An Introduction to mems (Micro-electromechanical Systems)
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| An Introduction to MEMS
Prime Faraday Technology Watch – January 2002 10
A piezoelectric element can also be used to force the ink through the nozzles (Figure 9). In this case, a piezoelectric crystal is located at the back of the ink reservoir of each nozzle. The piezoelectric crystal element receives a very small electric charge causing it to vibrate. When it vibrates inwards it forces a tiny amount of ink out of the nozzle. As the element vibrates back out, it pulls some more ink into the reservoir to replace the ink that was sprayed out. Epson patented this technology but it is also used by the majority of the other leading printer companies.
MEMS has enabled more and more heating elements and piezoelectric crystals to be incorporated into a printer head. Early printers had 12 nozzles with resolutions of up to 92 dpi possible. Today, modern inkjet printers have up to 600 nozzles which can all fire a droplet simultaneously enabling 1200 dpi. Epson, Lexmark, Hewlett-Packard, Olivetti, Xerox and Canon all use a form of these MEMS in their inkjet printers. Over 350 million units were sold in 2000.
Figure 9. Thermal inkjet print technology [16]. iv) Overhead projection display One of the early MEMS devices used for a variety of display applications is the Digital Micromirror Device (DMD) from Texas Instruments. The device contains over a million tiny pixel-mirrors each measuring 16 µm by 16 µm and capable of rotating by ±10º, over 1000 times a second (Figure 10). Light from a projection source impinges on the pupil of the lens (or mirror) and is reflected brightly onto a projection screen. DMD’s are used for displays for PC projectors, high definition televisions (HDTV’s) and for large venues such as digital cinemas where traditional liquid crystal technology cannot compete. MEMS has enabled the micromirrors to be only 1 µm apart, resulting in an image taking up a larger percentage (89 percent) of space on the DMD chip's reflective surface, as compared to a typical LCD (12 to 50 percent). This reduces the pixelation and produces an overall sharper and brighter image. Today over 30 manufacturers use the DMD (Kodak being the largest) and over 500,000 systems have been shipped.
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