Showing papers on "Radio frequency published in 1976"

A Probe for Measuring Temperature in Radio-Frequency-Heated Material (Short Papers)

Abstract: Measuring temperature in material being heated by radio-frequency (RF) fields is difficult because of field perturbations and direct heating caused by any conventional leads connected to the temperature sensor. A temperature probe consisting simply of a thermistor and plastic high-resistance leads appears to practically eliminate these problems. The design goals are described, and the performance of an initial test model of this type of probe is discussed.

Electrosurgical safety circuit and method of using same

Abstract: An improved electrosurgical safety circuit where the currents in the active and patient leads are monitored, the monitored currents being respectively rectified and then subtracted from one another. Whenever the active current exceeds the patient or return current by an amount corresponding to a dynamically variable threshold, an appropriate measure is taken such as the sounding of an alarm and/or the de-energization of the electrosurgical generator. The dynamic threshold varies in accordance with the level of the signal applied to the patient and compensates for leakage current through stray capacitance from the active lead to ground. The patient lead is substantially grounded at radio frequencies through a frequency sensitive network. The frequency sensitive network may include a capacitor, the value of which is such as to provide the foregoing frequency response. Since as small a capacitor as possible must be used to provide a high impedance at low frequencies, and since the radio frequency voltage across the capacitor must be kept low to thereby keep the voltage patient low at radio frequencies, a further network is employed to enable the use of a small capacitor while at the same time decreasing the effective voltage thereacross whereby protection of the patient is enhanced.

Radio frequency, electromagnetic radiation device having orbital mount

Abstract: A method and apparatus for treating tumors, both benign and malignant, involving radio frequency heating of the tumor within the body of the animal host, the method comprising precisely locating and monitoring the tumor to be treated and so positioning radio frequency apparatus that sufficient energy is absorbed therefrom by the tumor for a period of time and with intensity sufficient to cause necrosis of said tumor, but without substantially affecting the tissues surrounding said tumor. The preferred apparatus is adapted for connecting the radio frequency treatment equipment to the output of a body scanner or the like such that the exact position and configuration of the tumor can be plotted in terms of rectangular coordinates and the radio frequency equipment can then be directed or focused precisely on the tumor location. Moreover, to avoid excessive heating or thermal damage to the surrounding tissue, the applicator plates or discs are moved in an orbital manner such that the tumor always lies on the axis between the applicator plates, and the radio frequency energy is concentrated therein. However, by dint of the orbital movement of the applicators, the energy is not continuously being applied to a confined area, i.e., to immediately surrounding tissue but is rather applied over a comparatively large surface area so as not to affect the surrounding tissue adversely.

Analysis of Transit Time Effects on Doppler Flow Measurement

Abstract: A relation is derived between the transmitted spectral density and the output spectral density of broad bandwidth, random signal, Doppler flow measurement systems operating under conditions where the fluid transit time is limited by the transmitted signal bandwidth and not by beam geometry. The fact that this result is already known to hold for pulsed radio frequency (RF) Doppler proves that random or pseudorandom Dopplers will give the same output spectrum as pulsed RF Dopplers, provided that the transmitted spectral density of the RF system has the same envelope as that of the noise system.

Contactless measurement of semiconductor conductivity by radio frequency‐free‐carrier power absorption

Abstract: It is shown that, under suitable conditions, the power absorbed by a thin semiconductor slice in an oscillating magnetic field is accurately proportional to the material conductivity. The magnitude of this power absorption can be used to determine the conductivity by coupling the semiconductor to an amplitude‐stabilized marginal oscillator and noting the power needed to maintain the demanded level of oscillation. Instruments of this type have been constructed exhibiting ∼1% linearity over a 100:1 range of sample conductivity, a resolution of ∼1 in 104 and a limiting sensitivity of ∼10−5 mho/⧠. The method may be applied to the measurement of essentially any conducting material from semiconductors to metals.

