Three-phase GaAs Schottky-barrier CCD operated up to 100-MHz clock frequency

GaAs CCD's with 5-µm electrodes were fabricated using a process fully compatible to MESFET integrated circuits. The devices were operated at clock frequencies from 100 kHz to 100 MHz. The transfer inefficiency was found to be ≈ 1 × 10^-2in the frequency range from 100 kHz to 30 MHz. This is due to an incomplete charge transfer caused by interelectrode gaps larger than the layer thickness.     

On the Attenuation of Monofilar and Bifilar Modes in Mine Tunnels (Short Papers)

The modal equations for both the monofilar and bifilar modes of a two open wire transmission line located in a waveguide model of a rectangular mine tunnel are derived by extending an earlier general analysis. Attenuation curves of both modes in the frequency range 200 kHz-200 MHz are presented for two distinct configurations of the transmission line that may be used in practice. It is demonstrated that the proximity of the Iossy tunnel wall tends to increase greatly the attenuation rate for the monofilar modes but has relatively little effect on the bifilar modes.     

Bladder Volume Sensing by Resistance Measurement

The resistance of the urinary bladder, as measured between two electrodes attached to the external bladder wall at frequencies above 100 kHz, is proportional to the bladder volume for properly placed electrodes. The feasibility of using an oscillator, the frequency of which is controlled by the bladder interelectrode resistance, to provide an electrical signal proportional to bladder volume for use in connection with an electronic bladder stimulator is presented. The implications of this result are discussed.     

Transmission System for ISDB-T/sub SB/ (Digital Terrestrial Sound Broadcasting)

In the Integrated Services Digital Broadcasting-Terrestrial Sound Broadcasting (ISDB-T/sub SB/)transmission system, a narrow-band orthogonal frequency division multiplexing with one or three segment(s) is adopted. It is robust against multipath interferences in urban radio wave transmission. In addition, it is capable of mobile reception because of time interleaving. A transmission bandwidth of 432 kHz for one segment is narrow enough in order to allocate channels flexibly, and the "connected transmission" scheme, which allows multiple segment transmission with no guard band, is a highly efficient usage of the frequency resource. The ISDB-T/sub SB/ transmission system is consistent with ISDB-T, hence it enables a common receiver for partial reception of ISDB-T, digital television broadcasting. In this paper, the ISDB-T/sub SB/ transmission system,especially the differences from the ISDB-T transmission system, is introduced,and the current status of the ISBD-TSB digital terrestrial sound broadcasting service is shown.     

Results from the Virginia Tech propagation experiment using theOlympus satellite 12, 20 and 30 GHz beacons

A comprehensive set of propagation experiments was performed using the Olympus satellite 12, 20, and 30 GHz beacons. This set of experiments is unique in North America because of simultaneous reception of signals spanning the Ku- and Ka-bands from the same orbital slot, which permits direct inference of the frequency behavior of signal variations. The elevation angle from the receiving site in Blacksburg, VA, to the satellite was 14 degrees. Beacon, radiometric, and weather data for one year were analyzed. The statistical results for rain rate, beacon attenuation, attenuation ratios, radiometrically derived attenuation, fade duration and fade slope are presented. They are important to the design of Ku- and Ka-band satellite communication systems. The beacon attenuation results include cumulative statistics for attenuation with respect to free space and with respect to clear air. Attenuation ratio data are presented using attenuation with respect to clear air to focus on rain effects. Instantaneous attenuation ratios computed from instantaneous beacon levels were found to be nearly identical to statistical attenuation ratios obtained from cumulative attenuation statistics at each frequency     

Attenuation of the 5-mm wavelength band in a variable atmosphere

Effects of atmospheric changes on attenuation in the atmosphere are examined for the 5-mm wavelength region of the electromagnetic spectrum (48 to 72 GHz). Attenuation versus frequency and altitude for vertical transmission through the atmosphere, caused by oxygen absorption, are tabulated for geographical and seasonal model atmospheres. The attenuation effects of atmospheric water formations are discussed and compared to oxygen attenuation.     

