Center Conductor Research Articles

Motion-based microwave tomographic measurement device for three-dimensional coverage in a magnetic resonance system.

We have developed a fully 3D data acquisition system for microwave breast imaging which can operate simultaneously inside a magnetic resonance imaging (MRI). MRI is used regularly for breast imaging to distinguish tumors from normal tissue. It generally has poor specificity unless used with a gadolinium contrast agent. Microwave imaging could fill this need because of the good endogenous tumor:normal tissue property contrast, especially in light of safety concerns for gadolinium. The antenna array consists of 16 monopole antennas positioned in a horizontal circle surrounding the breast which can then be moved vertically for 3D coverage of the breast. The tank system materials were chosen to minimize artifacts in the MR image within the specific shared imaging zone. The support rods are stainless steel, albeit positioned sufficiently far from the imaging target to have little effect. The mechanical motion parts are all 3D printed plastic. Unlike many conventional antennas, the monopoles consist of just the center conductor and insulator of the coaxial cable, making it one of the least possible metallic structures. Data were acquired both inside and outside of the MR bore to confirm that the MR bore did not have adverse effects on the microwave imaging process. The imaging tank was filled with a mixture of glycerin and water to both provide a reasonable property match to the phantom and to highly attenuate the fields which also acted to suppress multi-path signals. Microwave images were reconstructed using our Gauss-Newton scheme combined with a log transformation for a more linear convergence. MR images were also acquired to assess the effects of the microwave tank structures on the imaging. The microwave measurement data were acquired in log magnitude and phase format at 200 MHz increments from 700-1900 MHz. Each antenna acted sequentially as a transmitter while the complement of 15 acted as a receiver. The single frequency images were reconstructed using a Gauss-Newton iterative technique with a standard log transformation to linearize the process. The data showed that the signal strengths were between 7-10 dB lower for the case when the array was inside the MRI versus when not. Notwithstanding, the image quality was still high because of the significant signal to noise ratio. The reconstructed images in both situations demonstrated good 3D object recovery of the vertically size and shaped varying object. The MR images were not adversely affected by the presence of antennas or feed structures. We have demonstrated that our technique can recover high-quality images of a 3D varying object within an MRI system. Compatibility issues have been addressed for both the microwave and MRI systems. The reduced SNR for the case operating in the MRI did not adversely affect the images. To the best of our knowledge, this is the first example of a microwave imaging system operating in an MRI with full 3D volumetric capability.

Observation and analysis of a large banana orbit in the diocotron mode of a coaxial Malmberg–Penning trap

The diocotron mode of an off-axis electron column is studied in a coaxial version of the Malmberg–Penning trap. Measurements of the diocotron frequency as a function of the bias on the central conductor agree well with a derived theory including finite-length corrections and confinement potential contributions. When the experimental parameters are adjusted to give a very low diocotron frequency, the column motion abruptly changes from an axis-encircling orbit to a large banana-shaped orbit in the r−θ plane with extent Δθ≈270° and Δr/R≈0.25, where R is the wall radius. This banana motion is apparently in response to a previously unknown background construction asymmetry. The size of the asymmetric potential is deduced from orbit data and found to be 45–100 mV. Theoretical modeling shows this to be consistent with a small radial offset δ in the center wire position of δ/R=0.034. Implications and applications of these findings are discussed and a note on obtaining the line density of an electron column in a coaxial trap is given.

General Coupling Method for Stripline Ferrite Circulators: Application on Dual-Band Devices With Complex Central Conductor Shape

This article presents two original, efficient, and rigorous methodologies for coupling ferrite circulators of complex shapes. Indeed, by using a central conductor of any shape or geometry, an optimized circulation phenomenon can be achieved because of both methods. This article details and analyzes the two methods developed. They will be validated by the measurement of a stripline circulator with a triangular central conductor operating around 8 GHz. At the end of this first study, one of the two methods will be selected and implemented in a more complex case since we will adapt it to a dual-band operation.

Superconducting microwave resonators with non-centrosymmetric nonlinearity

We investigated both theoretically and experimentally open-ended coplanar waveguide resonators with rf SQUIDs embedded in the central conductor at different positions. These rf SQUIDs can be tuned by an external magnetic field and thus may exhibit the non-centrosymmetric nonlinearity of type with suppressed Kerr nonlinearity. We demonstrated that this nonlinearity allows for efficient mixing of and λ modes in the cavity and thus enables various parametric effects with three wave mixing. These effects are the second harmonic generation, the halftone generation, the parametric amplification in both degenerate and non-degenerate regimes and deamplification in degenerate regime.

