Enhanced electromagnon excitations in Nd-doped BiFeO3 nanoparticles near morphotropic phase boundaries

Zhang, Yuan, Yi Zhang, Quan Guo, Dongwen Zhang, Shuaizhi Zheng, Ming Feng, Xiangli Zhong et al. "Enhanced electromagnon excitations in Nd-doped BiFeO 3 nanoparticles near morphotropic phase boundaries." Physical Chemistry Chemical Physics 21, no. 38 (2019): 21381-21388.

Abstract

In multiferroics, electromagnons have been recognized as a noticeable topic due to their indispensable role in magnetoelectric, magnetodielectric, and magnetocapacitance effects. Here, the electromagnons of Bi1−xNdxFeO3 (x = 0–0.2) nanoparticles are studied via terahertz time-domain spectroscopy, and the impacts of doping concentrations on electromagnons have been discussed. We found that the electromagnons in Bi1−xNdxFeO3 nanoparticles are associated with their phase transition. The total coupling weight of electromagnons is gradually increased in polar R3c structures and then reduces in the antipolar Pbam phase, and the weight in the antipolar phase is less than that of the pure R3c phase. Interestingly, a colossal electromagnon is observed at polar–antipolar and antiferromagnetic–ferromagnetic phase boundaries. Our work offers an avenue for designing and choosing materials with better magnetodielectric and magnetocapacitance properties.

for full paper see https://pubs.rsc.org/en/content/articlelanding/2019/cp/c9cp04194j/unauth#!divAbstract

The THz-TDS transmission spectra were measured by TeraView's terahertz spectrometers (TPS Spectra3000). 

Use of Terahertz Waves To Monitor Moisture Content in High-Pressure Natural Gas Pipelines

Fan, Shuting, Kwanghee Jeong, Vincent P. Wallace, and Zachary Aman. "Use of Terahertz Waves To Monitor Moisture Content in High-Pressure Natural Gas Pipelines." Energy & Fuels 33, no. 9 (2019): 8026-8031.

Abstract

Pipelines are considered to be the most economical method for large-quantity gas transportation. However, the presence of water in natural gas pipelines causes significant safety and economic issues and must be accurately monitored. In this work, we discuss the feasibility of the emerging technology, terahertz spectroscopy, for monitoring water vapor in natural gas pipelines. We also proposed a novel method by which the transmitted terahertz signal is captured at two different absolute pressures; the differential absorption, subtracted by a quadratic term accounting for the water vapor continuum, was found to be linearly proportional to the partial pressure of water in the vapor phase. Our results indicate that using terahertz waves, as a noncontact spectroscopic technique, combined with our proposed pressure-gradient-based methodology, a minimum of 62 ppm of water vapor can be detected with a path length of 14.7 cm at 100 bar, which satisfies industry requirements.

for full paper see https://pubs.acs.org/doi/abs/10.1021/acs.energyfuels.9b01112

… 2.1. Experimental Approach. This study deployed a commercial terahertz time-domain spectroscopy system (THz-TDS system), TeraPulse 4000 (TeraView Ltd, Cambridge, UK). The operation principle of the system can be found … 

Iterative Tree Algorithm to Evaluate Terahertz Signal Contribution of Specific Optical Paths Within Multilayered Materials

Cassar, Quentin, Adrien Chopard, Frederic Fauquet, Jean-Paul Guillet, Mingming Pan, Jean-Baptiste Perraud, and Patrick Mounaix. "Iterative Tree Algorithm to Evaluate Terahertz Signal Contribution of Specific Optical Paths Within Multilayered Materials." IEEE Transactions on Terahertz Science and Technology 9, no. 6 (2019): 684-694.


Abstract:

