Showing papers on "Radio frequency published in 1985"

Method and apparatus for proportional RF radiation from surface wave transmission line

Abstract: In a system for launching RF energy as a traveling surface wave onto a single wire transmission line and causing such energy to be radiated away from the line at a downstream location, a series of window radiators of annular shape are spaced along the line, coaxial therewith, each for radiating a portion of the surface wave energy. Each radiator has a conductive component that causes decoupling and radiation of a portion of the RF energy, and a dielectric window that allows the remaining portion of RF energy to pass therethrough and continue, as an attached surface wave, downstream to a succeeding, similarly formed radiator where the decoupling and partial radiation occurs again. Thus, from the same surface wave transmission line system, it is possible to radiate RF energy from two or more discrete locations along the line.

Power dissipated in low‐pressure radio‐frequency discharge plasmas

Abstract: The experimental study of capacitive radio‐frequency (rf) discharges was performed in mercury vapor at low pressures (10−4–10−2 Torr) and at rf applied voltage below 200 V. It was found that at pressures less than 10−2 Torr, plasma electrons gain rf energy basically through a noncollisional mechanism at the oscillating potential barrier formed in electrode sheaths. The rf power dissipated in this process turned out to be much larger than that received by electrons through their collisions with neutral atoms in the plasma bulk. Experimental results are in good agreement with the theoretical model of low‐pressure rf discharges developed earlier by one of the authors.

Implantable apparatus for localized heating of tissue

Abstract: With the object of repetitively treating deep-seated, inoperable tumors by hyperthermia as well as locally heating other internal tissue masses repetitively, a receiving antenna, transmission line, and electrode arrangment are implanted completely within the patient's body, with the receiving antenna just under the surface of the skin and with the electrode arrangement being located so as to most effectively heat the tissue to be treated. An external, transmitting antenna, driven by an external radio-frequency energy source, is closely coupled to the implanted receiving antenna so that the energy coupled across the air-skin interface provides electromagnetic energy suitable for heating the tissue in the vicinity of the implanted electrodes. The resulting increase in tissue temperature may be estimated by an indirect measurement of the decrease in tissue resistivity in the heated region. This change in resistivity appears as a change in the loading of the receiving antenna which can be measured by either determining the change in the phase relationship between the voltage and the current appearing on the transmitting antenna or by measuring the change in the magnitude of the impedance thereof. Optionally, multiple electrode arrays may be activated or inactivated by the application of magnetic fields to operate implanted magnetic reed switches.

Dual frequency surface probes

Abstract: A radio frequency surface probe for data acquisition in magnetic resonance systems. The probe is comprised of a plurality of inductors connected together with tuning capacitors in a balanced configuration. The configuration enables the probe to be impedance matched and to resonate at two separate frequencies without having to be tuned between frequency settings and without being effected by the impedance variations that are caused by the different samples or patients.

Mutual inductance nmr rf coil matching device

Abstract: A matching device uses mutual inductance to couple an NMR radio frequency (RF) coil to an RF power amplifier and RF receiver preamplifier. The device includes a matching coil connected to the RF power amplifier and preamplifier and which is positioned between the NMR RF coil and a decoupling shield in a region where RF flux density, produced by the NMR RF coil, is maximum. This ensures effective coupling to the NMR RF coil and provides a way for adjusting the degree of coupling (hence, input impedance) by varying the area of the matching coil available for intercepting the RF flux.

Mobile antenna and through-the-glass impedance matched feed system

Abstract: The present invention is a moisture-insensitive system adapted to couple radio frequency energy at a low impedance from a matched two conductor transmission line, through a vehicle windshield and to an antenna in a manner which minimizes stray radio frequency radiation within the passenger compartment of the vehicle. The system includes two pair of conducting plates, one pair mounted on each side of the windshield, each pair opposite the other pair. A coaxial feed line is coupled to the inside pair of plates and a matching circuit is connected across the outside pair of plates. A full-size, unloaded antenna element is connected to the output of the matching circuit. A decoupling device, such as a decoupling sleeve or a RF choke, can be used to minimize RF current flow on the shield conductor of the coaxial feed line. The coaxial cable is coupled directly through the windshield, without an intervening matching network, so that RF energy at a low impedance is coupled to the outside pair of plates. This low impedance minimizes parasitic coupling of the feed system to moisture on the windshield, windshield wipers and other foreign bodies. The elements of the invention cooperate to minimize the level of stray radiation within the passenger compartment of the vehicle and provide, in the illustrated embodiment, a 2.0:1 VSWR bandwidth that extends from 830 to 880 megahertz.

