Tube Waveguide Research Articles

Mathematical modeling of the technological process of twisting a waveguide

Twisted waveguides are part of waveguide paths of antenna- feeder devices of spacecraft. They have high requirements for accuracy and reliability. They are made of profiled rectangular pipes. The twisting of waveguide pipes with a cross- sectional size of less than 11x5.5 mm is carried out in the device using a rigid calibration mandrel. The calculation method determined the main parameters of the technological process of twisting the waveguide tube (torque M, drawing force Pпр). When twisting workpieces with cross sections according to GOST, the torques (M) and drawing forces (Pпр) from the cross- section sizes vary according to a nonlinear relationship. Twisting the workpiece from M4 requires less torque (M) and drawing force (Pпр) than for the workpiece from M1. By mathematical modeling, it is possible to select the optimal technological mode in advance, thereby ensuring high quality of waveguide twisting manufacturing. To substantiate the calculation results, the methods of control of technological parameters and quality control of the product manufacturing were considered. A problem has been found in measuring the torque and pulling force when twisting the workpiece. Therefore, the pulling force should be measured from the machine. A method for measuring torque using a non- contact torque sensor is proposed. The manufacturing quality is supposed to be carried out by the STRESSVISION mechanical stress scanner, and electrical tests.

Optical profile: A key determinant of antibacterial efficacy of photodynamic therapy in dentistry

BackgroundPeriodontal disease effects 20–50% of the population worldwide, posing a global health challenge. It has been reported to be more prevalent among adults. Actinobacillus actinomycetemcomitans (A. actinomycetemcomitans) is an important organism associated with localized juvenile periodontitis. Photodynamic therapy (PDT) has been widely utilized for the treatment of periodontal disease; however, the effect of laser (light) profile on the antibacterial efficacy of PDT remains to be established. The quantitative measurement of laser profile is required to confirm the in vitro efficacy of PDT. AimIn the present study, a low cost PDT system comprising of six copper tube waveguides (CTW) was developed to provide more uniform irradiation of the culture plate. MethodsThe antibacterial effect of PDT, in combination with 200 μg/mL methylene blue (MB) as photosensitizer and 60 sec of irradiation, was studied on A. actinomycetemcomitans and Streptococcus mutans (S. mutans). In the present case, 660 nm laser guided with unpolished CTW, polished CTW, and optical fiber waveguide (OFW) provided radiant exposure of 0.86, 1.38, and 1.36 J/cm2, respectively, for a 24‐well culture plate. ResultsThe designed PDT system provided antimicrobial efficacy of 98% and 91% for A. actinomycetemcomitans and S. mutans, respectively, which was significantly higher as compared to OFW guided PDT. ConclusionThe results of the study highlighted the importance of laser profile as a key parameter that determines the survival rate of bacteria at the edge of the culture plate. Thus, the dose of PDT at the margin of optical profile is important for antibacterial activity for in vitro evaluation.

Pressure measurements in detonation engines

The influence of waveguide tubes on the signals received by remote pressure sensors measuring pressure histories in pulsed detonation engines (PDEs) and rotating detonation engines (RDEs) is studied computationally. Two types of pressure sensors are considered: low-frequency static pressure sensors and high-frequency sensors of pressure pulsations. Three approaches to solving the problem are used: based on Euler (inviscid flow), Navier–Stokes (laminar flow), and unsteady Reynolds-averaged Navier–Stokes (turbulent flow) equations. The approaches based on the inviscid and laminar flow models are shown to provide the best predictive capability. The laminar flow model is applied to analyzing the readings of pressure sensors installed remotely in the waveguide tubes attached to the hydrogen-fueled PDE, RDE, and detonation ramjet (DR). It is shown that the measurements of static pressure and pressure pulsations by remote pressure sensors do not correspond to the time-averaged mean and local instantaneous values of pressure in the combustors. The pressure time histories can be recovered based on the measurements and computational fluid dynamics calculations of the operation process. The latter is demonstrated by analyzing the results of test fires with a dual-duct DR model.

