Terahertz Spectroscopy and Imaging

Probing the Influence of Water on the Molecular Mobility of PVP/VA using Terahertz Spectroscopy

2026-03-30T09:56:00.014+01:00

Santitewagun, Supawan, and J. Axel Zeitler. "Probing the Influence of Water on the Molecular Mobility of PVP/VA using Terahertz Spectroscopy." Molecular Pharmaceutics 22, no. 10 (2025): 5928-5938.

Abstract

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The presence of water significantly impacts the physical stability of amorphous solid dispersions (ASDs) by altering polymer molecular mobility. This study investigates the influence of low levels of absorbed water on the molecular dynamics and glass transition behavior of amorphous poly(vinylpyrrolidone-co-vinyl acetate) (PVP/VA). Melt-quenched PVP/VA discs were conditioned at controlled relative humidities (RH 8.5 to 75%) and characterized using variable-temperature terahertz time-domain spectroscopy (THz-TDS, 80 to 420 K) and differential scanning calorimetry (DSC). DSC confirmed a significant plasticizing effect, with the glass transition temperature (Tg) decreasing from 367 to 275 K with increasing hydration. THz-TDS absorption correlated linearly with water content at low temperatures and exhibited complex temperature dependence. Even the nominally dry sample displayed a high-temperature (ca. 350 K) absorption plateau, indicating tightly bound residual water, while the onset temperature of bulk water evaporation decreased systematically with increasing hydration, suggesting a greater proportion of loosely bound water. Empirical fitting (α(T) = AT + B + C/T) revealed characteristic temperatures correlating with sub-Tg dynamics (T12) and Tg (T23), both sensitive to water content. Furthermore, the underlying polymer mobility rate was extracted from the THz data by accounting for evaporation; this analysis confirmed that water enhances mobility, potentially reaching a saturation limit at the higher hydration levels studied. This work highlights the capability of THz-TDS to provide detailed molecular-level insights into water–polymer interactions and dynamics, complementing thermal analysis and offering valuable information for assessing ASD stability.

see https://pubs.acs.org/doi/pdf/10.1021/acs.molpharmaceut.5c00590

Non-destructive detection of coating delamination using reflected time-domain terahertz waveforms

2026-03-27T09:51:00.009+00:00

Tobar, Daniel, Sri Kambhampati, Anthony J. Fitzgerald, Brett Nener, Thunyaluk Pojtanabuntoeng, and Vincent P. Wallace. "Non-destructive detection of coating delamination using reflected time-domain terahertz waveforms." Scientific Reports 15, no. 1 (2025): 42401.

Abstract
Adhesive failure leading to delamination in anti-corrosion coating systems compromises structural integrity by creating thin gaps that allow the ingress of corrosive agents like water. This study investigates the capability of terahertz pulsed imaging to detect air gaps thinner than a THz system’s minimum resolvable thickness by measuring apparent thickness changes in overlaying layers. The minimum resolvable thickness in terahertz pulsed imaging, referred to as the axial resolution, is determined by the system’s bandwidth. To test this approach, THz measurements were conducted on a 2 mm thick quartz window positioned above a metal substrate with an intervening 19

μ

m air gap. An increase in the apparent thickness of the quartz window was observed, consistent with theoretical expectations, despite the air gap being undetectable as a distinct reflection. This analysis was extended to multi-layered paint systems consisting of top, mid, and base coatings on steel plates. Cyclic ageing induced a delamination layer between the metal substrate and base coating, estimated to be 10

μ

m by scanning electron microscopy. Terahertz pulsed imaging analysis showed a corresponding 9.9–13.1

μ

m increase in the apparent base coating thickness, consistent with the quartz window results. These findings demonstrate that terahertz pulsed imaging offers a non-destructive method for identifying sub-resolution air gaps, enabling early-stage detection of delamination in protective coatings.

see https://www.nature.com/articles/s41598-025-26552-6

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Reference-free humidity sensing based on terahertz time-domain spectroscopy

2026-03-25T09:47:00.011+00:00

Zhu, Ting, Shuting Fan, Jian Huang, Bin Ye, Di Zhao, Guangyou Fang, and Xuequan Chen. "Reference-free humidity sensing based on terahertz time-domain spectroscopy." Sensors and Actuators B: Chemical (2026): 139500.

Abstract

Humidity sensing is crucial across various applications, yet conventional electrical sensors rely on physical contact, limiting their accuracy, response speed, and spatial flexibility. Water vapor exhibits dense rotational transitions in the terahertz regime, making terahertz spectroscopy an attractive tool for humidity sensing. However, absorption-based spectroscopic sensing demands a frequently measured zero-concentration reference to extract intrinsic absorption spectra, hindering its practical deployment. In this work, we propose a reference-free humidity sensing method based on terahertz time-domain spectroscopy. The method employs a database-comparison strategy empowered by a two-step calibration procedure, which efficiently adapts the database to variations in optical path length, temperature and spectral response. By comparing any newly measured signal with the database, humidity levels can be directly determined from raw signals without reference and absorption models. The method achieved a root mean square error of relative humidity down to 0.62 % across various measurement conditions and systems. Furthermore, its contact-free nature enables spatially averaged and real-time response, as demonstrated in the respiration monitoring measurement. Overall, the technique outperforms conventional humidity sensing devices over multiple aspects, showing strong potential for applications in medical diagnosis, extreme industrial environments and advanced scientific instrumentation.