Terahertz time-domain spectroscopy is a specifically appropriated technique to analyze layered structure composition and dimension. Inverse electromagnetic problems are commonly solved to extract, from a recorded terahertz-signal, the distinctive layer dielectric properties and thicknesses. However, main origins and formation routes of the signal are left unassessed while it could be of great value to deepen and to enlarge stratified material terahertz-probing property knowledge and understanding. In this article, a new numerical method to reconstruct and to analyze terahertz experimental signals is reported. It consists of an iterative algorithm implementing a connected propagation tree where each node of the tree denotes the occurrence of the incident pulse division. Descendent pulses are individually monitored and their carried proportion of the incident power can be evaluated. Therefore, it provides a flowchart of the predominant optical paths contributing to the structure response. On this basis, a simplified global transfer function is automatically derived by the algorithm. The effectiveness of the numerical procedure is demonstrated through the reconstruction and the analysis of a reflected terahertz-signal from an aerospace coating structure with individual and different thicknesses of several tens of microns. The recovered signal is first discussed as a function of the sum of pulses detected at each iteration. Then, the power proportion distribution for each iteration is studied to delimit the meaningful number of required algorithm iteration. Finally, within each iteration are sorted the most contributing optical paths and a simplified global transfer function is derived. The present algorithm allowed to identify the main propagations inside this stratified material giving arise to the recorded signal and to reduce by 98.23% the number of considered and calculated optical paths compared to the standard signal reconstruction procedure.

for full paper see https://ieeexplore.ieee.org/abstract/document/8811611

… Terahertz measurements were made at the centre of each region, as indicated. Measurement were performed under water purged atmosphere.  Layers are measured by means of a commercially available TPS3000 from TeraView UK…

A Robust Protocol for In Vivo THz Skin Measurements

Lindley-Hatcher, Hannah, A. I. Hernandez-Serrano, Qiushuo Sun, Jiarui Wang, Juan Cebrian, Laurent Blasco, and Emma Pickwell-MacPherson. "A Robust Protocol for In Vivo THz Skin Measurements." Journal of Infrared, Millimeter, and Terahertz Waves 40, no. 9 (2019): 980-989.

Abstract

This work presents an experimental setup to control the way in which pressure interferes with the repeatability of in vivo THz skin measurements. By integrating a pressure sensor circuit into our THz system, it is possible to identify which measurements were taken within a previously specified pressure range. The live response of the pressure sensor helps to acquire data within the desired pressure leading to greater consistency of data between measurements. Additionally, a protocol is proposed to help achieve repeatable results and to remove the effects of the natural variation of the skin through the course of the day. This technique has been shown to be able to quantify the changes induced in the skin following the application of a moisturising skin product and shows the measured result to be significantly different from natural skin variation. This research therefore prepares the way for further studies on the effectiveness of different skin products using in vivo THz measurements.

for full paper see https://link.springer.com/article/10.1007/s10762-019-00619-8

… Furthermore, the circuit also provides a digital output to the THz system; for this study, the TeraView fibre coupled TeraPulse 4000 spectrometer 

Ex Vivo Breast Tumor Identification: Advances Toward a Silicon-Based Terahertz Near-Field Imaging Sensor

Pfeiffer, Ullrich R., Philipp Hillger, Ritesh Jain, Janusz Grzyb, Thomas Bucher, Quentin Cassar, Gaetan MacGrogan, Jean-Paul Guillet, Patrick Mounaix, and Thomas Zimmer. "Ex Vivo Breast Tumor Identification: Advances Toward a Silicon-Based Terahertz Near-Field Imaging Sensor." IEEE Microwave Magazine 20, no. 9 (2019): 32-46.


Terahertz waves cover photon energies that are orders of magnitude smaller (0.4– 40 meV) than the visual spectrum. Therefore, they provide additional information on intrinsic condensed-matter properties, making them attractive for imaging applications in the life sciences [1], [2]. Furthermore, they do not have an ionizing effect and are considered biologically innocuous. The ever-present water in organic matter strongly absorbs terahertz waves, and subtle changes in the water concentration can be indicative of disease [3]. However, the waves’ long wavelength (3 mm- 30 microns) severely limits their lateral resolution and creates challenges for high-resolution imaging of biological tissue on the cellular level, e.g., for tumor margin identification during cancer surgery.



For full paper https://ieeexplore.ieee.org/abstract/document/8792450

"A commercially available TeraPulse 4000 (TeraViewLtd., Cambridge, United Kingdom), with a modified reflection geometry setup as shown in Figure 3(a), was used in this study. The emitted submillimeter pulses were focused on a biological sample sandwiched between two 2-mm-thick C-cut sapphire substrates mounted on a motor stage to perform reflection terahertz imaging. The step sizes in the x and y directions were between 100 micron and 500  micron while the far-field limited spatial resolution at the sample was approximately 1 mm at 300 GHz. Coherent photoconductive detection of the reflected pulses"

Solvent-free and large-scale preparation of silver@polypyrrole core@shell nanocomposites; structural properties and terahertz spectroscopic studies

Ali, Safaa SM, Wael H. Eisa, and A. Abouelsayed. "Solvent-free and large-scale preparation of silver@ polypyrrole core@ shell nanocomposites; structural properties and terahertz spectroscopic studies." Composites Part B: Engineering 176 (2019): 107289.

