Large Metallic Structures Research Articles

Embedded multislotted PIFAs for remotely powered passive UHF RFID tags

We present a compact planar antenna that can be embedded within low-frequency UHF power-harvesting tag platforms.The antenna is a planar inverted-F antenna-type design with a set of optimized slots and provides large bandwidths, comparable to half-wave dipoles, while maintaining a low profile and small area. Hence, it can be embedded within the PCB of power-harvesting tags operating even at low UHF frequencies, resulting in a compact, slim overall device. We demonstrate this by embedding the antenna within a 430 MHz low-power discrete-component harvester tag, and we have designed and manufactured and verified antenna performance by both antenna measurements and tag link measurements. An added advantage of this topology is that tags with this antenna can be placed very near large metal structures without shorting or detuning, unlike tags with standard external dipole antennas. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:2379–2383, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27096

Influence of cutting parameters on cycle time, surface roughness, dimensional error and cutting forces in milling operations on aluminium 6082 sculptured surface geometry

Milling and especially high-speed milling (HSM) operations are widely used in manufacturing to obtain the final shapes of mechanical parts. Examples of this metal cutting process can be found in the production of moulds and dies, mainly in automotive, aerospace or aeronautical industries, where large amounts of material are removed from large metal structures in procedures that require high productivity and accuracy. Many factors and parameters have influences on the quality of manufactured parts, productivity and economics of manufacturing process. Not a lot of knowledge is available, making process planning enormously difficult and usually it is a task that fully depends on the operator expertise. The aim of this work is to experimentally analyse the influence of feed rate and cutting tool diameter on the cycle time, the cutting forces, the surface roughness and the dimensional accuracy of the part. The results show that the feed rate and the tool diameter have considerable effects over the productivity, the part quality and the requests of the metal removal process.

Three-dimensional stress intensity factor calibration for a stiffened cracked plate

Three-dimensional finite element analyses are used in this paper to calibrate the stress intensity factor in a cracked stiffened plate subjected to remote uniform traction. An accurate numerical determination of the stress field and stress intensity variation through the thickness of a central cracked plate was first carried out in order to evaluate three-dimensional effects. A stiffened cracked plate was then analysed, taking into account the results and the conclusions obtained in the previous study. Such a structure was chosen due to the growing interest for large integral metallic structures for aircraft applications, following the continuous need for low cost and the emergence of new technologies. The J-Integral technique was used to calculate the values of the stress intensity factor along the plate thickness. The plane strain behaviour near the crack front and the variation of the opening stress are discussed.

A linear magneto-optical imager for non-destructive evaluation

An integrated prototype of a new linear magneto-optical imager dedicated to real time inspection of large planar metallic structures is presented. The system provides images of the resulting normal magnetic field at the surface of the inspected structure, in amplitude and phase, in order to enable full defect characterization such as 3D image inversion. First raw images were obtained with an integrated linear magneto-optical imager, during the inspection of a flawed riveted lap joint mock-up similar to actual aeronautical structures.

Buried ordnance detection: electromagnetic modeling of munition-mounted radio frequency identification tags

In order to improve means for locating unexploded ordnance items (UXO) and significantly discriminating UXO from clutter, it is desired to tag ordnance items before they are delivered. The munition tagging envisioned will make use of current passive radio frequency identification (RFID) tag technology. The tags will provide information on the munition's location and identity when the UXO tag interrogation module is brought nearby. Knowledge of the magnetic field's behavior is essential in understanding the designs required to transmit energy from the above-ground interrogator to the tag and from the tag back to the above-ground receiver. The munition, being a large metal structure in such close proximity to the tags, will affect their operation because of electromagnetic boundary conditions and the tags' specific circuitry. To this end, modeling of the magnetic fields was required. This paper presents the results of this modeling effort and includes experimental findings. The modeling efforts demonstrated that detection depths to 1 m would be achievable, provided the system is magnetically optimized.

Linear magneto-optic imager for non-destructive evaluation

Magneto-optic (MO)/eddy current imagers appear to be good alternatives to conventional eddy currents sensors for defect detection in large metallic structures. Indeed, they allow short time inspection of large structures such as airplanes fuselage or wings, thanks to the visualization of large images relative to the integrity of the inspected structure. However, the existing MO imagers only allow “two-level” images to be produced, which are possibly highly degraded by perturbation patterns due to the magnetic domains of the MO sensor. These drawbacks severely limit the defect detection possibilities and forbid thorough defect characterization such as 3D image inversion to be carried out. In this paper, the authors present a patented linear MO imager (LMOI) dedicated to thorough defect detection and characterization. The device provides complex images obtained with high signal to noise ratio, which are the true measurement of the normal magnetic field at the surface of the inspected structure. The basic principle of the LMOI consists in the combination of a dedicated MO sensor featuring a linear and hysteresis-free magnetization loop, used with an original image acquisition system based on a stroboscopic approach, and a specific high sensitivity eddy current inductor. A first LMOI integrated prototype is described. Complex images obtained for the inspection of riveted lap joints featuring surface or buried flaws placed close to the rivets are presented and discussed. Finally further enhancements of the device are proposed.

