| 摘要 |
<p>A sheet (10) of known acoustic properties, e.g. glass, has ultrasonic transducers (20, 22) along adjacent edges. Depressing a chosen key (16) causes an impact on the sheet (10). The transit time for the acoustic wave to reach the transducers (20, 22) enables the x,y coordinates, respectively, of the point of impact to be established and these may be used to define an alphanumeric character via a look-up table. A graphics version using a stylus is also described. </p> |
