Showing papers on "Radio frequency published in 1989"

Constant current sources with programmable voltage source

Abstract: An implant for stimulating the vagus nerve receives commands over a radio frequency link. The communication protocol uses asynchronous communications devices with parity checking and echoing of communicated characters and passwords to improve communication error checking. The implant disables a voltage convertor used in providing the stimulation signal at periodic intervals to monitor for communications attempts. The implant provides radio frequency marker pulses before providing stimulation signals of certain frequencies. During the providing of stimulation signals the implant monitors the voltage overhead present between the voltage source and the load and adjusts the overhead to a desired level. The implant changes the voltage applied to certain internal components during stimulation periods to allow full power operation during those intervals and reduced power levels at other intervals. The implant is reset by the placing a magnet in a given location in conjunction with the application of a radio frequency transmission for a given period.

New ion trap for frequency standard applications

Abstract: We have designed a novel linear ion trap which permits storage of a large number of ions with reduced susceptibility to the second‐order Doppler effect caused by the rf confining fields. This new trap should store about 20 times the number of ions as a conventional rf trap with no corresponding increase in second‐order Doppler shift from the confining field. In addition the sensitivity of this shift to trapping parameters, i.e., rf voltage, rf frequency, and trap size, is greatly reduced.

Imaging radio frequency electron‐spin‐resonance spectrometer with high resolution and sensitivity for in vivo measurements

Abstract: We report the development of a novel radio frequency electron‐spin‐resonance spectrometer designed to provide measurements with high molar sensitivity and resolution in vivo. Radio frequency (250 MHz) is chosen to obtain good penetration in animal tissue and large aqueous samples with modest sacrifice of sensitivity. The spectrometer has a lumped component resonator and operates in continuous‐wave mode. The spectrometer is capable of two‐dimensional imaging, and with a modest addition should be capable of three‐dimensional imaging. We demonstrate 3‐mm spatial resolution for DPPH samples. For 10‐ml samples of aqueous nitroxide, we demonstrate sensitivity (normalized to spectral width of 1 G) to 3×10−8‐M concentrations and spectral resolution of 0.1 G. Spectra from nitroxide spin label injected into a live mouse are shown.

Nested-cone transformer antenna

Abstract: A plurality of conical transmission lines are concentrically nested to formn output antenna for pulsed-power, radio-frequency, and microwave sources. The diverging conical conductors enable a high power input density across a bulk dielectric to be reduced below a breakdown power density at the antenna interface with the transmitting medium. The plurality of cones maintain a spacing between conductors which minimizes the generation of high order modes between the conductors. Further, the power input feeds are isolated at the input while enabling the output electromagnetic waves to add at the transmission interface. Thus, very large power signals from a pulse rf, or microwave source can be radiated.

Radio Frequency Energy And Impedance Feedback

Abstract: The object of this study was to show the potential use of tissue electrical impedance as a feedback parameter for the control of therapeutic Radio Frequency (R.F.) energy. Radio Frequency energy is a form of electromagnetic energy with an usable frequency range between 200KHZ and 2MHZ. The low frequency limit is determined by the physiological stimulation of muscle, and the high frequency is limited by the physics of the delivery system.

Power scaling of large‐area transverse radio frequency discharge CO2 lasers

Abstract: We report experimental results on gain medium area scaling of laser output power for large‐area, transverse rf discharge excited carbon dioxide lasers. Power extraction to 20 kW/m2 has been achieved, indicating the significant potential of this technique.

Radio-frequency dielectric measurements at temperatures from 10 to 450 K

Abstract: A coaxial air line was constructed to connect a radio-frequency impedance analyzer and a temperature-stabilized sample holder. It is suitable for dielectric measurements in the frequency range 1 MHz-1 GHz and at temperatures between 10 and 450 K. The dielectric dispersion of Fe-doped BaTiO_3 and Na-doped KCN is presented. The results demonstrate the capability of this setup when investigating materials with high as well as with low dielectric constants.

