UWB Metamaterial-based miniaturized planar monopole antennas

In this paper, ultra wide band (UWB) metamterial based compact planar antennas have been designed and experimentally verified. Four novel unit cells have been realized and each unit cell dispersion characteristics are numerically calculated which follows CRLH-TL properties. These four CRLH-TL unit cells are loaded into monopole antennas which result, four open-ended MTM antennas respectively. Further, a novel via free version of CRLH-TL unit cells have been designed, which increases the fabrication flexibility. The compactness has been achieved by realizing ZOR (zeroth order resonance) mode and its bandwidth is increased by realizing small shunt capacitance and large shunt inductance. Further, by optimizing CRLH-TL unit cells, two closely spaced zeroth-order and first-order resonance modes are merged into a single pass band, which gives wide bandwidth. The each proposed antenna has a compact dimension of 0.27 λ₀ × 0.19 λ₀ × 0.02 λ₀ (22 × 15 × 1.6 mm³), where λ₀ is a free space wavelength at 3.8 GHz. The four proposed antennas have S₁₁ < −10 dB impedance bandwidths of 8.4 GHz, 8.5 GHz, 8.2 GHz and 8.3 GHz respectively. The optimum gain, good efficiency, desired radiation characteristics in frequency domain analysis and less distortion of waves in time domain analysis have been achieved for proposed antennas, which are most suitable for UWB applications. The CST-MWS has been used for the parametric study of the proposed antennas. A good agreement has been observed between simulated and experimental results.     

Via-less CRLH-TL unit cells loaded compact and bandwidth-enhanced metamaterial based antennas

The via-less composite right hand left hand (CRLH)-TL unit cells loaded compact and bandwidth-enhanced metamaterial (MTM) antennas have been designed and experimentally investigated. Four novel unit cells are designed and its dispersion characteristics of the proposed unit cells are numerically calculated which follows CRLH-TL properties. Further, the conventional metallic vias of CRLH-TL have been eliminated to increase the fabrication flexibility. The four CRLH-TL unit cells are loaded into monopole antennas which result, four via-less open-ended MTM antennas respectively. Its ZOR (zeroth order resonance) bandwidth is increased by realizing small shunt capacitance and large shunt inductance. Further, to increase overall antenna bandwidth, merging of ZOR mode to the higher and lower order modes into a single pass band has been done by realizing proper CRLH-TL unit cells. The each proposed antenna has a dimension of 0.13λ₀ × 0.08λ₀ × 0.0085λ₀, where the free space wavelength λ₀ at 1.6 GHz. The four proposed antennas have S₁₁ < −10 dB fractional bandwidths (FBW) 173% (1–13.6 GHz), 169% (1.2–14.5 GHz), 158% (1.6–13.5 GHz) and 158% (1.6–13.5 GHz) respectively. The optimum gain and desired radiation characteristics have been obtained for all proposed antennas, which can be suitable for UWB applications. The CST-MWS has been used for the parametric study of the proposed antennas. A good agreement has been observed between simulated and experimental results.     

Corrugated SIW K band horn antenna

In the recent years, the strong demand for high performance, low cost and high gain antennas for telecommunication, surveillance, and imaging applications has rapidly grown at microwave and higher frequencies. High speed wireless links require modular, compact size and high directivity with low cross polarization antennas. To demonstrate the proposed concepts and design features, in this paper, a substrate integrated waveguide (SIW) feeding technique has been created having well behaved gain and suitable −10 dB bandwidth from 23.8 GHz to 25.7 GHz (roughly 2 GHz bandwidth), while the impedance bandwidth for VSWR < 2.5 is nearly 3 GHz. The simulated antenna attains 12.5 ± 1 dB gain over majority of K band with an occupied size of 82 mm × 40 mm × 2.54 mm and has roughly 95% radiation efficiency. The proposed antenna is an excellent candidate for integrated low cost K band and even higher frequency systems. The simulations are done by two full wave packages i.e. ANSYS HFSS and CST MWS that associated with finite element method (FEM) and finite difference time domain (FDTD), respectively. The results show good agreements between these two methods.     