The Design of Impedance-Matching Networks for Radio-Frequency and Microwave Amplifiers

Abstract: The design of impedance-matching networks for radio-frequency and microwave amplifiers , The design of impedance-matching networks for radio-frequency and microwave amplifiers , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Voltage-controlled optical/RF phase shifter

Abstract: A new fiber-optic device designed to steer the radiation beam of a phased-array antenna has been demonstrated. A radiofrequency (RF) signal at 125 MHz is generated via photomixing at the output of a single-mode fiber-optic interferometer. The phase of the electrical signal is shifted over several cycles in direct proportion to a voltage applied to an optical controller. The controller consists of a Pockels-type optical phase modulator located in one arm of the heterodyne interferometer. Rapid changes in RF phase are feasible. A miniature low-voltage version of the device, based upon integrated optics, is proposed.

Matching circuit for delivering radio frequency electromagnetic energy to a variable impedance load

Abstract: A matching circuit is provided for delivering radio frequency electromagnetic energy from a radio frequency power supply to a variable impedance load such as a gas plasma. The matching network couples and impedance matches the power supply to the load. The matching network includes a ratio circuit for establishing a voltage ratio between the power supply and the load and a tuning circuit for tuning out a complex portion of the reactance of the load. Separation and control of the ratio and tuning variables is achieved through provision of a ratio control circuit comprising a lumped quarter wave transformer and a tuning control circuit comprising a variable tuning capacitance and a tuning inductance electrically connected in parallel to the load. The lumped quarter wave transformer comprises first and second ratio inductances electrically connected parallel to the load; a first variable ratio capacitance electrically connected in series with the load; and second and third variable ratio capacitances electrically connected parallel to the load. Ratio and tuning inductances are provided comprising toroidal-shaped forms having layers of electrically conductive material deposited or applied thereover. The ratio and tuning capacitances are provided with electrically floating butterfly-shaped rotors ganged on drive shafts driven by high speed torque motors.

Broad-Band RF Match to a Millimeter-Wave SIS Quasi-Particle Mixer

Abstract: An integrated superconducting microstrip is shown to be a convenient, flexible, and well-characterized matching element for a super-conductor-insulator- superconductor (S1S) quasi-particle heterodyne mixer. The resonant interaction (Fiske modes) between the Josephson oscillations of a voltage-biased junction and the microstrip provides a convenient method for determining the electrical length of the microstrip line. An open-circuited microstrip stub that reflects a parallel inductance across the junction is used to broaden the bandwidth of the RF match of a 36-40-GHz S1S- mixer. Measurements with Pb-alloy junctions in a full-height waveguide mixer with fixed mechanical tuning give an instantaneous bandwidth of '10 to 15 percent with a mixer noise temperature T /sub M/ (DSB) = 10+- 2.5 K.

Improved surface coil imaging in MR: decoupling of the excitation and receiver coils.

Abstract: We obtained magnetic resonance images with good sensitivity and radio frequency (RF) uniformity using separate transmitter and receiver coils. The excitation, namely, the rotation of the magnetization vector into a plane perpendicular to the magnetic field, was done by applying a homogeneous RF magnetic field produced by a large saddle-shaped coil. Surface coils were used for detection only. Because two coils that operated on the same resonance frequency were used, a coupling problem developed. This problem, which involved inhomogeneity of the RF magnetic field caused by the large current induced in the surface coil during excitation, could only be solved by minimizing the mutual inductance or maximizing the impedance of the surface coil resonance circuit during excitation. We were able to solve this problem using an electronic detuning method.

Nuclear quadrupole resonance detected at 30 MHz with a dc superconducting quantum interference device

Abstract: A dc superconducting quantum interference device is used as a tuned radio frequency amplifier at liquid helium temperatures to detect pulsed nuclear quadrupole resonance at ∼30 MHz. At a bath temperature of 4.2 K, a total system noise temperature of 6±1 K has been achieved, with a quality factor Q of 2500. A novel Q spoiler, consisting of a series array of Josephson tunnel junctions, reduces the ring‐down time of the tuned circuit after each pulse. The minimum number of Bohr magnetons observable from a free precession signal after a single pulse is ∼2×1016 in a bandwidth of 10 kHz.

