TY - JOUR
T1 - Submillimeter-Wave Permittivity Measurements of Bound Water in Collagen Hydrogels via Frequency Domain Spectroscopy
AU - Tamminen, Aleksi
AU - Baggio, Mariangela
AU - Nefedova, Irina
AU - Sun, Qiushuo
AU - Anttila, Juha
AU - Ala-Laurinaho, Juha
AU - Brown, Elliot R.
AU - Wallace, Vincent P.
AU - Pickwell-Macpherson, Emma
AU - Maloney, Thaddeus
AU - Salkola, Mika
AU - Deng, Sophie X.
AU - Taylor, Zachary D.
N1 - Funding Information:
Manuscript received December 17, 2020; revised April 9, 2021; accepted May 25, 2021. Date of publication June 10, 2021; date of current version September 2, 2021. The development of the quasioptical system and ex vivo sheep corneas are provided by Icare Finland Oy. This work has been funded as research project AGRUM through Academy of Finland programme Radiation Detectors for Health, Safety and Security (RADDESS). This work has been carried out in MilliLab, an external laboratory of the European Space Agency. (Corresponding author: Aleksi Tamminen.) Aleksi Tamminen, Mariangela Baggio, Irina Nefedova, Juha Anttila, Juha Ala-Laurinaho, and Zachary D. Taylor are with the Department of Electronics and Nanoengineering, Aalto University, Espoo, FI-02150, Finland (e-mail: aleksi.tamminen@aalto.fi; mariangela.baggio@aalto.fi; irina.nefedova@aalto.fi; juha.anttila@aalto.fi; juha.ala-laurinaho@aalto.fi; zachary.taylor@aalto.fi).
Publisher Copyright:
© 2011-2012 IEEE.
PY - 2021/9
Y1 - 2021/9
N2 - This article presents measurements of the permittivity of gelatin hydrogels between 220 and 330 GHz. Hydrated gelatin was treated as a binary mixture of free water and a compound consisting of water bound to collagen. Submillimeter-wave reflectometry was used to estimate the hydrated gelatin permittivity, hydrated gelatin density, and free-water volume fraction in phantoms composed of 62, 67, 72, and 77% water by weight. A hydrated dry/wet density ratio of 0.335 was validated with optical-coherence tomography. A constant nonfreezing bound-water mass of 0.6 g/g was observed and confirmed with differential-scanning calorimetry. Good agreement between results from different modalities supports the dielectric spectroscopy methods and data analysis. Depending on the hydrodynamics at the sample/air interface, measurements indicate a bound-water compound permittivity of 3.77-j2.52 to 3.95-j2.49 - contrasting the pure-water average permittivity of 5.16-j5.63. The loss related to bound water was much higher than anticipated and characterization will help reduce uncertainty in measurements of gelatin hydrogel-based tissue phantoms; particularly corneal phantoms where adjacent free water creates complex hydration gradients. This is the first known, submillimeter-wave, frequency domain measurement of complex permittivity of the bound-water component in solid, proteinaceous matter.
AB - This article presents measurements of the permittivity of gelatin hydrogels between 220 and 330 GHz. Hydrated gelatin was treated as a binary mixture of free water and a compound consisting of water bound to collagen. Submillimeter-wave reflectometry was used to estimate the hydrated gelatin permittivity, hydrated gelatin density, and free-water volume fraction in phantoms composed of 62, 67, 72, and 77% water by weight. A hydrated dry/wet density ratio of 0.335 was validated with optical-coherence tomography. A constant nonfreezing bound-water mass of 0.6 g/g was observed and confirmed with differential-scanning calorimetry. Good agreement between results from different modalities supports the dielectric spectroscopy methods and data analysis. Depending on the hydrodynamics at the sample/air interface, measurements indicate a bound-water compound permittivity of 3.77-j2.52 to 3.95-j2.49 - contrasting the pure-water average permittivity of 5.16-j5.63. The loss related to bound water was much higher than anticipated and characterization will help reduce uncertainty in measurements of gelatin hydrogel-based tissue phantoms; particularly corneal phantoms where adjacent free water creates complex hydration gradients. This is the first known, submillimeter-wave, frequency domain measurement of complex permittivity of the bound-water component in solid, proteinaceous matter.
KW - Gelatin hydrogel
KW - submillimeter-wave spectroscopy
KW - water content
UR - http://www.scopus.com/inward/record.url?scp=85114321871&partnerID=8YFLogxK
U2 - 10.1109/TTHZ.2021.3088273
DO - 10.1109/TTHZ.2021.3088273
M3 - Article
AN - SCOPUS:85114321871
SN - 2156-342X
VL - 11
SP - 538
EP - 547
JO - IEEE Transactions on Terahertz Science and Technology
JF - IEEE Transactions on Terahertz Science and Technology
IS - 5
M1 - 9451620
ER -