@misc{13338,
  abstract     = {{This work discusses the additive manufacturing of an axicon lens using cyclic olefin copolymer (TOPAS), and its characterization between 100 GHz and 300 GHz. The proposed manufacturing process followed by dip-coating post-processing provides an improved surface finish. Additionally, the terahertz output of the lens remains intact over the entire frequency range.}},
  author       = {{Shrotri, Abhijeet Narendra and Joshi, Suraj and Vogel, Lea and Starsaja, Annamarija and Stübbe, Oliver and Preu, Sascha}},
  booktitle    = {{2025 50th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz)}},
  keywords     = {{Manufacturing processes, Surface waves, Three-dimensional printing, Surface finishing, Surface treatment, Lenses}},
  location     = {{ Helsinki, Finland }},
  pages        = {{2}},
  publisher    = {{IEEE}},
  title        = {{{Terahertz Axicon Lenses}}},
  doi          = {{10.1109/irmmw-thz61557.2025.11319870}},
  year         = {{2026}},
}

@misc{13339,
  abstract     = {{Additive manufacturing (AM) paves the way for low-cost production of optical and terahertz (THz) components such as waveguides, fibers, and lenses [1]–[3]. This work addresses the fabrication and THz characterization of a 3D-printed waveguide composed of cyclic olefin copolymer (TOPAS). Such a waveguide is a convenient and inexpensive tool in the development of THz interconnects, and in applications such as biomedical sensing.}},
  author       = {{Joshi, Suraj and Starsaja, Annamarija and Shrotri, Abhijeet Narendra and Stübbe, Oliver and Preu, Sascha}},
  booktitle    = {{2025 50th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz)}},
  keywords     = {{Optical fibers, Optical fiber sensors, Optical interconnections, Biomedical optical imaging, Optical device fabrication, Production, Optical waveguide components, Three-dimensional printing, Optical waveguides, Lenses}},
  location     = {{Helsinki, Finland }},
  publisher    = {{IEEE}},
  title        = {{{Additively-Manufactured Terahertz Waveguides}}},
  doi          = {{10.1109/irmmw-thz61557.2025.11320095}},
  year         = {{2026}},
}

@misc{11977,
  abstract     = {{Additive manufacturing of lenses offers quick prototyping and characterization. This paper explains the additive manufacturing and characterization of axicon lenses using TOPAS material for Terahertz sensing applications. The beam patterns of additively manufactured axicon lens prototypes are characterized around 0.3 THz with silicon-based THz-camera to evaluate the depth of focus.}},
  author       = {{Shrotri, Abhijeet Narendra and Krause, Benedikt and Stübbe, Oliver and Pfeiffer, Ullrich and Preu, Sascha}},
  booktitle    = {{2024 49th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz)}},
  issn         = {{2162-2035}},
  keywords     = {{Additives, Prototypes, Three-dimensional printing, Sensors, Lenses}},
  location     = {{Perth, Australia }},
  publisher    = {{IEEE}},
  title        = {{{Evaluation of Additively Manufactured Axicon Lenses Using a THz-Camera}}},
  doi          = {{10.1109/irmmw-thz60956.2024.10697740}},
  volume       = {{2024}},
  year         = {{2024}},
}

@misc{13796,
  abstract     = {{Machine learning systems are increasingly integrated into security-relevant applications, making their vul-nerability to adversarial examples a potential risk. Banknote authentication is one such use case that ensures trustworthiness in financial transactions. In addition to traditional security features, the printing technique of banknotes itself is leveraged for authentication. The Intaglio printing produces particularly fine print structures that can be analyzed and differentiated using spatial frequency analysis, e.g. the wavelet packet transform. Ap-propriate feature engineering in the wavelet packet tree allows the extraction of features enabling fast and reliable authentication. This paper presents an approach that generates adversarial examples by manipulating the feature space, classifying counterfeit banknote specimens as genuine. To this end, the variance of the wavelet coefficient distribution of individual detail nodes in the wavelet packet tree is increased. The approach leads to minimally perturbed images that are visually indistinguishable from the original input. The majority of pixels remain unchanged, i.e. 77% for the lower-quality and 86% for the high-quality counterfeit. Furthermore, the limitations of this approach are discussed, shedding light on its applicability and potential challenges.}},
  author       = {{Knaup, Julian and Holst, Christoph-Alexander and Lohweg, Volker}},
  booktitle    = {{8th International Forum on Research and Technologies for Society and Industry : IEEE RTSI 2024 - Research and Technologies for Society and Industry, International Forum }},
  isbn         = {{979-8-3503-6214-5}},
  keywords     = {{Printing, Technological innovation, Wavelet domain, Perturbation methods, Authentication, Feature extraction, Wavelet analysis, Wavelet packets, Security, Wavelet coefficients}},
  location     = {{Milano, Italy}},
  pages        = {{560--565}},
  publisher    = {{IEEE}},
  title        = {{{Hidden in Plain Sight: Adversarial Attack on Wavelet-Based Banknote Authentication}}},
  doi          = {{10.1109/rtsi61910.2024.10761182}},
  year         = {{2024}},
}

