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In recent years,there has been an urgent need in world for electricity. It has being increased constantly with the expansion of energy consumption via traditional energy sources which are depleting. The world has needed to turn to alternative energy, which is represented by renewable energy. The most important and most efficient of these is solar energy, and to get the maximum value of this energy with the highest efficiency, there should be direct monitoring of the performance of these solar panels. So, in this study, the Internet of Things (IoT) was used as a remote monitoring system to obtain the main factors like load current, terminal voltage, consumption power, temperature, humidity, and light intensity. The values were real and accurate, depending on the use of Adriano and sensors to measure the above-mentioned determinants and then using Wi-Fi technology to send the data that was processed in the circuit. Then the thing speak platform was used to display, analyze, and store the results in real-time

The power factor (PF) is an important measurement in an AC electrical system that indicates how much power ‎is utilized to accomplish productive work by a load and how much power is consumed. As a result, it's one of ‎the primary causes of excessive energy costs and power outages. This paper aims to present a simple, cost-‎effective, and accurate PF metering and monitoring system implemented using an Arduino microcontroller with ‎a novel methodology different from other papers. The proposed method is to design the software code instead ‎of using external components of Zero-Crossing Detectors (Z-CDs) for both voltage (V) and current (I) signals, and ‎instead of using Exclusive-OR (X-OR) gates also. Determining the phase-angle and PF in an efficient manner ‎can be useful in many approaches to electrical systems: 1-for synchronization of parallel connections of ‎alternators; 2-for directional protection systems; 3-for PF correction and load management; and 4-for designing ‎watt/energy meters. Using the Proteus 8 Professional (ISIS program), the proposed designed circuit was ‎simulated for more verification. The simulation and experimental findings are presented to validate the ‎proposed metering system's effectiveness.‎

In this paper, a terahertz metasurface supercell consists of two ring resonators with slightly different radii is proposed. Electromagnetic-induced transparency (EIT)–like resonance is excited with an ultrahigh figure of merit. Furthermore, the impact of the coupling between the two rings is investigated on the transmission amplitude response, the quality factor, and the EIT peak amplitude by varying the radius of the top resonator. The achieved figure of merit of the EIT peak reaches 88.65 and almost 20,000 when gold and a perfect electric conductor are used for the metallic layer, respectively. The simplicity and unique properties of the proposed design could render it to be a desirable candidate for filtering, slow light applications, and sensing.

The prevalence of diabetes is increasing globally. More than 690 million cases of diabetes are expected worldwide by 2045. Continuous blood glucose monitoring is essential to control the disease and avoid long-term complications. Diabetics suffer on a daily basis with the traditional glucose monitors currently in use, which are invasive, painful, and cost-intensive. Therefore, the demand for non-invasive, painless, economical, and reliable approaches to monitor glucose levels is increasing. Since the last decades, many glucose sensing technologies have been developed. Researchers and scientists have been working on the enhancement of these technologies to achieve better results. This paper provides an updated review of some of the pioneering non-invasive optical techniques for monitoring blood glucose levels that have been proposed in the last six years, including a summary of state-of-the-art error analysis and validation techniques.

Terahertz metasurfaces with subradiant modes that allow excitation of a high-quality factor are potential candidates for label-free sensing of thin-film biomolecules. Nevertheless, sensing sub-micron analytes are rather difficult due to the normalization method that has been used so far. Here, we evaluate an amplitude difference referencing technique that exploits the response of the uncoated metasurface structure as a reference. Amplitude difference percentage has been calculated by subtracting the frequency response of coated metasurface from the frequency response of the uncoated metasurface for different analyte thicknesses. To our surprise, we observe significantly large values of the amplitude difference that can be easily measured using conventional terahertz time-domain spectrometers. In future, this technique can be utilized to detect analytes with sub-micron thickness and could be exploited across the electromagnetic spectrum.