see https://www.sciencedirect.com/science/article/abs/pii/S092540052600078X

THz Non-Destructive Testing Method for Internal Moisture Defects in Composite Insulators

2026-03-23T09:44:00.011+00:00

Wang, Pei, Yanyan Bao, Yongliang Yao, Yueyi Wang, Pin Jiang, Yushuo Wu, Pengzhen Wu, and Shuaibing Li. "THz Non-Destructive Testing Method for Internal Moisture Defects in Composite Insulators." IEEE Access 14 (2026): 7204-7216.

ABSTRACT

The presence of internal moisture defects at the interface between the core rod and skirt has been identified as a primary factor contributing to the failure of composite insulators. However, effective detection methods for such defects remain to be fully developed. In order to address this issue, the present paper puts forward a non-destructive testing method based on terahertz technology. Firstly, composite insulator samples containing moisture defects were fabricated in order to simulate real-world defects. Subsequent experimental testing yielded the terahertz time-domain/frequency-domain characteristics and imaging features of different samples. The optical parameters of the defective samples were extracted using an extended fourth-order Dedye model. The particle swarm optimization (PSO) method was then employed to overcome the limitations of traditional nonlinear fitting methods in dispersion models. Finally, based on the fitted parameters, time-domain finite-difference time-domain (FDTD) simulations were performed to invert the internal moisture defects within composite insulators in the terahertz frequency band, thus validating the accuracy of the experimental results. The findings demonstrate that the simulation inversion results align with actual test data, thus confirming that terahertz time/frequency domain parameters can effectively characterize internal moisture defects in composite insulators. The time-frequency domain characteristics facilitate qualitative analysis of defect occurrence and quantitative calculation of defect thickness. When combined with terahertz imaging results, this approach facilitates rapid determination of the location and geometric dimensions of moisture defects. Consequently, it achieves non-destructive testing of internal moisture defects in composite insulators, ensuring operational reliability and providing technical support for their safe and stable operation.

see https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=11343885

Monitoring Tensile-Induced Subsurface Damages of Woven Glass Fiber Reinforced Polymer Using Terahertz Time-of-Flight Tomography

2026-03-20T09:41:00.010+00:00

Zhai, Min, Haoyue Pan, Bin Xiao, Haolian Shi, Zhang Qu, Wenlong He, Cong Zhai, and Yi Tang. "Monitoring tensile-induced subsurface damages of Woven Glass Fiber Reinforced Polymer using terahertz time-of-flight tomography." NDT & E International (2026): 103645.

Abstract

Woven Glass Fiber Reinforced Polymer (GFRP) composites were studied using terahertz time-of-flight tomography to characterize failure modes in GFRP composite in a nondestructive and contactless fashion during in-situ tensile testing. The fracture morphologies of GFRP composite under different applied stresses were discussed by comparing terahertz C-and B-scan images to evaluate the dynamic evolution of tensile-induced microstructure. Our results show that significant THz-detectable damage initiation was observed at stress levels exceeding 60 MPa. In addition, tensile-induced damage can be observed not only on the surface, but also within the inner piles of GFRP composites. Finally, our work verifies the effectiveness of THz-based approach on three-dimensional dynamic monitoring the quality of GFRP composite in service and evaluating the influence of different loading conditions on structural properties and failure pattern of composite materials.

see https://www.sciencedirect.com/science/article/abs/pii/S0963869526000162

Real-time observation of coherent spin wave handedness

2026-03-18T22:02:00.011+00:00

Ha, Taewoo, Kyung Ik Sim, Howon Lee, Hyun Jun Shin, Sanghoon Kim, Se Kwon Kim, Jae Hoon Kim, Dong-Soo Han, Young Jai Choi, and Byung Cheol Park. "Real-time observation of coherent spin wave handedness." npj Spintronics 2, no. 1 (2024): 37.

Abstract

Magnonics, a crucial domain in information science and technology, utilizes spin waves in magnets as efficient information carriers. While antiferromagnets have been suggested for versatile magnonic platform because of the coexistence of right- and left-handed spin waves, their energetic degeneracy poses challenges for observation through spectral measurements, limiting their applicability. Recent observations of distinct spin wave handedness within the gigahertz regime have reported but, are yet to be demonstrated in terahertz (THz) frequencies of antiferromagnetic spin waves. Most of all, the coherence of spin waves is a key aspect of quantum information. Here, employing THz time-domain spectroscopy—a direct, precise, and easy probe for monitoring coherent spin wave dynamics—we discern chiral antiferromagnetic spin waves of opposite phase windings in the time domain, noting their handedness reversal across the angular momentum compensation temperature in ferrimagnets. We establish a principle for directly measuring the handedness of coherent antiferromagnetic spin waves in ferrimagnets with net magnetic moment M ≠ 0 but angular momentum L = 0. Our multidimensional access in the time and spectral domain enables the accurate determination of critical temperature and the dynamic observation of coherent chiral spin waves simultaneously in a single experiment, with potential applications in exploring other quantum chiral entities.

