An applicator for intracavitary hyperthermia treatment of cancer has been designed and tested. The applicator is a section of a dielectric-loaded circular ridge waveguide closed at both ends to form a transmission cavity. An aperture in the cavity wall can produce a directed heating of a tumor growing in the wall of a body cavity such as the vagina.
An actively mode-locked fiber laser (AMLFL) based on the hybrid gain of a dispersion-shifted fiber (as the Raman gain medium) and an Erbium-doped fiber (EDF) is introduced. The fiber Raman gain mechanism can effectively suppress the gain competition of an EDF, which usually results into the supermode noise in an actively mode-locked EDF laser. We experimentally demonstrated a stable AMLFL with the repetition of about 5 GHz, in which the supermode noise is believed to be suppressed by employing the hybrid gain medium.
A tunable and injection-switchable erbium-doped fiber (EDF) laser is proposed based on a line structure formed by a fiber Sagnac loop reflector and an fiber Bragg grating (FBG). Wavelength switching is achieved by controlling the power of the tunable injection laser. The self-seeded wavelength corresponding to the Bragg wavelength of the FBG can be tuned by, for example, heating the FBG, and the injection wavelength can be tuned over a wide range of about 50 nm. The characteristics of the wavelength switching for different levels of the EDF pump power and different wavelengths of the injection laser are studied experimentally. The present fiber laser has the advantages of tunability, stability, low amplified spontaneous emission noise, and high injection efficiency when compared with a fiber ring laser. Rapid wavelength switching is expected and the transient switching response of the laser is also studied.
This article presents a fully ESD-protected, highly tunable microwave oscillator based on magnetic tunnel junction (MTJ) spin torque oscillator (STO) technology. The oscillator consists of a compact MTJ STO and a 65 nm CMOS wideband amplifier, which amplifies the RF signal of the MTJ STO to a level that can be used to drive a PLL. The (MTJ STO+amplifier IC) pair shows a measured quality factor (Q) of 170 and a wide tunability range from 3 to 7 GHz, which demonstrate its potential to be used as a microwave oscillator in multiband, multistandard radios.
A low-profile, compact, concisely designed CPW-fed broadband circularly polarized wide slot antenna is proposed. By protruding the ground into the wide slot, the distribution of equivalent magnetic currents inside the slot is changed. Together with appropriate adjustment of the feeding structure, broad impedance bandwidth and broad axial ratio bandwidth (ARBW) can be achieved simultaneously. General design steps are given so that the antenna can be easily transplanted to other bands. The measured results show that the 3 dB ARBW is 1.85-3.15 GHz (52%) and the impedance bandwidth is 1.35-4.12 GHz (101.3%). Detailed design procedures and key parameters analysis are also given for further understanding of the antenna design.
An all-digital-phase-locked-loop (ADPLL) with a dual-mode Class-A/Class-C Digital-controlled-oscillator (DCO) is presented in this letter. During the start-up phase, the DCO operates in the Class-A mode with increasing tail current. A low-power amplitude-to-pulse-converter (APC) is proposed to detect the oscillating amplitude of the DCO. After the start-up, the DCO switches to the Class-C mode with reduced tail current, resulting in better phase noise and lower power consumption. The ADPLL with the proposed DCO is implemented in a 65-nm CMOS technology. The Class-C mode DCO exhibits a phase noise of −123.3 dBc/Hz at 1-MHz offset with a 2.7-GHz carrier frequency. Measured results show about a 2.9-dB phase noise improvement at 1-MHz offset among the tuning range of 2.5–2.9 GHz, compared to the Class-A DCO under the same power consumption. The figure-of-merit (FOM) and FOM including the tuning range (FOMT) of the DCO is 188.7 and 192.1, respectively.
We propose an experimental realization of flat-top filters by fabricating fiber Bragg gratings in graded-index multimode fibers (GI-MMF). Two types of GI-MMFs were used to make this kind of filters, and their spectra and polarization properties were experimentally investigated.
A frequency up/down-converter is proposed based on fiber-four-wave-mixing (FWM) between the output of a dual-wavelength fiber laser and the modulated optical carrier for bidirection radio-over-fiber (RoF) systems. Frequency, up-conversion from 1.50 to 11.08 GHz and down-conversion from 10.60 to 1.02 GHz are successfully demonstrated and a small efficiency difference between up- and down-conversions has been achieved. A proposal of setting up a bidirectional RoF system based on fiber FWM frequency converter is presented.
Based oil the spherical vector wave function in uniaxial anisotropic left-handed-material (LHM), the electromagnetic fields in unbounded uniaxial anisotropic left-handed material are expanded in terms of spherical vector wave functions in uniaxial anisotropic LHM. Applying the continuous boundary conditions of electromagnetic,fields in tangential direction in the spherical shell of uniaxial anisotropic left-handed material, the expansion coefficients of electromagnetic fields in the spherical shell of uniaxial anisotropic LHM can be derived, and then the radar cross sections (RCSs) can be obtained. Some numerical results have been given and the method in this article call be applied in the areas of antenna design and system optimization, wave propagation in complex media, and electromagnetic compatibility.
