Showing papers on "Radio frequency published in 1991"

Plasma sources based on the propagation of electromagnetic surface waves

Abstract: Microwave and RF plasmas are finding increasing use in materials processing, plasma chemistry, chemical analysis, and other fields. This is stimulating the search for suitable plasma sources. In the 1970s, electromagnetic surface waves were put to use to sustain plasmas and an efficient microwave device, called a surfatron, was developed for this purpose. Recent work has shown that such discharges can also operate at radio frequencies. A large number of on surface-wave plasmas experimental data have been accumulated-their modelling is well advanced and they have found applications in various fields of research and technology. This paper reviews the physical principles of operation and the design of surface-wave plasma sources. Since the wave launcher is the central component of the source, this review presents a unified description of several compact, efficient, and easy to operate launchers specifically intended for plasma generation that have been developed over the past fifteen years. It is now possible to sustain such plasmas at frequencies ranging from 1 MHz to 10 GHz, in a pressure domain extending from 10-5 Torr up to few times atmospheric pressure, and in a rich variety of plasma vessels and reaction chambers.

Temperature controlled rf coagulation

Abstract: Radiofrequency medical devices for ohmic heating of tissue of a patient include a temperature sensor (29) carried by and in thermally conductive relationship with a thermally conductive electrode (28). The sensor (29) is connected for feedback to a control circuit (6) that modulates RF power applied to the electrode according to the signal received from the temperature sensor (29). The control circuit (6) and RF power supply alternate between two operating modes. In the first mode the RF power supply applies RF power to the electrode (28). In the second mode the control circuit (6) senses a signal from the temperature sensor (29) in the absence of RF signal. The control circuit (6) compares the signal from the temperature sensor (29) to a set value and modulates the RF power applied to the electrode (28) in accordance with the set value.

Implanted apparatus having micro processor controlled current and voltage sources with reduced voltage levels when not providing stimulation

Abstract: An implant for stimulating the vagus nerve receives commands over a radio frequency link. 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 of a magnet in a given location in conjunction with the application of a radio frequency transmission for a given period.

Simultaneous radio frequency and magnetic field microprocessor reset circuit

Abstract: An implant for stimulating the vagus nerve receives commands over a radio frequency link. 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.

Fiber optic microcellular radio

Abstract: A distributed antenna system consisting of optical fiber connected canisters is proposed to replace or supplement the base station antennas required for cell splitting of growing cellular mobile radio systems. The end-to-end linear transmission of RF signal voltage can be maintained over the wide dynamic range of mobile radio. The technical feasibility of multiplexed subcarrier transmission using available lightwave components has been verified by signal-to-noise ratio and intermodulation distortion measurements. Measurements of a two-way audio link over both simulated and real radio paths have demonstrated the compatibility of a prototype lightwave transceiver, designed for the canister, with the existing base station and mobile equipment. >

Method and apparatus for magnetic resonance imaging and heating tissues

Abstract: The present invention relates to apparatus and a method for imaging and heating body tissues with one probe, through use of a magnetic resonance imaging radio frequency source. The device may also be configured with a thermocouple to provide temperature-controlled heat therapy with sufficient image definition to control that therapy.

Radio frequency or microwave plasma reactors? Factors determining the optimum frequency of operation

Abstract: It is now generally accepted that the frequency ω/2π at which a high frequency (hf) discharge is sustained has considerable influence on the properties of the plasma. For example, the electron density obtained for a given hf power density deposited into the plasma is usually higher at microwave than at radio frequencies (rfs). This paper reviews a series of experiments at the Universite de Montreal designed to investigate the influence of ω on the power balance between the hf field and the plasma, and the plasma processing of materials. For the two particular etching and deposition processes which are described here, the ‘‘optimum’’ frequency (at which the process is most efficient) appears to be in the range between 50 and 100 MHz. This suggests that converting a plasma process from 13.56 to 2450 MHz does not necessarily lead to the greatest possible process enhancement, and that optimization may require the plasma reactor to be constructed in such a way as to allow the excitation frequency to be changed. To provide insight into these results, the most recent models dealing with the influence of ω on the electron energy distribution are reviewed and extended to calculate parameters that can be compared with our experimental data.

Implanted apparatus disabling switching regulator operation to allow radio frequency signal reception

Abstract: An implant for stimulating the vagus nerve receives commands over a radio frequency link. 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.

Tumor treatment method

Abstract: A method of treatment of a tumor comprising the steps of catheterization of the arterial vessel that feeds the tumor, and transcatheter administration of a suspension of magnetically hard ferromagnetic material in an oil solution of an oil-soluble antitumor substance with simultaneous application of local magnetic field onto the area of the tumor. After 1-3 days the tumor is subjected to ultrahigh radio frequency electromagnetic field or ultrasonic waves to produce heating of the tumor tissue to the temperature of 43.0°-43.5° C. for a period of 5-45 minutes.

