Showing papers on "Radio frequency published in 1980"

Frequency-modulation spectroscopy: a new method for measuring weak absorptions and dispersions.

Abstract: A new type of wavelength-modulation laser spectroscopy is accomplished by utilizing an external phase modulator driven at radio frequencies large compared to the width of the spectral feature of interest. The spectral feature is probed by a single frequency-modulated (FM) sideband, and the associated absorption and dispersion are measured by monitoring the resulting radio-frequency beat signal. Experimental results are presented for the measurement of Fabry–Perot resonances, I2 vapor absorption lines, and saturation holes in Na vapor.

Apparatus and method for time-domain tracking of high-speed chemical reactions

Abstract: A novel apparatus and method for time-domain tracking of high-speed chemical reactions. The apparatus of this invention includes a feedback system for controlling the RF frequency of an RF radiator system to thereby provide the optimum RF frequency for heating the reaction. The apparatus and method of this invention are particularly useful in the recovery of products from oil shale wherein the oil shale is heated by RF dielectric heating and the feedback system adjusts the RF frequency as the permittivity of the oil shale changes during the heating process.

Sources of the strongest RF radiation from lightning

Abstract: Experiments performed at the Kennedy Space Center, Florida during TRIP-78 identified sources of the strongest RF radiation from lightning in the HF-VHF frequency range. Measurements were made of electric field changes associated with RF radiation using a field change system triggered on the output of an RF detector. The field changes associated with the strongest RF radiation are very fast (10 - 20 microseconds), bipolar pulses having an initial negative going half-cycle followed by a positive overshoot. These fast pulses consistently produced more RF radiation than was associated with return strokes, and their shape was remarkably consistent, independent of frequency.

Nuclear magnetic resonance systems

Abstract: Nuclear magnetic resonance methods have been proposed for examination of large bodies, including medical examination of patients. These include so-called steady state free precession methods. Such methods involve alternating excitation of a region of the body in such a way that an equilibrium condition is established at which a mean resonance signal is detectable. Typically for excitation of a planar region a radio frequency excitation field is provided in the presence of a field having an alternating gradient so that equilibrium is only reached in the plane. It is now proposed to achieve the same result by the application of two radio frequency fields having opposing gradients and pulsed in alternation to balance substantially only in the plane and provide equilibrium only there. The fields are provided by respective sets of saddle shaped coils divided into pairs of unequal dimension (1a, 1b, 2a, 2b) to provide the respective gradients.

Connector for electromagnetic impulse suppression

Abstract: A connector is provided for the suppression of electromagnetic impulses traveling a radio frequency cable. Paired first and second electrical connectors are provided for being operatively interposed along the signal cable. A spacer or mounting device is provided for electrically coupling the primary conductors and secondary conductors of one connector to their counterparts in the other paired connector. A gas discharge tube having a known breakdown voltage and a known capacitance is electrically and mechanically coupled between the first and second conductors of the mounting device. The inductance of the elements comprising the mounting device are determined such that this inductance interacts with the capacitance of the gas discharge tube and other stray capacitance of the combination thereof in order to produce a characteristic impedance which is generally equal to the characteristic impedance of the radio frequency signal cable, whereby the supressor will dissipate electrical surges while representing a low standing wave ratio to radio frequency energy being transmitted along the radio frequency signal cable.

Some heat transfer problems associated with heating by ultrasound, microwaves, or radio frequency.

Abstract: Heating deep-seated tumors requires not only deposition of energy in specific tissue volumes, but, equally important, sparing of other (normal) tissue to a point where the danger of creating “hot spots” outside the tumor volume is negligible. Accomplishing this involves difficult heat transfer problems because absorption and transmission characteristics of various tissues differ, reflections may modify intensity distributions, and blood flow characteristics differ for different tissues and may change during the treatments. The relative values of the absorption parameters are different for each modality of heat generation and usually vary for different frequencies. Thus, the final temperature distribution for a given tumor-normal-tissue geometry may vary appreciably, depending upon the mode of induction of hyperthermia. In this paper, we present a comparison of some salient features of ultrasound, microwaves, and radio-frequency (diathermy) heating. Clearly, no claim of completeness is made; our intent is to concentrate on a phenomenological description of specific aspects of the treatment modalities.

