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Table 1 Presentation of the thickness of typical delamination defects and the visualization methods present in the literature

From: Terahertz Spectroscopic Characterization and Thickness Evaluation of Internal Delamination Defects in GFRP Composites

Study

Type of THz source

THz bandwidth

Range of time delay signal

Sample side dimensions

Sample scanning step size

THz system configuration mode

Refs.

Incident angle

Sample description

Type of defect (thickness)

Sample measuring methodology

Humidity levels

Scan method

1

Fiber-coupled PCA, pulsed THz-TDS

Information not provided

From 80 ps to 300 ps

60 mm × 60 mm

1 mm

THz system configured in reflection and transmission modes

[20]

Information not provided

CFRP formed of 12 layers

Impact damage of unspecified thickness

Peak-to-peak and time-domain amplitude

Information not provided

Raster scanning of the CFRP composite samples

2

PCA, pulsed THz-TDS

Between 0.6–3 THz

From 0 ps to 45 ps

50 mm × 50 mm

0.1 mm

THz system configured in reflection and transmission modes

[13]

Information not provided

GFRP formed of 8 layers

Teflon film (250 μm)

Time-domain amplitude

Information not provided

Raster scanning of the GFRP composite samples

3

PCA, pulsed THz-TDS

Between 0.1–4.5 THz

From 0 ps to 40 ps

50 mm × 50 mm

0.5 mm

THz system configured in reflection mode

[27]

Information not provided

GFRP formed of 8 layers

Polytetrafluoroethylene (PTFE) films (205 µm)

Time-domain amplitude and time-of-flight tomography

Between 30%–32%

Raster scanning of the GFRP composite samples

4

PCA, pulsed THz-TDS

Between 0–3.5 THz

From 0 ps to 80 ps

100 mm × 100 mm

Information not provided

THz system configured in reflection mode

[22]

Information not provided

CFRP formed of 2 layers

Teflon film (150 μm)

Time-domain amplitude

Information not provided

Raster scanning of the CFRP composite samples

5

Fiber-coupled PCA, pulsed THz-TDS

Between 0.1–3 THz

From 26 ps to 48 ps

30 mm × 30 mm

1 mm

THz system configured in reflection mode

[26]

Incidence angle set to \(25^\circ\)

GFRP formed of 12 layers of glass fabrics

Simulated delamination defects (100 μm)

Time-domain amplitude

Information not provided

Raster scanning of the GFRP composite samples

6

Fiber-coupled PCA, pulsed THz-TDS

Between 0–2 THz

From 0 ps to 100 ps

22 mm × 44 mm

0.2 mm

THz system configured in reflection mode

[25]

N/A

A paper stack formed of 9 layers

Text (20 μm)

Time-gated spectral and time-domain amplitude

Information not provided

Raster scanning of the paper stack samples

7

Fiber-coupled PCA, pulsed THz-TDS

Between 0.1–4 THz

From 0 ps to 80 ps

150 mm × 150 mm

0.2 mm

THz system configured in the transmission and reflection modes

[24]

Reflection mode (\(43.2^\circ\)) and normal transmission

GFRP formed of 4 layers of glass fabrics

Teflon film (100 μm, and 150 μm)

THz time and frequency-domain amplitudes, and the peak time shift algorithms

Between 46%–51 %

Raster scanning of the GFRP composite samples