High-Throughput and High-Sensitivity Terahertz Scanners for Non-Destructive Evaluation of Non-Conductive Coatings and Thermal Protection Systems in Space Applications

To address NASAs need for advanced non-destructive evaluation (NDE) sensors, Lookin, Inc. proposes to develop a novel multi-pixel terahertz scanner, a transformative diagnostic tool to identify and localize visually inaccessible defects and damages in non-conductive coatings and thermal protection systems with significantly higher throughputs and over significantly larger volumes compared to what can be offered by existing NDE tools. During the Phase I SBIR program, Lookin performed feasibility studies and proved the suitability and superiority of its multi-pixel terahertz imaging systems for finding/localizing defects in materials commonly used as insulators in space applications, such as spray-on-foam insulator and cork, with a laboratory prototype multi-pixel terahertz scanner system. With the successful results obtained during the feasibility studies of the Phase I program, Lookin, Inc. proposes to extend its technological capabilities and develop a compact and portable field prototype multi-pixel terahertz scanner with enhanced resolution and scanning speed to be used for NDE of non-conductive coatings and thermal protection systems in field settings. More specifically, Lookin proposes to develop a contactless multi-pixel terahertz scanning system capable of capturing three-dimensional terahertz images of samples with a 5515 cm3 volume at a scan rate of 10 Hz, while providing a signal-to-noise ratio of 60 dB and lateral/depth resolution of at least 100/10 m. This terahertz imaging system is controlled by a data analysis algorithm that can create B- and C-scan images of the sample and automatically determine the position of the structural defects, such as cracks, voids, and delamination, within the samples. Thermal protection systems are crucial for spacecraft safety at extreme temperatures. Defects in thermal coatings can result in catastrophic failures, necessitating in-situ non-destructive evaluation (NDE) tools to detect their imperfections. However, existing NDE tools are either too slow to inspect large volumes or have specific requirements that limit their usage in practical settings. Lookin proposes to develop a contactless NDE instrument, a terahertz scanner, for the inspection of thermal protection systems at ground inspection facilities, offering large field-of-view, high throughput, and high resolution. State-of-the-art terahertz NDE systems can offer 60 dB SNR and 1 kHz scan rate when scanning a single sample spot. Since these systems consist of a single-pixel detector, raster scanning is required to inspect an object, which would be very slow when inspecting large volumes. Lookin’s proposed multi-pixel terahertz scanner can offer 60 dB SNR when scanning a 25 cm2 area and 15 cm depth with a 10 Hz scan rate, while providing a lateral/depth resolution of 100/10 µm. Lookin, Inc specified the following R/R&D objectives: -Development of a field prototype terahertz scanner based on a 2D THz-FPA, offering high scan speed and large FOV, which are required for operation in field settings. -Testing mass amount of thermal insulation samples with different thicknesses containing different types and sizes of defects, provided by our collaborators at NASA and Blue Origin who also provided these samples during the Phase I project’s feasibility studies. -Building a database from the terahertz measurement results and using this database to create an advanced data analysis framework empowered by machine learning techniques to further boost the resolution of the scanner system. -Developing a user-interface software for the users to control the equipment, specify scan parameters, and extract the scanning results. By reaching all these objectives, Lookin, Inc. will develop a terahertz scanner that will -Offer a scan rate of 10 Hz for a 5 cm × 5 cm area. -Create B and C-scans of the scanned area with less than 10/5 µm spatial/depth resolution. -Enable NDE of thermal insulation materials up to a thickness of 5 inches. -Offer a guided user interface (GUI) that allows the user to easily reach analysis results, defect locations and images.

The primary application of the proposed terahertz scanner is non-destructive inspection of non-conductive coatings for identification of inaccessible defects and damages on and below the surface with high resolution, precision, and throughput. The instrument can be used in ground inspection facilities for NDE and structural health monitoring of non-conductive insulation materials of spacecrafts, such as spray-on-foam insulators and cork panels. The proposed terahertz scanner is capable of inspecting many non-conductive polymers and composites including glass-fiber reinforced plastic, teflon, polyethylene. Thus, the same instrument can be used for NDE of many industrial products that heavily use non-conductive composites and other non-conductive polymers, such as those in battery, auto, aerospace, construction, and oil & gas industries.

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