First steps towards an innovative compressive sampling based-THz imaging system for early crack detection on aereospace plates

Abstract

The paper deals with the problem of early detecting cracks in composite materials for avionic applications. In particular, the authors present a THz imaging system that exploits compressive sampling (CS) to detect submillimeter cracks with a reduced measurement burden. Traditional methods for THz imaging usually involve raster scan of the issue of interest by means of highly collimated radiations and the corresponding image is achieved by measuring the received THz power in different positions (pixels) of the desired image. As it can be expected, the higher the required resolution, the longer the measurement time. On the contrary, two different approaches for THz imaging (namely, continuous wave and time domain spectroscopy) combined with a proper CS solution are used to assure as good results as those granted by traditional raster scan; a proper set of masks (each of which characterized by a specific random pattern) are defined to the purpose. A number of tests conducted on simulated data highlighted the promising performance of the proposed method thus suggesting its implementation in an actual measurement setup

Void and crack detection of polymethacrylimide foams based on terahertz time-domain spectroscopic imaging

“…Crack defects. The time domain spectral characteristics of a crack are mainly manifested as a measurable decrease of the reflected wave amplitude, with a small phase change (also discernible), and the frequency spectra of the PMI foam with and without cracks is not significantly different [23,24]. This is shown in Figure 5.…”

Non-Contact, Non-Destructive Testing in Various Industrial Sectors with Terahertz Technology

“…Novel signal processing techniques have also been explored that can reduce image acquisition time significantly; e.g., compressive sampling (CS), as demonstrated in [64]. The authors compared the performance of various CS solvers in reconstructing simulated images with different shape cracks.…”

THz Measurement Systems

“…Between THz emitter and detector, there is an ellipsoidal mirror that allows to collimate the laser beam. In this configuration scheme, the reference signal produced by the source and the output signal recorded by the detector is sent to a lock-in amplifier in order to provide a coherent detection [28]. In the following, the attention will be focused primarily on the characteristics and performance of THz measurement system working in the time domain (THz-TD).…”