Hilbert Fractal Antenna Research Articles

Hilbert Fractal Antenna for Abnormal Discharge Detection of Transmission Equipment

The safe and stable operation of the power system can ensure people’s basic electricity needs. It also plays an important role in energy security and economic development and can contribute to environmental protection and energy conservation. If there are problems in the power system, it will not only affect people’s normal life and work but also lead to power loss or waste, thereby exacerbating the impact on the environment. With the long-term operation of transmission equipment, insulation devices are aging, leading to frequent abnormal discharges and affecting the safety and stability of the power system. Therefore, timely detection and troubleshooting are necessary. When abnormal discharge occurs in transmission equipment, it will radiate radio frequency (RF) electromagnetic waves, which are mainly concentrated between 200 MHz and 300 MHz. RF antennas that can capture signals in this frequency band can be used for detection to determine whether abnormal discharge has occurred. This article uses the Hilbert fractal antenna as the research object to analyze the impact of different orders on antenna performance and optimizes the different feeding point positions of the antenna. Finally, the antenna structure for detecting abnormal discharge is obtained. By making an actual antenna and conducting experimental analysis, the discharge detection function of the designed antenna is verified.

A Compact High Isolation Four Elements MIMO Antenna System for 5G Mobile Devices

A Compact high isolation Multi Input Multi Output Antenna system working on 3.5 GHz (3400 - 3600) MHz is presented for the 5G mobile terminals. Four-antenna elements are employed to construct the proposed MIMO antenna system. These antennas are located over two slim side-edges frame of a mobile device to meet the present trend requirements of slim and full-screen smartphone devices. A modified Hilbert fractal monopole antenna and an I-shaped feeding line construct the antenna element’s front part, while an L-shaped shorted to the system’s ground plane are used to the antenna element’s back part. The overall monopole antenna element’s size printed on the mobile frame’s side edge is (9.72 mm × 5.99 mm) so the desirable antenna miniaturization is achieved. Based on the spatial diversity and self-isolated techniques, high isolation (better than 16.3 dB) is attained by the proposed four-element MIMO antenna system. To assess the proposed antenna element’s performance, the scattering parameters, antenna gains, antenna efficiencies, and radiation pattern characteristics have been evaluated. Besides, the MEGs and ECCs are investigated to appreciate the proposed system’s MIMO performance. Desired antenna and MIMO performances are achieved by the proposed four-element MIMO antenna system so it can be a good candidate for the future 5G mobile handsets.

Design and Analysis of a PDLC-Based Reconfigurable Hilbert Fractal Antenna for Large and Fine THz Frequency Tuning.

The proposed reconfigurable radiating antenna design is based on the integration of a reconfigurable fractal antenna and electro-optic substrate material. This antenna can be adjusted to achieve either re-configurability or tunability in the desired frequency range for wireless systems. The electromagnetic characteristics of the fractal antenna are manipulated at both the level of fractal geometry, electrical length and dielectric substrate. The designed antenna features multiband responses, in which the geometry and length change create a large frequency shift and the dielectric change using polymer dispersed liquid crystal (PDLC) creates fine and/or continuous tuning. The far field and scattering properties of the antenna are analyzed using the Computer Simulation Technology (CST) Microwave Studio Suite. The proposed approach has successfully demonstrated reconfigurable switching for up to four frequency bands between 0.2 and 0.6 THz. The dielectric constant change in the PDLC substrate shows fine and continuous frequency tuning with an 8% maximum frequency shift when operating around 0.54 THz and a high directivity of 7.35 dBi at 0.54 THz and 8.43 dBi at 0.504 THz. The antenna can also realize a peak gain of 4.29 dBi at 0.504 THz in the extraordinary polarization state of PDLC. The designed antenna can be readily integrated in the current communication devices, such as satellites, smart phones, laptops, and other portable electronic devices, due to its compact geometry and IC compatible design. In satellite applications, the proposed antenna can play a significant role in terms of security. The antenna could be extremely useful for satellites that want to keep their information secret; by constantly switching their operating frequency, spy satellites can evade detection and data collection from enemy ears.

