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The aging of the transformer oil-paper insulation distributes spatially, which results in changes in paper resistivity in different regions. This paper establishes an iterative inversion algorithm using the finite element method to calculate the oil-immersed paper resistivity in different regions of a transformer. This algorithm sets the transformer dielectric loss factor tan δ at low frequency, the dielectric parameters of the transformer oil as inputs and the oil-immersed paper resistivity as output. The resistivity obtained from inversion can be used as a reference to access the insulation state of the oil-paper insulation. This paper aims at achieving the nondestructive detection of the partial state of the oil-paper insulation.

A paper based simple, flexible, and perfect resonant electromagnetic wave absorber is proposed in this article. The absorber consists of the conducting grid patterns where unit cell of the pattern is a two-dimensional grid based structure and the bottom is a conducting ground plane. The grid based top conducting patterns are created by inkjet printing over a thin paper having conducting layer at the bottom. The proposed absorber undoubtedly attains a cost-effective and eco-friendly solution for designing a flexible electromagnetic absorber. The experimental and simulation results are found to be in excellent agreement. The proposed absorber exhibits perfect absorption of 99.99% at 10.84 GHz and possesses an overall thickness of 0.531 mm.

This paper introduced the field test of dielectric frequency response of 110kV and above high voltage AC oil-paper insulated bushings, and explained the mechanism of electromagnetic interference and proposed measures, such as increasing the test voltage, to suppress electromagnetic interference. And voltage dependence of dielectric frequency response of high-voltage AC bushings werestudied as well. The method of increasing test voltage was proved to be effectively in suppress the electromagnetic interference and improve the accuracy of the test result during field test in the converter stations and substations.

High-voltage bushing is an important part of the operation of transformer equipment. In order to accurately and effectively evaluate the moisture condition of the bushing, this paper uses the polarization and depolarization current (PDC) non-destructive measurement method to do it. In the current research, the characteristics of loss peaks and curve fluctuations of tanδ-f curve can judge whether the bushing is evenly damp, but it lacks the judgment of the high moisture position of the internal damp. This paper uses oil-paper samples of different moisture content to make a preliminary qualitative exploration of PDC measurement methods. Then the polarity reversal method is used to judge the bushings with different moisture conditions, Combined with the migration characteristics of hydrolyzed ions in the oil-paper insulation, it is analyzed to verify the effectiveness of the method.

The STM32H743 processor is the core of this device, and it adopts the method of the bridge free axis to measure the impedance of the paper between two plates, by 16 bit high precision AD accurate sampling impedance under test and the reference phase shift and amplitude value of the voltage on both ends of the impedance, the paper between the value calculated plates corresponding capacitance value, according to the capacitance between the plate and the thickness of the paper assumes the inverse relationship, finally realizes the pad paper for precise measurement. The device has the functions of capacitance acquisition, processing, self-calibration and judging the plate short circuit. Through testing, the device can detect the number of papers between plates and the test status (plate short circuit, in the testing, self-calibration, test completion) according to the actual situation and display it on LCD in real time.

A circularly polarised metasurface is proposed in this paper. The design of the surface aims at improving the performance of a hybrid radiating structure made of one dipole and an Archimedean spiral antenna designed on the same surface. The antennas operate in UHF and lower European UWB bands, respectively, and realize a compact single-port antenna for future generation autonomous RFID tags. A High Impedance Surface (HIS) is employed as the ground plane to serve as a Perfect Magnetic Conductor (PMC), with the double purpose to maintain both the circular polarization in the UWB band and the low-profile stack-up, while assuring an insensitive behaviour to the background material.

According to the mapping relationship between complex permittivity and moisture content, X-Y model is used to construct the equivalent model of complex permittivity of oil paper insulation of converter transformer, proposes a method of moisture content measurement based on frequency domain dielectric spectroscopy (FDS), and tests converter transformers with different aging degrees. From the test results, it can be seen that the water content of converter transformer before operation is greater than that after operation, and increases with the increase of aging degree, which is consistent with the theoretical analysis. Therefore, the moisture content based on the frequency domain dielectric spectrum provides a new research idea for the quantitative evaluation of the insulation operation status of converter transformers.