Abstract

There is a growing interest over the environmental safety and mass-production of polymer nanocomposites. Solvent-free synthetic pathways are considered as promising alternative green techniques because of their high efficiency, simplicity and negligible liberation of hazardous waste. A new synthetic route has been developed to synthesize silver@polypyrrole core@shell nanocomposites at ambient condition. The silver nanoparticles are directly synthesized via solid-state reaction with poly(vinylpyrrolidone) and then pyrrole is polymerized in Ag/PVP powder. The band gap value decreases with the increased addition of pyrrole in the preparation step due to the formation of more silver nanoparticles. Scanning and transmission electron microscope confirm the formation of core@shell structure. The negatively charged carbonyl group of poly(vinylpyrrolidone) can bind to polycationic polypyrrole by an electrostatic effect to form the core@shell structure. The terahertz spectroscopy characterizes the prepared core@shell nanocomposites that are well fit to the Drude-Smith model. The DC optical conductivity in the terahertz range (0.3–2 THz) is increased with increasing Py addition.

for full paper see https://www.sciencedirect.com/science/article/abs/pii/S1359836819325533

… (SII) Japan). Terahertz time-domain spectra (TDS) were collected using TPS spectra 3000 system (Teraview Ltd. England) equipped with ATR unit (35) with silicon crystal and under nitrogen gas atmosphere. 3. Results and discussion. 3.1. UV–vis studies … 

High-Speed Efficient Terahertz Modulation Based on Tunable Collective-Individual State Conversion within an Active 3 nm Two-Dimensional Electron Gas Metasurface

Zhao, Yuncheng, Lan Wang, Yaxin Zhang, Shen Qiao, Shixiong Liang, Tianchi Zhou, Xilin Zhang et al. "High-Speed Efficient Terahertz Modulation Based on Tunable Collective-Individual State Conversion within an Active 3 nm Two-Dimensional Electron Gas Metasurface." Nano letters 19, no. 11 (2019): 7588-7597.

Abstract

Terahertz (THz) modulators are always realized by dynamically manipulating the conversion between different resonant modes within a single unit cell of an active metasurface. In this Letter, to achieve real high-speed THz modulation, we present a staggered netlike two-dimensional electron gas (2DEG) nanostructure composite metasurface that has two states: a collective state with massive surface resonant characteristics and an individual state with meta-atom resonant characteristics. By controlling the electron transport of the nanoscale 2DEG with an electrical grid, collective-individual state conversion can be realized in this composite metasurface. Unlike traditional resonant mode conversion confined in meta-units, this state conversion enables the resonant modes to be flexibly distributed throughout the metasurface, leading to a frequency shift of nearly 99% in both the simulated and experimental transmission spectra. Moreover, such a mechanism can effectively suppress parasitic modes and significantly reduce the capacitance of the metasurface. Thereby, this composite metasurface can efficiently control the transmission characteristics of THz waves with high-speed modulations. As a result, 93% modulation depth is observed in the static experiment and modulated sinusoidal signals up to 3 GHz are achieved in the dynamic experiment, while the −3 dB bandwidth can reach up to 1 GHz. This tunable collective-individual state conversion may have great application potential in wireless communication and coded imaging.

for full paper see https://pubs.acs.org/doi/full/10.1021/acs.nanolett.9b01273

… Q-factor decrease slightly. In order to test the characteristics of manufactured meta-surface, the THz time- domain spectroscopy (THz-TDS) produced by TeraView company (TPS 3000) has been applied. The time domain waveforms … 

Actively tunable terahertz chain-link metamaterial with bidirectional polarization-dependent characteristic

Liu, Pengyu, Zihao Liang, Zhicheng Lin, Zefeng Xu, Ruijia Xu, Dongyuan Yao, and Yu-Sheng Lin. "Actively tunable terahertz chain-link metamaterial with bidirectional polarization-dependent characteristic." Scientific reports 9, no. 1 (2019): 1-8.

