Coaxial Feed Research Articles

Powder-flow behavior and process mechanism in laser directed energy deposition based on determined restitution coefficient from inverse modeling

In order to clarify the transportation mechanism of particles in continuous coaxial powder feeding (CCPF) process, a trial-and-matching method is developed to quantify the restitution coefficient which is used to describe the inelastic collision between the particle and the nozzle wall. The consistency of the outlet velocity and the spatial concentration distribution of particles between the experimental statistic and the numerical calculation shows that the restitution coefficient of 0.9 can be used to measure the inelastic collision behavior between particles and the nozzle wall. Employing the determined restitution coefficient, a semi-quantitative method based on optical diagnostic and quantitative analysis derived from numerical calculation are proposed to study the powder-gas flow transport characteristics from single-layer to multi-layer jet flow. It is found that the outer shielding gas flow (OSGF) has a great influence on the multi-layer jet flow field, and it is most conducive to powder focusing at the OSGF of 20 L/min. The velocity distribution of CGF determined by the inner structure of CCPFN and the inelastic collision between the particle and the wall are the two mutually coupled factors that determine the outlet velocity of particles. Frequent inelastic collisions and the decrease of the CGF velocity lead to velocity dispersion and trajectory fluctuation of particles. When the inlet velocity of particles is 1.33 m/s, the outlet velocity ranged from 0.4 m/s to 0.9 m/s. This paper aims to provide a general method to determine the restitution coefficient and offer a comprehensive understanding of transportation mechanism of power particles both inside continuous coaxial powder feeding nozzle (CCPFN) and multi-layer jet zone between substrate and the CCPFN outlet.

A Low Profile Microstrip Patch Antenna using a Polygon-Shaped Patch for Wireless Applications.

In this paper. a low profile microstrip patch antenna is presented. The FR4 substrate is chosen for the dielectric substrate with a height of 1.6 mm. The presented antenna employs a polygon-shaped patch as the radiator for operating at 2.4 GHz. Co-axial feed is selected to excite the resented antenna to retain the low profile property of the antenna. The simulated results of the proposed antenna were analyzed and the structure of the proposed antenna was validated through fabrication results. The vector network analyzer is used to measure the real-time return loss property of the presented antenna.

Wearable Dual Polarized Electromagnetic Knee Imaging System.

With the increasing uptake of sport activities, onsite detection of associated knee injuries at early stages is in high demand to avoid severe ligament tear and long treatment period. Portable electromagnetic imaging (EMI) systems have the potential to meet that demand, but there are challenges. For example, EMI is based on the contrast in the dielectric properties due to the accumulated fluid after knee injury. However, that fluid can be in any shape and orientation. Therefore, to capture enough data for processing, EMI should operate as a dual-polarized wearable system with compact antennas. Thus, the proposed system is a textile brace worn on the knee and consists of an 8-element dual-polarized aperture antenna array, which is matched with the knee. Each of the utilized antennas is fed by two orthogonal coaxial feed, occupies a small size of 36 ×36 ×3.1 mm3, and is backed by a full ground plane for unidirectional radiation. The antenna covers the band 0.7-3.3 GHz (130%), with front to back ratio of more than 10 dB. The textile wool-felt is used as the substrate to enable building flexible brace system. The system's capability to reconstruct knee images with different injuries is verified on realistic knee models and phantoms. The double stage delay, multiply and sum algorithm (DS-DMAS) is used to reconstruct those images, which demonstrate the efficiency of the dual-polarized system and its superiority over single-polarized systems.

Parallel-Plate Waveguide-Feeding Structure for Planar-Connected Arrays

A novel approach for the practical realization of the feeding lines in connected array of slots is presented. The proposed feed concept is based on a parallel-plate waveguide (PPW) structure and allows simplifying the unit cell design. When compared to the typical integrated coaxial feed, the PPW-based feeding structure can reduce the cost and complexity of the array, by resulting in a lower number of metal layers and by allowing for large diameter vias. Two examples of the unit cell design, based on this new feed concept, are presented; one consists in a single-polarized array of connected slot, covering the band from 70 to 140 GHz; another example is referring to a single- and dual-polarized connected slot array covering the 2–8 GHz range.

