TRANSCRIPTS
Now … er, let’s see … to start with, I’ll outline what MEMS is. Then I’ll look at some of the unique aspects of designing MEMS and why MEMS design requires an interdisciplinary mixture of skills. This will lead on to a discussion of some of the practical applications of MEMS technology in the real world. After that, I’ll talk about nanotechnology and why it is an exciting area of research. I’ll finish by looking at some of the current and future applications of nanotechnology.
Unit 5, Lesson 5.2, Exercise D ≤1.23
Part 2 So first of all, what is MEMS? You should already have read a description of MEMS in your pre- course notes, but just to remind you: MEMS concerns tiny, three-dimensional systems ranging from about 1–10,000 microns in size, which as we shall see later, are often used in tiny sensors. MEMS are usually a mixture of electronic and mechanical moving parts and, as a result, a MEMS engineer needs to be a ‘jack of all trades’ – that is, he or she has to know about quite a few different fields, from electronics to mechanics, heat transfer and materials science.
Fundamentally, in terms of design, MEMS devices
are made using similar techniques to those used to make silicon chips. In other words, the devices are usually planar and assembled in layers. They are often made of silicon combined with metals, but polymers also hold promise for the future. Well, this might sound like electronics, and it does, obviously, have a lot in common with electronics. But remember that MEMS is also about micro- mechanical systems – I mean, things that actually move. What’s interesting is that in order to make devices work, engineers need to use techniques such as the finite element method for stress analysis. As a matter of fact, it’s the same method that structural engineers use to analyze buildings! Other scientific topics such as fluid mechanics, heat transfer and electromagnetics, are also important. However, because of the small scale of MEMS, effects such as surface tension and electrostatic forces, which are often disregarded in larger scale designs, become very important and must be taken into account in MEMS analyses.
Now, in nanotechnology – which has even smaller scales, down to a billionth of a metre! – the assumptions of classical physics break down further. In fact, at the smallest scales in nanotechnology, you even have to start to consider effects due to quantum mechanics.
The interesting and exciting thing about nanotechnology is that, by manipulating materials on a really, really small scale, we can actually change their properties. For example, conductivity, strength and viscosity can be modified if we can work at scales of less than 100 nanometres. Another possibility is that we can change the way light moves through a material, and this might have exciting applications, for example, in solar cell design.
Manufacturing nanoparticles, however, is
difficult. Although we can manipulate individual atoms and molecules using techniques such as atomic force microscopy, the processes are slow and very difficult. Chemical synthesis and self- assembly techniques hold much promise for ‘bottom up’ molecular manufacturing. However, they are unproven for complex synthetic structural assemblies at the nanoscale.
Unit 5, Lesson 5.2, Exercise E ≤1.24
Part 3 Anyway, er … I will talk more about nanotechnology in a moment, but to return to the main point … I was going to look at some MEMS applications.
The market for MEMS devices is large, currently about $40 billion per year. But what do these devices actually do? Well, mostly, they are used for sensors. For example, airbags in cars are triggered by an accelerometer and this is often a MEMS device. Electronic pressure sensors, such as those used in car engine control systems, industrial processes and medical devices, also use MEMS technology. Small gyroscopes used to stabilize aircraft, satellites and so on, are often MEMS devices. And, of course, the humble inkjet printer actually includes a sophisticated piece of MEMS – the inkjet print head. MEMS devices also play a part in the popular Nintendo Wii and the Apple iPhone. Both gadgets include tiny MEMS accelerometers which make them respond as you move or shake them. For example, you can play tennis quite realistically on the Nintendo Wii, which would not be possible without MEMS.
Unit 5, Lesson 5.3, Exercise B ≤1.25
Part 4 To come back to nanotechnology … there are some really exciting applications for this technology. However, the media has misconceptions about it; for example, suggesting
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