Tube Waveguide Research Articles

Electrospinning and microwave absorption of polyaniline/polyacrylonitrile/multiwalled carbon nanotubes nanocomposite fibers

Electrical conductive nanocomposite fibers were prepared with polyaniline (PANI), polyacrylonitrile (PAN) and multi-walled carbon nanotubes (MWCNTs) via electrospinning. The morphology and electrical conductivity of the PANI/PAN/MWCNTs nanocomposite fibers were characterized by scanning electron microscope (SEM) and Van De Pauw method. Electrical conductivity of nanocomposite fibers increased from 1.79 S·m−1 to 7.97 S·m−1 with increasing the MWCNTs content from 3.0 wt% to 7.0 wt%. Compared with PANI/PAN membranes, the mechanical property of PANI/PAN/MWCNTs nanocomposites fiber membranes decreased. The microwave absorption performance of composite films was analyzed using waveguide tube, which indicated that with the thickness increasing the value of RL reduced from −4.6 to −5.9 dB.

Acoustic emission monitoring of a soil slope: Comparisons with continuous deformation measurements

Acoustic emission (AE) has become an established approach to monitor the stability of soil slopes. However, the challenge has been to develop strategies to interpret and quantify deformation behaviour from the measured AE. This paper presents the first comparison of continuous AE (measured using an active waveguide) and continuous subsurface deformation measurements. The active waveguide is installed in a borehole through a 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, generating AE that can propagate along the waveguide. This paper presents results from a field trial at a reactivated soil slope in North Yorkshire, UK. The measurements confirm that AE rates generated are directly proportional to the velocity of slope movement (e.g. the AE rate versus velocity relationship determined for a series of slope movement events produced an R2 value of 0·8) and demonstrate the performance of AE monitoring of active waveguides to provide continuous information on slope displacements and displacement rates with high temporal resolution.

Electromagnetic field and dispersion characteristic analysis of absorbing onion-like carbon tube waveguides

Here, we present our calculation results of the electromagnetic field distributions and the dispersion characteristics of open cylindrical tube waveguides. The analyzed waveguides are made of the onion-like carbon (OLC) material. The solution of the boundary problem was fulfilled by the partial area method (Nickelson et al. in electrodynamical analysis of open lossy metamaterial waveguide and scattering structures. InTech, UK, pp 27–58 [1]). We have determined the complex roots of the dispersion equation using of the Muller method. It 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. We have investigated the high-frequency cutoff frequency of the propagating hybrid modes HE11 and HE12 dependent on the tube waveguide external and internal radii. We found that it is possible to reach the one-mode regime of OLC tube waveguide.

Experimental study of air-core dielectric tube at terahertz frequencies

In this paper, an experimental study of air-core dielectric tube waveguide is proposed at terahertz frequencies. By using the THz time domain measure system, the terahertz dispersion characteristics, loss characteristic and energy focusing characteristic of air-core single-layer and dual-layer dielectric tube are obtained. The results show that this type of air-core dielectric tube can realize low dispersion characteristics. Due to the difference of refractive index between two dielectric materials, stronger energy focusing can be achieved in air-core dual-layer dielectric tube. After the coupling of the THz pulse using the dual-layer dielectric tube waveguide, the THz pulse increased 2.4 times compared with the single-layer dielectric tube waveguide at 1.5THz.

太赫兹波段折叠波导行波管的线性分析和计算

太赫兹波段折叠波导行波管的线性分析和计算

Theoretical study of air-core dielectric tube at terahertz frequencies

In this paper, the terahertz propagation characteristics of air-core dielectric tube waveguide, including air-core single-layer dielectric tube and dual-layer dielectric tube, are investigated by theoretical calculation. Due to the difference of refractive index between two polymer materials, stronger energy coupling can be achieved in dual-layer dielectric tube, and the field confinement is enhanced further. After the coupling of the THz pulse using the dual-layer dielectric tube, the THz pulse increased 5.2 times compared with the single-layer dielectric tube at 1THz. The ratio of power in polymers, air core and air cladding to the total power versus radiation frequency is presented, respectively. The dispersion and loss characteristic of the air-core dielectric tube is also demonstrated by using experimental method.