Investigation of deposition welding in vertical and horizontal position with a coaxial laser wire welding head

Deposition welding of components using the laser metal deposition (LMD) process is a proven method of creating 3D structures. It is used for the manufacturing of components, the repair of machine parts and for cladding. Up to now, claddings have mainly been investigated in the flat welding position. Some investigations on deposition welding in vertical orientation are available with different processes. For the cladding of large components, welding in the vertical direction offers advantages. So far, there are no investigations on the LMD process with coaxial wire feeding when welding in vertical direction. Therefore, in this study, the influence of the welding direction, i.e., vertical down and vertical up weld seams, and the influence of the welding speed are investigated. Single weld seams, claddings and a wall are welded. A stable welding process could be achieved for a welding speed parameter window of 100 to 1000 mm/min. The results show that there is a statistical correlation between the welding direction and the waviness of the weld seams. Vertical up weld seams have a lower waviness. Another influence on the waviness is the welding speed. As the welding speed decreases, the waviness increases. The weld seam geometry is strongly dependent on the welding direction. With vertical down weld seams, the width and height of the weld seam vary depending on the distance welded. This can be attributed to the influence of the gravitational force. Vertical up weld seams, on the other hand, have a more uniform shape.

A low profile single feed compact dual-band penta-polarization agile microstrip antenna for interference mitigation in point to point link in Ultra-Dense environment

This study takes an antenna perspective approach to mitigate signal interference issues in ultra-dense environment along with communication and signal processing domain. A compact single layered dual-band penta-polarization agile microstrip patch antenna (MSA) using single feed is studied and proposed. Each band switches between five distinct polarization states. Additionally, the proposed antenna possesses a very low profile of less than 0.01λ (λ free-space wavelength). A square patch is enclosed by a square ring to attain two distinct reconfigurable frequency bands by using switching diodes and biasing networks. Orthogonal microstrip lines connected with a single coax feed are selectively chosen by biasing network to excite the adjacent patch edges to achieve dual linear polarization (LP). Circular polarization (CP) with dual sense of rotation at each band is attained by switchable diagonal-truncated corners of outer ring. Subsequently, 45° slant polarization is achieved by simultaneous activation of the orthogonal feed lines with equal phases and amplitude. A penta-polarized antenna prototype is designed and fabricated to operate at 5.2 GHz and 5.8 GHz bands respectively. Simulation results of all ten reconfigurable states are found to be consistent with the measurement.

Modeling and Optimization of Laser Cladding Fixation Process for Optical Fiber Sensors in Harsh Environments.

In order to overcome the shortcomings of the poor shear resistance of the bare optical fiber whose coating layer falls off due to harsh conditions, such as on aero-engines and the marine environment, the coaxial powder feeding laser cladding method (CPFLCM) is proposed to connect the optical fiber sensor and the substrate. The concentration field model of the powder flow is established in sections, the effective number model of particles and the corresponding laser attenuation rate are obtained. Through simulation, the influence of relevant parameters of laser cladding on the temperature field was analyzed, and the accurate parameters of laser cladding were optimized. Finally, the temperature rise trajectory of the substrate temperature field was verified by using the fiber grating temperature sensor. Through experiments, the quality of the molten pool and the optical transmission loss of the optical fiber sensor were analyzed, and the consistency of the simulation optimization parameters was verified. Through this paper, it can be concluded that the proposed CPFLCM can realize the effective connection of the optical fiber sensor to the substrate. It is of great significance in the application of optical fiber sensors in harsh environments of oceans and aerospace.

Process development and mechanical properties of Ti-6Al-4V samples generated by laser material deposition with coaxial wire feed

The use of wire in laser material deposition (LMD) eliminates major disadvantages of powder-based LMD processes, namely, contamination of the process cell with metal powder, significant material losses during the process, health and safety issues, as well as the impact of insufficient powder quality. A processing head with coaxial wire feed is used with a closed annularly shaped laser beam surrounding the wire, which is one of the distinguishing features. The laser beam and wire are arranged coaxially to each other, with the wire being fed through the inside of an annularly shaped laser beam without any shadowing. In contrast to lateral wire feeding, two substantial technological advantages can be identified: the process is independent of the feed direction and can manufacture complex 3D geometries. In this paper, a novel approach to deposit Ti-6Al-4V with wire-based LMD to increase the deposition rate to 500 g/h and develop process strategies to build up 3D volumes is described. In addition, stability criteria for the LMD process are determined and used for process development. The paper also presents characterization of the deposited layers and the procedure for generating tensile test samples from Ti-6Al-4V. Finally, the results of the built-up, heat-treated, mechanically processed, and tested samples are discussed, and the results are compared with those from the literature on powder-based LMD. Finally, an outlook toward future research and possible applications is given.

