Coaxial Mode Research Articles

Nanofiberous coating for Bare Metal Stents: A comparative study of coaxial and monoaxial modes

Stents are coated with anti-thrombogenic/antiproliferative agents to improve the effectiveness. The techniques used to apply the drug/polymer solution to the stent are dipping, ultrasonic / electrospray, and electrospun nanofiber coating. Electrospun fibers have shown many outstanding properties such as large surface area, high length/diameter ratio, flexible surface functionality, and superior tensile performance. Nanofibrous coat can be prepared by monoaxial with single needle or coaxial mode using dual spinneret technique to control the drug release in a sustained manner. In this work, a comparative study of the three coating techniques using PLGA (50:50) and docetaxel has been done. The dip coated samples showed a very less porous structure, high mechanical strength and release was biphasic with maximum 80% cumulative release. In case of spray and nanofibrous coated samples, the surface morphology was porous with high surface area and only abluminal side coating. But the mechanical flexibility of spray coated samples was very less compared to the other two samples. The result was further compared for drug release behaviour with two modes of nanofibrous coating, i.e. coaxial and monoaxial. It has been observed that coaxial nanofibers give a sustained drug release with lesser concentration of drug compared to monoaxial mode. The biocompatibility study confirmed the compatibility of all the polymeric form for human blood cells. Therefore, the spray and nanofibrous coating are preferable over dip coating with improved coating and lesser drug wastage in the luminal side. Again, nanofiber drug release property can be modified using monoaxial and coaxial modes of coating as per application.

Design and experimental demonstration of a TEM-TE10 phase shifter for high-power microwave applications.

A novel phase shifter used to adjust the output phase of high power microwave (HPM) is investigated. The phase shifter is composed of two different circular polarizers, one of which can convert the coaxial transverse electromagnetic mode (TEM) into circularly polarized (CP) TE11 mode, and the other one can realize the transformation between the CP TE11 mode and the rectangular TE10 mode. The two circular polarizers are connected by a circular waveguide, and the TEM-TE11 circular polarizer can rotate around its axis continuously. In this way, the phase shifter can adjust the output phase of the TE10 mode in the range of 0°-360°. In this paper, the principle of a phase shifter working at 1.57 GHz, as well as the experimental results, is demonstrated. The experimental and simulation results are in good agreement. At the central frequency, the transmission efficiency in this range of phase-shifting process is over 94.6%, and the power-handling capacity is as high as 1.5 GW. This novel phase shifter is of interest to HPM spatial power combination technologies.

Compact Microstrip to Empty Substrate-Integrated Coaxial Line Transition

Substrate-integrated waveguides (SIWs) are increasingly being used due to their capability of combining the advantages of planar circuits and traditional waveguides. The development of empty SIWs has substantially reduced the related insertion losses, since waves propagate through air instead of propagating through a lossy dielectric medium. Recently, a new empty coaxial structure, completely built with printed circuit boards and integrated in a substrate, has been proposed. It has been named empty substrate-integrated coaxial line (ESICL). The resulting coaxial line has low cost, easy manufacturing, low radiation, low losses, high-quality factor, and nondispersive. A transition from grounded coplanar waveguide to ESICL already exists. In this letter, a transition from microstrip to ESICL is presented for the first time. In order to demonstrate its feasibility, a back-to-back structure and a bandpass filter have been manufactured and measured.

Color Image Reconstruction Based On Digital Holography

In this paper, a color image reconstruction algorithm based on digital hologram is proposed. The color image is decomposed into three primary color images, and the corresponding hologram is generated in each channel using the four step phase shift method. Then the image of each channel is reconstructed using the inverse Fourier transform, the reconstructed graph of three channels is superimposed to obtain the final color reconstruction image. The reconstructed image overcomes the zero-order image and the straight-through bright spot generated during Fresnel digital holographic image generation in the coaxial recording mode.

A compact ultra-wideband ridge waveguide to coaxial line transition.