Relations between the stress components and cross-sectional distortion of thin-walled rectangular waveguide tube in rotary draw bending process

The significant cross-sectional distortion is one of the major problems in the bending of thin-walled rectangular waveguide tube. The cross-sectional distortion, which contains the flange distortion and the web distortion, depends on the stress components distribution. In this paper, the cross-sectional distortion characteristics are investigated using a three-dimensional finite element (FE) model. Results show that: the maximum flange distortion locates at the symmetric line; meanwhile, the maximum web distortion locates at the extrados ridge of the tube. The deformation zone of the tube can be divided into three sub-zones considering the loads and deformation, viz., the clamp die affect zone, the middle zone, and the mandrel/cores affect zone. Then the underlying relations between the cross-sectional distortion and the stress components are obtained. It is found that the flange distortion has a close relation with the circumferential stress. At the same time, the web distortion is relevant to both the tangential and the circumferential stress. The above relations are verified by FE models with different cores number. Moreover, some guidelines are introduced to help reduce the cross-sectional distortion.

Effects of geometrical parameters on wrinkling of thin-walled rectangular aluminum alloy wave-guide tubes in rotary-draw bending

Inner flange and side wrinkling often occur in rotary-draw bending process of rectangular aluminum alloy wave-guide tubes, and the distribution and magnitude of wrinkling is related to geometrical parameters of the tubes. In order to study the effects of geometrical parameters on wrinkling of rectangular wave-guide tubes, a 3D-FE model for rotary-draw bending processes of thin-walled rectangular aluminum alloy wave-guide tubes was built based on the platform of ABAQUS/Explicit, and its reliability was validated by experiments. Simulation and analysis of the influence laws of geometrical parameters on the wave heights of inner flange and side wrinkling were then carried out. The results show that inner flange wrinkling is the main wrinkling way to rectangular wave-guide tubes in rotary-draw bending processes, but side wrinkling cannot be neglected because side wrinkling is 2/3 of inner flange wrinkling when b and h are smaller. Inner flange and side wrinkling increase with increasing b and h; the influence of b on side wrinkling is larger than that of h, while both b and h affect inner flange wrinkling greatly. Inner flange and side wrinkling decrease with increasing R/h; the influence of h on inner flange and side wrinkling is larger than that of R.

Shielding Effectiveness Improvement of Metallic Waveguide Tube by Using Wall Losses

The metallic waveguide tubes are frequently placed in the walls of high performance shielded enclosures to provide air ventilation and strong electromagnetic interference attenuation simultaneously. However, a waveguide tube gives no attenuation for frequencies higher than its cutoff frequency. Also, there is a trade-off between the shielded frequency range and the airflow capacity, since the cutoff frequency is inversely proportional to the wave-guide radius. In this paper, the idea to shield frequencies above cutoff by coating the inner wall of waveguide tube with lossy material is investigated in detail. The attenuation constants of the TE11 mode in a lossy circular waveguide are calculated for lossy conductive, dielectric, and magnetic material, respectively. It is shown that lossy magnetic material can provide the strongest attenuation and high-shielding effectiveness for frequencies above cutoff. This work presents a promising approach to relax the frequency-airflow tradeoff.

Waveguide Tubes Coated With Inhomogeneous Lossy Materials for Superior Shielding Above and Below Cutoff Frequency

A new approach for enhanced electromagnetic interference shielding of metallic waveguide (WG) tubes coated with inhomogeneous lossy materials is proposed based on numerical simulation. Shielding enhancement is achieved by using stepped variations of complex permittivity and complex permeability coating materials along the WG transverse direction. Such variation in the coating layer provides multiple wave reflections below and above the WG cutoff frequency. The underlying principle is applied to a rectangular WG operating in the dominant TE10 mode. Simulation examples of rectangular WGs coated with uniform and stepped lossy materials are demonstrated. The proposed approach shows remarkably better performance when compared with WGs coated with uniform lossy materials.

Minimum Loss Condition of a Bent Rectangular Tube Waveguide

The leakage loss of a tube dielectric waveguide is analyzed analytically and numerically. A minimum loss condition of a bent rectangular tube waveguide is derived in terms of the ratio of refractive index of the tube to the other region using the transverse transmission-line model. The validity of the derived minimum loss condition is confirmed by the two- and three-dimensional beam-propagation methods.

