Design considerations for rectangular microstrip patch antenna on electromagnetic crystal substrate at terahertz frequency

The effects of 2-D electromagnetic crystal substrate on the performance of a rectangular microstrip patch antennas at THz frequencies is simulated. Electromagnetic crystal substrate is used to obtain extremely broad-bandwidth with multi-frequency band operation of the proposed microstrip antennas. Multi-frequency band microstrip patch antennas are used in modern communication systems in order to enhance their capacity through frequency reuse. The simulated 10 dB impedance bandwidth of the rectangular patch microstrip antenna is 34.3% at THz frequency (0.6–0.95 THz). The radiation efficiency, gain and directivity of the proposed antenna are presented at different THz frequencies. The simulation has been performed using CST Microwave Studio, which is a commercially available electromagnetic simulator based on finite integral technique.     

Analysis of graphene based optically transparent patch antenna for terahertz communications

With and without multi walled carbon nanotube (MWCNT) loaded graphene based optically transparent patch antennas are designed to resonate at 6 THz. Their radiation characteristics are analyzed in 5.66–6.43 THz band. The optically transparent graphene is deployed as the patch and ground plane of the antennas, which are separated by a 2.5 μm thick flexible polyimide substrate. By shorting the microstrip line and ground plane of the antenna with a MWCNT via, the return loss of the antenna is improved. The peak gain of 3.3dB at 6.2 THz and a gain greater than 3dB in 5.66–6.43 THz band is obtained for antenna loaded without MWCNT. Both the antennas achieved a −10dB impedance bandwidth of 12.83%. Gain, directivity and radiation efficiency of the proposed antennas are compared with conventional transparent patch antennas and graphene based non-transparent antennas. The antenna structures are simulated by using finite element method based electromagnetic simulator-Ansys HFSS.     

Analysis of single band and dual band graphene based patch antenna for terahertz region

A microstrip patch antenna is designed using a very thin layer of graphene as the radiating patch, which is fed by a microstrip transmission line. The graphene based patch is designed on a silicon substrate having a dielectric constant of 11.9, to radiate at a single frequency of 2.6 THz. Further, this antenna is made to resonate at dual frequencies of 2.48 THz and 3.35 THz, by changing the substrate height, which is reported for the first time. Various antenna parameters such as return loss, VSWR, gain, efficiency and bandwidth are also determined for the single and dual band operation. For the single band operation, a bandwidth of 145.4 GHz and an efficiency of 92% was achieved. For dual band operation, a maximum bandwidth of 140.5 GHz was obtained at 3.35 THz and an efficiency of 87.3% was obtained at the first resonant frequency of 2.48 THz. The absorption cross section of the antenna is also analysed for various substrate heights and has maximum peaks at the corresponding resonating frequencies. The simulation has been carried out by using a full wave electromagnetic simulator based on FDTD method.     

Analysis on effect of low dielectric permittivity on indium-doped tin oxide based optically transparent terahertz patch antenna

Indium-doped tin oxide based optically transparent rectangular patch antennas are designed to resonate at 750 GHz; one on the glass substrate and the other on the polyimide substrate. Characteristics of both the transparent antennas such as impedance bandwidth, radiation efficiency, directivity and gain are analyzed and compared. Polyimide substrate has a lower dielectric permittivity than the glass substrate. The effect of low dielectric permittivity substrate on the radiation characteristics of the terahertz transparent patch antenna is analyzed. The transparent antenna on polyimide substrate is shown to have gain greater than 3.97dB in 714–795 GHz. The proposed transparent antennas are designed and simulated by using finite element method based electromagnetic solver, Ansys–HFSS.     

