Original Paper

Journal of Biological Physics

, Volume 35, Issue 3, pp 255-264

First online:

Evaluation of leaf water status by means of permittivity at terahertz frequencies

  • C. JördensAffiliated withInstitut für Hochfrequenztechnik, TU Braunschweig Email author 
  • , M. SchellerAffiliated withInstitut für Hochfrequenztechnik, TU Braunschweig
  • , B. BreitensteinAffiliated withInstitut für Pflanzenbiologie, TU Braunschweig
  • , D. SelmarAffiliated withInstitut für Pflanzenbiologie, TU Braunschweig
  • , M. KochAffiliated withInstitut für Hochfrequenztechnik, TU Braunschweig

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We present an electromagnetic model of plant leaves which describes their permittivity at terahertz frequencies. The complex permittivity is investigated as a function of the water content of the leaf. Our measurements on coffee leaves (Coffea arabica L.) demonstrate that the dielectric material parameters can be employed to determine the leaf water status and, therefore, to monitor drought stress in plant leaves. The electromagnetic model consists of an effective medium theory, which is implemented by a third order extension of the Landau, Lifshitz, Looyenga model. The influence of scattering becomes important at higher frequencies and is modeled by a Rayleigh roughness factor.


Terahertz time-domain spectroscopy Dielectric mixture Permittivity model Leaf water content Drought stress Coffea arabica