Abstract

A tunable terahertz (THz) chain-link metamaterial (CLM) is presented, which is composed of a tailored Au layer fabricated on Si substrate. CLM exhibits bidirectional polarization-dependent characteristic by applying a direct-current (dc) bias voltage on device. This CLM device can be heated up the surrounding temperature to tune the corresponding resonance. The tuning range is 0.027 THz from 0.318 THz to 0.291 THz on the bias of 0.60 V to 1.32 V. By reconfiguring the gap between CLM, there are single-resonance with red-shift at TE mode, and multi-resonance with blue-shift and red-shift at TM mode, respectively. These characterizations of CLM are polarization-dependence and bidirectional tunability. These results show the electromagnetic responses of proposed CLM device is suitable for the uses for resonator, filter, switch, and sensor in the THz frequency range.

for full paper see https://www.nature.com/articles/s41598-019-46436-w

Characterization

With the tunable CLM device, we experimentally explore the electrothermal and electrostatic effects to resonant frequency of CLM device. By increasing the dc bias voltage, the corresponding resonant frequency could be tuned. Our sample was mounted on a home-made printed-circuit board (PCB) with a transparent window. There are two conductive wires soldering on PCB and connected to a dc power supply. The sample on the PCB was placed in the chamber of THz measurement system under a nitrogen environment to eliminate water vapor. The THz transmission spectra characterization was measured using TeraView 3000 time-domain spectroscopy (THz-TDS) system. The transmission spectra were normalized with respect to transmission of pure Si substrate of the same thickness as the sample.

Dual-band refractometric terahertz biosensing with intense wave-matter-overlap microfluidic channel

Lan, Feng, Feng Luo, Pinaki Mazumder, Ziqiang Yang, Lin Meng, Zhengqiang Bao, Jun Zhou et al. "Dual-band refractometric terahertz biosensing with intense wave-matter-overlap microfluidic channel." Biomedical optics express 10, no. 8 (2019): 3789-3799.

Abstract

We theoretically and experimentally demonstrate a label-free terahertz biosensor with ultrahigh sensitivity and distinctive discretion. By constructing a metal-air-metal (MAM) metamaterial perfect absorber (MPA) with a metallic paired-ring resonator array, a hollow microfluidic channel, and a backed reflector, a novel dual-band absorptive sensing platform is proposed in the THz range. The near field coupling by dipole-induced trapped modes and the magnetic momentum caused a vertical to transverse power flux that dramatically enhanced the electromagnetic field on top of the metasurface and in the microfluidic channel, respectively. Both the resonant modes exhibit perfect absorption and produce ultrahigh normalized sensitivities of 0.47/RIU (refractive index unit, RIU) and 0.51/RIU at 0.76 THz and 1.28 THz, respectively. Compared with conventional microfluidic sensors, the salient advantages of our design are the perfect spatial overlap for light-matter interaction and polarization insensitivity. Characterized by THz time domain spectroscopic absorption quantification measurements with different concentrations of bovine serum albumin (BSA), the proposed sensor exhibits promising applications in microfluidic biosensing.

for full paper see https://www.osapublishing.org/DirectPDFAccess/E5A68527-E751-58C9-0EA1FAFBC1FCF41A_415013/boe-10-8-3789.pdf?da=1&id=415013&seq=0&mobile=no 

… The TDS modeled as TPS Spectra 3000 from TeraView, which supplies full access to 0.06-4 THz spectral region with 0.006 THz resolution and 80 dB dynamic range. The simulation and experimental results are shown in Fig. 7(d) and (e), respectively …

Peculiarities of the Perturbation of Water Structure by Ions with Various Hydration in Concentrated Solutions of CaCl 2, CsCl, KBr, and KI

Penkov, N. V. "Peculiarities of the Perturbation of Water Structure by Ions with Various Hydration in Concentrated Solutions of CaCl 2, CsCl, KBr, and KI." Physics of Wave Phenomena 27, no. 2 (2019): 128-134.

