Showing papers on "Radio frequency published in 1993"

Measurements and models of radio frequency impulsive noise for indoor wireless communications

Abstract: The authors present the results of average and impulsive noise measurements inside several office buildings and retail stores. The noise measurement system operated at 918 MHz, 2.44 GHz, and 4 GHz with a nominal 40-MHz, 3-dB RF bandwidth. Omnidirectional and directional antennas were used to investigate the characteristics and sources of RF noise in indoor channels. Statistical analyses of the measurements are presented in the form of peak amplitude probability distributions, pulse duration distributions, and interarrival time distributions. Simple first-order mathematical models for these statistical characterizations are also presented. These analyses indicate that photocopiers, printers (both line printers and cash register receipt printers), elevators, and microwave ovens are significant sources of impulse noise in office and retail environments. >

Apparatus for radio frequency bipolar electrosurgery

Abstract: Surgical apparatus for bipolar diathermy has a radio frequency generator connectible to a cutting assembly which includes a support structure having a pair of electrical supply conductors and, mounted at the distal end of the support assembly, a tissue cutting head. The cutting head comprises a loop of material which is electrically conducting and has a negative temperature coefficient (NTC) of resistance, such as silicon carbide. In operation, radio frequency power from the generator causes heating of the loop to a temperature at which its resistivity rises to level which exceeds that of living tissue with the result that diathermy currents pass through the tissue. Also disclosed is a pair of forceps with electrodes made of NTC material, for cauterization.

Superconducting terahertz mixer using a transition-edge microbolometer

Abstract: We present a new device concept for a mixer element for THz frequencies. This uses a superconducting transition‐edge microbridge biased at the center of its superconducting transition near 4.2 K. It is fed from an antenna or waveguide structure. Power from a local oscillator and a rf signal produce a temperature and resulting resistance variation at the difference frequency. The new aspect is the use of a very short bridge in which rapid (<0.1 ns) outdiffusion of hot electrons occurs. This gives large intermediate frequency (if) response. The mixer offers ≊4 GHz if bandwidth, ≊80 Ω rf resistive impedance, good match to the if amplifier, and requires only 1–20 nW of local oscillator power. The upper rf frequency is determined by antenna or waveguide properties. Predicted mixer conversion efficiency is 1/8, and predicted double‐sideband receiver noise temperatures are 260 and 90 K for transition widths of 0.1 and 0.5 Tc, respectively.

Invasive system employing a radiofrequency tracking system

Abstract: An invasive imaging system employs a self-contained RF transmitter attached to an invasive device which allows tracking of the invasive device within a subject without physical connections to a tracking/display system and without the use of ionizing rays. An imaging system obtains a medical diagnostic image of the subject. The self-contained RF transmitter is comprised of a power generator means, a power conversion means such as an oscillator which converts the generated power to a radiofrequency (RF) signal, and a broadcasting means such as a tuned transmit coil for radiating the RF signal. The radiated RF signal is received by receive coils of a tracing/display means which calculates the location of the RF transmitter. The tracking/display means displays the medical diagnostic image on a monitor and superimposes a symbol on the image at a position corresponding to the calculated location of the RF transmitter. Prior to operation, the power generator may be energized inductively, photo-voltaically, or by direct contact with an external power supply. The power generator means may also be a charged battery sealed inside the RF transmitter. The RF transmitter may be implanted to track the motion of internal tissues.

Radio frequency activated charge card

Abstract: A system for changing the activation status of a selected data card such as a charge card by broadcasting an appropriate RF signal. An antenna embedded in the card detects and decodes the signal, and operates a transducer which changes the card appearance, alters magnetic stripe information, or alters the information contained within the card.

Verification of frequency scaling laws for capacitive radio‐frequency discharges using two‐dimensional simulations*

Abstract: Weakly ionized processing plasmas are studied in two dimensions using a bounded particle‐in‐cell (PIC) simulation code with a Monte Carlo collision (MCC) package. The MCC package models the collisions between charged and neutral particles, which are needed to obtain a self‐sustained plasma and the proper electron and ion energy loss mechanisms. A two‐dimensional capacitive radio‐frequency (rf) discharge is investigated in detail. Simple frequency scaling laws for predicting the behavior of some plasma parameters are derived and then compared with simulation results, finding good agreements. It is found that as the drive frequency increases, the sheath width decreases, and the bulk plasma becomes more uniform, leading to a reduction of the ion angular spread at the target and an improvement of ion dose uniformity at the driven electrode.

