Showing papers on "Radio frequency published in 2001"

RF MEMS switches and switch circuits

Abstract: MEMS switches are devices that use mechanical movement to achieve a short circuit or an open circuit in the RF transmission line. RF MEMS switches are the specific micromechanical switches that are designed to operate at RF-to-millimeter-wave frequencies (0.1 to 100 GHz). The forces required for the mechanical movement can be obtained using electrostatic, magnetostatic, piezoelectric, or thermal designs. To date, only electrostatic-type switches have been demonstrated at 0.1-100 GHz with high reliability (100 million to 10 billion cycles) and wafer-scale manufacturing techniques. It is for this reason that this article will concentrate on electrostatic switches.

Repeaters for wireless communication systems

Abstract: A repeater and associated method of use includes at least one antenna element for communicating in one direction and at least one antenna element for communicating in another direction. A radio frequency uplink path and a radio frequency downlink path are coupled between the antennas. At least one of the radio frequency uplink path or the radio frequency downlink path includes an adaptive cancellation circuit. The adaptive cancellation circuit is configured to generate a cancellation signal without requiring an injected signal. The cancellation signal, when added to a radio frequency signal in the respective uplink and downlink paths, substantially reduces feedback signals present in the radio frequency signal.

Telemetry duty cycle management system for an implantable medical device

Abstract: A telemetry system enabling radio frequency (RF) communications between an implantable medical device and an external device, or programmer, in which the RF circuitry is normally maintained in a powered down state in order to conserve power. At synchronized wakeup intervals, one of the devices designated as a master device powers up its RF transmitter to request a communications session, and the other device designated as a slave device powers up its RF transmitter to listen for the request. Telemetry is conducted using a far field or near field communication link.

Multi-channel rf energy delivery with coagulum reduction

Abstract: A system for efficient delivery of radio frequency (RF) energy to cardiac tissue with an ablation catheter used in catheter ablation, with new concepts regarding the interaction between RF energy and biological tissue. In addition, new insights into methods for coagulum reduction during RF ablation will be presented, and a quantitative model for ascertaining the propensity for coagulum formation during RF ablation will be introduced. Effective practical techniques are presented for multichannel simultaneous RF energy delivery with real-time calculation of the Coagulum Index, which estimates the probability of coagulum formation. This information is used in a feedback and control algorithm which effectively reduces the probability of coagulum formation during ablation. For each ablation channel, electrical coupling delivers an RF electrical current through an ablation electrode of the ablation catheter and a temperature sensor is positioned relative to the ablation electrode for measuring the temperature of cardiac tissue in contact with the ablation electrode. A current sensor is provided within each channel circuitry for measuring the current delivered through said electrical coupling and an information processor and RF output controller coupled to said temperature sensor and said current sensor for estimating the likelihood of coagulum formation. When this functionality is propagated simultaneously through multiple ablation channels, the resulting linear or curvilinear lesion is deeper with less gaps. Hence, the clinical result is improved due to improved lesion integrity.

Low-loss RF transport over long distances

Abstract: Electromagnetic RF energy can be transported over a kilometer or more using antennas, but the efficiency is low unless the injecting and receiving antennas are extremely large. Other means of transporting RF energy such as waveguides and coaxial lines are cumbersome, heavy, costly, and suffer large attenuation. This paper offers a different system for long-distance RF transportation. The key is to use nonradiating electromagnetic surface waves that propagate along thin metallic strips. This means of moving RF energy between two points is simple, inexpensive, lightweight, and has low attenuation. For example, the attenuation is less than 2 dB/km for an Al foil 6-cm wide and 0.002-cm thick. Thus, efficient guidance of surface waves over distances of many kilometers requires neither large antennas, waveguides, nor coaxial lines. Moreover, electric interference with the surroundings is minimized due to the large reduction in the radial extension of the electric field, and the conversion of the radiating electromagnetic waves to surface waves and back is efficient (up to 90%).

System for multi-standard RFID tags

Abstract: A reader for a radio frequency identification system capable of simultaneously reading tags operating a multiple frequencies. The reader includes a radio frequency module for each operating frequency of the tags. The radio frequency modules are coupled to a bus which is connected to an interrogator control module. Each of the radio frequency modules receives the return signal from the tags at the associated operating frequency and converts the return signal into a pulse sequence. The interrogator control module locks to and decodes the pulse sequence according to the protocol associated with the tag type.

Wireless locating and tracking systems

Abstract: A locating and tracking system (10) is provided in which the assets desired to be located and tracked are associated with either radio frequency (RF) tags (40) or radio frequency identification and radio frequency data communication (RFID/RFDC) devices (30). Depending on which device is attached to the asset, the other device is located at known locations. The RFID/RFDC devices (30) interrogate and receive signals from the RF tags (40). The received information is sent to a host computer (20). With the location of either the RF tags (40) or RFID/RFDC devices (30) known, the assets may be located and tracked. An RF tag antenna design is also provided by using a switching mechanism connected to at least two antennas.

