A needle-form 3-omega sensor for thermal conductivity measurements of soft materials and biological tissues.

Soft materials, liquids, and biological tissues are of increasing interest as thermal materials for applications in energy storage, electrical/electrochemical systems, and cryopreservation, but thermal characterization of these materials can be challenging experimentally. Here, we extend the robust 3-omega method, which is traditionally based on a planar form factor with external sample contact, to a microfabricated needle-form sensor that can be plunged directly into a sample. We further demonstrate the reusability of this sensor, the ability to easily make thermal contact by plunging the sensor into the center of a sample, and the ability to sample systems undergoing phase transformations. We do so via application to solid ice as well as 4 representative materials at room temperature: water, glycerol, paraffin, and chicken liver, thereby demonstrating the sensor's utility for liquids, soft solid materials, and phase change materials. Data analysis is conducted by fitting to a three dimensional numerical model of the sensor and sample. These experiments show very good agreement of within 3% of literature values for thermal conductivity for the explored materials, which range in thermal conductivity from approximately 0.3 W/mK to 2.3 W/mK.