A new type of notch filter based on a balanced composite right/left-handed (CRLH) transmission line is proposed. Combining such two notch filters with a Y-junction divider, a novel diplexer is designed and studied. The diplexer bus a wide and flat-top pass-band and very good isolation between the two outputs. Both theoretical analysis and experimental results (ire given and they agree with each other.
In this article, a circuit model is proposed for the complementary split-ring resonators (CSRRs) loaded transmission line, and comparisons between the results derived from the equivalent circuit model and the experimental results are given and a good agreement between them over a wide frequency band supports the effectiveness of F the proposed modeling methodology. Both the results show the negative f permittivity at the vicinity of the resonance frequency of CSRR. By comparing the results of different periodic length (i.e., the capacitance per-unit-cell of the host microstrip line is changed), the validity of the equivalent circuit is further confirmed.
A novel concept of a compact, low insertion-loss dual-band-rejection filter (DBRF) is proposed, and its equivalent circuit model is given. The filter consists of single split ring resonators (SRRs) on the top of the host microstrip line and Complimentary SRR etched on the back ground plane. The dimensions of the structure are as small as 1.4 cm × 2 cm, while high frequency selectivity is achieved at both band edges due to the presence of two transmission zeros. The filter has an insertion loss of better than 1 dB, a return loss of larger than 10 dB in the passband from 3.3 to 4.0 GHz, and two rejections of greater than 30 dB within 2.5-2.6 and 5.2-5.6 GHz.
An apollonian shaped ultra-wideband circular monopole antenna based oil descartes circle theorem is presented. Different self similar geometries front DCT are analyzed and optmized for UWB applications. The proposed design is slightly modified to ensure all overall smooth current distribution limited by the Junction point nature of the fractal geometries. The experimental results are compared with conventional circular disk monopole (and annular monopole antenna. The measured return loss of the proposed design below - 10 dB is from 2.4 to over 40 GHz and its radiation pattern is omni-directional compared with circular disk and annular antennas in most of its impedance bandwidth. Moreover due to the fractal shape, the proposed design has less weight and wind loading effect.
A square monopole coplanar antenna with a circular base is proposed for ultra wideband (UWB) communications. The design parameters are analyzed and optimized to obtain a good performance and the measured return loss below -10 dB is front 2.8 to over 40 GHz. The proposed antenna has advantages of low profile, small size, UWB and omni-directional pattern.
A small size and low profile microstrip fed frequency notched planar monopole ultra wideband (UWB) antenna with an arc shaped slot etched on a circular disk is proposed. The effect of different dimensions of the slotted arc are analyzed and optimized to obtain simultaneously the UWB and the band rejected performance. The return loss from (3.5-23.64 GHz) along with a notched frequency band (5.23-5.8 GHz) and quasi omni-directional radiation pattern is observed.
A Sierpinski-like fractal patch antenna with a slant strip in the first iteration is proposed in this article. The parameters of this kind of antenna are analyzed and optamized for dual WLAN application. The added slant strip provides simple probe feeding for compactness and also helps bandwidth enhancement due to multiple modes, which can be evident from current distribution. Measured return loss below,front 2.38-2.45 GHz and 5.17-5.83 GHz, coinciding well -10 dB is with dual band WLAN standard. The boresight gain and radiation pattern in different planes are also presented.
A novel notch filter based on a composite right/left-handed (CRLH) transmission line is proposed. The proposed CRLH transmission line is different-from a conventional CRLH transmission line. The novel notch filter has a large notch depth, very small loss in the passband, and very sharp transitions at the two edges of the stop-band.
A novel composite right/left-handed transmission line unit is proposed. Using the structure, a new power divider is developed. By adjusting the parameters of the capacitors and the inductors, the simulation results show that the power divider has perfectly symmetric power division at 1.24 GHz, return loss up to -38 dB with the transmitted power being close to -3 dB (-3.01 dB). In addition, the performances of the novel power divider are demonstrated experimentally.
A novel dual band array for MIMO applications at 1766 and 2450 MHz is presented. The array consists of four patch elements placed on a 125 X 75 mm(2) device. The effect a of different orientation and element placement is discussed and the final array is analyzed with respect to antenna covariance calculated from measured radiation patterns. We conclude that the array differs from an ideal monopole array by a 1.3 dB lower radiation efficiency.
The quasi-TEM modes on a planar multiconductor transmission line embedded in an elliptically stratified cross section are considered. Electro- and magneto-static problems are solved using separation of variables in elliptical coordinates. It is shown that asymptotic solutions for the radial dependences of the terms of the series can be used, under certain conditions, on the profiles of stratification. Results about the convergence and the usefulness of the asymptotic solution are presented.