Self-calibrating microwave transponder

Abstract: A self-calibrating microwave transponder incorporating an amplifier, modulator, instantaneous frequency discriminator, memory and voltage controlled oscillator is described which may generate an RF signal in response to the carrier frequency of received low duty cycle pulse RF signals. The instantaneous frequency discriminator is used to provide an address signal from the pulse RF signals which is used to access a memory that contains the correct tuning data for the voltage controlled oscillator to generate an RF signal.

Comments on "Short-range radio-telemetry for electronic identification, using modulated RF backscatter"

Abstract: An electronic identification system which uses modulated backscatter from an RF beam-powered tag is described. A subcarrier is used in the return signal format to allow separation from the background clutter and to allow use of a novel method to avoid RF phase problems.

Millimeter-Wave Receivers with Subharmonic Pump

Abstract: Hybrid integrated downconverters which are pumped at half the frequency needed in a conventional downconverter have shown a conversion loss of 3 dB at 50 GHz and 6 dB at 100 GHz with a corresponding single-sideband (SSB) receiver noise figure of 7 dB at 50 GHz and 11 dB at 100 GHz. The circuits are linearly scaled from an optimized 5-GHz model. Each downconverter consists of a stripline conductor pattern, a novel transition from waveguide to stripline, and a Schottky-barrier diode pair. The circuits can be tuned over a useful RF bandwidth of 20 GHz, and they can be readily scaled to other frequency bands.

Radio-frequency tuned-circuit microdisplacement transducer

Abstract: An inductance-capacitance loop defines a resonant circuit and is arranged in a member subject to stress. Strains resulting from the stress vary the inductance or capacitance of the circuit, and its resonant frequency. A dip meter is used to detect the resonant frequency and thus provides a reading indicative of the stress in the member.

Reactively decoupled dual channel keying circuit for wide-band frequency modulated keyable control circuit

Abstract: A keyable control circuit, has sensing coils located in the vicinity of a plurality of locations where lock control is desired. At least one swept high-frequency oscillator, which is connected to each sensing coil, generates an rf signal, rapidly swept over a wide frequency band. When an external keying circuit, containing more than one resonant circuit, each correctly tuned to a predetermined keying frequency, is inductively coupled to a sensing coil, each resonant circuit absorbs rf energy as the oscillator frequency is swept past its resonant frequency. Electrical interaction between the resonant circuits is accomplished by reactive cancellation. Energy absorption in the external keying circuit induces corresponding reductions in rf energy in the sensing coil as the oscillator frequency is swept past the keying frequencies. Tuned detectors within the keyable control circuit produce a control signal when energy reduction is sensed at each of the predetermined keying frequencies. If correct absorption fails to occur at any one or more of the predetermined frequencies, the control signal is withheld. A time-gating system enables selective direction of the control signal to one or more using locations while excluding others. This function finds convenient application in automotive use where it is frequently desired to enable simultaneous unlocking of one or more doors while excluding unlocking of the deck lid. A dead-oscillator detector averts attempted actuation of the unlocking function by the coupling of untuned energy-absorbing material, such as iron, to a sensing coil.

Electromagnetic wave propagation well logging utilizing multiple phase shift measurement

Abstract: The invention disclosed herein includes methods and apparatus for determining true formation resistivity, flushed zone resistivity and invasion diameter of the earth formation in the vicinity of a well borehole. A radio frequency electromagnetic field in the frequency range from 800 kilohertz to 4 megahertz is generated in a borehole and the electromagnetic field is detected at a plurality of longitudinally spaced locations. Measurements of the attenuation and propagation velocity of the electromagnetic wave at the longitudinally spaced receivers may then be interpreted according to predetermined relationships in terms of the formation resistivity, flushed zone resistivity and invasion diameter surrounding the borehole.