In my speech, I intend to talk about engineering approach to antenna synthesis and its role in the research that our team conducts for the well known company "Reshetnev Information Satellite Systems".For communication via a geostationary satellite, a plurality of needle-like beams is required to cover the working area within its boundaries. Uneven solar heating distorts the surface of a huge umbrella-reflector, disrupting the required set of beams. In case of multibeam hybrid mirror antennas, cluster adaptive tuning paves the way for beams' stabilization. As the field of the terrestrial beacon, focused by mirror, bears the imprint of the reflector, its current state can be detected from the signals received by the antenna array.The synthesis of the best-fit paraboloid from the signals of a hexagonal cluster is reduced to minimizing the MSD using the concept of shapes' deviation, which we introduced for antenna synthesis. Finding six parameters of the paraboloid from seven (!) signals seems to be a simple task. However, the relationship between the sought-for parameters and the signals is so special that the gradient is oriented almost perpendicularly to the true direction even in the region close to the optimal point. It's amazing how the equipotential surface is shaped like a screw?Reconstruction of the reflector surface without any priori assumptions turned out to be possible within the framework of engineering heuristics, which partially steams from V.N. Dymski’ notion of energetically optimal solution of antenna synthesis. In the area near the reflector, the phase distribution of the field radiated by the antenna array, excited in accordance with the complex conjugate signals from the terrestrial beacon, is compared to the phases of a plane wave propagating towards the beacon. P.V. Romanov, my postgraduate student, raised a sound idea that the points at which the phase difference is constant are the sought reflector points.Evaluation of the consistency and effectiveness of the above approaches requires multivariate calculations. Therefore, the time consumption for modeling a large reflector antenna becomes a decisive factor. We use an extremely fast algorithm based on some robust engineering assumptions that we call acoustic approach.

As an important component of power transformer, transformer bushing cause thirty percent of transformer accidents. It is difficult to find defects in transformer bushing in advance because of the lack of on-site inspection methods. Frequency domain dielectric spectroscopy is widely used in the field of insulation evaluation of electrical equipment because of its frequency bandwidth and rich information. However, the frequency domain dielectric spectroscopy in the inspection of oil-paper insulated transformer bushing is affected by lacking substation test case and diagnostic criteria. In this paper, a dielectric response model of the transformer bushing is established to reveal the different defect types corresponding to the test curves in different frequency bands. In the low frequency band which is less than 0.0lHz, it is reflecting the water content of bushing. In the middle frequency band which is between 0.0lHz to 100Hz, it is reflecting the aging of bushing. Several cases of substation bushing defects detected by frequency domain dielectric spectroscopy have verified the above results. It is difficult to propose uniform fault diagnosis criteria for the frequency domain dielectric spectrum of transformer bushing which is affected by the structure and type. Based on a large number of substation case studies, a defect diagnosis criterion based on Frechet similarity method is proposed in this paper, which is universal for different structures and different types of bushing.

Oil immersed inverted current transformer is vulnerable to overvoltage in the transmission line during operation. The accumulative effect of switching impulse voltage can degrade the main insulation and lead to a reduction in insulating property. Frequency domain spectroscopy (FDS) can be used to reflect the insulating property of oil-paper insulation. In order to investigate the FDS characteristics of oil-paper insulation under repeated switching impulse voltage, samples of oil-paper insulation with different thickness were made. Afterwards, the FDS of samples was tested with different number of repeated switching impulse voltage and applied voltage. The results show that more impurities occur in oilpaper insulation under repeated switching impulse voltage, which has a greater impact on the FDS results. Therefore, the FDS characteristic curves can reflect the deterioration characteristics of oil-immersed inverted current transformers under repeated switching impulse voltage. The role of impurities concentration and motion characteristics in the degradation process of oil-paper insulation was analyzed.

As a non-intrusive measurement method, frequency domain spectroscopy (FDS) is widely used to diagnose the global defects (such as aging and dampness) of the insulation body in power equipment. However, the FDS method can only map the holistic dielectric response (DR) characteristics of composite oil-impregnated-paper (OIP) insulation that usually comprises both the insulation paper and oil. Under irregular insulation structure, the DR of each dielectric cannot be simply distinguished, which is unconducive to detect the insulation weakness therein. In this paper, a novel inverse problem model to analyze the separate DR of each dielectric within a compound insulation structure is proposed. Built on the modified Cole-Cole formula, the inverse problem is solved by an optimization process which combines the finite element method and GA-LMA numerical algorithm, and the dielectric variables of insulating oil and paper are back-calculated respectively. By comparing the error of the measured and reconstructed FDS traces, it is evidenced that the proposed model of DR inverse problem and its solution method are suitable for FDS measurements, which signifies new indications for refined state evaluation of OIP insulation by enabling inspecting the separate DR information of each dielectric within a real-life complex insulation structure.

Online surface quality inspection in Pulp and paper industries is important to anticipate and determine the final quality and printability of the paper and paper board using hi speed computers. Switching the dependencies from laboratory measurements to computer based online measurements needs prior authentication of online surface instrument and its limitation to the speed of the paper roll. The online measurements can be up to the speed of 2000 m/min in paper mills. The surface measurements can be influenced by processing velocities of the web mainly due to smearing effects. To know the measurement accuracy at different processing speed is important for any online topographical device. The degree of measurement correlation among different speeds determines the accuracy of the devices. In this study online measurements were performed at various speeds starting from 0 to 600 m/min and the correlation of measurements at different speeds was examined. Measurements were obtained from OnTop, a recently developed online profilometer. Overall measurements are presenting encouraging results and closely matching and correlating at different speeds up to 600 m/min. Some longer wavelength components are slightly deviating among various speeds depending on the type of paper and the dynamic behavior of the paper web. The measurement methods, challenges and the influence of velocities on surface topographical measurements are discussed and results are presented from standstill to 600 m/min velocity of the paper web.