A Compact Self-Isolated MIMO Antenna System for 5G Mobile Terminals

A compact self-isolated Multi Input Multi Output (MIMO) antenna array is presented for 5G mobile phone devices. The proposed antenna system is operating at the 3.5 GHz band (3400–3600 MHz) and consists of eight antenna elements placed along two side edges of a mobile device, which meets the current trend requirements of full-screen smartphone devices. Each antenna element is divided into two parts, a front part and back part. The front part consists of an I-shaped feeding line and a modified Hilbert fractal monopole antenna, whereas the back part is an L-shaped element shorted to the system ground by a 0.5 mm short stub. A desirable compactness can be obtained by utilizing the Hilbert space-filling property where the antenna element’s overall planar size printed on the side-edge frame is just (9.57 mm × 5.99 mm). The proposed MIMO antenna system has been simulated, analyzed, fabricated and tested. Based on the self-isolated property, good isolation (better than 15 dB) is attained without employing additional decoupling elements and/or isolation techniques, which increases system complexity and reduces the antenna efficiency. The scattering parameters, antenna efficiencies, antenna gains, and antenna radiation characteristics are investigated to assess the proposed antenna performance. For evaluating the proposed antenna array system performance, the Envelope Correlation Coefficients (ECCs), Mean Effective Gains (MEGs) and channel capacity are calculated. Desirable antenna and MIMO performances are evaluated to confirm the suitability of the proposed MIMO antenna system for 5G mobile terminals.

Partial discharge type detection and identification based on its sources

Partial discharge (PD) is a symptom of initial damage to high voltage equipment insulators which if left for a long period will cause total damage to high voltage equipment. This study aims to detect and identify the type of PD based on the source of its discharge so that it can be useful in terms of monitoring and maintenance of high voltage equipment. In this research, the Hilbert fractal antenna sensor is used in the detection process of surface, cavity, and corona PD with different input voltage variables that successfully produce a total of 600 PD signal data on the oscilloscope. To reduce noise on the PD signal, the denoising process is done by utilizing the sym4 wavelet feature found in the MATLAB software. The denoising process generates new data so that the research data becomes 600 original PD signal data and 600 denoising PD signal data. With a statistical approach, all PD signal data is extracted successfully into the mean, skewness, kurtosis, and standard deviation parameters which are useful as input for the PD type identification process. From each of the PD signal statistical data, 450 data are used in the training data process and 150 data are used in the data testing process. The PD type identification process is performed using a back propagation neural network with a mean square error (MSE) level of 0.01. The identification results show that back propagation neural networks are able to identify PD types based on statistical input accurately. In addition, the denoising process also affects the accuracy of the identification results of the PD type that is 95.33% for the original discharge signal to 97.33% for the denoising signal.

Design and Optimization of Detection Antenna for Corona Discharge in High-voltage Transmission Lines

Corona discharge on high-voltage transmission lines is a common phenomenon in power systems. It results from poor contact between insulators and lines, and broken strands on transmission lines. Long-term corona discharges may lead to more serious power grids accidents. Hence, it is of great importance to effectively detect the occurrence of corona discharge. The Hilbert Fractal Antenna is a wide-band, small-sized antenna which can be carried by the unmanned aerial vehicle for close-range detection and accurately position fault points of corona discharge. In this paper, the finite element method is used to study the 5th order Hilbert fractal antenna. The research focuses on the different feeding positions of the antenna. By studying the different feeding positions of the antenna, we determine a miniaturized antenna which can be used for corona discharge detection of high-voltage transmission lines.

Design of electrically small Hilbert fractal NFRP magnetic monopole antennas

ABSTRACTElectrically small, Hilbert fractal, near-field resonant parasitic (NFRP) antennas are reported and investigated in this paper. This type of electrically small antennas (ESAs) consists of Hilbert fractal curves as the NFRP resonators and small vertical monopoles as the driven elements. By offsetting the driven monopole off the centre position, good impedance matching can be easily realized. The current distributions on the fractal NFRP elements and the driven monopoles manifest that strong electric coupling could excite loop-mode currents along the Hilbert fractal NFRP structures, and thereby horizontal magnetic monopole patterns with broadside radiation property are realized. The results show that the 2nd-step evolution Hilbert fractal NFRP antenna witnesses an electrically size reduction of 25% compared to ka = 0.9622 of the square capacitively loaded loop (CLL) NFRP antenna, while maintaining its original broadside radiation. It is also demonstrated that there is a performance trade-off, i.e. higher fractal iteration orders leading to smaller resonant frequencies, narrower bandwidth and lower radiation efficiencies.