Radio frequency beam forming network

Abstract: A radio frequency beam forming network is disclosed wherein a plurality of antenna feed elements arranged in the focal plane of a radio frequency lens is coupled to corresponding input ports of a radio frequency energy distributing means. Output ports of such radio frequency energy distributing means are coupled to a receiver/transmitter through different paths. Disposed in the different paths are active elements, including variable phase shifters and attenuators. The active elements, in response to control signals, provide proper attenuation and phase shift to the signals passing therethrough thereby to form a desired antenna beam. Such antenna beam is comprised of one or more "spot" beams. With such arrangements failure of a single one of the active elements will only slightly degrade system performance without resulting in a complete loss of any one of the "spot" beams.

Radio frequency cautery instrument and control unit therefor

Abstract: An improved radio frequency cautery instrument comprising a radio frequency signal generator for supplying both monopolar and bipolar radio frequency signal outputs for medical applications. A control unit is interposed between the radio frequency outputs of the signal generator and the hand-held electrode assembly, and further interposed between a finger-operated switch on the electrode assembly and the power circuit of the signal generator, whereby the application of radio frequency energy to the electrode of the electrode assembly can be controlled by the user through manipulation of the finger-operated switch on the electrode assembly.

Large area motion sensor using pseudo-random coding technique

Abstract: A system primarily for industrial security; to detect intruder movement in interior areas. A Doppler detecting, bi-static system utilizing range (time-delay) areas of varying shapes. The detection containment obtained is orders of magnitude more absolute than conventional systems which depend on antenna beam shaping to obtain varying detection coverage. Range discrimination is effected by bi-phase modulating the transmitted CW radio frequency waves according to a maximal length pseudo-random code. The autocorrelation function provides the ideal range discrimination response for the application. Omni antenna coverages are provided and a lower rf band is used than in conventional systems for this use, affording lower moving clutter susceptibility and better coverage. The general pseudo-random coding techniques are available within the state of the Radar Arts.

RF power monitor utilizing bi-directional coupler

Abstract: The coupler inserts in an RF transmission line and produces a pair of DC signals whose level is representative of the magnitude of forward or reverse power flow therethrough. Power flow is sensed via a pair of non resonant loops, each of which is terminated and oriented such that AC signals, whose amplitudes correspond to the forward or reverse power flow magnitude, are produced. Since the RF signals produced by the loops are dependent on the RF power flow frequency, unique circuitry processes the RF signals and compensates for this frequency dependence whereby the processed AC signals are substantially frequency independent. Also disclosed are improved rectification circuitry, and a means to compensate the coupler against error due to thermal drift of coupler components.

An Integrated Optical RF Spectrum Analyzer

Abstract: A concept for performing RF spectrum analysis using the technology of Integrated Optics is described. Such devices could achieve frequency resolution of about 1 MHz over bandwidths up to 1 GHz in a very small and potentially low cost package. The principles of operation, design constraints, and possible circuit configurations are discussed. The state -of- the -art of key component technologies

A circuit approach to SAW filterbanks for frequency synthesis

Abstract: A SAW filterbank (2.5 × 0.9 cm) coupled to a miniature silicon-on-sapphire (SOS) p-i-n diode, multiple-input single-output RF switch array (2.5 × 0.25 cm) forms the basis of a very compact UHF frequency synthesizer. In this paper the operation, design, fabrication, and performance of rapid-switching SAW frequency synthesizers is described. Experimental measurements depicting the spectral purity of the waveforms synthesized by two devices; one fabricated on LiTaO 3 and the other on AlN-on-sapphire, operating over respective frequency ranges of 520-650 MHz and 970-1210 MHz are provided.

Radio-frequency coupler

Abstract: A radio-frequency coupler comprising a first terminal for interconnection with a conventional automobile receiving antenna used for receiving rf transmissions within a first radio-frequency band, a second terminal for interconnection with a receiver operating within the first radio-frequency band and a third terminal for interconnection with a transceiver operating within a second frequency band different from the first band. A first rf transmission path extends between the first terminal and the second terminal and a second rf transmission path extends between the first terminal and the third terminal. A first resonant circuit is connected in the first rf transmission path and tuned to pass rf transmissions in the first band but substantially block those in the second band. A second resonant circuit is connected in the second rf transmission path and tuned to resonate at a frequency within the second band so that rf transmissions within the second band are passed but those within the first band are substantially blocked. A third resonant circuit is connected between the third terminal and electrical ground and tuned to resonate at a frequency outside the second band. The second and third resonant circuits form a series-connected path between the first terminal and electrical ground and the impedance of the third resonant circuit at the second frequency band allows maximum rf energy within the second band to be transferred between the antenna and the transceiver thereby permitting the conventional automobile receiving antenna normally used only for receiving rf transmissions within the first frequency band to also be used for sending and receiving rf transmissions within the second frequency band.