Abstract

The degree of water structuring in solutions of four salts (CsCl, KBr, and KI with a concentration of 1M and CaCl2 with a concentration of 0.5M) has been analyzed using THz time-domain spectroscopy. It is shown that the degree of water structuring in a solution of salt, prepared based on a highly diluted aqueous solution of the same salt, differs in some cases from the degree of structuring of similar solutions prepared on the basis of highly diluted aqueous solutions of other salts and similarly prepared water. The degree of water structuring increases in salt solutions containing ions with pronounced positive hydration, decreases in salt solutions containing ions with pronounced negative hydration, and does not differs from control in salt solutions containing no ions with pronounced positive or negative hydration.


for full paper see https://link.springer.com/article/10.3103/S1541308X19020079

… Spectra were measured with a TPS Spectra 3000 spectrometer (Teraview, UK) in the
range of wave numbers from 1.2 to 120cm −1 with a resolu- tion of 4 cm −1. Averaging
over 3600 scans was per- formed to obtain one spectrum 

Terahertz tomographic imaging of freshly excised human breast tissues

Bowman, Tyler, Nagma Vohra, Keith Bailey, and Magda O. El-Shenawee. "Terahertz tomographic imaging of freshly excised human breast tissues." Journal of Medical Imaging 6, no. 2 (2019): 023501.

Abstract

Terahertz imaging and spectroscopy characterization of freshly excised breast cancer tumors are presented in the range 0.15 to 3.5 THz. Cancerous breast tissues were obtained from partial or full removal of malignant tumors while healthy breast tissues were obtained from breast reduction surgeries. The reflection spectroscopy to obtain the refractive index and absorption coefficient is performed on experimental data at each pixel of the tissue, forming tomographic images. The transmission spectroscopy of the refractive index and absorption coefficient are retrieved from experimental data at few tissue points. The average refractive index and absorption coefficients for cancer, fat, and collagen tissue regions are compared between transmission and reflection modes. The reflection mode offers the advantage of retrieving the electrical properties across a significantly greater number of points without the need for sectioning or altering the freshly excised tissue as in the transmission mode. The terahertz spectral power images and the tomographic images demonstrated good qualitative comparison with pathology.

for full paper see https://www.spiedigitallibrary.org/journals/Journal-of-Medical-Imaging/volume-6/issue-2/023501/Terahertz-tomographic-imaging-of-freshly-excised-human-breast-tissues/10.1117/1.JMI.6.2.023501.short

 The spectroscopy and imaging procedures in this work were performed using
the TPS Spectra 3000 pulsed THz imaging and spectroscopy system (from TeraViewLtd., United Kingdom) at the University of Arkansas; system details are shown in Ref. 16 

Influence of chemical substitution on broadband dielectric response of barium-lead M-type hexaferrite

Alyabyeva, Liudmila N., Victor I. Torgashev, Elena S. Zhukova, Denis A. Vinnik, Anatoliy S. Prokhorov, Svetlana A. Gudkova, David Rivas Góngora et al. "Influence of chemical substitution on broadband dielectric response of barium-lead M-type hexaferrite." New Journal of Physics 21, no. 6 (2019): 063016.

Abstract

We report on the electrodynamic properties of the single crystalline lead-substituted M-type barium hexaferrite, Ba0.3Pb0.7Fe12O19, performed in the broad frequency range including radio-frequency, terahertz and sub-terahertz bands, which are particularly important for the development of microelectronic devices. We demonstrate how changing on a molecular level the chemical characteristics(composition, intermolecular interaction, spin-orbital interaction) of lead-substituted M-type hexaferrite influences its radio-frequency and terahertz electrodynamic response. Our results indicate a critical temperature range, 50 K < T < 70 K, where significant changes of the electrodynamic response occur that are interpreted as freezing of dynamical oscillations of bi-pyramidal Fe(2b)ions. In the range 5–300 K, the heat capacity shows no sign of any phase transition and is solely determined by electron and phonon contributions. An anomalous electrodynamic response is detected at 1–2 THz that features a rich set of absorption resonances which are associated with electronic transitions within the fine-structured Fe2+ ground state and are visualized in the spectra due to magnetostriction and electron–phonon interaction. We show that lead substitution of barium in barium hexaferrite, BaFe12O19, leads to the emergence of a pronounced dielectric and magnetic relaxational dynamics at radio-frequencies and that both dynamics have the same characteristic relaxation times, thus evidencing the bi-relaxor-like nature of Ba0.3Pb0.7Fe12O19. We associate the origin of the relaxations as connected with the motion of magnetic domain walls. In order to unveil crucial influence of chemical substitution on electrodynamic characteristics of the compound, we analyze our results on substituted compound in comparison with the data available for pristine barium (BaFe12O19) and pristine lead (PbFe12O19) hexaferrites. The obtained spectroscopic data on the dielectric properties of Ba0.3Pb0.7Fe12O19 provide insight into fundamental phenomena responsible for the absorption mechanisms of the compound and demonstrates that chemical ionic substitution is an effective tool to tune the dielectric properties of the whole family of hexaferrites.