We report on an experimental, W-band, uplink for hybrid fiber-wireless systems which enables high speed communication from the wireless end users to the central server. Overall system performances for an OFDM signal format are discussed in detail.
An efficient finite-difference time-domain method is proposed for the full-wave analysis of guided modes in photonic crystal fibers. The three-dimensional hybrid guided modes can be calculated by a two-dimensional mesh, if one assumes that the propagation constant along the z-direction (propagation direction) is fixed. Furthermore, only real variables are used in the present method. Therefore, the computation time and computer memory are significantly reduced. The results for a honeycomb-based silica-air photonic crystal fiber are in very good agreement with the results from the plane-wave expansion method.
Micro-cavities in two-dimensional silicon-on-insulator (SOI) photonic-crystal slabs are studied. A combination of the finite-difference time-domain (FDTD) technique and the Pad approximation with Baker's algorithm is used to accurately compute the resonant-frequencies and quality,factors simultaneously. The simulations show that, for similar cavity structures, the mode quality factors of cavities in SOI-type photonic-crystal slabs are much smaller than those in membrane photonic-crystal slabs, and deep etching of air holes is still required to obtain relatively higher Omega.
A new patch antenna system, which has both a photonic bandgap (PBG) substrate and a PBG cover, is proposed in the present paper. The impedance, radiation pattern, and directivity of such an antenna are studied by the finite-different time-domain method. The results show that the directivity of the PBG antenna is significantly improved. The dependence of the directivity on the frequency and other parameters is also studied.
Devices based on two-dimensional (2D) photonic crystals (PCs) arc typically realized as 3D structures consisting of an array of holes (or rods) vertically etched through a slab waveguide. The existence of holes in a slob waveguide may induce strong radiation losses to the slab claddings. Exact modeling of devices affected by such losses requires 3D calculations. In the present Letter, with the use of the effective-index method to account for the vertical confinement and the effective losses method by the nonvanishing conductivity, the 3D modeling is reduced into 2D. It is then shown that good agreement with experiments can be obtained for slab-waveguide-based photonic crystal devices.
The letter presents the design, fabrication, and measurement of a configurable radio frequency identification (RFID) tag based on time-domain reflections. The tag circuit contains a microstrip line (ML) that propagates radio frequency (RF) signals, and a group of capacitors that introduce impedance discontinuities to encode binary codes. The configurability of the tag circuit is allowed by connecting the nearby-placed capacitors with the ML. Ink-jet printing technology is employed to implement the layout of the proposed tag on paper substrate. To overcome the limitations of printed metallic tracks, a linearly tapering technique is proposed. With this technique, a four-bit configurable passive chipless RFID tag is realized. Both time-domain reflectometry (TDR) measurements and ultrawideband (UWB) characterizations were conducted for the proposed tag, and the results are in good consistence with the simulation ones from the circuit simulator advanced design system (ADS). Owing to its low cost fabrication and environmentally friendly nature, the proposed tag has great potential to be widely employed in low-end RFID applications. (C) 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53: 2781-2786, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26412
This article presents the design and implementation of a chipless radio frequency identification (RFID) tag on flexible substrate.The tag is designed based on the sympathetic oscillations of multiple LC (inductor–capacitor) circuits that possess distinct resonant frequencies. Information is encoded by controlling placement of these resonant frequencies. To trade off the readability and size of the tag, the optimizations including capacitor placements and different LC combinations are studied. The tag is then realized onto flexible polyimide substrate using toner-transferring process. The detection system is also constructed and used to measure the proposed tag. The measurement results show that the tag can provide an excellent readability more than 20 cm reading range. In addition, this tag is fully printable and configurable, hence making it more feasible and considerably cheaper to be used. This tag can provide a meaningful approach toward the realization of ultralow-cost RFID tags attached onto low-value items.
The Doppler effects for the reflected wave from moving media are systemically analyzed in this paper. The theoretical formula for the Doppler shift in left-handed material, which is described by Drude's dispersion model, is presented. This formula is examined by first-principles numerical experiments, which are in agreement with the theoretical results.
In this article, the ordinary optical waveguides are investigated by the near field optical microscopy (NSOM). Three kinds of experimental systems are set up and the corresponding operation modes of NSOM (illumination mode, illumination-collection mode and collection mode) are realized and analyzed.
A new technique to realize left-handedness in microstrip tramsimission line is proposed by periodically loading combination of split-ring resonators (SRRs) and complementary split-ring resonators (CSRRs). Because of the negative permeability offered by SRRs and the negative permittivity of the CSRRs in the designed frequency (5 GHz), a pass-band is achieved. The design is compact in size, low profile and independent of substrate permittivity. It is also 50% smaller comparing with EBG structure. These features are valuable for future microwave devices like couplers, filters, etc. Comparisons between the simulated and measured results are discussed in details.