Influence of System Performance on Layer Thickness Determination Using Terahertz Time-Domain Spectroscopy

Weber, Stefan; Liebelt, Lukas; Klier, Jens; Pfeiffer, Tobias; Molter, Daniel; Ellrich, Frank; Jonuscheit, Joachim; Freymann, Georg von

doi:10.1007/s10762-020-00669-3

Cited by 14 publications

(6 citation statements)

References 16 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Its potential is demonstrated by applying it to the measurement of sample thicknesses, where a standard deviation of 4 fs (corresponds to about 1.3 µ m on average) is achieved for measurement times below one second. The measurements are carried out for six different samples and are in good agreement with reference measurements performed using a standard time-domain spectroscopy (TDS) system [16]. 1.…”

Section: Introductionsupporting

confidence: 66%

“…With the wavelength of the terahertz radiation, the averaged ∆ϕ values for each sample can be used to calculate the additional optical path length of the terahertz radiation introduced by the sample. These values are compared to reference measurements performed with a state of the art terahertz TDS measurement system [16]. Figure 6 shows the results for all samples as a bar plot, with the reference TDS measurement results in blue and the results of the upconversion measurement in red.…”

Section: Sample Measurementsmentioning

confidence: 99%

See 1 more Smart Citation

Sample thickness measurements by phase-sensitive terahertz upconversion detection

Pfeiffer¹,

Klier²,

Freymann³

et al. 2022

Preprint

Self Cite

View full text Add to dashboard Cite

Nonlinear frequency conversion provides an elegant method to detect photons in a spectral range which differs from the pump wavelength, making it highly attractive for photons with inherently low energy. Aside from the intensity of the light, represented by the number of photons, their phase provides important information and enables a plethora of applications. We present a phase-sensitive measurement method in the terahertz spectral range by only detecting visible light. Using the optical interference of frequency-converted photons and leftover pump photons of the involved ultrashort pulses, fast determination of layer-thicknesses is demonstrated. The new method enables phase-resolved detection of terahertz pulses using standard sCMOS equipment while achieving sample measurement times of less than one second with a precision error of less than 0.6%.

show abstract

Section: Introductionsupporting

confidence: 66%

Section: Sample Measurementsmentioning

confidence: 99%

Sample thickness measurements by phase-sensitive terahertz upconversion detection

Pfeiffer¹,

Klier²,

Freymann³

et al. 2022

Preprint

Self Cite

View full text Add to dashboard Cite

show abstract

“…A sensor detects the reflecting parts and the film thickness of the individual layers is calculated with known material parameters. For a detailed description and comparison to conventional film thickness measurement methods like magnetiv-inductive the reader is referred to Pfeiffer et al [5] and Weber et al [6,7].…”

Section: Modules 2 and 3: Path Generation And Paintingmentioning

confidence: 99%

A self-programming painting cell "Equation missing" SelfPaint"Equation missing" : Simulation-based path generation with automized quality control for painting in small lot sizes

et al. 2021

Self Cite

View full text Add to dashboard Cite

The increasing diversity of products and variants requires a flexible and fast path generation in robot-based painting processes. In the state of the art, path generation in the painting industry is a time consuming and cost-intensive iteration process in which the generated paths are evaluated and optimized via painting trials. In this paper, we present a novel concept for a self-programming painting cell, which is based on the key technologies 3D-scanning, multi-physics painting simulations, and a contactless film thickness measurement using terahertz technology. The core element of this cyber-physical painting system is a unique combination of numerical painting simulations with a gradientbased multi-objective optimization method, to virtually compute painting paths that produce a homogeneous thickness on the painted object. In order to drastically reduce the time and computationally intensive numerical fluid dynamic simulations, a step-by-step coupling of an offline and online simulation was implemented. In a final step, a collision free robot motion without singularities is generated automatically from the computed painting path. The concept was validated under pilot plant conditions by the painting of a fender using an electrostatically assisted high-speed rotary bell atomizer. The paint film thickness, measured with terahertz technology was used as the target and validation criterion, as it shows a strong correlation to other quality values. The results show that the achieved film thickness was within the process specification, although deviations between simulated and measured film thicknesses were found in the edge zones of the workpiece.

show abstract

“…In recent years, however, terahertz time-domain spectroscopy (THz-TDS) has reached a promising technology readiness level 4,5 and has been shown to reliably measure layer thicknesses down to ∼10 µm. 6 THz-TDS systems generate and detect electromagnetic pulses of (sub-)picosecond duration, with each pulse comprising frequencies from about 100 GHz to several THz. 7 Similar to echo-location technology, THz pulses reflect at material boundaries.…”

Section: Introductionmentioning

confidence: 99%

Online thickness measurements of acrylate-based coatings on knitted polyester fabric using terahertz time-domain spectroscopy

Vieweg,

Regner,

Dutzi

et al. 2023

Journal of Industrial Textiles

View full text Add to dashboard Cite

Three different institutions combined their expertise in a joint R&D project to demonstrate the suitability of terahertz time-domain spectroscopy for thickness measurements of acrylate-based coatings on polyester fabric. First, we spectroscopically analyzed the materials involved using a high-precision terahertz spectrometer and determined optical properties such as the refractive index and loss coefficient. Raster scans were then performed across the sample, and terahertz images were created to identify material boundaries and thickness inhomogeneities. Finally, we applied a fast scanning terahertz time-domain spectrometer based on electronically controlled optical sampling and a customized reflection head for online thickness measurements in a coating line. The textile moved at a speed of 0.5 m/min, while the measurement system records terahertz pulses at a rate of 1600 traces/s. Coating thicknesses of between 63 µm and 99 µm were calculated in a post-processing step. To classify these non-contact and non-destructive measurements, these thicknesses were compared with the results of standard methods. Online and offline (62-83 µm) terahertz and SEM (66-75 µm) measurements delivered the best agreement for average coating thickness. In contrast, mechanical testing methods gave either too low or too high values for layer thickness, which were not comparable. Terahertz time-domain spectroscopy and imaging technology enable the first non-destructive quality control of acrylate-based textile coatings immediately following coating in the production line. Measurable variables are coating thicknesses and the detection of defects such as air inclusions.

show abstract

Influence of System Performance on Layer Thickness Determination Using Terahertz Time-Domain Spectroscopy

Cited by 14 publications

References 16 publications

Sample thickness measurements by phase-sensitive terahertz upconversion detection

Sample thickness measurements by phase-sensitive terahertz upconversion detection

A self-programming painting cell "Equation missing" SelfPaint"Equation missing" : Simulation-based path generation with automized quality control for painting in small lot sizes

Online thickness measurements of acrylate-based coatings on knitted polyester fabric using terahertz time-domain spectroscopy

Contact Info

Product

Resources

About