A novel compact single-ridge waveguide (SRW) to coaxial line ultra-wideband transition is proposed in this paper. The transition using shorter matching networks between the coaxial port and the SRW port achieves maximum matching bandwidth; meanwhile, a wideband short circuit is also introduced to further broaden bandwidth performance. The whole structure is very simple and can be readily fabricated with a conventional computer numerical control machine. The prototype transitions were designed, manufactured, and measured. The measured results are reasonably consistent with the simulated results. Measurements show that the return loss and insertion loss of the back-to-back transition are better than 18 dB and 0.2 dB, respectively, from 6 to 18 GHz, with 100% fractional bandwidth. Besides, the measured return loss of the single transition is higher than 23 dB in the entire bandwidth. Compared with some other reported SRW transitions, the proposed SRW transition exhibits extreme compactness, lower insertion loss, and more excellent bandwidth performance. The dimensions of the transition structure are only 0.75λ * 0.7λ * 0.35λ (λ is the wavelength at the center frequency) for the central frequency of 12 GHz. The design's transition is completely scalable to other needed frequency band.

Dual-Band Bandpass Double Ground Plane Coaxial Resonators and Filters

This paper proposes a novel double ground plane coaxial resonator that allows to realize two independent coaxial cavity modes in reduced physical volume. This configuration of compact high performance filters is an enabler for multiband transmitter architectures using modern radio frequency data convertors. The proposed approach benefits from simple design and design flexibility. The benefit of the proposed approach is the ease of design and the design flexibility. The proposed filters provide the ability to control the frequency, the bandwidth, and the introduction of transmission zeros separately for each band. A number of designs are presented to demonstrate the operation principle and the performance characteristics of the proposed filters. A $2 \times 4$ pole filter has been manufactured and tested with very good obtained results.

Comparison of downstream scour of single and combined free-fall jets in co-axial and non-axial modes

Downstream plunge pools of dams have been exposed to erosion caused by falling jets of the hydraulic structure’s outlets. This damages the foundation and body of the dam and its constituent structures. Therefore, investigating the scouring phenomenon of plunge pools is one of the important issues in hydraulic engineering. The present research investigates the characteristics of scour holes by single jets and combined jets in different operational modes of dam spillway and outlet. Using experimental modeling, 36 experiments were conducted with various discharges and two tail water depths in single and combined jet modes. The results show that combined jet has lower scour depth and hill height than single jets in all conditions. Comparing the depth and length of the hole and hill height caused by scouring reveals that combined jet is approximately between 5 and 10% greater for a co-axial than for non-axial combined jets in all tail water conditions. But the width of the scour hole of the non-axial combined jets is more than the co-axial one. With the aid of dimensional analysis, an equation is proposed for calculating the scouring characteristics of the combined jets, which is a good determination coefficient between calculated and observational data. Also, the dimensionless results show that the length of the scour hole and the length of mound are about one and a half times the position where the maximum scour depth is formed. Thus, a unit non-dimensional curve can be obtained for the longitudinal profile of scour. The results of the study indicate that, given the case of combining jets as non-axial, the depth and length of the scour holes are lower than the single mode, and that downstream scour can be controlled and reduced relative to the co-axial state by combining the non-axial spillway outlet jet with the orifice jet.

Tunable circularly-polarized turnstile-junction mode converter for high-power microwave applications**Project supported by the National Natural Science Foundation of China (Grant No. 61671457).

Frequency tunability has become a subject of concern in the field of high-power microwave (HPM) source research. However, little information about the corresponding mode converter is available. A tunable circularly-polarized turnstile-junction mode converter (TCTMC) for high-power microwave applications is presented in this paper. The input coaxial TEM mode is transformed into TE10 mode with different phase delays in four rectangular waveguides and then converted into a circularly-polarized TE11 circular waveguide mode. Besides, the rods are added to reduce or even eliminate the reflection. The innovations in this study are as follows. The tunning mechanism is added to the mode converter, which can change the effective length of rectangular waveguide and the distance between the rods installed upstream and the closest edge of the rectangular waveguide, thus improving the conversion efficiency and bandwidth. The conversion efficiency of TCTMC can reach above 98% over the frequency range of 1.42 GHz–2.29 GHz, and the frequency tunning bandwidth is about 47%. Significantly, TCTMC can obtain continuous high conversion efficiency of different frequency points with the change of tuning mechanism.