Analysis and detection of fault for substation GIS insulating part based on integrated automation system data

Insulators are important components in gas-insulated metal-enclosed switchgear (GIS), and their safe operation is of great engineering significance. In an air leakage fault accident caused by the cracking of the insulating part of the grounding knife switch of 500kV HGIS equipment, the following measures were taken to find out the cause of the failure: disassembly inspection, equipment assembly review, insulation performance test and residual stress analysis during casting and curing. It turned out that the failure was caused by a lack of cache firmware in the production process. The thermal conductivity and thermal expansion coefficient of the central copper conductor and epoxy resin are different. When the two are solidly adhered, the incompletely reacted insulating parts shrink too quickly when the temperature difference is too large. The copper conductor locally produces excessive residual stress to the epoxy resin, which causes the insulation to crack. According to the causes of the fault, suggestions are put forward, such as replacing the central copper conductor with aluminum material, adding secondary pre-curing procedure in the production process, and adding Remote longitudinal Wave probe on the Insulated Basin side to monitor residual stress in real time.

EVALUATION OF SYSTEMATIC ERRORS OF STRIP ASYMMETRIC HUMIDITY SENSOR

The methodical estimation of the methodical component of the error arising at measurement of humidity of heterogeneous dispersed dielectrics by the band asymmetric sensor is carried out. In the process of evaluation it was shown that the most significant component of methodological error occurs due to changes in temperature and frequency of the information wave. Temperature-dependent values included in the mathematical model of the band asymmetric humidity sensor are: relative dielectric constant of the substrate dielectric and the object of control, length and width of the central conductor, substrate dielectric thickness. The dielectric constant of the dielectric of the object of control depends on the frequency of the information wave, and this parameter is directly included in the coefficients of the sensor conversion equation. The results of the research showed that in the process of measuring the conversion of humidity in the band asymmetric sensor there is a methodological component of the error associated with changes in temperature and instability of the frequency of the information wave. To ensure a frequency error at a level not exceeding 0.5%, the error of instability of the frequency of the information wave when converting humidity into the output amplitude of the information wave should not exceed ± 3 kHz, provided by existing RF generators. It is advisable to remove the temperature component of the error using the method of correction. The mathematical model of band asymmetric measurement of moisture conversion of heterogeneous dispersed dielectrics in the high-frequency region was also improved.

Broadband Coplanar Waveguide to Air-Filled Rectangular Waveguide Transition

This article introduces a novel transition between coplanar waveguide (CPW) and air-filled rectangular waveguide (RWG). A rectangular radiator etched with a semi-elliptic slot is connected to the center conductor of CPW to realize the transition, which broadens the bandwidth. This direct transition does not require intermediate transition or air-bridges. Moreover, the planar circuit of the transition can be designed with high- and low-permittivity materials (εr = 10.2 and 2.22), which offer more benefits in both PCB and MMIC design. Two back-to-back transition prototypes at X-band are designed, fabricated and measured. The 15 dB fractional bandwidths are expanded to 44.7% and 47.6% respectively, which have been demonstrated in both of the transitions (εr = 10.2 and 2.22). The measurement results agree well with simulation results, which validate the feasibility of this design.

Passive Intermodulation Distortion in Connectors With Nonlinear Interaction in Electrical Contacts and Magnetic Materials

Nonlinearities in electrical contacts and magnetic materials are two main contributors to passive intermodulation (PIM). In this study, mechanisms of thermally induced current truncation and hysteresis effect are introduced to provide explanations for PIM generation and to make predictions for the third-order intermodulation (IM3) products resulting from coaxial connectors. Equivalent circuit models are presented to provide insight into the nonlinear sources both in contact junction and body area with the relative contribution of various physical parameters. The finite element analysis (FEA) model of the central conductor of a DIN-to-N coaxial adapter is developed to identify the current density and temperature distribution in the contact area, while an FEA model of simplified connector cross section is presented to simulate the magnetization effect in the body area. Combined with two nonlinear sources, an equivalent circuit model predicting the PIM behavior is developed. The simulation results show that the material nonlinearity contributes to frequency dependence, while the power dependence is dominated by both nonlinear mechanisms. Connectors with different contact surface are obtained by designed accelerated tests, and two types of connector with different materials are manufactured. Good agreements are observed in experimental measurements, verifying the proposed model of contact–material interaction-induced PIM.

