Cost Effective Soft Material Conductivity, Temperature and Depth (CTD) Sensors

PI: Xia, Zhiyong – Johns Hopkins University Applied Physics Laboratory (JHU/APL)
Co-PI(s): MacMahan, Jamie at the Naval Postgraduate School (Academia), RBR-Global (Industry), Materials Dynamics & Devices, Inc. (Industry)
Start Year: 2018 | Duration: 3 years

Project Abstract:

JHU/APL will use the unique features of poly(N-isopropylacrylamide) PNIPAM and polyacrylic
acid (PAA) based hydrogels and modify them for measuring the temperature, salinity and pressure
of ocean subsurface environment. We will investigate the hydrogel structure, especially the
intermolecular network structure on the temperature induced volumetric change. In order to
improve the sensitivity of PNIPAM for temperature sensing, we will study the effect of hydrogel
loading level on the Lowest Critical Solution Temperature (LCST). LCST dictates the temperature
range of the volumetric change. That is at temperatures below LCST, the volume of PNIPAM
increases with temperature and after LCST, volume decreases with the increase in ocean
temperature. For the salinity measurement, we will use a charged PAA polyelectrolyte for
creating a conductive media in order to measure the electrical conductivity of the polyelectrolyte.
More importantly, in order to further enhance the salinity measurement sensitivity, we will dope
the PAA with sodium and potassium salts to further enhance the ion conductivity. Lastly for the
pressure sensing, we will use a modified PNIPAM hydrogel and build it into a capacitor. With
the change in the size of the PNIPAM, the capacitance will be changed. Thus, the pressure can be
measured. Once all three components are proven, we will work with RBR to package them
together. To improve the fouling resistance of such system, we will graft a layer of polyethylene
glycol (PEG) hydrogel on the top surface. The high water permeability through PEG enables the
function of each sensor. Finally, the overall power supply to the three proposed sensors will be
provided by a novel thermoelectric technology made with superlattice structures. Finally, we will
work with Naval Postgraduate School and perform system testing in ocean environment. Our
initial testing will be based on divers. We will demonstrate functionality and reliability of the
system in this effort and test the sensors on sea mammals in follow-on efforts. Due to the different
features involved in this proposed work, we believe our solution is cost effective and the use of
reliable, standalone thermoelectric power will enable the durability and persistence of such system.

BAA: ONR BAA N00014-17-S-B016
BAA Topic: