Tube Waveguide Research Articles

Asymmetric trapped modes in a tube waveguide with a bulge

Asymmetric trapped modes in a waveguide of a cylindrical hollow tube with a local bulge are studied. The problem is converted to solving a nonaxisymmetric boundary value problem associated with the three-dimensional Helmholtz equation subject to Dirichlet boundary condition. The domain decomposition method and matching technique are invoked for an infinitely long tube with a bulge and a semi-infinitely long tube with an end bulge. Asymmetric trapped modes along with the frequencies are determined and can be decomposed into a linear combination of those with the n-fold periodic symmetry. For each n-fold periodic trapped mode, whether azimuthal trapped modes exist depends on the radius and width of the bulge. The influence of the bulge’s size on the frequencies and intensity location of localized vibration is analyzed. The obtained results can be extended to analyze bound states in quantum wires.

Optimizing the control process parameters for the induction soldering of aluminium alloy waveguide paths11The reported study was funded by Russian Foundation for Basic Research, Government of Krasnoyarsk Territory, Krasnoyarsk Region Science and Technology Support Fund to the research project № 16-48-242029

The paper describes the problem of selecting the optimal initial values of algorithm parameters for the process of the induction soldering of aluminium alloy waveguide paths. The authors consider some factors influencing the quality of waveguide soldered joint elements. These factors depend on the correct choice of initial values for control parameters. The problem of optimizing such parameters for further analytical and numerical studies is researched by authors. For solving the stated task, the random search method is selected, allowing for an acceptable field study within the stated time to solve the problem of control optimization with the level of accuracy required by the technological process. Therefore, optimal initial values of the induction soldering technological process were found for three sizes of waveguide tubes and flanges.

Study on cross-sectional deformation of rectangular waveguide tube with different materials in rotary draw bending

Abstract

Dispersion characteristics of dielectric tube waveguide loaded with plasma for leaky wave antenna application

The leaky mode dispersion characteristics (ω-β) of a Dielectric Tube Waveguide Loaded with Plasma (DTWLP) is analytically solved and numerically computed using Muller’s complex root search algorithm with an aim to define its complex propagation constant behaviour. Consequently, complex leaky mode characteristics and its classification as guided mode, reactive mode and antenna mode have been investigated. These modal characteristics reveal wide fundamental antenna mode (TM01) with the variation in plasma density, which can find prospective application in high resolution radar and communication system where “re-tuning” of the antenna to a new frequency or making it electrically invisible is required. A computational cum simulation study is also performed using CST Microwave Studio software, which confirms our analytical findings.

Wave generation and source energy distribution in cylindrical fluid-filled waveguide structures

The paper deals with an analytically based computer simulation of wave fields generated by a monopole source in a multilayered fluid-filled tube waveguide in an elastic or porous-elastic space. The mathematical problems considered relate to various practical applications ranging from a micro scale for fibers and nano-tubes to a macro scale for seismo-acoustics and well production. To be specific, the presentation is given for borehole waveguides, aiming at estimating the efficiency of an in-hole source for various surrounding media. The time-harmonic and transient solutions are obtained in terms of inverse Fourier integrals. The tube, body, and leaky waves propagating from the source to infinity are derived from those path integrals as an asymptotic contribution of the residues, stationary points, and approaching complex poles and stationary points. On this basis, the wave energy radiation from the source, which is dependent on the geometry and material properties of a cased fluid-filled borehole and formation, is numerically studied. The analysis is focused on the peculiarities of the source power distribution among the generated waves as well as between the radial and axial directions of wave propagation. A qualitative difference in source energy radiation modes for hard and soft environments and the role of leaky waves in the power transport into a soft formation are discussed. The emergence of additional tube waves due to a fluid saturation of porous interlayers is revealed.