Enhanced Terahertz Spectral‐Fingerprint Detection of α‐Lactose Using Sub‐Micrometer‐Gap On‐Chip Waveguides

AbstractWe investigate using finite element methods how sub‐micrometer to micrometer‐scale coplanar waveguide (CPW) can be used for the detection of fingerprint spectra of very small (of order 10−14 mL) volumes of analytes in the terahertz (THz) frequency range. The electric field distribution is investigated near the waveguide for various gap widths between the center conductor and ground plane using a finite element simulation (ANSYS High Frequency Structure Simulator, HFSS). Taking lactose monohydrate as an exemplar material, a Drude–Lorentz model is combined for its real and imaginary permittivities with this numerical simulation, finding a significant enhancement in fingerprint detection as the gap width is reduced; the electric field in the CPW is found to increase by a factor ≈14 times moving from a 20 to 0.5‐µm‐wide gap between center conductor and ground plane, while the on‐resonance THz absorption increases ≈14 times. The effective absorption coefficient of the lactose at 530 GHz is investigated as a function of the slot width for various lactose block thicknesses to understand how change in the field confinement and in the effective overlap between the lactose block and incident THz waves affect the effective absorption coefficient.

Partial Discharge and Movement Characteristics of Micron-sized Metal Particles on Insulator Surface in Gas-Insulated Switchgear with Long-time AC Stress

During the transport., assembly., installation., and operation of a gas-insulated switchgear (GIS), the introduction of metal particles into the unit is inevitable. The presence of metal particles on the insulator surface is regarded as a critical factor in insulation failures. Thus, a thorough understanding of the characteristics of metal particles on the insulator surface is critical. In this study, a 126-kV GIS experiment platform with a highly sensitive partial discharge (PD) detection system is established. The movement and PD characteristics of micron-sized metal particles on the insulator surface in a 126-kV GIS under long-time alternating current (AC) stress are investigated. The results demonstrate that the PDs triggered by the micron-sized metal particles are weak and sporadic: the apparent charge of most PDs is lower than 1 pC, and the discharge repetition rate can be as low as once per minute. When two metal particles are sufficiently close to each other, they are charged by the PDs between them. This causes the metal particles to move away from each other and tend to be evenly distributed over the entire insulator surface. Some metal particles can move to stay at the triple junction near the grounded enclosure and center conductor or jump to adhere to the surface of center conductor. This study is anticipated to be a beneficial reference for further understanding the movement and PD characteristics of micron-sized metal particles on the GIS insulator surface.

A Microwave Quantum-Defined Millivolt Source

We demonstrate a tenfold increase in the amplitude of microwave-frequency waveforms generated by a quantum-defined superconducting voltage source, with an open-circuit signal of 17.56 mV rms at 1.005 GHz. The voltage source is an RF Josephson arbitrary waveform synthesizer (RF-JAWS) that utilizes a circuit that is cooled to 4 K and is composed of an array of 4500 Josephson junctions. These junctions are connected in series along the center conductor of a 50- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $ </tex-math></inline-formula> superconducting coplanar waveguide transmission line. We introduce a new zero-forcing equalization technique for reducing distortion in drive current pulse patterns. This technique allows an increase in the amplitude of the quantum-based voltage waveforms while suppressing parasitic feedthrough signals to −75 dBc. Synthesizing a two-tone delta–sigma waveform, we monitor an audio-frequency 10-kHz tone of less than 100- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{V}$ </tex-math></inline-formula> rms amplitude while simultaneously measuring the 1.005-GHz tone of −28.12-dBm power in a 50- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $ </tex-math></inline-formula> environment. The two-tone synthesis allows simultaneous verification of correct operation of the voltage source using time-efficient low-frequency measurement techniques as well as slower microwave measurements.

To the question of the pathways of the autonomic nervous system in the medulla oblongata

Our knowledge of the pathways of vegetative n. with. have not yet achieved such clarity and clarity that are required by the clinician for topical diagnosis. While it is quite understandable that it is impossible to obtain all the necessary data by means of an experiment on animals, clinical observations are of particular importance, which sometimes, in their simplicity and clarity, are not inferior to experiment. Not entirely convincing in isolation, they, when collected and studied, can give fairly accurate answers to the questions of interest to us. With this message, we begin to use the material of the clinic of nervous diseases of the VGMI in order to study the course of the central conductors of vegetative n. s.

A Low-Loss Broadband Planar Transition From Ground Coplanar Waveguide to Substrate-Integrated Coaxial Line

In this letter, a three-dimensional ground coplanar waveguide (3D-GCPW) structure is proposed as a broadband planar transition between the conventional GCPW and substrate integrated coaxial line (SICL). The proposed 3D-GCPW contains a 3-D central conductor constructed by two copper layers which are connected together by metallized blind vias and two side ground planes. Its characteristic impedance is mainly determined by the width of the 3-D central conductor and the gap to the side ground plane; thus, the requirement for machining accuracy of metallized blind vias in 3D-GCPW can be reduced during the machining process. A back-to-back structure of the 3D-GCPW transition is fabricated by a multilayer printed circuit board (PCB) process and measured to validate the good performance. The experimental results show that the proposed 3D-GCPW transition exhibits a reflection coefficient less than −10 dB and an acceptable insertion loss within dc to 42 GHz, making it promising for high-performance multiple-channel transceiver or massive integrated applications.