A bound state in the continuum (BIC) is a nonradiating state of light embedded in the continuum of propagating modes providing drastic enhancement of the electromagnetic field and its localization at micro–nanoscale. However, access to such modes in the far-field requires symmetry breaking. Here, it is demonstrated that a nanometric dielectric or semiconductor layer, 1000 times thinner than the resonant wavelength (λ/1000), induces a dynamically controllable quasi-bound state in the continuum (QBIC) with ultrahigh quality factor in a symmetric metallic metasurface at terahertz frequencies. Photoexcitation of nanostrips of germanium activates ultrafast switching of a QBIC resonance with 200% transmission intensity modulation and complete recovery within 7 ps on a low-loss flexible substrate. The nanostrips also form microchannels that provide an opportunity for BIC-based refractive index sensing. An optimization model is presented for (switchable) QBIC resonances of metamaterial arrays of planar symmetric resonators modified with any (active) dielectric for inverse metamaterial design that can serve as an enabling platform for active micro–nanophotonic devices. Ministry of Education (MOE) National Research Foundation (NRF) Accepted version The authors acknowledge the funding support from the Singapore Ministry of Education (MOE) (Grant Nos. MOE2016-T3-1-006 and MOE2017-T2-1-110), National Research Foundation Singapore (Grant No. NRF-CRP23-2019-0005), and the UK’s Engineering and Physical Sciences Research Council (Grant Nos. EP/M009122/1 and EP/T02643X/1).

In this paper, we utilized functional near-infrared spectroscopy (fNIRS) technology to examine the hemodynamic responses in the motor cortex for two conditions, namely standing and sitting tasks. Nine subjects performed five trials of standing and sitting (SAS) tasks with both real movements and imagery thinking of SAS. A group level of statistical parametric mapping (SPM) analysis during these tasks showed bilateral activation of oxy-hemoglobin for both real movements and imagery experiments. Interestingly, the SPM analysis clearly revealed that the sitting tasks induced a higher oxy-hemoglobin level activation compared to the standing task. Remarkably, this finding is persistent across the 22 measured channels at the individual and group levels for both experiments. Furthermore, six features were extracted from pre-processed HbO signals and the performance of four different classifiers was examined in order to test the viability of using SAS tasks in future fNIRS-brain-computer interface (fNIRS-BCI) systems. In particular, two features-combination tests revealed that the signal slope with signal variance represents one of the three best two-combined features for its consistency in providing high accuracy results for both real and imagery experiments. This study shows the potential of implementing such tasks into the fNIRS-BCI system. In the future, the results of this work could pave the way towards the application of fNIRS-BCI in lower limb rehabilitation.

Metamaterials that can support ultrasharp resonances using conductively coupled split ring resonators are potential candidates for designing label-free biomedical sensors. The sharp spectral response, as well as the ability to confine the field, increases the interaction between the electromagnetic field and unidentified analytes. A sensitivity level of 3 × 104 nm/RIU/unit-volume is achieved when the whole area of the sensor is covered with the analyte. More interestingly, we demonstrate that the sensitivity can be significantly enhanced by a factor of 19 reaching a value of 5.7 × 105 nm/RIU/unit-volume when selected spots are covered with the analyte. These results will pave the way for designing practical biomedical sensors in the terahertz frequency range.

In the past decade, the concept of metasurfaces has gradually dominated the field of metamaterials owing to their fascinating optical properties and simple planar geometries. At terahertz frequencies, the concept has been driven further by the availability of advanced micro-fabrication technologies that deliver sub-micron accuracy, well below the terahertz wavelengths. Furthermore, terahertz spectrometers with high dynamic range and amplitude and phase sensitivity provide valuable information for the study of metasurfaces in general. In this paper, we review recent progress in terahertz metasurfaces mainly in the last 5 years. The first part covers nonuniform metasurfaces that perform beamforming in reflection and transmission. In addition, we briefly overview four different methodologies that can be utilized in realizing high-quality-factor metasurfaces. We also describe two recent approaches to tuning the frequency response of terahertz metasurfaces using graphene as an active medium. Finally, we provide a brief summary and outlook for future developments in this rapidly progressing field.

A highly sensitive metamaterial device has been designed based on free-standing complementary asymmetric split ring resonators at terahertz (THz) frequencies. A thin-film overlayer deposited on the surface of the metal causes a red-shift in the THz transmission response. The results show the potential of such a device due to a high level of interaction between the overlayer analyte with the device that leads to a high-level sensitivity even with quite thin samples.