RF tagging system with multiple decoding modalities

Abstract: An RF tagging system includes an RF tag (10, 30) and an RF tag reader 80. The RF tag includes a plurality of RF resonant circuits. Each RF resonant circuit is resonant at a given RF frequency. A group of decoder RF resonant circuits (12, 32) have resonant frequencies defining one of a plurality of predetermined decoding modalities. A group of data RF resonant circuits (14, 34) have resonant frequencies corresponding to a predetermined identification code when the resonant frequencies of the data RF resonant circuits are decoded in accordance with the one decoding modality. The RF tag reader detects the resonant frequencies of the decoder RF resonant circuits and determines the one decoding modality. The RF tag reader is operative in each of the plurality of predetermined decoding modalities, detects the resonant frequencies of the group of data RF resonant circuits, and decodes the resonant frequencies of the group of data RF resonant circuits in accordance with the one decoding modality to provide the identification code. The decoder RF resonant circuits may also indicate the number of data RF resonant circuits on the RF tag. The RF tag reader determines the predetermined number from the decoder RF resonant circuits to confirm the accurate detection of the data RF resonant circuits. The RF tag reader, when selecting a decoding modality in accordance with the detected resonant frequencies of the decoder RF resonant circuits, determines various frequency bands and alters the RF tag reader frequency detection operation for accurate detection of the data RF resonant circuits.

Location monitoring system

Abstract: A location monitoring system is provided having a radio frequency transmitter for a person or object and radio frequency receiver for someone to monitor movement of said person or object, said receiver sounding an alarm at a predetermined time after failure to receive a signal The transmitter is made having an intermittent transmitted signal and the receiver is made having an off-timer to coordinate with said intermittent signal, said off times saving battery power The radio frequency receiver has an electronic switching means controlled by said radio frequency transmitter for sounding an alarm An antenna is located in part of the carrying strap of said transmitter The radio frequency transmitter can have various devices for sounding the alarm

A Highly Linear 1-GHz CMOS Downconversion Mixer

Abstract: A highly linear, closed loop CMOS architecture is demonstrated for the mixing of RF waveforms to baseband as sampled-data signals. In converting a 915 MHz RF waveform to a 20 MHz spread spectrum baseband signal, the measured third-order intercept lies at +27 dBm of input power. As the 1-?m CMOS prototype dissipates only 12 mW from a 5V supply, and is capable of operation at 3V, it is expected to be of use in advanced handheld wireless receivers.

High frequency semiconductor wafer processing apparatus and method

Abstract: A plasma process apparatus capacitor 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.

Radio frequency monitor for semiconductor process control

Abstract: A RF sensor for monitoring voltage, current and phase angle of a RF signal being coupled to a plasma reactor Outputs from the sensor are used to calculate various properties of the plasma These values are then utilized to characterize the process and/or used to provide feedback for in-situ control of an ongoing plasma process

Comparison of the performance of the RF cross correlation and Doppler autocorrelation technique to estimate the mean velocity of simulated ultrasound signals

Abstract: In pulsed Doppler systems the received RF (radio frequency) signal is multiplied by a quadrature reference signal and subsequently averaged over a short depth range to obtain a sample of the complex Doppler signal. The mean frequency of the sampled Doppler signal, obtained with the autocorrelation function, reflects the mean velocity of the scatterers moving through the sample volume. An alternative is to evaluate the two-dimensional cross correlation function of a short segment of the RF signals over subsequent lines, giving the mean velocity of the scatterers. Both methods of velocity estimation were applied to computer-generated RF signals with varying RF bandwidth, signal-to-noise ratio, and mean and width of the imposed velocity distribution. The length of the RF signal segment and the number of lines for velocity estimation (package length) affects the accuracy of the velocity estimate. It can be concluded that the cross correlation technique behaves superiorly especially for a low velocity dispersion. Furthermore, the standard deviation of the velocity estimate decreases for an increasing sample volume length and package length, while the performance of the conventional Doppler technique is rather independent of the length of the sample volume. The difference between both techniques decreases for a greater package length or for signals simulating a wide velocity distribution.