Dielectric Properties of Snow

Abstract: The dielectric properties of snow in the radio frequency range from 100 KHz to 35 GHz are reviewed. Applicable dielectric mixing formulas are discussed and compared to available experimental data.

Mapping radio sources with uncalibrated visibility data

Abstract: There are many situations in which it is possible to detect interference fringes, but with large systematic errors in amplitudes. A new method is described for mapping objects from such data. In principle this method is applicable to any system which can produce detectable fringes, and is not limited to radio frequencies.

Vehicle collision avoidance system

Abstract: An automatically guided vehicle (110) is disclosed which follows guide lines positioned in a predetermined guide path (102) on the floor. The guide path (102) includes coded markings and the vehicle comprises sensing circuitry (210) capable of sensing the markings and generating proximity signals indicative thereof. The coded markings can indicate approach of the vehicle into a "congestion" zone wherein other vehicles similarly situated can cause hazardous conditions therein. Radio frequency (RF) transmission circuitry (240) on the approaching vehicle (110) is responsive to the congestion zone indication signals to transmit and receive RF signals to and from other vehicles on the guide path (102). The approaching vehicle (110) performs various collision avoidance operations as determined by the received RF signals.

Radio‐frequency therapy: clinical experience

Abstract: The concept of utilizing radio-frequency (RF) treatment to destroy cancer tissue is based on the differential heating of cancer tissue when that portion of the body containing cancer tissue is heated by radio-frequency diathermy.' This differential heating occurs because the blood supply to cancerous tissue is sluggish, and it is the blood supply that carries away the heat and cools the heated tissue. Our anatomic investigations of tumor vascularity are diagrammatically represented in FIGURE 1. The tumor arises in vivo from a few cells that lie in the intestinal tissue supplied by a preexisting vasculature. As the tumor grows, it pushes the normal blood supply away. Tumor vasculature arises by angiogenesis, but the new vessels are only capillaries, which make connections at the periphery of the tumor only with other capillaries. The tumor vasculature is a bed of interlacing capillaries presenting high resistance to flow. Therefore, tumor perfusion is quite sensitive to perfusion pressures. Vasodilator drugs reduce blood pressure and decrease circulation through the tumor.' Heat causes extensive vasodilation in normal tissue, but since tumor tissue does not vasodilate, the differentia1 blood flow is a~centuated.~

Ultrasound Phased Array Delay Lines Based on Quadrature Sampling Techniques

Abstract: Two signal processing techniques are presented for applica- tion to ultrasonic phased array delay line systems. By using bandwidth considerations, it is shown that the signals may be either mixed to a lower frequency range or sampled at a rate commensurate with the signal bandwidth, rather than the highest frequency component, prior to delay. Both techniques lower the bandwidth requirements of the delay lines and neither require reconstructing a delayed version of the original radio frequency (W) waveform. The latter approach requires no mixers, however, as samples of the in-phase and quadrature compo- nents are obtained directly from the RF signal. The required focused signal is produced by delaying and summing the samples. It is shown that RF signals with 60 percent fractional bandwidth may be processed in this way by sampling in quadrature at only 5 of the center fre- quency. (Quadrature sampling requires that two samples be taken 90' apart with respect to the center frequency every sampling interval.) This was implemented in a four-element 5-MHz annular array system, and the results, including beam plots and tissue scans, are shown.

Power density, field intensity, and carrier frequency determinants of RF-energy-induced calcium-ion efflux from brain tissue

Abstract: To explain a carrier frequency dependence reported for radiofrequency (RF)-induced calcium-ion efflux from brain tissue, a chick-brain hemisphere bathed in buffer solution is modeled as a sphere within the uniform field of the incident electromagnetic wave. Calculations on a spherical model show that the average electric-field intensity within the sample remains the same at different carrier frequencies if the incident power density (Pi) is adjusted by an amount that compensates for the change in complex permittivity (epsilon *r) and the change of wavelength, as a function of carrier frequency. The resulting formula for transforming Pi is seen to follow the pattern of both positive and negative demonstrations of calcium-ion efflux that have been observed at carrier frequencies of 50, 147, and 450 MHz. Indeed, all results obtained at these three frequencies, when related by Pi's that produce the same average electric-field intensity within the sample, are seen to be in agreement; no prediction is contradicted by an experiment.