for full paper see https://iopscience.iop.org/article/10.1088/1367-2630/ab2476/pdf

… At THz frequencies, ν=8-100 cm-1, time-domain TeraView spectrometer was used to directly determine the real ε' and imaginary ε" parts of the complex dielectric permittivity ε*=εʹ+iε" from the complex (amplitude and phase) …

Terahertz Analysis of Phthalocyanine Pigments

Squires, A. D., and R. A. Lewis. "Terahertz Analysis of Phthalocyanine Pigments." Journal of Infrared, Millimeter, and Terahertz Waves 40, no. 7 (2019): 738-751.

In situ, non-invasive and non-destructive analysis of important artworks and cultural pieces is largely important in art conservation science. Terahertz time-domain spectroscopy and imaging delivers these requirements but lacks a materials database with fundamental understanding of salient pigments, binders and substrates. In this study, the most important synthetic pigments, the copper phthalocyanines, are investigated through terahertz time-domain spectroscopy. The terahertz spectrum reveals a series of characteristic modes in a 0.1–3-THz range across 14 pigment samples. Identification and distinction of copper phthalocyanines’ α, β and 𝜖 crystal polymorphs is demonstrated. This uniqueness within the terahertz regime is extended to two halogenated variants and a metal-free form. This invites the use of THz spectroscopy in investigation of contemporary artworks, post 1935, containing these pigments and promotes applications such as identifying fraudulent works of art.

For full paper see https://link.springer.com/article/10.1007/s10762-019-00599-9

… 3 Experiment Transmission spectra were obtained using a TeraViewTeraPulse 4000
time-domain spectroscopy system … Fig. 3 Free space transmission of TeraViewTeraPulse4000 system purged with N2 gas over a 0–3-THz range …

Thin-Film SUEX as an Anti-Reflection Coating for mmW and THz Applications

Sahin, Seckin, Niru K. Nahar, and Kubilay Sertel. "Thin-Film SUEX as an Antireflection Coating for mmW and THz Applications." IEEE Transactions on Terahertz Science and Technology 9, no. 4 (2019): 417-421.

We present a simple process for depositing SUEX dry films to realize effective antireflection coatings on high-resistivity silicon wafers and lenses. Heat-assisted conformal deposition of SUEX film followed by curing via ultraviolet exposure achieves robust adhesion to the silicon lens surface. Due to its relatively low material loss and commensurate refractive index, quarter-wavelength-thick SUEX coatings minimize reflection losses and significantly improve signal coupling into high-index silicon lenses. As an example, a 150-μm-thick SUEX layer was conformally coated on a 1-cm-diameter high-resistivity silicon lens to reduce reflection loss to less than 4% over the 220-325 GHz band. 



for full paper see https://ieeexplore.ieee.org/abstract/document/8709698

… Alternatively, green SUEX film can be laminated onto the wafer as detailed in [8]. For
transmission measurements, we have utilized a commer- cial Time Domain
Spectroscopy (TDS) system (TPS Spectra 3000 from TeraView,Inc.) …

The Influence on the Q Value of the THz Metasurface From the Tip Charge Accumulation Coupling

Sun, Han, Yaxin Zhang, Lan Wang, Shixiong Liang, Feng Lan, Kang Xue, and Ziqiang Yang. "The influence on the Q value of the THz metasurface from the tip charge accumulation coupling." IEEE Transactions on Terahertz Science and Technology 9, no. 3 (2019): 307-312.

Abstract:

With the adventure of metamaterials, there has been a tremendous advancement in the manipulation of the terahertz (THz) wave. However, the excitation of high-Q-factor resonance has been a great challenge in traditional metamaterials due to ohmic and radiation losses. In this paper, the influence of the tip charge accumulation effect on the high-Q-value meta-surface has been studied within the triangular array meta-surface. It is found that when the tip charges accumulate from each pair of triangular elements, they can couple with each other to construct a significant resonant mode which can trap more energy to achieve higher Q value. Moreover, the stacking of the induced charges distributed at the surface of the meta-unit making the coupling strength is further increased so that the strong tip charge accumulation effect could also affect the Q value. The experiment verified this phenomenon, which shows the stronger coupling resonance, and tip charge accumulation could result in the enhancement of the Q value. This research has potential applications in high-Q THz devices.

