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Metamaterial absorbers have attracted considerable attention for applications in the terahertz range. In this Letter, we report the design, fabrication, and characterization of a terahertz dual band metamaterial absorber that shows two distinct absorption peaks with high absorption. By manipulating the periodic patterned structures as well as the dielectric layer thickness of the metal-dielectric-metal structure, significantly high absorption can be obtained at specific resonance frequencies. Finite-difference time-domain modeling is used to design the structure of the absorber. The fabricated devices have been characterized using a Fourier transform IR spectrometer. The experimental results show two distinct absorption peaks at 2.7 and 5:2 THz, which are in good agreement with the simulation. The absorption magnitudes at 2.7 and 5:2 THz are 0.68 and 0.74, respectively.

We present the simulation, implementation, and measurement of a polarization insensitive broadband resonant terahertz metamaterial absorber. By stacking metal-insulator layers with differing structural dimensions, three closely positioned resonant peaks are merged into one broadband absorption spectrum. Greater than 60% absorption is obtained across a frequency range of 1.86 THz where the central resonance frequency is 5 THz. The FWHM of the device is 48%, which is two and half times greater than the FWHM of a single layer structure. Such metamaterials are promising candidates as absorbing elements for bolometric terahertz imaging.

Prognostic performance evaluation has gained significant attention in the past few years.*Currently, prognostics concepts lack standard definitions and suffer from ambiguous and inconsistent interpretations. This lack of standards is in part due to the varied end-user requirements for different applications, time scales, available information, domain dynamics, etc. to name a few. The research community has used a variety of metrics largely based on convenience and their respective requirements. Very little attention has been focused on establishing a standardized approach to compare different efforts. This paper presents several new evaluation metrics tailored for prognostics that were recently introduced and were shown to effectively evaluate various algorithms as compared to other conventional metrics. Specifically, this paper presents a detailed discussion on how these metrics should be interpreted and used. These metrics have the capability of incorporating probabilistic uncertainty estimates from prognostic algorithms. In addition to quantitative assessment they also offer a comprehensive visual perspective that can be used in designing the prognostic system. Several methods are suggested to customize these metrics for different applications. Guidelines are provided to help choose one method over another based on distribution characteristics. Various issues faced by prognostics and its performance evaluation are discussed followed by a formal notational framework to help standardize subsequent developments.

We present a sensing system operating at millimetre (mm) waves in transmission mode that can measure glucose level changes based on the complex permittivity changes across the signal path. The permittivity of a sample can change significantly as the concentration of one of its substances varies: for example, blood permittivity depends on the blood glucose levels. The proposed sensing system uses two facing microstrip patch antennas operating at 60 GHz, which are placed across interrogated samples. The measured transmission coefficient depends on the permittivity change along the signal path, which can be correlated to the change in concentration of a substance. Along with theoretical estimations, we experimentally demonstrate the sensing performance of the system using controlled laboratory samples, such as water-based glucose-loaded liquid samples. We also present results of successful glucose spike detection in humans during an in-vivo Intravenous Glucose Tolerance Test (IVGTT). The system could eventually be developed into a non-invasive glucose monitor for continuous monitoring of glucose levels for people living with diabetes, as it can detect as small as 1.33 mmol/l (0.025 wt%) glucose concentrations in the controlled water-based samples satisfactorily, which is well below the typical human glucose levels of 4 mmol/l.

Piezocatalysis is a promising alternative of photocatalysis where the strained state of a piezoelectric material is exploited for electrochemical surface reactions under dark conditions. Among various piezoelectric materials, ZnSnO 3 has immense potential as piezocatalyst because of the noncentrosymmetric structure and strong ferroelectric polarization. Herein, we report orthorhombic ZnSnO 3 nanoparticles as efficient piezocatalysts under ultrasound treatment. A small particle size of 4−5 nm, phase purity, room temperature ferroelectric behavior, and the colloidal form of ZnSnO 3 are responsible for efficient piezocatalysis. It is shown that hydroxyl radicals are generated during piezocatalysis which is responsible for degradation activity. This work demonstrates the bright prospect of ZnSnO 3 nanoparticles for ultrasound-assisted piezocatalytic decontamination of polluted water and other applications.

The highly reactive nature of reactive oxygen species (ROS) is the basis for widespread use in environmental and health-related fields. Conventionally, there are only two kinds of catalysts used for ROS generation: photocatalysts and piezocatalysts. However, their usage has been limited due to various environmental and physical factors. To address this problem, herein, we report thermoelectric materials, such as Bi2Te3, Sb2Te3, and PbTe, as thermocatalysts which can produce hydrogen peroxide (H2O2) under a small surrounding temperature difference. Being the most prevalent environmental factors in daily life, temperature and related thermal effects have tremendous potential for practical applications. To increase the practicality in everyday life, bismuth telluride nanoplates (Bi2Te3 NPs), serving as an efficient thermocatalyst, are coated on a carbon fiber fabric (Bi2Te3@CFF) to develop a thermocatalytic filter with antibacterial function. Temperature difference induced H2O2 generation by thermocatalysts results in the oxidative damage of bacteria, which makes thermocatalysts highly promising for disinfection applications. Antibacterial activity as high as 95% is achieved only by the treatment of low-temperature difference cycles. The current work highlights the horizon-shifting impacts of thermoelectric materials for real-time purification and antibacterial applications.

Graphene quantum dots are known to exhibit tunable photoluminescence (PL) through manipulation of edge functionality under various synthesis conditions. Here, we report observation of excitation dependent anomalous m-n type fingerprint PL transition in synthesized amino functionalized graphene quantum dots (5-7 nm). The effect of band-to-band π*-π and interstate to band n-π induced transitions led to effective multicolor emission under changeable excitation wavelength in the functionalized system. A reasonable assertion that equi-coupling of π*-π and n-π transitions activated the heterogeneous dual mode cyan emission was made upon observation of the PL spectra. Furthermore, investigation of incremented dimensional scaling through facile synthesis of amino functionalized quantum graphene flakes (20-30 nm) revealed it had negligible effect on the modulated PL pattern. Moreover, an effort was made to trace the origin of excitation dependent tunable heterogeneous photoluminescence through the framework of energy band diagram hypothesis and first principles analysis. Ab initio results suggested formation of an interband state as a manifestation of p orbital hybridization between C-N atoms at the edge sites. Therefore comprehensive theoretical and experimental analysis revealed that newly created energy levels can exist as an interband within the energy gap in functionalized graphene quantum structures yielding excitation dependent tunable PL for optoelectronic applications.