In many non-destructive testing and medical diagnostic applications, photoacoustic generation by optical fiber is an effective approach to meet the requirements of broad bandwidth and compact size. The energy absorption layer coated onto the fiber endface plays an important role in the conversion of laser energy into heat used to excite acoustic waves. Gold nanostructures are promising solutions to be utilized as energy absorption layers due to their capability of absorbing maximum optical energy at plasmon resonant frequencies. The appropriate selection of the organization and dimensions of the gold nanostructures is the key to achieving high absorption efficiency. Numerical modeling is an efficient way to predict the behavior of the system as a variation of select parameters. A 3D finite integral technique model was established to simulate the dependency of absorption efficiency on the organization and dimensions of the gold nanospheres and nanorods. The simulation results provided practical clues to the design and fabrication of fiber-optic photoacoustic generators.
In this paper, the characteristics of novel modified composite right/left-handed (CRLH) transmission lines are discussed, and an ultra-wideband (UWB) bandpass filter (BPF) using the modified CRLH transmission lines is presented. Design formulas of a novel modified CRLH unit cell are theoretically derived. Based on the design formulas, the UWB bandpass filter with three unit cells is designed, fabricated, and measured. The measurement results show that the UWB bandpass filter has an insertion loss of less than 1 dB, bandwidths of 2.9~4.9 GHz, and a rejection of greater than 50 dB at 5.8 GHz.
The design and analysis of a high power and high efficiency helix traveling-wave tube operating in the Ka-band are presented. First, the double-slotted helix slow-wave structure is proposed and employed in the interaction circuit. Then, negative phase-velocity tapering technology is used to improve electronic efficiency. From our calculations, when the design voltage and beam current are set to be 18.45 kV and 0.2 A, respectively, this tube can produce average output power over 800 W ranging from 28 GHz to 31 GHz. The corresponding conversion efficiency varies from 21.83% to 24.16%, and the maximum output power is 892 W at 29 GHz.
An ultra-wideband (UWB) antenna with triple band-notched characteristics is presented in this paper. The triple-notched bands (5.15-5.35 GHz and 5.725-5.825 GHz for WLAN, 7.9-8.395 GHz for X-band) are achieved by using only one novel composite resonator with multiple resonant characteristics. The resonator is placed on the back surface of the substrate and connected to the radiation patch through one via-hole. An equivalent circuit model is built for analyzing the band-notched characteristics. Moreover, the notched bands can be adjusted independently, and the resonator structure is very compact.
The one-step stair-shaped dielectric resonator antennas (DRAs)with a circular cross-section are studied theoretically and experimentally in this paper. The reasons why the one-step stair-shaped DRA shave a wideband performance have been investigated. It is shown in this paper that the modes excited in the one-step stair-shaped DRA with circular cross-section can be regarded as pseudo HEM111 and pseudo HEM113 modes. The pseudo HEM111/ HEM113 mode exhibits similar radiation patterns but a different resonant frequency and radiation Q factor to the HEM111/ HEM113 mode of the cylindrical DRA. By properly choosing the dimensions of the one-step stair-shaped DRA, the two modes can be used to obtain a wideband antenna.
A mathematical investigation of a normal mode helical antenna (NMHA) is presented to provide an equivalent model. The vector potential of a single-turn NMHA using a developed helix line is first derived. To avoid complexity in the vector potential, a useful relationship between the source point and the helix line is established. Employing this relationship, the integral of the vector potential can be calculated as that of a linear current antenna, and the result leads to an equivalent model that is a combination of the electric dipole and the magnetic dipole, i.e., exactly the same as assumed in previous work. A helix line of several turns can be regarded as a combination of the turns. Thus a general NMHA can be analysed as the sum of the vector potentials of the turns in the helix. To verify the obtained formulas, the calculated radiation characteristics are compared with the results of the commercial simulation, showing good agreement.