@misc{7670,
  abstract     = {{Additive manufacturing (AM) and rapid prototyping process (RPP) have revolutionized the production of 3D objects in the last few decades. RPP has considerably increased the rate of production and the possibility of manufacturing prototypes in the fields of electrical, optical, and mechanical engineering. The manufacturing of optical prototypes including spherical, aspheric, and special kinds of lenses and lens arrays has reformed the fabrication of optical components. In this paper, specifically designed lens array prototypes for application in visible light communication (VLC) are introduced. These lens array prototypes are manufactured using the stereolithography apparatus (SLA) process. These lens arrays are designed to achieve optimal transmission of the light beam for VLC systems. One of the prototypes from the lens arrays contains primarily four spherical lenses and one thicker convex lens and the other contains one fresnel lens as a substitute for thicker convex lens. These lens arrays are further post-processed to achieve the required transparency. These lens array prototypes are tested using laser and LEDs. The ON-OFF keying modulated light beam was transmitted through the lens array at the sender side and focused on the photo-receiver using another lens array at the receiver side which is 200 cm apart. After evaluating these lens prototypes, it can be concluded that with appropriate post-processing and high-resolution stereolithography based manufacturing, a low data rate VLC link can be formed.}},
  author       = {{Shrotri, Abhijeet Narendra and Beyer, Micha and Schneider, Daniel Johann and Stübbe, Oliver}},
  booktitle    = {{Laser 3D Manufacturing VIII}},
  editor       = {{Helvajian, Henry and Gu, Bo and Chen, Hongqiang}},
  isbn         = {{978-1-5106-4189-1}},
  issn         = {{1996-756X}},
  keywords     = {{Additive manufacturing, 3D printing, Stereolithography apparatus, Spherical lenses, Fresnel lenses, Visible light communication}},
  location     = {{San Francisco }},
  publisher    = {{Society of Photo-Optical Instrumentation Engineers}},
  title        = {{{Manufacturing of lens array prototypes containing spherical and fresnel lenses for visible light communications using stereolithography apparatus}}},
  doi          = {{10.1117/12.2586907}},
  volume       = {{11677}},
  year         = {{2021}},
}

@misc{7676,
  author       = {{Shrotri, Abhijeet Narendra and Beyer, Micha and Stübbe, Oliver}},
  booktitle    = {{3D Printed Optics and Additive Photonic Manufacturing II : 6-10 April 2020, online only, France }},
  editor       = {{von Freymann, Georg and Herkommer, Alois M. and Flury, Manuel}},
  isbn         = {{978-1-5106-3470-1}},
  issn         = {{1996-756X}},
  keywords     = {{Fresnel lenses, Stereolithography apparatus, 3D printing, Photo-polymerization}},
  location     = {{Strasbourg (online)}},
  publisher    = {{SPIE}},
  title        = {{{Manufacturing and analyzing of cost-efficient fresnel lenses using stereolithography}}},
  doi          = {{10.1117/12.2555367}},
  volume       = {{11349}},
  year         = {{2020}},
}

@misc{7679,
  author       = {{Shrotri, Abhijeet Narendra and Beyer, Micha and Stübbe, Oliver}},
  booktitle    = {{	 Production engineering and management : proceedings 9th international conference, October 03 and 04, 2019, Trieste, Italy}},
  editor       = {{Padoano, Elio and Villmer, Franz-Josef}},
  isbn         = {{978-3-946856-04-7}},
  keywords     = {{3D printing, stereolithography, optical lens, light forming structures, convex lenses, concave lenses, refraction of light, focal length}},
  location     = {{Trieste}},
  pages        = {{227--240}},
  publisher    = {{Technische Hochschule Ostwestfalen-Lippe}},
  title        = {{{Evaluation of stereolithograghy processes for the production of lens prototypes}}},
  volume       = {{2019, 01}},
  year         = {{2019}},
}

@inproceedings{585,
  abstract     = {{Many low-cost 3D printers have been brought to market over the last couple of years. Most of them apply a Fused Layer Manufacturing (FLM) process, and have made 3D printing a great success amongst hobbyists, the maker community and students. One drawback of such inexpensive equipment is a limited build envelope, which prevents this from becoming a significant contributor to industrial production. To overcome these limits, it is not sufficient to simply upscale dimensions, but the overall concept of such machines must be completely re-thought, as well as the concepts behind several building blocks, components and the process software system.
Problems such as shrinkage of build material, support material and machine parts in combination with long printer head travels, temperature distribution and moisture effects all have to be solved. In addition, larger parts need longer process times. Therefore, reduction of process times and an increase in productivity are necessary in order to enable economic production.
Some of these problems can be solved by using more than one printer head for production, by using new materials and inventing new nozzle systems as distinct solutions for big printers. Nevertheless, to solve all these problems, the development of special machines for large parts is necessary: not component-wise but as a whole system. Large parts could then be successfully produced in several industries, using large, inexpensive FLMmachines.
}},
  author       = {{Villmer, Franz-Josef and Witte, Lars}},
  booktitle    = {{Production Engineering and Management}},
  editor       = {{Padoano, Elio and Villmer, Franz-Josef}},
  isbn         = {{978-3-941645-11-0}},
  keywords     = {{3D printing, FLM, build envelope, large-scale, thermoplastic polymers}},
  location     = {{Trieste, Italy}},
  number       = {{1}},
  pages        = {{111--122}},
  title        = {{{Large Scale 3D-Printers: The Challenge of Outgrowing Do-It-Yourself}}},
  year         = {{2015}},
}