In this work, a large area, low cost and flexible polymer/paper-based double touch mode capacitive pressure sensor is demonstrated. Garage fabrication processes are used which only require cutting, taping and assembly of aluminum (Al) coated polyimide (PI) foil, PI tape and double-sided scotch tape. The presented pressure sensor operates in different pressure regions i.e. normal (0 to 7.5 kPa), transition (7.5 to 14.24 kPa), linear (14.24 to 54.9 kPa) and saturation (above 54.9 kPa). The advantages of the demonstrated double touch mode capacitive pressure sensors are low temperature drift, long linear range, high pressure sensitivity, precise pressure measurement and large die area. The linear output along with a high sensitivity range (14.24 to 54.9 kPa pressure range) of the sensor are utilized to wirelessly control the movement of a robotic arm with precise rotation and tilt movement capabilities.

Air-gap discharge is the main type of partial discharge within the power transformer. It is of great significance to study the discharge development stage for the monitoring and diagnosis of transformer potential faults. This paper builds an air-gap discharge model in a simulated transformer tank, obtaining the development process of the phase-resolved partial discharge (PRPD) spectrum of the whole process from initial discharge to breakdown of the sample by the measurement system. Based on the Gaussian pyramid and gray level co-occurrence matrix, the feature of the PRPD spectrum is extracted during the whole discharge process. The results show that according to the change of the PRPD spectrum, the whole discharge process can be divided into the discharge development stage, discharge duration stage, and near breakdown stage. Based on the different morphology of the PRPD spectrum in each stage, ASM, ENT, CON, CORRLN and other features extracted by multi-scale gray-level co-occurrence matrix (GLCM) method can be used to characterize the discharge stage effectively.

Capacitive pressure sensors have several advantages in areas such as robotics, automation, aerospace, biomedical and consumer electronics. We present mathematical modelling, finite element analysis (FEA), fabrication and experimental characterization of ultra-low cost and paper-based, touch-mode, flexible capacitive pressure sensor element using Do-It-Yourself (DIY) technology. The pressure sensing element is utilized to design large-area electronics skin for low-cost prosthetic hands. The presented sensor is characterized in normal, transition, touch and saturation modes. The sensor has higher sensitivity and linearity in touch mode operation from 10 to 40 kPa of applied pressure compared to the normal (0 to 8 kPa), transition (8 to 10 kPa) and saturation mode (after 40 kPa) with response time of 15.85 ms. Advantages of the presented sensor are higher sensitivity, linear response, less diaphragm area, less von Mises stress at the clamped edges region, low temperature drift, robust structure and less separation gap for large pressure measurement compared to normal mode capacitive pressure sensors. The linear range of pressure change is utilized for controlling the position of a servo motor for precise movement in robotic arm using wireless communication, which can be utilized for designing skin-like structure for low-cost prosthetic hands.

In this letter, a novel design concept for circularly-polarized (CP) performance improvement of a single microstrip patch antenna (MPA) is studied and summarized via multiresonant modes. By investigating the internal E-field, it demonstrates that the direction of the equivalent magnetic currents (EMCs) at the patch edge are significantly changed under different feeding positions. Hence, two types of CP antennas are simulated and designed. Firstly, by reallocating three orthogonal modes in proximity to each other without sequential rotation, an extremely small frequency-ratio of about 1.04 is generated for the dual-polarized CP MPA. Secondly, by reallocating three orthogonal modes closely to each other with sequential rotation, the dual working bands of the MPA with same CP-polarization are merged to extend its CP bandwidth. In final, these MPAs are fabricated and measured. The measured results verify these predicted performances and the antenna keeps several advantages, i.e., low-profile, single-layer, single-element, wide AR-bandwidth, small frequency-ratio, and high efficiency.

Using THz spectroscopy, we show how to uniquely determine parameters for industrial quality control of paper sheets. We carry out measurements within the industrial setting: no averaging, fast acquisition in ambient conditions, and quasi-real-time analysis. Paper parameters are extracted using a combination of statistical evaluation and physical interpretation of the light-matter interaction. We show that THz spectroscopy offers additional value as compared to currently used industrial sensors.

