Module team Dr Peter Lewis (Chair) Dr George Weidmann (Lecturer in Materials) Dr Bob Dyson (Senior Lecturer, University of North London) Richard Black (Microphotographer) Dr Keith Cavanagh (Editor) Dr Clive Fetter (Editor) Sarah Hofton (Designer) Caryl Hunter-Brown (Technology Librarian) Gordon Imlach (Technician) Mike Levers (Photographer) Laurence Newman (Course Manager) Jennifer Seabrook (Secretary) Ian Spratley (BBC)<
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Author(s):
6.4.1 Materials selection Among the common thermoplastics available in the mid-1970s, polypropylene appeared as a front runner on grounds of toughness, density and cost Table 9). However, it is subject to creep (being uncrosslinked) and possesses a low tensile modulus of ca. 1500 MN m−2. Its merit index is 12.7 due to the low density of 0.
6.4 Case history: the Topper boat Replacement of one polymeric material by another may be undertaken entirely for manufacturing reasons, and this is what happened in the redesign of the Topper dinghy for thermoplastic polymer. The dinghy was originally designed for hand lay-up GRP in 1969 by Ian Proctor, a well known designer of small boats and yachts (Figure 61
3.5 Wavelength multiplexing and demultiplexing Wavelength multiplexers and demultiplexers are needed in order to be able to use wavelength division multiplexing. With just two wavelengths, the multiplexers and demultiplexers can be based on directional couplers because, as mentioned earlier in Section 3.2, couplers are naturally wavelength-de
2.7 Cabling A distinction must be made between the optical fibre – a single strand of glass fibre – and the optical-fibre cable consisting of one or more strands of fibre and various protective coverings. Bare optical fibre is fragile and vulnerable, and the cabling must provide the properties given below.
Tensile strength: The cable should prevent the fibre being strained when the cable is under tension. When the cable is being laid, for exampl
2.6.1 Connectors Many techniques have been used to design connectors that align the fibre ends accurately with high reliability and a long lifetime. The development of such components, at a low enough price, has been an important part of the overall development which has made fibre a feasible proposition for commercial transmission systems. With fibre attenuation down to 0.2 dB km−1 (for single-mode fibre), the losses resulting from connectors and splices can be very significant over a whol
2.5 Non-Linearity A linear system can be defined in two ways: (1) one which obeys the principle of superposition, and (2) one possessing the frequency-preservation property. If we consider an optical fibre with electromagnetic field as the input and output, then provided that the power level of the input signal is not too great (less than 1 mW, which is 0 dBm), the fibre may be well modelled by a linear system for most purposes. When fibre is used for a single point-to-point link to convey a digita
2.4 Pulse spreading and bandwidth Calculate the maximum signalling rate given by the Nyquist rate for the 1550 nm window, assuming that it runs from 1450 nm to 1610 nm. Using the 2.3 Attenuation At approximately what wavelength is the attenuation of optical fibre lowest? What, approximately, is the attenuation at that wavelength? What other wavelengths are used and why? 1.1 Uses of optical fibre in communication Using optical fibres, very high data rates (gigabits per second and higher) can be transmitted over long distances (tens of kilometres) without amplifiers or regenerators. As a consequence, optical fibre has completely superseded copper wires as the primary medium for cabled transmission over long distances. Until recently, however, optical fibre has been used less in LANs, where twisted-pair copper cable has been dominant. Similarly, fibre has been slow to penetrate the access network, from Introduction This unit is from our archive and it is an adapted extract from Digital Communications (T305) which is no longer in presentation. If you wish to study formally at The Open University, you may wish to explore the courses we offer in this curriculum area. By using optical fibre, very high data rates (gigabits per second and higher) can be transmitted over long d Module team Rosalind Armson, author Joyce Fortune, case study author Ray Ison, author Martin Reynolds, course chair Laurence Newman, course manager Mike Aiken, critical reader Mandy Anton, graphic designer Simon Bell, critical reader Victor Bignell, critical reader Chris Blackmore, critical reader Jake Chapman, critical reader Tony Duggan, project controller (Technology) Pip Harris, compositor Mike Haynes, critical Acknowledgements Except for third party materials and otherwise stated (see terms and conditions), this content is made available under a Creative Commons Attribution-NonCommercial-ShareAlike 2.0 Licence Grateful acknowledgement is made to the following sources for permission to reproduce material within this unit: Activity answers
Study Note: As outlined in the text I have not provided answers to all Activities. This is for two reasons:
For some activities only you can devise the answer and any I gave would be distracting or unhelpful.
For others in-text answers are given. 6 A problem with sensors The problem we will look at in this section concerns the analysis of the design of a component used in cars that are fitted with airbags. The airbag has to be inflated rapidly when an electronic circuit in the system decides that a serious collision is taking place. The crucial component in the electronics is the accelerometer, which therefore has to be extremely reliable. Motor manufacturers have turned to a technology called MEMS (micro-electromechanical systems) for these accelerometers, b 5.12 Pole and Stewart report Apparently prepared using the same methodology as Law, Pole and Stewart produced a report that calculated the loads at various points in the bridge under live locomotive loads and wind loading at various pressures. Stewart was employed by Bouch to perform the original design calculations for the bridge, while Pole was brought in as an independent expert. He had extensive experience of use of different materials in bridges, and indeed, had written a standard text book for engineers on the subj 5.9 Mechanical tests by David Kirkaldy In order to determine which of the several parts of the joint were weakest, and gain some idea of the scatter in strength, David Kirkaldy was employed by Henry Law to test various samples he had collected from the bases of the fallen piers. David Kirkaldy had a good reputation for accurate and rigorous mechanical testing of materials using a large tensometer he had designed and built in London (see Input 9, linked below). Click 'View document' below to open Input 9 3.4 Compact cassettes The use of magnetic tape for home use has always been somewhat problematic. Whilst it offers several advantages over discs, being capable of high-quality sound, substantially free from surface noise and able to make personal recordings, tape never became so popular as to make any serious inroads into the sales of discs. Why should this be the case? The answer is one of convenience, for magnetic tape has always been difficult to handle compared with discs – threading the tape through the mac 2.3 Berliner experiments with plates Emile Berliner was a young German immigrant to the USA with an interest in science. Whilst working in several menial jobs he educated himself in basic physics and chemistry, eventually building a small laboratory at his boarding house. Experiments with electricity and acoustics led to his invention of a new telephone transmitter, which he sold, enabling him to set up as a full-time inventor. He became interested in recording sound through studying a device called the phonoautograph. This appa
Activity 3
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Activity 2