Synthesis of SiON films by helicon-wave plasma and their characteristic analysis

SiON becomes a kind of new functional material because it has many excellent mechanical and chemical properties such as high hardness, corrosion resistance, oxidization resistance. It is reported that the coating of SiON has many important applications in optical device. For example, it can be used as the protective layer of Edmund optics, touch panel of mobile phone, waveguide tube et al. the Mohs hardness of SiON is about 9H. In addition, the transmittance of the coating is 98% in the visible region. Lately, lots of researchers are interested in the biomedical applications of SiON coatings due to its favourable mechanical properties and the good hemocompatibility of the material. Such as hip implants, it can help patient recover soon because the coating is smooth and the Si–N and Si–O–N chemical bonding are more to the hydrophilicity than Si–O or Si–Si bonds. There is also lots of significant application of SiON films in the field of microelectronics. According to the reports, SiON has the inhibiting effect on hot-carrier injection, impurity diffusion and water vapor permeability. As the dielectric layer, SiON also possesses better electronic mobility and the trap densities of electron. So far, the main synthetic method of SiON is plasma enhanced chemical vapor deposition (PECVD) including inductive coupled plasma source (ICP), capacitive coupled plasma source (CCP) and microwave electron cyclotron resonance (ECR). It is found that selectivity of PECVD is bad along with the further study of it. In addition, the SiON dielectric layer contains impurities unavoidably, for example, it will affect the insulation and dielectric properties if adding H atom into the dielectric layer, which can restrict application in large scale integrated circuit. Helicon wave plasma source (HWP) comes to the notice of many researchers because of its high density (about 1013 cm-3) at low pressure (0.1~10 Pa). Chen said that “Interest in helicon discharges stems from their unusually high ionization efficiency: plasma densities n achieved are almost an order of magnitude higher than in other discharges at comparable pressures and input powers.” During the discharge, high-energy electron collides with gas particle adequately. In this experiment, it can divide N2 into N2+ efficiently along with steady-state helicon wave discharge. In addition, there is no impurity element mixed in the SiON (such as C, H) which can improve the quality of the SiON films. In this experiment, SiON films were synthesized by nitridation on the surface of Si sputtered by N2/Ar helicon-wave plasma. During the mixed helicon-wave discharge, the mass flow ratio of N2 and Ar was different. X-ray photoelectron spectroscopy (XPS) showed that the SiON films were constituted of Si–O–N and Si–N. Atom force microscopy (AFM) indicated that the surface of the film was very flat and smooth, and the RMS was less than 1.2 nm. We collected Plasma discharge parameters by optical emission spectroscopy (OES) when the Si wafer was sputtered using N2/Ar helicon-wave plasma, and studied the relationship between the particle in the plasma and structure of SiON films.

Study on the ridge grooves deformation of double-ridged waveguide tube in rotary draw bending based on analytical and simulative methods

Cross sectional deformation of double-ridged waveguide tube easily occurs in rotary draw bending due to its structural features of hollowness, thin-wall and shape complexity. Particularly, the ridge grooves deformation would largely affect the transmission characteristics of double-ridged waveguide tube. Thus, using plasticity deformation theory, an analytical method to investigate the ridge grooves deformation is proposed, in which the ridge grooves deformation is considered to be resulted from three parts of deformation, including flange sagging, web deflection and variation of flange width. Then, the analytical method is verified by a FE model from various viewpoints. Finally, the contribution of every part to the ridge grooves deformation under different conditions is analyzed combining analytical and simulative methods. The results show that: (1) The contribution of flange sagging to the width deformation of outer and inner ridge grooves is usually far small and can be omitted. The web deflection results in the decrease of width deformation of outer ridge groove, but the variation of flange width increases that. The web deflection and variation of flange width all lead to the increase of width deformation of inner ridge groove. (2) With the increase of bending angle, the width deformation of outer ridge groove changes little while the absolute value of width deformation of inner ridge groove increases. When the bending radius decreases, the absolute value of width deformation of outer and inner ridge grooves all increase. With the increase of core number, the width deformation of outer ridge groove changes from shrinking to widening while there is no change for the width deformation of inner ridge groove.

