most popular areas of research in photovoltaics because of their exceptional qualities such as high optical absorption coefficients, high charge mobility, broad spectrum absorption, and high charge carrier density. Optimizing power conversion efficiency of perovskites is critical for commercial use of perovskite solar panel technology. Various electrochemical and fabrication strategies are currently being researched in order to optimize power conversion efficiency and minimize energy loss. There are current results which suggest the addition of particular ions in the perovskite crystal have a positive impact on the power conversion efficiency. The qualities of the cell such as crystallinity, defects, and grain size play important roles in the electrical properties of the cell. Along with the quality of the perovskite crystal, its interfacing with the transport layers plays a critical role in the operation of the device. This paper investigates the current methods in power conversion efficiency optimization. We also examine the sources of energy loss in the perovskite and passivation methods. By continuing the upward trend in enhanced power conversion efficiency, commercial perovskite solar panels will be a near future reality, thereby transforming our energy infrastructure.

In this paper, a transmissive metasurface with high efficiency and 2-bit compensation phases is proposed for circularly polarized applications. The proposed structure consists of three identical metallic layers separated by two identical dielectric slabs. By using the Pancharatnam-Berry phase theory, four different unit cells are designed to provide four transmissive phases with a consistent step of 90°. Simulations demonstrate their validation. The transmission efficiency higher than 0.9 is from 11.9 GHz to 12.75 GHz, about 7.2%, and the 3-dB axial ratio bandwidth is 11.5-12.7 GHz. about 9.6%.

Resorting to the superposition principle of mutual inductance, multi-antiparallel coil (MAC) is able to obtain stable mutual inductance as the separation between transmitting and receiving coils changes, which is attractive for range-stable wireless power transfer. This paper presents a new method for the optimal design of MAC. The status of every coil is denoted by a ternary code, and the status code is optimized by a genetic algorithm (GA) to maximize a properly designed fitness function. The global searching ability of GA allows for achieving better design performance than the point matching design method. Besides, with the aid of ternary coding, the GA searching space is limited, and the optimization effort can be reduced.

Random frequency diverse array (RFDA) based directional modulation (DM) was proposed as a promising technology in secure communications to achieve a precise transmission of confidential messages, and artificial noise (AN) was considered as an important helper in RFDA-DM. Compared with previous works that only focus on the spot of the desired receiver, in this work, we investigate a secrecy region around the desired receiver, that is, a specific range and angle resolution around the desired receiver. Firstly, the minimum number of antennas and the bandwidth needed to achieve a secrecy region are derived. Moreover, based on the lower bound of the secrecy capacity in RFDA-DM-AN scheme, we investigate the performance impact of AN on the secrecy capacity. From this work, we conclude that: 1) AN is not always beneficial to the secure transmission. Specifically, when the number of antennas is sufficiently large and the transmit power is smaller than a specified value, AN will reduce secrecy capacity due to the consumption of limited transmit power. 2) Increasing bandwidth will enlarge the set for randomly allocating frequencies and thus lead to a higher secrecy capacity. 3) The minimum number of antennas increases as the predefined secrecy transmission rate increases.

Electromagnetic inverse problems have been traditionally solved in frequency domain. The time-reversal method has been developed to offer an alternative approach in time domain with natural time stepping computations. However, in its applications to electromagnetic source reconstruction, much work so far has not considered possible different excitation times. In this paper, the concept of entropy used in image processing is incorporated into the time-reversal process, which leads to reconstructions of not only the spatial locations but also the excitation times of the sources. Experiments are also set up for verification purposes and the proposed work may pave the way for practical applications of the time-reversal method. The effectiveness of the method is proposed to solve realistic problems in future experimental test.

