Terahertz Spectroscopy and Brewster Angle Reflection Imaging of Acoustic Tiles

Abstract

A Brewster angle reflection imaging apparatus is demonstrated which is capable of detecting hidden water-filled voids in a rubber tile sample. This imaging application simulates a real-world hull inspection problem for Royal Canadian Navy Victoria-class submarines. The tile samples represent a challenging imaging application due to their large refractive index and absorption coefficient. With a rubber transmission window at approximately 80 GHz, terahertz (THz) sensing methods have shown promise for probing these structures in the laboratory. Operating at Brewster’s angle allows for the typically strong front surface reflection to be minimized while also conveniently making the method insensitive to air-filled voids. Using a broadband THz time-domain waveform imaging system (THz-TDS), we demonstrate satisfactory imaging and detection of water-filled voids without complicated signal processing. Optical properties of the tile samples at low THz frequencies are also reported.

From Local Structure to Overall Performance: An Overview on the Design of an Acoustic Coating

“…Examples are specified in Table A1 of Appendix A. Owing to its complicated structure, preparation of acoustic coating is difficult, which cannot be verified by experiments, thus making it more difficult for practical applications.Few researches focus on other performance requirements for acoustic coatings during design, such as temperature performance [52], inspection [53]. In different seas, depths, and seasons, seawater temperature changes significantly [1].…”

“…Few researches focus on other performance requirements for acoustic coatings during design, such as temperature performance [52], inspection [53]. In different seas, depths, and seasons, seawater temperature changes significantly [1].…”

Speckle pattern based single pixel imaging

“…In the first study, a pulsed THz system was used to study the pressure scaling of the rotational spectra of carbon monoxide (CO) using THz-TDS [20]. In the second study, another pulsed time-domain THz system was used to conduct Brewster angle reflection imaging of concealed water filled voids [21].…”

Terahertz reflection time-domain spectroscopy for imaging and identifying concealed interfaces in multilayered systems

“…to absorption spectroscopy for the identification of drugs/explosives [18], to security screening applications [11], and finally to the detection of flaws in materials within insulated systems such as submarine hulls [19] and the NASA space shuttle foam insulation [20]. Imaging with THz can be performed in a transmission or reflection geometry, each of these methods specialized for certain applications based on their respective strengths and weaknesses.…”

“…It is also complicated by the fact that a well-defined reference, required for spectroscopy, is not always possible to collect. THz-TDS reflection imaging is involved in art conservation [7], under paint corrosion detection [26], and concealed interface inspection such as foam insulation defect detection in the NASA space shuttle [20] and void detection in submarine acoustic tiles [19]. Fukunaga and Picollo demonstrate the impact that THz reflection spectroscopy could have on art conservation [7].…”