Search results

Metamaterials are artificially tailored complex media with extraordinary properties, not available in nature. Due to their unique performance, they are considered as a crucial component of modern radio-frequency technology, especially in the THz regime. However, their lack of wide spectral bandwidths introduce constraints for realistic applications. The purpose of this paper is to propose piezoelectric micro-electromechanical systems (MEMS) actuators to modify the shape of electric field-driven LC (ELC) resonators. A THz modulation capability is revealed by connecting/disconnecting the associated metal parts.

Piezoelectric MEMS actuators are proposed to provide the desired bandwidth enhancement along with THz modulation. Two setups with different degrees of freedom in altering the behaviour of the novel modulator are investigated. A variety of numerical data, acquired via the finite element method, substantiate the advantageous characteristics of the proposed structures.

The novel devices enable the modification of the structural features of an ELC-based complex medium, unveiling in this manner a significant THz modulation capability along with improved bandwidth tunability. Two discrete cases are presented involving different degrees of freedom to shape the overall performance of the metamaterial modulator.

Development of a THz modulator, which utilises metamaterials as its fundamental component. Incorporation of tunable piezoelectric metamaterials into THz technology allowing increased reconfigurability. Bandwidth enhancement of metamaterial systems and alternative design via multiple controllable gaps enabling more degrees of freedom for design purposes.

This paper aims to focus on research work related to metamaterial-based sensors for material characterization that have been developed for past ten years. A decade of research on metamaterial for sensing application has led to the advancement of compact and improved sensors.

In this study, relevant research papers on metamaterial sensors for material characterization published in reputed journals during the period 2007-2018 were reviewed, particularly focusing on shape, size and nature of materials characterized. Each sensor with its design and performance parameters have been summarized and discussed here.

As metamaterial structures are excited by electromagnetic wave interaction, sensing application throughout electromagnetic spectrum is possible. Recent advancement in fabrication techniques and improvement in metamaterial structures have led to the development of compact, label free and reversible sensors with high sensitivity.

The paper provides useful information on the development of metamaterial sensors for material characterization.

A wide band perfect THz absorber is presented in this work. The structure includes two layers of graphene disks on the silicon dioxide dielectric layer while a golden plate is placed at the bottom to act as a fully reflecting mirror against THz waves. According to the simulations, the device is robust enough to show independent operation versus layers thicknesses variations, chemical potentials mismatches and changing of electron relaxation time. The designed THz absorber in this work is an appropriate basic block for several applications in THz optical systems such as sensors, detectors and modulators.

The layers in the proposed device are modeled via passive circuit elements and consequently, the equivalent circuit of the device is calculated. Leveraging the developed equivalent circuit model (ECM) and impedance matching concept, the proposed device is designed to perfect absorption with 4.7 THz bandwidth that possesses over 90% absorption. Ample simulations are performed using MATLAB (ECM) and CST (finite element method) to verify the superior performance of the device. According to the simulations, the device is robust enough to show independent operation versus layers thicknesses variations, chemical potentials mismatches and changing of electron relaxation time.

This work reports a wideband THz absorber, composed of two graphene layers. This paper considers the circuit model representation for two different layers of the device. For a unique structure, a highly tunable response versus chemical potential is obtained. The circuit model approach and impedance matching theory are exploited to reduce computational time regarding conventional approaches.

A wide band absorber in THz band is presented. Leveraging circuit model approach and impedance matching theory, the design procedure is simplified regarding CPU time and memory requirements compared to conventional methods. Detailed calculations and ample simulations verify the performance excellency of the device to absorb THz incident waves in 2–6.5 THz frequencies. Also, the robustness of the device is investigated versus parameters mismatches like layers thicknesses and chemical potentials values. According to the simulations and absorption response, the proposed device is an appropriate block to be used in THz optical systems such as detectors, imaging systems and optical modulators.

The purpose of this paper is to study the spectral sensitivity characteristics of new pyroelectric sensor based on tetraaminodiphenyl film within the wavelength range of 0.4-10 µm and 300-3,000 µm.

Mylar film with the thickness of about 70 µm was used as the input window. The MDR-41 monochromator-based spectrometric complex and the quasi-optical spectrometer with the set of backward-wave oscillators were used for measurements of the pyrodetector spectral characteristics within the 0.4-10 µm and 300-3,000 µm ranges, respectively.

Mylar was found to have absorption lines within the range of 0.4-10 µm, which must be taken into account when broadband detectors developing. The noise equivalent power in the visible and infrared ranges was less than 6 × 10^–10 W/Hz^1/2, which is about five times lower than for analogue ones. In the sub-THz range, the pyrodetector sensitivity is 2-8 times higher than the Golay cell. The sensitivity of such pyrodetector weakly depends on the wavelength in the total measured range.

The pyroelectric sensor has good prospects for use in super wide spectral range, from ultraviolet to millimeter radiation, in spectrometers for scientific research, in industry for the operational control of THz radiation sources, as well as in security THz-systems.