System and method for reducing SAR values

Abstract: A system and method for reducing the Specific Absorption Rate (SAR) of a mobile communication device employs a sensor assembly for sensing when the mobile communication device is in proximity to a body such as a human body, animal body, or the like. The average power of the radio frequency electromagnetic energy radiated by the mobile communication device may then be reduced only when necessary so that the SAR value for the device is maintained below a predetermined acceptable level.

Gas Breakdown in an Atmospheric Pressure Radio-Frequency Capacitive Plasma Source

Abstract: Gas breakdown is studied in an atmospheric pressure rf capacitive plasma source developed for materials applications. At a rf frequency of 13.56 MHz, breakdown voltage is largely a function of the product of the pressure and the discharge gap spacing, approximating the Paschen curve. However, breakdown voltage varies substantially with rf frequency due to a change in the electron loss mechanism. A large increase in breakdown voltage is observed when argon, oxygen, or nitrogen is added to helium despite their lower ionization potential. Discussion is given for optimal breakdown conditions at atmospheric pressure.

Ultra-wide band radio: introducing a new technology

Abstract: UWB (ultra wide band) signaling is the modern art of reusing previously allocated RF bands by hiding signals under the noise floor. Government regulators are testing UWB emissions to ensure that adequate protection exists to current users of the communications bands, and are on the brink of authorizing its use. Technology basics for short-pulse time coded UWB and for a direct sequence UWB approach are described, and applications of UWB devices are presented. Commercial and government uses of UWB are described. Short pulse low power techniques have enabled practical through-the wall radars, centimeter precision 3D positioning and communications capabilities at high data rates.

Variable frequency automated capacitive radio frequency (RF) dielectric heating system

Abstract: A food product is heated by maintaining the food product in an AC electrical field generated by an RF signal. As the heating takes place, maximum energy is delivered to the food product using automatic impedance matching to adjust the rate of the process.

High-efficiency power modulators

Abstract: The present invention, generally speaking, incorporates the power amplifier as a fundamental constituent of a modulator, using polar modulation techniques. Thus, it is possible to achieve the combination of precision signal generation (including envelope variations) along with high energy efficiency in combinations not possible heretofore. In accordance with one embodiment of the invention, a modulated radio (passband) signal generator produces high quality signals of general type, which specifically includes signals with varying envelopes. Signals are generated with high energy efficiency in the conversion of applied DC power to output RF signal power. The result is longer battery life for products such as mobile phone handsets. Dramatically improved efficiency also allows for a dramatic reduction (10 to 1 or greater) in the size of any required heatsink for the radio transmitter, which significantly lowers both cost and size. Furthermore, continuous operation of these radio transmitters is made possible with small temperature rises using small heatsinks, or even without any heatsink components. This provides for high operating reliability, as well as for greater throughput due to the longer operating time allowed. Another aspect of the invention allows the generation of high quality signals with wide bandwidth, without the need for continuous feedback during operation. This further reduces costs by greatly simplifying the design, manufacturing, and complexity of the transmitter circuitry.

Radio frequency detection and identification system

Abstract: A system (10) is disclosed for detecting the presence of an article. The system (10) includes a transmitter (12) for radiating a first electromagnetic signal at a predetermined primary frequency and a resonant tag (20) secured to the article. The resonant tag generates a second electromagnetic signal in response to receiving the first electromagnetic signal. The second electromagnetic signal has components at the primary frequency and at a predetermined secondary frequency different from the primary frequency. The system also includes a receiver (14) for receiving the second electromagnetic signal and a computer (46) connected to an output (48) of the receiver (14). The computer (46) processes the received second electromagnetic signal and generates an output signal when the secondary frequency is detected in the second electromagnetic signal.

Stabilization of Femtosecond Lasers for Optical Frequency Metrology and Direct Optical to Radio Frequency Synthesis

Abstract: We have actively stabilized the comb of frequencies from a mode-locked femtosecond laser using a Fabry-Perot reference cavity. This technique offers the ability to synthesize a comb of highly stable radio frequencies directly from optical transitions. The measured fractional frequency instability of the components of the frequency comb relative to the reference cavity was $l5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}$ in 0.1 sec. The variation of the optical mode spacing versus frequency of the reference cavity was also directly measured using this technique.

