Wave Transmitter Research Articles

Plasma Model in Aluminum Nano-Films

The mode of electromagnetic response of aluminum nano-films has been suggested by meaning of electromagnetic wave reflectance, transmittance and carrier density of the films. The carrier density of the films and dependence of their plasma frequency on the film thickness have been obtained. On the other hand, the dependence of absorptance on the frequency of electromagnetic wave field has been set up by using the measured reflectance and transmittance, which provides relationship between plasma frequency and film thickness. Both plasma frequency and film thickness proved plasma resonance.

The Whisper Relaxation Sounder Onboard Cluster: A Powerful Tool for Space Plasma Diagnosis 1, 2 around the Earth

The WHISPER relaxation sounder that is onboard the four CLUSTER spacecraft has as its main scientific objectives to monitor the natural waves in the 2 kHz–80 kHz frequency range and, mostly, to determine the total plasma density from the solar wind down to the Earth's plasmasphere. To fulfill these objectives, the WHISPER uses the two long double sphere antennae of the Electric Field and Wave experiment as transmitting and receiving sensors. In its active working mode, the WHISPER works according to principles that have been worked out for topside sounding. A radio wave transmitter sends an almost monochromatic and short wave train. A few milliseconds after, a receiver listens to the surrounding plasma response. Strong and long lasting echoes are actually received whenever the transmitting frequencies coincide with characteristic plasma frequencies. Provided that these echoes, also called resonances, may be identified, the WHISPER relaxation sounder becomes a reliable and powerful tool for plasma diagnosis. When the transmitter is off, the WHISPER behaves like a passive receiver, allowing natural waves to be monitored. This paper aims mainly at the resonance identification process description and the WHISPER capabilities and performance highlighting.

Structure and dynamics of sporadic layers of ionization in the ionospheric E region

Layers of ionization that appear in the ionospheric E region sporadically in time have been named sporadic‐E layers, or Es. These sporadic ionization layers play a crucial role in small‐scale irregularity generation (as they guarantee a plasma density gradient necessary for gradient‐drift processes to develop) and in providing reliability of radio communication and navigation. Despite the fact that Es layers have been studied since the late sixties, a method to visualize the Es horizontal structure was suggested for the first time only recently [Kagan et al., 2000]. In the present paper we propose a new type of experiment for the reconstruction of the patchy‐type Es structure and dynamics using a combination of the above‐mentioned method with the method of artificial periodic irregularities (API) [Belikovich et al., 1999]. This combined method allows us for the first time to carry out Es tomography, to trace the three‐dimensional (3‐D) dynamics of sporadic ionization clouds and their associated 3‐D neutral motions, and to study the effects of high‐frequency radio waves on the sporadic‐E layers. The procedure includes recording of the Es horizontal structure and dynamics with an all‐sky camera via radio‐wave‐induced optical emissions in combination with measurements of the Es vertical structure and dynamics by the API method. Both methods complement each other and can be used simultaneously. The experiment is to be equipped with a powerful HF radio wave transmitter, all‐sky cameras, an ionosonde, and an HF digital receiver.

A model and experimental study of fiber orientation effects on shear wave propagation through composite laminates.

The strong elastic anisotropy of the discrete unidirectional plies in a composite laminate interacts sensitively with the polarization direction of a shear ultrasonic wave propagating in the thickness direction. The transmitted shear wave can therefore be used to detect errors in the ply orientation and stacking sequence of a laminate. The sensitivity is particularly high when the polarization directions of the shear wave transmitter and receiver are orthogonal to each other. To understand the interaction between normal-incident shear waves and ply orientations in a laminate, a complete analytical model was developed using local and global transfer matrices. The model predicted the transmitted signal amplitude as a function of polarization angle of the transmitter and time (or frequency) for a given laminate and input signal. To alleviate the experimental problems associated with shear wave coupling, electromagnetic acoustic transducers (EMATs) and metal delay lines were used in the angular scan of the transmitted signal. The EMAT system had the added advantage of being applicable to uncured composite laminates. Experiments were performed on both cured and uncured laminates with common layups for model verification. The sensitivity of the measured shear wave signals to fiber misorientation and stacking sequence errors was also demonstrated.