see https://www.nature.com/articles/s44306-024-00040-5

Optical and terahertz methods for studying easel oil paintings

2026-03-16T21:58:00.018+00:00

Bolshakov, Ivan S., Anastasiya A. Lykina, Olga V. Kravtsenyuk, Sergey V. Sirro, Vyacheslav Y. Toropov, Andrey R. Tsvetkov, Philip F. Taday, Donald D. Arnone, and Olga A. Smolyanskaya. "Optical and terahertz methods for studying easel oil paintings." Journal of Optical Technology 91, no. 5 (2024): 323-329.

Abstract

Subject of study. This study focuses on the application of terahertz tomography methods to easel oil paintings.

Aim of study. The aim of this study is to assess the effectiveness of terahertz tomography in analyzing the layered structure of artworks and detecting hidden damage, elements, and annotations.

Method. The study employed traditional analysis methods, such as infrared, ultraviolet fluorescence, and X-ray imaging. Special emphasis was placed on terahertz tomography, which enables non-invasive imaging of internal structures.

Main results. The study showed that terahertz tomography allows for the differentiation of materials used in oil paintings. This method enables a detailed examination of the layered structure without damaging the object under investigation, revealing elements that cannot be detected using other methods. The novelty of this study lies in the proposed application of terahertz tomography for preliminary in situ examination of paintings to detect hidden defects and possible inscriptions on the reverse side of artworks.

Practical significance. The results obtained from this study are valuable for researching, assessing the preservation status of, and restoring oil paintings. Specifically, the proposed method is suitable for detecting defects and hidden elements beneath paint layers without damaging the colorful surface. The terahertz tomography method proves particularly effective when applied in situ, as it does not require paintings to be dismantled.

see https://opg.optica.org/jot/abstract.cfm?uri=jot-91-5-323

Measuring Solute Concentration with Terahertz Time-Domain Spectroscopy in Single and Multiphase Systems

2026-03-13T16:08:00.001+00:00

Kolbel, Johanna, Qi Li, Terence L. Threlfall, and J. Axel Zeitler. "Measuring solute concentration with terahertz time-domain spectroscopy in single and multiphase systems." Analytical Chemistry 94, no. 3 (2022): 1713-1716.

Abstract

A versatile setup based on a microfluidic platform allows investigation of liquid samples at various temperatures with terahertz time-domain spectroscopy. The setup is applied to develop a novel method that performs temperature and concentration calibrations of liquid samples at terahertz frequencies. Other than measuring the concentration of pure liquid phase solutions, it enables the studies of local concentration of semicrystalline systems. An equivalent solute concentration during crystallization can be calculated from the extracted absorption at low frequencies. The MgSO4–water system is discussed as an example to illustrate the idea of this method.

see https://pubs.acs.org/doi/10.1021/acs.analchem.1c04279

Terahertz imaging of titanium dioxide-free film coating hydration and tablet core interactions

2026-03-11T19:15:00.001+00:00

Abstract

Titanium dioxide (TiO2) is often used as a white base pigment in film coatings, but recent EU restrictions on its use in food have prompted pharmaceutical manufacturers to seek alternatives. Terahertz pulsed imaging (TPI) was used to examine the hydration of TiO2-free immediate release formulations, either without an opacifier or using calcium carbonate (CaCO3). The coatings, made from polyvinyl alcohol (PVA) or hydroxypropyl methylcellulose (HPMC), were approximately 100 µm thick. TPI results indicated that the type of film coating influenced hydration and scattering effects. However, there was no evidence that TiO2-free coatings compromised tablet disintegration. Although the HPMC coating with CaCO3 gelled upon hydration, the tablets fully hydrated within the required time. These findings offer insights into the mechanistic impacts of alternative coatings in the industry.

The 2023 terahertz science and technology roadmap

2026-03-06T16:04:00.009+00:00

Leitenstorfer, Alfred, Andrey S. Moskalenko, Tobias Kampfrath, Junichiro Kono, Enrique Castro-Camus, Kun Peng, Naser Qureshi et al. "The 2023 terahertz science and technology roadmap." Journal of Physics D: Applied Physics 56, no. 22 (2023): 223001.