Nuclear magnetic resonance radio frequency antenna

Abstract: A nuclear magnetic resonance radio frequency coil. The disclosed coil provides high frequency resonance signals for perturbing a magnetic field within the coil. The coil is impedance matched and tuned with adjustable capacitors. A balanced configuration is achieved with a co-axial cable chosen to phase shift an energization signal coupled to the coil. The preferred coil is a thin metallic foil having a shorting conductor, four wing conductors, and uniquely shaped parallel cross conductors connecting the shorting and wing conductors. When mounted to a rf transmissive plastic substrate and energized the coil produces a homogeneous field within a region of interest the size of a patient head. A semicircular balanced feedbar arrangement is used to minimize undesired field contributions.

Fsk or fm burst signal generating apparatus

Abstract: The invention relates to a burst signal generating method and apparatus for use in a TDMA communication system. The apparatus comprises a modulator circuit (19) for modulating a carrier wave of an intermediate frequency with a modulating signal, a frequency converter circuit (20) for converting the output frequency of said modulator circuit into a radio frequency, an amplitude control unit (20A) responsive to a burst control signal for controlling the amplitude of the carrier wave of said radio frequency, and means responsive to said burst control signal for switching the carrier wave of said intermediate frequency. The method and apparatus permit ready suppression of the carrier wave during the pauses of burst signals.

Optical signal processing with magnetostatic waves

Abstract: Magneto-optical devices based on Bragg diffraction of light by magnetostatic waves (MSWs) offer the potential of large time-bandwidth optical signal processing at microwave frequencies of 1 to 20 GHz and higher. A thin-film integrated-optical configuration, with the interacting MSW and guided-optical wave both propagating in a common ferrite layer, is necessary to avoid shape-factor demagnetization effects. The underlying theory of the MSW-optical interaction is outlined, including the development of expressions for optical diffraction efficiency as a function of MSW power and frequency, device geometry, materials properties, and other relevant parameters. Recent experimental observations of anisotropic Bragg diffraction and collinear TE↔TM mode conversion induced by MSWs in yttrium iron garnet (YIG) thin films suggest that high-performance MSW integrated-optical devices are feasible. Diffraction levels as large as 4% (7-mm interaction length) and a modulation dynamic range of ∼30 db have been demonstrated. Potential signal processing applications are mentioned, including: spectrum analyzers, convolvers/correlators, deflectors, non-reciprocal optical isolators, and tunable narrowband optical filters. Advantages of these MSW-based devices over the analogous acousto-optical devices include: much greater operating frequencies, tuning through the MSW dispersion relation by varying either the rf frequency or the applied bias magnetic field, simple MSW transducer structures (e.g., a single stripline), and the potential for very high diffraction efficiencies.

RF tuning circuit which provides image frequency rejection

Abstract: A radio frequency tuning circuit, for use in a transmitter or receiver, which rejects image frequencies of the frequency band of a supplied RF signal to which it is tuned The circuit comprises an N-path filter and a feedback loop connecting the output of such filter to the input of an RF amplifier to which the RF signal is applied The filter includes a tunable local oscillator and a pair of quadrature related signal paths including mixers therein driven by such oscillator, the outputs of such paths being combined by a summing amplifier which produces the output RF signal The output of the summing amplifier is also supplied to the feedback path, causing the center frequency of the transfer characteristic of the N-path filter to be displaced from the local oscillator frequency The RF output signal thereby includes substantially only single sideband of the signals produced by the two signal paths

Fire detection alarm system

Abstract: A fire detecting system utilizing existing electrical wiring in conjunction with circuit protecting devices provided in a main panel box Various sensors which sense the presence of a fire condition are directly affixed to plug receptacles or wall switches These sensors activate a short circuit device or a controlled overload which is utilized to trip a circuit breaker and activate various visual or aural alarms An alternative embodiment employs an encoded RF signal transmitted over the existing wiring, tripping the circuit breaker by an electromechanical device, thereby activating the aural and visual alarms

Plasma excitation system

Abstract: A radio frequency excitor apparatus and method produce an inductively coupled plasma to heat an analytic sample. The apparatus includes a radio frequency generator mechanism for producing electrical power of selected radio frequency. The generator mechanism has a power output tuning mechanism comprised of at least one output tuning inductor for determining the generator radio frequency. A separate plasma load circuit is coupled to the generator mechanism and is comprised of a work coil and a series connected, impedance matching capacitor. The work coil is adapted to produce an inductively coupled plasma and the capacitor is adapted to substantially balance the combined inductive reactances of the work coil and plasma. A control mechanism for controlling the power input into the plasma load circuit stabilizes the plasma.

