Sharif Digital Repository

Aromatic aldehydes and ketones are readily acetalized or ketalized under microwave irradiation in the presence of water as a solvent  

γ-Alumina is used to catalyze the Cannizzaro reaction in the absence of any base under microwave irradiation in high yields. In the case of terephthalaldehyde the reaction is carried out with high selectivity  

This paper presents an unilateralization technique for distributed amplifiers (DAs) based on the transformer coupling between the gate and drain lines. Theoretical analysis of the DA indicates that the voltage waves in the gate and drain lines can be described by a system of linear partial differential equations. The transformer coupling between the lines allows for cancellation of the reverse transmission coefficient of the system. There is an optimal value for the coupling coefficient between the lines that unilateralizes the DA. This optimal coupling coefficient is derived in terms of the gate-drain capacitance and capacitances of the gate and drain lines. Using the proposed technique,... 

We propose a flexible numerical framework for extracting the energy spectra and photon transfer dynamics of a unit kagome cell with disordered cavity-cavity couplings under realistic experimental conditions. A projected-entangled pair state (PEPS) Ansatz to the many-photon wave function allows us to gain a detailed understanding of the effects of undesirable disorder in fabricating well-controlled and scalable photonic quantum simulators. The correlation functions associated with the propagation of two-photon excitations reveal intriguing interference patterns peculiar to the kagome geometry and promise at the same time a highly tunable quantum interferometry device with a signature for the... 

We use a nonlinear analytic approach to predict the main oscillation mode power and spurious levels in ultrapure microwave optoelectronic oscillators (OEOs). This approach takes into account N simultaneously mode falling inside the RF filter bandwidth and calculates all the dominant InterModulation Products (IMPs) that fall in the fundamental zone. We show that nonlinear microwave photonic links exhibit the capture effect. By considering this effect, we derive analytical expressions that govern the behavior of the OEOs in the steady state. We find that when the small-signal open-loop gain is increased beyond a critical value, OEOs start a multimode operation from which the spurious levels... 

Quarter-wavelength superconducting spiral resonators have been used to realize a coplanar waveguide bandpass filter and bandstop filter around the center frequency of 6 GHz. These compact coplanar waveguide filters have been made from 300-nm-thick NbTiN thin film on a 525-μm-thick silicon substrate. The bandpass filter is a six-pole Chebyshev filter with two zero transmissions due to nonadjacent coupling in its structure. Accurately microfabricated air-bridges have been used to suppress the undesired slot-line mode in this filter. The bandstop filter is a very simple two-pole structure that used wire bonding to suppress the slot-line mode. Measurements have been done at a temperature of 4.2... 

An electromagnetically induced phase grating (EIG) controlled by coherent population trapping (CPT) in a fourlevel Y-type atomic system is studied. The CPT condition promotes significantly the dispersion of light into the first-order diffraction in constructing a phase modulation grating by transferring energy from zero-order to firstorder diffraction. The diffraction efficiency of the phase grating is enhanced by up to 30% of the total probe intensity at the first-order diffraction. The present atomic scheme takes full advantage of the microwave-driven field for generating the EIG, which induces the quantum coherence and controls linear and nonlinear behaviors of the present system.... 

This paper presents a harmonic termination technique for single-and multi-band high-efficiency class-F monolithic microwave integrated circuit (MMIC) power amplifiers (PAs). The harmonic termination network (HTN), realized with the minimum possible number of elements, can be used to terminate an arbitrary number of harmonics in a single-band PA or harmonics of multiple frequencies in a concurrent multi-band PA. The drain and gate bias lines are embedded in the HTNs to obviate the need for RF chokes and reduce the chip area. A single-and a dual-band MMIC PA are designed using the proposed technique and implemented in a 0.25-μm AlGaAs-InGaAs pHEMT technology. The single-band 5.5-GHz PA... 

In this paper, extended composite right/left-handed (E-CRLH) transmission line (TL) metamaterial structures, with two left-handed (backward) and two right-handed (forward) pass bands, are investigated. Also, design procedures in order to design dual- and quad-band E-CRLH-TLs are presented in detail and the parameters of these structures are extracted by clean formulas, while satisfying arbitrary phase shifts at the operating frequencies. Finally, the dispersion and characteristic impedances of these transmission lines are derived and plotted. The results of this paper can be applied to any type of TL-based dual- and quad-band microwave component  

We propose to use a compressed sensing recovery method called IMATCS for improving the resolution in microwave imaging applications. The electromagnetic inverse scattering problem is solved using the Distorted Born Iterative Method combined with the IMATCS algorithm. This method manages to recover small targets in cases where traditional DBIM approaches fail. Furthermore, by applying an L2-based approach to regularize the sparse recovery algorithm, we improve the algorithm's robustness and demonstrate its ability to image complex breast structures. Although our simulation scenarios do not fully represent experimental or clinical data, our results suggest that the proposed algorithm may be... 

