Terahertz Imaging for Paper Handling of Legacy Documents

Abstract

Despite predictions of the paperless office, global demand for printing and writing paper remains strong, and paper appears to be here to stay for some time. Not only firms, but also governments, libraries, and archives are in possession of large collections of legacy documents that still must be sorted and scanned. In this study, terahertz-based techniques are demonstrated to address several routine tasks related to the automated paper handling of unsorted legacy documents. Specifically, we demonstrate terahertz-based counting of the number of sheets in unconsolidated paper stacks, as well as locating stapled documents buried in paper stacks.

Nondestructive Tertiary Mill‐Scale Thickness Measurement on Commercial Hot‐Rolled Steel Strip: Terahertz Time‐of‐Flight Tomography

“…Owing to displacement limitations of our measurement stage, as well as the pronounced bend induced accidentally by shearing, for steel strip #851, the binary THz B-scan begins at %4 cm from the right edge of the steel strip and ends at %12 cm from the left end in Figure 2a,b, while for steel strip #0848, #0849, and #0850, binary B-scans begins at %4 cm from the right edge of the steel strip and ends at %5 cm from the left end. Figure 10 shows a binary B-scan from the THz TOFT experiment with AR reconstruction, where a valid peak is assigned a value of "1" and the other positions are assigned a value of "0", regardless of the sign or height of the peak, [53,54] along the long axis of the obverse of #0851. Similar results (not shown) were also found in the reverse of steel strip #0851 and both sides of steel strips #0848-0850.…”

Terahertz and Millimeter Wave Sensing and Applications

“…This Special Issue of MDPI Sensors is intended to bring together some recent publications related to the application of millimeter and/or terahertz technology to specific application-related implementations in various fields. It covers a number of particular application examples employing terahertz radiation [7][8][9][10][11][12], presents methodological approaches for measurements techniques and concepts [13][14][15][16][17][18][19], as well as some contributions dedicated to recent achievements from the technology side of source and detector development [20][21][22].…”

“…Effective medium theory is applied to TDS signals between 0.1 and 0.5 THz to identify different volume ratios of HDPE and salt mixtures in powder form. Zhai et al show in their publication that terahertz TDS can also be useful to support the automated handling of paper documents [12]. By extracting page counts of paper stacks as well as detecting sheet thickness, moisture content, and possible foreign objects, the technique could be employed in, e.g., paper feeders of document scanners.…”