Terahertz Time-of-Flight Tomography Beyond the Axial Resolution Limit: Autoregressive Spectral Estimation Based on the Modified Covariance Method

Zhai, Min, Alexandre Locquet, Cyrielle Roquelet, and D. S. Citrin. "Terahertz Time-of-Flight Tomography Beyond the Axial Resolution Limit: Autoregressive Spectral Estimation Based on the Modified Covariance Method." Journal of Infrared, Millimeter, and Terahertz Waves (2020): 1-14.

Abstract

We present a time-of-flight tomography method for exceeding the naïve axial (i.e., depth) resolution limit of terahertz (THz) deconvolution by autoregressive spectral extrapolation (AR) based on the modified covariance method (AR/MCM). In contrast to Wiener filtering combined with wavelet denoising, AR/MCM does not discard any frequency components in the low signal-to-noise (SNR) regions of the measured data, and unlike the AR approach based on the Burg method (AR/BM), no peak splitting (single peaks in the impulse response function appearing as double peaks) as well as frequency bias (spectral peaks shifted with respect to their correct positions) is observed after deconvolution. After verifying the advantages of AR/MCM over Wiener filtering in conjunction with wavelet denoising as well as over AR/BM, using synthetic data, AR/MCM is employed to reconstruct a single layer of mill scale on a steel coupon from experimental THz time-of-flight tomography data. The reconstruction shows good agreement with the film thickness obtained from destructive cross-sectional measurements. In addition, unlike AR/BM, optimizing the parameters to obtain stable reconstruction is straightforward relying of Akaike’s information criterion suggesting that AR/MCM can be an easier to implement for THz nondestructive characterization of stratigraphy under noisy conditions, particularly when estimates of the stratigraphy may not a priori be available.

Full paper can be found at https://link.springer.com/article/10.1007/s10762-020-00722-1

… that minimizes the AIC. Experiment. The measurement in this work is carried out using a pulsed, broadband THz time domain system from TeraView Ltd. (TPSSpectra 3000), shown schematically in Fig. 1. The GaAs photoconductive …

Microwave shielding and DC Electrical Properties of Carbon Black Loaded Rubber Nano-Composites

Abstract

In this work, ten carbon black (CB) loaded elastic acrylonitrile butadiene rubber (NBR) nano-composites have been prepared to be used in microwave shielding applications. The DC electric properties of these CB loaded NBR composites have been studied. The evolution of DC conductivity of CB loaded NBR composites with loading level revealed S-shapes curve in accordance with the percolation theory. The current (I)-voltage (V) relations have been studied for these samples at room temperature. All CB loaded NBR composite samples showed Ohmic behavior with the exception of two samples namely CB30 and CB40 in which space charge limited conduction is obvious. Microwave shielding has been calculated from the transmittance data measured using terahertz time domain spectroscopy (THz-TDS) technique. The analysis of microwave shielding data revealed that the sample CB70 has the highest shielding effectiveness. The results of the microwave shielding effectiveness of CB loaded NBR composites were correlated to their DC electric conductivities. Results showed that there is a strong relationship between the DC electric conductivity of the samples and their activity regarding microwave shielding effectiveness. The current investigation of microwave shielding properties of CB loaded NBR composites magnifies the importance of DC electric conduction losses as a major mechanism for microwave shielding.

http://www.jmest.org/wp-content/uploads/JMESTN42350842.pdf

TPS Spectra 3000, (TeraView, UK) was used for measuring transmittance of the samples in the frequency range 10-1000 GHz

Microelectromechanically tunable multiband metamaterial with preserved isotropy

Abstract

We experimentally demonstrate a micromachined reconfigurable metamaterial with polarization independent characteristics for multiple resonances in terahertz spectral region. The metamaterial unit cell consists of eight out-of-plane deformable microcantilevers placed at each corner of an octagon ring. The octagon shaped unit cell geometry provides the desired rotational symmetry, while the out-of-plane movable cantilevers preserves the symmetry at different configurations of the metamaterial. The metamaterial is shown to provide polarization independent response for both electrical inductive-capacitive (eLC) resonance and dipolar resonance at all states of actuation. The proposed metamaterial has a switching range of 0.16 THz and 0.37 THz and a transmission intensity change of more than 0.2 and 0.7 for the eLC and dipolar resonances, respectively for both TE and TM modes. Further optimization of the metal layer thickness, provides an improvement of up to 80% modulation at 0.57 THz. The simultaneously tunable dual band isotropic metamaterial will enable the realization of high performance electro-optic devices that would facilitate numerous terahertz applications such as compressive terahertz imaging, miniaturized terahertz spectroscopy and next generation high speed wireless communication possible in the near future.