Electromagnetic Radiation Characteristics of Series DC Arc Fault and Its Determining Factors

A dc arc fault can be a serious threat to the safe operation of a low-voltage dc system. Typically, a fair amount of electromagnetic radiation (EMR) accompanies the arcing process. To investigate the characteristics of EMR of the series dc arc fault, a fourth-order Hilbert fractal antenna is used to detect the EMR signals generated by the dc arc. The factors influencing the characteristics of EMR including electrode material, diameter, current, and pressure are considered. The amplitudes of the EMR pulses at the arc initiation moment are measured, and fast Fourier transform is used to analyze the characteristics of the frequency spectrums. The test results indicate that the amplitudes of the EMR pulses generated by stainless steel electrodes are higher than those generated by brass, copper, and aluminum electrodes. Furthermore, the trends of the amplitudes of the EMR pulses with increasing current are different for electrodes with different diameters. Finally, it is observed that the influence of the pressure is different for different electrode materials. The characteristic frequency band of the EMR pulses of the dc arcs generated under various test conditions is in a certain range (36–41 MHz), which can be used as a detecting characteristic parameter for the series dc arc.

Antena fraktalna Hilberta do detekcji i monitoringu wyładowań niezupełnych w transformatorach energetycznych

This article describes the design of UHF Hilbert curve fractal antenna (HCFA) specially adapted for the partial discharge monitoring system. The authors present the mathematical apparatus for calculating resonant frequencies of Hilbert fractal antenna and results of a computer simulation of the developed prototype. In the design process, the antenna’s working environment (mineral oil) and the mechanical construction of the transformer inspection window were taken into consideration as well. The article also shows the results of laboratory tests carried out in the transformer tank model with different type of partial discharge sources. Both simulations and partial discharge measurements showed that the HCFA, due to such properties as: multi-resonance, small size, low fabrication cost and high sensitivity, is an interesting alternative to other UHF probes installed in transformer inspection window

From narrow-band to ultra-wide-band microwave sensors in direct skin contact for breast cancer detection

In this paper, the design and test of different microwave antennas and sensors for breast cancer detection are presented. The sensors are designed and optimized to be used in direct skin contact, and for this purpose a specific breast phantom model is proposed. First, a miniaturized microstrip back-cavity Hilbert fractal antenna, operating in the ISM band (2.4–2.5 GHz), was designed. Then, this antenna was used to investigate the possibility of detecting the presence of breast tumors based on a narrowband frequency method that monitors the shift of the antenna frequency response. The antenna prototype was fabricated and tested in real in vivo measurement conditions on two different patients diagnosed with breast cancer. Measurement results have led after a comparison with the retro-simulation results of the structure to a more realistic breast model and to draw the limitations of this narrowband frequency method. As a time domain study seems to be more relevant, an UWB monopole antenna of dimensions 3 cm × 3 cm, to be used in direct contact with the breast model was designed. This antenna was optimized to both enhance the antenna/human body matching and to maximize the transfer of energy into the breast phantom by using a cavity, increasing by this way the detection potential. In order to improve the sensor’s directivity and enhance the electromagnetic field level inside the breast, a balanced antipodal Vivaldi antenna was also designed and optimized for a direct breast contact to operate in the 3.1–10.6 GHz band. A mono static and a bi static study in the time domain are finally proposed to investigate the presence of the tumor.

Design of Hilbert Fractal Antenna for Partial Discharge Classification in Oil-Paper Insulated System

This paper presents the design of a wideband Hilbert fractal antenna for the purpose of detecting and classifying different common partial discharge (PD) types in an oil-paper insulated system. Three common types of PDs are considered for the multi-class classification problem, namely, PD from a sharp point to ground plane, surface discharge, and PD from a void in the insulation. The different PD types showed variation in the detected frequency contents. The collected samples were processed using pattern recognition techniques to identify their corresponding PD types. A recognition rate of 95% was achieved when K-nearest neighbors was used as the classifier.