Ball lens based lensed patch cord probes for optical coherence tomography in the field of dentistry

A lensed patch cord probe has been made with a ball lens packaged in a metal cylinder. By simply placing a ball lens directly in front of a fiber patch cord, a compact and potentially disposable sampling probe for optical coherence tomography (OCT) could be implemented. To achieve a sufficiently long working distance and a good transverse resolution simultaneously, the proper ball lens diameter and the distance between the ball lens and the fiber patch cord were investigated. Experimentally, a working distance of up to 5.2 mm, 3 dB bandwidth of 2 mm, and transverse resolution of 16 μm were achieved. With the patch cord probe, a common path swept source OCT system was implemented and used to demonstrate the feasibility as the dedicated probe for dentistry.     

Performance analysis and comparison of MWCNT loaded ITO and TIO based optically transparent patch antennas for terahertz communications

Multiwalled carbon nanotube (MWCNT) loaded transparent conducting oxide materials (TCOMs) based optically transparent antennas are designed to resonate at 750 GHz. TCOMs such as indium-doped tin oxide (ITO) and titanium-doped tin oxide (TIO) are used for designing the transparent terahertz patch antennas. Shorting pin technique is used to improve the impedance performances of the transparent antennas. The MWCNT is used for shorting the microstrip line with the ground plane of the antenna. By varying the position of short with respect to the antenna patch, the resonant frequency of the antennas are optimized to resonate at 750 GHz. The impedance and radiation performances of the MWCNT loaded transparent antennas are compared. A broad impedance bandwidth (−10 dB) is achieved for both the proposed antennas. The MWCNT shorting pin effect on radiation performances of the transparent antennas are discussed in detail. The antennas are simulated using finite element method (FEM) based electromagnetic solver, Ansys-HFSS.     

Frequency agile antennas based on aluminum nitride ceramics

In this paper, the frequency agile antennas made using aluminum nitride ceramic substrate are investigated theoretically and experimentally. The aluminum nitride ceramic substrates are prepared by pressing and sintering aluminum nitride powders. The operating frequency of antenna is designed to operate at 2.45 and 5.80 GHz. The shape of the patch attaching on the aluminum nitride substrate was rectangular form, and the dc bias is applied between patch and ground plane. This simple technique is used to implement electronically tunable antenna. Deformation of the antenna due to the applied dc bias is obtained as the computation of thickness and extension strains. The simulated frequency shifts at 2.45 and 5.80 GHz, are 7.42 and 7.70 MHz, and the experimentally measured frequency shifts at the same frequencies are 7.50 and 8.50 MHz, respectively. The theoretically simulated results show an average error of less than 4.45% compared with the experimental results.     

A bridged waveguide intersection in two-dimensional photonic crystal structures

In this work we introduce a symmetric waveguide intersection in photonic crystal structures, which passes the optical power entering from each one of its four ports, directly to the forward port. This junction allows designers to easier and more efficient design of photonic integrated circuits (PICs) and to create bridge-junctions in a 13.3 μm² area with just one linear material in its construction. The minimum pass to stop contrast ratio is 26 db with an 18.1 nm bandwidth for contrast ratio over 15 db. Conformal finite difference time domain (CFDTD) method has been used to analysis the system and numerically demonstrates its working.     

V-band directional tandem coupler of monolithic uniplanar structure

We present a uniplanar coplanar-waveguide 3-dB tandem coupler operating at V-band frequencies. The uniplanar structure is monolithically fabricated by using two-section parallel-coupled lines and air-bridge crossovers replacing the conventional multilayer or bonded structures. Due to an optimized tandem structure and non-bonded crossovers minimizing the parasitic components, a maximum coupling of 2.5 dB is measured at 62 GHz with a 2 dB bandwidth of 83%, while a high directivity factor of 33 dB is simultaneously obtained at 58–62 GHz. Over the entire design frequency range of 30–90 GHz, we achieve good phase unbalance of 90 ± 6.0°, as well as return loss and isolation lower than −23 and −16 dB, respectively.     