Abstract

Terahertz (THz) radiation encompasses a wide spectral range within the electromagnetic spectrum that extends from microwaves to the far infrared (100 GHz–∼30 THz). Within its frequency boundaries exist a broad variety of scientific disciplines that have presented, and continue to present, technical challenges to researchers. During the past 50 years, for instance, the demands of the scientific community have substantially evolved and with a need for advanced instrumentation to support radio astronomy, Earth observation, weather forecasting, security imaging, telecommunications, non-destructive device testing and much more. Furthermore, applications have required an emergence of technology from the laboratory environment to production-scale supply and in-the-field deployments ranging from harsh ground-based locations to deep space. In addressing these requirements, the research and development community has advanced related technology and bridged the transition between electronics and photonics that high frequency operation demands. The multidisciplinary nature of THz work was our stimulus for creating the 2017 THz Science and Technology Roadmap (Dhillon et al 2017 J. Phys. D: Appl. Phys. 50 043001). As one might envisage, though, there remains much to explore both scientifically and technically and the field has continued to develop and expand rapidly. It is timely, therefore, to revise our previous roadmap and in this 2023 version we both provide an update on key developments in established technical areas that have important scientific and public benefit, and highlight new and emerging areas that show particular promise. The developments that we describe thus span from fundamental scientific research, such as THz astronomy and the emergent area of THz quantum optics, to highly applied and commercially and societally impactful subjects that include 6G THz communications, medical imaging, and climate monitoring and prediction. Our Roadmap vision draws upon the expertise and perspective of multiple international specialists that together provide an overview of past developments and the likely challenges facing the field of THz science and technology in future decades. The document is written in a form that is accessible to policy makers who wish to gain an overview of the current state of the THz art, and for the non-specialist and curious who wish to understand available technology and challenges. A such, our experts deliver a ‘snapshot’ introduction to the current status of the field and provide suggestions for exciting future technical development directions. Ultimately, we intend the Roadmap to portray the advantages and benefits of the THz domain and to stimulate further exploration of the field in support of scientific research and commercial realisation.

see https://iopscience.iop.org/article/10.1088/1361-6463/acbe4c/meta

Application of Terahertz Time-Domain Spectroscopy to Study the Microheterogeneities of Solutions: A Case Study of Aqueous Sugar Solutions

2026-03-02T16:01:00.012+00:00

Penkov, Nikita V. "Application of terahertz time-domain spectroscopy to study the microheterogeneities of solutions: a case study of aqueous sugar solutions." In Photonics, vol. 10, no. 8, p. 887. MDPI, 2023.#

Abstract

The phenomenon of the formation of microheterogeneities (MHs) in solutions, which, according to chemical handbooks, are considered true solutions, has been known for a long time. MHs have been found in more than 100 binary solutions, many of which are used both in various scientific studies and in life. However, the nature of this phenomenon is largely unclear. It is only well-known that MHs are stable areas of increased concentration of one of the components of the solution. The main reason for the poor knowledge of MHs is the use of very few experimental methods, mainly light scattering methods. In this paper, the terahertz time-domain spectroscopy method was used for the first time to study MHs using the example of aqueous solutions of three sugars: glucose, fructose, and sucrose. This method gives the spectra of complex permittivity in the terahertz range, which are very informative when studying the hydrate shells of molecules in solutions. The idea of this study was that structuring sugar molecules with the formation of MHs changes their hydration. The characteristics of sugar hydration in solutions before and after filtration through a 20 nm filter, leading to the destruction of MHs, were compared. It has been shown that the water binding in the MHs of all three solutions is increased compared with the hydrate shells of individual sugar molecules. Also, for MHs’ fructose solution, a decrease in the number of hydrogen bonds between water molecules and an increase in the number of free water molecules was shown, which is not observed in MH glucose and sucrose solutions. This is explained by mutarotations of fructose molecules, leading to permanent significant rearrangements of the water structure in MHs. Thus, terahertz time-domain spectroscopy provides fundamentally new information about the MHs of aqueous solutions at the level of their hydration characteristics. The presence of MHs in solutions is a significant factor that has never been taken into account when studying the hydrate shells of various molecules in solutions using THz spectroscopy.

see https://www.mdpi.com/2304-6732/10/8/887

Application of Terahertz Pulses to Non-Destructive Testing

2026-02-25T15:59:00.016+00:00

Zarrinkhat, Faezeh, Philip F. Taday and Donald D. Arnone. "Application of terahertz pulses to non-destructive testing." Journal of Non Destructive Testing and Evaluation (JNDE) 20, no. 2 (2023): 35-43.

Abstract
For the past twenty years, TeraView has been a world leader in the application of terahertz pulses to solve problems for industry .Terahertz technology provides the opportunity of remote, safe, fast and accurate sensing. In recent years, there has been a growing interest from industry in applying terahertz pulses to process control .In this paper, there is a brief review of the generation and detection of terahertz waves (0.1 THz to 6THz) using photoconductive antennas. The applications of time-domain spectroscopy to gas, liquid and solids are discussed. Then, a number of industrial applications of terahertz pulsed imaging such as solar cells, pharmaceutical, battery production and automotive industries are highlighted.

see https://jnde.isnt.in/index.php/JNDE/article/view/51

Terahertz time-domain spectro-imaging and hyperspectral imagery to investigate a historical Longwy glazed ceramic

2026-02-23T15:57:00.014+00:00

Fauquet, Frédéric, Francesca Galluzzi, Philip F. Taday, Rémy Chapoulie, Aurélie Mounier, A. Ben Amara, and Patrick Mounaix. "Terahertz time-domain spectro-imaging and hyperspectral imagery to investigate a historical Longwy glazed ceramic." Scientific Reports 14, no. 1 (2024): 19248.

