Molded RF Materials for Hypersonic Sensors and Seekers

Hypersonics and the materials needed therein are critical to both our nation’s defense and our national economy. (Image: USAF)

April 1, 2022

With hypersonics vital to national security, LIFT, the Detroit-based Department of Defense manufacturing innovation institute, along with the Department of Defense (DoD), recently awarded ATC Materials, Inc. one of the institute’s nationwide Hypersonics Challenge projects. The challenge goal: To demonstrate the repeatable and reliable production of their RIPS molded radio frequency (RF) material. Operating at speeds of Mach 5 or higher, hypersonic and counter-hypersonic vehicles are among the Department of Defense’s top priorities, as well as the development of a safe and secure domestic supply base.

RIPS samples have had three exoatmospheric flights aboard the International Space Station with MISSE (Image: NASA)

Based in Westlake, Ohio, with a second facility in Flagstaff, Arizona, ATC specializes in engineered RF materials for extreme environments. ATC’s Reduced-density Injection-moldable Pressureless-sintered Silicon-nitride (RIPS) was developed specifically for RF performance at elevated temperatures and is currently undergoing qualification tests for DoD applications. RIPS fills a gap in the performance of conventional materials by optimizing RF, thermal, and mechanical properties for hypersonic applications.

Materials

Conventional monolithic materials capable of withstanding aerothermal heating of hypersonic flight, including full-density sintered silicon nitride, have dielectric properties that impede or prohibit effective RF transmission. Low loss dielectric materials often fail at a temperature well below those experienced in hypersonic flight, which can see surface temperatures above 1400°C. Emerging technologies in carbon-carbon and ceramic matrix composites face similar tradeoffs plus the challenges of non-homogeneous materials exhibiting non-uniform dielectric performance.

RIPS provides stable, repeatable performance while reducing cost and manufacturing complexity by molding to net shape. RIPS is manufactured via a patented formulation and process that enables molding to net-shape or near-net-shape with conventional tooling and equipment.

A proprietary preform maintains dimensional stability through a traditional ceramic process resulting in a pure silicon nitride component with controlled uniform porosity and reduced density. The microstructure developed by this process imparts the physical properties of the material which allow for excellent dielectric (dK <5) and thermal performance (>1400°C) while maintaining mechanical strength for survivability. Molding allows for production of complex shapes while reducing or eliminating the need for difficult and expensive post-sinter final machining.

The optimization of RF, thermal, and mechanical properties make RIPS an ideal candidate for RF apertures on hypersonic vehicles. RIPS has demonstrated stable and predictable multiband dielectric performance throughout a notional hypersonic trajectory while meeting survivability requirements of ultimate strength, maximum use temperature, and thermal shock.

Testing

Characterization and qualification testing is underway to ensure reliable and repeatable performance for hypersonic and other extreme environment applications. Testing includes room temperature and elevated temperature mechanical and dielectric tests, as well as thermal conductivity and shock tolerance. Tests have been completed with support from DoD partners including Air Force, Army, and Navy programs. RIPS also has completed exoatmospheric testing during three flights aboard NASA’s MISSE program aboard the ISS. Testing was supported from prototype development efforts and SBIR and STTR Phase I and II projects.

Thermophysical testing of RIPS with university partner University of Dayton Research Institute (Image: UDRI)

ATC also works closely with university partners to complete advanced material characterization. This includes studies with University of Dayton Research Institute, The Ohio State University Center for Design and Manufacturing Excellence, and Georgia Tech Research Institute.

Production

RIPS may be molded to net shape including complex thin wall sections like this notional radome for prototype development. (Image: ATC)

To advance manufacturing readiness, ATC is working to improve manufacturability and enhance material performance. Enhancements for future formulations of RIPS may include process changes to produce different material structures as well as more significant formulation and molding changes to enhance or impart specific features in the finished part. One, or a combination of several, of these techniques could be used to increase strength, create different in-plane and through-plane thermal conductivities, and control RF transmission and reflection through the material. These efforts are supported in part through the OSD funded LIFT program as well as an OSD ManTech effort through DEVCOM AvMC Redstone.

With suitable mechanical, thermal, and dielectric properties, RIPS provides performance while moldability to net shape simplifies manufacture and reduces part cost. RIPS is well-suited for hypersonic sensors and seekers of several embodiments including radomes, RF windows, and conformal apertures located along the OML of the vehicle. Additionally, RIPS’ extreme environment performance may be utilized in applications such as space-based communications, industrial sensing such as material processing and power generation, and within turbines and rocket nozzles.

The LIFT challenge project will investigate the effects of net shape molding on finished component microstructure to identify performance advantages and establish best practices for production of the RIPS RF material. RF materials for extreme environments are critical for hypersonic sensors and seekers, specifically in prototype production of DoD hypersonic RF windows, conformal apertures, radomes, and antenna.

As-molded and molded-machined components will be manufactured, then tested for mechanical, thermal, and dielectric properties. Fractography and other analysis of finished components will relate physical microstructure to performance. An enhanced understanding of the molding process, its influence on finished component microstructure, and the effects of microstructure on part performance will be realized.

Hypersonics and the materials needed therein are critical to both our nation’s defense and our national economy. ATC Materials is currently partnering with The Ohio State University Center for Design and Manufacturing Excellence (CDME) and University of Dayton Research Institute to advance this important research.

This article was written by Matt Raplenovich, Director of Business Development, ATC Materials, Inc. (Flagstaff, AZ). For more information, visit here .