The frequency modulated continuous wave (FMCW) radar has been used to determine the position and movements of a target. In this paper, we design a liner FMCW radar-based indoor position system for better target localization and trajectory detection. First, with the received radar signals, we construct a two-dimensional range-Doppler map. Using the map, We extend the one-dimensional constant-false-alarm rate (CFAR) technique into the two-dimensional one and develop a two-dimensional cell-averaging CFAR detector; it effectively eliminates the outliers of the original CFAR results and hence reduces localization error significantly. Finally, we adopt the Kalman filter to optimize the target trajectory. The experimental results are provided and they show that the accuracy of the estimated range is improved by about 38% and 11% in stationary and moving target localization, respectively, as compared with the current detectors.

A compact nested ring patch antenna with grounded vias is proposed in this paper. The outer ring and the meandered inner ring of the proposed antenna are nested in a single radiation layer for miniaturization. The antenna size is further reduced through embedding four small patches with grounded vias in the meandered inner ring. The side length of the inner square ring is only .16 λg (guided wavelength), while the side length of the outer square ring is 0.25λg.

The major problem in applying a meshless (RPIM) method is that when a large number of sampling nodes is used, the condition number of the moment matrix increases, and numerical solution becomes unstable due to the required inversion of the matrix. To address the problem, in this paper, with the radial point interpolation meshless (RPIM) method as an example, the moment matrix is first diagonalized and then the associated singular eigenvalues that cause the instability are truncated. As a result, the dependence of the stability on the number of the sampling nodes is removed. Numerical experiments are conducted, and the results have shown that the proposed algorithm are stable irrespective of number of sampling nodes; they pay the way forward for the meshless method to be applied to practical structures.

The direct time-reversal (TR) method has been proposed for source reconstructions. However, it has limited capability in reconstructing clustered sources due to signal interferences generated by neighbouring sources. In this paper, we first develop the time-reversal theory in frequency domain. Then based on the analysis, we derive an important condition that formulates a time-reversal process with its solution being found by application of the regularized least squares (RLS) method. A numerical reconstruction of three-dimensional two-element linear array and a numerical diagnosis of faculty array elements in three dimensions are presented to verify the proposed method.

We present PayFlow, a fine-granularity QoS micro-payment system that allows end devices in a software-defined network to make and pre-pay for guaranteed bandwidth reservations for their flows within the network for an arbitrary period of time. PayFlow combines payments using digital currency and storage of transaction records in a distributed ledger with queue-based QoS management using software-defined networks. While the PayFlow architecture is agnostic to the choice of digital currency, ledger technology and SDN platform used, we present a proof of concept implementation of PayFlow using OpenFlow and the IOTA cryptocurrency and distributed ledger, that we evaluate using the Mininet emulator.

This paper presents our recent work on the node-based meshless numerical method and the time-reversal method. The meshless method can serve as a platform to unify or hybridize numerical methods and is well fit for solving multiscale and Multiphysics problems. The time reversal method is reformulated as an optimization problem and can be used for reconstruction of clustered sources and diagnosis of faulty antenna elements; they pave the way for automatic locations of EMC/EMI radiation sources for automatic synthesis, design and diagnosis of antenna and antenna array.

Wireless power transfer (WPT) is the means that can cut the last wires in electronic wireless applications. Among the WPT technologies developed so far, magnetically coupled resonance (MCR) techniques have gained much attention to potentials for mid-range power transfers. However, misalignments between transmitters and receivers have become one of the major obstacles in improving the power transfer efficiency. This paper presents our recent progress in developing new MCR-WPT systems in mitigating the misalignment effects for wireless power transfers. Prototypes are developed and tested to demonstrate the effects of our proposed systems.

Array element failure is one of the challenges in application of antenna arrays. The existing methods are of frequency-domain, and they can be complicate, expensive or time consuming. In this paper, we propose the use of the time-reversal method for array diagnosis. The method can directly reconstruct both operating and defect elements without matrix operations. Both theoretical analysis of the time-reversal method and computation of an example are presented to verify the effectiveness of the time-reversal method.