Waveguiding mechanism in tube lattice fibers

Waveguiding mechanism and modal characteristics of hollow core fibers consisting of a single or a regular arrangement of dielectric tubes are investigated. These fibers have been recently proposed as low loss, broadband THz waveguides. By starting from a description in terms of coupling between air and dielectric modes in a single tube waveguide, a simple and useful model is proposed and numerically validated. It is able to predict dispersion curves, high and low loss spectral regions, and the conditions to ensure the existence of low loss regions. In addition, it allows a better understanding of the role of the geometrical parameters and of the dielectric refractive index. The model is then applied to improve the tradeoff between low loss and effectively single mode propagation, showing that the best results are obtained with a heptagonal arrangement of the tubes.

Fracture Cause Analysis and Improvement on Waveguide Tube of Satellite Calibration Antenna in Random Vibration

Satellite calibration antenna suffered rigorous vibration environment in the course of lunching. Random vibration is being specified for acceptance tests by spacecraft structure. The waveguide tube of antenna was cracked in the random vibration test. Fracture analysis using scanning electron microscopic showed that failure were induced by fatigue damage. Finite element model of antenna was built and root mean square (rms) stress of waveguide tube was obtained in random vibration analysis. The maximum rms stress was 35.6MPa and located at the flange base. Then fatigue life of waveguide tube was estimated, using the Palgren-Miner rule and the three-band method. The estimated fatigue life of 109 seconds showed the waveguide tube couldn’t ensure safety during 120 seconds of the random vibration. Finally two ribs were added at each flange base for decreasing the stress concentration. The fatigue life of improved waveguide tube was 811 seconds. Then it passed the random vibration test.

A miniaturized spatial temperature gradient capillary electrophoresis system with radiative heating and automated sample introduction for DNA mutation detection

A miniaturized spatial temperature gradient CE system with automated sample introduction for DNA mutation detection was established. Continuous electrokinetic sample injection was achieved by combining an automated slotted-vial array sample introduction device to the spatial temperature gradient CE system. The temperature gradient was produced by a radiative heating system with a single graphite block heater, and the stability of the temperature gradient was investigated. The temperature variation of each measure point was 0.12-0.21% RSD (n=7) within 6 h. A 14-cm Teflon AF-coated silica capillary was used both as the separation channel and as the liquid-core waveguide tube of fluorescence signal. Under a temperature gradient from 54.8 to 59.5°C, a low range control mutation standard (209 bp) was separated within 4 min with only 5.6 nL sample consumption. Automated continuous sample introducing and changing were realized with a carryover of 3.3%. Utility of the system was further demonstrated by detecting K-ras gene mutations in paraffin tissue sections from two colorectal cancer patients.

Direct Simulation of Reed Wind Instruments

��� The synthesis of sound based on physical models of wind instruments has traditionally been carried out in a variety of ways. Digital waveguides (Smith 1986; Scavone 1997; van Walstijn and Campbell 2003; van Walstijn 2007) have been extensively explored, especially in the special cases of cylindrical and conical tubes, in which case they yield an extreme efficiency advantage. A related scattering method, wave digital filtering (Fettweis 1986), is also used to connect waveguide tube models with lumped elements such as an excitation mechanism (Bilbao, Bensa, and Kronland-Martinet 2003) or toneholes (van Walstijn and Scavone 2000). Another body of techniques, closely related to digital waveguides, and based around impedance descriptions, has been developed recently (Guillemain 2004). Other techniques, employing finite-difference approximations to the reed model (as opposed to wave- and scattering-based methods) bear a closer resemblance to the direct simulation methods to be discusssed here (Avanzini and Rocchesso 2002; van Walstijn and Avanzini 2007; Avanzini and van Walstijn 2004). Most of these methods owe a great deal to the much earlier treatment of self-sustained musical oscillators by McIntyre, Schumacher and Woodhouse (1983). All of these methods rely, to some degree, on simplified descriptions of the resonator (tube). For example, digital waveguides make use of a traveling wave decomposition, accompanied by frequencydomain (impedance or reflectance) characterizations of lumped elements or phenomena such as bell radiation and tone holes. Other methods make use of the Green’s function or impulse response of the tube directly (McIntyre, Schumacher and Woodhouse 1983). These methods are, in the end, implemented in the time domain, but the notion of the spatial extent of the tube is suppressed: The system is viewed in an input–output sense. When it comes to sound synthesis, however, it is not clear that it is necessary to do so; once one has arrived

Effect of backward radiation of electromagnetic waves by a metamaterial waveguide structure

The anomalous properties of electromagnetic radiation from an antenna in the form of a rectangular section waveguide tube made of a metamaterial with the negative real parts of permittivity and permeability have been demonstrated. The metamaterial is an isotropic two-dimensional array of left and right-twisted coils placed on a thin polyurethane substrate. The coils of the sample are directed in equal numbers along the x, y, and z axes. The possibility of the preferential backward radiation of the structure has been shown on the basis of numerical calculations with the use of the method of moments and the measurements of the radiation pattern of the antenna in an anechoic chamber at frequencies close to the 3-GHz resonance frequency of the metamaterial. The causes and existence conditions of the effect have been revealed.