Characterization of a coherent optical RF channelizer based on a diffraction grating

Abstract: A coherent optical RF channelizer has been constructed and characterized. The optical channelizer is based on a free-space optical diffraction grating, and utilizes coherent optical heterodyne detection to translate all of the frequency channels to a common intermediate frequency (IF). The designed optical channelizer has a 1-GHz channel spacing, and a nominal 5-GHz IF and can offer an instantaneous bandwidth greater than 100 GHz. The channelizing receiver has been characterized for its frequency response, crosstalk, and spur-free dynamic range, and the results are in a good agreement with the theoretical values.

RF signal detector circuit with reduced sensitivity to transmission line impedance mismatches

Abstract: An RF signal detector circuit and a method for monitoring the level of Radio Frequequency signals flowing through a trasmission line are disclosed. The RF detector circuit comprises: a first RF coupling device (181) connected to a transmission line (12) for receiving RF samples; and a first RF detector (201) responsive to an output of the RF coupling device (181). It is characterized in that it also comprises a further RF coupling device (182); and a further RF detector (202) responsive to said further RF coupling device (182), both said RF coupling devices (181, 182) being connected to the transmission line and placed at a distance ( I C ) from each other that is an odd multiple of one-quarter of wavelength λ.

RF power amplifiers

Abstract: In this thorough overview, Mihai Albulet presents a full account of RF amplifiers and shows that understanding large-signal RF signals is simply a matter of understanding basic principles and their applications. In addition to discussing the basic concepts used in the analysis and design of RF power amplifiers, detailed mathematical derivations indicate the assumptions and limitations of the presented results, allowing the reader to calculate their usefulness in practical designs. Covered are amplification classes, circuit topologies, bias circuits, and matching networks.

Hybrid spread spectrum method and system for wirelessly transmitting and receiving wideband digital data

Abstract: A “software” radio in the form of a system is completely configurable and controllable in real-time by software and has a coordination capability to enable scaling to network aggregate data rates in the 10s of megabits per second per base station with no interference among the multiple radios. Base stations can, in turn, be time and frequency coordinated. Scalability is provided by the addition of substantially identical relay radios at each base station. A hybrid spread spectrum method and system of the invention include a protocol which facilitates coordinated frequency hopping. The system does not dwell more than a few milliseconds at any frequency center to achieve high scalability of the system in, for example, a metropolitan area. A single coaxial cable feeds control signals, electrical power signals and RF signals to a microwave antenna to reduce system hardware and installation costs.

Apparatus and method for reading radio frequency identification transponders used for livestock identification and data collection

Abstract: A portable apparatus for reading radio frequency identification transponders such as with livestock data collection and management. The preferred embodiment includes a single wound radio frequency identification antenna coil; a radio frequency transmitter; a power control, system timing and driver including a low battery indicator, and an optical switch; a rechargeable battery; a main power switch; an infrared activation switch; a radio frequency link antenna, a receiver analog section, a micro controller, an exciter drive and a read switch; and audio feedback to confirm receipt of data.

SAW-based radio sensor systems

Abstract: Surface acoustic wave (SAW) devices can be used as identification and sensor elements (SAW transponders) for mea- suring physical quantities such as temperature, pressure, torque, acceleration, humidity, etc., that do not need any power supply and may be accessed wirelessly. The complete wireless sensor system consists of such a SAW transponder and a local radar transceiver. An RF burst transmitted by the radar transceiver is received by the antenna of the SAW transponder. The passive transponder responds with an RF signal—like a radar echo—which can be received by the front-end of the local transceiver. Amplitude, frequency, phase and time of arrival of this RF response signal carry information about the SAW reflection and propagation mechanisms which in many cases can be directly attributed to the sensor effect for a certain measurand. Usually no intersymbol interference (ISI) due to environmental echoes occur, due to the high delay time of the SAW transponder in the order of some s. The present work reviews the operating principles of such sensor systems and their state-of-the-art performance by way of some examples which include the wireless measurement of temperature, pressure, torque, acceleration, tire-road friction, magnetic field, and water content of soil. Index Terms—Acceleration, local radar transceiver, magnetic field, passive SAW transponder for sensing, pressure, temper- ature, tire-road friction, torque, water content of soil, wireless measurement.

Communication system using an aerostat tethered above the earth surface and linked to a base station by an optical fibre

Abstract: A communication system comprises a base station (27) connected to a communications network and arranged to provide a radio frequency communications signal to radio transmitting means (23) carried by an aerostat (1) tethered above the base station. The radio frequency communications signal is conveyed from the base station to the transmitting means by an optical fibre communications link (21) carried by the tether (20).

Digital generation of RF signals for wireless communications with band-pass delta-sigma modulation

Abstract: This paper demonstrates a high speed digital technique to produce binary (digital) signals that encode representative RF signals (with time varying envelope) as needed for wireless communications. Specifically, it shows that IS-95 format CDMA signals can be generated with a single bit digital data stream at 3.6 Gb/S. The technique uses band-pass delta-sigma modulation so that the quantization noise is shaped out of the frequency band of interest. This approach points the way to single-chip, DSP-based transmitters, used in conjunction with switching mode power amplifiers and simple analog filters, to implement all the functions of a wireless transmitter.