Dielectric response measurements are an important maintenance and diagnostic tool for large oil filled power transformers. Regardless of if the measurements being performed in the time domain or in the frequency domain, the developed tools rely on the dielectric response being linear with excitation voltage magnitude. This paper details work done in an initial investigation into the measurement of the non-linear dielectric response in oil-paper insulated power transformers using frequency domain measurements. Measurements were performed on two transformers, with non-linear response currents measured at the higher excitation voltage levels. It was found that non-linearity in the dielectric response will result in the generation of harmonics currents particularly 3rd and 5th harmonics. There will also be effects on the fundamental current magnitude due to the higher order dielectric susceptibilities. The higher order susceptibilities will thus be evident in the measured fundamental complex admittance of the dielectric.

In this paper, a wideband flexible antenna using paper as substrate is proposed. The simulated antenna bandwidth covers 270–1000 MHz. Simulation shows that the proposed antenna has stable bandwidth with changing dielectric constant and thickness of the substrate. The antenna keeps table bandwidth when twisted around of cylindra. The simulated antenna bandwith is 270–1000 MHz.

The main function of the transformer bushing is to support and connect the transformer lead-out line. In recent years, bushing faults have occurred frequently but there is not good online monitoring method for bushing. The ultra-high frequency (UHF) detection method has the characteristics of strong anti-interference ability and no influence on equipment operation while achieving non-contact measurement. This paper has studied the propagation characteristics of two different UHF electromagnetic waves generated by partial discharge inside the oil impregnated paper (OIP) by simulations of finite element analysis. The attenuation of TEM mode is small, and higher modes below its cutoff frequency is exponentially attenuated. The electromagnetic wave leakage path generated by partial discharge inside the bushing is mainly in the OIP and the oil channels on both sides and the variation trend of the Poynting vector is the same. The externally received field strength spectrum shows that the signal strength is relatively high in the range of 1-2 GHz, considering the equipment used in the actual situation, such as amplifiers it provides a reference for subsequent experiments.

A reconfigurable microstrip antenna with a dual-polarization beam-scanning feature is proposed in this paper. The proposed antenna is based on microstrip Yagi-Uda antenna comprised of a driven square patch and four parasitic square patches. Two different feed ports are utilized to separately excite two orthogonal modes for dual-polarization operation. The capability of beam-scanning is realized by loading a narrow loop slot and four varactors within each parasitic patch. By tuning the capacitance value of the varactors, the parasitic patch can act as a director or a reflector for the driven patch. Simulation results demonstrate that the beam can be scanned in 2D plane. The simulated cross-polarization discriminations are higher than 20 dB in all seven states presented in this paper. The proposed antenna is in fabrication and experimental results will be provided in the final submission.

Ultrasonic signal will be generated when a partial discharge occurs in the oil/paper insulation system, thereby enabling partial discharge detection of the transformer. In order to explore the ultrasonic characteristics of partial discharge of oil/paper insulation system, a partial discharge detection platform based on ultrasonic method is developed in this paper. Based on the platform, the ultrasonic signal filtering method is analyzed, and the typical defect model of oil/paper insulation is built and tested in the laboratory, obtaining partial discharge signal of typical defective. Finally, the accuracy of the waveform acquired in this paper and its effectiveness in fault diagnosis are verified by the application on the actual transformer.

This paper presents a brief review on functionality-improved patch antennas with loading shorting pins that are recently proposed by the authors' group. Firstly, shorting pins can increase (reduce) the feeding current (voltage) of a patch antenna, so the edge-fed impedance can be reduced. Meanwhile, the cross-polarization can be kept in low level when the shorting pins are symmetrically loaded. Secondly, the shunt inductive effect of shorting pins significantly increases the resonant frequency of fundamental mode, resulting in enlarged radiating area, and so enhanced gain can be obtained. Thirdly, by properly adjusting the electrical size of patch through loading of shorting pins, the two orthogonal far-field components will have close beamwidth and beam shape, and then wide axial-ratio beamwidth (ARBW) can be realized.