All THz transmission spectra measured in this paper were acquired using TeraView's TPS Spectra 3000.

http://www.nature.com/srep/2015/150626/srep11678/full/srep11678.html

Properties of two-component nematic liquid crystal mixtures in the range of 0.3–3.0 THz

TeraView's TPS Spectra 3000 was used to investigate nematic liquid crystals in the range of 0.3–3.0 THz.


http://www.tandfonline.com/doi/abs/10.1080/02678292.2015.1036816#.VYvdFvlViko


Abstract

In this work, we present the results of terahertz measurements of five nematic liquid crystal materials. Optical properties like refractive indices, birefringence and absorption coefficients of liquid crystals (LCs) for ordinary and extraordinary polarisation were compared. The aim of this study was to check the impact of the structure of LC molecules on above properties. The compounds with different core structure and various number of laterally substituted fluorine atoms were chosen. A standard terahertz Time-Domain Spectrometer to measurements from 0.3 THz to 3 THz was used.

TeraView at IRMMW-THz 2015

TeraView invites you to visit us at IRMMW-THz 2015!

"Since 2000, the IRMMW-THz conference series has alternated between Asia, Europe and America on a continuous three year cycle. In 2015, the conference returns to the Asian leg, and will be held in Hong Kong for the first time from August 23 to 28 at the Chinese University of Hong Kong."


TeraView's CEO, Dr. Don Arnone will be in attendance for the event and will be one of the plenary speakers.


TeraView's Dr. Philip Taday will also be attending the event, and will be demonstrating TeraView's flagship instrument, the TeraPulse 4000 in our booth over.


If you would like to pre-arrange a meeting, or a chance to view a demonstration of the TeraPulse 4000, please e-mail Dr. Phil Taday at philip.taday@teraview.com.

Impact of Processing Conditions on Inter-tablet Coating Thickness Variations Measured by Terahertz In-Line Sensing

HUNGYEN LIN, ROBERT K. MAY, MICHAEL J. EVANS, SHUNCONG ZHONG, LYNN F. GLADDEN, YAOCHUN SHEN,

J. AXEL ZEITLER

Abstract

A novel in-line technique utilising pulsed terahertz radiation for directmeasurement of the film coating thickness of individual tablets during the coating process was previously developed and demonstrated on a production-scale coater. Here, we use this technique to monitor the evolution of tablet film coating thickness and its inter-tablet variability during the coating process under a number of different

process conditions that have been purposefully induced in the production-scale coating process. The changes that were introduced to the coating process include removing the baffles from the coater, adding uncoated tablets to the running process, halting the drum, blockage of spray guns and changes to the spray rate. The terahertz sensor was able to pick up the resulting changes in average coating thickness in the coating drum and we report the impact of these process changes on the resulting coating quality. C⃝ 2015 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci

This study was performed using TeraView's Spectra 3000 system. (TeraView, Cambridge, UK)