Abstract

In this paper, we present the potential of Terahertz Time-Domain Imaging (THz-TDI) as a tool to perform non-invasive 3D analysis of an ancient enamel plate manufactured by Longwy Company in France. The THz data collected in the reflection mode were processed using noise filtering procedures and an advanced imaging approach. The results validate the capability to identify glaze layers and the thickness of ceramic materials. To characterize the nature of the pigments, we also use with X-ray images, visible near-infrared hyperspectral imaging spectroscopy, and p-XRF (portable X-ray fluorescence) to qualitatively and quantitively identify the materials used. The obtained information enables a better understanding of the decoration chromogens nature and, thus, to determine the color palette of the artists who produced such decorative object. We also establish the efficiency of a focus, Z-tracker, which enables to perform THz imaging on non-flat samples and to attenuate artifacts obtained with a short focus lens. Then, 3D images are extracted and generated, providing a real vision. We also report the evaluation of the internal damage state through the detection of fractures.

see https://www.nature.com/articles/s41598-024-69697-6

Terahertz Assessment of the Battery Electrodes Save Production Costs of Electric Vehicles

2026-02-20T15:53:00.001+00:00

Khat, F. Zarrin, A. Pentland, P. F. Taday, and D. D. Arnone. "Terahertz Assessment of the Battery Electrodes Save Production Costs of Electric Vehicles." Journal of Non Destructive Testing and Evaluation (JNDE) 21, no. 2 (2024): 33-40.

Abstract

The electric vehicle market has experienced remarkable growth in recent years. A primary objective within this industry is to lower production costs. Notably, battery packs, which constitute up to 40% of the total production cost, allocate about 64% of this to the manufacturing of electrodes. It is vital to monitor key battery parameters such as thickness, loading, density, conductivity, and porosity to minimize waste during electrode production. Until recently, there was no technology capable of simultaneously tracking these parameters. However, terahertz technology has emerged as a powerful, non-destructive, and safe method for assessing battery electrodes.

Battery electrodes are coated on substrates made of materials like aluminium and copper. Since metals completely reflect terahertz waves, it's possible to measure the electrodes in reflection mode. This approach allows for the determination of the coating's thickness and its complex refractive index, which can be interpreted to deduce key electrode parameters.

In our study, we utilized TeraView's latest advancement, the TeraCota, a terahertz system designed for industrial applications, equipped with a self-referencing terahertz sensor. The sensor, mounted on a gantry, provided a terahertz image of the electrode loading and allowed for a direct comparison with an optical image, revealing defects on the cathode. We achieved an accuracy of 0.01 g/cm3 when comparing density measurements obtained through a terahertz sensor with those measured physically in the lab. Furthermore, the thickness measurements via the terahertz system agreed with those obtained using a micrometre to within less than 1 µm. Similarly, when comparing the conductivity measured by terahertz with DC conductivity measured via a four-point probe, the trends were consistent. Ongoing research into porosity has shown that the refractive index correlates with the porosity of specific electrode sets, indicating the potential for broader application. This comprehensive approach demonstrates the significant advantages of integrating terahertz technology into the battery electrode manufacturing process, potentially revolutionizing the industry by enhancing efficiency and reducing waste.

see https://jnde.isnt.in/index.php/JNDE/article/view/84

Exploring Porosity in Battery Electrodes: Terahertz Technology Unveiling Remote Sensing

2026-02-18T15:55:00.010+00:00

Zarrinkhat, Faezeh, Arturo I. Hernandez-Serrano, Alasdair Pentland, Philip F. Taday, Donald D. Arnone, and Michael Pepper. "Exploring porosity in battery electrodes: terahertz technology unveiling remote sensing." In 2024 49th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), pp. 1-2. IEEE, 2024.

Abstract:

Porosity significantly influences lithium-ion battery performance, impacting cell capacity, voltage, and specific power - critical to designers. Terahertz technology enables non-destructive, remote porosity assessment, addressing limitations in current measurement methods.

see https://ieeexplore.ieee.org/abstract/document/10697663

Optical and terahertz methods for studying easel oil paintings

2026-02-16T15:51:00.001+00:00

Abstract

Subject of study. This study focuses on the application of terahertz tomography methods to easel oil paintings. Aim of study. The aim of this study is to assess the effectiveness of terahertz tomography in analyzing the layered structure of artworks and detecting hidden damage, elements, and annotations. Method. The study employed traditional analysis methods, such as infrared, ultraviolet fluorescence, and X-ray imaging. Special emphasis was placed on terahertz tomography, which enables non-invasive imaging of internal structures. Main results. The study showed that terahertz tomography allows for the differentiation of materials used in oil paintings. This method enables a detailed examination of the layered structure without damaging the object under investigation, revealing elements that cannot be detected using other methods. The novelty of this study lies in the proposed application of terahertz tomography for preliminary in situ examination of paintings to detect hidden defects and possible inscriptions on the reverse side of artworks. Practical significance. The results obtained from this study are valuable for researching, assessing the preservation status of, and restoring oil paintings. Specifically, the proposed method is suitable for detecting defects and hidden elements beneath paint layers without damaging the colorful surface. The terahertz tomography method proves particularly effective when applied in situ, as it does not require paintings to be dismantled.