Comparison of different fourth order Hilbert fractal antennas for partial discharge measurement

Three Hilbert fractal antenna designs are proposed in this work to capture and classify common types of partial discharge (PD) in an oil insulated system. Each antenna design shows unique characteristics in terms of resonant frequencies, inception voltage, classification capabilities and noise performance. Three types of PD signals are artificially generated; namely, corona, surface and sharp PD. The captured signals from each antenna design are analyzed then fed to a trained artificial neural network for classification. A recognition rate of 97% is achieved when classifying the different types of PD using one of the proposed antennas. Moreover, the SNR of signals captured from each antenna design are analyzed to determine the best antenna for PD detection under intense noisy environments.

UHF Moore Fractal Antennas for Online GIS PD Detection

A sensor for a Moore fractal antenna was designed to detect partial discharge (PD) in gas-insulated substations. This worked at an ultrahigh frequency. First, the multifrequency characteristics of this antenna were analyzed and ANSYS HFSS was used to simulate the Moore fractal antenna and the Hilbert fractal antenna for comparison. The results show that the Moore fractal antenna had good directivity and omnidirectional radiation features. We then developed physical models for them according to the simulation results. The two antennas were tested using a vector network analyzer. The results show that the Moore fractal antenna had more frequency bands than the Hilbert fractal antenna. The PD was tested in the laboratory and detected by the Moore fractal antenna and the Hilbert fractal antenna. A comparison of the measured results showed that the proposed antenna was promising for online PD detection applications.

Miniaturized stacked implant antenna design at ISM band with biocompatible characteristics

Purpose – A vertically stacked, three layer hybrid Hilbert fractal geometry and serpentine radiator-based patch antenna is proposed and characterized for medical implant applications at the Industrial, Scientific and Medical band (2.4-2.48 GHz). Antenna parameters are optimised to achieve miniaturized, biocompatible and stable transmission characteristics. The paper aims to discuss these issues. Design/methodology/approach – Human tissue effects on the antenna electrical characteristics were simulated with a three-layer (skin, fat and muscle) human tissue model with the dimensions of 180×70×60 mm3 (width×height×thickness mm3). Different stacked substrates are utilized for the satisfactory characteristics. Two identical radiating patches are printed on Roger 3,010 (ε r=10.2) and Alumina (ε r=9.4) substrate materials, respectively. In addition, various superstrate materials are considered and simulated to prevent short circuit the antenna while having a direct contact with the metallization, and achieve biocompatibility. Finally, superstrate material of Zirconia (ε r=29) is used to achieve biocompatibility and long-life. A finite element method is used to simulate the proposed hybrid model with commercially available Ansoft HFSS software. Findings – The antenna is miniaturized, having dimensions of 10×8.4×2 mm3 (width×height×thickness mm3). The resonance frequency of the antenna is 2.4 GHz with a bandwidth of 100 MHz at return loss (S11) of better than −10 dB characteristics. Overall, the proposed antenna have 50 Ω impedance matching, −21 dB far field antenna gain, single-plane omni-directional radiation pattern properties and incident power of 5.3 mW to adhere Specific Absorption Rate regulation limit. Originality/value – Vertically stacked three layer hybrid design have miniaturized characteristics, wide bandwidth, biocompatible, and stable characteristics in three layer human tissue model make this antenna suitable for implant biomedical monitor systems. The advanced simulation analysis of the proposed design constitutes the main contribution of the paper.

Hilbert fractal antenna for UHF detection of partial discharges in transformers

Electromagnetic waves generated due to partial discharge (PD) can be captured by ultra-high-frequency (UHF) antennas. The size and frequency band of an UHF antenna for PD online monitoring are critical factors for practical installation inside a transformer. This paper presents a compact multi-band UHF Hilbert fractal antenna with wide frequency band and suitable size for easy installation. Design criteria of a PD antenna were proposed and the Hilbert fractal antenna was selected as an appropriate candidate for PD detection. Principle of Hilbert fractal antenna was discussed and a fourth order Hilbert fractal antenna was optimized for detecting PD signals. Actual PD experiments have been carried out for two typically artificial insulation defect models while the antenna was used for the PD measurement. More simulation studies and actual PD experiments have been done to further examine the effects of electromagnetic wave refraction and reflection by transformer components. The results show that the proposed UHF antenna is qualified for PD online monitoring.