Full Article: http://onlinelibrary.wiley.com/doi/10.1002/jps.24503/full

Photonics West - Call for Papers

This conference brings together researchers and engineers from academia, industry, and government laboratories to explore and present work in the frequency range covering approximately less than 1 GHz (300 mm) to greater than 3 THz (100 μm). Papers on RF and millimeter technology including advances in wireless communications, radar, lidar, microwave and mm-wave photonics, metamaterials, antennas, phased array radar, modulation, security, monitoring, detection, imaging are encouraged. Papers in photonic-related fields including, but not limited to, radio over fiber (RoF) RF photonics including photonic generation of microwave signals, photonic processing of microwave signals, and photonic distribution of microwave signals and semiconductor (including Si, SiC, SOI, GaAs, GaN, InP, SiGe, diamond, graphene and other materials) RF, mm-wave and terahertz devices and related applications are also encouraged, as well as the hybrid photonic systems and applications. Terahertz (THz) technology deals with the generation and utilization of electromagnetic energy covering what is also known as the sub-millimeter wave region of the spectrum. In this region, which lies between the millimeter wave and far infrared spectral regions, materials exhibit properties that can be exploited to advantage for use over a broad range of important technologies and applications. Papers on terahertz photonics including photonic generation and detection of terahertz waves, THz lasers are also encouraged.

Abstracts are due on the 3rd of August 2015, and papers are solicited in the following areas: 

• Terahertz sources
• RF, sub-millimeter-wave and millimeter-wave sources
• Detectors
• High-power sources, modules, and systems
• Terahertz, RF, millimeter-wave, and sub-millimeter-wave passive components
• Materials for THz and GHz devices
• Enhancements, improvements and advances in RF, millimeter-wave and sub-millimeter wave generation, modulation and detection
• Simulations and modeling
• Spectroscopy
• Biomedical applications
• Communication and sensing systems
• Imaging and security
• Astronomy and space and other areas of photonics, light, and matter
• Innovations
• Power supplies and electronic power conditioners
• Organic electronics

For more information please visit http://spie.org/PWO/conferencedetails/thz-rf-mm-submm-wave-technology

An Effective Method for Substance Detection Using the Broad Spectrum THz Signal with a “Terahertz Nose”

Vyacheslav A. Trofimov  and Svetlana A. Varentsova 

Abstract

We propose an effective method for the detection and identification of dangerous substances by using the broadband THz pulse. This pulse excites, for example, many vibrational or rotational energy levels of molecules simultaneously. By analyzing the time-dependent spectrum of the THz pulse transmitted through or reflected from a substance, we follow the average response spectrum dynamics. Comparing the absorption and emission spectrum dynamics of a substance under analysis with the corresponding data for a standard substance, one can detect and identify the substance under real conditions taking into account the influence of packing material, water vapor and substance surface. For quality assessment of the standard substance detection in the signal under analysis, we propose time-dependent integral correlation criteria. Restrictions of usually used detection and identification methods, based on a comparison between the absorption frequencies of a substance under analysis and a standard substance, are demonstrated using a physical experiment with paper napkins. 

Full Article: http://scholar.google.co.uk/scholar_url?url=http://www.mdpi.com/1424-8220/15/6/12103/pdf&hl=en&sa=X&scisig=AAGBfm1LSPK_lrl8QysLaqcq1c3X8gkORg&nossl=1&oi=scholaralrt

Careers at TeraView!

TeraView Ltd. are currently recruiting for a range of exciting new roles within the company! 

TeraView offers an excellent salary and benefits package, along with the opportunity for highly-motivated staff to work together and shape the development of products in one of the newest and most exciting areas of technology. 

For all the information you need on the wide range of roles TeraView are currently recruiting for, please visit our careers page at: http://www.teraview.com/about/careers-jobs.html

Current vacancies at TeraView

• Financial Controller 
• Instrument Assembly Technician 
• Mechanical Design Engineer 
• Product Manager 
• Software Developer 
• Software Developer Team Leader

Company Overview

TeraView Ltd is the world’s first and leading provider of Terahertz solutions to Fortune 500 companies, in a variety of industries. TeraView’s advanced portfolio of Terahertz applications knowledge, system design, product range and intellectual property (63 patents granted) is unrivalled in breadth and depth.  There now exists an unprecedented opportunity to exploit this first mover advantage in select, commercially validated markets, to establish a commercially dominant position in this last unconquered region of the electromagnetic spectrum. 

TeraView’s vision is to establish Terahertz as the premier imaging tool for the 21st century, comparable to the enormous success of X-Ray the latter half of the last century, and more recently ultrasound. Ultrasound progressed from research to become an extensively used tool in inspection and other applications, as a result of technological advances similar to those now transforming Terahertz. The current ultrasound market is valued at close to $3.2B per annum, and has an annual growth rate of 30% +.