An RHCP and LHCP polarization reconfigurable microstrip antenna for ISM band smart city applications

Abstract In this article, a microstrip antenna having circular polarization switching capability is presented. This antenna consists of a circular-shaped radiating patch with a single co-axial probe feed line. The polarization reconfigurability is achieved by introducing four symmetrical U-shaped slots and silicon PIN diodes on the radiating patch. A prototype of the design is fabricated on an FR-4 substrate with overall dimension of 70 × 70 × 1.6 mm to verify the performances. The measured results of the antenna exhibit an impedance bandwidth (S 11 < −10 dB) of 5% in the frequency range of 2.37–2.49 GHz. The maximum gain of the antenna is found to be 2.99 dBic at 2.43 GHz. The antenna shows stable radiation performances at 2.4 GHz with 4.1% of 3-dB axial ratio bandwidth, and more than 105° of 3-dB axial ratio beamwidth for both right-hand circular polarization and left -hand circular polarization which make it suitable for ISM band Smart city applications.

Design of a Compact Omnidirectional Leaky-Wave Antenna Fed by Higher Order Mode

This article presents a novel leaky-wave antenna (LWA) based on a dielectric-filled rectangular waveguide (RWG) and fed by a higher order mode. The proposed quasi-uniform LWA has a compact configuration that is suitable for microwave applications, featuring the omnidirectional radiation patterns and low cross-polarization. In the frequency band of interest, the higher order mode, i.e., the TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode, performs as a fast wave in the proposed quasi-uniform LWA, radiating via the transverse slots etched on the walls. The advantage of the TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode for LWA applications is analyzed and demonstrated. This higher order mode is excited via a mode convertor from an inline coaxial line to the dielectric-filled RWG. For the reduction in sidelobe levels at high frequencies, −25 dB Taylor amplitude distribution is applied to the etched slots. The dielectric-filled LWA with the inline coaxial feeding is fabricated and measured. The measurement is consistent with the simulation, showing frequency-driven beam-scanning capability with low cross-polarization in the elevation plane. The simulated and measured radiation patterns in the azimuth plane illustrate the omnidirectional radiation patterns and thus confirm the radiating performance of the TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode in the proposed LWA. The advantages of the scanned beams and omnidirectional radiations are promising for radar systems.

Fe-Co-based coating with high hardness and high saturation magnetization deposited by co-axial powder feeding plasma transferred arc welding

Fe-Co-based monolayer coating with extremely high saturation magnetization (Ms) exceeding 1.9 T was deposited on AISI 1010 substrate by a co-axial powder feeding plasma transferred arc welding (PTAW), using (Fe0.8Co0.2)85B14Si1 feedstock powders. The phase composition, microstructure, microhardness and magnetic properties of the coating were investigated. The results show that the coating has a dendrites-eutectics composite structure, the columnar or equiaxed sorbitic pearlite dendritic cores surrounded by network-like eutectics (α-Fe + Fe2B). The body-centered cubic (BCC) α-Fe contributes to a high Ms of 1.92 ± 0.005 T, and Fe2B in eutectics causes a high coercivity (Hc) of 49.2 ± 0.2 Oe and a higher microhardness HV0.3 (>4.60 GPa). This work reveals the potential of fabricating Fe-Co-based soft magnetic alloy with high hardness and high Ms via PTAW.

Design and analysis of circular microstrip patch probe array for precise specific absorption rate measurement at quad-band

AbstractThis paper distinguishes the design and analysis of 3 × 2 circular microstrip patch probe array for specific absorption rate (SAR) measurement at quad-band. This novel approach consists of FR4 substrate radial dimension of 88 mm and it has six circular array elements with a radius of 17 mm; out of these six elements, three array elements are having rectangular slots with dimensions of 1.8 × 1.5 × 1.5 mm3. The array elements are coupled with six probes which have a dimension of 100 mm with a 2.5 mm tip radius; these six probes are embedded into a tissue-equivalent liquid-filled human head mannequin. In this mannequin, instantaneous SAR at any six positions has been investigated. The proposed design resonates at 1.8, 2.1, 2.4, and 2.5 GHz with a return loss of −11.53, −15.90, −15.73, and −25.49 dB. The circular microstrip probe array is fed by a 50 Ohm coaxial feed. In addition, the 3D human head model analysis is also presented. The precisely estimated SAR values are 0.135, 0.108, 0.167, and 0.244 W/kg at 1 g of tissue. For the traceable measurements, each source of uncertainty budget has been estimated.