Due to the huge increase in the number of the patients diagnostic with diabetes around the world, a new generation of reliable, accurate, and painless blood glucose monitoring techniques are needed to fit the patient comfort. Blood glucose levels must be maintained in order to limit the severe consequences of diabetes. Nowadays, different technologies provide limited monitoring devices for diabetic patients. In this paper, we discuss a quite new noninvasive technology that has several beneficial features. Near-infrared (NIR) spectroscopy has become a promising technology for blood glucose measurements. The main objective of our project is to detect glucose concentration based on transmitted light intensity through a human sample, which is measured by a detector. Hence, this will enable us to classify the subject as normal, hypoglycemia, or hyperglycemia.

This work reports on the characteristics of the insulator-to-metal transition (IMT) of reactive pulsed laser deposited vanadium dioxide (VO 2 ) films in the terahertz (THz) frequency range, namely the transition temperature T IMT , the amplitude contrast of the THz transmission over the IMT Δ A , the transition sharpness Δ T and the hysteresis width Δ H . XRD analysis shows the sole formation of VO 2 monoclinic structure with an enhancement of (011) preferential orientation when varying the O 2 pressure ( P O2 ) during the deposition process from 2 to 25 mTorr. THz transmission measurements as a function of temperature reveal that VO 2 films obtained at low P O2 exhibit low T IMT , large Δ A , and narrow Δ H . Increasing P O2 results in VO 2 films with higher T IMT , smaller Δ A , broader Δ H and asymmetric hysteresis loop. The good control of the VO 2 IMT features in the THz domain could be further exploited for the development of advanced smart devices, such as ultrafast switches, modulators, memories and sensors.

Fano resonances in metasurfaces are important due to their low loss subradiant behavior that allows excitation of high-quality (Q) factor resonances extending from the microwave to the optical regime. High-Q Fano resonances have recently enabled applications in the areas of sensing, modulation, filtering, and efficient cavities for lasing spasers. Highly conducting metals are the most commonly used materials for fabricating the metasurfaces, especially at the low-frequency terahertz region where the DC, Drude, and perfect electric conductivity show similar resonant behavior of the subwavelength meta-atoms. Here, it is experimentally and theoretically demontrated that the Q factor of a low asymmetry Fano resonance is extremely sensitive to the conducting properties of the metal at terahertz frequencies. Large differences in the Q factor and figure of merit of the Fano resonance is observed for perfect electric conductors, Drude metal, and a DC-conducting metal, which is in sharp contrast to the behavior of the inductive–capacitive resonance of meta-atoms at terahertz frequency. Identification of such a low asymmetry regime in Fano resonances is the key to engineer the radiative and nonradiative losses in plasmonic and metamaterial-based devices that have potential applications in the microwave, terahertz, infrared, and the optical regimes.

A novel conceptual design methodology for strongly interacting metamaterials allows an ultrahigh angular sensitivity. Among others, this methodology enables precise sensing of the wave vector or the exclusion of unwanted directional radiation components. By diligently tailoring the dimensions of the primitive unit cell, an orders of magnitude enhanced sensitivity is achieved.

A thorough understanding of the stability of graphene under ambient environmental conditions is essential for future graphene-based applications. In this paper, we study the effects of ambient temperature on the properties of monolayer graphene using terahertz time-domain spectroscopy as well as time-resolved terahertz spectroscopy enabled by an optical-pump/terahertz-probe technique. The observations show that graphene is extremely sensitive to the ambient environmental conditions and behaves differently depending on the sample preparation technique and the initial Fermi level. The analysis of the spectroscopic data is supported by van der Pauw and Hall effect measurements of the carrier mobility and carrier density at temperatures comparable to those tested in our THz spectroscopic experiments.

Graphene as a zero-bandgap two-dimensional semiconductor with a linear electron band dispersion near the Dirac points has the potential to exhibit very interesting nonlinear optical properties. In particular, third harmonic generation of terahertz radiation should occur due to the nonlinear relationship between the crystal momentum and the current density. In this work, we investigate the terahertz nonlinear response of graphene inside a parallel-plate waveguide. We optimize the plate separation and Fermi energy of the graphene to maximize third harmonic generation, by maximizing the nonlinear interaction while minimizing the loss and phase mismatch. The results obtained show an increase by more than a factor of 100 in the power efficiency relative to a normal-incidence configuration for a 2 terahertz incident field.