The application of an external electric field has been shown to enhance the impregnation of resin monomers used in restorative dentistry. Further to experimental investigations that have related the migration of monomers to their electrical properties, additional insight into the conduction mechanism within the tooth can be gained by numerical modelling of the current conduction through the tooth. This paper presents the development of a three-dimensional realistic voxel model of a human tooth from a data set of digital images and the computation of the currents in the dental tissues by means of a low-frequency numerical code (scalar potential finite difference). Results for the electric potential and current density magnitude in various cross sections of the tooth model are presented for an applied 10 V dc voltage between the electrodes.
A simple compact wideband aperture coupled rectangular dielectric resonator antenna (RDRA) loaded with similar parasitic dielectric elements separated by low dielectric spacers as air gap layers is designed. The bandwidths of the proposed RDRAs are significantly enhanced as compared with the bandwidth of the driven DRA without an air gap. The measurement results are verified experimentally for a one parasitic element case. A bandwidth of 18% and 27% with VSWR better than 2 is achieved for double and triple gaps, respectively. It is interesting to point out that radiation patterns are stable in the entire operation band.
This paper presents a circularly polarized compact antenna based on the concept of Yagi-Uda antenna. By properly arranging three ring resonators operating at the fundamental mode, a compact Yagi-Uda like antenna is proposed to form directional pattern. This proposed antenna has comparable size with the ring resonator of quarter-wavelength, while the performances are comparable with the conventional microstrip antenna of half-wavelength. To validate the proposed design methodology, an antenna working at UHF radio-frequency identification (RFID) band is benchmarked. Both simulated and measured results are shown for comparison.
A compact decoupling network for enhancing the ports isolation of two coupled antennas is proposed in this letter. Parallel coupled lines (PCLs) and transmission lines (TLs) with different electrical lengths are considered to control the magnitude and phase of this decoupling network, respectively. The coupling coefficient of the PCLs is adjusted with various line widths and coupled gaps so that the magnitude of this network will be equal to that of the coupled antennas. And the electrical length of the series TLs can be controlled to make the signals of coupled antennas and decoupling network out of phase. Thus, the mutual coupling between the coupled antennas can be canceled. A prototype is fabricated on a RO4003 print circuit board (PCB) for demonstration. The measured results agree quiet well with the simulation ones. High antenna isolation and good matching are simultaneously achieved at the center frequency, i.e., 925 MHz for global system mobile communications (GSM) which shows the compact decoupling network is suitable for reducing the isolation of size limited multi-antenna systems.
A type of closed exterior algebra in R3 under the cross product is revealed to hold between differential forms from the three Whittaker scalar potentials, associated with the fields of a moving electron. A special algebraic structure is revealed in the context of Clebsch reparametrization of these scalars, and a special prescription for the construction of permutation invariant electromagnetic fields is given as well as a superposition with parallel electric and magnetic components.
A compact shorted annular patch antenna for global positioning system is presented in this paper. Multipath-rejection capability is realized with two stacked shorted annular patches (SAP). The broadband characteristic of the (-10 dB return loss) input impedance bandwidth and the 3 dB bandwidth of axial ratio is achieved by employing capacitively coupled feed structure while the shorted pins located between the upper and the lower patches will realize the impendence matching of the high frequency, which can cover L5/L2/L1 bands for GPS and the relative input impedance bandwidth can achieve 50.6%. The size is 0.3λ×0.3λ for 1.1 GHz.
A method of plasma density measurement based on microwave resonant cavity perturbation (Kornegay [13]) is described. Resonant cavity theory was analyzed and a resonant cavity with special structure was designed for measuring the low density plasma. In the middle of the closed cavity, there were cut-off tubes which were extended a little into the cavity to get through the plasma. It was found that the distribution of the electrical field intensity was the densest near the cut-off tubes when the cylindrical cavity operating with TM010 mode. By using the method of resonant equivalent circuit analysis, both the amplitudes and phases of the Scattering matrices (S matrices) were obtained before the plasma came and at the time of the plasma passing through. Then the electron line density (Ne) and the electron-molecule collision frequency for momentum transfer (vm) were calculated. A modified formula was proposed based on our simulation which was conducted in HFSS and experimental results. With the comparison of our results and Kornegay's, it was found that the accuracy of the plasma dielectric constant calculation was improved about 5 percent.