see https://opg.optica.org/jot/abstract.cfm?uri=jot-91-5-323

The Measurement of the Coating Uniformity of Lithium Iron Phosphate Cathodes on Metal Substrates with Terahertz Time-domain Spectroscopy

2026-02-09T15:47:00.001+00:00

Zarrinkhat, Faezeh, Alasdair Pentland, Carl Reynolds, Emma Kendrick, and Philip F. Taday. "The Measurement of the Coating Uniformity of Lithium Iron Phosphate Cathodes on Metal Substrates with Terahertz Time-domain Spectroscopy." In 2023 48th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), pp. 1-2. IEEE, 2023.

Abstract:

For the first time, the thickness uniformity of lithium iron phosphate (LFP) cathodes are measured using terahertz time-domain spectroscopy. Cathodes are widely manufactured with cobalt, however providing cobalt material comes with supply and health issues. LFP cathodes are introduced as an alternative to tackle this challenge. The aim is to use terahertz pulses to generate an on-line tool to undertake manufacturing process control. Different thickness of cathodes compressed to different densities is measured and the uniformity of their coating is inspected.

see https://ieeexplore.ieee.org/abstract/document/10299358

Self-referencing Reflection Sensor for Industrial Applications

2026-02-06T15:45:00.001+00:00

Zarrinkhat, Faezeh, Bryan Cole, Alasdair Pentland, and Philip F. Taday. "Self-referencing reflection sensor for industrial applications." In 2023 48th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), pp. 1-2. IEEE, 2023.

Abstract:

Terahertz sensors have found their way into many industrial applications, though undertaking regular reference measurements could be inconvenient on some occasions. A sensor with a self-referencing (SR) mechanism (in a linear configuration) is designed and manufactured to tackle the challenge. The sensor head is used on Lithium Iron Phosphate (LFP) cathodes to report the thickness and refractive index of the material.

see https://ieeexplore.ieee.org/abstract/document/10299020

Incorporating Time-Domain Reflectometry in Chip-Level Failure Analysis Workflow: Case Studies

2026-02-04T15:27:00.005+00:00

Liao, Joy Y., Khanh Giang, Timothy Pham, and Howard Lee Marks. "Incorporating time-domain reflectometry in chip-level failure analysis workflow: case studies." In International Symposium for Testing and Failure Analysis, vol. 84741, pp. 145-150. ASM International, 2023.

Abstract

Non-destructive electrical fault isolation (FI) techniques such as emission- and laser-based techniques have been utilized widely for chip-level failure analysis (FA). However, these techniques by themselves can sometimes be inadequate for certain failure modes. In this paper, we present six FA case studies using Time-domain Reflectometry (Electro-optical terahertz pulse reflectometry, EOTPR) in combination with the traditional FI techniques. We also present continuing development in making EOTPR accessible to the semiconductor process and packaging communities.

see https://dl.asminternational.org/istfa/proceedings-abstract/ISTFA2023/84741/145/28577

Recent Developments in EOTPR Towards a Fully Automated Tool for High Volume Failure Analysis

2026-02-02T15:24:00.001+00:00

White, Tom, Jesse Alton, Brett Gibson, Martin Igarashi, Joy Liao, Timothy Pham, and Howard Marks. "Recent Developments in EOTPR Towards a Fully Automated Tool for High Volume Failure Analysis." In 2025 IEEE International Reliability Physics Symposium (IRPS), pp. 1-5. IEEE, 2025.

Abstract

Developments in backside power delivery (BPD) technology will become increasingly important for advanced semiconductors, but will present new challenges for failure analysis (FA) labs. Electro-Optical TeraHertz Pulsed Reflectometry (EOTPR) is a well-established electrical FA technique for package level open and leakage faults, but has comparatively little use for detecting die-level faults. Here, two case studies are presented that demonstrate how EOTPR can be used to localize faults within a die, highlighting how EOTPR could be utilized for BPD devices. Recent and future key developments in EOTPR are also presented.

see https://ieeexplore.ieee.org/abstract/document/10983830

Reduction in Reflection Signal Losses in Complex Terahertz Optical Elements Through Tailored Oil Application

2026-01-28T15:22:00.001+00:00

Kaluza, Mateusz, Adrianna Nieradka, Mateusz Surma, Wojciech Krauze, and Agnieszka Siemion. "Reduction in Reflection Signal Losses in Complex Terahertz Optical Elements Through Tailored Oil Application." Applied Sciences 15, no. 20 (2025): 11167.