Composition monitor and monitoring process using impedance measurements

Abstract: Radio frequency bridge techniques are used to parameterize the complex dielectric properties of solids, liquids, gasses and mixtures thereof. This parameterization is performed in an electrically isolated, physically open structure (Fig. 12) which allows continuous or batch monitoring of the materials and their mixtures. A method and apparatus are provided for measuring the composition of multicomponent process streams flowing in pipes or ducts. The method uses the pipe in which the mixture flows as a waveguide in which propagating radio frequency electromagnetic energy (Fig. 15) is induced through dielectric loaded apertures (137). The dielectric measurement is performed in an electrically isolated, flow through test section (135) which induces constructive or destructive interference patterns at characteristic frequencies. The characteristic frequency determines the dielectric constant of the mixture. The dielectric properties are used in turn to determined mixture composition. A density measurement is also provided for three component streams such as oil, water, and gas. Temperature and pressure measurements are made to correct for temperature and pressure induced variations in calibrated component impedance and density values.

Radio frequency tap unit which can be reconfigured with minimal disruption of service

Abstract: A modular cable television tap unit includes a base module which receives a cable television signal having an operational power signal component from a cable distribution network. The base unit includes circuitry for separating radio frequency (RF) components and the operational power signal component from the cable television signal. The separated operational power signal is passed through the base module to another cable in the network. The base module includes a set of connectors for receiving a removable directional coupler module and a single connector for receiving a removable addressable signal splitter module. The signal splitter module includes connectors for providing the RF components of the cable television signal to subscribers. The connection for the directional coupler module provides only the RF component of the cable television signal. The connection for the signal splitter module provides a compound signal which includes an RF signal provided by the directional coupler module and the operational power signal component of the cable television signal for operating the addressable tap circuitry. A relatively large number of different types of tap units having different tap loss values and different numbers of subscriber connections may be made from a relatively small number of different module types.

High capacity sectorized cellular communication system

Abstract: A cellular radiotelephone communication system cell site equipment is provided. The cell site equipment includes a radio frequency transmitter operating as one signal frequency source. In addition, the cell site equipment includes a first and a second signal combiner device tuned to a first and a second signal frequency, respectively. Further, the cell site equipment includes a radio frequency switching mechanism, operatively coupled to the radio frequency transmitter, the first signal combiner device, and the second signal combiner device, for coupling the radio frequency transmitter to either of the first and the second signal combiner devices. In one embodiment, each signal combiner device includes a resonant cavity for isolating a signal frequency source from other signal frequency sources and a coupling for coupling the isolated signal frequency source to a common transmitter output. In an alternative embodiment, each signal combiner device includes a resonant cavity for isolating a signal frequency source from other signal frequency sources and a coupling for coupling the isolated signal frequency source of the first and the second signal combiner device to a first and a second common transmitter output, respectively.

Resonant radio frequency wave coupler apparatus using higher modes

Abstract: An improved apparatus for generating a uniform electron cyclotron resonance (ECR) region in a plasma region (16) of a chamber (15) is described. The apparatus uses higher modes of electrical field cusps (16b) which are essentially perpendicular to the magnetic field cusps (16a) in a controlled manner to produce the ECR. The modes are optimal in the ECR region.

Dual-mode microwave/radio frequency plasma deposition of dielectric thin films

Abstract: Thin films have been deposited in a ‘‘dual frequency mode’’ plasma, in which differing amounts of radio frequency (rf, 13.56 MHz) power were applied to the substrate, while sustaining the plasma with constant microwave (2.45 GHz) power. We report results pertaining to deposition of silicon oxide and organosilicon thin films. The rf‐induced negative dc self‐bias voltage is shown to affect plasma‐chemical reactions, causing very significant changes in the deposition rate, film composition, and dielectric properties of the resulting materials. This provides a powerful new technique for producing ‘‘tailored’’ films, while preserving the important advantages of high deposition rates and low substrate temperatures.