Wheel shaped modified fractal antenna realization for wireless communications

A compact, low profile circular fractal patch antenna with low latency, low cost, high speed and multiband is presented. With the help of CST Microwave Studio Suite TM the proposed structure has been designed and analyzed. The simulated results are fixed experimentally. The suggested antenna has dimension of 32 × 36 mm² (W × L) and operating from 2.93 GHz–9.53 GHz with VSWR ≤ 2. The aerial is assembled on FR-4 (ε_r = 4.4) substrate with a thickness of substrate 1.25 mm. Detailed parametric studies of the antennas have been carried out. This microstrip fed antenna is suitable for ultra wideband (UWB), S, C and part of the X band applications.     

Multiband monopole antenna loaded with Complementary Split Ring Resonator and C-shaped slots

This paper presents a compact semi circular monopole antenna loaded with Complementary Split Ring Resonator (CSRR) and two C-shaped slots is proposed for Global System for Mobile Communication (GSM), Worldwide Interoperability for Microwave Access (WiMAX) and C-band applications. The size of the proposed antenna is 20 × 20 × 0.5 mm³. The resonance frequency of WiMAX (3.73 GHz) is achieved by introducing CSRR slots on the ground plane. To realize multiband characteristics for GSM (1.77 GHz), WiMAX (2.6 GHz) and C-band (4.15 GHz), two C-shaped slots of quarter wavelength are introduced in radiating element. The extraction procedure of negative permittivity for the proposed CSRR is discussed in detail. The proposed antenna is fabricated and measured. Simulated and measured results are in good agreement. Omni directional radiation pattern is obtained in H-plane and bi directional radiation pattern is obtained in E-plane. Parametric study of CSRR and C-shaped slot are examined to obtain best results. The proposed antenna has significant advantages, including low profile, miniaturization ability, and good impedance matching.     

Design and analysis of implantable CPW fed bowtie antenna for ISM band applications

A novel implantable coplanar waveguide (CPW) fed crossed bowtie antenna is proposed for short-range biomedical applications. The antenna is designed to resonate at 2.45 GHz, one of the industrial-scientific-medical (ISM) bands. It is investigated by use of the method of moments design equations and its simulation software (IE3D version 15). The size of the antenna is 371.8 mm³ (26 mm × 22 mm × 0.65 mm). The simulated and analyzed return losses are −23 and −25 dB at the resonant frequency of 2.45 GHz. We have analyzed some more performances of the proposed antenna and the results show that the proposed antenna is a perfect candidate for implantation. The proposed antenna has substantial merits like low profile, miniaturization, lower return loss and better impedance matching with high gain over other implanted antennas.     

Carrier transport mechanisms and photovoltaic properties of Au/p-ZnPc/Al device

The dark current density–voltage characteristic of Au/ZnPc/Al device at room temperature has been investigated. Results showed a rectification behavior. At low forward bias, the current density was found to be ohmic, while at high voltages, space charge limited the current mechanism dominated by exponential trapping levels. Junction parameters such as rectification ratio (RR), series resistance (R_s), and shunt resistance (R_sh) were found to be 9.42, 9.72 MΩ, and 0.88 × 10³ MΩ, respectively. The current density–voltage characteristics under white light illumination (100 W/m²) gives values of 0.55 V, 3 × 10⁻³ A/m², 0.18 and 5.8 × 10⁻⁴% for the open circuit voltage, V_oc, the short circuit current density (J_sc), the fill factor (FF), and conversion efficiency (η), respectively.     