Characterization of signals and noise rejection with bipolarlongitudinal intrafascicular electrodes

Longitudinal intrafascicular electrodes (LIFEs) are fine electrodes threaded into the extracellular space between axons in peripheral nerves or spinal roots. The authors are developing these electrodes for application in functional electrical stimulation and in basic physiology. An area of concern in chronic recording application of LIFEs is the possibility of electromyogram and other external noise sources masking the recorded neural signals. The authors characterized neural signals recorded by LIFEs and confirmed by three independent methods that increasing interelectrode spacing for bipolar LIFEs increases signal amplitude. The spectrum of neural signal from bipolar and monopolar LIFE lies between 300 Hz and 10 kHz. The amplitude of the spectrum increases with increasing interelectrode spacing, although the distribution is not affected. Single unit analysis of LIFE recordings show that they record selectively from units closest to the electrode active site. Units with conduction velocities ranging from 50-120 m/s were identified. Extraneural noise, as stimulus artifact or electromyogram, is much reduced with bipolar LIFE recording, as compared to monopolar recordings. Relative improvement in neural signal to extraneural noise increases with interelectrode spacing up to about 2 mm. Since there is no further improvement beyond 2 mm, the authors conclude that the preferred interelectrode spacing for bipolar LIFEs is 2 mm     

Medium wave DRM field test results in urban and rural environments

This paper presents the results of the first Spanish field trial carried out to analyze a DRM (Digital Radio Mondiale) system in the medium-wave band. A 4-kW average power omni directional ground-wave experimental DRM transmission at a frequency of 1359 kHz was surveyed by means of a measurement vehicle for fixed and mobile reception. Several radial routes starting from the transmitter site provided rural and suburban behavior features of the system. Urban reception trials were performed in several dense and open streets of Madrid, within the expected coverage area. Field strength threshold values were determined for the tested transmission configurations and compared with the AM ground-wave ITU model predictions. Reliability versus distance from the transmitter is stated in this paper for different transmission configurations and the causes of dropouts for different reception conditions are explained. This analysis took into account subjective quality features of each configuration, providing practical planning parameter values.     

Quasi-Optical Surface Waveguide and Other Components for the 100- to 300-Gc Region

Components and techniques for the generation, transmission, and detection of energy in the 100- to 300-Gc frequency region were investigated theoretically and experimentally. The design and construction of fundamental components, such as harmonic generators and detectors, were necessary since many items are not available commercially. A detailed theoretical analysis was performed for the propagation characteristics of single-conductor transmission lines, and attenuation calculations were made for several dielectric image lines. Experimental measurements were made at 105 and 140 Gc on these two types of surface waveguides. Attenuation of these lines is compared with that of dominant-mode rectangular waveguide. An analysis of phase-correcting Fresnel zone plates was carried out, and several zone plates were designed, constructed and successfully tested at frequencies of 140, 210, and 280 Gc. Zone plates were used at several frequencies to make relatively long path transmission measurements and were also used in a specially designed Michelson interferometer. The frequency stability of the source klystron and the dielectric properties of a number of plastic materials were determined by measurements made with the interferometer. A method of frequency filtering by focal isolation was demonstrated with this equipment.     

Transmission Characteristics of Hybrid Modes in Corrugated Waveguides Above the Bragg Frequency

We studied the transmission characteristics of hybrid modes in a corrugated circular waveguide above the Bragg frequency to develop a broad-band transmission line for millimeter waves. Millimeter waves at 294 GHz were transmitted into a straight waveguide. From observed power profiles in waveguide cross-sections, a high attenuation rate of 0.13 dB/m was obtained. To match a theoretical attenuation constant with the experimental one, we introduced an ad hoc coefficient of conventional surface reactance in the waveguide wall. This was necessary because the wall began to look like the surface with a decreasing anisotropic reactance owing to the frequency above the Bragg frequency. Using nonlinear optimization for mode content analysis, the observed power profiles in the waveguide cross-section were matched with theoretical profiles. There was good agreement between the calculated and observed centers of power profiles and attenuation rate along the waveguide. The theoretical analysis showed that the magnetic field at the waveguide wall increases and the substantial attenuation takes place. Above the Bragg frequency coupling to backwards propagating modes is a point of consideration. A combination of the backwards propagating EH_1,26 and the forward propagating HE₁₁ modes satisfied the Bragg condition at 294.7 GHz which was the nearest frequency of operating frequency. A strong attenuation of the incoming HE₁₁ mode by Bragg resonance was not expected due to large difference of 0.7 GHz. It becomes clear that the observed high transmission loss outside of the Bragg resonance can be explained by a decrease in anisotropic surface reactance at the wall.     