Radio frequency suppression for fuel pump

Abstract: An end cap (10) for a fuel pump provides suppression of radio frequency noise generated by the motor of the pump. The unitary end cap (10) includes radio frequency suppression circuitry (20, 28) disposed therewithin and is configured so as to be a direct replacement for conventionally utilized end caps.

Method and apparatus for measuring phase accuracy and amplitude profile of a continuous-phase-modulated signal

Abstract: A method and apparatus for determining the phase and amplitude accuracy of continuous-phase-modulated signals is described. A modulated RF signal generated by a transmitter is down converted to a relatively low intermediate frequency which is filtered and sampled by a high sampling rate analog-to-digital convertor. A digital signal processor processes the digital signals to produce a measured amplitude function and a measured phase function corresponding to the modulated RF signal. From the measured amplitude and phase functions, an ideal phase function corresponding to the modulated RF signal is calculated and synthesized. The ideal phase function is compared to the measured phase function to determine the phase function from which the modulated RF signal phase error and frequency error are computed.

The energy distribution of ions bombarding electrode surfaces in rf plasma reactors

Abstract: A model is presented for the energy distribution of ions bombarding electrode surfaces in planar rf plasma reactors at low pressures, where collisions in the sheath may be ignored. Given the waveform for the voltage difference across the sheath adjacent to an electrode, the model predicts the ion bombardment energy distribution in the limits tr <1/f and tr ≫1/f, where tr is the transit time of the ions across the sheath and f is the frequency of the applied rf voltage. Utilizing sheath voltage waveforms from a previously published equivalent circuit model of a rf reactor [A. Metze, D. W. Ernie, and H. J. Oskam, J. Appl. Phys. 60, 3081 (1986)], the model shows that the ion bombardment energy distribution is bimodal and skewed toward lower ion bombardment energies. The model also demonstrates one of the mechanisms responsible for narrowing of the ion bombardment energy distribution with increasing rf frequency. These results are compared with experimental measurements.

Cyclotron with yokeless superconducting magnet

Abstract: A cyclotron having a cylindrical superconducting magnet which generates an axial magnetic field and has a central opening or chamber of substantially circular cross-section. The accelerating beam space is located in this chamber lying normal to the axis of the magnetic field. The azimuth variation of magnetic field as well as the isochronous radial variation of magnetic field required to control the orbiting of the ion beam in the beam space, are provided by ferro-magnetic pole pieces located in the axial chamber, which interact with the magnetic field to cause the required field variations. Interposed between the pole pieces are resonant frequency members which provide the radio frequency energization to accelerate the ion beam around the beam space. Having the whole of the central chamber free for top and bottom access enables the pole pieces to be given an efficient design shape. Also, the radio frequency members are able to be interposed between the pole pieces and are not restricted as to axial length and so can be made a very efficient length, such as quarter wave length resonators. The radio frequency members have axially extending hollow interiors which open into the beam space and this enables vacuum pumping to communicate through these interiors thus allowing very efficient pumping of the beam space. There is no iron yoke for the magnet and the weight and size are consequently much reduced and the cyclotron is highly transportable.

Method of high-speed magnetic resonance imaging

Abstract: A method of high-speed magnetic resonance imaging in which the object to be imaged is placed in a high static magnetic field. Nuclear spins are excited in an image area by applying a pulse of radio frequency magnetic field. Optionally, a first gradient field, termed a slice selection gradient, may be applied in conjunction with the RF excitation pulse such that spins are excited only in a selected plane of the object. Following an encoding pulse sequence and rephasing of the nuclear spins by the application of a 180° radio frequency pulse, mutually orthogonal phase-encoding and readout gradients are alternatively applied in the image plane to effect a traversal through spatial frequency domain (k-space). In a preferred embodiment of the invention, the readout gradient is applied as a continuous sinusoidal wave, resulting in a slight overlap between the phase-encoding and readout gradients. If phase errors vary slowly in time, only a partial k-space trajectory is required. Chemical shift is eliminated either by the application of a suppression pulse of RF field or by tailoring the frequency spectrum of the rephasing pulse so as to preclude rephasing of one or other of the chemical moieties.

