Terahertz spectroscopic study of optical and dielectric properties of typical electrical insulation materials

Nsengiyumva, Walter; Zhong, Shuncong; Wang, Bing; Zheng, Longhui; Zhang, Zhenhao; Zhang, Qiukun; Zhong, Jianfeng; Luo, Manting; Peng, Zhike

doi:10.1016/j.optmat.2021.111837

Cited by 27 publications

(19 citation statements)

References 58 publications

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“…Using the expression of the transmission function given in Eq. ( 7), the equations for the optical parameters of the GFRP composite sample are obtained as follows [16]:…”

Section: Extraction Of the Sample's Optical Parametersmentioning

confidence: 99%

“…Among the many advantages of the THz waves include the fact that they pose little to no harmful effects to biological tissues (i.e., they can also be used to inspect tissues in biomedical engineering) [11,12], and they can provide high spatial resolution due to their relatively shorter wavelengths. All these remarkable properties confer THz waves the capabilities to detect and evaluate various types of defects in GFRP composites [13][14][15], measure their optical and dielectric properties [8,16], and the fiber orientation in unidirectional GFRP composites [17] and the stacking sequence of angled GFRP composites [18], etc. THzbased NDT applications have been delayed for many years due to some technical issues that limited the development of efficient THz emission and detection devices, and the THz region of the electromagnetic spectrum was formerly known as the "THz gap".…”

Section: Introductionmentioning

confidence: 99%

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

Nsengiyumva

Zhong

Luo

et al. 2023

Chin. J. Mech. Eng.

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The use of terahertz time-domain spectroscopy (THz-TDS) for the nondestructive testing and evaluation (NDT&E) of materials and structural systems has attracted significant attention over the past two decades due to its superior spatial resolution and capabilities of detecting and characterizing defects and structural damage in non-conducting materials. In this study, the THz-TDS system is used to detect, localize and evaluate hidden multi-delamination defects (i.e., a three-level multi-delamination system) in multilayered GFRP composite laminates. To obtain accurate results, a wavelet shrinkage de-noising algorithm is used to remove the noise from the measured time-of-flight (TOF) signals. The thickness and location of each delamination defect in the z-direction (i.e., through-the-thickness direction) are calculated from the de-noised TOF signals considering the interaction between the pulsed THz waves and the different interfaces in the GFRP composite laminates. A comparison between the actual and the measured thickness values of the delamination defects before and after the wavelet shrinkage denoising process indicates that the latter provides better results with less than 3.712% relative error, while the relative error of the non-de-noised signals reaches 16.388%. Also, the power and absorbance levels of the THz waves at every interface with different refractive indices in the GFRP composite laminates are evaluated based on analytical and experimental approaches. The present study provides an adequate theoretical analysis that could help NDT&E specialists to estimate the maximum thickness of GFRP composite materials and/or structures with different interfaces that can be evaluated by the THz-TDS. Also, the accuracy of the obtained results highlights the capabilities of the THz-TDS for the NDT&E of multilayered GFRP composite laminates.

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“…Using the expression of the transmission function given in Eq. ( 7), the equations for the optical parameters of the GFRP composite sample are obtained as follows [16]:…”

Section: Extraction Of the Sample's Optical Parametersmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Nsengiyumva

Zhong

Luo

et al. 2023

Chin. J. Mech. Eng.

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“…Using the expression of the transmission function given in Eq. ( 7), the equations for the optical parameters of the GFRP composite sample are obtained as follows [11]: (10) 2.2. The determination of the thickness of the sample and defect…”

Section: Extraction Of the Sample's Optical Parametersmentioning

confidence: 99%

“…2n GFRP (11) where T GFRP represents the thickness of the sample, Δt the time between successive re ections, c the speed of light in air, n GFRP the refractive index of sample, and θ the incident angle of the THz waves. The factor of one-half arises since the THz waves are measured in the re ection mode.…”

Section: Extraction Of the Sample's Optical Parametersmentioning

confidence: 99%

“…Among the many advantages of the THz waves include the fact that they pose little to no harmful effects to biological tissues (i.e., they can also be used to inspect tissues in biomedical engineering) [7], and they can provide high spatial resolution due to their shorter wavelengths. All these remarkable properties confer THz waves the capabilities to detect and evaluate various types of defects in GFRP composites [8]- [10], measure their optical material parameters [11], and the ber orientation [12], etc. THz NDT applications have been delayed for many years due to some technical issues limiting the development of e cient THz emission and detection devices, a condition that is commonly referred to as the THz gap.…”