(Invited) Gold Nanobridge Enhanced Fiber Optic Sensor

A wide variety of optical sensors have been used for gas detection. Hollow core waveguides have shown particular usefulness due to the larger interaction volume of the optical signal with the gas species through direct absorption instead the lower interaction volume of evanescent field spectroscopy. In particular porous capillary tube waveguides (PCTW) have been of particular interest because of their very fast response time. One limitation, in particular, is the increased loss due to the nearly free space transmission through the hollow core. PCTWs have been successfully tested on a variety of gases and across a wide temperature range by our group previously. In this paper, we present the results for a fiber optic sensor structure which is composed of gold nanobridges. The gold nanobridges are formed by coating the inside of a microcapillary glass tube with gold. The glass tube is phase separated and one of the phases is removed by a leaching process. This leaves a three dimensionally interconnected porous phase and a three dimensionally interconnected glass phase which is coated with gold. The structure was analyzed for topology and chemistry using a scanning electron microscope. SEM micrographs of the microcapillary tubes both before and after phase separation were obtained. In addition, EDAX was used to confirm the presence of the gold coating on the samples after the leaching process. The porous gold film was found to be composed of approximately 100nm ligaments in an interconnected network and the glass had approximately 30nm pores around these ligaments. The process to produce these gold coated nanoporous elements is abbreviated here due to word count restriction for this abstract. Porous capillary tubes were produced from a phase separable glass composition. This type of glass produces 3-dimensionally interconnected phases through a compositional phase separation process induced by heat treatment. Porosity is created when the secondary phase or soluble phase is removed by immersion in a dilute acid solution that dissolves and leaches out the secondary phase. Capillary tubes to be plated were drawn with an inner diameter of 170-220 µm and an outer diameter range of 400-500 µm. Dimensions were selected to provide an adequate ID for plating and then the insertion of the lead-in and lead-out fibers. Drawn capillary tubes were plated using a commercially available electroless gold plating solution. Plating was accomplished after fibers were annealed to induce phase separation in order to minimize thermal changes to the gold film that the necessary heat treatment would cause. The inner diameter of the capillary tube was coated by flowing the plating solutions through the tubes. Plating was carried out per the manufacturer’s directions with the exception that the solutions were in a flowing state compared to the static application recommended. Plating occurred in a three step process with the first step being a sensitizing solution, then a brief rinse, followed by a combined mixture of an activated gold salt and a reducing agent. Flow rates of the plating solution ranged from 0.5 mL/min-2mL/min depending on tube ID. After plating, the tube and gold film was air dried followed by acid leaching of the secondary phase. Optical transmission spectra were characterized over the spectral range from 1520-1570 using a commercially available spectrometer which contained a swept laser interrogator. A Micron Optics Si-720 Component Testing System (CTS) and SMF-28 lead-in and lead-out fibers were used in the transmission testing. The apparatus constructed for the transmission tests consisted of the CTS unit with the swept laser being used as the light source connected to a SMF optical fiber as the lead-in fiber. A MMF was used for the lead out fiber to the oscilloscope which was attached to a photodetector for detection. The transmission spectrums were studied as a function of the microcapillary tubing length. By comparing the transmission spectrums of the microcapillaries before gold coating and after gold coating, it was shown that the gold coated microcapillaries had higher transmission than the uncoated for each length studied. The gold coated nanobridge enhanced fiber optic sensor system was tested in a gas cell using acetylene gas. Test concentrations ranging from 10% Acetylene down to 100ppm were obtained using a Sierra Instruments gas mixing system. From the optical spectrums measured, it was shown that the absorption peaks associated with the acetylene gas are clearly visible in the optical spectrums. The absorption peak strengths were in the range from 5-10dB depending upon which line in the acetylene absorption spectrum one is considering and what the gas concentration was. Figure 1

(Invited) Gold Nanobridge Enhanced Fiber Optic Sensor

We report a method for improving the transmission of a porous capillary tube waveguide gas sensor by applying a thin metallic coating to the inside surface. Using commercially available electroless gold plating solutions and a simple pressure setup, gold thin films were plated on the inner diameter surface of the capillary tube. Nano-porous gold coating was produced during the leaching process used to make the phase separated glass tube porous. Transmission spectra were characterized and determined that to the porous gold coating on the porous glass contributed to signal improvement. Detection of acetylene gas was accomplished but at higher concentrations than uncoated porous capillary tube waveguide. Detection limitations were attributed to lower transmitted power due to optical alignment difficulties.

