Radiation from cylindrical leaky waves

Formulas are derived for the far-infrared radiation pattern of cylindrical leaky waves propagating on a planar surface. The formulas can be used to predict the radiation pattern of a general class of leaky-wave antennas, consisting of a finite-size source which excites a radially propagating leaky wave on some planar surface. Leaky-wave antennas consisting of antenna elements embedded in dielectric layers (microstrip elements) fall into this category. Using the equivalence principle, formulas are derived for both transverse electric (TE) and transverse magnetic (TM) leaky waves with arbitrary propagation constants. The formulas allow for radiation from cylindrical apertures of arbitrary size, so that the effect of truncating the supporting planar surface with an absorbing material can be determined. Particular attention is devoted to the case of a leaky wave for which the real and imaginary parts of the complex propagation constant are equal, since this type of wave has been shown to be responsible for broadside radiation in certain leaky-wave antennas comprised of dielectric layers     

Laboratory evaluation of a field-portable dielectric/soil-moistureprobe

An evaluation of an L-band dielectric soil-moisture probe conducted to examine its capabilities, calibration, and performance under laboratory conditions is discussed. Results indicated that the probe can estimate the real part of the dielectric constant over a wide range of values. The imaginary part of the dielectric constant was overestimated. Since the soil moisture estimate is made using only the real part of the dielectric constant, the probe should produce reliable estimates of soil moisture. Studies utilizing a variety of soils, ranging from a loamy sand to a clay loam, produced results which were not as variable as those predicted by the dielectric models     

An algorithm for calculating the coupling between MMICs with blockdielectric coverings

In this paper, a computer-aided design (CAD) algorithm is presented for determining the coupling between sealant covered monolithic microwave integrated circuits (MMICs) in a multichip module. It is assumed that the MMICs are sufficiently separated that near-field coupling can be neglected and that TM₀ parallel-plate fields dominate. It is also assumed that the MMICs are each covered by a sealant of size commensurate with the MMIC. The technique presented is computationally simple, appropriate for use with layout-based circuit CAD software, and uses no numerical electromagnetics. It has been tested by comparison to full-wave electromagnetic simulation. In simple test cases, this technique showed over two orders of magnitude increase in speed. For larger problems, the increase in speed will be more pronounced     

OC-48 capable InGaAsN vertical cavity lasers

A selectively oxidised InGaAsN/GaAs three quantum well vertical cavity laser (VCSEL) demonstrated continuous wave (CW) lasing with a single-mode output power of 0.749 mW at 1266 nm. This is the first reported InGaAsN VCSEL capable of meeting the power and wavelength requirements for both OC-48 SR and OC-48 IR-1 compliant links. The VCSEL uses two low absorption n-type GaAs/AlGaAs distributed Brag reflectors and a tunnel junction to achieve current injection into the active region. A multimode version of the VCSEL had a output power of 1.43 mW at 1.26 μm. CW lasing continued up to temperatures as high as 107°C. The VCSEL material was grown by solid source molecular beam epitaxy with an RF nitrogen plasma source     

Examination of gradual-junction p-MOS structures for hot carriercontrol using a new lifetime extraction method

The effect of junction engineering on the hot carrier lifetimes of p-MOS transistors is examined. A normalizing method for predicting lifetimes is developed and used to show that a critical parameter controlling the lifetimes of submicrometer p-MOS devices is the size of the hot-carrier-damaged region. This is verified on conventional and gradual-junction transistors, where different implant species and energies were used to alter the source and drain junction profiles. Conventional junction devices with gate currents up to 100 times larger than those of gradual junction devices were found to have the same lifetimes as gradual junctions devices for the same effective transistor length. It is concluded that, contrary to n-MOS transistors, controlling the size of the damage region is as important as, if not more important than, reducing the hot electron gate currents by junction engineering in p-MOS devices     

Resistance Compression Networks for Radio-Frequency Power Conversion

A limitation of many high-frequency resonant inverter topologies is their high sensitivity to loading conditions. This paper introduces a new class of matching networks that greatly reduces the load sensitivity of resonant inverters and radio frequency (RF) power amplifiers. These networks, which we term resistance compression networks, serve to substantially decrease the variation in effective resistance seen by a tuned RF inverter as loading conditions change. We explore the operation, performance characteristics, and design of these networks, and present experimental results demonstrating their performance. Their combination with rectifiers to form RF-to-dc converters having narrow-range resistive input characteristics is also treated. The application of resistance compression in resonant power conversion is demonstrated in a dc-dc power converter operating at 100MHz     

Applications of static and dynamic iterated rippled noise to evaluate pitch encoding in the human auditory brainstem

This paper presents a new application of the dynamic iterated rippled noise (IRN) algorithm by generating dynamic pitch contours representative of those that occur in natural speech in the context of EEG and the frequency following response (FFR). Besides IRN steady state and linear rising stimuli, curvilinear rising stimuli were modeled after pitch contours of natural productions of Mandarin Tone 2. Electrophysiological data on pitch representation at the level of the brainstem, as reflected in FFR, were evaluated for all stimuli, static or dynamic. Autocorrelation peaks were observed corresponding to the fundamental period (tau) as well as spectral bands at the fundamental and its harmonics for both a low and a high iteration step. At the higher iteration step, both spectral and temporal FFR representations were more robust, indicating that both acoustic properties may be utilized for pitch extraction at the level of the brainstem. By applying curvilinear IRN stimuli to elicit FFRs, we can evaluate the effects of temporal degradation on 1) the neural representation of linguistically-relevant pitch features in a target population (e.g., cochlear implant) and 2) the efficacy of signal processing schemes in conventional hearing aids and cochlear implants to recover these features.     

Small signal equivalent circuit for Geiger-mode avalanchephotodiodes

The first small signal equivalent circuit for a Geiger-mode avalanche photodiode (GMAP) is presented. The equivalent circuit is derived from a 20 μm-diameter GMAP with 3 μm virtual guard ring overlap; the photodetector has peak responsivity at 600 nm and a calculated electrical bandwidth of 5.97 GHz     

8.8 W diode-cladding-pumped Tm3+,Ho3+-dopedfluoride fibre laser

A maximum output power of 8.8 W was generated from a diode pumped Tm³⁺,Ho³⁺-doped ZBLAN glass fibre laser. The laser operated with a maximum slope efficiency of 36% with respect to the incident pump power. The wavelength was measured to be 2056 nm and some instability was observed in the output