Unused time slot detection and selection in a mobile radio communication system

Abstract: A mobile radio communication system includes a plurality of base stations connected to a network through wire lines, and a plurality of mobile stations connected to the base stations through radio channels. The base and mobile stations share a plurality of radio frequencies and transmit at least one transmission signal at one of the shared radio frequencies. The transmission signal is arranged into time frames each having a plurality of time-division multiplexed slots. The base and mobile stations both include a control circuit having means for detecting unused time slots within the transmission signal and means for selecting one of the unused time slots. A radio channel establishing circuit establishes a channel between the mobile radio communication apparatus and the base station in accordance with the selected time slot.

Electroconvergent cautery system

Abstract: A surgical tool for surgically treating tissue in a patient comprising a radio frequency power generator for creating an alternating current having an impedance matching circuit connected thereto for matching the impedance of a surgical instrument with the radio frequency generator. A loading and tuning coil is connected to a watts/ampere meter which is connected to the impedance matching circuit. The loading and tuning coil is connected to a surgical instrument which has a tip for focusing the radio frequency current at the region of the tissue such that the tissue being contacted is instantaneously vaporized and cut and/or cauterized.

Frequency multiplication in actively mode‐locked semiconductor lasers

Abstract: We report a method that enables an external‐cavity semiconductor laser to be actively mode locked at multiples of the radio frequency (rf) drive frequency. The key to this method is the choice of the relationship between the external cavity resonance frequency and the rf drive frequency. The repetition rate of the output pulses is the lowest common multiple of the external cavity resonance frequency and the rf modulation frequency. The method has been demonstrated in a laser with a cavity resonance frequency of 1 GHz; 17 GHz pulse streams were generated using rf drive frequencies of 8.49 and 5.67 GHz.

Tuned signal detector for use with a radio frequency receiver

Abstract: Disclosed is a tuned channel detector which includes a cable path between a radio frequency source and a receiver such as a TV, wherein the radio frequency source passes first through an attenuator and second through a signal selection module comprising two opposing directional couplers and a single-pole/double-throw switch. The channel to which the TV is tuned is determined by measuring the TV's local oscillator signal from the cable which feeds the radio frequency signal to the TV and, additionally or alternatively, by comparing the signal strength of the input and reflected TV carrier signals at and around the channels under test. Signal detection is further enhanced by modulating the signal mixed with the local oscillator with a tone and/or testing only during certain intervals such as the vertical synchronization interval or the power line cycle. A tone detector having a synchronous rectifier is used to detect low level local oscillator signals. Tuned channel detection is further enhanced through the use of artificial intelligence techniques.

Principles of Communications Satellites

Abstract: Introduction to Link Budgets Orbits for Communications Satellites Radio Frequencies Modulation, Multiplexing, and Multiple Access Antennas Power, EIRP, and Illumination Transmission Losses and Power Flux Density Receivers and Noise Temperatures System Performance Telemetry, Tracking, and Command Electric Power Spacecraft Attitude Propulsion Structure Thermal Control Spacecraft Testing Reliability Index.

Analysis and design of transparent conductive coatings and filters

Abstract: Four types of transparent electrically conductive filters commonly used for a variety of applications are (1) a free-standing conducting inductive mesh, (2) a substrate coated with a conducting inductive mesh, (3) a conducting substrate, and (4) a substrate coated with a continuous conducting coating. Each can be designed to provide high visible, near infrared, and/or far infrared transmittance and high radio frequency (rf) and/or microwave attenuation. Theoretical models developed at Itek to predict the optical, rf, and electrical properties of each type of filter as a function of conductivity, relaxation time, electronic mobility, thickness, mesh period, and mesh line width are described. The temperature and angle of incidence dependence are also discussed. Simple expressions for predicting the performance of these four types of filters at both optical and rf frequencies provide both insight and useful starting designs.