Multi-layer hollow-core PMMA grating tube waveguides for THz sensing applications

Multi-layer hollow-core PMMA tube waveguides with varying grating structures were theoretically and experimentally investigated for the terahertz (THz) chemical material sensor applications. Compared with single-layer tube, the multi-layer cases can produce a delayed response in the time domain with an improved extinction ratio. A double tube combination consisted of a thick double-groove chirped grating tube and a thin single-groove chirped grating one can realize an improved detection sensitivity. With different extinction ratio of the measured THz spectra, ethanol and vinegar can be distinguished with a sensitivity of about 18 dB/mL. The proposed multi-layer hollow-core grating waveguide can be further applied for the THz gas sensing applications.

Shear wave dispersion analysis of incompressible waveguides.

A suite of methodologies is presented to compute shear wave dispersion in incompressible waveguides encountered in biomedical imaging; plate, tube, and general prismatic waveguides, all immersed in an incompressible fluid, are considered in this effort. The developed approaches are based on semi-analytical finite element methods in the frequency domain with a specific focus on the complexities associated with the incompressibility of the solid media as well as the simplification facilitated by the incompressibility of the surrounding fluid. The proposed techniques use the traditional idea of selective reduced integration for the solid medium and the more recent idea of perfectly matched discrete layers for the surrounding fluid. Also, used is the recently developed complex-length finite element method for platelike structures. Several numerical examples are presented to illustrate the practicality and effectiveness of the developed techniques in computing shear wave dispersion in a variety of waveguides.

Highly stable in-fiber integrated silica microresonator

We demonstrate a compact in-fiber integrated microresonator based on a silica microsphere and microstructure fiber. Whispering-gallery-modes (WGMs) are effectively excited through evanescent field coupling between the silica microsphere and one of the input tube waveguides of negative curvature fiber. The WGM spectrum with the Q-factor of ∼2.56 × 103 and the extinction ratio of ∼15.2 dB is achieved. The transmission spectra evolution for 5 h reveals the long-term stability of WGM excitation. The experimental results indicate that the in-fiber integrated resonator has the advantages of high stability, high integration, robustness, alignment-free assembly structure, and low cost, motivating potential applications in the lab-in-fiber platform.

Plastic bending of the waveguide tubes with rectangular cross-section

This paper focuses on a new mathematical model of plastic bending of waveguide tubes with rectangular cross-section. The analysis of the known approaches and decisions is carried out, their shortcomings are shown and a new model of a thin-walled waveguide on the basis of the theory of plates and shells is offered. The solution is obtained by combining the semi-inverse Saint-Venant method and Airy functions. The received solution allows to generalize the available private solutions and have good agreement with known private empirical dependences for a plastic bending of tubes with rectangular cross-section.

Design and coupling characteristics of terahertz dual-core anti-resonant fiber

The THz wave has good photonic and electronic properties, and has high penetration for non-polar materials, but its own photon energy is low. In addition, the THz wave also has characteristics such as wide bandwidth and large communication capacity, thereby making the THz wave possess important academic value and wide application prospects in the fields of non-destructive testing, biomedical imaging and communication. The development of THz technology requires not only high-performance THz waveguide technology for efficient transmission of THz waves, but also important optical devices such as optical switches, modulators, and couplers that are suitable for THz bands. With the in-depth study of THz waveguide technology, researchers have proposed many high-performance THz waveguide structures, such as metal hollow core tube waveguide, parallel metal plate waveguide, photonic crystal fiber and microstructure hollow core fibers, among which hollow-core photonic crystal fibers and hollow-core anti-resonant fibers (HC-ARF) have developed rapidly in recent years. So far, THz single-mode single-polarization fiber and high-birefringence fiber have been widely studied, but the researches on the fiber structure and devices that realize THz wave directional coupling are relatively rare. In this paper, we study the influences of the arrangement and distribution of the inner and outer claddings of HC-ARF on transmission characteristics, and thus design a new type of THz dual-core anti-resonant fiber. Compared with ordinary quartz fiber couplers and dual-core photonic crystal fibers, it can utilize a relatively simple structure and achieve directional coupling above 2 THz. Using the finite element analysis method to theoretically analyze the loss characteristics and coupling characteristics of the fiber, it is found that HC-ARF changes the periodic arrangement and distribution of the inner cladding tube within a certain range, which can achieve mode leakage without affecting the fiber transmission characteristics. So the THz dual-core anti-resonant fiber can be designed by using the mode leakage coupling mechanism. By changing the core distance and core gap size, the directional coupling with a coupling length of 0.72 m is realized at a transmission frequency of 2.5 THz. This terahertz dual-core anti-resonance fiber will have an important application value in terahertz optical devices such as terahertz optical switches, modulators and couplers.