Portable field-programmable detection microchip

Abstract: A read/write device includes a transmitter for producing an RF signal and a modulator coupled to said transmitter for modulating the RF signal and, finally a data receiver for receiving RF data signals from a portable microchip. The microchip includes a resonant circuit tuned to the RF frequency of the read/write transmitter and a receiver that is coupled to the resonant circuit for detecting the RF signal. There is also provided a charging capacitor capable of storing the electrical energy from the RF signal so that the microchip can be powered during pulse pauses of the RF signal. The microchip includes a memory circuit for storing the identification code of the microchip, and a code generator that is coupled to the memory circuit for generating an RF signal that is modulated with the identification data. A switching element that couples the resonant circuit to the code generator de-tunes the resonant circuit when the identification data is transmitted back to the read/write device. The same resonant circuit also serves to field program the memory circuit of the microchip by receiving pulse pause modulation signals (PPM) of the RF carrier signal thus allowing the identification code of the microchip to be altered by the read/write device.

A single-chip VHF and UHF receiver for radio paging

Abstract: The authors describe a signal-chip radio receiver for VHF and UHF digital wide-area paging transmissions up to 500 MHz with frequency-shift-keying (FSK) data rates up to 1200 Bd. All channel filtering is on-chip and the IC requires only 28 surface mounted external components and a quartz crystal to make a complete receiver. With -126-dBm sensitivity, 70-dB adjacent channel rejection, and 60-dB intermodulation immunity, it satisfies all known pager specifications, worldwide, using the POCSAG paging code. High-dynamic-range mixers, integrated gyrator filters, small-area high-pass filters, and an efficient FSK demodulator combine to give good performance with a current consumption of only 2.7 mA from a 2-V supply. High-density on-chip capacitors in a bipolar process designed for analog RF applications give a chip size of only 4.6*3.8 mm. >

TV signal receiving double conversion television tuner system having automatic gain control provisions

Abstract: A TV signal receiving system, in order to tune a broadcasting frequency of a desired channel after receiving a TV signal, converts the TV signal into an intermediate frequency having a frequency higher than the maximum frequency in a TV broadcasting frequency band and then converts again the frequency of the signal into another intermediate frequency in conventional TV systems so as to improve the rejection characteristics of image and IF signals. The system comprises a first converter for tracking a desired channel frequency from a TV RF signal and converting the frequency into a first IF of 2 GHz, a band-pass filter of the 2 GHz IF for filtering only the first IF frequency signal in the first converter, and a second converter for converting the filtered first IF into 45 MHz of the conventional TV IF.

Power control circuitry for achieving wide dynamic range in a transmitter

Abstract: Power control circuitry (100) uses two attenuators in the transmit path to achieve wide dynamic range. An intermediate frequency (IF) attenuator (200) is placed before a mixer (212) in the IF section of the transmit path and a radio frequency (RF) attenuator (221) is placed after the mixer (212) in the RF section of the transmit path. Power control circuitry (236) controls setting of the two attenuators in response to a magnitude control signal (102) related to a RF output signal at a desired power level. To conserve battery power of the subscriber unit, only the RF attenuator (221) is adjusted when the desired power level is to be within a given range below the maximum transmission level. For ranges below the given range, the RF attenuator (221) is set for maximum attenuation and the IF attenuator (200) is adjusted.

Regenerative RF bi-directional amplifier system

Abstract: A regenerative RF bi-directional communications system (10) is provided for establishing RF coverage within a RF block tunnel area (12) The system uses a plurality of cascaded amplifier stages (18) for periodically regenerating signals which are transmitted and received along a series of radiating cable length (16) which link base station transceivers (14) to hand-held or like mobile communication units An intermediate frequency distribution system is used so that the required level of amplification is achieved through the several cascaded amplifier stages (18) at the level of low-power IF signals generated from the original RF signals in conjunction with the appropriate oscillator and pilot signals The IF distribution system restricts the cascading effect occurring due to the plurality of cascaded amplifier stages on the relatively low-power IF signals, thereby producing a negligible amount of intermodulation

High‐density plasma mode of an inductively coupled radio frequency discharge

Abstract: Experimental observations concerning the formation of a high‐density plasma in an inductively coupled radio frequency (11.4 MHz) discharge in argon are described. These observations are complemented by probe measurements that provide a quantitative description of plasma properties over an useful range of vapor pressure, 0.02–0.2 Torr, and rf power, 50–400 W. It is shown that a dense plasma of the order of 1012 cm−3 can be easily formed, having the configuration of a luminous plasmoid embedded in a low‐density, 1010 cm−3, diffuse plasma.