Three ferrite component structures are presented and incorporated into the planar magnetically coupled resonance (MCR) wireless power transfer (WPT) systems in this paper. They are then employed to build two WPT systems which are simulated and tested. The ferrite core and ferrite plate being introduced improve the transmission efficiency by 16.2%. The ferrite plate and ferrite sheet effectively mitigate the magnetic leakage and restore the transmission efficiency when metal object placed in proximity of the receiver. Our results show that the proposed ferrite configurations can benefit the planar WPT systems for small electronic devices.

This paper presents a novel reconfigurable array for magnatically-coupled resonant wireless power transfer (R-MCRWPT) system. In this system, the transmitter includes three connected resonant element modules, and the receiver includes two connected element modules. It allows both the transmitting and receiving arrays to be reconfigurable in shapes and positions for the best performance. Unlike the conventional system, the reconfigurability of the proposed system is achieved without any control circuits and changes of resonant and matching capacitances. A prototype was developed and tested. Within the coverage range, the proposed system achieves the power transfer efficiency above 80%. Thus, the proposed system presents a good and simple technique for practical wireless power transfer applications.

Frequency modulated continuous wave (FMCW) radars have been widely used for measuring target range and speed. In this paper, we investigate and analyze its performances for indoor localization application. We develop a simple method to correct errors in finding beat frequency and present a two-step process to reduce background reflections from stationary objects. We use Matlab Simulink for simulations and employ USRP and GNU Radio platforms to construct a FMCW test setup. Both simulations and experimental results show the proposed method improve accuracy by 1.6 to 18 times over the conventional method.

In this paper, a generalized nonlinear detector (GND) is proposed for impulse radio ultra-wideband (IR-UWB) receiver employed the nonlinear square law (SL) technology (SL-GND). By using a generalized nonlinear detector, the received signal processed by SL operator is exploited by it's high-order statistic. Simulation results show that comparing with the conventional ED receivers using SL technology and other nonlinear detector-based receiver, the proposed SL-GND receiver can significantly improve the bit-error-rate performance, especially when strong narrowband interference presents.

This paper presents a device-free indoor localization system using frequency-modulated continuous-wave (FMCW) technology. The system localizes a target by using the two round-trip distances obtained with the two Rx-Tx links. To improve the accuracy, a frequency correction approach is proposed and the extended Kalman filter is applied to track a target. Experiments were conducted to demonstrate the validity of the proposed system and method. Future directions in further improvement of the locating accuracy are presented.

Frequency modulated continuous wave (FMCW) radar technique has been widely used in tracking system, e.g., WiTrack System. In this paper, based on fourth order statistic, i.e., Kurtosis (KD), we propose a non-coherent CFAR detection method for FMCW indoor positioning. We develop mathematical model, investigate impacts of parameters and conduct performance evaluations. Our results show the proposed Kurtosis based detection outperforms the conventional FMCW detection technique under additive white Gaussian noise (AWGN), line-of-sight (LOS) and non-line-of-sight channel conditions. The detection probability with the proposed method can be twice better than the conventional method.

This letter presents a multilayer relay wireless power transfer system of coupled magnetic resonance for power supply to devices or sensors mounted inside electrical appliances. With a refrigerator as a test case, it contains a transmitter at the bottom of the interior cabin, two relay coils in the middle, a third relay of a 2×2 coil array at the top and a receiver in between the second and the third relays. As a result, the entire interior of a refrigerator can be covered with wireless power supply, which is impossible with the conventional wireless power transfer system. A prototype of the proposed system is fabricated with FR4 printed circuit boards and is experimentally tested. The simulated and measured results show that the proposed system is relatively easy to implement and fabricate with good performances; therefore, it can serve as a good candidate for wireless power supply to electrical appliances (such as a refrigerator) for household applications.