Design of a dual-band radiation system for a complex magnetically insulated line oscillator

In this paper, a dual-band radiation system for a complex magnetically insulated line oscillator (MILO) is designed and investigated numerically. The radiation system comprises a coaxial plate-inserted mode converter, a power combiner and a conical horn antenna. The mode converter converts the coaxial TEM mode microwaves (1.775 GHz and 3.175 GHz) which are generated by the complex MILO into the coaxial TE11 mode microwaves, and then the coaxial TE11 mode microwaves are combined by the power combiner in a circular waveguide. Lastly, the microwaves are radiated by a conical horn antenna into the air. The gains of the dual-band radiation system are calculated to be 17.8 dB at 1.775 GHz and 18.9 dB at 3.175 GHz. The 3 dB beam widths are 20.5° in E-plane, 26.4° in H-plane at 1.775 GHz and 20.8° in E-plane, 15.1° in H-plane at 3.175 GHz. The power transmission efficiencies of the dual-band radiation system are 98.5% at 1.775 GHz and 95.7% at 3.175 GHz respectively. The power handling capacities of the dual-band radiation system are 4.2 GW at 1.775 GHz and 4.7 GW at 3.175 GHz, respectively.

Frequency and Time Domain Responses of Cross-Bonded Cables

Cross-bonded cable models are compared against their versions with normal bonding (no bonding) for propagation characteristics, frequency, and time-domain responses. Contrary to no-bonding cables, coaxial modes cannot propagate in cross-bonded cables. Instead, intercore modes propagate, being always accompanied by intersheath modes. The latter property cannot be observed if a cross-bonded cable is modeled with its homogeneous equivalent. It is shown that sheath cross-bonding induces intersheath modes circulating between grounding points and impacts on the cable response at resonant frequencies. Alternate models for cross-bonded cables, including both homogeneous and nonhomogeneous equivalents, are compared based on frequency- and time-domain responses, including a field test on a 225 kV 64 km cable with 17 major sections.

A Design Method for Mode-Selective Waveguide Couplers in Dual-Polarized Wideband Matched-Feed Antennas

A novel type of multihole directional coupler is presented as well as a design method involving novel procedures. The device couples two orthogonal TE11 modes in a circular waveguide into two orthogonal TE21 modes with specified excitations in a surrounding coaxial waveguide, which has the circular waveguide as the inner conductor. A simple, novel analytical procedure is used to determine azimuthal hole positions, such that each of the input modes couples to only the desired coaxial TE21 mode. The method is applied to a specific coupler which is designed to couple −14 dB to both higher order coaxial modes in the band from 10 to 14 GHz. The suppression of undesired modes is generally better than 40 dB. The coupler is intended for broadband dual-polarized matched feeds, which are able to compensate for the intrinsically high cross polarization of offset single reflector antenna systems.

Analysis and Design of a Wideband Coaxial Transition to Metal and Printed Ridge Gap Waveguide

In this paper, a wideband coaxial to ridge gap transition is proposed and implemented. The transition has a compact size, wide bandwidth, and simple structure. It can be used to excite ridge gap waveguides implemented by the printed circuit board or computer numerical control (CNC) technologies. A similar circuit model for a coax-to-microstrip junction is proposed and used to establish a systematic design procedure for the proposed transition. Perfect electric conductor and perfect magnetic conductor (PMC) boundaries are used to make the procedure independent of the fabrication technology. The PMC is replaced by a bed of nails for ridge gap realized by CNC technology and mushroom-shaped structure in the case of PCB technology. The proposed transition based on the PCB technology is fabricated and measured. There is a good agreement between simulated and measured results which validates the proposed design. The transition has a 59.22% bandwidth with $S_{11} dB and $S_{21} > -0.5$ dB.

