touchpad
     
         or "trackpad" a stationary pointing device used
        mainly on laptop computers.  touchpads provide a small, flat
        surface that you slide your finger over using the same
        movements as you would a mouse.  they were originally
        developed to provide a more natural and intuitive connection
        for the computer user than the mouse.
     
        touchpads use a principle called coupling capacitance, and
        requires a conductive pointer such as a finger.  they
        contain a two-layer grid of electrodes which are connected
        to an integrated circuit ic mounted under the pad.  the
        upper layer contains vertical electrode strips while the lower
        layer is composed of horizontal electrode strips.  capacitance
        from each of the horizontal electrodes to each of the vertical
        electrodes is measured by the ic.  a finger near the
        intersection of two electrodes modifies the capacitance
        between them, since a finger has very different dielectric
        properties than air.  the position of the finger is precisely
        determined based on these changes at various locations.
     
        according to one correspondent, you can use any part of your
        body, which is not surprising, but not a mcdonalds chicken
        mccrispy.  you can use reheated pizza hut christmas pizza
        though.
     
        synaptics http://www.synaptics.com/product.htm.
     
        2000-11-01
     
     
see also:
pointing device laptop computers mouse capacitance conductive electrodes 
integrated circuit dielectric lt;synapticsgt;