Occupational exposure to radio-frequency electromagnetic fields

Abstract: Occupational exposure to radio-frequency (RF) electro-magnetic (EM) fields occurs in various industrial processes. The exposure usually takes place in the near field, i.e., within one free space wavelength from the RF source. When a survey of a workplace is performed from a leakage radiation point of view, the near-field situation implies that the electric as well as the magnetic field strengths have to be monitored in order to assess the health hazard. This paper discusses the field strengths typically encountered in some of these occupational situations. Thin sheets of plastic materials can be joined or sealed by application of RF energy. The plastic welding machine, using for this purpose, usually does not have shielded electrodes and this may lead to high levels of RF fields in the immediate vicinity of the machines. The ANSI standard is exceeded in several cases near the plastic welding machines. In medicine, for instance, RF energy is used in shortwave therapy. Due to the construction of the apparatus (i.e. presence of electrodes and cables) the physiotherapist as well as the maintenance personnel may be exposed to very high levels of both E and H fields. The results of measurements of these fields in the vicinity of shortwave diathermy apparatus are discussed. The maintenance personnel working in FM/TV broadcast towers are another group of workers subject to occupational exposure of intense RF fields, and some recent studies of the exposure are presented.

Radio-frequency annealing effects in amorphous Fe 40 Ni 40 B 20

Abstract: The influence of radio frequency (rf) magnetic fields on the properties of amorphous Fe40Ni40B20 was studied using Mossbauer spectroscopy. The measurements were performed with frequencies of 67 and 53 MHz and rf field intensity in the range of 1 to 12 Oe. The narrowing of the hyperfine spectra due to the rf field and the formation of rf sidebands were observed. The effect of instability and crystallization of the amorphous metal enhanced by the rf field at temperatures much lower than the crystallization temperature was observed.

Design of a tunnel relay system with a leaky coaxial cable in an 800-MHz band land mobile telephone system

Abstract: System design of a tunnel relay system in an 800-MHz band land mobile telephone system is described. Several dozen RF signals from a base station or many different mobile units in the tunnel are directly amplified in the RF stage, without frequency conversion, by a common amplifier in the relay equipment installed near the tunnel entrance, then radiated into the tunnel through a leaky coaxial cable (LCX) or to the base station by a unidirectional antenna. Repeaters are inserted along the LCX to compensate for transmission loss in RF signal power inside the cable. Amplifying a number of RF signals simultaneously, a common amplifier generates intermodulation products and radiates spurious signals. The required amplifier linearity to suppress the spurious signals is discussed in detail. The combination of LCX and service area in the tunnel is determined according to the amplifier performance, the number of radio channels assigned to the base station, and the radio wave propagation characteristics in the tunnel.

Theoretical studies of a simulcast digital radio paging system using a carrier frequency offset strategy

Abstract: In a multistation simulcast digital radio paging system, each base station transmits the same RF signal simultaneously with the resulting efficient frequency utilization and simplified receiver design. In this system a paging receiver in the overlapping area receives several RF signals transmitted from different base stations. When frequency-shift keying (FSK) is used as a modulation method, experimental test results have already shown that the timing of each RF signal should be synchronized as closely as possible, but that the carrier frequency of each transmitter should be set following a certain offset assignment. The signal transmission performance in a multipath fading environment can then be markedly improved. The cause of this improvement effect is theoretically analyzed. It is clarified that the improvement effect is caused by transforming the probability distribution of time-averaged signal power.