Electromagnetic analysis of the main and higher modes on the onion-like carbon tubes

ABSTRACTThe electric and magnetic field distributions as well as the dispersion characteristics of open cylindrical tube (hollow-core) waveguides are analysed in this work. The analysed waveguides are made of an onion-like carbon (OLC) material. The solution of the boundary problem was fulfilled by the partial area method. It was discovered the very complicated dependencies of the phase and attenuation constants on the waveguide radii. Such dependencies arise because the OLC material is the highly dispersive and absorbing one. The fundamental and four higher modes can propagate in our investigated waveguides. We have analysed the high-frequency cut-off frequency of modes that is dependent on the tube waveguide external radius. The certain electromagnetic (EM) mode can propagate only on the frequencies lower than the mentioned cut-off frequency. For this reason, this cut-off frequency has an important use in practical applications. We presented here the EM field distributions of modes. We discovered that it is possible to reach the one-mode regime of OLC tube waveguide at the certain external radius. The fundamental and first higher modes’ EM energy is concentrated in the OLC material between the internal and external surfaces of the waveguide.

3D-Printed Broadband Dielectric Tube Terahertz Waveguide with Anti-Reflection Structure

We demonstrate broadband, low loss, and close-to-zero dispersion guidance of terahertz (THz) radiation in a dielectric tube with an anti-reflection structure (AR-tube waveguide) in the frequency range from 0.2 to 1.0 THz. The anti-reflection structure (ARS) consists of close-packed cones in a hexagonal lattice arranged on the outer surface of the tube cladding. The feature size of the ARS is in the order of the wavelength between 0.2 and 1.0 THz. The waveguides are fabricated with the versatile and cost efficient 3D-printing method. Terahertz time-domain spectroscopy (THz-TDS) measurements as well as 3D finite-difference time-domain simulations (FDTD) are performed to extensively characterize the AR-tube waveguides. Spectrograms, attenuation spectra, effective phase refractive indices, and the group-velocity dispersion parameters β2 of the AR-tube waveguides are presented. Both the experimental and numerical results confirm the extended bandwidth and smaller group-velocity dispersion of the AR-tube waveguide compared to a low loss plain dielectric tube THz waveguide. The AR-tube waveguide prototypes show an attenuation spectrum close to the theoretical limit given by the infinite cladding tube waveguide.

A miniaturized fiber-optic colorimetric sensor for nitrite determination by coupling with a microfluidic capillary waveguide.

A microfluidic-capillary-waveguide-coupled fiber-optic sensor was developed for colorimetric determination of hazardous nitrite based on the Griess-Ilosvay reaction. The sensor was modularly designed by use of a light-emitting diode as the light source, silica fiber as the light transmission element, and a capillary waveguide tube as the light reaction flow cell. With the light interacting with the azo dye generated by the Griess-Ilosvay reaction between nitrite and Griess reagents, nitrite could be determined by a colorimetric method according to Beer's law. By use of the inexpensive and micro-sized elements mentioned above, the sensor provided a new low-cost and portable method for in situ and online measurement of nitrite. The sensor had a wide linear range for nitrite from 0.02 to 1.8 mg L(-1) and a low detection limit of 7 μg L(-1) (3σ), with a relative standard deviation of 0.37% (n = 10). With a low reagent demand of 200 μL, a short response time of 6.24 s, and excellent selectivity, the sensor is environmentally friendly and has been applied to nitrite determination in different water samples. The results were compared with those obtained by conventional spectrophotometry and ion chromatography, indicating the sensor's potential for practical applications.

Research on the temperature sensing characteristics of triple cladding quartz specialty fiber based on cladding mode resonance

