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3.2 Directional couplers

A simple yet valuable device is the directional coupler (Figure 19). A directional coupler can be constructed from two single-mode fibres by bringing them into close contact and heating so that the glass melts and the two fibres fuse. Light can then pass from one fibre to the ot
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3.1 Introduction

The basic optical-fibre link consisted of the source (laser or LED), the fibre and the detector, as was shown in Figure 1. Improvements in these components can increase the data rate, but the system is still a point-to-point transmission link and all signal processing, such as routeing
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2.6.2 Splicing

The usual technique for splicing in the field is electric arc fusion splicing. This involves aligning the two fibre ends and then fusing them with an electric arc.

Figure 17
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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
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Activity answers

Study Note: As outlined in the text I have not provided answers to all Activities. This is for two reasons:

  1. For some activities only you can devise the answer and any I gave would be distracting or unhelpful.

  2. For others in-text answers are given.


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6.1 Articulating your appreciation of complexity

I have organized the material in this section so that you can follow the activity route shown in Figure 6.

This section is primarily concerned with what can be understood by the term complexity, and how to compare it with the ideas of difficulty and mess. To do this, you are firs
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5.4 Intellectual property rights and value

Another important theme raised in the play is intellectual property rights (IPR). Ned's fortunes seem to rely on control of the IPR issues surrounding his invention. He challenges the rights of others to share in the IP because, as he sees it, they have not contributed anything. The assumption is that those that have the idea have IPR, but the IPR has value and, therefore, any proceeds accrued should be due to the person who has the idea. A problem arises here because of the phrase ‘intelle
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1 Putting the unit in context

This unit, taken from T883 Business operations: delivering value, is concerned with the management of ‘processes’ – the organised set of resources and related activities that are essential for the delivery of goods and/or services to customers. These processes or ‘operations’ form the very essence of any enterprise, and it is critically important that they are managed well to be effective and efficient.

The full course consists of three main blocks of study:


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Learning outcomes

By the end of this unit you should be able to:

  • make an effective business case for a change to an operations activity or similar using appropriate written and/or oral forms of communication;

  • show the widespread utility of operations management principles at all levels across all types of organisation;

  • introduce a transformation model of operations management, with stakeholder value as the principle output;

  • provide models, concepts and
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8.4.3 Self-limiting etches

In practice, it is often possible to design microsystems in such a way that there is no need to pay great attention to knowing the precise moment when the etching has gone far enough. A good example is the etching of the movable structures in surface-micromachined electromechanical devices.

Figure 41 sho
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8.4.1 Open-loop control

Open-loop is the crudest way of controlling etch depth. It relies on ensuring that every aspect of the process that can affect the rate of progress of the etch is kept under tight control. This can add up to a sizeable list. Table 5 shows just some parameters that affect both wet and dry etching.

Whether
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7.3.4 Physical vapour deposition (PVD), sputtering

An ion hitting a metal surface after acceleration through more than 100 V will not stick or bounce off but will burrow into the surface, splashing atoms outwards. This is known as sputtering and provides a versatile alternative to thermal evaporation for metal-vapour deposition: more controllable, with adjustable uniformity, able to cope with alloys and high-melting-point metals and suitable for production-line automation. Given these advantages, it is also worth the effort to heat the
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7.3.2 Evaporation

The simplest vacuum deposition technique is to heat an ingot of metal in a crucible under vacuum, releasing metal vapour that coats everything in its path. This can be done either under high vacuum (< 0.1 mbar), in which case only surfaces in a line of sight from the source will be coated, or in a low-pressure atmosphere, when the vapour is scattered by gas atoms and can go around corners, making batch processing of multiple wafers possible.

This rather simple technique is fast and chea
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5.1.2 Dipole-dipole forces

In the case of dipole-dipole interactions, the molecules that bond together have a fixed asymmetry in their charge distributions (as is the case in Figure 22); if their orientations are favourable the two will bond together. All molecules produce London forces. The dipole-dipole interactions are in addition to t
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4.2 The piezoelectric effect at the atomic scale

It has been mentioned above that by changing the state of polarisation of a piezoelectric material we can generate movement, and vice versa. Let's examine a little more deeply what is meant by ‘state of polarisation’ and how we can maximise its effect to get the best out of electrically controlled micro-actuators.

In order to electrically polarise a material we need, by definition, to cause a separation of charges within the material. The more we can do this the greater the d
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4.1 The piezoelectric effect

The phenomenon of piezoelectricity was first predicted and demonstrated in the late nineteenth century using naturally occurring materials. It has a vast number of applications, ranging from spark ignitors to inkjet printers. It is also utilised in timing circuits, where an oscillating electric field is used to make a quartz crystal resonate at its natural frequency. In MEMS, the effect is used to generate small-scale movements in a range of devices known as micro-actuators.

The effect
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3.6 Design considerations for AFM probes

AFMs have proved so useful in so many areas of science and engineering that they are now to be found in most universities and many manufacturing companies. The making of probes for these instruments is no longer a cottage industry, partly because of the sheer numbers involved, but also because of the need for consistency of performance from probe to probe. This requires precise shaping, both of the tip itself and of the cantilever on which it is mounted. The quality of image obtained from an
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3.5.1 Contact mode

Contact mode produces images with the highest resolution. This is because when the probe tip is as close as it can be to the surface, the influence of atoms other than the one directly under the probe tip is relatively small. This is a simple geometrical effect – if the tip were withdrawn a large distance from the surface, a large number of atoms would be at a very similar distance from the tip, and therefore would have a similar contribution to the overall force. In contact mode, the repul
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Learning outcomes

After you have completed this unit you should be able to demonstrate that you have achieved the following learning outcomes:

  • an understanding of how to relate physical dimensions and materials properties to static and dynamic behaviour;

  • an awareness of how small features are cut out in solid materials, and how small features are built up in solid materials;

  • describe the piezoelectric effect and its use for producing small-scale movement in mechanica
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7.2 The professional engineer

It has been suggested that there are four main criteria that identify a profession:

Custody of a clearly definable and valuable body of knowledge and understanding associated with a long period of training.

A strong unitary organization which ensures that the profession generally speaks with ‘one voice’.

Clearly defined and rigorous entry standards, backed up by a requirement to register with the profes
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