Coherent dynamics of multilevel systems

Abstract: In this paper we report the results of an experimental study of the coherent dynamics (CD) of the (2J+1), with J=1, 2⋅⋅⋅6, low‐field, equally spaced Zeeman components of the oxygen molecule O322 (O16–O16) and O342 (O16–O18) driven by a radio frequency (rf) field in a supersonic molecular beam. A supersonic molecular beam magnetic resonance spectrometer has been employed in the ’’flop out’’ mode, where two intense inhomogeneous magnetic fields are antiparallel, so that the resonating Zeeman levels are defocused at the detector, diminishing the beam intensity. The experimental signal interrogates the total number of molecules in a given total angular momentum state J which changed their initial MJ component. The rf amplitude spectroscopy has been applied to study the dependence of the signal on the amplitude of the rf field for various Zeeman manifolds on‐resonance, and to investigate the dependence of the signal on the rf frequency. An analytical solution for the coherent dynamics of a spin J system driven...

Digitally tuned electrically small antenna

Abstract: An antenna system suitable for airborne use is disclosed. The system is of the type having a blade forming a folded monopole antenna with one terminal serving as a radio frequency input and a second terminal connectable to tuning apparatus. Tuning components switchable to various values are connected at the second terminal. A processor receives the value of a new frequency to be used, computes from stored reference values the values of tuning components calculated to render the antenna in tune at the selected frequency, and commands the switching of the tuning components to the calculated values. A phase discriminator at the first terminal provides the processor with an indication of the extent to which the antenna is in tune at the selected frequency. If it is not in tune, the processor iteratively commands the switching of the tuning components until new values are reached for which the antenna is in tune. Then, in response to the new tuning component values, the processor can compute and store new reference values. After some period of use, the adaptive nature of the system results in an antenna which can switch from frequency to frequency at speeds compatible with contemporary radio designs.

Passive ring laser rate of turn device with acousto-optic modulation

Abstract: A ring resonator wherein the frequency of a laser beam is altered by passing the beam through an acoustooptic modulator which is controlled by a voltage controlled oscillator (VCO) in a stabilization feedback loop. The acoustooptic modulator is capable of modulating the laser at modulation frequencies well up into the radio frequency range as is required for cavity stabilization.

Optical impedance spectroscopy

Abstract: A generalized technique of impedance spectroscopy is implemented through the detection of perturbations measured at radio frequencies in the electromagnetic impedance of a medium. The perturbations are caused by the absorption of optical photons. At low powers this offers a complementary method to existing schemes in optical spectroscopy that can be used with high sensitivity. In the limit of high powers it becomes equivalent to optogalvanic spectroscopy with several important advantages.

Method for automatically searching for an RF station

Abstract: A method of automatically searching for an RF carrier uses a synthesized frequency. The synthesized frequency is generated by a voltage controlled oscillator which is part of a phase locked loop. The phase locked loop has a programmable divider which is controlled by a phase locked loop controller. The phase locked loop controller receives inputs from a frequency discriminator which is a portion of an RF receiver which is receiving the RF signals. The search is accomplished by using a frequency sweep rather than searching for a carrier at allocated frequency positions. When the search is initiated, large frequency steps are taken until a carrier signal is passed up and then the steps are decreased in size and inversed until the carrier signal is encountered again.

Observation of radio-frequency-driven plasma current in the Octopole tokamak

Abstract: A toroidally unidirectional slow wave is launched at a frequency well above the lower hybrid resonance. The effects of the wave on the toroidal plasma current are presented and compared with predictions of quasi-linear electron Landau damping theory.

Noise blanking circuitry in a radio receiver

Abstract: A radio receiver including an RF amplifier stage arranged to receive transmitted RF signals and noise signals from an antenna, a mixer stage for converting the RF signals to intermediate frequency (IF) signals and supplying the IF signals to a blanker gate receiving blanking signals from a blanking signal source, the gate normally passing IF signals to discriminator means to demodulate the IF signals to audio signals, but decoupling the mixer stage from the demodulator when the blanking signal is present. The audio signal output from the discriminator is applied to a noise squelch circuit which detects noise frequencies above a predetermined frequency. If the predetermined frequency is exceeded, a squelch signal is generated to block or mute the audio signals. In the present invention, the squelch circuit employs an averaging detector instead of a peak detector in order to eliminate short duration spikes in the squelch circuit. The blanking signal generator circuit employs a tracking pulse detector which is immune to false triggering by maintaining the detector threshold.