Mixing and combustion enhancement of Turbocharged Solid Propellant Ramjet

Turbocharged Solid Propellant Ramjet is a new concept engine that combines the advantages of both solid rocket ramjet and Air Turbo Rocket, with a wide operation envelope and high performance. There are three streams of the air, turbine-driving gas and augment gas to mix and combust in the afterburner, and the coaxial intake mode of the afterburner is disadvantageous to the mixing and combustion. Therefore, it is necessary to carry out mixing and combustion enhancement research. In this study, the numerical model of Turbocharged Solid Propellant Ramjet three-dimensional combustion flow field is established, and the numerical simulation of the mixing and combustion enhancement scheme is conducted from the aspects of head region intake mode to injection method in afterburner. The results show that by driving the compressed air to deflect inward and the turbine-driving gas to maintain strong rotation, radial and tangential momentum exchange of the two streams can be enhanced, thereby improving the efficiency of mixing and combustion in the afterburner. The method of injecting augment gas in the transverse direction and making sure the injection location is as close as possible to the head region is beneficial to improve the combustion efficiency. The outer combustion flow field of the afterburner is an oxidizer-rich environment, while the inner is a fuel-rich environment. To improve the efficiency of mixing and combustion, it is necessary to control the injection velocity of the augment gas to keep it in the oxygen-rich zone of the outer region. The numerical simulation for different flight conditions shows that the optimal mixing and combustion enhancement scheme can obtain high combustion efficiency and have excellent applicability in a wide working range.

Classifying the impact of progressively evacuating hexagonal lattices of C-C bond in DWCNT-based nano resonators

This paper investigates the effect of gradually vacating a ring of hexagonal lattices containing Carbon–Carbon bond in double-walled carbon nanotube (DWCNT)-based nano resonator. The behaviour of zigzag and armchair DWCNTs have been studied by utilizing the Molecular Structural Mechanics approach for modelling and simulations. The process of vacating is performed on the outer wall of DWCNT by keeping the inner wall length as constant. The resonant frequencies and frequency shift corresponding to the attached masses and different boundary conditions have been analysed. Coaxial mode of vibrations are found to exist at higher values of length ratio, which tends to become non coaxial at lower values of the same. With a higher value of length ratio, a reduction in the frequency shift is observed for lower values of mass and is found to be maximum for approximately 50% reduction in the outer tube. The model suggested has been validated with the published literature.

인쇄형 다이폴을 이용한 Ku-대역 원형도파관－동축선 변환부 설계

원형도파관은 반사경 안테나 피드, 직교모드변환기, 편파기, 필터/멀티플렉서, 로터리 조인트 등의 구현에 널리 사용되고 있다. 원형도파관을 송신부/수신부와 연결하기 위해 흔히 원형도파관-동축선 변환부가 요구된다. 본 논문에서는 인쇄형 다이폴을 이용한 일직선형 원형도파관-동축선 변환기를 설계하였다. 제안한 변환부는 원형도파관 종단에 도파관 축과 일직선형으로 구현되며 단락된 원형도파관, 마이크로스트립 급전선, 마이크로스트립 벌룬, 인쇄형 다이폴, 광대역 동작을 위한 기생소자, 동축선 프로브 등으로 구성된다. 설계변수에 따른 변환부의 반사계수 변화를 분석한 후 이로부터 최적 설계를 얻었다. 설계된 변환부를 제작하여 반사계수를 측정하여 시뮬레이션과 비교하였다. 제안한 변환부는 13.5~17.0GHz 대역에서 -15dB 이하의 반사계수, -20dB 이하의 고차모드 레벨 특성을 가진다.

Comparison of coaxial higher order mode couplers for the CERN Superconducting Proton Linac study

Higher order modes (HOMs) may affect beam stability and refrigeration requirements of superconducting proton linacs such as the Superconducting Proton Linac, which is studied at CERN. Under certain conditions beam-induced HOMs can accumulate sufficient energy to destabilize the beam or quench the superconducting cavities. In order to limit these effects, CERN considers the use of coaxial HOM couplers on the cutoff tubes of the 5-cell superconducting cavities. These couplers consist of resonant antennas shaped as loops or probes, which are designed to couple to potentially dangerous modes while sufficiently rejecting the fundamental mode. In this paper, the design process is presented and a comparison is made between various designs for the high-beta SPL cavities, which operate at 704.4 MHz. The rf and thermal behavior as well as mechanical aspects are discussed. In order to verify the designs, a rapid prototype for the favored coupler was fabricated and characterized on a low-power test-stand.