Radio frequency linear accelerator control system

Abstract: A control system for controlling a radio frequency resonant cavity type linear accelerator so as to be power-supplied always at a resonance frequency of a resonat cavity constituting the accelerator. The system consists essentially of a signal pick-up coil inserted in the resonat cavity, a voltage-controlled oscillator assembly, a phase detector for detecting a phase difference between a signal picked up from the cavity by the signal pick-up coil and an output from the voltage-controlled oscillator assembly. An output from the phase detector controls the voltage-controlled oscillator assembly so as to make it oscillate at a frequency equal to a resonance frequency of the resonant cavity.

Ice detection system

Abstract: A system and method for detecting the state and thickness of water accumulation on a surface incorporates a plurality of spaced, thin, electrically resonant circuits bonded to the surface and a radio frequency transmitter for exciting the circuits to resonance. A receiver detects the resonant signal from each circuit, determines the resonant frequency and quality factor of the circuit and correlates that information with predetermined data representing changes in resonant frequency and quality factor as a function of liquid water and ice accretion to thereby establish the state and thickness of water overlaying the circuits.

Phase modulation compensated amplitude modulator using digitally selected amplifiers

Abstract: An RF amplitude modulated amplifier system is presented incorporating a plurality of RF amplifiers which are compensated for unwanted phase modulation. The system includes a common RF driver for supplying a common RF driver signal. A plurality of actuatable RF amplifiers are provided with each having an input circuit for receiving the common RF drive signal. Each amplifier has a fully on condition for amplifying the common drive signal to provide an amplified RF signal, and a fully off condition. Each of these RF amplifiers exhibits a characteristic in that its input circuit has an input impedance which is greater when fully on than that when fully off, thereby tending to present unwanted phase modulation of the plurality of RF amplifiers. One or more of the RF amplifiers are selectively turned fully on in dependence upon the magnitude of an input signal. The amplified RF signals provided by the RF amplifiers that are turned on are combined so as to provide a combined signal which is amplitude modulated in accordance with the magnitude of the input signal. Circuitry is provided for selectively adding a compensating impedance to the input circuit of each of the RF amplifiers that is not actuated to be fully on. This serves to compensate for any unwanted phase modulation of the plurality of RF amplifiers.

Microwave and millimeter-wave QWITT diode oscillators

Abstract: The authors present DC, microwave, and millimeter-wave characteristics of different quantum-well-injection transit-time (QWITT) devices. Small-signal and large-signal device models are used to provide physical design parameters to maximize the output power density at any desired frequency of operation. A peak output power density of 3.5-5 kW/cm/sup 2/ in the frequency range 5-8 GHz has been obtained from a planar QWITT oscillator. This appears to be the highest output power density obtained from any quantum-well oscillator at any frequency. This result also represents the first planar circuit implementation of a quantum-well oscillator. Good qualitative agreement between DC and RF characteristics of QWITT devices and theoretical predictions based on small-signal and large-signal analyses is achieved. The device efficiency has been increased from 3% to 5% by optimizing the design of the drift region in the device through the use of a doping spike with optimized concentration, without compromising the output power at X-band. Self-oscillating QWITT diode mixers are also demonstrated at X-band in both waveguide and planar circuits. The self-oscillating mixer exhibits a conversion gain of about 10 dB in a narrow bandwidth and a conversion loss of about 5 dB if broadband operation is desired. >

Radio trunking fault detection system with power output monitoring and on-air monitoring

Abstract: A trunked radio frequency (RF) repeater system for public service trunking (PST) or the like includes a fault detection system having an RF output power monitoring, over-the-air RF monitoring and other repeater transceiver testing capabilities. An over-the-air monitor continually tests the digital signalling transmitted by different transceivers within the repeater system. The site controller automatically removes transceivers that test faulty, and does not permit tested faulty transceivers to go back on line until they have passed poll response, power output and RF digital signalling tests.