Antenna system with automatic depolarization correction

Abstract: A spectrum reuse antenna system is described for transmitting orthogonally polarized RF waves at one frequency band to a satellite and for receiving orthogonally polarized RF waves from a satellite at a second frequency band through a common antenna. A local generator provides a first control signal which varies as a function of the typical rotation of the polarization of a transmitted wave at the one frequency band travelling through the ionosphere. The local generator also provides a second control signal which varies as a function of the typical rotation of the polarization of a received wave at the second frequency band travelling through the ionosphere. A driven means responsive to the first control signal causes a rotation of the polarization of the transmitted waves to correct for Faraday rotation in the ionosphere and a driven means responsive to the second control signal causes rotation of the polarization angle of the antenna system for the received waves to correct for the Faraday rotation.

Method of and apparatus for the radio frequency sputtering of a thin film

Abstract: A method of an apparatus for controlling the deposition of a thin film upon a substrate by a radio frequency (RF) sputtering apparatus is disclosed. The apparatus utilizes the predetermined bias voltage vs. vacuum pressure characteristic of the RF sputtering apparatus to control, by a single pressure controller, both the vacuum pressure and the bias voltage. A substrate tuning bias circuit generates an effective DC bias voltage that is determined by the RF impedance of the substrate holder to ground. Through a voltage level shifting circuit, a detected change in the DC bias voltage, e.g., a decrease, causes the pressure controller to adjust, e.g., increase, the vacuum pressure. The change in the vacuum pressure then produces a corresponding adjustment, e.g., an increase, of the bias voltage to stabilize the bias voltage back at a predetermined level.

Doubly balanced mixer with optimized dynamic range

Abstract: A circuit for mixing first and second rf signals to produce an output signal containing a beat frequency comprises a pair of switches each of which has a four diode bridge controlled by the first rf signal. The first rf signal is coupled to a balanced current divider with common mode signal rejection. Load resistors coupled to the bridges provide matched termination of the first rf signal irrespective of the conductive state of the bridges. The value of the resistors and the characteristic impedance of the drive circuit is related to the characteristics of the diodes utilized to maximize the dynamic range of the mixer. Circuitry is provided for coupling all diodes of each bridge in series with respect to the average dc component of the first rf signal and to properly terminate the average dc component. The two diode bridges are conductive and nonconductive in opposing half cycles of the first rf signal. A hybrid has its summing port coupled to the switch port of one bridge and its difference port coupled to the switch port of the other bridge. The second rf signal is coupled to input port of the hybrid which includes a balun for balancing and rejecting common mode signals from the second rf signal. The beat frequency is provided at the output port of the hybrid which also includes a balun for rejecting common mode signals. The desired and filtered frequency components of the second rf signal are properly terminated.

Microwave 180° phase-bit device with integral loop transition

Abstract: A 180° microwave phase-bit device implemented in a stripline medium with integral transitional coupling into a waveguide by means of an H plane loop within the waveguide. The device is particularly well suited for use in digital diode phase shifters attached to waveguide feed networks, such as in the case of corporate feed of plural antenna elements within a phased array. The device is shown both independently and in connection with diode phase shifters providing intermediate values of phase shift such as 22°, 45° and 90°. PIN type radio frequency diodes would normally be used to provide the necessary switching function.

