Page 16 - ITU Journal Future and evolving technologies Volume 2 (2021), Issue 7 – Terahertz communications
P. 16

ITU Journal on Future and Evolving Technologies, Volume 2 (2021), Issue 7














































                                Fig. 2 – THz‑enabled drone sensor networks: Applications, challenges, and solutions.


          2.2  Terahertz for sensing                           An example of detecting a dangerous gas, such as carbon
                                                               monoxide is illustrated in Fig. 1.  Here, a THz wave with
                                                               spectrum ranging from    to    is transmitted through a
                                                                                     1
                                                                                          3
          Unlike  infrared  and  microwaves,  THz  waves  hold  many
                                                               drone Tx, which is then received by the drone Rx.  If the
          unique  transmission  properties  such  as  a  quasi‑optical
                                                               dangerous gas pertaining an  absorption  at     is  available,
          nature and molecular absorption,  making the THz band                                      2
                                                               the  received  THz  wave  level  at     shall  be  lower  as
          an appropriate candidate for some sensing applications,                             2
                                                               compared  to  the  other  frequencies.  Thus,  the  gaseous
          such  as  gas  and  material  sensing,  quality  control,  che-
                                                               presence  is  sensed/detected.  For  the  gas  sensing,
          mical  and  biological  sensing,  bearing  unique  THz
                                                               THz  band  of  0.2‑1  THz  has  been  considered  in  the
          spectral signatures.  Hence,  THz‑enabled  DSNs  can  be
                                                               literature  [27].  After  detecting  the  gas  successfully,
          deployed  in  a  variety  of  practical  sensing  applications.
                                                               again,  the  THz  band  can  be  utilized  for  relaying
          THz  signals possess  distinctive  spectral  signatures,  i.e.,
                                                               (communicating) the sensed information via drone net‑
          quasi‑optical  nature  having  varying  absorption  loss
          across  the  THz  band,  due  to  the  molecular  rotations/  works  to  a  nearby  monitoring  station  for  rapid  rescue
                                                               operations.  Thus,  an  all‑in‑one  operation  (sensing  and
          vibrations,  promising  that  THz  waves  can  be  highly
                                                               communication)  can  be  conveniently  achieved  by
          suitable  for  applications  related  to  the  rotational
                                                               deploying THz‑enabled DSNs and drone networks.
          spectroscopy,  such as gas detection  [6,  22].  Consequently,
          it  becomes  possible  to utilize  THz  waves  for  the  purposes
                                                               2.3  Localization
          of  detecting  various  poisonous/dangerous  gases  like
          hydrogen  cyanide,  carbon  monoxide,  etc.,  possibly  over   Besides  other  requirements  of  the  prospective  6G
          disaster‑struck  places,  including    ire  eruption,  massive   systems,  high  precision  localization  is  also  expected.
          earthquakes,  volcanic  eruptions,  etc.  THz‑enabled  DSNs,   It  is  predicted  that  the  THz  band  will  promise
          here,  can  be  employed  to  promptly  detect/sense  such   localization  accuracy  in  the  order  of  centimeters  [28],
          poisonous  gases  with  the  aid  of  THz  waves  by  rapid   which  is  far  better  than  the  existing  localization‑
          detection  and  relaying  such  vital  information,  saving  any   based  ser‑  vices,  such  as  Global  Positioning  System
          further  victims  and  avoiding  other  secondary  disasters.   (GPS), and cell‑ multilateration.  Localization methods at
          Both active and passive sensing  methods  can  be  employed   higher frequencies, such as across the THz band rely on
          for  poisonous  gas  detection  using  THz  spectroscopy.   the  technique  of  Simultaneous  Localization  and  Mapping

          4                                  © International Telecommunication Union, 2021
   11   12   13   14   15   16   17   18   19   20   21