Section: Introductionmentioning

confidence: 99%

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ISSI 2021: Terahertz Spectroscopic Characterization and Thickness Evaluation of Internal Delamination Defects in GFRP Composites

Nsengiyumva,

ZHONG,

Luo

et al. 2022

Preprint

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In recent years, terahertz time-domain spectroscopy (THz-TDS) has attracted significant attention due to its superior time and spatial resolution as well as its capabilities of localizing and characterizing internal defects in glass-fiber-reinforced polymer-matrix (GFRP) composite materials. In this study, the THz-TDS system is used to detect and evaluate hidden multi-delamination in plastic multilayered GFRP composite laminates. To remove the noise from the time-of-flight (TOF) signals, a wavelet shrinkage de-noising algorithm was used, leading to enhanced THz signals and further enabling an easy localization and evaluation of overlapping multi-delamination defects in GFRP composite laminates. In particular, both the thicknesses and locations of these delamination defects in the z-direction (i.e., through-the-thickness direction) were analyzed and measured considering the interaction between pulsed THz waves and the GFRP composite laminate. THz wave power and absorbance levels at every interface with different refractive indices in the GFRP composite samples were discussed based on analytical and experimental results. The present study shows the capabilities of the THz-TDS for the spectroscopic characterization of composite materials and helps users to know how they can theoretically estimate the thickness of the composite material that can be nondestructively evaluated by the THz-TDS.

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Toward tailoring the mechanical and dielectric properties of short glass fiber‐reinforced epoxy composites

Nsengiyumva,

Zhong,

Chen

et al. 2023

Polymer Composites

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Glass fiber‐reinforced polymer‐matrix (GFRP) composites are used to manufacture devices such as radomes, electrical insulators, and radar‐absorbing structures, many of which are used in applications with strict mechanical and dielectric property requirements. As such, designs and properties of GFRP composite materials should be regularly improved to guarantee their safe operation and meet their constantly evolving application requirements. In this study, glass fiber (GF) particles and epoxy resin 128 (EP‐128) were used to manufacture high‐performance EP/GF‐X composites with GF particle contents ranging from 5% to 40%. An investigation into their mechanical and dielectric properties revealed that EP/GF‐20 composite specimens presented the best mechanical performance with their bending strength and modulus reaching 159.68 MPa and 6521.92 MPa, respectively, and an average dielectric constant of 4.862 within the 10–105 Hz frequency range. A theoretical analysis of the EP/GF‐X composite specimens' dielectric constants using classic dielectric models based on the Lichtenecker, Bruggeman, Jaysundere‐Smith, and Maxwell‐Garnett rule‐of‐mixture equations indicated that the dielectric model based on the Bruggeman rule‐of‐mixture equation provided the dielectric constants closest to the measured values with a maximum deviation of less than −0.321% for EP/GF‐40 composites. This study provides a feasible strategy to control the mechanical and dielectric properties of GFRP composites.Highlights Glass fiber (GF) particles and epoxy 128 (EP‐128) resin were used to manufacture high‐performance glass fiber‐reinforced epoxy (EP/GF‐X) composites. The composite manufacturing process was carefully controlled to ensure uniform distribution and orientation of GF particles in the EP‐128 resin. The mechanical and dielectric properties of the manufactured EP/GF‐X composites were effectively tailored by controlling the content and distribution of GF particles in the EP‐128 resin matrix. The dielectric constants of the EP/GF‐X composites were measured experimentally and predicted using various theoretical dielectric models. The Bruggeman model provided the dielectric constants of the EP/GF‐X composites closest to the measured values.

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Terahertz spectroscopic study of optical and dielectric properties of typical electrical insulation materials

Cited by 27 publications

References 58 publications

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

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

ISSI 2021: Terahertz Spectroscopic Characterization and Thickness Evaluation of Internal Delamination Defects in GFRP Composites

Toward tailoring the mechanical and dielectric properties of short glass fiber‐reinforced epoxy composites

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