Design of broad-band radar-absorbing materials for large angles of incidence

Abstract: A numerical technique, called the (modified) Powell method, is used to design radar-absorbing materials (RAMs) made up of several dielectric layers, usually on top of a conducting (ground) plane. The absorption of RF energy occurs mostly in the last layer. The other layers are used to match the wave impedance of the RAM to that of the medium on which the radiation is incident, for the desired angles of incidence, frequencies, and polarizations. The technique is very flexible, allowing the design of RAMs tailored for specific applications or general use. One important example is the design of RAMs that can maintain a minimum absorption rate from normal to almost grazing incidence, over a specified frequency bandwidth. >

Method and apparatus for radio frequency bandwidth sharing among heterogeneous radio communication system

Abstract: An etiquette controller (112) in a transmitter (14) in a first radio frequency (RF) communications system (10) enables radio frequency communications in a frequency bandwidth shared with heterogeneous RF communication systems (15). The etiquette controller (112) monitors the first RF signals in an isochronous frequency channel in a sub-band of the shared frequency bandwidth to determine whether (124) a frequency channel is free or whether (130, 136) the frequency channel comprises a communication channel which is free. In addition, the etiquette controller (112) causes the RF transceiver (102) to transmit (148) a channel relinquishment signal, monitors (150) the isochronous frequency channel for a predetermined monitoring time, and determines (152) whether the isochronous frequency channel is then free for the channel access.

Optical Frequency Metrology with Solid State Lasers

Abstract: Due to their high intrinsic stability, solid state lasers can be powerful tools for the precise measurement of optical frequencies The rapid increase in reacent years of the spectral bandwidth covered by semiconductor lasers offers new perspectives foroptical frequency measurements In the visible up to now only an interferometric comparison with the I2 stabilized HeNe laser, a secondary optical frequency standard, has been possible, and the accuracy was limited by the errors introduced by dispersion, wavefront, and calibration problems occurring in an interferometric measurement By contrast, a direct frequency comparison, the counting of the zero crossings of the beat signal between two optical frequencies, can be performed with radio frequency accuracy, that is to better than 1 Hz An absolute measurement of optical frequencies therefore only is limited by the frequency standard

Design and characterization of a radio-frequency-powered glow discharge source for double-focusing mass spectrometers

Abstract: A radio-frequency- (rf-) powered glow discharge has been interfaced to a double-focusing mass spectrometer. This type of discharge allows direct analysis of nonconducting, as well as conducting, solids. The rf discharge source and electrical system overcome several problems which have inhibited success in prior efforts. Problems of inadequate rf shielding, maintaining the necessary dc bias potential on the sample surface, preventing rf modulation of ion energies, and coupling of the accelerating potential to the discharge are resolved. Representative spectra of glass, soil, and brass matrices are presented. Preliminary relative sensitivity factors for conducting and non-conducting matrices show relatively small differences in ion yields across the periodic table. 31 refs., 9 figs., 2 tabs.

Polarization-rotation modulated, spread polarization-rotation, wide-bandwidth radio-wave communications system

Abstract: A wide bandwidth radio wave communication system having a dual feed pair of cross-polarized antennas having a common axis and being at orthogonal angles to each other. A source of RF signals is coupled to the antennas and a shifter device is between at least one of the pair of cross-polarized antennas and the source of RF signals for modulating the polarization of RF signals launched by the pair of cross-polarized antennas.

EAS System with Frequency Hopping

Abstract: An EAS system in which a transmitter transmits an RF transmitter signal into an interrogation zone and a receiver receives RF signals from the interrogation zone. The received RF signals include any RF tag signals generated by tags situated in the zone and adapted to respond to the RF transmitter signal. In order to reduce interference effects, the RF carrier frequency of the transmitter signal is adapted to take on a plurality of different frequency values during different ones of a plurality of finite dwell time periods of the RF transmitter signal.