液体中激光声传输特性

为了了解激光声在液体中的传输特性，理论分析了激光声的传输特性，并采用高速照相机、光纤MEMS水听器对激光声进行了实验研究，利用小波变换对采集的不同位置上的激光声信号各级频谱特性进行了分析。结果表明:激光声属于一种脉动球源，激光声信号传输过程中幅度与距离成反比关系；激光声的分析频带内存在明显的优势频率，峰值频率稳定在3.1 kHz，带宽稳定在3 kHz；低频信号的能量占总能量的70%以上，高频部分主要是噪声；从功率谱波形分析看，低频信号的强度幅值随时间、距离变化衰减较慢，而高频噪声随时间、距离变换衰减较快。     

Employment of Voice Band Modems in Subscriber Loop Qualification

This letter presents the method useful in subscriber line qualification for asymmetric digital subscriber line service. It is based on the results of the line frequency response measurement in the voice band by V.34 modems. The response is related to the line attenuation at 300 kHz. The measurement results are also presented.     

Polarization Switching in Vertical-Cavity Surface-Emitting Lasers by Asymmetrical Current Injection

Polarization switching between two orthogonal linear polarizations was experimentally demonstrated in newly designed 980-nm vertical-cavity surface-emitting lasers ( VCSELs ). A square-shaped mesa structure was prepared in a p-type distributed Bragg reflector mirror. Four p-side electrodes were placed in contact with the four sides of the square mesa. When the same current was injected into the four electrodes, the VCSEL oscillated with 0$^{circ}$ or 90$^{circ}$ linear polarizations. When the current was asymmetrically injected (the same current for two electrodes on the opposite sides of the square, but different for neighboring electrodes), the direction of the linear polarization became perpendicular to the direction of the line connecting the two electrodes injected with the larger current. It was confirmed that the VCSELs oscillated with a single frequency and the lowest order transverse mode in all cases.      

Analysis of current density and specific absorption rate in biological tissue surrounding transcutaneous transformer for an artificial heart

This paper reports on the current density and specific absorption rate (SAR) analysis of biological tissue surrounding an air-core transcutaneous transformer for an artificial heart. The electromagnetic field in the biological tissue is analyzed by the transmission line modeling method, and the current density and SAR as a function of frequency, output voltage, output power, and coil dimension are calculated. The biological tissue of the model has three layers including the skin, fat, and muscle. The results of simulation analysis show SARs to be very small at any given transmission conditions, about 2-14 mW/kg, compared to the basic restrictions of the International Commission on nonionizing radiation protection (ICNIRP; 2 W/kg), while the current density divided by the ICNIRP's basic restrictions gets smaller as the frequency rises and the output voltage falls. It is possible to transfer energy below the ICNIRP's basic restrictions when the frequency is over 250 kHz and the output voltage is under 24 V. Also, the parts of the biological tissue that maximized the current density differ by frequencies; in the low frequency is muscle and in the high frequency is skin. The boundary is in the vicinity of the frequency 600-1000 kHz.     

