Advances in Terahertz Imaging
163
online production [115]. At the time of paper production, both moisture content and
thickness need to be monitored. Technique to differentiate two different samples of
paper by THz with similar accuracy to other sensors has been shown [116]. In the
polymer industry, online supervision of polymeric processes, conductive properties,
the fibre orientation, etc. has been demonstrated by terahertz systems. Most of the
polymeric materials appear to be transparent for terahertz radiation. By measuring
the decreasing THz transmission, wood polymer composites can be examined by
THz spectroscopy to monitor the increase in water content within the material.
6 Conclusion
Though THz technology has gained boost with invent of various sources and detectors, however, many aspects have to be considered to implement THz technology on
a commercial basis. At room temperatures, blackbody radiation is present at THz
frequencies and hence detection of terahertz signals becomes difficult. SNR for terahertz images can be improved by mechanically scanning the sample each pixel-wise
by using a coherent source. But, this is possible only for static objects. As it has
already been discussed, that to overcome such an issue, imaging array is to be used.
Again atmospheric transmission is a big concern for THz imaging, as the attenuation
suffered by THz radiation in the atmosphere is much more severe compared to other
spectral regions [117]. Appropriate optics selection for imaging systems is another
major problem in THz domain. One of the major limitations of terahertz systems is
the difficulty to construct advanced lenses. Similar to any other imaging systems, the
diffraction phenomenon also limits THz solutions.
References
1. M. Mittleman Daniel, Twenty years of terahertz imaging. Opt. Express 26(8), 9417–9431
(2018)
2. C. Yu, S. Fan, Y. Sun, E. Pickwell-Macpherson, The potential of terahertz imaging for cancer
diagnosis: a review of investigations to date. Quant. Imaging Med. Surg. 2(1), 33–45 (2012)
3. Z.D. Taylor, J. Garritano, S. Sung, N. Bajwa, D.B. Bennett, B. Nowroozi, P. Tewari, J.W.
Sayre, J.P. Hubschman, S.X. Deng, E.R. Brown, W.S. Grundfest THz and mm-wave sensing
of corneal tissue water content: in vivo sensing and imaging results. IEEE Trans. THz Sci.
IEEE Trans. Terahertz Sci. Technol. 5(2), 184–196 (2015)
4. E. Pickwell, V.P. Wallace, Biomedical applications of terahertz technology. J. Phys. D Appl.
Phys. 39(17), R301–R310 (2006)
5. S. Hadjiloucas, L.S. Karatzas, J.W. Bowen, Measurements of leaf water content using terahertz
radiation. IEEE Trans. Microw. Theory Tech. 47(2), 142–149 (1999)
6. M. Koch, S. Hunsche, P. Schumacher, M.C. Nuss, J. Feldmann, J. Fromm, THz-imaging: a
new method for density mapping of wood. Wood Sci. Technol. 32(6), 421–427 (1998)
7. J.H. Teng, A. Maier Stefan, D.D. Willis Karl, 9 Disruptive Technologies Changing The World.
Report 2015 (PreScouter Inc., 2015), p. 73
163
online production [115]. At the time of paper production, both moisture content and
thickness need to be monitored. Technique to differentiate two different samples of
paper by THz with similar accuracy to other sensors has been shown [116]. In the
polymer industry, online supervision of polymeric processes, conductive properties,
the fibre orientation, etc. has been demonstrated by terahertz systems. Most of the
polymeric materials appear to be transparent for terahertz radiation. By measuring
the decreasing THz transmission, wood polymer composites can be examined by
THz spectroscopy to monitor the increase in water content within the material.
6 Conclusion
Though THz technology has gained boost with invent of various sources and detectors, however, many aspects have to be considered to implement THz technology on
a commercial basis. At room temperatures, blackbody radiation is present at THz
frequencies and hence detection of terahertz signals becomes difficult. SNR for terahertz images can be improved by mechanically scanning the sample each pixel-wise
by using a coherent source. But, this is possible only for static objects. As it has
already been discussed, that to overcome such an issue, imaging array is to be used.
Again atmospheric transmission is a big concern for THz imaging, as the attenuation
suffered by THz radiation in the atmosphere is much more severe compared to other
spectral regions [117]. Appropriate optics selection for imaging systems is another
major problem in THz domain. One of the major limitations of terahertz systems is
the difficulty to construct advanced lenses. Similar to any other imaging systems, the
diffraction phenomenon also limits THz solutions.
References
1. M. Mittleman Daniel, Twenty years of terahertz imaging. Opt. Express 26(8), 9417–9431
(2018)
2. C. Yu, S. Fan, Y. Sun, E. Pickwell-Macpherson, The potential of terahertz imaging for cancer
diagnosis: a review of investigations to date. Quant. Imaging Med. Surg. 2(1), 33–45 (2012)
3. Z.D. Taylor, J. Garritano, S. Sung, N. Bajwa, D.B. Bennett, B. Nowroozi, P. Tewari, J.W.
Sayre, J.P. Hubschman, S.X. Deng, E.R. Brown, W.S. Grundfest THz and mm-wave sensing
of corneal tissue water content: in vivo sensing and imaging results. IEEE Trans. THz Sci.
IEEE Trans. Terahertz Sci. Technol. 5(2), 184–196 (2015)
4. E. Pickwell, V.P. Wallace, Biomedical applications of terahertz technology. J. Phys. D Appl.
Phys. 39(17), R301–R310 (2006)
5. S. Hadjiloucas, L.S. Karatzas, J.W. Bowen, Measurements of leaf water content using terahertz
radiation. IEEE Trans. Microw. Theory Tech. 47(2), 142–149 (1999)
6. M. Koch, S. Hunsche, P. Schumacher, M.C. Nuss, J. Feldmann, J. Fromm, THz-imaging: a
new method for density mapping of wood. Wood Sci. Technol. 32(6), 421–427 (1998)
7. J.H. Teng, A. Maier Stefan, D.D. Willis Karl, 9 Disruptive Technologies Changing The World.
Report 2015 (PreScouter Inc., 2015), p. 73