Class IV Flextensional Transducer with a reflector

Class IV Flextensional Transducers (FTs), which are the most popular among the various FTs used for underwater sound projection, are inherently omni-directional and therefore their possible application areas are limited. In this work, we investigate the possibility of getting directional performance from a 3 kHz Class IV FT, using a reflector. Finite element modeling (FEM), with the help of a commercially available package ATILA, has been made use of. Results indicate that a parabolic reflector with a air–water interface as the reflecting surface, would give an excellent directivity of 60° (3 dB) with a front-to-back ratio better than 30 dB. Experimental results, making use of a sound-reflecting coating as the reflector has shown a directivity of 82°, with a front-to-back ratio of 21 dB. It is also observed that the reflector causes the FTs to vibrate in asymmetrical modes, the long-term implications of which needs to be studied to ensure the reliability of the device.     

Fault detection of antenna arrays using infrared thermography

A fast and easy method for fault detection in antenna arrays using infrared thermography is presented. A thin, minimally perturbing, microwave absorption screen made of carbon loaded polymer is kept close in front of the faulty array. Electromagnetic waves falling on the screen increase its temperature. This temperature profile on the screen is identical to electric field intensity profile at the screen location. There is no temperature rise observed on the screen corresponding to non-radiating (faulty) elements and hence can be easily detected by IR thermography. The array input power is modulated at a low frequency which permits thermography to detect even weak fields. It also improves the resolution of thermal images. The power fed to the array is only 30 dBm. In order to show the utility of this technique, an example of 14 GHz 4 × 4 patch antenna array is given. The simulations are carried in CST Microwave Studio 2013. A good agreement between simulation and experimental results is observed.     

980 nm Yb-doped double-clad photonic crystal fiber amplifier and its frequency doubling

In this paper, we report on a large-mode-area double-clad 980 nm Yb-doped photonic crystal fiber (PCF) amplifier. In the experiment, an output power of 1.21 W at 980 nm with 2.5 nm bandwidth has been yielded when the PCF length was 40 cm. Through frequency doubling the 980 nm amplified laser with a BIBO crystal, an output power of 51 mW at 490 nm has been generated.     

A novel polarization splitter based on dual-core elliptical-holes hybrid photonic crystal fiber

A novel kind of polarization splitter in dual-core elliptical holes hybrid photonic crystal fiber is proposed. Numerical results show that the splitter can reach small coupling length ratio of 0.5, for wavelength from 1.15 μm to 1.9 μm. At wavelength 1.55 μm, the extinction ratio can achieve ?64 dB and the 1.92-mm-long splitter is suggested to achieve extinction ratio better than ?10 dB, a bandwidth of 150 nm. The fiber has small coupling length ratio, small coupling length and high extinction ratio and it is more suitable for fabricating polarization splitter.     

A novel proposal for DWDM demultiplexer design using modified-T photonic crystal structure

We propose an ultra compact structure to realize demultiplexing operation for Dense Wavelength Division Multiplexing (DWDM) communication systems using resonant cavity in modified-T Photonic Crystal (PC) structure. To the best of our knowledge, this is for the first time that a PC-based demultiplexer has been achieved with 1 nm channel spacing and 0.45 nm mean value of bandwidth without using either specific materials or complexities in fabrication process. Designs offering improvement of channel spacing and bandwidth of the proposed demultiplexer is our aim in this work. The attained characteristics are approximately in the range of the DWDM communication systems. Accurate resonant cavities have been used in terms of location and size of holes in the proposed structure in order for them to capture desired wavelengths in optical telecommunication range. Our simulations indicate the average amount of crosstalk (Xt) and the average quality factor (Q) to be ?21.1 dB and 3488, respectively. Two-dimensional (2D) Finite-Difference-Time-Domain (FDTD) is chosen for simulation of the proposed structure. The footprint of the structure is approximately 536 μm² and can be fabricated and integrated densely and easily.     

Multifrequency super-thin cloaks

Bandwidth and thickness have become the most troublesome problems for EM cloaks. In this paper, we propose to solve the two problems using connected patches based on the microwave network model. By covering an obstacle with combined connected patches, cloaking effect can be achieved at multiple frequencies so as to expand the operating band. As an explicit example, a dual-band super-thin cloak using two different connected patch unit cells is demonstrated. Cloaking effect can be achieved at 3.50 GHz and 4.14 GHz simultaneously with an 8 dB transmission enhancement. The cloak design method provides a new route to broadening the bandwidth of thin EM cloaks.     

