Accuracy and linearity of time-domain THz paint thickness measurements

Abstract

An analysis of the single point reproducibility of TD-THz based paint thickness measurements demonstrated a precision of 130 nm, corresponding to 0.1% of the measured thickness. A detailed model of the anticipated TD-THz waveforms from samples of varying thickness indicates that an intrinsic uncertainty of 0.09% is anticipated in the absence of environmental fluctuations. Therefore, the influence of oscillations in the THz field associated with the initial reflection does not adversely impact the ability to extract accurate paint thickness information, and the noise associated with these oscillations could limit the measurement uncertainty of a calibrated instrument under optimum laboratory conditions. In the case of a deployed sensor, we anticipate that the accuracy will be degraded by environmental fluctuations.

Error Assessment and Mitigation Methods in Transient Radar Method

“…Divergence of the beam due to nonlinearity (systematic error) was considered during the calibration by means of a PSMR as a reference, slid along the propagation direction [21][22][23]. Another systematic error that must be taken into account is the angle of the two antennas [7].…”

“…Due to the Angle between the Two Antennas David J. Cook and his colleagues described the systematic error introduced due to the angle between transmitter and receiver antennas [7]. The subsequent dependence of the ratio between the real and experimental thickness on the angle between the antennas can be derived by Equation (20).…”

“…Solutions proposed for this important challenge in NDT show one or more disadvantages, such as the time-consuming process, a need for higher frequency resolution, a need for larger frequencies up to the THz range, stability [5], increased bandwidth for creating ultra-narrow pulses in the time domain or sweeping frequency in spectroscopy, etc. [5][6][7]. In the following, some other limitations, especially in the THz range, will be mentioned.…”

Defect feature extraction of marine protective coatings by terahertz pulsed imaging

“…They were developing a standoff sensor based on THz pulsed imaging system in reflected mode for the real-time thickness measurement of wet (uncured) marine paints for the purpose of providing feedback to an automated system for painting ships in drydock. However, the studies were not cover the embedded defects detection and feature extraction for multilayered medium [5][6].…”

Dynamics of the Stratification Process in Drying Colloidal Dispersions Studied by Terahertz Time-Domain Spectroscopy

“…20 However, significant approximations of the analysis applied on data with low signal-to-noise ratios provided relative inaccurate bulk thickness estimates. [21][22][23] Precise material properties of solids can be obtained from terahertz data using dedicated analysis methods. 24 Chemistry often deals with liquidlike samples, for which traditionally spectroscopic peak analyses are performed.…”