Method for embedding optical fibers in an aluminum matrix by ultrasonic consolidation

The overall aim of the research, part of which is outlined in this paper, was to utilize the ultrasonic consolidation (UC) process for the fabrication of smart metal structures, capable of measuring an external stimulus and responding to this stimulus by adapting its structure accordingly through embedding both active and passive functional elements. This paper presents a fundamental study of embedding methods for the fabrication of optical fibers embedded within aluminum structures. The methods considered in this paper produced embedded optical fiber specimens in which large amounts of plastic flow were observed within the matrix. The matrix material deformed around the fibers, resulting in fully embedded optical fibers capable of transmitting a bright light source and without damaging the fibers. Based on light responses, a general process window was drawn to show the range at which optical fibers can be embedded within aluminum structures using the UC process. The outcomes lay down initial investigative principles for the further development of the technology for embedding or cladding of optical fiber sensors, such as fiber Bragg grating devices, within or on metal structures: for example, the cladding of large free-form metal structures or smart "skinned" metal foam or metal honeycomb structures.

Omnidirectional guided wave inspection of large metallic plate structures using an EMAT array

The design of an electromagnetic acoustic transducer (EMAT) array device for the inspection of large areas of metallic plate-like structures using the S0 guided wave mode is described. The reasons for using the S0 mode are discussed and it is shown how the choice of mode determines the nature of the EMAT array elements. A novel array construction technique is shown to be necessary whereby the EMAT coils for adjacent elements are overlapped in order to achieve the required element density. Results are presented that illustrate the operation of the device on steel and aluminum plate specimens in the thickness range from 5 to 10 mm. An area of at least 10 m2 can be inspected from a single location. Spurious signals in the results are caused both by the unwanted A0 mode and by S0 sidelobes, the latter occurring at the same radial distance from the array as the genuine S0 signal from a reflector, but in the wrong direction. The signal-to-coherent noise performance of the complete system is determined by the amplitude ratio of the largest genuine S0 signal to the largest spurious signal. This is typically around 30 dB. The sensitivity of the device to artificial defects and genuine corrosion patches is demonstrated and the limitations of its operation are discussed. The feasibility of using the device with the S1 guided wave mode to inspect a 20 mm thick plate is also demonstrated.

Plasma Electric-Arc Cleaning of Metal Products

A technology and several experimental units have been developed to clean individual products (wheel sets, castings, forgings, metal structures), and plasma-arc modules that operate at atmospheric pressure have been developed to clean pipelines. Plasma-arc modules which operate at atmospheric pressure and use protective and reducing gases are being developed to clean large metal structures (bridges, trusses, ships).

Annual General Meeting December 2004: The s.v. Cutty Sark: Electrochemistry in Conservation

The s.v. Cutty Sark is the last surviving example of an extreme clipper built for the profitable China Tea trade. Although expected to be in service for 30 years, the ship has survived to the present day with approximately 80% of the original structure remaining. However, the ship is now showing signs of deterioration, particularly chloride sponsored corrosion of the bolts used to secure the iron frame. As the s.v. Cutty Sark is one of three remaining vessels of composite construction, its preservation is vital for UK and World Marine Heritage. This paper describes an evaluation of the possibility of using an electrochemical method to remove the aggressive chloride ions from the wood/metal matrix structures on the ship. The presence of these species is a major problem associated with the conservation of marine artefacts and although studies have proven the usefulness of this technique for the conservation of large metal structures, e.g. the World War I gunboat M33, its effects on chloride-ion contaminated wood/metal composites had not been evaluated. The results from this work showed that by careful selection of the electrochemical and microbiological control parameters it is possible to successfully electrolyse wood and iron assemblies without degradation of the either the wood or the iron. A subsequent pilot study in the Aft Peak area of the ship further confirmed the feasibility of using electrolysis to remove chloride ions from the wood/iron matrix.

Flying in the face of convention [robotic assembly

The manufacture of large fabricated metal structures poses a number of significant problems, particularly when attempts are made to automate the process. This article describes some new techniques that are being developed to solve many of these problems, thereby opening up the possibility of automating the assembly of many products such as aircraft, transportation systems or large pre-fabricated structures. One of these techniques combines simulation based control with non-contact metrology, mathematical modeling and innovative robot end-effectors to provide practical solution and allow the effective and safe use of industrial robots within a partially defined environment. Using this technique, a working demonstrator cell was developed and is being evaluated using fuselage components from the Canadair CRJ700 regional jet. The system has been developed primarily for use in the manufacture of airframes but the technique is applicable to any structures that are liable to deformation during assembly.