Ultrasonic signals can be utilized as a viable communication method to transmit information through gas, liquid, and solid channels or a mixed media consisting of a solid interfaced with liquid and/or gas. Underwater communication channels using sound waves cause many challenges, often unforeseen, due to absorption, scattering, refractions, reverberations, multipaths, doppler shifts, temperature, salinity, and acoustic scintillation. Ultrasonic communication through the air is less prone to the environmental challenges that are often encountered in the underwater communications. Ultrasonic communication in solid channels is also adversely affected by absorption, scattering, refractions, reverberations, beam skewing, dispersion, mode conversation, multipaths, and above all these challenges are compounded by the geometrical structure of solids and type of ultrasonic waves. With solid structures many different ultrasonic wave types can be generated including Longitudinal (Compressional), Shear (Transverse), Surface-Rayleigh, Plate-Lamb (Symmetrical or Extensional Mode and Asymmetric or Flexural Mode), Plate-Love, and Stoneley (Leaky Rayleigh). The type of waves is governed by the frequency and angle of the incident waves on a solid structure where the quality of the signal for communication is limited by the composition and geometrical shape of the solids. For this study we have developed a testbed platform using the ZYNQ SoC (System-on-Chip) FPGA by Xilinx which offers reconfigurability and high-performance computational capability, high speed signal converters, power amplifiers for excitation of transducers, low noise receiving amplifiers and high frequency ultrasonic transducers for transmitting and receiving information. Theoretically, ASK (amplitude shift keying) or any form of digital modulation can be realized with the system using the concept of the software-defined ultrasonic communications (SDUC). In practice, the received signal is very complex, primarily caused by dispersion, reverberation, and multipath effects. We have examined SDUC system using AM (Amplitude Modulation), OOK (on and off keying), BPSK (Binary Phase Shift Keying), QPSK (quadrature phase shift keying), and OFDM (orthogonal frequency-division multiplexing). This system is tested using differently structured solid channels (such as blocks, plates and pipes); and bitrates and bit rate errors are compared using 2.5 MHz ultrasonic transducers. Furthermore, this paper presents an overview of using EMAT for ultrasonic communications in metal channels.

Stimulated Electromagnetic Emission (SEE) is secondary radiation produced during experiments where high power high frequency (HF) radio waves interact with the ionosphere. SEE has been a vibrant area of investigation for the past three decades and SEE has been developed into an important remote sensing tool for the ionosphere with substantial potential for aeronomy studies. Past experiments primarily considered emissions within a bandwidth of 100 kHz of the pump (transmit) frequency, so-called wideband SEE (WSEE), but more recent work has concentrated on SEE within 1kHz of the pump frequency, so-called narrowband SEE (NSEE), as well as the pump frequency harmonic. A brief review of the recent experimental observations of NSEE are presented as well as some basic concepts of the nonlinear wave-wave processes that produce NSEE. Some new potential applications are discussed as well.

In this paper, a frequency selective paper with X-band reflection characteristics is designed for the crack detection of concrete building structures and the change of resonant frequency characteristics according to cracks are investigated. Based on the crossed dipole unit cell known to have narrow-band reflection characteristics, a frequency selective paper operating in the X-band was designed and the frequency characteristics of the frequency selective paper unit structure including cracks were observed. As the crack width increased by 0.2mm, the resonance frequency tended to move to the higher band by about 90MHz. It was confirmed through simulation that the existence and the width of the crack can be predicted. Designed frequency selective paper was fabricated and frequency reflection characteristics were measured for six types of cracks. From the measurement result, the existence of cracks and the shape of cracks can be predicted according to the polarization of the incident angle.

Typically, electrical breakdown and electrical aging of power transformer are initiated by partial discharge. There are plenty of factors that influence partial discharge, one significant factor is harmonics issue. In this paper, harmonics impact on partial discharge behavior under HVAC is studied, which uses needle-plane as the electrode configuration because of its widely existing within power transformer. Oil-paper insulation is the test object in this research to observe for PD activity such as PD inception voltage and phase-resolve PD. This research aim is not only focuses on several specific impacts of harmonic source on partial discharge, but also wants to demonstrate the significance of harmonics awareness. Nowadays, there are so many high voltage equipment that are working under harmonic component, it is risky enough to face against an unexpected danger under working operation. The experiment of this research focuses on HVAC superimposed with various composition harmonic component, which means that the order and percent THD (Total Harmonic Distortion) are discussed. The selected THD is designed to be able to observe for the differences clearly. Harmonic order from 3rd, 5th, 7th, 9th and 11th is applied, which is the main component that is generated by the power electronics. Phase shift of injecting harmonic component is designed up to 270-degree angle. Meanwhile, in order to get the partial discharge characteristics under different magnitude of harmonics, the percent of each harmonic order is also changed, which can be calculated to find for THD.

In this paper, two monopole antenna structures called by the authors as “Hello 1” and “Hello 2” have been designed based on screen printing technology on the flexible paper substrate of 210-um thickness to cover very wide frequency range focusing on two WLAN bands. The designed antennas have the dimensions of 42 × 28 mm2 with the return loss of over 20 dB for “Hello 1”, and over 25 dB for “Hello 2” at both frequencies 2.45 GHz and 5.5 GHz. Both antennas have nearly omni-directional radiation patterns at 2.45 GHz while more directive at 5.5 GHz. The total efficiency of the antennas is of 67.3% and 68.9% at 2.45GHz, 65% and 67% at 5.5GHz for “Hello 1” and “Hello 2”, respectively. Two prototypes of each design have been realized and measured to compare with the simulation. As a result, acceptable agreement has been obtained.