@inbook{2076,
  abstract     = {{Segmentation and feature extraction algorithms based on Wavelet Transform or Wavelet Packet Transform are established in pattern recognition. Especially in the field of texture analysis they are known to be practical. One difficulty of texture analysis was in the past the characterization of different printing processes. In this paper we present a new algorithmic concept to feature extraction of textures, printed by different printing techniques, without the necessity of a previous teaching phase. The typical characters of distinct printed textures are extracted by first order statistical moments of wavelet coefficients. The algorithm uses the 2D incomplete shift invariant Wavelet Packet Transform, resulting in a fast execution time of O(<i>N</i>log<sub>2</sub>(<i>N</i>)). Since the incomplete shift invariant Wavelet Packet Transform was exclusively defined for 1D-signals, it has been modified in this research. The application describes the detection of different printed security textures. }},
  author       = {{Glock, Stefan and Gillich, Eugen and Schaede, Johannes and Lohweg, Volker}},
  booktitle    = {{Pattern Recognition}},
  editor       = {{Denzler, J. and Notni, G. and Süße, H.}},
  isbn         = {{978-3-642-03797-9}},
  keywords     = {{Discrete Wavelet Transform, Wavelet Transform, Wavelet Packet, Decomposition Level, Printing Technique}},
  pages        = {{422--431}},
  publisher    = {{Springer}},
  title        = {{{Feature Extraction Algorithm for Banknote Textures based on Incomplete Shift Invariant Wavelet Packet Transform}}},
  doi          = {{https://doi.org/10.1007/978-3-642-03798-6_43}},
  volume       = {{5748}},
  year         = {{2009}},
}

@inproceedings{2068,
  abstract     = {{The production of printing goods is laborious. Furthermore, the print quality, especially in banknotes, must be assured. It is accepted, that print defects are generated because printing parameters, also machine parameters can change unnoticed. Therefore, a combined concept for a multi-sensory learning and classification model based on new adaptive fuzzy-pattern-classifiers for data inspection is proposed. This inspection concept, which combines optical, acoustical and other machine information, comes up with a large amount of data, which leads to multivariate methods for data analysis. Multivariate methods are useful for analysis of large and complex data sets that consist of many variables measured on large numbers of physical data.}},
  author       = {{Dyck, Walter and Türke, Thomas and Schaede, Johannes and Lohweg, Volker}},
  isbn         = {{978-1-4244-1565-6}},
  issn         = {{1551-2541 }},
  keywords     = {{Sensor fusion, Inspection, Optical sensors, Printing machinery, Data security, Data analysis, Production, Degradation, Principal component analysis, Karhunen-Loeve transforms}},
  pages        = {{accepted for publication}},
  publisher    = {{MLSP 2007 - International Workshop on MACHINE LEARNING FOR SIGNAL PROCESSING}},
  title        = {{{A Fuzzy-Pattern-Classifier-Based Adaptive Learning Model for Sensor Fusion}}},
  doi          = {{10.1109/MLSP.2007.4414320}},
  year         = {{2007}},
}

@inproceedings{2062,
  abstract     = {{Bank note inspection is a complex task. As more and more print techniques and new security features are established, total quality security and bank note printing must be assured. Therefore, this factor necessitates change of a sensorial concept in general. We propose an optical-acoustical inspection method based upon the concepts of information fusion and fuzzy interpretation of data measures. Furthermore, we present a simplified scheme for information fusion for pattern recognition and data classification based on parametrical unimodal potential functions and a Sugeno-type score value analysis. Digital Object Identifier: 10.1109/ICIF.2006.301779 <br />}},
  author       = {{Dyck, Walter and Schaede, Johannes and Türke, Thomas and Lohweg, Volker}},
  booktitle    = {{ 2006 9th International Conference on Information Fusion}},
  isbn         = {{ 1-4244-0953-5}},
  keywords     = {{Information security, Inspection, Printing machinery, Optical sensors, Data security, Personnel, Fuzzy systems, Sensor systems, Expert systems, Ink}},
  pages        = {{1--8}},
  publisher    = {{9th International Conference on Information Fusion, 2006. ICIF '06}},
  title        = {{{Information Fusion Application On Security Printing With Parametrical Fuzzy Classification}}},
  doi          = {{10.1109/ICIF.2006.301779}},
  year         = {{2006}},
}