Chemically deposited ZnS thin film as potential X-ray radiation sensor

In this article X-ray radiation sensitivity of ZnS thin film prepared by a chemical bath deposition technique has been reported. The films were prepared under 0.10, 0.15 and 0.20 molarity (M). Characterization reports show that the 0.20 M film has the best quality than the other low molarity films. I-V characteristics of the films were studied under dark condition and observed that the film prepared at 0.20 M has an electrical conductivity of 2.06×10⁻⁶ (Ω cm)⁻¹ which is about 10 times greater than the other lower molarity films. Further, the I-V characteristic of this film has studied under UV and X-ray radiations. The current under X-ray radiation is found to be significantly higher than that under the UV radiation. At a fix bias voltage of 1.0 V, the conductivity under UV radiation is found to be 3.26×10⁻⁶ (Ω cm)⁻¹ whereas that under the X-ray is 4.13×10⁻⁵ (Ω cm)⁻¹. The sensitivity under X-ray radiation is significantly greater than that under the UV radiation. This analysis suggests that the ZnS thin film which is used as a UV radiation sensor can also be used as a potential X-ray radiation sensor.     

A new wideband planar antenna with band-notch functionality at GPS,Bluetooth and WiFi bands for integration in portable wireless systems

Empirical results are presented for a novel miniature planar antenna that operates over a wide bandwidth (500 MHz to 3.05G Hz). The antenna consists of dual-square radiating patches separated by two narrow vertical stubs to reject interferences from GPS, Bluetooth and WiFi bands. Radiating patches and stubs are surrounded by a ground-plane conductor, and the antenna is fed through a common coplanar waveguide transmission line (CPW-TL). The two vertical stubs generate pass-band resonances enabling wideband operation across the following communications standards: cellular, APMS, JCDMA, GSM, DCS, PCS, KPCS, IMT-2000, WCDMA, UMTS and WiMAX. Embedded in the ground-plane conductor is an H-shaped dielectric slit, which has been rotated by 90°, whose function is to reject interferences from GPS, Bluetooth and WiFi bands. Measurements results confirm the antenna exhibits notched characteristics at frequency bands of GPS (1574.4–1576.4 MHz), Bluetooth (2402–2480 MHz) and WiFi (2412–2483.5 MHz). The impedance bandwidth of the antenna is 2.55G Hz for VSWR < 2, which corresponds to a fractional bandwidth of 143.66%. Measured results also confirm that the antenna radiates omnidirectionally in the E-plane with appreciable gain performance over its operating frequency range. The antenna has dimensions of 15 × 15 × 0.8 mm³.     

Operation of 4H-SiC high voltage normally-OFF V-JFET in radiation hard conditions: Simulations and experiment

Operation of high-voltage 4H-SiC vertical-JFET in radiation hard environment was investigated by simulation and experiment. Commercial 1700 V normally-OFF SiC JFETs in TO-247 package were irradiated with fast neutrons to fluences of 4.0 × 10¹⁴ cm^− 2 (1 MeV Si equivalent) and the effect of radiation on their characteristics was then thoroughly analyzed. Four degradation mechanisms were identified, of which the most important is the increase of JFETs ON-state resistance due to the mobility degradation and removal of carriers from transistor's light doped channel and drift regions. As a result, the JFET ON-state losses grow and, at fluences higher than 4 × 10¹⁴ cm^− 2, the low doped n-regions are fully compensated and transistor loses its functionality. On the contrary, irradiation slightly improves JFET's switching characteristics. The effect of neutron irradiation on operation of SiC V-JFET in a real application was then investigated on the step-UP 15 V/60 V DC-DC converter where the SiC JFET was used as an active switch. Converter characteristics were analyzed by means of the mixed-mode simulation using the developed 2D model of the neutron irradiated transistor. Results showed that the duty cycle of the PWM regulator is growing due to the increase in the voltage drop on the switching JFET. This effect, which is caused by the abovementioned increase the JFET's ON-state resistance, increases power dissipation and deteriorates converter efficiency. Finally, the effect of neutron irradiation on operation SiC V-JFET in the 850 V/24 V auxiliary flyback switching mode power supply was analyzed. We showed that the growth of the ON-state resistance increases transistor's conduction losses and decreases converter efficiency. Exceeding the fluence of 3.3 × 10¹⁴ cm^− 2 neutrons then causes JFET overheating and subsequent destruction.     