Partial Discharge (PD) characteristics of typical defects in oil-paper insulation under AC, DC and AC-DC combined voltages have been studied extensively. However, there is still limited material available for the pattern recognition of partial discharge under actual stress withstood by valve side windings in converter transformers. In this paper, the PD of needle-plane defect is measured under actual stress in converter transformers. The stress is DC voltage superimposed harmonics, which has been analyzed in PSCAD at first. Then DC voltage superimposed both single harmonic and multiple harmonics, including simulated actual stress and approximate square waveform, have been applied on electrode. PD parameters and patterns are acquired by detector using pulse current method. The test results indicate that the inception voltage and pulse repetition rate of PD have no direct relationship with harmonic order due to the accumulation of space charges injected by DC voltage. PD amplitude shows a growing trend and phase distributions of PD expand with the increase of harmonic order. PD patterns are also closely related to the waveform of applied voltage. PD amplitude rises with the increase of voltage change rate, and the majority of PD pulses occur in the phase range which has a higher voltage change rate. Experimental results show that harmonic order exerts a great effect on PD characteristics of needle-plane defect under DC superimposed harmonic waveforms. The findings of the current study are useful in further research on the pattern recognition of PD and diagnose in converter transformers.

This paper presents a novel technique for monitoring microwave power deposition based on thermoacoustic imaging. It can be applied in breast cancer hyperthermia using a microwave antenna array to focus microwave energy at breast tumor. Compressive thermoacoustic imaging technique is applied to expedite the imaging and monitoring process. Simulation results using a realistic breast phantom are provided.

This paper presents results from the (to our knowledge) first dynamic double-directionally resolved measurement campaign at mm-wave frequencies for an outdoor microcellular scenario. The measurements are performed with USC's real- time channel sounder equipped with phased array antennas that can steer beams electrically in microseconds, allowing directional measurements in dynamic environments. Exploiting the phase coherency of the setup, the multi-path components can be tracked over time to investigate the temporal dependencies of the channel characteristics. We present results for time-varying path-loss, delay spread, mean angles and angular spreads observed at the transmitter (TX) and receiver (RX) in the presence of moving vehicles and pedestrians. Additionally, we investigate excess losses observed due to blockage by vehicles and compare the cases when TX and RX are using fixed beams or when they are capable of adjusting beam directions dynamically.

There are plenty of factors that influence partial discharge (PD), one significant factor is the harmonic issue. The minor insulation of valve side windings within converter transformers withstands complex electrical stress, which is fundamental AC voltage superimposed with harmonics. In this paper, partial discharge tests were performed on needle-plane electrode. Single harmonics with 3rd, 5th, 7th and 9th order, and fundamental AC voltage superimposed harmonics with different harmonic frequency and component, were applied on the defect model. Statistical phase distributions and typical parameters of PDs were acquired by detector using pulse current method. Test results showed that harmonic has a significant impact on PD phenomenon. PD inception voltage has no direct relationship with harmonic order and component. Pulse repetition rate per cycle decreases while that of per second increases with the increase of single harmonic order. In addition, PD magnitude grows bigger and PD phase core moves left toward 0° and 180°. As harmonic order and its component increase, both maximum and mean PD amplitude, as well as pulse repetition rate increase. The applied voltage waveform and its change rate dU/dt both indicate the PD distribution in the case of phase-resolved measurements. These results will assist the understanding of partial discharge behaviors under complex voltage waveforms within converter transformers.

This paper presents an analysis for the electromagnetic interference (EMI) related common-mode (CM) noise in differential high-speed data links with different signal modulation schemes, e.g. non-return-to-zero (NRZ) and 4-level pulse amplitude modulation (PAM-4). The CM noises, introduced by the mismatch of data rising and falling edges in both cases, exhibit the similar positive correlation with signal swing, but due to the complexity of PAM-4 signal, the amplitude distortion leads to different CM noise behavior.

Method for increasing thermometer response speed by extrapolating temperature data in a transient measurement mode with electric active heating of the sensitive element has been proposed.

Increasing frequency is favorable to boost the efficiency of transporting electricity, but it leads to critical insulation challenge inside transformer. To explore the deterioration characteristics of oil-paper insulation system under high-frequency voltage, a column-plate model is adopted to simulate the surface discharge defect and an experimental platform for partial discharge test is established. Tests under high-frequencies of 10 kHz, 20 kHz and 30 kHz and power frequency of 50 Hz are carried out when constant voltages are applied. Video camera is taken to observe the column-plate model, and Rogowski coil is used to collect the partial discharge (PD) signal. Then characteristics of partial discharge signals and dissolved gas under different frequencies are compared and analyzed. Conclusions are drawn that the content of gas produced from oil-paper insulation system under high frequencies are much more than that of 50 Hz, while the content of key gases especially H2 are boosted. As for the PD amplitude-phase diagram, the PD signals center on the moment when the polarity of voltage changes. Besides, the discharge phase range under high frequencies are wider than that under power frequency. Finally, the average amplitude and number of partial discharge (PD) present a peak value around 20 kHz in a single period.

