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Copyright © 1999, MCB UP Limited
It's a hard world
It's a hard world
When I selected "Micro sensors" as this issue's theme it was in anticipation of contributions covering the fields of semiconductor manufacture and the integration of computational capabilities within sensors for purposes such as auto-calibration, linearisation and bus communication protocols.
Whilst these areas are well covered we also see evidence of the considerable impact of nanotechnology or micromachining. These technologies enable us to produce very small mechanical elements that can be used for sensor delivery or as part of the sensing element itself.
Over the years, the trend has been to replace mechanisms with computer software both in assembly machines that are now much more flexible in their application and in end products such as computer printers. What was once a noisy, not too reliable mechanism has now been replaced by a whisper-quiet inkjet and very simple mechanics for paper and print head presentation.
However, software has its failings and limitations and mechanisms are now making a comeback. One example of this is a microminiature combination lock recently announced by Sandia National Laboratories. Apparently computer hackers are now so sophisticated that "computer firewalls" that rely on software to check the identity of a user/hacker are inadequate. The microminiature combination lock (300mm across) allows the user/hacker just a single one-in-a-million chance to open the lock and gain access. Failed attempts block future access until the lock is reset by the owner. The device includes six code wheels driven by electrostatic comb drives and the complete unit is just 9.7mm by 4.7mm.
The real advantage of such mechanisms beyond their small size is that they can now be readily mass produced using established semiconductor manufacturing techniques with obvious price and reliability advantages.
I wonder what other fundamentally mechanical sensors we may see being developed? What about miniature resettable fuses (current sensors) to replace the variable resistance semiconductors that I have struggled with recently? Or a set of miniature laboratory balances that place tiny weights on one side of a counterbalance while the object being weighed is on the other? Balances are well established as a most accurate method of weighing as they are not subject to the temperature effects which can thwart other techniques.
One of the basic rules of sensing is that you should start off with the best possible data. By all means then process them and filter them and stretch them and bend them using fancy algorithms to acquire the information that you are after. However, if the starting data are of poor quality then you will never do as well as if more attention had been given to the basic data acquisition. With this in mind I consider it is well worth revisiting old established measurement techniques to see if their implementation using nanotechnology would give them a new lease of life and provide data that are closer to being perfect.