Abstract

In complex terahertz (THz) systems, multiple optical elements are often combined to achieve advanced functionalities. However, unwanted Fresnel reflections at their interfaces and between components lead to parasitic interference effects and signal losses. This study presents oil-based refractive-index-matching fillers integrated with additively manufactured assemblies to suppress Fresnel reflections and enhance overall optical system performance. The optical properties of 20 plant-based, synthetic, and mineral oils were investigated using terahertz time-domain spectroscopy (THz TDS). Furthermore, a multilayer structure was designed and experimentally verified, fabricated via fused deposition modeling (FDM) using highly transparent cyclic olefin copolymer (COC). The results demonstrate that the use of tailored oils reduces Fresnel reflection signal losses and also mitigates parasitic interference within the system, thereby improving the effective efficiency of the optical system. Additionally, THz TDS measurements on multilayer structures revealed that, in imaging configurations, the application of refractive-index-matched oils increases the signal gain by 2.33 times. These findings highlight the potential of oil-based index-matching fillers for imaging multilayered objects and mitigating delamination effects in optical elements.

see https://www.mdpi.com/2076-3417/15/20/11167

The first annual Showcase of the EPSRC NetworkPlus in Terahertz System

2026-01-27T09:38:00.001+00:00

📣 We are pleased to announce that the first annual Showcase of the EPSRC NetworkPlus in Terahertz Systems will take place in Leeds on 21st and 22nd April 2026 📣

The Showcase will bring together academics and representatives working in industry and non-academic research organisations for two days of engaging discussions on future prioritisation areas for THz science and technology across the UK and Europe. We will also provide information on our Flexible Fund, which will support researchers in exploring some of these opportunities through seedcorn projects. There will be plenty of opportunities for networking – including a poster session and conference dinner – and for helping to shape the future of the NetworkPlus.

For further details and to register your interest in attending the meeting, please see below 👇 The deadline for EOIs is Friday 30th January.

Using density changes to monitor blending with magnesium stearate by terahertz time-domain spectroscopy

2026-01-26T15:17:00.001+00:00

Anuschek, Moritz, Thea Nilsson, Anne Linnet Skelbæk-Lorenzen, Thomas Kvistgaard Vilhelmsen, J. Axel Zeitler, and Jukka Rantanen. "Using density changes to monitor blending with magnesium stearate by terahertz time-domain spectroscopy." International Journal of Pharmaceutics 672 (2025): 125303.

Abstract

Magnesium stearate (MgSt) is among the most common excipients and the most common lubricant in solid oral products. It is primarily added to tablet formulations to ease ejection during tablet compression. While commonly present in low concentrations, the addition of MgSt substantially affects the final tablet properties. Its impact is further not only concentration dependent but also varies with exposure of the formulation to shear, which worst-case results in over-lubrication. The presented study investigated the applicability of terahertz time-domain spectroscopy (THz-TDS) to monitor the shear-induced blend densification of microcrystalline cellulose blended with MgSt over a range of concentrations (0.3, 0.7, and 1.0 %). The effect of shear was investigated by variation of blending times (5 – 20 min) in a diffusion blender. THz-TDS measurements of the powder blends were acquired in transmission by measuring directly through the mixing container. The refractive index at terahertz frequencies was found to be sufficiently sensitive to resolve the densification of the blend with increased blending times. Thus, THz-TDS blend density measurements can be used as a surrogate parameter to evaluate the total shear exposure of a blend. Considerations regarding implementation are discussed. In the context the approach was integrated with the well-described THz-TDS-based tablet porosity analysis into a unified model to monitor and predict the tensile strength. Including the THz-TDS measurement on the blend allowed for a more accurate description of the tensile strength, reducing the root mean squared error by over 40 % (0.33 MPa). The possibility of monitoring the density changes of a blend non-invasively makes THz-TDS a promising process analytical technology approach for controlling the total shear impact on lubricated blends and tablet quality.

see https://www.sciencedirect.com/science/article/pii/S0378517325001395

Terahertz non-destructive testing of thin self-lubricating bearing coating thickness based on SOMP sparse representation

2026-01-23T15:13:00.001+00:00

Huang, Yi, Hailiang Wang, Weiqiang Chen, Shuncong Zhong, Tingting Shi, Caihong Zhuang, Fuwei Sun, Yonglin Huang, and Zhenghao Zhang. "Terahertz non-destructive testing of thin self-lubricating bearing coating thickness based on SOMP sparse representation." Infrared Physics & Technology (2025): 106223.

Abstract

The thickness of aviation solid thin self-lubricating bearing coatings gradually decreases during wear, which leads to severe echo overlapping in terahertz non-destructive testing. This adversely affects the extraction of coating thickness information. In this paper, a thin coating thickness measurement method that integrates secondary orthogonal matching pursuit (SOMP) sparse representation with the time-of-flight (TOF) is proposed. The propagation characteristics of terahertz waves are firstly investigated, and the convolutional dictionary matrix is constructed based on the reference signal. Subsequently, a series of suboptimal atoms are selected by maximizing the inner product between the reflected signal and the column vector. On this basis, the optimal atoms are further identified using the minimum envelope entropy index to reconstruct the impulse response. The coating thickness is finally quantitatively calculated using the TOF method. The experiments demonstrate that this method can detect coatings thinner than 15 μm with a relative error below 5 %. This study is expected to provide an effective method for accurately measuring the thickness of thin self-lubricating bearing coatings.

see https://www.sciencedirect.com/science/article/abs/pii/S135044952500516X

Polarimetry terahertz imaging of human breast cancer surgical specimens

2026-01-22T21:57:00.002+00:00

Gurjar, Nikita, Keith Bailey, and Magda El-Shenawee. "Polarimetry terahertz imaging of human breast cancer surgical specimens." Journal of Medical Imaging 11, no. 6 (2024): 065503-065503.

