Submillimeter-Wave Permittivity Measurements of Bound Water in Collagen Hydrogels via Frequency Domain Spectroscopy

Aleksi Tamminen, Mariangela Baggio, Irina Nefedova, Qiushuo Sun, Juha Anttila, Juha Ala-Laurinaho, Elliot R. Brown, Vincent P. Wallace, Emma Pickwell-MacPherson, Thaddeus Maloney, Mika Salkola, Sophie X. Deng, Zachary D. Taylor

Research output: Contribution to journalArticlepeer-review

7 Citations (Scopus)


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.

Original languageEnglish
Article number9451620
Pages (from-to)538-547
Number of pages10
JournalIEEE Transactions on Terahertz Science and Technology
Issue number5
Publication statusPublished - Sept 2021


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