THz Components Research Articles

THz behavior of indium-tin-oxide films on p-Si substrates

This paper reports broadband THz free-space transmission measurements and modeling of indium-tin-oxide (ITO) thin films on p-doped Si substrates. Two such samples having ITO thickness of 50 and 100 nm, and DC sheet conductance 260 and 56 Ω/sq, respectively, were characterized between 0.2 and 1.2 THz using a frequency-domain spectrometer. The 50-nm-film sample displayed very flat transmittance over the 1-THz bandwidth, suggesting it is close to the critical THz sheet conductance that suppresses multi-pass interference in the substrate. An accurate transmission-line-based equivalent circuit is developed to explain the effect, and then used to show that the net reflectivity and absorptivity necessarily oscillate with frequency. This has important implications for the use of thin-film metallic coupling layers on THz components and devices, such as detectors and sources. Consistent with previous reported results, the sheet conductance that best fits the THz transmittance data is roughly 50% higher than the DC values for both samples.

Tailorable Zero-Phase Delay of Subwavelength Particles toward Miniaturized Wave Manipulation Devices.

Adjustable zero-phase delay and equiphase control are demonstrated in single and multilayer dielectric particle arrays with high index and low loss. The polarization-independent near-zero permeability is the origin of the wave control near the first Mie magnetic resonance. The proposed design paves the way for subwavelength devices and opens up new avenues for the miniaturization and integration of THz and optical components.

Evanescent wave coupling in terahertz waveguide arrays

We study energy transfer among an array of identical finite-width parallel-plate waveguides in close proximity, via evanescent wave coupling of broadband terahertz waves. We observe stronger coupling with larger plate separations and longer propagation paths. This work establishes a platform to investigate new opportunities for THz components and devices based on evanescent wave coupling.

Diminishing relative jitter in electrooptic sampling of active mm-wave and THz circuits

In this work a novel approach in synchronization of electrooptic sampling systems for the ultra-broadband characterization of active mm-wave and THz devices is presented. The relative time jitter between sampled circuit and probing electrooptic head is eliminated by using a femtosecond laser system both as the generator of CW driving the device under test as well as the impulsively probing element. Previous ultra-broadband approaches were applicable to passive components driven by THz impulses, only. The presented system is more generally applicable to active mm-wave and THz components driven by conventional CW electronic sources. Broadband analysis on silicon nonlinear transmission line elements up to a frequency of 300 GHz is presented in order to illustrate the capabilities of the concept.

Multiband Metamaterials Based on Multiple Concentric Open-Ring Resonators Topology

In this paper, a new design of multiband metamaterial (MTM) to be employed in novel electromagnetic components and devices is presented both numerically and experimentally. The structure is designed based on the concentric multiple open-ring architecture in which each ring provides a magnetic resonance at different frequencies. The number of resonances depends on the number of the ring resonators composed by the unit cell. The proposed design enables an application as creating multiband left-handed MTMs by combining the proposed structure with a conducting strip. In addition, an HF application is also designed and presented. The investigated structure, supporting multiband operation, is a potential candidate to achieve efficient electrically small microwave/terahertz (THz) structures and can suitably be used for the miniaturization of microwave and THz components.

THz Chemical Imaging for Biological Applications

THz spectroscopy is advantageous in analytical chemistry because it can detect and identify intermolecular interactions in chemical compounds, such as hydrogen bonds and hydrations, and molecular networks. Recent advances in THz components, such as ultrashort pulsed lasers and photoconductive antennas, have improved the sensitivity of THz time-domain (TDS) spectroscopy and have made the THz chemical imaging possible. THz chemical imaging can reveal hydrogen bond distributions and will be a very powerful tool in biology, pharmacology, and life sciences. THz-TDS is also promising for the quantitative chemical analysis and detection of molecules and clusters in nanospace and ice.

Investigation of several terahertz electromagnetic band gap structures

AbstractSeveral THz electromagnetic band gap (EBG) structures are investigated and demonstrated.Various design, fabrication, and characterization methods and techniques are utilized and compared. These THz EBG structures may enable future high performance EBG based THz components. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 678–686, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24986

Conformational Control by Thiazole and Oxazoline Rings in Cyclic Octapeptides of Marine Origin. Novel Macrocyclic Chair and Boat Conformations

A comparison of a closely related set of cyclic octapeptides demonstrates how Nature has adapted two common amino acid building blocks (Thr, Cys) as conformational ring constraints (oxazoline, thiazole) to regulate the three-dimensional structures and reactivities of marine macrocycles. A 2D NMR spectroscopic study shows that conversion of two Cys residues in the flexible cyclic octapeptide 1, c[Ile-Thr-D-Val-Cys-Ile-Thr-D-Val-Cys-], to 5-membered thiazole rings (Thz) leads to the formation of a novel pseudochair conformation in 2, c[Ile-Thr-D-(Val)-Thz-Ile-Thr-D-(Val)Thz-]. The conformational flexibility of 2 is significantly restricted by three intramolecular hydrogen bonds induced by the D-(Val)Thz components, resulting in a single solution conformation with non-C2 symmetric side chains. Additional modification, through conversion of the two threonine side chains to 5-membered oxazoline rings (Oxn), produces a highly constrained pseudoboat or saddle-shaped macrocycle, c[(Ile)Oxn-D-(Val)-Thz-(Ile)Oxn-D-(Val)Thz-] (7), having C2 symmetric side chains. Acid hydrolysis of 7, previously isolated from the ascidian Lissoclinum patella, selectively opens the two oxazoline rings with further conformational rearrrangement to a novel cyclic octapeptide (8) possessing a shallower pseudoboat conformation. The comparison reveals that oxazoline and thiazole rings impose severe conformational restrictions upon these cyclic octapeptides, creating unusual shapes and clefts with varying capacities to capture organic or metal ion guests (e.g. 10). Such dramatic changes in macrocycle shape may be related to the differential antitumour and metal-binding properties of this class of molecule.