An Introduction to mems (Micro-electromechanical Systems)
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| An Introduction to MEMS
Prime Faraday Technology Watch – January 2002 9
iii) Inkjet printer head One of the most successful MEMS applications is the inkjet printer head, superseding even automotive and medical pressure sensors. Inkjet printers use a series of nozzles to spray drops of ink directly on to a printing medium. Depending on the type of inkjet printer the droplets of ink are formed in different ways; thermally or piezoelectrically.
Invented in 1979 by Hewlett-Packard, MEMS thermal inkjet printer head technology uses thermal expansion of ink vapour. Within the printer head there is an array of tiny resistors known as heaters. These resistors can be fired under microprocessor control with electronic pulses of a few milliseconds (usually less than 3 microseconds). Ink flows over each resistor, which when fired, heat up at 100 million ºC per second, vaporizing the ink to form a bubble. As the bubble expands, some of the ink is pushed out of a nozzle within a nozzle plate, landing on the paper and solidifying almost instantaneously. When the bubble collapses, a vacuum is created which pulls more ink into the print head from the reservoir in the cartridge (Figure 8). It is worth noting there are no moving parts in this system (apart from the ink itself) illustrating that not all MEMS devices are mechanical.
Figure 8. Thermal inkjet print technology [16]. Figure 7. (a) Disposable blood pressure sensor connected to an IV line [14], (b) disposable blood pressure sensors (as shipped) [15], and (c) intracardial catheter-tip sensors for monitoring blood pressure during cardiac catheterisation, shown on the head of a pin [13].
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