WRIGHT-PATTERSON AFB, OH. – Having the ability to manipulate electromagnetic waves (EM) can lead to more effective wireless communications or aircraft navigation through radio frequencies (RF). However, the effectiveness can break down in harsh environments. Tackling that issue has resulted in two patents for a group of Air Force Research Laboratory (AFRL) scientists and engineers.
United States Patent Office #11,787,109 B1 and #11,613,077 B1: 3-D Structures Having High Temperature Stability and Improved Microporosity started out as research to discover various new materials for printed electronics. James Hardin, PhD., Clive Liu, PhD., and Dan Berrigan, PhD. -- all at the AFRL Materials and Manufacturing Directorate (RX) at the time -- began researching in this area six years ago. They were attempting to create a light porous material with low permittivity. Permittivity is the measure of electric polarizability in an electrical insulator – which is also called a dielectric.
“Electromagnetic waves reflect off surfaces based off how different the material is from air. Air is said to have what we call a relative permittivity of one. Most materials are significantly above one,” Hardin explained. “So, if we can tune the material that is interfacing with air as close to one as possible, we basically improve our ability to control how EM radiation and RF radar go through this material.”
The team’s overall goal was to be able to create items of arbitrary shape with controlled distributions of permittivity, good mechanical, and thermal stability, enough to survive in harsh environments. The team began developing a new 3D printing ink, which could form microporous (pore diameters less than two nanometers) or mesoporous (pore diameters between two and 50 nanometers) high-temperature polymer materials.
“That’s where the 3D printing aspect really shines in that we can print it. This is something we can create complex shapes with high-performance dielectric properties without extra tooling. We can also tune its material properties and overall properties by how we print it. It gives us the ability to reach towards an important material characteristic while still maintaining customizability,” Hardin said.
Since the ink could be structured into different shapes, it could more greatly affect the EM behavior of whatever they produced. Hardin said Liu began experimenting with different ways to try to generate foams from polyimides (high-temperature polymers) and was having difficulties. That’s where Greg Horrocks, PhD., at the Materials & Manufacturing Directorate, and his work with good solvent / bad solvent battery material technology came in, according to Hardin.
“(This) technology is built on this idea that you suspend a polymer in a solvent. Essentially, the good solvent / bad solvent techniques involve dissolving a polymer in mixture of solvents. As the good solvent is removed, the bad solvent form droplets in the solidifying polymer. Once this bad solvent is removed, air-filled voids are left behind. This lets you generate porosity, but in many cases not only do you get to generate that, but you don’t have the typical dimensional change that you see with foams.”
Hardin said he could envision this being useful to the Department of the Air Force (DAF) and the Department of Defense (DoD) in general by possibly creating substrates for antenna components or protective elements to cover them, or in things like radomes and other kinds of RF communication arrays.
The team is currently working with Montana-based MilTech, which has a Partnership Intermediary Agreement (PIA) with the Office of the Secretary of Defense (OSD) to identify potential partners and other uses for this technology. MilTech assists the OSD by engaging industry partners, subject matter experts (SMEs), and academia in addition to advancing innovation.
United States Patent Office: #11,787,109 B1 and #11,613,077 B1
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