Fujitsu ScanSnap iX1500 Basic Operation Manual page 191

For details, refer to the ScanSnap Manager Help.
4.
In [Scanning side] in the [Scanning] tab, select [Duplex Scan (Double-sided)]
and click the [Apply] button.
ATTENTION
If [Simplex Scan (Single-sided)] is selected, the ScanSnap outputs the same result as performing
a simplex scan in [two separate images (front and back)] mode.
191
Scanning Documents with iX1500