Theoretical investigations on radiation generation of TEM, linearly or circularly polarized TEn1 coaxial waveguide mode in relativistic magnetron

The physical mechanism of the radiation generation of all possible output modes of the relativistic magnetron (RM) with all cavity-magnetron axial extraction technique is theoretically analysed, and the necessary conditions for generating these modes are obtained respectively. Assuming that n0 is the number of the electron spokes, N ≥ 4 as the total number of the cavities is an even number, and k is a nonnegative integer, some conclusions can be drawn as follows. If n0 = kN is true, no mode can be excited in the coaxial waveguide; if n0 = (2k + 1)N/4 is true, the linearly polarized modes can be excited in the coaxial waveguide; if n0 = (4k + 2)N/4 is true, the TEM mode and the linearly polarized modes can be excited in the coaxial waveguide; if n0 takes other value, the left and right circularly polarized modes can be excited in the coaxial waveguide and the directions of rotation of the circularly polarized modes can be reversed with the reversion of the direction of rotation of the electron spokes; in addition, some other regular characteristics of the corresponding mode excitation are presented in detail in this paper. Such unique attractive properties that have been verified by the cold and hot simulations in this paper make it possible for this type of RM to meet application requirements of various high power microwave (HPM) modes.

A relativistic backward-wave oscillator with frequency-selectable across X- and Ku-bands

The mechanism and realization of a relativistic backward-wave oscillator (RBWO) with frequency-selectable across X- and Ku-bands are presented. Both the transverse and the longitudinal mode selections contribute to the frequency-selectable across different bands. The transverse mode selection is achieved using the property of “surface wave” of the slow-wave structures to excite the coaxial TM01 mode (Ku-band) or the hollow TM01 mode (X-band) without exciting the higher TM modes. The longitudinal mode selection is achieved by the introduction of a coaxial extractor, which contributes to the compact structure and the restraints of the longitudinal mode competitions. In simulation, a Ku-band microwave with a frequency of 12.6 GHz and an X-band microwave with a frequency of 10.6 GHz are radiated when the inner-conductor length is 10.2 cm and 0 cm, respectively. The output power of both bands is above 2 GW. This technical route of RBWO with frequency-selectable across different bands is feasible and provide a guide to design other types of frequency tunable high power microwave sources operating at high frequency bands.

A high-efficiency tunable TEM-TE11 mode converter for high-power microwave applications

The tunable high power microwave source (HPM’s) is considered to be an important research direction. However, the corresponding mode converter has been researched little. In this paper, a high-efficiency tunable mode converter (HETMC) is investigated for high-power microwave applications. The HETMC that is consisted of coaxial inner and outer conductors, with four metal plates arranged radially, at 90° in the coaxial gap, and matching rods can transform coaxial transverse electromagnetic (TEM) mode to TE11 coaxial waveguide mode. The results show that adjusting the length of the downstream plate, and the distance between the rods installed upstream and the closest edges of the plates, can improve the conversion efficiency and bandwidth remarkably. Moreover, when the frequency ranges from 1.63 GHz to 2.12 GHz, the conversion efficiency is above 95% between 1.63 GHz and 2.12 GHz with a bandwidth of 26.1%. Besides, the unwished reflection and transmission can be eliminated effectively in the HETMC.

Technique of totally robotic delta-shaped anastomosis in distal gastrectomy.

BACKGROUND:We aimed to clarify the utility of delta-shaped anastomosis (Delta), an intracorporeal Billroth-I anastomosis-based reconstruction technique used after laparoscopy-assisted distal gastrectomy (LADG), in robot-assisted distal gastrectomy (RADG).METHODS:RADG was performed in patients with clinical Stage I gastric cancer, and reconstruction was performed using Delta. The Delta procedure was the same as that performed after LADG, and the operator practiced the procedure in simulated settings with surgical assistants before the operation. After gastrectomy, the scope and robotic first arm were reinserted from separate ports on the right side of the patient. Then, a port on the left side of the abdomen was used as the assistant port from which a stapler was inserted, with the robotic arm in a coaxial mode. The surgical assistant performed functional end-to-end anastomosis of the remnant stomach and duodenal stump using a powered stapler.RESULTS:The mean anastomotic time in four patients who underwent Delta after RADG was 16.5 min. All patients were discharged on the post-operative day 7 without any post-operative complications or need for readmission.CONCLUSIONS:Pre-operative simulation, changes in ports for insertion of the scope and robotic first arm, continuation of the coaxial operation, and use of a powered stapler made Delta applicable for RADG. Delta can be considered as a useful reconstruction method.