for full paper see https://ieeexplore.ieee.org/abstract/document/8691625

… size for reference. The sample is placed in the TDS (THz time-domain spectroscopy)
system in a dry environment. This TDS system is produced by Teraview(TPS-3000),
with a frequency range of 0.06–3THz. The position of … 

Arbitrary linear THz wave polarization converter with cracked cross meta-surface

Sun, Han, Lan Wang, Yaxin Zhang, Shixiong Liang, Jiaguang Han, Feng Lan, Xinlan Zhou, and Ziqiang Yang. "Arbitrary linear THz wave polarization converter with cracked cross meta-surface." Chinese Optics Letters 17, no. 4 (2019): 041602.

Abstract

This Letter presents a double-layer structure combining a cracked cross meta-surface and grating surface to realize arbitrary incident linear terahertz (THz) wave polarization conversion. The arbitrary incident linear polarization THz wave will be induced with the same resonant modes in the unit cell, which results in polarization conversion insensitive to the linear polarization angle. Moreover, the zigzag-shaped resonant surface current leads to a strong magnetic resonance between the meta-surface and gratings, which enhances the conversion efficiency. The experimental results show that a more than 70% conversion rate can be achieved under arbitrary linear polarization within a wide frequency band. Moreover, around 0.89 THz nearly perfect polarization conversion is realized.

for full paper see https://www.osapublishing.org/col/abstract.cfm?uri=col-17-4-041602

… The high-resolution THz time-domain spectrometer (TDS), which is produced by Teraview Company, is utilized in the system setup. The schematic of the experimental system is

Guided wave mode conversion phenomenon in composite materials: numerical and experimental study

Wandowski, Tomasz, Paweł Kudela, Paweł Malinowski, and Wiesław Ostachowicz. "Guided wave mode conversion phenomenon in composite materials: numerical and experimental study." In Health Monitoring of Structural and Biological Systems XIII, vol. 10972, p. 109720N. International Society for Optics and Photonics, 2019.

In this paper results of numerical and experimental analysis of S0/A0 elastic wave mode conversion phenomenon at various discontinuities in glass fibre reinforced polymer (GFRP) panels are presented. Analysis of S0/A0 mode conversion effect at Teflon inserts simulating delamination and impact damage with energies 5 J, 10 J and 15 J is conducted....................

 The aim of its application is to indicate the depth of discontinuity and to prove that delamination was created in the case of impact damage. The auxiliary method is based on terahertz spectroscopy (THz) where the analysis of propagation of electromagnetic waves in the terahertz band is conducted. The THz spectroscopy is a useful technique for damage assessment in the dielectric materials.

for full paper and abstract see https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10972/109720N/Guided-wave-mode-conversion-phenomenon-in-composite-materials--numerical/10.1117/12.2512682.short?SSO=1 

… The THz spectroscopy could be also utilised for non-destructive testing of dielectric
materials like GFRP [26], [27]. Terahertz spectrometer Teraview TPSSpectra 3000+ utilised
during the research generates impulses in the frequency range from 0.1 - 3 THz … 

Dielectric Properties of Low-Loss Polymers for mmW and THz Applications

Sahin, Seckin, Niru K. Nahar, and Kubilay Sertel. "Dielectric properties of low-loss polymers for mmW and THz applications." Journal of Infrared, Millimeter, and Terahertz Waves 40, no. 5 (2019): 557-573.

Abstract

We present a systematic characterization of dielectric permittivity of 6 commonly used, low-loss polymers namely polystyrene, parylene, polyimide, SLA resin, SU-8, and SUEX for the 100-GHz to 2-THz bands using transmission mode time domain spectroscopy. The dielectric constant and loss tangent for each polymer was systematically recorded using the commercially available TeraView TPS-3000 system and an analytical multilayered media transmission model is used to extract sample permittivity and loss through curve fitting the measured data. Among the studied polymers, polystyrene exhibits the lowest material loss with a loss tangent less than 0.0069 up to 100 GHz to 2 THz. Also, effects of lithographic processing on permittivity and loss for commonly used epoxy-based photoresists SU-8 and SUEX are documented and compared. We show that the dielectric properties of dry film SUEX is comparable with those of SU-8. As such, SUEX is an easy-to-process alternative to commonly used SU-8 for mmW and THz frequency applications.

For full paper see https://link.springer.com/article/10.1007/s10762-019-00584-2