High power radio frequency tunable circuits

Abstract: A high power tunable radio frequency circuit which may be used, for example, in a power oscillator, frequency discriminator, diplexer, filter, or a multicoupler comprising a stripline distributed circuit in the influence of a variable magnetic field introduced orthogonally to the plane of the stripline circuit. The stripline is laminated between two layers of planar ferrite members and the D.C. magnetic field intensity is varied to bias the material to a predetermined but variable permeability level, thus changing the propagation velocity of the R.F. signal in the stripline and, therefore, acting to tune the device. Alternately, a microstrip embodiment may be employed utilizing a planar ferrite substrate on one side of the circuit configuration only.

Anticollision car radar

Abstract: The radar has two antennas which radiate RF signals of different frequencies and whose radiation patterns overlap The frequencies of the radiated signals are generated by amplitude-modulating a single RF signal with two low frequency signals The signals received by one of the two antennas are evaluated by determining, in an evaluating device, the difference between the amplitudes of the RF signals of different frequency which are reflected from an object A DC voltage signal proportional to the above difference is generated and the DC voltage signal is fed to a threshold circuit whose threshold is determined by a predetermined azimuth range Therefore, it can be determined if the reflecting object is in the same road lane as a car equipped with the radar

Multi-beam radio frequency array antenna

Abstract: An array antenna having a plurality of radiating elements coupled to a first plurality of radio frequency lenses, such first plurality of radio frequency lenses being coupled to receiving or transmitting apparatus through a second plurality of radio frequency lenses. With such an arrangement, sidelobes associated with any one of the radio frequency lenses in the first plurality thereof are reduced by the focusing effect of the second plurality of radio frequency lenses.

Aircraft proximity warning indicator

Abstract: An aircraft proximity warning indicator incorporating an RF receiver, optical sensor, and display is described which may receive an RF signal followed by an optical radiation pulse from another aircraft where the received RF signal is used to control the optical sensor and display so that it senses and displays the optical radiation pulse.

Decametric radio emission from four pulsars

Abstract: WE have reported earlier1 on the reception at low radio frequencies of radio pulses from three pulsars. A similar method2 was used during 1973–74, and four more pulsars were detected.

Apparatus for and method of measuring radio frequency signals

Abstract: Apparatus for detecting and measuring the values of radio frequency (RF) signals comprises two intermediate frequency (IF) channels having mixers fed by local oscillators (LO) with output frequencies having a predetermined frequency difference. The LO frequencies are selected to produce IFs from overlapping or coincident RF bands which are higher and lower, respectively, than the LO frequencies. The outputs of the mixers are measured in identical frequency discriminators, respectively, and the outputs of the discriminators are compared by logic circuits which determine the presence of signals in either or both of the channels and the value of the corresponding RF signal. This receiver eliminates the need for an RF preselector for the superheterodyne process and thereby broadens the RF bandwidth receiving capability of the system. The invention also comprehends the method of determining the value of RF signals in a receiving system which consists of dividing the RF signal into two parts, mixing the first RF part from either first or second RF bands with a first LO frequency, mixing the second RF part with a second LO frequency to produce a second IF signal from either said second or a third RF band, measuring the values of the first and second IF signals in identical frequency discriminators, and comparing the outputs of the discriminators to determine from which of the first, second, or third RF bands the signal is derived, and measuring the RF value of the signal.

Electromagnetic generation of ultrasonic waves - in specimen undergoing inspection involving reflection of ultrasound involves RF generator

Abstract: A system is used for electromagnetic generation of ultrasonic waves in a specimen undergoing inspection involving the detection of reflected ultrasonic waves. A magnet produces a constant magnetic field within the specimen. An emitting coil is connected to a radio frequency generator and mounted near the poles of the magnet thus inducing a radio frequency field in the specimen. A receiving coil is connected to a reciver and mounted near the poles of the magnet. This receives reflected ultrasonic signals from the specimen corresponding to the emitted signal. Two coils are laterally spaced relative to each other. The two coils (8) are mounted near the same pole (1) of the magnet which produces a magnetic field normal to the surface of the speciment (5).