Thin-wall cyclic olefin copolymer tube waveguide for broadband terahertz transmission

A thin-wall cyclic olefin copolymer (COC) tube terahertz (THz) waveguide was proposed and fabricated for broadband terahertz transmission. A dynamic coating method was developed to prepare highly uniform COC tube waveguide samples with an inner diameter of 2.8 mm and three different wall thicknesses from 33.0 to 58.6 μm. The resonant frequencies and transmission bandwidths were measured by the THz time domain spectroscopy and proven to be adjustable by the wall thickness of the COC tube waveguides. The measured minimum losses of the waveguide sample with the wall thickness of 58.6 μm for the straight and bending transmissions are 0.10 dB/cm and 0.18 dB/cm at 1.05 THz, respectively.

Forming quality of thin-walled rectangular waveguide tube during small-radius rotary draw bending under different push assistant matching conditions

In the small-radius rotary draw bending (RDB) process of thin-walled rectangular tubes, push assistant matching consisting of pressure die and booster die is proposed to improve the forming quality of tube in this paper. Based on ABAQUS platform, the reliable 3D-FE models without and with booster die were established, and the cross-sectional deformation and wall thickness variation under different push assistant levels were analyzed. The results show that: (1) Adding the booster die or increasing push assistant level can reduce the cross-sectional deformation and wall thinning ratio of tube during small-radius RDB process. (2) The influence of adding the booster die or increasing push assistant level on the cross-sectional deformation in mandrel support zone (MSZ) is smaller than that in non-mandrel support zone (NMSZ), while the influence of that on wall thickness variation is opposite. (3) Increasing the push assistant level not only results in the variation of deformation degree of tube, but also makes the distribution zone of wall thickness thinning and thickening changed. Besides, the reasonable push assistant matching conditions are obtained.

Dependence of Waveguide Properties of Anti-Resonant Hollow-Core Fiber on Refractive Index of Cladding Material

Anti-resonant hollow-core fiber is featured by the broadband and low-loss transmission of light in the hollow core thanks to the optical property of anti-resonance cladding design. In this paper, we numerically explore the antiresonance of cladding from a new angle and confirm unique and important roles of refractive index of cladding material played in the confinement, bend and material losses of modes in anti-resonant hollow-core fibers. The numerical simulations demonstrate the dependence of confinement loss in anti-resonant hollow-core fiber on the cladding material refractive index which differs from the capillary waveguide and 1.5 refractive index is found favorable to achieve the lowest confinement loss ever in anti-resonant hollow-core fiber. Meanwhile, higher material refractive index can more effectively mitigate the material absorption and consequent contribution to the overall fiber loss in the anti-resonant hollow-core fiber than in the tube waveguide, by reducing the modal overlap factor. Besides, to the best of our knowledge, it is for the first time to discover that the modal dispersion of anti-resonant hollow-core fiber can be effectively altered by the cladding material refractive index, which was usually regarded to be determined by the core dimension and filled-in gas only. The refractive index around 1.8 is preferred to achieve a flattened profile of group dispersion over the transmission spectral window in anti-resonant hollow-core fibers. Our results bring in a new perspective to investigate the guidance mechanism of anti-resonant hollow-core fibers and provides guidance for material selection in the fiber design for optimization of waveguide properties.