Analysis and design of liquid antenna

A generic field analysis technique for a liquid antenna along with a novel high-gain structure of water antenna is presented in this article. The antenna design has liquid material as a conducting radiator contained within a tube, placed on a grounded dielectric substrate. This monopole antenna is fed by a coaxial feed, having the radiating pin inside liquid. The antenna is divided into different regions, and boundary conditions are applied to obtain the resultant field equation. The proposed technique is validated using simulated and measured results, with an existing design with seawater as radiator, and helps to predict the E-field of water antenna in advance to be used as a reconfigurable antenna. Parametric analysis is done to achieve the best antenna design, and a high-gain water antenna with gain value of 23.53 dB, resonating at 2.9 GHz having a bandwidth of 1.08 GHz is proposed and fabricated. The high gain is achieved by placing a superstrate on top of the structure at a cavity height of 11 mm. This seawater monopole antenna delivers broad bandwidth with high gain and is an attractive option to be used as a reconfigurable antenna.

Influence of tool path planning on process stability and deposition accuracy in laser material deposition with coaxial wire feed

Laser material deposition (LMD) is a laser-based additive manufacturing process that is widely used for fabrication, diversification, and repair of parts in various industries. LMD processes can be distinguished by the form of the filler material. In terms of availability, storage, safe handling, and price, filler material in wire form often has advantages over powdered materials. In this work, the influence of tool path planning on the deposition accuracy and the process stability of LMD with coaxial wire feed is studied. The laser beam and wire are arranged coaxially to each other, with the wire being fed through the inside of an annular shaped laser beam without any shadowing. While the process is completely directionally independent, the stability is linked to the wire feed rate, laser power, and process feed rate. Additionally, the ratio between the wire and the laser beam diameter affects the stability. Movement of the wire inside the annular beam may result in shadowing and process abort. Changes in the working distance (defocusing) lead to changes in the beam diameter, which affects the process stability. This can result in imperfections, i.e., bonding defects, or pores in the tracks and layers that will add up in the built components and must be avoided for imperfection-free three-dimensional geometries. On even surfaces, the geometry of the deposited tracks is controlled by changing the laser power, the wire feed speed, and the process speed. When building three-dimensional parts, critical points of the tool path planning are acute angled corners and crossing points. In the experiments, boundaries for the process stability in critical points are established and track geometries are compared to previous results. Furthermore, different strategies for the avoidance of material accumulation at the start, end, and crossing points are investigated. The different approaches are discussed, and finally an outlook for further use and possible applications is given.

Design of ultra-compact ISM band implantable patch antenna for bio-medical applications

AbstractIn this paper, an ultra-compact implantable antenna for biomedical applications is proposed. The proposed implanted meandered compact patch antenna is implanted inside the body at a depth of 2 mm. The proposed antenna was designed with Roger RO3003 (ɛr= 3) as substrate with an overall size of dimensions 5 × 5 × 0.26 mm3. The radiating element is a square patch antenna with different size rectangular slots and coaxial feeding. The proposed implantable antenna resonates at 2.45 GHz (from 2.26 to 2.72 GHz) frequency with a bandwidth of 460 MHz and a gain of −22.6 dB. The specific absorption rate has been considered for health care considerations, and the result is within the limits of the federal communication commission. The measured and simulated scattering parameters are compared, and good agreements are achieved. The proposed antenna is simulated and investigated for biomedical applications suitability.

Pyrometry-based closed-loop control of the melt pool temperature in Laser Metal Deposition with coaxial wire feeding

Laser metal deposition with coaxial wire feeding is a directed energy deposition process that enables near-net-shape and direction-independent additive manufacturing of metal parts. However, the high sensitivity of the process to disturbances poses a major challenge, as this frequently leads to defective components and rejects. To counteract this, a pyrometer was coaxially coupled into the beam path of the laser processing head to accurately determine the melt pool temperature without limiting accessibility. Applying deterministic test signals, a system model describing the dynamic relationship between the temperature and the laser power was identified. Based on this model, a closed-loop process control was designed. The control system was validated by introducing various disturbances, for which the reference temperature could be tracked with good approximation. The designed temperature control results in reduced effort for tuning the deposition process as well as a lower probability of defects, which saves manufacturing time and cost.