A Design of Terahertz Broadband Filters and Its Effect in Eliminating Asymmetric Characteristics in Device Structures

Zhu, M. ; Lee, C.

Abstract

We report a straightforward way to design and fabricate polarization-insensitive broadband bandstop filters in terahertz range by fabricating identical metal patterns on both sides of a dielectric substrate with one layer rotated 90o to the other. The unit cells used in such designs are the well-studied split-ring-resonators, hence the frequency range of the stop band can be easily tuned by varying the dimensions of the unit cell structures. Through simulation analysis, we show that such fabrication method requires no alignment in lithography step and works with common dielectric substrates. Two types of substrates, 1 mm-thick quartz and 100 μm-thick polyethylene terephthalate, were used as a demonstration. The transmission level stayed below 12% for a stopband of 0.42 THz frequency range. Lastly, we reasoned with simulation results that the proposed broadband filters give consistent performance regardless of the gap location in the unit cell, which will further extend their use in practical applications.

This study was performed using TeraView's Spectra 3000 system. (TeraView, Cambridge, UK)

Full Article: http://ieeexplore.ieee.org/xpl/abstractAuthors.jsp?tp=&arnumber=7105824&url=http%3A%2F%2Fieeexplore.ieee.org%2Fxpls%2Fabs_all.jsp%3Farnumber%3D7105824

Computationally Assisted (Solid-State Density Functional Theory) Structural (X-ray) and Vibrational Spectroscopy (FT-IR, FT-RS, TDs-THz) Characterization of the Cardiovascular Drug Lacidipine

Kacper Drużbicki, Jadwiga Mielcarek, Anna Kiwilsza, Loic Toupet, Eric Collet, Aleksandra Pajzderska, and Jan Wąsicki

Abstract

The structural properties of a second-generation dihydropyridine calcium antagonist, lacidipine, were explored by combining low-temperature X-ray diffraction with optical vibrational spectroscopy and periodic density functional theory (PBC DFT) calculations. Crystallographic analysis cannot discriminate between two possible molecular symmetries in crystals made of pure lacipidine: the space group Ama2, where the lacipidine molecule lies on mirror symmetry, or a Cc space group with distorted lacipidine molecules. Intermolecular interactions analysis reveals an infinite net of moderate-strength N–H···O hydrogen-bonds, which link the molecular units toward the crystallographic b-axis. Weak interactions were identified, revealing their role in stabilization of the crystal structure. The vibrational dynamics of lacidipine was thoroughly explored by combining infrared and Raman spectroscopy in the middle- and low-wavenumber range. The given interpretation was fully supported by state-of-the-art solid-state density functional theory calculations (plane-wave DFT), giving deep insight into the vibrational response and providing a complex assignment of spectral features. The vibrational analysis was extended onto the lattice-phonon range by employing time-domain terahertz spectroscopy. Analysis of the anisotropic displacement parameters suggests noticeable dynamics of the terminal (tert-butoxycarbonyl)vinyl moiety. The terahertz study provides direct experimental evidence of “crankshaft” type motions in the terminal chain. By combining low-wavenumber vibrational spectroscopy with the first-principles calculations, we were able to prove that the quoted thermodynamically stable phase corresponds to the monoclinic Cc space group.

This study was performed using TeraView's Spectra 3000 system. (TeraView, Cambridge, UK)

Full Article: http://pubs.acs.org/doi/abs/10.1021/acs.cgd.5b00251

Experimental (X-Ray, IR, RS, INS, THz) and Solid-State DFT Study on (1:1) Co-crystal of Bromanilic Acid and 2,6-Dimethylpyrazine

Katarzyna Łuczyńska , Kacper Drużbicki , Krzysztof Lyczko , and Jan Czeslaw Dobrowolski