UHF Stacked Hilbert Antenna Array for Partial Discharge Detection

This communication proposed an ultra-high frequency (UHF) stacked Hilbert antenna array to broaden bandwidth and increase gain of Hilbert fractal antenna. Two parasitic curves were added to improve the third order Hilbert curve and stacked structure was applied to the new antenna element. The UHF stacked Hilbert antenna was designed as antenna array that involved 2 × 2 elements and fed by the Wilkinson's four-way power divider. Measurement results show that the UHF stacked Hilbert antenna array achieves a maximum gain of -1 dBi and exhibits a wide impedance bandwidth. Actual partial discharge (PD) experiments were carried out for typical artificial insulation defect models, while the proposed antenna array and an existing Hilbert fractal antenna were both used for PD measurements. The proposed antenna array was superior in this respect and effective for UHF online monitoring of PDs in electrical apparatus.

Modified Hilbert fractal geometry, multi‐service, miniaturized patch antenna for UWB wireless communication

PurposeThe purpose of this paper is to describe a modified Hilbert‐based fractal antenna for ultra wideband (UWB) wireless applications. Simulation results show excellent multi‐band characteristics for UWB wireless applications.Design/methodology/approachA Hilbert curve‐based fractal is optimised for self‐replicating, space‐filling and self‐avoiding properties. In the proposed design, the Hilbert curve is applied to a rectangle as an initial iteration and maintained for the later iterations. Additionally, a Yagi‐like strip is removed from the second iteration of the Hilbert patch and a hexagonal portion is removed from the substrate to achieve good optimization. The antenna feed is created through a micro‐strip line with a feeding section. Finally, a partial ground plane technique is used for improved impedance matching characteristics. A finite element method (FEM) is used to simulate the modified Hilbert model with commercially available Ansoft HFSS software.FindingsThe proposed antenna is miniaturized (39 mm length×30 mm width) and has multi‐band characteristics. The simulation results show that the antenna has a reflection coefficient characteristic of <−10 dB, a linear phase reflection coefficient, better than 65 percent radiation efficiency, 2.2‐4 dBi antenna gain and nearly omni‐directional radiation pattern properties over the UWB bandwidth (3.1‐10.6 GHz).Originality/valueThe antenna shows promising characteristics for the full 7.5 GHz UWB bandwidth. In addition, the performance is achieved by using laceration techniques on the Hilbert patch and substrate, respectively. A partial ground plane ensures impedance matching of 50 over full UWB bandwidth. The simulation analysis of the modified Hilbert fractal antenna design constitutes the main contribution of the paper.

Optimization of UHF Hilbert Antenna for Partial Discharge Detection of Transformers

Partial discharge (PD) online monitoring is an effective tool of inspecting insulation defects and identifying potential faults in power transformers. Ultra-high-frequency (UHF) approaches have caught increasing attention recently and been considered as a promising technology for online monitoring PD signals. The size of a UHF sensor for PD online monitoring of transformer is a critical factor for practical installation inside transformer. This communication presents a compact fourth order UHF Hilbert fractal antenna with desired performance and suitable size for easy installation. Actual PD experiments were carried out for four typical artificial insulation defect models while the antenna was used for PD measurements. The experimental results show that the proposed Hilbert fractal antenna is suitable and effective for UHF online monitoring of PDs in transformers.

Resonant Frequency Calculation and Optimal Design of Peano Fractal Antenna for Partial Discharge Detection

Ultra-high-frequency (UHF) approaches have caught increasing attention recently and have been considered as a promising technology for online monitoring partial discharge (PD) signals. This paper presents a Peano fractal antenna for UHF PD online monitoring of transformer with small size and multiband. The approximate formula for calculating the first resonant frequency of the Peano fractal antenna is presented. The results show that the first resonant frequency of the Peano fractal antenna is smaller than the Hilbert fractal antenna when the outer dimensions are equivalent approximately. The optimal geometric parameters of the antenna were obtained through simulation. Actual PD experiments had been carried out for two typically artificial insulation defect models, while the proposed antenna and the existing Hilbert antenna were both used for the PD measurement. The experimental results show that Peano fractal antenna is qualified for PD online UHF monitoring and a little more suitable than the Hilbert fractal antenna for pattern recognition by analyzing the waveforms of detected UHF PD signals.