A paper-based electromechanical system (PB-EMS) driven by means of the Lorentz force excitation method is introduced in this work. Such a system consists of a paper-based cantilever beam that is fabricated using conventional printer paper, printable electronics, and standard cutting tools. The results show the feasibility to develop PB-EMS using the Lorentz force actuation principle. In addition, the influence of the driven current on the dynamic response of the PB-EMS is analyzed. A softening effect is identified when increasing the magnitude of the excitation current. This softening effect is evaluated using a lumped model. The spring constant as a function of the excitation current exhibits a linear relationship. Moreover, the frequency response of the system is experimentally studied by using image processing. The maximum variation of the resonance frequency is measured as 16.5% of the nominal frequency when using an excitation current of 300 mA. Thus, it is expected that the Lorentz force excitation can be applied to both drive and tune the behavior of the proposed PB-EMS.

A dual band antenna is inkjet-printed and then folded as part of a paper unmanned aerial vehicle (UAV). The patterns of the antenna are reproduced on a standard photo paper substrate using an off the shelf inkjet printer. Readily available cartridges with nanoparticle silver conductive ink are employed. A single-layer planar antenna is fed by coplanar waveguide (CPW). The geometry of the radiating element consists of a semicircle with a centered square slot. In order to examine the effect of bending on performance, the antenna is tested unfolded and then folded when integrated onto the airplane. Two configurations of the folded antenna on the plane are analyzed. The aim is to investigate the feasibility of fabricating foldable antennas for paper airplanes using low-cost inkjet printing techniques. The antenna operates at the existing 2.4 GHz and 5.2 GHz WLAN bands. Finite different time domain simulations compare well with measurement.

The authors have evaluated the possibility of deterioration diagnosis of Oil-filled (OF) cable systems by PD measurement so far. In our previous studies, we confirmed continuous occurrence of PDs even under the design electric field of 275 kV OF cables. Also we confirmed the progress of intermittent occurrence of PDs to continuous one by repeated superimpositions of lightning impulse voltage corresponding to switching surge. However, correlation between PD characteristics and internal conditions of the oil gap defect was not obtained. Therefore, in this study, we experimentally investigated the effects of the switching impulse voltage superimposition that can occur in practical operation of 275 OF cable systems on PD characteristics and we observed the conditions inside the oil gap defect by a CCD camera.

The Frequency Domain spectroscopy is a nondestructive electric diagnosis. It's very suitable for transformer oil-paper insulation condition of field detection, the actual development of the internal oil paper insulation status can be reflected accurately, especially in the low frequency and the ultra-low frequency. Because of the frequency domain dielectric spectroscopy at low frequency measurement requires a very long time, and it's vulnerable to environment. In order to ensure the accuracy of the insulating condition, the FDS needs to be better applied to the nondestructive quantitative assessment in transformer oil paper insulation system. The aged ample of oil-paper insulation is first prepared, and then this sample tested at thermostat 30°C in the FDS. To obtain the insulation information contained in dielectric loss factor (tanδ) as more as possible, the integral of dielectric loss factors (S tanδ ) in the characteristics frequency ranges are introduced as characteristics parameters for assessing insulation condition. Due to the FDS requires a very long time in characteristics frequency ranges, and it's vulnerable to environmental factors, In this paper, the method of predicting S tanδ in low frequency FDS based on the parameter identification of the X-Y equivalent circuit is put forward. then, the measured data and calculated data are compared, in order to confirm the availability of this method.

The onset of Partial Discharge (PD) activity within an insulation system is often an important signature of degradation. Changes in the PD pattern aid assessment of the insulation degradation level. High voltage transients such as lightning and switching impulses are inevitable phenomena in power systems. They can impose electrical stresses on the insulation system of power components such as power transformers and their bushings which may lead to their failure. After the arrival of a transient the AC PD pattern may change, in a way that is influenced by the type of PD source. In this paper, the effect of HV impulses on the change of surface and cavity discharges of oil-impregnated paper has been investigated. With resemblance to the real situation, insulation samples have been subjected to an impulse voltage superimposed on the AC voltage. The behavior of PDs before and after the impulse for different defects and moisture content levels in oil-impregnated paper has been studied. The results show a distinctive behavior of PD due to the impulse for each defect and insulation condition, either by change in the PD rate and magnitude or by causing PD inception or extinction. Recording the voltage signals and associated PD measurements during and after the incident of high voltage transients can be used for assessing the insulation condition of power transformers and their bushings and interpretation of the recorded signals can be used for online diagnostics.