Analysing software log files has become a challenging task due to the diversity in file structure and the nonstandardisation of log syntax. During the process of extracting log data, it is required to manually decode the log syntax and interpret data semantics, which can become tedious and is often error-prone if not performed carefully. Contemporary log analysis software tools do exist in the market and most of them offer numerous options to analyse log files, however, their sheer focus is on providing log management solutions instead of log analysis capabilities. In particular, none of them offers a generic parsing and extracting solution that can discover hidden data structures, a critical and effortful task in log analysis. We thereby devise such a solution that is able to automatically identify hidden patterns in a given log file and extract useful information by generalising the patterns. The solution is implemented as an intelligent Web-based system known as iLSE (intelligent Log Structuring and Extraction) whose users are not required to possess fluent programming skills. This paper presents a reference architecture for the system as well as a comparison study on how the system performs against contemporary log analysis systems.

ExpanStor is proposed to provide high security and reliability in multi-cloud storage. Compared with the existing multi-cloud storages, expanStor have the following distinctive features and advantages. Firstly, expanStor uses client-server architecture to realize multiple-devices, multiple-user use case. The combination of local database and remote database storing the metadata of the files avoids the single point of failure. Secondly, expanStor supports LDPC codes to provide high level of security and reliability with high efficiency. Thirdly, a dynamic distributor is proposed to place the data dynamically so that higher reliability and even distribution can be achieved when there are more available Cloud Storage Providers.

A general numerical dispersion relationship of the two-dimensional (2-D) radial point interpolation meshless (RPIM) method is deduced in detail in this paper. The characteristics of the numerical dispersion of the RPIM method based on Gaussian and Multiqudric basic functions are both observed. Recommendations for parameter selection of two basic functions are given. And the numerical dispersion of the finite-difference time-domain method (FDTD) is calculated to validate the effectiveness of the proposed numerical dispersion relationships.

This paper presents the use and formulation of generalizing node-based meshless method for a computational platform allows unification and hybridization of different numerical methods. It is based on the node-based meshless method with the applications of the method of weighted residuals (MWR). Numerical example shows the effectiveness and validity of the platform.

Meshless methods have proposed recently to solve electromagnetic problems for some advantages. This paper extends the meshless radial point interpolation method (RPIM) to the application of electromagnetics with the plasma media. The discretized equations for a plasma driven by an electric field is derived with the shape function expansion. Consequently, this paper shows a numerical experiment solved with finite-difference time-domain (FDTD) method and RPIM respectively. The results from the RPIM show a good agreement with ones from the FDTD method. This verifies the accuracy and applicability of the RPIM. Numerical results also show that the plasma media can change the spectrum of wave propagating inside.

This paper presents a new transmitting array system of magnetically-coupled resonance for uniform spatial wireless power transfer coverage. Unlike a conventional array system in which each resonant coil element has its own respective resonant tuning capacitor, the proposed array system consists of four identical resonant coil elements with only one common tuning capacitor. Four resonant coils are connected in two planar spiral patterns of number ‘8’ to ensure right magnetic couplings with improved performances. The prototype is fabricated and tested. Both simulations and measurements show that the proposed array system can produce (i) easier tuning and higher power transfer efficiency and (ii) a more uniform transfer efficiency distribution in the intended wireless power cover region than the conventional array. The proposed array can be considered as a good candidate for developments of practical wireless power transfer systems for applications such as charging mobile devices.

Time reversal (TR) techniques have been introduced for many applications in acoustics, seismology, medical imaging, electromagnetics, and so on. One of the applications is source locating in a time-invariant environment. By performing the TR process, temporal and spatial focusing occurs at the original source location and consequently the source locations are identified. In this paper, we propose a new TR method which allows the location identifications of narrow-band sources and moving sources which have not been considered. The proposed method is built on the conventional time-reversal method and therefore retains the simplicity and robustness of the conventional TR technique. Numerical examples are given to verify the effectiveness of the proposed method.