Transmitter/receiver stethoscope and holder therefor

An electronic stethoscope and holder comprises a chestpiece (100), an earpiece (400), and a casing (500) for holding the chestpiece (100) and earpiece (400). The chestpiece (100) includes a sound sensing (130) device for sensing auscultatory sounds and converting them into an electrical signal. The chestpiece (100) includes a radio wave transmitter (140) for transmitting the electrical signal. The earpiece (400) includes a receiver (440) for receiving a transmitted signal and converting it into an audible form. The earpiece (400) may be held in a user's ear and includes a speaker (450) for providing an audible signal to a user. The chestpiece (100) is configured to be held between two fingers of a user's hand. A casing (500) includes a channel (560) recessed in a front wall (510) and includes a pair of laterally spaced apart slots for insertion of the chestpiece (100) therein. The casing (500) includes a chamber (570) in communication with an aperture (590) for releasably holding one or more earpieces (400).

Ultrasonic technique spectram tomography

This is a study about a technique for distinguishing a speckle pattern by a fine structure of a size of about wavelength of the observation waves from a large structure image. Speckle pattern is the one of the major factors that disturbs the observation of fine structure. It is generated by interference caused from spacious frequency factor and not by existence of the object. This echo image forming apparatus comprises: a wave transmitter for transmitting an observation wave pulse of a wide band; a wave receiver for receiving an echo of the observation wave pulse transmitted to generate a reception signal; a filter for extracting signal components of a plurality of different frequencies predetermined from the reception signal obtained by the wave receiver; and a display device for imaging separately, respectively, the signal components of each frequency extracted by the filter and displaying images corresponding to resultant frequencies mutually relating to each other. The signal components of the plurality of frequencies predetermined are extracted from the reception signal of the wide band by use of the filter. The speckle patterns by the fine structure of about wavelength in correspondence with the corresponding frequency emerge respectively in each extracted frequency component.

Nanoscale inhomogeneities and optical properties of doped cuprates

We propose a new approach to theoretical description of doped HTSC cuprate, assuming phase separation and treating it as inhomogeneous composite material, containing the dielectric and metallic nanoparticles. The formalism of effective medium theory is applied for calculation of dielectric permittivity and optical spectra of Sr-doped La214 system for a broad range of doping concentrations. The model is able to reproduce all essential features of optical conductivity, electron energy-loss function at zero wave vector and transmittance both for thin films and bulk single-crystalline samples. Substantial difference in spectral and doping dependence of optical absorption for the thin-film and bulk samples is easily explained by assuming different shape of metallic and dielectric regions in both materials. New peaks of optical conductivity, that emerge in the infrared range near 0.5 and 1.5 eV upon doping, are attributed to surface plasmon resonances.

An Approach to Biochemical Imaging of Heterogeneity in the Bio-tissue Simultaneously Using the Data of Reflectance and Transmittance of Diffuse-Photon Density Waves**The project supported by National Natural Science Foundation of China under Grant No. 19774127

An algorithm for the biochemical imaging of heterogeneity in the bio-tissue with finite parallel-plane geometry simultaneously using the data of reflectance and transmittance of diffuse-photon density waves is presented. In this algorithm, the priori knowledge of heterogeneity is not needed. This algorithm is suitable for the imaging of heterogeneity in the large volume tissue and in small organs. To reduce the errors produced by the algorithm, it is suggested that the experiment should be performed in two steps, at first step the light source should be placed at one boundary to measure the data of reflectance and transmittance, and these data are used to construct the heterogeneous function in the half space close to the light source; at the second step the light source should be placed at another boundary to measure the data of reflectance and transmittance, these data are used to construct the heterogeneous function in another half space closed to the light source; after taking above two steps the heterogeneous function in the whole space is constructed.