Photo stability enhancement of Poly(3-hexylthiophene)-PCBM nanocomposites by addition of multi walled carbon nanotubes under ambient conditions

Poly(3-hexylthiophene)-Phenyl-C61-butyric acid methyl ester (P3HT–PCBM) composites find wide application in optoelectronic devices, especially bulk-hetero junction (BHJ) solar cells. These composites, even though could give efficient polymer solar cells with ∼4–5% power conversion efficiencies (PCE), a major problem of photo stability is associated with it and remains unsolved. P3HT–PCBM composite was found to be degrading on irradiation with ultraviolet radiation or a solar simulator providing AM1.5G illumination (1000 W m^–2, 72 ± 2 °C or 330 W m⁻², 25 °C), in presence of oxygen and moisture. Here, we have studied the photo stability of P3HT–PCBM under ambient conditions and showed that a new ternary composite, P3HT–PCBM–MWCNT (multi walled carbon nanotube) has superior photo stability even on extended UV–Vis exposure. A total of 7% (w/w) PCBM and 3% (w/w) MWCNT with respect to P3HT resulted in optimum stability. UV–Visible and fluorescence spectral analysis have been used to study the photo stability, both in solution state and solid/film state. Transmission electron micrograph (TEM) along with selected area electron diffraction (SAED) pattern and Field Emission Scanning Electron Microscopy (FE-SEM) micrographs have been used to show the well coating of MWCNT on P3HT–PCBM composite. Since MWCNT is one of the very important carbon based nanomaterial with several supreme characteristics, this new ternary composite has great importance for optoelectronic applications.     

Determination of contact parameters of Ni/n-GaP Schottky contacts

The electrical analysis of Ni/n-GaP structure has been investigated by means of current–voltage (I–V), capacitance–voltage (C–V) and capacitance–frequency (C–f) measurements in the temperature range of 120–320 K in dark conditions. The forward bias I–V characteristics have been analyzed on the basis of standard thermionic emission (TE) theory and the characteristic parameters of the Schottky contacts (SCs) such as Schottky barrier height (SBH), ideality factor (n) and series resistance (R_s) have been determined from the I–V measurements. The experimental values of SBH and n for the device ranged from 1.01 eV and 1.27 (at 320 K) to 0.38 eV and 5.93 (at 120 K) for Ni/n-GaP diode, respectively. The interface states in the semiconductor bandgap and their relaxation time have been determined from the C–f characteristics. The interface state density N_ss has ranged from 2.08 × 10¹⁵ (eV^?1 m^?2) at 120 K to 2.7 × 10¹⁵ (eV^?1 m^?2) at 320 K. C_ss has increased with increasing temperature. The relaxation time has ranged from 4.7 × 10^?7 s at 120 K to 5.15 × 10^?7 s at 320 K.     

A printed monopole ellipzoidal UWB antenna with four band rejection characteristics

An antenna design with four band rejection characteristics for UWB application is demonstrated. The proposed unique UWB antenna has shape of an embedded ellipse at top of trapezoidal patch (named as ellipzoidal), 50 Ω impedance microstrip line feed and a truncated beveled ground plane. To realize four band stop characteristics, three inverted U-shaped and a single I-shaped slots each of half guided wavelength are utilized on radiating element. The fabricated antenna has dimensions of 27 mm × 36 mm × 1.6 mm. This four band notched ellipzoidal UWB antenna has measured frequency bandwidth 2.8–14 GHz for magnitude of S₁₁ < −10 dB level. The measured ellipzoidal antenna exhibits four band rejection characteristics for magnitude of S₁₁ > −10 dB at 3.55 GHz for WiMAX band (3.26–3.9 GHz), 4.55 GHz for ARN band (4.35–5.05 GHz), 5.7 GHz for WLAN band (5.5–6.65 GHz) and 8.8 GHz for ITU-8 band (7.95–9.35 GHz). The proposed ellipzoidal UWB antenna maintains omnidirectional radiation pattern, gain, linear phase response, <1 ns group delay, and transfer function in the whole UWB operating bandwidth except at notched frequency bands.     