Broadband Acoustic Vibration Sensor Based on Cladding-Mode Resonance of Double-Cladding Fiber

We have proposed and demonstrated a double-cladding fiber (DCF) with cladding-mode resonance property for broadband acoustic vibration sensing. Since the fundamental mode in the core waveguide is able to be coupled to LP05 mode in the tube waveguide once the phase-matching condition is fulfilled, the transmission spectrum can exhibit a dip with a large extinction ratio. An acoustic vibration could induce the wavelength shift of such transmission spectrum, so that the intensity variation at a wavelength near the dip is coded with the information of the acoustic vibration signal. By demodulating the response of intensity variation, the frequency of the applied acoustic vibration signal can be recovered. Such a DCF-based sensor with an intensity modulation could measure the acoustic vibration with a broadband frequency range from 1 Hz to 400 kHz and exhibits the maximum signal-to-noise ratio (SNR) of ~80.79 dB when the vibration frequency is 20 kHz. The obtained results show that the proposed DCF-based acoustic vibration sensor has a potential application in environmental assessment, structural damage detection, and health monitoring.

Double-groove terahertz chirped grating waveguide tube for gas pressure detection

A PMMA grating waveguide tube-based terahertz (THz) gas pressure sensor was developed, and the transmission properties were investigated experimentally and theoretically. A double-groove chirped grating structure with a gradient etching depth was adopted to enhance the extinction ratio and improve the detection sensitivity. Nitrogen pressure detection was realized and compared between the tube waveguides with and without the grating structure by a THz time-domain spectroscopy system. The results indicate that a better extinction ratio and detection sensitivity can be realized with the double-groove chirped grating waveguide tube, which can achieve a pressure detection sensitivity of 26.33 dB MPa−1. The presented double-groove chirped grating waveguide tube with a gradient etching depth is expected to have wide application prospects for THz gas sensing applications.

Electric Field and Dispersion Characteristic Calculations of Glass Tube Waveguides Filled with Biological Substances

This study presents calculation of dispersion characteristics in the frequency range 1–100 GHz as well as electric field distributions in an open cylindrical waveguide with a central channel. The waveguide is made of glass material. The channel can be either empty or filled with blood plasma or blood cells. We investigated two kinds of electromagnetic (ЕМ) waves, the “tube” and “core” modes, each having a different structure of their electric fields. In the current study, the analysis focused on the fundamental and the first higher hybrid magnetic and electric “tube” modes. The fundamental “tube” mode that propagates in the waveguide filled with blood plasma is characterized by a very small loss at frequencies above 65 GHz. Meanwhile, the first higher mode suffers from strong attenuation in the same frequency range. This calls for finding ways to improve the waveguide’s broad-bandwidth. Our approach involves determining the dependence of this parameter on the inner radius of the waveguide. Extremes of the waveguide’s broad-bandwidth are observed at certain values of its inner radius. When the waveguide is filled with blood plasma or blood cells, the electric fields of the magnetic “tube” mode concentrate around the channel, and the electric field intensity decreases with the propagation of this mode along the waveguide, i.e., with increase of coordinate z. If the channel is filled with blood cells, the electric field of the hybrid magnetic “core” mode is concentrated in the center of the waveguide. This mode is characterized by a large attenuation h”, which reaches 500 m−1 at 30 GHz.

Modulation of the SPP wave in helical metal waveguide by geometry phase

This paper introduces a new way to modulate the surface plasmon polariton (SPP) wave, that is, the use of geometric phase modulation. A silver tube waveguide is designed to generate a geometric phase when the waveguide is wound into a solenoid. We use intuitive physical images instead of geometric formulas to obtain the geometric phase. The eigenfunctions of SPP in the helical waveguide are obtained theoretically. In order to exhibit the geometric phase effect, an ideal experiment is proposed, and the modulation of the energy flux of the 1st mode by the geometry phase is calculated.

Nonlinear coupling of photons via a collective mode of transparent superconductor

At the first glance, the expression "transparent superconductor" may seem an oxymoron. Still, the first principle calculations and experiments show that the materials that behave as superconductors at low frequencies and do not absorb in the optical domain may exist. Virtual excitation of the collective electronic modes of such superconductors in a magnetic field appears as an efficient way to realize the nonlinear interaction of light at the level of two single photons. The essence of the effect is in the fact that the pondermotor energy is proportional to the ratio of the charge squared to the mass of the "collective particle" interacting with radiation, $e^2/m$, and therefore, for a "particle" representing a collective motion of many electrons, it scales linearly-, and its second-order correction quadratically with the number of the electrons involved. This general situation is analyzed in detail in the framework of a simple model of a fiber tube waveguide equipped with a clean superconductor layer. It turns out that for realistic parameters, at the micron-scale of the tube diameter and the centimeter-scale of the fiber length, such a system is capable of performing the logic gate operation on the polarization variables of a pair of optical photons.