Integrated 460 GHz photonic transmitter module

A photonic sub-millimetre (sub-mm) wave transmitter module has been developed and fabricated. The module consists of a 1.55 /spl mu/m waveguide InP photodetector monolithically integrated with a planar full wave slot antenna and passive lowpass filter for DC bias supply. For the first time, optical heterodyne 460 GHz sub-mm signal generation is demonstrated It is further shown that the module can effectively replace the classical solid-state oscillator of an astronomical superconductor-insulator-superconductor heterodyne receiver The module generates sufficient sub-mm wave power to operate the receiver under optimum conditions.

Phononic crystals with planar defects

We study the effect of planar defects in phononic crystals of spherical scatterers. It is shown that a plane of impurity spheres introduces modes of vibration of the elastic field localized on this plane at frequencies within a frequency gap of a pure phononic crystal; these show up as sharp resonances in the transmittance of elastic waves incident on a slab of the crystal. A periodic arrangement of impurity planes along a given direction creates narrow impurity bands with a width which depends on the position of these bands within the frequency gap of the pure crystal and on the separation between the impurity planes. We show how a slight deviation from periodicity (one impurity plane is different from the rest) reduces dramatically the transmittance of elastic waves incident on a slab of the crystal.

Sub-THz spectroscopic system using a multimode laser diode and photoconductive antenna

A system for measuring transmittance of electromagnetic waves in the sub-THz region is proposed. The electromagnetic radiation is generated by the excitation of a photoconductive antenna with a commercially available multimode laser diode. The spectral coverage of the radiation is increased by defocusing the light spot on the photoconductive antenna. Transmitted radiation is detected by a hot-electron bolometer through a Martin–Puplett-type interferometer. Transmittance is measured for n-type Si wafers with various doping levels. The carrier densities calculated from the transmittance agree well with those obtained from the dc conductivity measurement.

Low-threshold nine-channel waveguide grating router-based continuous wave transmitter

This paper demonstrates a nine-channel waveguide grating router-based laser with low (18-22 mA) thresholds, which we believe to be a record for a monolithically integrated multiwavelength laser with a 1.1-cm long cavity and a single nondistributed amplifier. This result was achieved through a combination of techniques including reduced intracavity loss, improved router design and optimal active/passive transitions.

Percolation thresholds in chemical disordered excitable media

The behavior of chemical waves advancing through a disordered excitable medium is investigated in terms of percolation theory and autowave properties in the framework of the light-sensitive Belousov-Zhabotinsky reaction. By controlling the number of sites with a given illumination, different percolation thresholds for propagation are observed, which depend on the relative wave transmittances of the two-state medium considered.

Forecasting global lightning for atmospheric noise prediction

In this paper we discuss an investigation into the feasibility of using current and forecasted weather data to forecast lightning occurrence. These lightning occurrence forecasts are intended to be used to improve the accuracy of near‐term long wave communication systems coverage predictions. Various weather information sources were reviewed to determine which data and parameters could be used to predict lightning and which techniques were best suited for selected forecast periods. Review of atmospheric and lightning physics resulted in several methods for establishing relationships between weather data parameters and lightning flash rates for selected forecasting periods. We review these methods and show results of tests which were conducted to compare the forecasted lightning occurrence with measured data. These tests were limited to the continental United States where empirical data on lightning occurrence from the National Lightning Detection Network are available. The results of the techniques developed for several example days are shown, as is the impact that using the techniques might have on the coverage prediction for an example long wave transmitter.

Golden Jubilee Year of Independence: Roadmap of Broadcasting in India

Broadcasting in India during last fifty years, has seen a tremendous growth in terms of its reach and impact. Starting from six medium wave and twelve short wave transmitters in 1947, it has at present a massive network of 192 programme generating centres, 144 medium wave, 52 short wave and 101 FM transmitters for sound broadcasting. On the TV side, it has 41 programme generating centres, 92 high power and 831 low power transmitters. This paper traces the history of this growth and the future of broadcasting in the country.

