Fujitsu ScanSnap N1800 Operator's Manual page 532

Resolution
A measure of the fineness of details or grain of images. The customary metric of
resolution is dpi (dots per inch). For any given image, the higher the resolution, the
more dots or pixels that can be used, and the greater the resulting fineness of detail
that can be expressed.
Simplex scan mode
A scan mode where only one side of each document sheet is scanned. See also
"Duplex scan mode".
Ultrasonic sensor
A type of sensor that uses ultrasonic sound waves, in this case to detect document
multifeeds by recognizing differences in how the sound penetrates single versus
multiple sheets.
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