Optically patterned RF shield for an integrated circuit chip for analog and/or digital operation at microwave frequencies

Abstract: The invention relates to the provision of an RF shield for an individual or a collection of integrated circuit chips in a module containing a plurality of hybrid interconnected chips generating interfering RF fields that would interfere with operation of that chip if unshielded. The chips in the module may function in the analog and/or digital mode. The RF shield comprises separate metallizations under and over the chip, the two metallizations being interconnected by a line of discrete electrically conductive vias forming cage-like sides to complete an electrically conductive enclosure about the chip. The vias are spaced closely enough to prevent the escape or entry of RF waves at the frequencies of interest. The RF shield is advantageously fabricated using metallizations and vias that are optically patterned by the same process steps used to effect hybrid interconnection of the chips.

Repeater with feedback oscillation control

Abstract: An apparatus for detecting excessive output power from a cellular radio telephone system booster includes input circuitry for receiving incoming radio frequency signals from a mobile source. Amplifiers are provided for amplifying the radio frequency signals either directly or by means of intermediate frequency channels. The output power amplifiers have variable gain. Circuitry detects when the transmitted radio frequency signals exceed a predetermine threshold and reduce the amplifier gain accordingly.

Automatic rf equalization in passenger aircraft video distribution system

Abstract: A passenger aircraft video distribution system distributes modulated RF signals (lines 16,26) provided from a central signal source to be used at each passenger seat (208-1 through 208-15). The RF signals are distributed by means of various RF components, including amplifiers (14, 24, 34), taps and splitters (22, 30), positioned at different mutually distant stations (12, 18, 28), with at least some stations being interconnected by relatively long lengths of coaxial cable (16,26). In order to ensure proper RF levels for best tuner (36) operation and to compensate for different cable losses at different frequencies, one or more of the stations (18) in the distribution system is provided with a variable equalizer (23) controllable by a microprocessor (52). A separate service line (64,66) enables a central microprocessor (50) to monitor RF levels at different frequencies at at least one station (28) to automatically provide, via the same service line, appropriate equalization control signals to obtain proper compensation for the different cable losses at different frequencies. The monitored RF signals are also employed for diagnostic purposes.

Finite element modeling of the RF heating process

Abstract: The heating of heterogeneous materials by radio frequency excitation is modeled by sequential electromagnetic and thermal analysis using the finite-element method. The electromagnetic analysis comprises electrostatic modeling using temperature-dependent complex dielectric permittivity to account for the energy dissipating losses in the material. The thermal analysis consists of a transient finite-element procedure with temperature-dependent thermal and material properties. The results show good agreement with transient thermal measurements. >

Design study on a direct conversion receiver front-end for 280 MHz, 900 MHz, and 2.6 GHz band radio communication systems

Abstract: The authors describe the required RF stage performance for a direct conversion receiver for 280 MHz, 900 MHz, and 2.6 GHz system applications. The required attenuation level for LO (local-oscillator) leakage for the assumed system terminal is calculated. Furthermore, from test receiver measurements, it was found that LO circuit shielding is necessary for practical system applications. The required out-of-band attenuation level of an RF filter for interference signals was also investigated quantitatively from experimental data obtained from bit-error-rate measurements in an actual radio wave environment and from calculations based on a 1 dB gain compression point of the mixer. Thus, it has been found that an interference rejection filter is necessary for practical direct conversion receiver applications. However, the filter specification is largely relaxed compared with the image rejection filter in a conventional superheterodyne architecture. >

Plasma reactor using UHF/VHF resonant antenna source, and processes

Abstract: A plasma reactor (10) uses a ring antenna (25) driven by RF energy (HF, VHF, or UHF) and produces a circularly polarized electromagnetic wave inside the ring. Inside the ring, this wave has a transverse circular electric field and a longitudinal magnetic field. A static magnetic field may be used with the E/M field (typically with direction perpendicular to the wave's electric field component). Placed adjacent to a dielectric window, dome, or bell jar (17), the above apparatus generates a high density, low energy plasma inside a vacuum chamber for etching metals, dielectrics and semiconductor materials (5). When operated at resonance (antenna (25) tuned to resonance with excitation frequency, and magnetic field tuned to resonance with excitation frequency), plasma density may be maximized. Auxiliary bias energy applied to the wafer support cathode (32C) controls the cathode sheath voltage and controls the ion energy independent of density. Various etch processes, deposition processes and combined etch/deposition processes (for example, sputter/facet deposition) are disclosed. Processing of sensitive devices without damage and without microloading can thus be achieved providing high yields.