Electromagnetic applicator for localizing hyperthermia heating in a system

Abstract: An electromagnetic applicator (10) is provided for heating internal biological tissue, such as cancerous tumors, where applicators generate an electromagnetic field propagating across a gap (20) for forming a relative maximum power density adjacent the internal tumor volume. Conductive elements (12, 14) are spaced a predetermined distance to form a gap (20) and power is applied at radio frequencies through a balancing and matching circuit to generate the electromagnetic field which propagates across the gap (20). A plurality of applicators (10) may be placed about a body location to enable the maximum relative power density to be placed at a selected location within the body portion. A radiating dipole antenna (46) may be used to radiate a signal from which transmitted signal parameters are derived for forming a local power density maximum at a location approximated by the radiating dipole antenna (46). A controller (42) provides power source (40) outputs to applicators (10) having the same relative amplitudes and opposite phase angles of signals received from the transmitting dipole antenna (46) at locations approximating the locations of applicators (10) at the desired body location.

Dual frequency microstrip antenna

Abstract: A single element patch microstrip antenna for dual frequency operation is disclosed. By placing shorting pins at appropriate locations in the patch, the ratio of two band frequencies can be varied from 3 to 1.8. By also introducing slots in the patch, the ratio can be reduced from 3 to less than 1.3. A second embodiment of the antenna uses a c-shaped slot to obtain an even smaller ratio of two band frequencies.

Echo Projection Imaging-A Method to Obtain NMR Images Undistorted by Magnetic Field Inhomogeneities

Abstract: It is proposed to use a modified form of Mansfield's echo planar imaging to obtain NMR images which are entirely undistorted by background inhomogeneities of the magnetic field. In the proposed method, a train of 180° pulses is applied in the presence of a periodically switched or sinusoidally modulated linear field gradient. The time-domain signal is sampled at half the distance between the 180° pulses. At these points the magnetization will be modulated by the gradient, but will be independent of any mechanisms of inhomogeneous broadening, such as static field inhomogeneities, local susceptibility effects, or chemical shifts. A Fourier transform of the function comprising these points will therefore yield a faithful projection of the spin density, although the magnitude of the superimposed gradient need not be large compared to the inhomogeneous broadenings. This paper demonstrates the application of the proposed pulse sequence to a small-scale one-dimensional phantom. The major problem in upscaling this technique to human-scale dimensions lies in the limited available and allowed RF power, which in turn limits the maximal tolerable field inhomogeneities as well as the maximal practical field strength. An analysis of the tolerance of the proposed technique to these factors is presented, based on numerical simulation of its performance, using the Bloch equations. It is concluded that its use may be feasible on low-field systems, providing the advantages of increased signal-to-noise, lower required gradient strength, and drastically reduced sensitivity to the homogeneity and stability of the magnetic field, at the expense of larger RF power.

Measuring the radio frequency environment

Abstract: 1 Radio Frequency Measurements.- Fundamental Relationships: System Noise Factor.- 2 The Radio Frequency Environment.- Surface Electromagnetic Ambients.- Airborne Electromagnetic Ambients.- Satellite Electromagnetic Ambients.- References.- 3 Radio Propagation Fundamentals.- Propagation Processes Encountered in Radio Frequency Surveys.- Expressions for and Representation of Radio Propagation Processes.- References.- 4 Survey Planning.- Measurement Objectives and Procedures.- Site Evaluation and Selection.- Data Set Dimensions.- Test Duration Planning.- Measurement Risk Assessment in Power Density Surveying.- References.- 5 Characterization of Specialized Test Sites.- Electromagnetic Measuring Sites.- Measurements.- References.- 6 Antennas.- Antenna Parameters.- Relationships between Antenna Parameters.- Types of Receiving Antennas.- Antenna Calibration.- References.- 7 Receiving Equipment.- Receiving System.- Detector Functions.- Calibration of the Receiving System Predetection Circuit.- Detector Calibration.- Computer Support.- References.- 8 Survey Execution.- Documentation.- General Procedures of Surveying.- Power Distribution System Surveys.- References.- 9 Data Analysis Techniques.- Statistical Data Functions.- Sampling Quantization Error.- Least Squares Curve Fitting to Measured Data.- Correlation.- Signal Signature Correlation Measure.- References.- Glossary of Symbols.