Study on Structure Type and Operation Condition of UHVDC Wall Bushing

When the ±800kV UHVDC capacity is increased to 10000MW, the transmission current is 5kA and 6.25kA, which will put forward new requirements for the key technology of UHVDC through wall bushing: in UHV level, the key of through wall bushing lies in the research of basic technology of voltage sharing and field sharing. In the case of large current carrying capacity, the key lies in the basic technology research of current sharing and heat sharing. When the DC wall bushing, converter bushing and outgoing line device operate at the rated voltage, the central conductor is heated due to the carrying large DC current. Therefore, the temperature field distribution inside and at the tail of the bushing core is uneven, and the resistivity is the function of temperature, resulting in the change of resistivity with temperature and the change of potential and electric field distribution with resistivity during operation. Therefore, under the above high current operation conditions, in-depth key technology research is required for the design of bushing current carrying device, calculation of internal potential and electric field distribution, voltage sharing, field sharing, current sharing and heat sharing technology. The combined action of electrical and thermal stress will significantly affect the internal electric field distribution of converter transformer core and accelerate the aging rate of core composite insulation material, which introduces new research topic for the key technology of UHVDC converter bushing. The electric field and voltage distribution of UHVDC bushing are theoretically analyzed, the insulation structure is optimized from the aspects of material and structure, and the manufacturing process and the test technology are deeply and systematically studied.

Simulation analysis and calculation of electric field distribution characteristics of UHV wall bushing

Facing the unbalanced development of resource distribution and productivity, China needs long-distance power transmission and distribution. The long-distance power transmission will lead to a lot of power loss in the process of transmission. In order to achieve long-distance, large capacity, low loss power transmission, it is necessary to build UHV transmission and transformation lines in the power grid for cross regional power allocation. As the key equipment in UHV transmission and transformation, UHV bushing plays a very important role in UHV transmission and transformation line. However, due to working in UHV electric field for a long time, the reduction of UHV bushing failure rate is very important for the smooth operation of UHV transmission line. Therefore, it is necessary to study the electric field distribution characteristics of UHV bushing. In this paper, the electric field distribution characteristics of UHV through wall bushing are studied. The simulation analysis and calculation of electric field are carried out by using COMSOL Multiphysics finite element software. By analyzing the electric field distribution of the complex field areas such as the central conductor of the bushing, the end of the liner, the sheath and the capacitor core, the electric field distribution law and the edge electric field diagram of the bushing and its adjacent key areas under different voltage types are obtained. The radial axial electric field distribution of the capacitor core and the edge electric field distribution of the upper and lower steps are compared and analyzed Based on the analysis of the characteristics and local complex field, the variation law of the electric field distribution of the bushing with the structure design is obtained, which provides an optimization idea for the insulation structure design of UHV through wall bushing.

The Coax Dipole: A fully flexible coaxial cable dipole antenna with flattened current distribution for body imaging at 7 Tesla.

PurposeThe coax dipole antenna, a flexible antenna for body imaging at 7T is presented. Similar to the high impedance coil, this coaxial cable antenna is fed on the central conductor and through gaps in the shield, the current passes to the outside of the antenna to generate B1 field. This could achieve more favorable current distributions and better adaptation to the body curvature.MethodsFinite difference time domain (FDTD) simulations are performed to optimize the positions of the gaps in the shield for a flat current profile. Lumped inductors are added to each end to reduce losses. The performance of a single antenna is compared to a fractionated dipole using B1 maps and MR thermometry. Finally, an array of eight coax dipoles is evaluated in simulations and used for in‐vivo scanning.ResultsAn optimal configuration is found with gaps located at 10 cm from the center and inductor values of 28 nH. In comparison to the fractionated dipole antenna, in single antenna phantom measurements the coax dipole achieves similar B1 amplitude with 18% lower peak temperature. In simulations, the eight‐channel array of coax dipoles improved B1 homogeneity by 18%, along with small improvements in transmit efficiency and specific absorption rate (SAR). MRI measurements on three volunteers show more consistent performance for the coax dipoles.ConclusionThe coax dipole is a novel antenna design with a flattened current distribution resulting in beneficial properties. Also, the flexible design of the coax dipoles allows better adaptation to the body curvature and can potentially be used for a wide range of imaging targets.