High-frequency semiconductor wafer processing method using a negative self-bias

Abstract: A plasma process apparatus capable of operation significantly above 13.56 MHz can produce reduced self-bias voltage of the powered electrode to enable softer processes that do not damage thin layers that are increasingly becoming common in high speed and high density integrated circuits. A nonconventional match network is used to enable elimination of reflections at these higher frequencies. Automatic control of match network components enables the rf frequency to be adjusted to ignite the plasma and then to operate at a variable frequency selected to minimize process time without significant damage to the integrated circuit.

Cross polarization interference canceller

Abstract: In a cross-polarization interference conceller for use in a digital radio communication system which transmits digital modulated signals over radio frequencies having planes of polarization orthogonal to each other, signals from the interfering polarized wave are sampled with a frequency equal to double the frequency of the affected polarized wave and, after latching the sampled signals with the frequency of the symbol rate, interference cancelling signals are generated by adding the products of their multiplication with control signals. Therefore, the digital multipliers and the digital adders for generating the interference cancelling signals can be operated at low speed.

Quantized current in a quantum dot turnstile

Abstract: We have performed RF experiments on a lateral quantum dot defined in the two dimensional electron gas (2DEG) of a GaAs/AlGaAs heterostructure. The small capacitance of the quantum dot gives rise to single-electron charging effects, which we employed to realize a quantum dot turnstile device. By modulating the tunnel barriers between the quantum dot and the 2DEG leads with two phase-shifted RF signals, we pass an integer number of electrons through the quantum dot per RF cycle. This is demonstrated by the observation of quantized current plateaus at multiples ofef in current-voltage characteristics, wheref is the frequency of the RF signals. When an asymmetry is induced by applying unequal RF voltages, our quantum dot turnstile operates as a single-electron pump producing a quantized current at zero bias voltage.

Field emission triodes

Abstract: Triode RF amplifier structures using field emission cathodes have been investigated from both the theoretical and experimental viewpoint. The physically large experimental structure used and the theoretical calculations for that structure are described. The agreement between theory and experiment for both DC and AC measurements is shown to be very good. The theoretical circuit modeling has produced information useful in work on higher-frequency operation. A RF voltage gain of about 11 dB has been measured at low frequencies, dropping to 0 dB at 200 kHz; the cathode had a transconductance of only 38 mu S. Model calculations on the large structure used show operation to about 2 MHz with a more typical transconductance of 380 mu S for a 1000-cone field emission cathode. >

Automatic RF leveling in passenger aircraft video distribution system

Abstract: A passenger aircraft video distribution system distributes modulated RF signals provided from a central signal source to be used at each passenger seat. The RF signals are distributed by means of various RF components, including amplifiers (90, 14a, 164, 24a, 24b, 34a), taps (180, 210) and splitters (108, 182, 214). In order to ensure proper RF levels for best tuner operation, each of a number of stations in the distribution system is provided with a variable gain amplifier (90, 14a, 164, 24a, 24b, 34a) controllable by a microprocessor (92, 50a, 220, 52a, 56a, 216). A separate service line (222, 224, 226, 228, 230, 232, 234) enables a central microprocessor to monitor RF levels at different stations to automatically provide, via the same service line, appropriate gain control signals to obtain proper RF levels. The monitored RF levels are also employed for diagnostic purposes.

Gallium arsenide monolithically integrated sampling head using equivalent time sampling having a bandwidth greater than 100 ghz

Abstract: A high bandwidth RF sampler using equivalent time sampling comprising an RF coplanar waveguide integrated with sampling diodes on a gallium arsenide substrate. A monolithic, integrated coplanar strip nonlinear transmission line is integrated on the same substrate to receive sample pulses. These pulses are reshaped by the nonlinear transmission line to have a very fast edge. This edge is differentiated by a shunt inductance of a short circuit termination of a slot line portion of the RF signal coplanar waveguide. The resulting delta function sample pulses cause the sample diodes and integrated capacitors to develop an intermediate output frequency which is a replica of the RF signal at a lower frequency and no voltage conversion loss. RF signals of up to 300 Ghz can be sampled using this circuit.

Plural switch circuits having RF propagation networks and RF terminations

Abstract: A radio frequency circuit includes a first RF switch having a first common port coupled to an input port of the switch circuit and a first pair of branch ports and a second RF switch having a second common port coupled to an output port of the circuit and a second pair of branch ports. The radio frequency circuit further includes an RF propagation network having a first end coupled to a first one of said first pair of branch ports of said first RF switch and a second end coupled to a first one of said second pair of branch ports of said second RF switch. The radio frequency circuit further includes an RF termination having an impedance characteristic corresponding to an impedance characteristic of said first common port and having a first end coupled to a second one of said first pair of branch ports of said first RF switch and a second end coupled to a first reference potential.