The spectral sensitivity characteristics of the pyroelectric photosensor based on TADPh in the visible, infrared and terahertz ranges were measured. The prospects for the use of such sensors were determined.

A novel and simple six-band metamaterial absorber is proposed in the terahertz region, which is composed of an I-shaped absorber and circular ring with four gaps and a continuous metal ground plane separated by only 0.125 mm polyimide dielectric substrate. Initially, I-shaped resonator gives three bands at 0.4, 0.468 and 0.4928 THz with the absorptivity of 99.3%, 97.9% and 99.1%, respectively. The purpose of this paper is to improve the number of bands, for which the authors added the circular ring with four gaps, so the simulated metamaterial absorber exhibited six absorption peaks at 0.3392, 0.3528, 0.3968, 0.4676, 0.4768 and 0.492 THz, with the absorption rate of 91.4%, 94.2%, 94.9%, 90.3%, 77.5% and 97.4%, respectively. The surface current distribution and angle independence are explained for all the six frequencies which are used to analyze the absorption mechanism clearly. Structure maximum uses the squares and circles, so it will make the fabrication easy. The multiband absorbers obtained here have potential applications in many engineering technology, thermal radiation, material detection and imaging and optoelectronic areas.

This paper presents the design of the six-band metamaterial absorber which is from the I-shaped resonator and circular ring with four gaps and the metallic ground plane separated by the 0.125 polyimide dielectric substrate. The absorber exhibited six absorption peaks at 0.3392, 0.3528, 0.3968, 0.4676, 0.4768 and 0.492 THz, with the absorption rate of 91.4%, 94.2%, 94.9%, 90.3%, 77.5% and 97.4%, respectively. From the fabrication point of view, the proposed six-band metamaterial absorber has a very simple geometrical structure, and it is very easy to be fabricated.

The authors present a new and simple design of six-band absorber based on an I-shaped absorber and circular ring with four gaps and a metallic ground plane separated by a polyimide layer having the thickness of 0.125 mm. Six different resonance absorption peaks are found at 0.3392, 0.3528, 0.3968, 0.4676 , 0.4768 and 0.492 THz. Surface current distribution and angle independence plot have been studied to understand the absorption behavior of the designed terahertz metamaterial absorber.

The multiband absorbers obtained here have potential applications in many engineering technology, thermal radiation, material detection, security, sensors, imaging and optoelectronic areas.

The proposed metamaterial absorber (MMA) has the following advantages: first, the structure of the MMA consists of one planar metallic resonator, which presents a new design approach to obtain a multiband absorption response, rather than using multiple unit-cells in the one large unit cell or stacking different layers. Second, the simultaneous realization of triple-band and dual-band absorption (or bi-functional absorption) at five different frequencies can integrate the respective advantages of the triple functions of the triple-band MMA and double-band MMA, and therefore, the bi-functional MMA will find more application prospects than multiple-functional devices of triple-band and dual-band. Third, the authors simulated the three combinations of MMA here, which is indium tin oxide (ITO)-Polyimide-ITO, ITO-Teflon-ITO and ITO-polyethylene terephthalate (PET)-ITO for the same planar structure and achieve a high absorption rate. Finally, the proposed structure is polarization and angle independent in nature.

This absorption device consists of the top circular resonator, the middle insulating SiO₂ medium layer and the bottom metallic copper ground plane placed on a substrate. The conductivity of the copper metal is s = 5.8 × 10⁷ s/m. As the transmission of the MMA structure is zero, the substrate materials can be selected randomly. Totally four combinations of terahertz MMA are designed and simulated here which are ITO- SiO₂ –ITO, ITO-Polyimide-ITO, ITO-Teflon-ITO and ITO- PET-ITO for the same planar structure.

Compared with previous MMAs, the proposed MMA has the following advantages: First, the structure of the MMA consists of one planar metallic resonator, which presents a new design approach to obtain a multiband absorption response, rather than using multiple unit-cells in the one large unit cell or stacking different layers. Second, the simultaneous realization of triple-band and dual-band absorption (or bi-functional absorption) at five different frequencies can integrate the respective advantages of the triple functions of the triple-band MMA and double-band MMA, and therefore, the bi-functional MMA will find more application prospects than multiple-functional devices of triple-band and dual-band. Third, the authors simulated the three combinations of MMA here, which is ITO-polyimide-ITO, ITO-Teflon-ITO and ITO- PET-ITO for the same planar structure and achieve a high absorption rate. Finally, the proposed structure is polarization and angle independent in nature.

