Frequency drift

About: Frequency drift is a research topic. Over the lifetime, 5054 publications have been published within this topic receiving 56191 citations. The topic is also known as: chirp rate.

Determination of fundamental frequency of a physical oscillator by the period fitting method

Abstract: A period fitting method, which is a variant of the classical least-square fitting method, is proposed to determine the fundamental frequency of a physical oscillator. The root mean square deviation used as the criterion in this method is a single-parameter function of the fundamental frequency of the oscillator, so it makes the fitting process optimize the period fit at the expense of a lesser evaluation of the other parameters such as the amplitude and the phase. Theoretical analysis shows that this method is intrinsically independent of the disturbances of the high order harmonic frequencies oscillation, and the computer simulation experiments show that it is effective to overcome the disturbances of the finite quality factor and the monotonic drift of an oscillator system, as well as the white noise, and this method can determine the fundamental frequency or period of a physical oscillator with a relative precision of 10−7 orders.

Simple photonic-assisted radio frequency down-converter based on optoelectronic oscillator

Abstract: A photonic-assisted radio frequency (RF) down-converter integrating with the optoelectronic oscillator (OEO)-based high quality local oscillator (LO) has been proposed and experimentally demonstrated. The LO and the RF input signal are mixed at the same phase modulator and photo-detector (PD) of the OEO-loop without any additional modulator or PD. The working bandwidth of the proposed RF down-converter is nearly from 2.5 to 10 GHz. The performance of the proposed down-converter is presented and the spurious frequency dynamic range at frequency of 5.5 GHz with the LO at 6.138 GHz is measured to be 98.4 dB–Hz2/3. The influences that the frequency range and power of the RF input signal bring to the system are discussed as well.

Observations at geosynchronous orbit of a persistent Pc5 geomagnetic pulsation and energetic electron flux modulations

Abstract: . A long lasting narrow-band (4–7 mHz) Pc5 fluctuation event at geosynchronous orbit is presented through measurements from GOES-8 and GOES-10 and the response of energetic electrons with drift frequencies close to the narrow-band pulsation frequency is monitored through a spectral analysis of flux data from the LANL-SOPA energetic electron instrument. This analysis shows electron flux modulations at the magnetospheric pulsation's frequency as well as at various other frequencies in the Pc5 range, related to the particles' drift-frequencies and their harmonics. A drift resonance effect can be seen, with electron flux modulation becoming more evident in the energy channels of electrons with drift frequencies closer to the wave frequency; however no net increase or decrease in energetic electron flux is observed, indicating that the net energy transfer and transport of electrons is not significant. This Pc5 event has a long duration, being observed for more than a couple of days at geosynchronous orbit over several traversals of the two GOES satellites, and is localized in azimuthal extent. Spectral analysis shows that most of the power is in the transverse components. The frequency of the narrow-band event, as observed at geosynchronous orbit shifts during the time of the event from 7±0.5 mHz to about 4±0.5 mHz. On the ground, CARISMA magnetometers record no distinct narrow-band fluctuation in the magnetic field, and neither does Geotail, which is traversing the outer magnetosphere a few RE further out from geosynchronous orbit, at the same UT and LT that GOES-8 and -10 observe the pulsations, suggesting that that there is no connection to external fluctuations originating in the solar wind. An internal generation mechanism is suggested, such as could be provided by energetic ring current particles, even though conclusive evidence could not be provided for this particular event. Through a statistical study, it is found that this event belongs to a class of similar events, occurring predominantly in the post-noon region in the inner magnetosphere.

Method and device for transmitting magnetic resonance power

Abstract: PROBLEM TO BE SOLVED: To efficiently achieve non-contact power transmission using a coil by self-resonance. SOLUTION: A power receiving device includes a frequency characteristic detector for detecting frequency characteristics of receiving power from a power-receiving coil, and a transmitter for transmitting power frequency information comprising the maximum power frequency, where the frequency characteristics or the receiving power obtained from the frequency characteristics is maximized, to a power transmission apparatus. The power transmission apparatus includes a transmission frequency varying device for varying a frequency of transmission power, a frequency scanning device for sequentially changing a frequency of transmission power transmitted from a power-transmitting coil, a receiver for receiving the power frequency information transmitted from the transmitter, and a frequency control unit for allowing the frequency of the transmission power by the transmission frequency varying device to coincide with the detected maximum power frequency based on the power frequency information received via the receiver. COPYRIGHT: (C)2011,JPO&INPIT

Magnetic resonance spectroscopy with real-time correction of motion and frequency drift, and real-time shimming

Abstract: Disclosed are MR Spectroscopy and MR Spectroscopic Imaging (MRSI) methods comprising the sequential steps of water suppression, spatial prelocalization and spatial-spectral encoding, wherein the water suppression is modified to additionally measure and correct the frequency drift, the change in magnetic field inhomogeneity in the volume of interest, and the object movement. By inserting between the water suppression RF pulse and the dephasing gradient pulses either a phase sensitive MRI encoding module, or a 1D, 2D or 3D high-speed MRSI encoding module with simultaneous acquisition of the decaying water signal it is possible to measure frequency drift, magnetic field inhomogeneity and object movement. This information is used to dynamically change the synthesizer frequency of the scanner, the shim settings and to rotate the encoded k-space. In the preferred implementation this information is computed in real-time during the ongoing scan and via feedback loop downloaded to the acquisition control unit to update the aforementioned parameters before the subsequent data acquisition.