Electro-thermal Coupling Model for Radial Temperature and Electric Field Distribution Computation and Experimental Research of 550kV RIP AC Oil-gas Bushings

The condenser of 550kV RIP oil-gas bushings is in the solid structure of resin-epoxy impregnated paper(RIP), which has large difference with the oil-immersed one (OIP). Oil-gas bushings has compact configuration and heat conduction condition is harsh, while temperature distribution has direct relationship with bushings’ long-term stable operation performance, so it’s essential to carry out research in radial temperature within condenser during production of RIP oil-gas bushing prototype. In this paper, radial temperature distribution principle of bushing condenser under linear material conditions has been summarized by building electrothermal coupling theoretical model of bushing condenser. The model has been generalized by electro-thermal coupling finite element mode under nonlinear material conditions, and electrothermal coupling iterative computation process has also been proposed, then experimental measurement study in local temperature points of bushing condenser has been carried out. The study shows that plate model has advantages of high accuracy and simple form in calculating radial temperature distribution of bushing condenser; the hot-spot temperature of 550kV RIP oil-gas bushings is about 95°C which appears near the center conductor; radial temperature of bushings under nonlinear material conditions is lower than that under linear material conditions and the thermal breakdown voltage of condenser under rated current is 538kV which is higher than the maximum operation phase voltage. This paper provides theoretical foundation for radial temperature computation within RIP bushing condenser and has some reference value for the design of HVAC RIP bushings.

Strong Coupling of an Fe - Co Alloy with Ultralow Damping to Superconducting Co-planar Waveguide Resonators

We report on the strong coupling between a metallic ferromagnetic Fe75Co25 thin film patterned element and a range of superconducting Nb half-wavelength co-planar waveguide (CPW) resonators. By varying the volume of the ferromagnet we demonstrate that the coupling rate scales linearly with the square root of the number of spins and achieve a coupling rate over 700 MHz, approaching the ultrastrong coupling regime. Experiments varying the center conductor width while maintaining constant magnetic volume verify that decreasing the center conductor width increases coupling and cooperativity. Our results show that the frequency dependence of the coupling rate is linear with the fundamental and higher order odd harmonics of the CPW, but with differing efficiencies. The results show promise for scaling planar superconducting resonator/magnetic hybrid systems to smaller dimensions.

Theoretical Analysis of Electric Heating Field and Insulation Accident of High Voltage AC Basin Insulator

Basin insulator is widely used in GIS equipment. It is an important insulating part to realize electrical isolation between central conductor and grounding flange. In this paper, the insulation properties of the materials used for the basin insulator are analyzed experimentally, and the distribution of the electric field of the basin insulator is obtained through the electro-thermal coupling analysis process, and the relationship between the hottest spot temperature and the current carrying capacity is calculated. The heating curve of the basin insulator is obtained by using the theoretical model, and the basin insulation accident is analyzed by using the curve. Considering that the basin insulator is in the SF6 gas atmosphere for a long time, the local temperature rise caused by overheating fault of the basin insulator, and then the variation law of SF6 gas pressure and density caused by the overheating fault of the basin insulator are theoretically analyzed in this paper. Research shows: there is significant non-linear relationship between the insulation performance parameters of the basin body and the temperature. The eddy current field and harmonic field analysis method based on the finite element method can effectively calculate the heating of the center guide rod and the basin body under the power frequency condition. The maximum electric field intensity appears at the interface between the basin and the center conductor, with the value of 6.033kV/mm. The maximum temperature is near center conductor side of the basin, with value of 0.033kV/mm. When the current carrying capacity is higher than 1.5 times of the rated value, the thermal breakdown phenomenon of sudden temperature rise occurs. The calculation process of thermal electric coupling proposed in this paper provides way for verification of thermal electric performance of basin insulator design scheme, and also provides theoretical guidance for its on-site maintenance and accident analysis.

Analysis and Modeling of various Tapered Coplanar Waveguide

This paper proposes the analysis of investigations on various tapered Coplanar Waveguide (CPW) structures to achieve increase in phase shift per unit length and the reduction in line length. The analysis of the tapered CPW is important in order to obtain the characteristic impedance and phase velocity of the transmission line. The step tapered CPW structures proposed have the center conductor, the gap/ground or both the widths varying having constant characteristic impedances for a fixed line length. The conformal mapping method is applied to the proposed tapered CPW structures to obtain the electrical parameters of the transmission line. The obtained impedance can be utilized in the design of RF circuits such as phase shifter using MEMS bridges.