First, the structure of the MMA consists of one planar metallic resonator, which presents a new design approach to obtain a multiband absorption response, rather than using multiple unit-cells in the one large unit cell or stacking different layers. Second, the simultaneous realization of triple-band and dual-band absorption (or bi-functional absorption) at five different frequencies can integrate the respective advantages of the triple functions of the triple-band MMA and double-band MMA, and therefore, the bi-functional MMA will find more application prospects than multiple-functional devices of triple-band and dual-band. Third, the authors simulated the three combinations of MMA here, which is ITO-polyimide-ITO, ITO-Teflon-ITO and ITO-PET-ITO for the same planar structure and achieve a high absorption rate. Finally, the proposed structure is polarization and angle independent in nature.

The coupling characteristics between adjacent circuits are crucial for their efficient design in terms of electromagnetic compatibility features. Specifically, either the wireless power transfer can be enhanced or the interference can be limited. This paper aims to the extraction of the coupling characteristics of surface plasmon polariton waves propagating onto graphene layers to facilitate the telecommunication system design for advanced THz applications.

The surface conductivity of graphene is described at the far-infrared spectrum and modelled accurately by means of a properly modified finite-difference time-domain) scheme. Then, a series of numerical simulations for different coupling setups is conducted to extract an accurate generalised parametric coupling model that is dependent explicitly on the fundamental propagation features of graphene.

The coupling coefficients of two basic waveguiding setups are examined thoroughly. The initial one includes two parallel graphene layers of infinite dimensions, and it is observed that the coupling is influenced via the ratio between their distances to the confinement of the surface wave. The second scenario is composed of graphene microstrips that are parallel to their small edge, namely, microstrip width. The extracted numerical results indicate that the coupling coefficient depends on the ratio between widths to wavelength.

The accurate extraction of the generalised coupling coefficients for graphene surface wave circuits is conducted in this work via an adjustable numerical technique for a novel family of plasmonic couplers. It is derived that only the fundamental propagation features of graphene, such as the wavelength and the confinement of the surface waves, have an effect on the coupling calculation, thus enabling a consistent electromagnetic compatibility study.

This paper aims to propose and demonstrate novel microphone sensors based on the frequency delta-sigma modulation (FDSM) technique, which replaces the conventional delta-sigma modulator in the delta-sigma analog-to digital converters. A key of the FDSM technology is to use a voltage-controlled oscillator (VCO) for converting an input analog signal to a 1-bit pulse-density modulated digital signal. High-performance sensors can be realized if the VCO is replaced by an oscillator whose oscillation frequency depends on an external physical parameter.

Microphone sensors are proposed based on FDSM that uses a suspended microstrip disk resonator, where the backside ground plane is replaced by a thin metal diaphragm. A resonant tunneling diode (RTD) oscillator is also used, as the performance of these sensors significantly depends on the oscillation frequency. To demonstrate the basic operation of the proposal, prototype devices were fabricated with an InGaAs/AlAs RTD.

A satisfactory noise shaping property, which is a significant nature of delta-sigma modulation, was demonstrated over three decades for the prototype device. A sound-sensing peak was also clearly observed when applying 1 kHz sound from a speaker.

High-performance ultrasonic microphone sensors can be realized if the sensors are fabricated by using a thin InP substrate with high-frequency oscillator design.

In this study, the authors proposed and experimentally demonstrated novel microphone sensors, which are promising as future ultrasonic sensors that have high dynamic range with wide bandwidth.

Metamaterials have been utilised in several exciting configurations such as tuneable reflectors, reconfigurable absorbers, and programmable modulators, triggering intense research efforts. Among them, the ability to steer the radiation pattern of a single antenna component by employing a metamaterial-based superstrate is considered crucial for the development of advanced beam forming applications. The purpose of this paper is to introduce an adjustable omega-inspired metamaterial module to facilitate the design of beam steering implementations, involving beam forming capabilities, as well.

A variable capacitive diode is properly positioned at the novel omega element, hence advancing the controllability of its electromagnetic performance and circumventing the requirement of extra bias networks. When an array of these particles is placed in front of an antenna, several negative refractive index profiles can be realised, allowing the manipulation of the beam direction. Furthermore, a pyramidal horn antenna, loaded with this complex medium superstrate, is thoroughly investigated in terms of programmable beam steering and beam forming attributes. Several numerical data derived via the finite element method unveil the merits of the featured configuration.

The proposed structure allows programmability of the electromagnetic behaviour, but also circumvents the necessity of complicated bias networks, while minimising interference. The numerical assessment of a standard gain pyramidal horn antenna, associated to the featured metamaterial superstrate, sufficiently proves the controllable beam steering and beam forming attributes. Several parametric studies clarify the principal characteristics of the proposed setup, facilitating the design of high-end systems.

Development of tuneable metamaterial, which utilises variable capacitive diodes to enable controllability. Incorporation of reconfigurable metamaterials into antenna technology. Design of a pyramidal horn antenna, loaded with a complex medium superstrate exhibiting programmable beam steering and beam forming attributes. The proposed device circumvents the necessity of complicated bias networks, while minimising interference.