A triple-cladding quartz specialty fiber (TCQSF) temperature sensor based on cladding mode resonance is made. The sensor is fabricated by just splicing a short, few-centimeter-long segment of TCQSF between two standard single-mode fibers (SMFs), so the sensor structure is simple. In order to explain its sensing principle in detail, we assume that the TCQSF is equivalent to three coaxial waveguides based on coupling mode theory. Utilizing the scalar method and the relationship between Bessel function and mode field distribution of step-index circular symmetry waveguide, the mode field distribution of these waveguides and their characteristic equation can be easily obtained. Then the dispersion curves of each mode which is transmitted in the three waveguides can be calculated. The intersection between the fundamental core mode LP01(rod) in the rod waveguide and the cladding mode LP01(tube) in the tube waveguide I indicates that the two modes have the same propagation constant, and satisfy the phase-matching condition when the wavelength is 1563.7 nm which is known the resonant wavelength. And only when the sensor length is equal to the beatlength, can the light be coupled completely from the core to the fluorine-doped silica cladding. Thus, the cladding mode resonance phenomenon occurs and a band-stop filter spectrum will be obtained. Then the sensor is applied to the simulation calculation of the temperature sensing characteristics. With increasing temperature, both the refractive index of each layer and the sizes of the axial and radial fibers will change, which will finally lead to a big difference on the dispersion curves of LP01(rod) and LP01(tube). Therefore, the resonant wavelength shift of the sensor can be obtained by just calculating the dispersion curves of these two modes at different temperatures, and the scope of curvature sensitivity is 70.76-97.36 pm/℃. Finally, a straight forward experiment is performed to prove the temperature sensing properties. Experimental results show that the sensor has a sensitivity in temperature of 73.74 pm/℃ at 35 ℃-95 ℃, which is completely consistent with the theoreticaly calculatied results. Thus, the proposed sensor has the advantages of simple structure, easy fabrication, highly sensitivity, controlled cladding mode excitation, and so on. It can be used in industrial production, biomedical and other temperature sensing areas.

Metallic and 3D-printed dielectric helical terahertz waveguides.

We investigate guidance of Terahertz (THz) radiation in metallic and 3D-printed dielectric helical waveguides in the frequency range from 0.2 to 1 THz. Our experimental results obtained from THz time-domain spectroscopy (THz-TDS) measurements are in very good agreement with finite-difference time-domain (FDTD) simulations. We observe single-mode, low loss and low dispersive propagation of THz radiation in metallic helical waveguides over a broad bandwidth. The 3D-printed dielectric helical waveguides have substantially extended the bandwidth of a low loss dielectric tube waveguide as observed from the experimental and simulation results. The high flexibility of the helical design allows an easy incorporation into bench top THz devices.

Terahertz transmission and sensing properties of microstructured PMMA tube waveguide.

A terahertz (THz) tube waveguide with grating structure has been designed, fabricated and characterized as a microstructure waveguide sensor. The resonance and polarization properties of this microstructured tube have been experimentally and theoretically investigated, which indicates that the grating etched on the tube surface has a remarkable modulation effect on the tube resonance and polarization dependence for THz waves. Moreover, a real-time quantitative sensing has been realized based on this tube waveguide in the THz time-domain spectroscopy system. Compared with the bare tube without grating, the grating structure strongly enhances the interaction between THz evanescent field on the tube surface and analytes, improving the sensitivity. This microstructured PMMA THz tube reveals a high sensitivity of 50GHz/μl and precision of larger than 0.125μl with a good linear relationship for THz sensing applications.

Terahertz low-loss hollow-core pipe waveguides

A low-loss terahertz (THz) hollow-core pipe waveguide constructed of plastic material is demonstrated. The structure is designed to be especially effective in transmitting THz waves of 110 GHz, which has important applications in communications, imaging, and sensing. Guiding of the electromagnetic wave is based on the principle of antiresonant reflection. Through careful theoretical analyses and systematic modeling and simulation, followed by a thorough experimental investigation, we show that the proposed structure can successfully transmit THz waves with low attenuation. Furthermore, when the structures of the pipe waveguides are varied for optimization, we find that cladding thickness and the refractive index under antiresonant conditions as well as the core diameter are important physical parameters in designing the low-loss THz waveguide. Considering not just attenuation loss but such factors as volume, weight, and flexibility of the tube waveguide, along with other practical issues such as cost, we arrive at an optimal design of the pipe waveguide, which has an inner diameter of 35 mm and cladding thickness of 5 mm. Teflon is chosen as the material for a guiding 110-GHz THz wave. The attenuation constant is determined by the simulation to be as low as 0.0228 m−1. However, due to nonuniformity of the waveguide wall thickness and random small bending of the waveguide, as well as moisture content in the air filling the pipe core, all of which strongly impede propagation in the waveguide, the experimentally measured attenuation loss (3.65 m−1) of the waveguide is much more significant than the theoretical prediction, with the latter serving as a design benchmark under perfect conditions.