Imaging method for nuclear magnetic resonance utilizing balanced gradient fields

Abstract: There is disclosed an improved NMR imaging method utilized for forming images of a subject by determining the relative densities of nuclei within the subject. A main magnetic field is applied to the subject to create aligned nuclear spins in the nuclei. Radio frequency energy is applied to the subject at a predetermined Larmor frequency to create a radio frequency field acting in a direction substantially perpendicular to the main magnetic field. A gradient magnetic field is applied to the subject along a selected axis at a time substantially coincident to the time of application of the radio frequency energy so that the nuclei in only a thin slice of the subject are excited. The application of radio frequency energy is terminated after a predetermined time. Thereafter, two time varying balanced gradient magnetic fields are applied to the subject along two perpendicular axes, which are both perpendicular to the first magnetic gradient field. The resulting precession of the nuclear spins is detected during substantially the entire time of the free induction decay period of the spins. An image is then formed from the detected information. These steps are repeated so that many slices of the subject are imaged substantially simultaneously.

Stabilization of interchange modes in mirror plasma devices by radio-frequency sideband coupling.

Abstract: We present results from an analysis of the ion cyclotron range of frequencies (ICRF) wave interactions with flute-interchange modes. The analysis is valid for arbitrary wave vector of the ICRF waves, and shows that these modes can be stabilized by ICRF sideband coupling to them. The modes can be stabilized in a variety of ways, depending on details of the ICRF wave structure. We also find a new rf-driven fluid instability for a range of parallel (to the magnetic field) rf wavelengths.

High-frequency semiconductor device

Abstract: A semiconductor device includes a metallic container (30) or containing a radio frequency semiconductor circuit (3) on a )ottom surface (1) thereof; a cap (19) for covering the con- ainer; and input and output terminals (13a, 13b) connected to he circuit (3) and penetrating through a side wall (2a) of the container at locations opposite to each other The bottom surface (1) of the container includes space for mounting the radio requency semiconductor circuit (3) and supplementary space or mounting elements (17) of a supplementary circuit A cut- off member (15) for increasing the cutoff frequency of the waveguide mode wave propagation between the input and output terminals within the container is provided on a part of the supplementary space, so that the cutoff frequency is higher than the wave frequency used in the radio frequency semiconductor circuit

Optical RF filtering system

Abstract: An optical notching filter in which a band of radio frequencies such as the RF input of a radio receiver is an input signal. The input signal modulates a laser beam and the modulated beam is optically Fourier transformed. A programmable optical notching filter spatially filters the electromagnetic interference noise from the transformed beam and the thus filtered beam is optically inverse Fourier transformed. A photo-combining of the filtered beam with a focused laser local oscillator beam down-converts the filtered beam to the original input signal minus electromagnetic interference.

Dual mode target seeking system

Abstract: A dual mode target seeking system for airborne vehicles which operates under two different frequencies simultaneously includes a radio frequency antenna comprising a slotted plate defining a ground plane with an image plate positioned in front of the ground plane at a distance chosen such that multiple reflected rays are in phase with each other and with waves incident on the image plate. The slotted plate and image plate have aligned central openings through which an electro-optical system for operating under a chosen electro-optical frequency range, for example under infrared frequencies, projects. The electro-optical system includes a detector unit positioned behind the antenna and a focussing system for directing incoming electro-optical radiation into the detector unit. The focussing system includes first and second lenses mounted in the openings in the image plate and slotted plate, respectively. The lenses each transmit radiation in the chosen electro-optical frequency range while at least partially reflecting radio frequency radiation.

Wideband 180-degree phase shifter bit

Abstract: A wideband 180-degree digital phase shifter bit is provided which is operable independently of input rf frequency over a predetermined bandwidth of interest. The phase shifter bit comprises a coupled transmission line segment and a pi network segment, with switching means for alternatively connecting the rf input and rf output first to the coupled transmission line segments, and then to the pi network.

Portable, X-Band, Linear Accelerator Systems

Abstract: Three light-weight, x-band, electron accelerators have been developed to provide a series of highly portable sources of x-rays and neutrons for nondestructive testing. The 1.5 MeV x-ray unit has a 200 kW magnetron for an RF source and an air-cooled, traveling wave accelerating structure to minimize Its weight. The 4 and 6 MeV units share the same drive system which contains a 1.2 MW magnetron. The 4 MeV unit uses a traveling-wave guide to produce x-rays and the 6MeV unit uses a standing-wave guide to produce x-rays or neutrons. The choice of 9.3 GHz was dictated by the availability of a high power coaxial magnetron and by the obvious dimensional and weight advantages of a higher frequency over the more common S-band frequencies around 3 GHz.