Light emission of GaAs power MESFETs under RF drive

Abstract: Light emission from microwave power GaAs MESFETs was observed under rf operating conditions. It is shown that the light emission occurs at the drain side of the gate stripe and the light intensity can be correlated with the rf input drive and the output power saturation characteristic of the device.

Synchrotron Radiation as a Modulated Source for Fluorescence Lifetime Measurements and for Time-Resolved Spectroscopy

Abstract: The fundamental properties of synchrotron radiation as a spectroscopic source are enhanced by the additional quality of time modulation of the source intensity over a broad range of modulation frequencies. This time modulation is a result of the dynamics of accelerators and storage rings. It depends mainly on a balance between longitudinal focusing and damping due to the magnetic lattice and the radio frequency drive and to excitation due to the emission of synchrotron radiation. The spectral profile, state of polarization, and angular distribution of emitted radiation as a function of frequency can be calculated explicitly for any accelerator or storage ring source in terms of its known parameters. The time modulation of the emitted intensity is proportional to the electron beam current modulation seen traversing a single azimuth in the accelerator. The circulating beam in the storage ring is preserved by continuously restoring energy lost to synchrotron radiation with radio frequency (rf) power, usually in the range of from 10 to 500 MHz. In a working storage ring, although the bunch length is set primarily by the frequency of the accelerating field, the bunch shape is also modified by the magnitude of the circulating current and by the internal geometry of the vacuum chamber that contains the electron beam. The complexity of the interactions between the bunch and the walls of the vacuum chamber are such that the bunch shape is difficult to predict exactly for a new storage ring and is best determined empirically as a function of the various operating parameters of the storage ring.

Wave action device for radio frequencies

Abstract: A wave action device for beams of radio frequency waves operates as an electromagnetic lens at an electromagnetic wave relay station to redirect the electromagnetic beam in selective high concentration of the beam to one or more specific points. The device is positioned in the region of an electromagnetic wave link and intercepts the electromagnetic beam, barring that portion of the beam which forces the appearance of a null field at selected points of reception. The phase and the amplitude of the remaining portion of the intercepted electromagnetic beam are modified to redirect the remaining portion of the beam in a passive manner. The remaining portion of the beam is selectively concentrated and diverged with respect to the selected points of reception.

An Ultra Broad-Band (200 kHz-26 GHz) High-Sensitivity Probe

Abstract: The RF properties of a thin-film resistive strip in free space are derived using a transmission line analysis approach in conjunction with an appropriate equivalent circuit. The broad-band matching network for a properly chosen Schottky diode is then designed on the basis of this circuit model. Theoretical response, isotropic construction, and experimental results of the probe are presented. A 100-fold improvement in sensitivity over existing probes has been realized.

Beamed microwave power transmitting and receiving subsystems radiation characteristics

Abstract: Measured characteristics of the spectrum of typical converters and the distribution of radiated Radio Frequency (RF) energy from the terminals (transmitting antenna and rectenna) of a beamed microwave power subsystem are presented for small transmitting and receiving S-band (2.45 GHz) subarrays. Noise and harmonic levels of tube and solid-state RF power amplifiers are shown. The RF patterns and envelope of a 64 element slotted waveguide antenna are given for the fundamental frequency and harmonics through the fifth. Reflected fundamental and harmonic patterns through the fourth for a 42 element rectenna subarray are presented for various dc load and illumination conditions. Bandwidth measurements for the waveguide antenna and rectenna are shown.

Singularities of an I-V Curve and Voltage Fluctuations in "Ideal" Superconducting Nb Point Contact

Abstract: A method of constructing a point contact Josephson device with “ideal” I - V characteristics is described. Radio frequency (RF) outputs are detected with no intentionally applied external RF fields. Enhancements of output RF intensities occur at the gap and sub-gap voltages. Strong sharp peaks of RF outputs of approximately 10 -12 W are observed at lower voltage regions. Effects of thermal and shot noises are discussed in relation to the singularities of an I - V curve.