Wireless radio frequency technique design and method for testing of integrated circuits and wafers

Abstract: The present invention is for an apparatus and method for the wireless testing of Integrated Circuits and wafers. The apparatus comprises a test unit external from the wafer and at least one test circuit which is fabricated on the wafer which contains the Integrated Circuit. The test unit transmits an RF signal to power the test circuit. The test circuit, comprising a variable ring oscillator, performs a series of parametric tests at the normal operating frequency of the Integrated Circuit and transmits the test results to the test unit for analysis.

RF MEMS switch

Abstract: A radio frequency (RF) microelectromechanical systems (MEMS) switch is manufactured by independent processing and subsequent bonding together of a MEMS substrate in alignment with an RF substrate. The RF MEMS switch is designed so as to encapsulate a flexing diaphragm supporting a switch electrode used with electrostatic flexing potentials to move electrodes of the MEMS substrate up and down over an RF transmission line structure of the RF substrate. The bonded combined MEMS switch structure is used to create an encapsulated RF MEMS switch suitable for direct coupling, AC coupling, and direct modulation of RF signals. The resulting MEMS RF switch device provides a reliable, minimally distorting RF transmission line geometry, free of contamination for use in high speed RF signal switching applications well suited for advance communication RF switching requirements.

Optical clockworks and the measurement of laser frequencies with a mode-locked frequency comb

Abstract: Femtosecond laser-frequency comb techniques are vastly simplifying the measurement and synthesis of optical frequencies. A single mode-locked femtosecond laser, with its spectrum broadened by self-phase modulation in a microstructured or tapered nonlinear fiber, can produce millions of sharp laser lines in a precise evenly spaced grid spanning much of the visible and near-infrared spectrum. The absolute frequency of each line is determined by two observable radio-frequency signals. The pulse repetition rate gives the spacing of the comb lines and the rate at which the phase of the lightwave slips, relative to the intensity envelope from pulse to pulse determines the offset frequency by which each line is displaced from a precise integral multiple of the repetition frequency. This offset frequency can be measured most easily if the comb spans more than an optical octave so that one can observe a radio frequency beat note between the second harmonic of the infrared comb lines with the corresponding comb lines at the blue end. Such an optical-frequency synthesizer makes optical oscillations readily countable and provides the long-awaited compact optical clockwork for an all-optical clock.

System and method for skin treatment using electrical current

Abstract: A system and method for selective thermal treatment of skin irregularities. The system comprises one or more RF electrodes that are adapted to apply RF energy to the skin. An RF pulse generator generates voltage pulses in the RF range at the electrodes, where the voltage pulses have a duration of 2-500 ms. The method comprises applying RF electrodes to the skin and generating voltage pulses at the electrodes in the RF range, where the pulses have a duration in the range of 2-500 ms.

Hybrid polar modulator differential phase cartesian feedback correction circuit for power amplifier linearization

Abstract: The present invention, generally speaking, provides a method of obtaining very accurate estimates of the phase and amplitude distortions introduced by radio frequency or microwave power amplifiers even where polar modulation is used.

Hand-off between ultra-wideband cell sites

Abstract: Briefly, the present invention provides a dynamic channel re-assignment capability between mobile units, base stations and sectors within base station coverage areas. The wireless devices used in the present invention may include impulse radio communication devices such as, for example ultra-wideband radio (also known as digital pulse wireless) communication devices. Ultra-wideband bandwidth and channel allocation can be effectively managed, even though link quality generally deteriorates near the outer boundary of the base station. By maintaining dual communications with an adjoining base station, the present invention reduces the bit error rate and maintains signal strength (e.g., RF signal strength). This procedure is termed a “soft-handoff”.

Pulsed RF power delivery for plasma processing

Abstract: A system and method for overcoming the above-described problems relating to the delivery of pulsed RF power to a plasma processing chamber The power reflected from the chamber is reduced using one or more of the following techniques: (1) varying the RF frequency within a pulse period; (2) ramping up the pulse heights at the leading edge of the pulse train; (3) simultaneously transmitting a relatively low CW signal along with the pulsed signal; and (4) rapidly switching the shunt capacitance within a local matching network within a pulse period The amount of power delivered to the plasma by the pulses is measured by way of a time-averaging mechanism coupled to a directional coupler connected to the transmission line The time-averaging mechanism may comprise circuitry to measure temperatures of loads attached to the directional coupler, or analog integrating circuitry attached to the directional coupler, or digital integrating circuitry attached to the directional coupler