Abstract

A combined structural, vibrational spectroscopy and solid-state DFT study of hydrogen-bonded complex of bromanilic acid with 2,6-dimethylpyrazine is reported. The crystallographic structure was determined by means of low-temperature single-crystal X-ray diffraction, which reveals the molecular units in their native protonation states, forming one-dimensional infinite nets of moderate-strength O∙∙∙H-N hydrogen bonds. The nature of the crystallographic forces, stabilizing the studied structure, has been drawn by employing the non-covalent interactions analysis. It was found that in addition to the hydrogen bonding, the intermolecular forces are dominated by stacking interactions and C-H∙∙∙O contacts. The thermal and calorimetric analysis was employed to probe stability of the crystal phase. The structural analysis was further supported by computationally assisted 13C CP/MAS NMR study, providing a complete assignment of the recorded resonances. The vibrational dynamics was explored by combining the optical (IR, Raman, TDs-THz) and inelastic neutron scattering (INS) spectroscopy techniques with the state-of-the-art solid-state density functional theory (DFT) computations. Despite of quasi-harmonic approximation assumed throughout the study, an excellent agreement between the theoretical and experimental data was achieved over the entire spectral range, allowing for deep and possibly thorough understanding of the vibrational characteristics of the system. Particularly, the significant influence of the long-range dipole coupling on the IR spectrum has been revealed. Based on a wealth of information gathered, the recent implementation of dispersion-corrected linear-response scheme has been extensively examined.

This study was performed using TeraView's Spectra 3000 system. (TeraView, Cambridge, UK)

Full Article: http://pubs.acs.org/doi/abs/10.1021/acs.jpcb.5b03279

Passive imaging of concealed objects in terahertz and long-wavelength infrared

Marcin Kowalski, Mariusz Kastek, Michal Walczakowski, Norbert Palka, and Mieczyslaw Szustakowski

Abstract

Terahertz and infrared radiation have unique properties applicable to the field of surveillance and security systems. We investigated the possibility of detecting potentially dangerous objects covered by various types of clothing using passive imagers operating at 1.2 mm (250 GHz) and long-wavelength infrared at 6–15 μm (20–50 THz). We developed a measurement methodology that assumes to investigate theoretical limitations, performance of imagers, and physical properties of fabrics. To evaluate stability of the detection capabilities of imagers, we performed measurement sessions each lasting 30 min. We present a theoretical comparison of the two spectra and results of experiments using state-of-the-art equipment.

This study was performed using TeraView's Spectra 3000 system. (TeraView, Cambridge, UK)

Full Article: http://www.opticsinfobase.org/ao/abstract.cfm?uri=ao-54-13-3826

Don’t Miss the Impressive Line-up at the CLEO Plenary Session

Monday Plenary Session

Eric Betzig, Howard Hughes Medical Institute, USA

Nobel Prize Winner in Chemistry 2014

Imaging Life at High Spatiotemporal Resolution

Tony Heinz, Columbia University, USA

Electrons in Atomically Thin Two-dimensional Crystals

Stephan W. Hell, Max Planck Institute for Biophysical Chemistry, Germany

Nobel Prize Winner in Chemistry 2014

Nanoscopy with Focused Light

W. E. Moerner, Stanford University, USA

Nobel Prize Winner in Chemistry 2014

Foundations of Super-Resolution Microscopy

Tuesday Plenary Session

Hiroshi Amano, Nagoya University, Japan

Nobel Prize Winner in Physics 2014

Current and Future of Solid State Lighting

Steven Chu, Stanford University, USA

Nobel Prize Winner in Physics 1997

Microscopy 2.0

Wednesday International Year of Light Plenary Session

Shuji Nakamura, University of California Santa Barbara, USA

Nobel Prize Winner in Physics 2014

Energy Savings by LED Lighting

Miles Padgett, University of Glasgow Scotland, UK

Light’s Twist

Continuously tunable and fast-response terahertz metamaterials using in-plane switching dual-frequency liquid crystal cells

Chia-Yi Huang, Chia-Chun Chen, Wei-Fan Chiang, Min-Cheng Tsai, Shun-An Jiang, Tsung-Hao Chang, and Song-Hang Wang

Abstract

A metamaterial that is embedded into an in-plane switching dual-frequency liquid crystal cell is used to develop an electrically controllable terahertz metamaterial. The resonance peak of the metamaterial can be redshifted and blueshifted as the frequency of an external voltage is switched, and the response times for the redshift and blueshift are 1.044 ms and 1.376 ms, respectively. A simulation confirms the spectral redshift and blueshift. The variation in the peak frequency as a function of applied frequency at the external voltage is presented. Experimental results show that the resonance peak of the metamaterial can be continuously tuned within a frequency range of 15 GHz as the applied frequency is switched between 19 kHz and 22 kHz. Therefore, this metamaterial is a continuously tunable and fast-response terahertz filter and could be used for terahertz imaging and terahertz telecommunications.