This research presents a passive UHF RFID tag antenna design. The compact size antenna can be achieved by using modified split ring resonator (SRR). The structure contains a square SRR connected with a circular SRR on the radiating part to increase the antenna length. The proposed tag antenna is a paper-based which uses the paper as the substrate. It is a low-cost, flexible and suitable for mass production. The proposed tag antenna size is 38 mm × 38 mm and the |S11| of better than -10 dB that can cover the frequency range of 920–925 MHz. The maximum read range is 3.20 m. The modified SRR can decrease the antenna size.

This paper presents an advanced method for condition monitoring of oil-paper insulation of the transformer using accelerated dielectric response measurement. In frequency domain spectroscopy, dielectric response current is measured for a period of two cycles over a wide range of frequencies. Such measurements on real life transformers take long time in practice especially in the lower frequency range which is practically problematic. Considering the above-said fact, a new technique has been developed in the present work that can reduce the measurement time significantly. Instead of using the excitation for two cycles, quarter cycle of the excitation is applied on insulation under test. The method is verified on three test samples having different preset moisture contents. The dielectric dissipation factors of the test samples computed from the proposed method, are then compared with the corresponding values calculated for two cycles of the applied excitation. The results show negligible differences in the values of dissipation factors of the test samples obtained with the applied excitation for two cycles with that of quarter cycle.

In this paper, channel characterization of Rayleigh fading channel at 28 GHz band is investigated. FMCW (Frequency-modulated continuous wave) radar is used as a channel sounder. The measurement is carried out inside the reverberation chamber with two different received antennas; one has 72.29° and the other has 2.40o of 3 dB beamwidth on azimuth plane. Different cases has examined with different arrangements of microwave absorbers. The obtained scattered plots and envelope distributions of Rayleigh fading channel has shown and discussed.

The radio propagation characteristics of 28 GHz were investigated by using a FMCW (Frequency Modulated Continuous Wave) radar system in a reverberation chamber for the small-fading of Rayleigh and Rician conditions.

Based on the platform for testing development characteristics of partial discharge in laboratory, typical surface discharge model was built up at first. Constant voltage testing on the model was performed to research the development process of surface discharge. The variation of total partial discharge energy per unit of time (W total ) was analyzed and the results show that the surface discharge development process is divided into 5 stages. Three-dimensional spectra and grayscale images in different discharge stages were also built in order to make the process more comprehensive and visual. As traditional moment parameter has its shortages, the wavelet theory was introduced to extract the moment characteristics of partial discharge grayscale images. According to the wavelet moment features extracted at different discharge times, under the condition of no prior knowledge, the Euclidean distance clustering method was used to divide the whole surface discharge process.

Oil-impregnated cellulose material, such as Kraft paper, is an essential part of the insulation system of a power transformer. The mechanical strength of Kraft paper directly impacts the safety of operating a power transformer. Obtaining structural subsurface images of the transformer paper would offer significantly more information than from current optical methods. This subsurface imaging could allow accurate estimation of the operational age of the transformer insulation, beyond only classifying it as belonging to a broad age group. In this work, optical coherence tomography (OCT), a subsurface imaging technique, is used to acquire subsurface structural images of the thermally-aged Kraft paper samples. Statistical texture analysis is applied to these OCT images to convert each image into a spatial grayscale level dependence matrix (SGLDM), from which three Haralick texture features are calculated. These three features are used to estimate the ageing time of thermally-aged Kraft paper.

This paper presents a precise sampling microstructure formed as a paper strip. We have been developing dialysis system that can be implanted into a human body as an artificial kidney. For the safe use of our artificial kidney, the patients' urine needs to be constantly monitored to detect the abnormal value of ion concentration essential for human life. We are conceiving the monitoring system based on sampling by a paper strip. In this study, we fabricated the strip consisting of slanted and interlocked micropillars for the sampling, known as synthetic microfluidic paper. The paper-like substrate can be fabricated with a well-controlled geometry and subsequently enables precise sampling. Through the conducted experiments, it was shown that synthetic microfluidic paper had better mechanical properties, showed more precision in sampling than paper filter as well as corresponding liquid holding capability to the paper filter. Our proposed paper-based sampling system is expected to lead to the development of minimally invasive ion monitoring system with quantitative sampling strip.

This letter proposes a very simple solution to reduce the propagation loss between two antennas/sensors on body at 2.45 GHz by utilizing a flexible conductive strip line (CSL). The performance of the CSL is comparable to that of the free-access transmission line in the work by Tran et al. in some certain cases. The transmission improvement by the CSL is verified by measurement results on a perfect electrical conductor plane, on a phantom, and on a real body more than 20 dB for non-line-of-sight scenarios. Dimension parameters of the CSL are optimized so that the highest improvement by the CSL can be achieved and it is easy to be integrated into clothes. Moreover, the specific absorption rate is satisfied when the CSL is deployed near body.