Characteristics of GaAs PCSS triggered by 1 μJ laser diode

Various kinds of switches exhibit significant function in the field of pulse power. Among them Photoconductive Semiconductor Switch (PCSS) stands out because of its numerous advantages, such as low time jitter, fast response, high repetition rate, compact size, easy integration and so on. Laser Diode (LD) is small in size, low-cost and can be easily integrated compared with traditional laser devices. Waveguide tube is a kind of laser transmission device. By using LDs which emits laser pulse with a dominant wavelength of 905 nm and a waveguide tube, three different shapes of laser spot are obtained to trigger a semi-insulating GaAs PCSS which has vertical structure. Laser energy and laser power are fixed to 1 μJ and 33.3 W separately. As the illuminating area on the PCSS differs with different shapes of laser spot, the influences of average trigger energy per unit area to the output characteristics of the PCSS are studied. The experiment results demonstrate that not only the total trigger energy but also the energy density influences the characteristics of PCSS. This paper presents related experiment results, and some further discussions are given.

Quantification of landslide velocity from active waveguide–generated acoustic emission

Acoustic emission (AE) has become an established approach to monitor stability of soil slopes. However, the challenge has been to develop strategies to interpret and quantify deformation behaviour from the measured AE. AE monitoring of soil slopes commonly utilizes an active waveguide that is installed in a borehole through the slope and comprises a metal waveguide rod or tube with a granular backfill surround. When the host slope deforms, the column of granular backfill also deforms and this generates AE that can propagate along the waveguide. Results from the commissioning of dynamic shear apparatus used to subject full-scale active waveguide models to simulated slope movements are presented. The results confirm that AE rates generated are proportional to the rate of deformation, and the coefficient of proportionality that defines the relationship has been quantified (e.g., 4.4 × 105 for the angular gravel examined). It is demonstrated that slope velocities can be quantified continuously in real time through monitoring active waveguide–generated AE during a slope failure simulation. The results show that the technique can quantify landslide velocity to better than an order of magnitude (i.e., consistent with standard landslide movement classification) and can therefore be used to provide an early warning of slope instability through detecting and quantifying accelerations of slope movement.

Refractive index insensitive temperature sensor based on specialty triple-clad fiber.

A refractive index (RI) insensitive temperature sensor based on specialty triple-clad fiber (STCF) is proposed. Based on coupling mode theory, the STCF can be equivalent to a rod waveguide and two tube waveguides. Then the cladding mode resonance characteristic of STCF is analyzed by calculating different mode dispersion curves, which indicates that it works only on the mode resonance from core to the fluorine-doped silica cladding, and finally a resonance wavelength can be obtained. Two straightforward experiments are performed to prove its sensing properties. Experimental results show that it has sensitivities of 72.17 pm/°C at temperature range from 35°C~95°C with characteristics of insensitive to external RI in the range from 1.3450 to 1.4607. Thus, this proposed sensor can be used for solution temperature monitoring in real time.

Dielectric tube waveguides with absorptive cladding for broadband, low-dispersion and low loss THz guiding.

Research on terahertz waveguides is experiencing a tremendous growth due to their importance for compact and robust THz systems. However, designing compact, broadband, mechanically stable and environmentally shielded THz waveguides is still a challenge due to high losses of both metals and dielectrics in this frequency range. Here we report on a novel twist on the classical tube waveguide where we deliberately introduce a thick and highly lossy cladding layer. By this we attenuate the field in the cladding and thus prevent interference with the core field. This mechanism breaks the well-known ARROW guiding mechanism, and as a result, extremely broad bandwidth and low dispersion can be achieved with a very simple design. Since the main part of the field propagates inside the air-core, the propagation loss is still kept at a very low level. Simulations, analytical modelling and experiments verify our findings. The proposed THz waveguide is robust, insensitive to external perturbation and easy to handle, and thus the design represents a significant advance of the field of THz dielectric waveguides suitable for the 0.3–1 THz band which in the future will be important for ultrafast wireless communication systems.