A density-matrix formalism within the length gauge is developed for the purpose of calculating the nonlinear response of intrinsic bilayer graphene at terahertz frequencies. Employing a tight-binding model, we find that interplay between the interband and intraband dynamics leads to strong harmonic generation at moderate field amplitudes. Specifically, we find that at low temperature (10 K), the reflected field of undoped suspended bilayer graphene exhibits a third harmonic amplitude that is 30% of the fundamental in the reflected field for an incident 1 THz single-cycle pulse with a field amplitude of 1.5 kV/cm. More interestingly, we find that as the central frequency of the incident radiation is increased, the third harmonic amplitude also increases; reaching a maximum of 53% for an incident frequency of 2 THz and amplitude of 2.5 kV/cm., Comment: 11 pages, 9 figures

The use of laser ablation of a thin metal film, which allows for rapid prototyping of various free-standing terahertz devices, is reported. The technique will provide a simple way to fabricate devices without complicated photolithography procedures. This could be a solution for a multitude of new optical elements for the terahertz regime. The fabricated samples are free-standing films and, hence, benefit from the absence of a supporting dielectric substrate, which could induce dispersion, losses or alter the reflection properties. Three devices are demonstrated: a wire-grid polariser, a polarisation converter and bandpass filters, and their performance is characterised.

In this paper, we review recent research on terahertz (THz) metamaterials focusing on structures which exhibit sharp resonances with high quality factors. After a short introduction to common design concepts, near-field measurements are presented to discuss the resonant coupling and excitation mechanisms. High- Q-factor metasurfaces based on symmetric and asymmetric resonators, characterized by far-field transmission measurements, are discussed including structures with trapped and high-order resonance modes. Numerical simulations of the current distributions inside the metaatoms give insight into the resonance mechanisms. The novel structures discussed here offer intriguing properties and have potential applications in design and development of filters, thin-film sensors, and slow-light devices.

The spectral characteristic of a Fano resonance is a distinct and unique asymmetric line shape. It arises from the destructive interference between a bright continuum mode and a discrete dark mode. Metamaterials and plasmonics have facilitated the observation of Fano resonances in the realm of classical electrodynamics and have spurred intense interest to study and to exploit their peculiarities due their low loss and very sharp resonant features. Here, we survey the excitation of Fano resonance at terahertz frequencies by using asymmetric metamaterial structures. In particular, we discuss the high Q of Fano resonances, their sensitivity to the asymmetry parameter and potential applications. We believe that the manipulation of terahertz radiation by exploiting Fano resonances in terahertz metamaterials could usher in next-generation terahertz photonic devices for delay, storage, filtering, sensing, and nonlinear applications.

We report thermal effects on carrier dynamics in graphene revealed by terahertz spectroscopy. We attribute our observations to extreme sensitivity of carrier density and mobility to environmental changes.

We study nonlinear THz effects in photoexcited gated graphene, using optical-pump/Zwtewse-THz-probe spectroscopy. A crossover from negative to positive differential THz transmission has been observed at the lowest doping concentration when the THz field is increased. Using a simple Drude model of the graphene photoconductivity, we attributed the observed behavior to a transition from a domain in which the increase in the Drude weight dominates over the increase in the scattering rate after photoexcitation, to a domain with the opposite properties when the THz probe field is increased.

We report the passive as well as active modulation of the sensitive Fano resonances in terahertz asymmetric metamaterial structures. The strength of the Fano resonances can be completely switched off passively by changing the asymmetry of the structures and also actively by shininh the sample with very low pump powers. These devices can be used as ultrasensitive sensors, low threshold modulators and ultrafast switches in real world device based applications.

In the past two decades, the development and steady improvement of terahertz technology has motivated a wide range of scientific studies designed to discover and develop terahertz applications. Terahertz sensing is one such application, and its continued maturation is virtually guaranteed by the unique properties that materials exhibit in the terahertz frequency range. Thin-film sensing is one branch of this effort that has enjoyed diverse development in the last decade. Deeply subwavelength sample thicknesses impose great difficulties to conventional terahertz spectroscopy, yet sensing those samples is essential for a large number of applications. In this article we review terahertz thin-film sensing, summarizing the motivation, challenges, and state-of-the-art approaches based predominately on terahertz time-domain spectroscopy.