Varying load resistances of zinc oxide ultraviolet photodetectors: A simple method to change responsivity

The metal–semiconductor–metal structured ultraviolet photodetector has been fabricated based on Zinc oxide thin films grown by a radio frequency magnetron sputtering technique, and Au is used as the contact metal. The dark current of the photodetector is as low as 1.17 nA at 3 V bias in the current–voltage measurements. The photoresponse properties are characterized by varying the load resistors (1 kΩ, 10 kΩ, 100 kΩ, 1 MΩ and 22 MΩ), and the corresponding responsivities are 2.69, 1.27, 0.25, 0.02 and 7.20×10⁻⁴ A/W. It can be found that the responsivity of the photodetector is enhanced with the load resistors decreasing; however, the signal-to-noise ratio decreases. It is demonstrated that the best method to make the ZnO-based photodetector suitable for different application environments is with the appropriate load resistance.     

High electron mobility triazine for lower driving voltage and higher efficiency organic light emitting devices

The triazine compound 4,4′-bis-[2-(4,6-diphenyl-1,3,5-triazinyl)]-1,1′-biphenyl (BTB) was developed for use as an electron transport material in organic light emitting devices (OLEDs). The material demonstrates an electron mobility of ∼7.2 × 10⁻⁴ cm² V⁻¹ s⁻¹ at a field of 8.00 × 10⁵ V cm⁻¹, which is 10-fold greater than that of the widely used material tris(8-hydroxyquinoline) aluminum (AlQ₃). OLEDs with a BTB electron transport layer showed a ∼1.7–2.5 V lower driving voltage and a significantly increased efficiency, compared to those with AlQ₃. These results suggest that BTB has a strong potential for use as an OLED electron transport layer material.     

Electrical and photovoltaic properties of SnSe/Si heterojunction

Thin film of SnSe is deposited on n-Si single crystal to fabricate a p-SnSe/n-Si heterojunction photovoltaic cell. Electrical and photoelectrical properties have been studied by the current density–voltage (J–V) and capacitance–voltage (C–V) measurements at different temperatures. The fabricated cell exhibited rectifying characteristics with a rectification ratio of 131 at ±1 V. At low voltages (V<0.55 V), the dark forward current density is controlled by the multi-step tunneling mechanism. While at a relatively high voltage (V>0.55 V), a space charge-limited-conduction mechanism is observed with trap concentration of 2.3×10²¹ cm⁻³. The C–V measurements showed that the junction is of abrupt nature with built-in voltage of 0.62 V which decreases with temperature by a gradient of 2.83×10⁻³ V/K. The cell also exhibited strong photovoltaic characteristics with an open-circuit voltage of 425 mV, a short-circuit current density of 17.23 mA cm⁻² and a power conversion efficiency of 6.44%. These parameters have been estimated at room temperature and under light illumination provided by a halogen lamp with an input power density of 50 mW cm⁻².     

Optimizing n-type contact design and chip size for high-performance indium gallium nitride/gallium nitride-based thin-film vertical light-emitting diode

The effects of the n-contact design and chip size on the electrical, optical and thermal characteristics of thin-film vertical light-emitting diodes (VLEDs) were investigated to optimize GaN-based LED performance for solid-state lighting applications. For the small (chip size: 1000×1000 µm²) and large (1450×1450 µm²) VLEDs, the forward bias voltages are decreased from 3.22 to 3.12 V at 350 mA and from 3.44 to 3.16 V at 700  mA, respectively, as the number of n-contact via holes is increased. The small LEDs give maximum output powers of 651.0–675.4 mW at a drive current of 350 mA, while the large VLEDs show the light output powers in the range 1356.7–1380.2 mW, 700 mA, With increasing drive current, the small chips go through more severe degradation in the wall-plug efficiency than the large chips. The small chips give the junction temperatures in the range 51.1–57.2 °C at 350  mA, while the large chips show the junction temperatures of 83.1–93.0 °C at 700  mA, The small LED chips exhibit lower junction temperatures when equipped with more n-contact via holes.     