Greenhouse Climate Control: an integrated approach

Controlling a greenhouse microclimate requires energy consumption for heating and cooling the greenhouse inside air. The radiative heat transfer process inside a greenhouse depends on the spectral radiative properties of different components especially on the greenhouse covering material. There is a lack of information about the precise spectral radiative properties of the available commercial plastic sheets used as greenhouse covers. In this research, the spectral radiative properties of several commercial greenhouse covers are measured in a wide wavelength range from 0.2 to 28 μm. The measured properties are then used in a developed model to simulate the indoor climate of a greenhouse. In the developed model, the covering material is treated as a semi-transparent medium, the soil surface is considered as partially reflective surface, and the inside air is assumed as an absorbing-emitting medium. Finally, under a specific hourly climate conditions, the impacts of using different commercial covers on heating and cooling load demands are investigated. The measured total solar transmittance was 70.3–92.1% and the long wave transmittance was 18.1–61.8% for selected samples. The results indicated that using the appropriate covering plastic reduced the annual cooling load by 9.8% and heating load by 6.3%.

Modulation of submillimeter wave radiation by laser-produced free carriers in semiconductors

When a semiconductor substrate is illuminated by an optical beam whose photon energy exceeds its band-gap energy, free carriers are produced in the substrate, which provides a means of control for the substrate reflectance and transmittance of submillimeter electromagnetic waves. This paper is concerned with submillimeter wave modulation by an optically-excited semiconductor. High-resistivity silicon and GaAs are used as the substrate. Continuous radiation with a wavelength of 214 μm is used as the submillimeter wave. A Q-switched Nd:YAG laser is used to excite the free carriers. The experimental results are presented. Effects of semiconductor substrate material, wavelength of the excitation beam, and incident surfaces of the submillimeter wave and the substrate excitation beam, on the modulation waveforms are analyzed. As an application of the proposed modulation technique, submillimeter wave short pulses with variable duration are successfully generated. © 1998 Scripta Technica. Electron Comm Jpn Pt 2, 80(6): 1–9, 1997

Light propagation in tissues with controlled optical properties

Theoretical and computer modeling approaches, such as Mie theory, radiative transfer theory, diffusion wave correlation spectroscopy, and Monte Carlo simulation were used to analyze tissue optics during a process of optical clearing due to refractive index matching. Continuous wave transmittance and forward scattering measurements as well as intensity correlation experiments were used to monitor tissue structural and optical properties. As a control, tissue samples of the human sclera were taken. Osmotically active solutions, such as Trazograph, glucose, and polyethylene glycol, were used as chemicals. A characteristic time response of human scleral optical clearing the range 3 to 10 min was determined. The diffusion coefficients describing the permeability of the scleral samples to Trazograph were experimentally estimated; the average value was DT'(0.960.5)31025 cm2/s. The results are general and can be used to describe many other fibrous tissues.

Light propagation in tissues with controlled optical properties

Theoretical and computer modeling approaches, such as Mie theory, radiative transfer theory, diffusion wave correlation spectroscopy, and Monte Carlo simulation were used to analyze tissue optics during a process of optical clearing due to refractive index matching. Continuous wave transmittance and forward scattering measurements as well as intensity correlation experiments were used to monitor tissue structural and optical properties. As a control, tissue samples of the human sclera were taken. Osmotically active solutions, such as Trazograph, glucose, and polyethylene glycol, were used as chemicals. A characteristic time response of human scleral optical clearing the range 3 to 10 min was determined. The diffusion coefficients describing the permeability of the scleral samples to Trazograph were experimentally estimated; the average value was DT'(0.960.5)31025 cm2/s. The results are general and can be used to describe many other fibrous tissues.

A new system for three-dimensional kinematic trajectory acquisition and analysis—I. The application of an ultrasonic technique to human gait analysis

This paper discusses some techniques of kinematics analysis, and describes a new system for movement recording and analysis. The new system, which is inexpensive and easy to use, consists mainly of some ultrasonic wave transmitters, receivers, a distributive multiprocessor system and software. The system can record kinematics parameters of anatomical landmarks (e.g. space coordinates, movement trajectories and angles of hips, knees and ankles). Such a system, combined with foot pressure equipment and a force plate, forms an advanced gait analysis system.