FDTD ABC for waveguides with a new discrete Green's function andits effective implementation

The authors propose a new discrete Green's function and an effective implementation for the absorbing boundary condition for the FDTD simulation of waveguide problems. The Green's function is given analytically in a simple, closed-form formula. A simple exponential approximation method is used for an efficient ABC implementation     

Surface deformation of amorphous silicon thin film on elastomeric substrate

Stiff thin layers on compliant substrates can generate various surface structures using equi-biaxial stress caused by large thermal expansion rate differences. We investigated the detailed understanding on the evolution of self-assembled wrinkle patterns of ultra-thin amorphous silicon (a-Si) layers on polydimethylsiloxane substrate. It turns out that the generation of various wrinkle patterns depends on the position of their orientation, film thicknesses, mechanical properties of the a-Si films, and the amount of pre-strain. The various self-assembled patterns include one-dimensional wavy patterns, randomly ordered two-dimensional structured patterns, and herringbone structures. The self-assembled wrinkles can be characterized by the wavelength and amplitude of the distinct structures: the amplitudes of the various patterns increase as the amount of pre-strain increases, while the wavelengths remain constant within our experimental ranges. The experimental results of the wavelengths and amplitudes for the wavy structured patterns of 270-nm-thick a-Si layer are in good agreement with the theoretical solutions of the single crystalline silicon (c-Si) model, which implies that the theoretical modeling of the deformation of c-Si film can be expandable to the case of a-Si film deformations.     

High-Q active resonators using amplifiers and their applications to low phase-noise free-running and voltage-controlled oscillators

This paper presents a new technique to design high-Q active resonators. The active resonators are then used in the design of low phase-noise oscillators. The proposed new technique uses an amplifier to generate a negative resistance, which compensates for the resonator losses and increases the Q factor. The active resonator using this technique shows a high loaded Q factor of 548.62 from measurement at the fixed 10-GHz resonant frequency. Considerations to design a voltage tunable active resonator is given and measurements show that the loaded Q factors exceed 500 with a 120-MHz tuning range. A low phase-noise free-running and voltage-controlled oscillator (VCO) were designed as an application of the proposed active resonators. The phase noise of the free-running oscillator using the active resonator is -114.36 dBc/Hz at 100-kHz offset, which is 14 dB lower than the phase noise of the passive resonator oscillator. In the case of a VCO using the active resonator, the phase-noise performance is below -110 dBc/Hz over the whole tuning range, which is lower 13 dB compared to the passive resonator VCO. The total dc power consumptions are approximately 500 mW.     

A 4.1 unequal Wilkinson power divider

This letter presents the design and measured performances of a microstrip 4:1 unequal Wilkinson power divider. The divider is designed using the conventional Wilkinson topology with the defected ground structure (DGS). The DGS on the ground plane provides an additional effective inductive component to the microstrip line. This enables the microstrip line to be realized with very high impedance of over 150 Ω. By employing the DGS to the unequal Wilkinson topology, 4:1 power dividing ratio can be obtained easily without any problem in realization, while it has been impractical to fabricate a 4:1 divider using the conventional microstrip line because of very thin conductor width and extremely low aspect ratio (W/H). As an example, a 4:1 divider has been designed and measured at 1.5 GHz in order to show the validity of the proposed DGS and unequal divider. The measured performances of the 4:1 unequal power divider well agree with the exactly same dividing ratio as that expected     

n-Type silicon quantum dots and p-type crystalline silicon heteroface solar cells

Heteroface devices have been realized by depositing phosphorus-doped silicon (Si) quantum dots (QDs) (n-type) on a p-type crystalline silicon substrate. To compare the quantum confinement effect, different sizes (3, 4, 5, and 8±1 nm) of Si QD were fabricated, whose optical energy bandgaps are in the ranges of 1.3–1.65 eV. The electrical and photovoltaic properties of heterojunction devices were characterized by illuminated and dark I–V measurements, C–V measurements, and spectral response measurements. The diodes showed a good rectification ratio of 5×10⁶ for 4 nm Si QDs at the bias voltage of ±1.0 V at 298 K. The ideality factor and junction built-in potential deduced from current–voltage (I–V) and capacitance–voltage (C–V) plots are 1.86 and 0.847 V for 3 nm QD device, respectively. From the illuminated IV characteristics, the open circuit voltages were 556, 540, 512, and 470 mV for mean QD diameters 3, 4, 5, and 8±1 nm, respectively. Temperature-dependant dark I–V measurements suggest that the carrier transport in the devices is controlled by recombination in the space-charge region. This study indicates the silicon QDs can be good candidates for all-silicon tandem solar cells.     

Measurements of the heat release rate integral in turbulent premixed stagnation flames with particle image velocimetry

A new definition of turbulent consumption speed is proposed in this work that is based on the heat release rate integral, rather than the mass burning rate integral. Its detailed derivation and the assumptions involved are discussed in a general context that applies to all properly defined reaction progress variables. The major advantage of the proposed definition is that it does not require the thin-flame assumption, in contrast to previous definitions. Experimental determination of the local turbulent displacement speed, SD, and the local turbulent consumption speed, SC, is also demonstrated with the particle image velocimetry technique in three turbulent premixed stagnation flames. The turbulence intensity of these flames is of the same order of the laminar burning velocity. Based on the current data, a model equation for the local mean heat release rate is proposed. The relationship between SD and SC is discussed along with a possible modeling approach for the turbulent displacement speed.