A miniaturized Vivaldi antenna by loading with parasitic patch and lumped resistor

A miniaturized Vivaldi antenna is presented in the paper. On the basis of original antenna, the miniaturized Vivaldi antenna applies parasitic patch and lumped resistor to improve impedance characteristics. The proposed load can expand the lower operating frequency to 1.96 GHz without changing antenna dimensions. The size of antenna is set as 43 × 40 mm². This size is about 0.28λ_L × 0.26λ_L, where λ_L is the free space wavelength at 1.96 GHz. The loaded Vivaldi antenna is fabricated and measured. The simulated and measured results clarify the viability and effectiveness of the proposed design. The measured impedance bandwidth (VSWR ≤ 2) is from 2 GHz to more than 18 GHz. In addition, the measured radiation patterns and a peak gain between −1 and 9 dB can be obtained in the band of 2–18 GHz.     

The effect of oxide layer thickness on the quantification of 1.5 MeV γ–radiation induced interface traps in the Ag/SiO2/Si MOS devices

This work presents the effect of varied thickness of oxide layer and radiation dose on electrical characteristics of Ag/SiO₂/Si MOS devices irradiated by 1.5 MeV γ–radiations of varied doses. SiO₂ layers of 50, 100, 150 and 200 nm thickness were grown on Si substrates using dry oxidation and exposed to radiation doses of 1, 10 and 100 kGy. The exposure to radiation resulted in generation of fixed charge centers and interface traps in the SiO₂ and at the Si/SiO₂ interface. Capacitance-conductance-voltage (C-G-V) and capacitance-conductance-frequency (C-G-f) measurements were performed at room temperature for all MOS devices to quantify the active traps and their lifetimes. It is shown that accumulation and minimum capacitances decreased as the thickness of SiO₂ layer increased. For the unexposed MOS devices, the flat band voltage V_FB decreased at a rate of −0.12 V/nm, density of active traps increased by 4.5 times and depletion capacitance C_DP, increased by 2.5 times with the increase of oxide layer thickness from 50 to 200 nm. The density of active traps showed strong dependence on the frequency of the applied signal and the thickness of the oxide layer. The MOS device with 200 nm thick oxide layer irradiated with 100 kGy showed density of active interface traps was high at 50 kHz and was 3.6×10¹⁰ eV⁻¹ cm⁻². The relaxation time of the interface traps also increased with the exposure of γ–radiation and reached to 9.8 µs at 32 kHz in 200 nm thick oxide MOS device exposed with a dose of 100 kGy. It was inferred that this was due to formation of continuum energy states within the band gap and activation of these defects depended on the thickness of oxide layer, applied reverse bias and the working frequency. The present study highlighted the role of thickness of oxide layer in radiation hard environments and that only at high frequency, radiation induced traps remain passivated due to long relaxation times.     

Effects of thermal annealing on the photophysical properties of bisfluorene-cored dendrimer films

Annealing is widely used in the processing of organic semiconductors, and can modify their film morphology and photophysical properties. A study of the effect of annealing on films made from a blue emitting bisfluorene-cored dendrimer is reported. Annealing causes a 15 nm blue-shift in the photoluminescence (PL) spectrum and an 11 nm blue-shift in the amplified spontaneous emission (ASE) spectrum. It causes the PL efficiency to decrease only slightly from 0.92 to 0.83. The radiative decay rate of 1.3 × 10⁹ s^?1, the ASE threshold of 1.5 × 10¹⁸ cm^?3 and the singlet–singlet exciton annihilation rate of 5.5 × 10^?10 cm³ s^?1 are unaffected by annealing. The results indicate a scope for colour adjustment of dendrimer light-emitting diodes and lasers without affecting their efficiencies. Investigation by spectroscopic ellipsometry shows that on annealing, the films become anisotropic, with larger values of the refractive index and extinction coefficient observed for light polarised in the plane of the film than the corresponding out-of-plane values in the absorption region of the bisfluorene core. This anisotropy indicates a preferential in-plane orientation of bisfluorene cores upon annealing.