Lightning Injury: Changi Hospital Experience

IntroductionLightning injury is a major concern in Singapore, which has one of the highest incidences of lightning activity in the world. This study examined the frequency and type of lightning injuries that presented to an Accident and Emergency (A&E) department situated in the east of Singapore to identify the groups at risk and the spectrum of injuries sustained.Materials and methodsThis is a case series study with a sample size of 24. Cases that were seen in the A&E department of Changi General Hospital from July 1997 to June 2002 with the International Classification of Disease diagnosis code of E907 for lightning injury were collected and analyzed.ResultsIn our study, 83% lightning injuries were work-related and 79% occurred in those below 40 years old. In the work-related category, a significant proportion occurred at the airport (45%) with most of the incidents occurring while working near or in contact with the aircraft (7 out of 9). The other major proportion occurred at construction sites (40%) with a significant number of cases occurring while in contact with cranes (6 out of 8). There was one telephone-related injury. In the non-work related incidents, two out of four occurred while playing golf. Most of the injuries (87.5%) were minor with no long-term morbidity. There was one death and one critical case requiring cardiopulmonary resuscitation. The latter survived and recovered quite remarkably. One patient had serious depression requiring prolonged treatment.ConclusionPrecaution should be taken during lightning-prone weather conditions in workplaces that involve large metal structures like cranes and aircrafts and in open space. This also applies to recreational sports like golf. Lightning injury, though rare, is not uncommon and emergency room doctors should be conversant with the treatment of this condition and its complications. Immediate basic and advanced cardiac life support administered to a lightning casualty who collapsed can be life saving.

Identification of CTOA and fracture process parameters by drop weight test and finite element simulation

This paper presents a new technique that is able to predict ductile fracture propagation occurrences in large metallic structures, by means of an appropriate application of the finite element modelling. This technique takes account of a cohesive zone in the vicinity of the crack tip, where a nodal release technique is implemented. Two parameters, governing the process zone of the material under investigation, have to be determined: the process zone dimension (named “ Δ distance”) and the critical value of crack tip opening angle (CTOA). CTOA C can be determined through an experimental laboratory procedure two specimen CTOA test (TSCT) that is already known and used by researchers who study fracture propagation on pipelines [Demofonti G, et al. Step-by-step procedure for the two specimen CTOA test. In: Proceedings of the Second International Conference on Pipeline Technology, Ostend, vol. II. 1995]. The second parameter required, Δ distance, is determined minimizing the differences of Finite Element results towards experimental data of an instrumented impact test (drop weight tear test). Some interesting improvements, concerning distinction between the initiation energy and the propagation energy accounted in TSCT procedure, are also discussed, in order to successfully extend its use to both high strength and high toughness steels.

Release of multi-layer metal structure in MEMS devices by dry etching technique

Reactive ion etching technique was used to remove interleave photoresist layer for free standing metal structure in microelectromechanical systems (MEMS) devices. Mixture of oxygen and CF 4 gas was used to get isotropic etching profile. Etching process was optimized to get large metal structure of 100×100 μm 2 without any surface bending. The etching rate of 0.7 μm/min at 60 W of RIE plasma power is found to be optimum process for the particular application. The reported dry release technique is fully compatible with standard silicon IC processing and hence can be used for hybridize process used in MEMS array application.

Large Torsional Oscillations in Suspension Bridges Visited Again: Vertical Forcing Creates Torsional Response

Click to increase image sizeClick to decrease image size Additional informationNotes on contributorsP. J. MckennaP. J. MCKENNA, (Pat or Patrick to telemarketers but Joe to friends and acquaintances) did his undergraduate work at University College Dublin and his graduate work in Ann Arbor with Lamberto Cesari. The central theme in his research is finding ‘non-obvious' solutions of nonlinear boundary value problems. He especially delights in finding applications of this work to large metal structures, such as bridges and ships, that move and occasionally break.Cillian Ó TuamaÓ TUAMA was born in Cork, Ireland in 1978. From an early age he showed a keen interest in mathematics, physics, chemistry, and computing. He completed his undergraduate degree in mathematics and applied mathematics at University College Cork in 2000. Ó Tuama was named Science Student of the Year in 1997. At UCC, he developed an interest in computational mathematics and undertook various research projects in pure and applied mathematics. Ó Tuama is also a distinguished athlete at the international level, and works as a software engineer, developing algorithms to be used in next-generation communications devices.