Linear analysis of traveling sheet electron beam in sine waveguide tubes

A theoretical model is proposed for linear analysis of the beam–wave interaction in a sine waveguide (SWG) with slow-wave structure. The field expressions and “hot” dispersion equation are obtained by means of field matching. The ohmic loss and attenuation constant due to imperfect conductors are also derived using the theoretical model. Moreover, the effects of voltage, current, beam thickness, period, and oscillation amplitude on the linear gain and bandwidth are calculated. The results indicate a peak gain and 3-dB bandwidth of 6.82 dB/cm and 19.5%, respectively, for a 0.22-THz SWG traveling-wave tube upon selecting reasonable structural parameters and electron-beam dimensions. Furthermore, by considering the ohmic losses for the finite conductivities of 5.8 × 107 S/m and 2.2 × 107 S/m, the theoretical results are compared with those of particle-in-cell simulations performed using Computer Simulation Technology Particle Studio.

Direct fabrication of metal tubes with high-quality inner surfaces via droplet deposition over soluble cores

Droplet-based 3D printing is very promising for the fabrication of complex thin-wall microwave devices such as antenna horns and waveguide tubes since it can print a shell by utilizing only several layers of droplets. However, due to the naturally scalloped shape of metal droplets, conventional droplet-based 3D printing methods cannot produce thin-wall tubes with high-quality inner surfaces that can meet the requirement of electromagnetic transmission. Here, combining the conventional casting procedure and droplet printing, a hybrid printing process is proposed. Uniform aluminum droplets were first rotationally deposited on a soluble core, and then the core was dissolved and left behind a tube with a high-quality inner surface. The deposition parameters (i.e., number of layers and deposition frequency) were adjusted according to the rotation of the core to form a dense shell over its surface. A hexagonal metal tube was fabricated by using the proposed method to prove its effectiveness. The standard Archimedes test shows that the density of the formed part was up to 98.89%. The industrial CT scanning results also prove a porosity-free inner structure. The inner surface roughness (Ra) was measured to be 4.38 μm by using a laser confocal microscope scanning, and the roughness is only 0.37% of the droplet diameter.

Uniform Field Resonators for EPR Spectroscopy: A Review.

Cavity resonators are often used for electron paramagnetic resonance (EPR). Rectangular TE102 and cylindrical TE011 are common modes at X-band even though the field varies cosinusoidally along the Z-axis. The authors found a way to create a uniform field (UF) in these modes. A length of waveguide at cut-off was introduced for the sample region, and tailored end sections were developed that supported the microwave resonant mode. This work is reviewed here. The radio frequency (RF) magnetic field in loop-gap resonators (LGR) at X-band is uniform along the Z-axis of the sample, which is a benefit of LGR technology. The LGR is a preferred structure for EPR of small samples. At Q-band and W-band, the LGR often exhibits nonuniformity along the Z-axis. Methods to trim out this nonuniformity, which are closely related to the methods used for UF cavity resonators, are reviewed. In addition, two transmission lines that are new to EPR, dielectric tube waveguide and circular ridge waveguide, were recently used in UF cavity designs that are reviewed. A further benefit of UF resonators is that cuvettes for aqueous samples can be optimum in cross section along the full sample axis, which improves quantification in EPR spectroscopy of biological samples.

Application of Ray Model for Terahertz Transmission Simulations of Tube Waveguide

Terahertz (THz) transmission simulations play an important role in THz technology researches, especially for the structural design of a THz waveguide. Ray model takes into account both structure parameter of waveguide and the divergence angle of beam light and could be an alternative way for THz transmission behavior simulations. In this paper, the ray model is used to calculate the transmission loss of tube waveguide, and the simulated transmission losses are presented to compare with the results calculated by COMSOL. The suitable THz frequency range of ray model is discussed by analyzing the transmission loss spectra of tube waveguides with various core sizes. The credibility of ray model on terahertz transmission simulations is demonstrated based on the experimental results tested by THz-TDS and calculated results.