This study was performed using TeraView's Spectra 3000 system. (TeraView, Cambridge, UK)

Full Article: http://www.opticsinfobase.org/ol/upcoming_pdf.cfm?id=235253

Comparison of damage behaviour of different plant fibre composites under laser impact loading

F. Touchard, L. Berthe, P. Malinowski, S. Opoka, M. Boustie, L. Chocinski-Arnault and W. Ostachowicz

Abstract

The high strain rate behaviour of the eco-composites, when submitted to laser impact loading, is not well known yet. Crucial questions are still open: influence of plant fiber length and distribution on the composite impact behaviour, types of damage induced by impact loading, the way the failure occurs, etc. We present the very first results of a collaborative research involving the institutions PPRIME- Poitiers and PIMM-Paris, and IMP PAN-Gdansk-Poland. A comparison of laser shock induced damage is realised, based on observations of sample back faces for several types of eco-composites. Spallation, residual blister and inside delamination, depending on the fibre length in tested composites have been observed. The ability of the Terahertz technique for internal damage detection is demonstrated.

This study was performed using TeraView's Spectra 3000 system. (TeraView, Cambridge, UK)

Full Article: http://www.mattech-journal.org/articles/mattech/abs/2015/01/mt150022/mt150022.html

New trends in non-destructive assessment of aerospace structures

Wieslaw M. Ostachowicz ; Pawel H. Malinowski ; Tomasz Wandowski

Abstract

The scope of the paper includes non–destructive assessment of the structure's material condition, for the aerospace structures during its useful lifetime. The paper presents multidisciplinary technologies devoted to development and implementation of methods and systems that realize inspection and damage detection by non–destructive methods. The paper covers several disciplines which are based on topics such as piezoelectric transducers, elastic waves propagation phenomenon, structural vibrations analysis, electro–mechanical impedance method, terahertz technique, laser induced fluorescence and 3D laser vibrometry applications. Among various techniques available the paper presents selected numerical simulations and experimental validations of considered structures. Authors address also the problem of adhesive bonding in the case of carbon fiber reinforced polymers (CFRP). Techniques for detection of weak bonds are presented together with signal processing approaches. The reported investigations concern weak adhesive bonds caused by both manufacturing (e.g. release agent, poor curing) and in–service contaminations (e.g. moisture). Also the paper provides helpful information about dispersion, mode conversion and wave scattering from stiffeners and boundaries. It addresses the problem of optimisation of excitation signal parameters and sensor placement, as well as analysis of signals reflected from damage. It also includes a variety of techniques being related to diagnostics (damage size estimation and damage type recognition) and prognostics. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

This study was performed using TeraView's Spectra 3000 system. (TeraView, Cambridge, UK)

Full Article: http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=2213453

Terahertz single conductance quantum and topological phase transitions in topological insulator Bi2Se3 ultrathin films

Byung Cheol Park, Tae-Hyeon Kim, Kyung Ik Sim, Boyoun Kang, Jeong Won Kim, Beongki Cho, Kwang-Ho Jeong, Mann-Ho Cho & Jae Hoon Kim

Abstract

Strong spin-orbit interaction and time-reversal symmetry in topological insulators generate novel quantum states called topological surface states. Their study provides unique opportunities to explore exotic phenomena such as spin Hall effects and topological phase transitions, relevant to the development of quantum devices for spintronics and quantum computation. Although ultrahigh-vacuum surface probes can identify individual topological surface states, standard electrical and optical experiments have so far been hampered by the interference of bulk and quantum well states. Here, with terahertz time-domain spectroscopy of ultrathin Bi2Se3 films, we give evidence for topological phase transitions, a single conductance quantum per topological surface state, and a quantized terahertz absorbance of 2.9% (four times the fine structure constant). Our experiment demonstrates the feasibility to isolate, detect and manipulate topological surface states in the ambient at room temperature for future fundamental research on the novel physics of topological insulators and their practical applications.