Hyperthermic power delivery system

Abstract: A system for providing hyperthermic treatment of tumerous tissue using a phased array antenna for focusing radio frequency (RF) energy on the tumorous tissue. A magnetic resonance system generating free induction decay (FID) signals from the tumorous tissue. The FID signals are used to determine the relative phase and amplitude of RF excitations which are to be transmitted by each element of the phase array antenna.

X‐band magneto‐optic Bragg cells using bismuth‐doped yttrium iron garnet waveguides

Abstract: Guided‐wave magneto‐optic Bragg cells at X‐band microwave frequencies using magnetostatic forward volume waves (MSFVWs) in bismuth‐doped yttrium iron garnet‐gadolinium gallium garnet (Bi‐doped YIG‐GGG) waveguides are reported for the first time. Performance figures that have been obtained at an optical wavelength of 1.303 μm include a center frequency tuning range of 3.7–12.0 GHz, a diffraction efficiency of 12% at the magnetostatic wave power of 56 mW, a linear dynamic range >40 dB, and a −3 dB magneto‐optic bandwidth of 150 MHz. These results represent a significant improvement over those obtained previously with the Bragg cells using pure YIG‐GGG waveguides. Maximum scan angle of 6° and 5.3° were also measured, respectively, by tuning the rf frequency ∼10.0 GHz at a fixed dc magnetic field of 3660 Oe and by varying the dc magnetic field ∼3660 Oe at a fixed rf frequency of 10.0 GHz. A frequency resolution of 30 MHz was measured with rf spectral analysis experiments carried out at 12 GHz. Finally, a Fara...

Multiple rf signal amplification method and apparatus

Abstract: A wideband communication system and method for wideband communication that provide plural signals to a single transmitting antenna. Each signal is independently modulated and amplified, and then combined with other signals for transmission on the antenna. The independent amplification, that is, amplification without prior combination with other signals, reduces the number of intermodulation products (IP), thereby reducing the need for complicated IP cancellation techniques. A distribution circuit provides that when the number of signals exceeds the number of amplifiers, two signals may be combined before amplification. The amplified signals may be combined before transmission in combiners that include transformers that reduce IP caused by RF interference. The transformers are formed by enclosing the transmission line within a cavity in a block of ferrite material.

Radio transceiver capable of avoiding intermodulation distortion

Abstract: A radio transceiver comprises an RF amplifier 13 and a first frequency mixer 15 which converts and amplified RF signal into a first IF signal and whose output may include intermodulation distortion. A second frequency mixer 19 converts the output of first frequency mixer into a second IF signal. An interference detector 28 detects the intermodulation distortion by seeing if a beat is included in the second IF signal. Upon detection of intermodulation distortion, a controller 29 minimizes the gain of RF amplifier to decrease or eliminate the intermodulation distortion. Responsive to the end of conversation (hook switch 41) the controller maximizes the gain of RF amplifier to increase the reception sensitivity. The controller may periodically maximise the RF amplifier gain after the detection of the intermodulation distortion. If no intermodulation distortion is detected during this gain-maximized period, the controller keeps the gain to be a maximized value. If the intermodulation distortion is not decreased or eliminated even though the RF amplifier gain is minimized, the controller may change frequency used for communication.

Gallium arsenide antenna switch

Abstract: An RF signal is transformed (12 and 12') to increase its current component, while reducing its voltage component below the voltage that would damage a GaAs switching device (16 or 16'). The current and voltage transformation are selected so that the power of the RF signal remains substantially constant. Subsequent to the GaAs switching device, the signal is converted (24 and 24') to increase the voltage component while decreasing its current component to substantially recreate the original RF signal.

RF production of high density plasmas for accelerators

Abstract: Preliminary experimental results are shown on the production of plasmas by low frequency helicon waves. At constant rf frequency and power, the results show a maximum in density as the dc magnetic field is varied. The measurements confirm the theoretical expectation that the plasma is ionized by Landau damping of the radiofrequency waves.