The Space Shuttle Columbia's catastrophic failure is thought to have been caused by a dislodged piece of external tank spray on foam insulation (SOFI) striking and significantly damaging the left wing of the orbiter, which may have been due to a flawed section of SOFI. Microwave and millimeter wave nondestructive evaluation (NDE) methods have shown great potential detecting anomalies in SOFI such as small air voids using a horn and lens in a (real) focused configuration. Synthetic focusing methods may also be used to detect air voids in SOFI and may additionally offer the ability to locate the defect in three dimensions. To this end, two different methods were investigated; namely, frequency domain synthetic aperture focusing technique (FD-SAFT) and wide-band microwave holography. To illustrate the performance of these methods they were applied to two different SOFI samples. The results of these investigations demonstrate the capabilities of these methods for SOFI inspection.

Meeting Name

IEEE Instrumentation and Measurement Technology Conference (2006: Apr. 24-27, Sorrento, Italy)


Electrical and Computer Engineering

Keywords and Phrases

Microwave Holography; Microwaves; Millimeter Waves; Synthetic Apertures; Air Voids; Spray On Foam Insulation (SOFI); Synthetic Aperture Focusing; Synthetic Focusing; Nondestructive Examination; Foam; Microwave; Millimeter Wave; Nondestructive Testing; SOFI

International Standard Book Number (ISBN)


International Standard Serial Number (ISSN)


Document Type

Article - Conference proceedings

Document Version

Final Version

File Type





© 2006 Institute of Electrical and Electronics Engineers (IEEE), All rights reserved.

Publication Date

01 Apr 2006