Perchloric acid immobilized on silica gel (SiO2-HClO4) has been utilized as a mild and cheap reagent for onepot preparation of different varieties of flavylium salts via tandem reaction of different acetophenones with Salicylaldehydes under solvent-free conditions. Different reaction conditions such as conventional heating and microwave irradiation have been investigated. The corresponding flavylium salts have been prepared in high yields. The procedure is milder and more convenient than the known procedures  

The noise performance of intensity-modulation direct-detection microwave photonic links (MWPL) operating under large-signal conditions has been studied in this paper. A sinusoidal signal plus narrow-band white Gaussian noise is applied at the radio frequency input of the link, and the output spectrum is derived using a nonlinear analytical approach. We show that the output SNR can be severely affected by the interaction of signal and noise due to the nonlinearity of the MWPL combined with the large input modulating signal. It is shown that the large-signal noise figure (NF) of an MWPL depends on the input power, a dependence that is not readily apparent under small-signal conditions, due to... 

We propose a circularly polarized antenna with a wide axial ratio (AR) beamwidth that consists of a normally magnetized ferrite disk mounted on a ground plane. The device uses the resonant modes of the disk, which rotate only in the clockwise or counter-clockwise sense in the frequency range where the effective permeability of ferrite is negative. A semianalytical model is derived for the antenna fed by a single, conventional current probe and is validated numerically by finite element method. For a yttrium iron garnet disk with the radius and height of 5 and 1 mm, respectively, the results show a 3 dB AR beamwidth of 90° with an operation frequency, which can be tuned in the 4-4.5 GHz range... 

We have synthesized ZnxCd1-xS nanocrystals (NCs) using a microwave assisted method. Zn(Ac)2, CdSO4 and Na2S2O3 were used as the precursors and thioglycerol (TG) was used as the capping agent. Na2S 2O3 is a photo and heat sensitive material, which supplies S species needed for the reaction upon dissociation. In this facile method, microwave irradiation provides the activation energy for the dissociation of Na2S2O3 in and leads to the formation of ZnxCd1-xS NCs in 2 min. The question that to what extent Zn is incorporated into CdS structure was addressed using UV-Vis spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Our results showed that the real value of x in... 

A novel nanocomposite of ZnO-PbO with flower-like nanostructure was fabricated from zinc acetate and lead nitrate as principle raw materials via an in situ process. The novelty of this study consists in the use of a common approach for fabricating of ZnO and PbO nanoparticles simultaneously. From these experiments the conclusion might be drawn that Zn(NH4) 2 4+ ions and Pb(OH)2 act as precursors for the nucleation and growth of ZnO and PbO respectively under microwave irradiation. The precursors formation were carried at two stages: reaction between zinc ions and lead nitrate with ammonium ion and hydroxide sodium respectively. The average crystalline size of Zno and PbO has been analysed by... 

SrFe12-xTix/2Zn x/2O19 (x = 0-2.5) powders were synthesized by use of chlorides through co-precipitation method. The obtained powders were then milled by high energy ball mill to crash hard agglomerates and achieve nanoparticles. In order to evaluate microwave absorption versus frequency, composites including ferrite, as a filler, and matrix of polyvinylchloride (PVC) with weight ratio of 70% ferrite were prepared. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), vibrating sample magnetometer (VSM) and vector network analyzer (VNA) were employed to study the structural, magnetic and microwave absorption properties... 

This paper presents a bandwidth enhancement technique for broadband Darlington amplifiers. A detailed analysis of the high-frequency performance of the Darlington amplifier and the effect of bandwidth enhancement is provided. A design procedure is also given for broadband feedback Darlington amplifiers with bandwidth enhancement and gain flattening. A single- and a three-stage feedback amplifier with the proposed improvements are designed and implemented in a 0.25-μm Al-GaAs-InGaAs pHEMT technology. The single-stage amplifier provides 6 ± 0.4 dB of small-signal gain in the frequency band of 1-30 GHz. The three-stage amplifier features 17.8 ± 0.8 dB of small-signal gain in the frequency band... 

A mm-wave transition from coplanar waveguide (CPW) to substrate integrated waveguide (SIW) is presented based on a U-shaped coplanar slot antenna. Using 3D FEM simulations the input impedance exhibited by the structure is analyzed, and simple equations are extracted to design an ultra-wide band transition once the substrate material and the waveguide cut-off frequency are chosen. As an example, a W-band transition on a high resistivity silicon-filled waveguide is implemented: an input matching better than -14.5 dB from 79 to 110 GHz and insertion loss of 0.6 dB at 110 GHz are measured  

We present a technology for the manufacturing of silicon- filled integrated waveguides enabling the realization of lowloss high-performance millimeter-wave passive components and high gain array antennas, thus facilitating the realization of highly integrated millimeter-wave systems. The proposed technology employs deep reactive-ion-etching (DRIE) techniques with aluminum metallization steps to integrate rectangular waveguides with high geometrical accuracy and continuousmetallic side walls. Measurement results of integrated rectangular waveguides are reported exhibiting losses of 0.15 dB/ at 105GHz.Moreover, ultra-wideband coplanar to waveguide transitions with 0.6 dB insertion loss at 105... 

Phase noise is one of the most important specifications of microwave oscillators. External factors such as mechanical vibrations increase the phase noise of the oscillator. A novel technique is introduced to reduce vibration-induced phase noise using inter-injection locking of two coupled oscillators. Two similar oscillators with equal free running frequencies are chosen and are subjected to sinusoidal vibration. The mechanical configuration is such that vibration sensitivity vector increases the frequency of one oscillator and decreases the other one's frequency of oscillation. Coupling these two oscillators using inter-injection locking, the common after-lock frequencies of both...