Abstract

Purpose
We investigate terahertz (THz) polarimetry imaging of seven human breast cancer surgical specimens. The goal is to enhance image contrast between adjacent tissue types of cancer, healthy collagen, and fat in excised breast tumors. Based on the biological perception of random growth of cancer and invasion of surrounding healthy tissues in the breast, we hypothesize that cancerous cells interact with the THz electric field in a different manner compared with healthy cells. This difference can be best captured using multiple polarizations instead of single polarization.
Approach
Time domain pulsed signals are experimentally collected from each pixel of the specimen in horizontal–horizontal, vertical–horizontal, vertical–vertical, and horizontal–vertical polarizations. The time domain pulses are transformed to the frequency domain to obtain the power spectra and 16 Mueller matrix images. The whole-slide pathology imaging was used to interpret and label all images.
Results
The results of the cross and co-polarization power spectrum images demonstrated a strong dependency on the tissue orientation with respect to the emitted and detected electric fields. At the 130-deg rotation angle of the scanned samples, the detector showed the strongest reflected signal in cross-polarization. Furthermore, the Mueller matrix images consistently demonstrated patterns in fresh and block tissues confirming the differentiation between tissue types in breast tumor specimens.
Conclusions
THz polarimetry imaging shows a potential for improving image contrast in excised tumor tissues compared with single polarization imaging. Cross-polarization signals demonstrated smaller amplitudes compared with co-polarized signals. However, averaging the signal during measurements has tremendously improved the image. Furthermore, in post-processing, averaging the frequency domain images and the Mueller matrix elements with respect to frequency has led to better image contrast. Some patterns in the Mueller matrix images were difficult to interpret leading to the necessity of more investigation of the Mueller matrix and its physiological interpretation of breast tumor tissues.

see https://www.spiedigitallibrary.org/journals/journal-of-medical-imaging/volume-11/issue-6/065503/Polarimetry-terahertz-imaging-of-human-breast-cancer-surgical-specimens/10.1117/1.JMI.11.6.065503.full

Terahertz Spectroscopy and Imaging

Probing the Influence of Water on the Molecular Mobility of PVP/VA using Terahertz Spectroscopy

Non-destructive detection of coating delamination using reflected time-domain terahertz waveforms

Reference-free humidity sensing based on terahertz time-domain spectroscopy

Abstract

THz Non-Destructive Testing Method for Internal Moisture Defects in Composite Insulators

Monitoring Tensile-Induced Subsurface Damages of Woven Glass Fiber Reinforced Polymer Using Terahertz Time-of-Flight Tomography

Real-time observation of coherent spin wave handedness

Optical and terahertz methods for studying easel oil paintings

Measuring Solute Concentration with Terahertz Time-Domain Spectroscopy in Single and Multiphase Systems

Terahertz imaging of titanium dioxide-free film coating hydration and tablet core interactions

Ma, Mingrui, Marwa Nassar, Jason Teckoe, and J. Axel Zeitler. "Terahertz imaging of titanium dioxide-free film coating hydration and tablet core interactions." International Journal of Pharmaceutics (2026): 126596.

Abstract

see https://www.sciencedirect.com/science/article/pii/S037851732600044X

The 2023 terahertz science and technology roadmap

Abstract

Application of Terahertz Time-Domain Spectroscopy to Study the Microheterogeneities of Solutions: A Case Study of Aqueous Sugar Solutions

Application of Terahertz Pulses to Non-Destructive Testing

Terahertz time-domain spectro-imaging and hyperspectral imagery to investigate a historical Longwy glazed ceramic

Terahertz Assessment of the Battery Electrodes Save Production Costs of Electric Vehicles

Abstract

Exploring Porosity in Battery Electrodes: Terahertz Technology Unveiling Remote Sensing

Optical and terahertz methods for studying easel oil paintings

The Measurement of the Coating Uniformity of Lithium Iron Phosphate Cathodes on Metal Substrates with Terahertz Time-domain Spectroscopy

Self-referencing Reflection Sensor for Industrial Applications

Incorporating Time-Domain Reflectometry in Chip-Level Failure Analysis Workflow: Case Studies

Abstract

Recent Developments in EOTPR Towards a Fully Automated Tool for High Volume Failure Analysis

Reduction in Reflection Signal Losses in Complex Terahertz Optical Elements Through Tailored Oil Application

Abstract

The first annual Showcase of the EPSRC NetworkPlus in Terahertz System

Using density changes to monitor blending with magnesium stearate by terahertz time-domain spectroscopy

Abstract

Terahertz non-destructive testing of thin self-lubricating bearing coating thickness based on SOMP sparse representation

Polarimetry terahertz imaging of human breast cancer surgical specimens