Spectral Analysis of Electrical Impedance Measurements on the Lower Limbs

Electrical impedance signals from the lower limbs of normal individuals and patients with atherosclerosis have been studied in the frequency domain. A current of 1 mA at 40 kHz was introduced with strip electrodes around the ankles, and voltage differences were measured with electrodes above the knee and above the current electrode of the same limb. The impedance signal AZ and the ECG were recorded on magnetic tape and transferred to a digital computer. The first derivative of the impedance signal, dZ/dt, was calculated by numerical methods from the coherent average of at least 20 AZ signals, and the spectra were obtained by an FFT algorithm. For young normal individuals, only 1 percent of the dZ/dt signal energy lies above 12 Hz. Patients with arterial obstructions present a greater attenuation in the lower harmonics, stretching the 99 percent energy bandwidth to 32 Hz. Although the amplitude of some spectral components can be used for noninvasive evaluation of arterial disease with a precision of up to 90 percent, it was found that the phase spectra are very little influenced by atherosclerosis.     

Dipole distance for minimum threshold current to stimulate unmyelinated axons with microelectrodes

Excitation thresholds for long nerve or muscle fibers with two point sources parallel to the fiber axis depend on the dipole length. The aim of this study was to find the optimal interelectrode distance for the minimum stimulation current. For a specific electrode-fiber distance (z_el) dipole length is constrained by the energy efficacy of the electrodes requiring small interelectrode distances, and by rather low stimulation currents requiring large dipole distances. Far-field values for optimal dipole distance (approximately 1.4 *z_el) can be explained by the superposition of the positive parts of the activating functions for the monopolar elements of the dipole. A current redistribution effect in a target fiber close to the electrodes shifts the dipole length for threshold stimulation from the theoretical optimal activating function approach value towards greater dipole distances. Spike initiations in straight fibers and retinal ganglion cell axons are investigated.     

Closed-loop control of ankle position using muscle afferentfeedback with functional neuromuscular stimulation

Describes a closed-loop functional neuromuscular stimulation system that uses afferent neural activity from muscle spindle fibers as feedback for controlling position of the ankle joint. Ankle extension against a load was effected by neural stimulation through a dual channel intrafascicular electrode of a fascicle of the tibial nerve that innervated the gastrocnemius muscle. Ankle joint angle was estimated from recordings of tibialis anterior and lateral gastrocnemius spindle fiber activity made with dual channel intrafascicular electrodes. Experiments were conducted in neurally intact anesthetized cats and in unanesthetized decerebrate cats to demonstrate the feasibility of this system. The system was able to reach and maintain a fixed target ankle position in the presence of a varying external moment ranging in magnitude between 7.3 and 22 N-cm opposing the action of the ankle extensor, as well as track a sinusoidal target ankle position up to a frequency of 1 Hz in the presence of a constant magnitude 22- or 37-N-cm external moment     

Guided Beam Waves Between Parallel Concave Reflectors

A new guided beam wave transmission system is proposed here, which is composed of two parallel concave reflectors. The principle is a combination of waveguide and beam wave transmission. The shape of the reflector cross section and the corresponding mode functions were obtained. Attenuation due to wall current and limited aperture of the reflectors were calculated. Experiments were made to confirm the modes and the attenuation. One of the remarkable features of this transmission system is its field distribution, which is concentrated into a belt-shaped space between reflectors. Considering this feature, this system seems to be effectively applied to the railways as a medium for obstacle detection and communication.     

16-Channel Integrated Potentiostat for Distributed Neurochemical Sensing

We present the architecture and VLSI circuit implementation of a BiCMOS potentiostat bank for monitoring neurotransmitter concentration on a screen-printed carbon electrode array. The potentiostat performs simultaneous acquisition of bidirectional reduction-oxidation currents proportional to neurotransmitter concentration on 16 independent channels at controlled redox potentials. Programmable current gain control yields over 100-dB cross-scale dynamic range with 46-pA input-referred rms noise over 12-kHz bandwidth. The cutoff frequency of a second-order log-domain anti-aliasing filter ranges from 50 Hz to 400 kHz. Track-and-hold current integration is triggered at the sampling rate between dc and 200 kHz. A 2.25-mmtimes2.25-mm prototype was fabricated in a 1.2-mum VLSI technology and dissipates 12.5 mW. Chronoamperometry dopamine concentration measurements results are given. Other types of neurotransmitters can be selected by adjusting the redox potential on the electrodes and the surface properties of the sensor coating