Modeling of converter transformers using frequency domain terminal impedance measurements

Abstract: Frequency-dependent node-to-node impedance function (NIF) models of power system equipment based on systematic broad frequency range (50 Hz to 1 MHz) external driving point impedance measurements are described. Such models are needed to calculate and predict the radio frequency electromagnetic (EM) noise produced by the valve ignition of a converter station. The application of the transformer frequency-domain NIF model related to HVDC converter station EM noise calculations is demonstrated. Calculated performance data are compared with field measurements. >

Optically controlled oscillators for millimeter-wave phased-array antennas

Abstract: An approach for the design of optically synchronized millimeter-wave local oscillators based on a subharmonically injection-locked phase-lock-loop technique is introduced. The experimental results support the desired goal of frequency and phase coherency, phase shift control of millimeter-wave oscillators, and self-oscillating mixing to downconvert a millimeter-wave RF signal. Experimental results and theoretical analysis show the advantages of the proposed approach: large locking range of two subharmonically locked oscillators, lower FM noise degradation, and smaller phase error caused by frequency detuning. >

Ferroelectric scanning RF antenna

Abstract: The ferroelectric scanning RF antenna includes a ferroelectric material having conductors deposited thereon that are connected to an adjustable d.c. or a.c. voltage source. The scanning antenna is placed in an RF transmission line that includes appropriate input and output impedance matching devices such as quarter-wave transformers. The scanning section of the RF scanning antenna is constructed of two prismatic structures of a ferroelectric material. When the two prismatic structures are at the same zero bias voltage, then the RF energy passing through the antenna is not deflected and a boresight radiation pattern is obtained. Application of a bias voltage reduces the permittivity and the refractive index of the outer prismatic structure. The RF energy is refracted away from the normal at the interface between the prismatic surfaces and the radiation pattern is scanned in one direction. Application of a bias voltage reduces the permittivity and the refractive index of the inner prismatic structure. The input RF energy is refracted towards the normal at the boundary of the two prismatic surfaces and the RF radiation pattern is scanned in the opposite direction. The scanning part of the ferroelectric scanning RF antenna may be embedded as part of a monolithic microwave integrated circuit. The scanning part of the ferroelectric scanning RF antenna may be constructed of a thin ferroelectric film. The copper losses is reduced by using a high Tc superconductor material as the conducting surface. The ferroelectric material is operated in the paraelectric phase slightly above its Curie temperature.

Post detection weighted vector combining diversity receivers using phase metrics for mobile and indoor radio channels

Abstract: A digital radio communications system employs a digital information source for providing digital information such as message bits, a transmitter for transmitting encoded digital information into data symbols in a radio-frequency (RF) signal to a plurality of antennae which sense the transmitted RF signal. A post detection measure of signal quality, the signal-to-impairment ratio, (SIR), is utilized by the receiver to perform post detection combining of signals received by a plurality of antennae. The antennae are coupled to a receiver which for each received signal: digitizes the signal, determines phase angles of the digitized signal, converts the signal to unit vectors, determines a signal-to-impairment ratio (SIR) estimates γ j of the digitized signals. The SIR estimate γ j is weighted by combining weight computation element and multiplied by each unit vector to provide an in-phase is component and a quadrature component for each signal. The in-phase components are combined into a in-phase composite signal I c (n). The quadrature-phase components are combined into a quadrature-phase composite signal Q c (n). The composite signal (I c (n), Q c (n) is then decoded into phase angles which are reversed mapped to message bits which are utilized by an output device resulting in a radio communication system exhibiting improved performance during radio "fade" periods.

Observation of radio‐frequency discharges at various driving frequencies

Abstract: Radio‐frequency discharges at various driving frequencies f in the range of 1.9–28 MHz are observed, especially from the viewpoint of the sheath structure. The results reveal that for f≥10 MHz, the sheath thickness Zs measured by an emissive probe varies directly as f−1, while for f≤10 MHz, Zs∝f−1/2. The electron density estimated from the ion saturation current of a needle probe is almost proportional to f2 in the former case. High‐energy electrons accelerated by the expanding rf sheath can contribute to sustaining rf plasmas in the high‐frequency region, whereas in the low‐frequency region, secondary electrons emitted from an electrode can contribute to it in a similar manner to dc and ac discharges.