This study was performed using TeraView's Spectra 3000 system. (TeraView, Cambridge, UK)

Full Article: http://www.nature.com/ncomms/2015/150316/ncomms7552/full/ncomms7552.html#figures

Quantification of residual crystallinity of ball-milled, commercially available, anhydrous β-lactose by differential scanning calorimetry and terahertz spectroscopy

Geoff Smith, Amjad Hussain, Nadeem Irfan Bukhari, Irina Ermolina

Abstract

The quantification of crystallinity is necessary in order to be able to control the milling process. In this study, the changes in the amount of residual crystallinity of ball-milled anhydrous β-lactose (β-LA), for periods up to 60 min, were evaluated by differential scanning calorimetry (DSC) and by terahertz pulsed spectroscopy. The percentage of residual crystallinity using DSC was estimated by two methods: The first method was based on the measurement of the melting of the crystalline part, while the second was based on the measurement of the devitrification of the amorphous part. Peaks in THz spectra, related to the residual crystalline material were analyzed by two methods: (1) area under peak and (2) partial least square. The milled samples of β-LA show a monotonic decrease in crystallinity with milling time, although the quantitative analysis performed by different techniques reveals very different results. THz technique gives significantly lower estimates for % crystallinity (in the early time period) than that calculated from the DSC data, possibly because of the recrystallization of amorphous form during sample preparation. The comparison of residual crystallinity of β-LA with its hydrated counterpart [i.e., α-lactose monohydrate (α-LMH)] has shown that the amount of amorphous material produced from the α-LMH is 20–30 % greater than from β-LA at extended milling times (i.e. 60 min).

This study was performed using TeraView's Spectra 3000 system. (TeraView, Cambridge, UK)

Full Article: http://link.springer.com/article/10.1007%2Fs10973-015-4469-4

Comparisons of intra-tablet coating variability using DEM simulations, asymptotic limit models, and experiments

Ben Freireich, Rahul Kumar, William Ketterhagen, Ke Su, Carl Wassgren, J. Axel Zeitler

Abstract

Discrete element method (DEM) computer simulations are used to investigate intra-tablet coating thickness variability. Two new post-processing algorithms are presented. The first algorithm uses an image-based method to track the exposure to a simulated spray of small area panels on each tablet's surface so that the distribution of spray exposure times over the tablet's surface can be determined directly from DEM data. The second algorithm predicts the asymptotic limit of intra-tablet coating uniformity. This second algorithm includes the influence of tablet orientation and shadowing when considering exposure to the spray, averaged over many tablets.

The DEM simulations produce the first direct evidence that non-spherical tablets approach asymptotic intra-tablet coating variability values. The asymptotic limits are predicted well using the new asymptotic prediction model. In general, tablet caps have thicker coatings than tablet bands. Moreover, tablets that have a more elongated shape tend to have less coating on the smaller radius of curvature portions of the bands. Of particular importance in this new asymptotic modeling approach is the inclusion of shadowing effects. When shadowing is not included and only tablet orientation is considered, the predictions over-predict the asymptotic intra-tablet coating variability values and also change the observed rank order of the asymptotic values for different tablet shapes. The asymptotic intra-tablet coating variability values using the new algorithm correlate reasonably well with tablet sphericity, with increasing sphericity improving coating uniformity.

This paper also presents the first attempt to directly compare experimental and simulated coating thickness distributions. The asymptotic coating thickness predictions compare well qualitatively with terahertz thickness measurements made on tablets from coating experiments. Unfortunately, only qualitative comparisons could be made due to the limited number of tablets sampled experimentally and differences in spray zone areas and flux distributions. The tablets in the experiments, however, displayed similar features as those found in the simulations.

This study was performed using TeraView's Spectra 3000 system. (TeraView, Cambridge, UK)

Full Article: http://www.sciencedirect.com/science/article/pii/S0009250915001852