Electrosensory avoidance of metal obstacles by the paddlefish

Paddlefish Polyodon spathula detected and avoided obstacles with an exposed metallic surface but not plastic objects. An aluminium obstacle was avoided from significantly greater minimum approach distances than were any of the other obstacles. No significant difference was detected between the plastic and plastic‐covered aluminium obstacles, while control values were significantly less than for all obstacle types. Avoidance distances measured at different water conductivities were not significantly different. Fish collided frequently with the plastic and plastic‐covered aluminium obstacles, and with the control site, suggesting that these obstacles were not detected by the electrosensory apparatus. The aluminium obstacle was avoided successfully in all test runs. The unambiguous avoidance behaviour elicited by the aluminium obstacle suggests that large metallic structures, such as locks and dams, have the potential to interfere with paddlefish migrations. ©2000 The Fisheries Society of the British Isles

Efficient analysis and modelling of the radiation of microstrip lines and patch antennas by the TLM-integral equation (TLM-IE) method

A rigorous analysis of printed circuits and antennas requires a great computational effort, due to the necessity of an accurate modelling of large metallic structures, including radiating patches and feeding lines. The computational effort increases if we have to deal with radiation phenomena in large free space regions. In this contribution we present an accurate and efficient modelling of the electromagnetic field radiated by a microstrip line and by a patch antenna. The electromagnetic analysis is performed using a hybrid method, the Transmission Line Matrix-Integral Equation (TLM-IE) method. This method combines the advantages of the Transmission Line Matrix (TLM) method and the Integral Equation (IE) method, i.e. the high flexibility of the TLM method with respect to arbitrary object shapes and the effectivity of the IE method in analysing large homogeneous regions. Copyright © 1999 John Wiley & Sons, Ltd.

A comparison of radome‐ and astrodome‐enclosed large radio telescopes at millimeter wavelengths: The Large Millimeter Telescope

We present a systematic comparison of the main figures of merit for an open‐air radio telescope and two different types of enclosed antennas: (1) an ordinary radome, with a metal space frame providing the required mechanical rigidity and a dielectric membrane, and (2) an “astrodome,” i.e., a corotating rigid dome with a large window covered by a tensile membrane structure. The analysis is limited to submillimeter and millimeter wavelengths and large (≳30 m) antenna/enclosure systems, where the window tensile structure is very unlikely to be removable and is supported by either a metal space frame or cable networks. As compared with previous studies of this type, here we concentrate on the specific effects that these large metallic support structures have on sensitive astronomical observations. In particular, we critically discuss how the wind‐induced random motions of the metal space frame can limit the sensitivity of continuum observations, as a result of fluctuating shadowing and spillover effects combined with various beam‐chopping techniques. Using the Large Millimeter Telescope as a benchmark, we provide baselines for future projects where a similar comparison is needed.

Systematic distortions in magnetic position digitizers.

Medical devices equipped with position sensors enable applications like image guided surgical interventions, reconstruction of three-dimensional 3D ultrasound (US) images, and virtual or augmented reality systems. The acquisition of three-dimensional position data in real time is one of the key technologies in this field. The systematic distortions induced by various metals, surgical tools, and US scan probes in different commercial electromagnetic tracking systems were assessed in the presented work. A precise nonmetallic six degree-of-freedom measurement rack was built that allowed a quantitative comparison of different electromagnetic trackers. Also, their performance in the presence of large metallic structures was quantified in a phantom study on an acrylic skull model in an operating room (OR). The trackers used were alternating current (ac) and direct current (dc) based systems. The ac trackers were, on average, distorted by 0.7 mm and 0.5 degree by metallic objects positioned at a distance greater than 120 mm between the geometrical center of the sample and the sensor. In the OR environment, the ac system exhibits mean errors of 3.2 +/- 2.4 mm and 2.9 degrees +/- 1.9 degrees. The dc trackers are more sensitive to distortions caused by ferromagnetic materials (averaged value: 1.6 mm and 0.5 degree beyond a distance of 120 mm). The dc tracker shows no distortions from other conductive materials but was less accurate in the OR environment (typical error: 6.4 +/- 2.5 mm and 4.9 degrees +/- 2.0 degrees). At distances smaller than approximately 100 mm between sample and sensor error increases quickly. It is also apparent from our measurements that the influence of US scan probes is governed by their shielding material. The results show that surgical instruments not containing conductive material are to be preferred when using an ac tracker. Nonferromagnetic instruments should be used with dc trackers. Static distortions caused by the OR environment have to be compensated by precise calibration methods.

Metal silos

AbstractMost solids which are handled in large quantities are stored in the form of small particles, for ease of handling. The storage containers for these solids are generically termed silos, though several other words are in use for special applications. Silos are used in most countries in the world to store a huge variety of different particulate or granular solids in bulk. Large silos are of particular importance in agriculture, food processing, power generation, mining, steel, cement, plastics, and chemical process industries. There has been no structural design standard applicable to these large metal structures until the drafting of Eurocode 3 Part 4.1, which is about to be published.This article reviews the current state of knowledge concerning metal silo structures and presents some of the background and philosophy of the new rules in the draft European standard for steel silos.