Evaluation of nano-slot antenna for mid-infrared detectors

To improve the response performance of superconducting infrared detectors, we propose using a photonic antenna with a micro-detector in conjunction with a nano-structure. In this paper, we report evaluation results that show the basic characteristics of a photonic antenna in the mid-infrared region. The antenna consists of a nano-slot antenna and a thin-film load resistance placed in the center of the antenna. The antennas were designed for operation at approximately several tens of THz by using an electromagnetic simulator. Through measurements of the spectral reflectance characteristics, clear absorptions caused by the antenna properties were observed at approximately 50 THz, and high polarization dependencies were also observed. The results of the simulation qualitatively agreed with the results of the experiment. The effective area of the antenna was also evaluated and was found to be approximately 3.5 μm² at 54 THz.     

Low-cost micro-lens arrays fabricated by photosensitive sol–gel and multi-beam laser interference

In this paper, we introduce a low-cost approach for fabricating micro-lens arrays that is based on photosensitive sol–gel and multi-beam laser interference. UV photosensitive ZrO₂ gel films are prepared with Zr(O(CH₂)₃CH₃)₄ and BzAcH as the precursor and chemical modifier, respectively. With UV laser irradiation via different dose, nonlinear photodecomposition occurs in this film. Large scale 2D micro lens arrays with the sizes of 830 nm × 830 nm and 280 nm × 280 nm are fabricated by four-beam laser interference. The surface profile modeling shows that the micro lens is plano convex lens, and the effective focal lengths are 812.0 nm and 317.6 nm, respectively.     

Ultra-broad and flat supercontinuum generation in short photonic crystal fiber combined with conventional fibers

In order to gain ultra-broad and flat super-continuum (SC) spectrum, we propose and demonstrate a new scheme. By coupling a train of short pulses with 100 fs width and 16.2 mW average power generated by a mode-locked laser into the scheme – short photonic crystal fiber (PCF) combined with conventional fibers. The SC spectrum has 491 nm bandwidth at −15 dBm below the spectral peak with ±0.5 dBm uniformity 100 nm in only 0.45 m PCF. The spectral bandwidth generated in the scheme increases 292 nm than spectrum generated in the two conventional fibers, and increases 152 nm than spectrum generated in the three convention fibers.     

Phase errors in FSE signals due to low frequency electromagnetic interference

ObjectiveTo quantitatively evaluate induced phase errors in fast spin echo (FSE) signals due to low frequency electromagnetic inference (EMI).MethodsSpecific form of Bloch equation is numerically solved in time domain for two different FSE pulse sequences (ETL = 8) with two different bandwidths. A single spin is modeled at x = 10 cm, EMI frequencies are simulated from 1 to 1000 Hz and phase errors at different echo times are calculated.ResultsPhase errors in the received echo signals induced by EMI are significantly higher at low frequencies (< 200 Hz) than at high frequencies and the phase errors at low frequencies can be effectively reduced by using high receiving bandwidth.ConclusionPulse sequence bandwidth can be used to control the phase errors in the FSE signals due to low frequency EMI.     

Antenna length and polarization response of antenna-coupled MOM diode infrared detectors

This work focuses on the fabrication and response of dipole antenna-coupled metal–oxide–metal diode detectors to long-wave infrared radiation. The detectors are fabricated using a single electron beam lithography step and a shadow evaporation technique. The detector’s characteristics are presented, which include response as a function of incident infrared power and polarization angle. In addition, the effect of dipole antenna length on detection characteristics for 10.6 μm radiation has been measured to determine resonant lengths. The response of the detector shows a first resonance at a dipole length of 3.1 μm, a second resonance at 9.3 μm, and third at 15.5 μm. The zeros intermediate to the resonances are also evident.