Application of Novel Ultrasonic Cleaning Equipment Using Waveguide mode for Post-Chemical-Mechanical-Planarization Cleaning

In this paper, we propose the application of novel ultrasonic cleaning equipment using a waveguide mode, which we called the Megatube, to post chemical mechanical planarization (CMP) cleaning. Waveguides can be created in a curved shape, and ultrasonic waves of 1 MHz, within the megasonic frequency range, can propagate along such waveguides. It is possible to supply ultrasonic waves at a distance from the equipment, which has the advantage of enabling ultrasonic emission in a narrow space. For single-wafer processing, this technique has the advantage of removing particles, known as slurry residues, from both the front and back sides of the wafer by exposure to ultrasonic waves of megasonic frequency. In the Megatube, cavitation is generated by controlling the input power and the dissolved gas concentration. Particle removal efficiency (PRE) using the Megatube was evaluated for various input powers, waveguide tube lengths, and concentrations of dissolved gas in a cleaning solution.

Acoustic wave transmission in time-varying phononic crystals

Phononic crystal effects are typically narrowband and highly dependent on the size andspacing of the scatterers within the crystal—properties that are fixed and unchangeable.We propose that it may be possible to dynamically alter the behaviour of phononic crystalsby varying the material properties in time. In this paper we seek to extend the existingstatic phononic crystal theory so as to handle time-varying material parameters and also toprovide insight into the factors that govern their behaviour. Beginning with thetransmission matrix method, we develop a new method to determine the acousticwave transmission through a time-varying corrugated tube waveguide, which isanalogous to a one-dimensional (1D) phononic crystal. These expressions arefurther developed for periodic material parameter variation signals. Our methodpermits the development of a closed-form solution to the acoustic wave transmissionthrough a 1D time-varying phononic crystal. It shows excellent agreement withfinite-difference time-domain simulations and with execution times several orders ofmagnitude faster. Preliminary results show that the band-gap properties can besignificantly altered using material parameter time variation as the driving mechanism.

Characterisation of RF propagation in metal pipes for passive RFID systems

In this paper we extend the theory of Radio Frequency (RF) propagation as it relates to propagation within metal circular pipes. This work is motivated by a need to understand the operation of UHF Radio Frequency IDentification (RFID) systems when the tags are placed within the pipes. These circular pipes are shown to be similar to metal tube waveguides which are hollow. We derive the Bessel function that is used to identify the propagation constants, the different transverse electric and transverse magnetic modes, cut-off frequencies and the multimode attenuation. These parameters are used within the theory to identify operating limitations of passive RFID systems in hollow metal pipes. A comprehensive general theory is developed to enumerate the workings of passive RFID systems in circular metal pipes. Analytical evaluations are used to visualise the tags within the metal pipes and to validate the theory presented in this paper.

Acoustic emission monitoring of slope instability: development of an active waveguide system

This paper introduces the concept of using active waveguides as part of an acoustic emission monitoring system for assessing the stability of soil slopes. In soil, acoustic emissions are generated by inter-particle friction, and hence the detection of acoustic emission is an indication of straining. The components of a field monitoring system are introduced, and the factors controlling design and performance of waveguides are discussed. It is proposed that active waveguides (i.e. those that generate acoustic emission when deformed by the host soil) can be used as an efficient method of obtaining signals from depth within a deforming soil body. The results of laboratory tests conducted to validate the active waveguide model are presented. The role played by the soil surrounding the steel tube waveguide is highlighted. Results from two full-scale field trials that involved monitoring unstable slopes provide evidence for the relationship between detected acoustic emission and slope deformation rate. It is shown that active waveguides in conjunction with relevant signal processing methods can be used to provide an early indication of slope instability.