In most research, fabrication of high performance perovskite solar cells (PSCs) has been carried out in a well-controlled environment (glove boxes), which may result in high cost for eventual manufacturing. Therefore, fabrication of efficient perovskite solar cell in ambient air is of great interest. We fabricated CH3NH3PbI3(MAPbI3) solar cells in ambient air without control of relative humidity (~20-50%RH) using the antisolvent method. The effect of both the antisolvent and the annealing process on the solar cell performance has been investigated. Solar cells with power conversion efficiency of over 15% and negligible hysteresis were obtained, which are close to the performance of solar cells fabricated at nitrogen environment in a glove box. It may pave the way for fabrication of highperformance PSCs in ambient air.

This paper presents a new transmitting array of magnetically-coupled resonance system for multi-receiver wireless power transfer systems. It consists of several resonant coils driven by a single source loop. Our analysis shows that it can deliver power wirelessly to multiple receivers evenly and automatically without any control circuits with a relatively high power transfer efficiency. The proposed array makes a good candidate for developments of practical wireless power transfer systems for applications such as charging multiple mobile devices simultaneously.

Due to increasing demands for a large number of users and a large amount of data transmission, a 4G LTE communication system will require its antenna to have omnidirectional radiation patterns and wide frequency bandwidth. To this end, in this paper, a novel omnidirectional horizontally polarized (HP) antenna is presented for the 4G communication systems. The antenna consists of four pairs of flag-shaped radiators, eight pairs of parasitical striplines. With return loss better than 10 dB, it has a relatively wide fractional bandwidth of 55% working from 1.7 to 3.0 GHz and size of 45×45×2.5 mm3.

In this paper, a multichannel energy detection (MED) receiver based on nonlinear square law (SL) technology is proposed for ultra-wideband (UWB) system. By using a group of band-pass filters, the received signal processed by SL device is separated into multiple channels, and then the channel with serious narrow band interference (NBI) will be omitted to improve the NBI mitigation ability of the receiver. Simulation results show that comparing with conventional ED receivers, the proposed SL-MED receiver can significantly improve the bit-error-rate performance when one or two NBIs are present and even no NBI presents.

Electromagnetics forms the foundation of modern electrical and electronic systems that see the technologies we enjoy and take for granted today. It has been used to transfer information and power in daily lives. In the wireless domain, however, it had not been considered and employed much for power transfer until 2008 when a MIT research team lead by Prof. Marin Soljacic successfully demonstrated the mid-range wireless power. Since then, many efforts and much progress have been made to improve power transfer efficiency, reduce system size and include more functionality; the goal is to cut the last wires in electrical and electronic devices and systems if all possible. In this talk, we will first present the principles of the wireless power harvesting and transfer and then focus on mid-range wireless power transfer and its applications and commercialization. We will present the challenges, progresses, and future directions in the areas.

The late-time instability has been an issue of main concern for time-domain integral equation (TDIE) method using the march-on-time algorithms. It can be identified with by analyzing the eigenvalues of the synthetic impedance matrix of the methods. In this paper, we reformulate the TDIE methods and analyze the late-time instability of different types of TDIE. A new category of the eigenvalues is presented based on the analysis results.

Considered as an alternative to ERP and a pre-condition to the future Enterprise 4.0 based on IoT and Cyber physical system principle, this paper tentatively presents a proposal to develop an Enterprise Operating System (EOS). At first a set of requirements and functionalities are identified. Then a survey on existing relevant works is presented and mapped to the requirements. The architecture of envisioned EOS is outlined and followed by a simplified case example in the service sector. The last part draws some conclusions and gives future perspectives.

It is well known that Joule heat losses in integrated circuits (ICs) may change electrical behaviors of devices, especially semiconductor components. In this paper, a meshless approach based on a radial point interpolation method (RPIM) is developed to numerically model the coupled electrical-thermal process in time domain. The effectiveness of the proposed RPIM is verified through simulation of thin-film resistors.