It is shown that metal gratings can be used to improve the cross polarization of circularly-polarized aperture-coupled microstrip antennas. The metal gratings reduce edge diffraction from the finite-size grounded dielectric slab on which the antennas are printed. The edge diffraction is due to surface waves that can propagate in the grounded dielectric slab. The design of the metal grating is based on an analytical model, which results in a first-order estimation for the design of the metal grating structure. The model provides physical insight and appears to be accurate enough for the application. Using this model, a prototype was developed, consisting of a circularly-polarized 2×2 microstrip array with associated feeding network. Measurements show that the axial ratio can be reduced down to 1.75 dB within the beam width of the antenna.
In this letter, a novel microstrip-fed monopole ultrawideband (UWB) antenna with triple notched band is proposed. By embedding a novel modified capacitively loaded loop (CLL) resonator beside the microstrip feed line, band-rejected filtering properties in 3.3-3.6 GHz for WiMAX, 5.15-5.825 GHz for WLAN, and 7.25-8.295 GHz for the X-band satellite is generated. The notched frequencies can be adjusted according to specification by altering the parameters of the modified CLL resonator. Both the experimental and simulated results of the proposed antenna are presented, indicating that the antenna is a good candidate for various UWB applications.
Difference patterns are vital for the successful function of tracking radar employing monopulse techniques to estimate target direction. Traditional monopulse antenna pattern synthesis methods require the use of two independent distributions, e.g. Taylor and Bayliss distributions, for formation of sum and difference patterns for one antenna. Hence, these approaches require a feed network of considerable complexity. In this letter, a method for forming difference pattern in linear arrays using a very simple beamforming network and two additional elements is described. The sum pattern is determined by adding signals received by original radiating elements of the array whereas the difference pattern is determined by subtracting the output of the sum pattern from signals received from two external edge elements. The proposed method used to generate these two patterns offers significant hardware and software savings over current methods.
A compact wideband bandpass filter is proposed in this letter by means of short-circuited-stub loaded ring resonator and tapped feed lines. After the principle of an initial filter with wide operating bandwidth is described, a prototype filter with center frequency at 3.23 GHz and fractional bandwidth of 86.1% is designed and fabricated. Measured results well agree with the predicted ones, verifying the design principle.
In this paper, a compact tunable dual-stop-band filter is proposed. The proposed filter is based on the combination of double H-shaped defected ground structure (HDGS) and E-shaped defected microstrip structure (EDMS). The loaded HDGS/EDMS varactor diode is introduced to realize the tunable dual-stop-band filter. The equivalent-circuit models and theoretical analysis of the proposed structure are presented; also its performance evaluation is compared with traditional structure. The proposed filter has the characteristic of two independently adjustable stopbands and wide tuning range. EDMS also shows size reduction up to 38% compared with the T-shaped defected microstrip structure. The measured performance of the tunable dual-stop-band filter agrees well with the simulation results.
The Omnidirectional reflection characteristics of one-dimensional (1D) superconducting-dielectric binary graded photonic crystals (PhCs) are studied by using transfer matrix method. The influences of thickness changing rate, numbers of periods, incident angles are analyzed. And the omnidirectional photonic band gaps are extended markedly in the 1D thickness-graded superconducting-dielectric PhC.
A new sensor device is reported to measure the change in dielectric permittivity or refractive index of liquid samples. This novel device is extremely compact in nature and can be fabricated on a chip by integrated optical design method. The device works on change in surface plasmon (SP) amplitude to obtain permittivity values of samples adjacent to a specially designed metal-dielectric interface in a waveguide. The geometry of the interface has a distinct effect on sensitivity of measurement. The performance of the device is analyzed, and predicted through analytical and numerical calculations.
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