Numerical Analysis of the Temperature Field during Single-pass Two-layers Laser Additive Manufacturing of Fused Silica Glass

Laser-based additive manufacturing (AM) of glass is rare and complex, which involves highly non-linear thermodynamic problems. The temperature gradient is essential in analyzing the residual stress distribution and thermal deformation. At present, there is no accurate formula to describe the temperature field, and it is also difficult to measure the real-time temperature of the molten pool during the AM process. The numerical method in predicting the temperature field of fused silica glass laser becomes attractive. In this work, a finite element (FE) model for laser AM of quartz glass is established, and the temperature field of laser AM of quartz glass based on the principle of coaxial powder feeding is simulated by combining a moving heat source and birth-death element method. The temperature fields under different laser powers and scan speeds are investigated respectively. Results show that the peak temperature increases with the decrease of laser scan speed and the increase of laser power; The temperature of the upper layer is higher than that of the lower layer because of the heat accumulation effect; The increment rate of laser power and scan speed is set in the range of - 12.5% to 37.5% to ensure the temperature of AM region is slightly above the melting point of quartz glass. It is found that the influence of power change on the temperature field is more significant than that of scanning speed. Meanwhile, the peak temperature-dependent linearly on those two variables disused. The results provided here are instructive for subsequent laser AM of glass material including coaxial powder feeding method, powder cladding, etc.

Direction-independent temperature monitoring for Laser Metal Deposition with coaxial wire feeding

Among the Directed Energy Deposition (DED) processes, Laser Metal Deposition with wire (LMD-w) combines the advantages of a high precision and a high deposition rate. Recently, optical systems have been developed that allow to coaxially feed the wire through the center of a hollow laser beam into the induced melt pool. When a pyrometer is coupled to such an optical system, the measurement spot features the same annular shape as the laser spot. In this work, the temperature signal of such a setup was studied and the system was qualified for inline process monitoring. The size of the measurement spot was systematically varied, and the temperatures that resulted from the two modalities of a one-color as well as a two-color measurement were compared. It was shown that the size of the annular measurement spot significantly influences the temperature signal for both modalities. A better understanding of the measurement is essential to monitor the process reliably.

Miniaturized Circularly Polarized Vicsekcross-Shaped Slot Antenna for UHF-RFID Reader Handset Applications

In this research, a circularly polarized antenna employing fractal slot geometry is proposed for UHF-RFID handset reader application. The proposed antenna consists of vicsekcross-shaped slot etched at diagonal axis to achieve circular polarization with a coaxial feed placed 45&#x2218; with respect to the slot. The evolution of Vicsekcross shaped fractal slot is developed in different iteration stages for achieving wide impedance bandwidth covering U.S. UHF-RFID band with good axial ratio bandwidth performance. The single slotted reader antenna was investigated first followed by multi-slot antenna for size miniaturization, impedance bandwidth and axial ratio bandwidth performance. The impedance bandwidth and axial ratio bandwidth of the designed antenna were observed to be 25 MHz (903-927 MHz) and 7 MHz (911-917 MHz), respectively. Additionally, the designed antenna exhibited LHCP with a maximum measured gain of 2.9 dBic. The size of the final Vicsekcross-shaped four slot CP reader antenna is compact with dimensions of 57 x 57 x 1.6 mm.

Wideband Bidirectional Same Sense Endfire Circularly Polarized Antenna

In this paper, a wideband bidirectional endfire circularly polarized (CP) antenna is proposed by combining two endfire CP antennas with a single coaxial probe feed. The wideband characteristics are achieved with the help of a two-layered substrate separated by an air gap, and the excitation of CP waves in the endfire directions is yielded by the wideband magnetic dipoles and tapered electric dipoles. The proposed CP antenna has shown wide 10-dB impedance bandwidth (IBW) and 3-dB axial ratio bandwidth (ARBW) of 20.76% (5.05 - 6.22 GHz) and 16.10% (5.14 - 6.04 GHz), respectively. Besides showing an overall size of 0.733&#x03BB;_L &#x00D7; 0.863&#x03BB;_L&#x00D7; 0.058&#x03BB;_L (&#x03BB;_L is the wavelength corresponding to the lowest operating frequency) with wide operational bandwidth, the proposed CP antenna has also demonstrated a desirable peak gain of 4.45 dBic.