37 results about "Time domain algorithm" patented technology

Signals of interest in magnetic resonance imaging (MRI) systems comprise narrowband, circularly polarized (CP) radio-frequency magnetic fields from rotating atomic nuclei. Background “body noise” may comprise broadband, linearly polarized (LP) magnetic fields from thermally-activated eddy currents, and may exceed the signal in a band of interest, limiting the imaging resolution and requiring excessive averaging times. Noise may be selectively detected and substantially suppressed, while enhancing the signal of interest, using appropriate digital time-domain algorithms. At least two quadrature receiving antennas may be employed to distinguish and separate the LP noise from the CP signal. At least one broadband receiver may be used to identify and localize fast noise sources and to digitally filter the representation of their radio-frequency magnetic fields in the signal. Selective body noise reduction may allow enhanced signal-to-noise ratio of the system, leading to improved imaging resolution and shorter scan time.

The invention provides a pilot protection method of a VSC-HVDC (Voltage Source Converter-High Voltage Direct Current) power transmission circuit based on shunt capacitance parameter identification. According to the pilot protection method, internal and external faults are distinguished by identifying shunt capacitance values at two sides of the VSC-HVDC power transmission circuit by adopting a time domain algorithm. When the direct-current power transmission circuit generates an external fault, the capacitance values at two sides of the circuit can be accurately identified simultaneously; and when the direct-current power transmission circuit generates an external fault, the capacitance values at two ends of the circuit cannot be identified simultaneously. According to the characteristics, pilot protection criteria are constructed. The pilot protection method is simple in principle, easy to implement, not affected by transition resistance, circuit distributed capacitance and control modes and can be used for rapidly and reliably distinguishing the internal and external faults under various working conditions. The pilot protection method can be not only used for supplementing main protection of the traditional VSC-HVDC power transmission circuit, but also used for accelerating backup protection action. The pilot protection method provided by the invention is not only suitable for a two-end VSC-HVDC system, but also suitable for a multi-end VSC-HVDC system.

The invention belongs to the field of aeronautical material performance test, and relates to a piezoelectric crystal plate resonant frequency measurement method. According to the method, a short-term high-voltage pulse method is adopted to excite a piezoelectric crystal plate, the piezoelectric crystal plate generates response vibration, a high voltage pulse is used as wideband excitation, the piezoelectric crystal plate responds selectively to vibration, and the vibrational frequency of the piezoelectric crystal plate is the resonant frequency of the piezoelectric crystal plate. According to the method, a pure time domain algorithm is adopted, the method is direct and simple and convenient, is small in interference factor, and high in accuracy. The piezoelectric crystal plate in a certain shape corresponds to more than one resonant frequency. For example, a round crystal plate has a high-frequency thickness mold vibration resonant frequency and a low-frequency radial mold resonant frequency. The method can totally measure the resonant frequency of mold vibration in different directions.

The invention discloses an external radiation source radar direct wave recovery method adopting blind source separation. The method comprises the following steps that: (1) a linear array receives signals x1(n), ..., xN(n), and a digital wave beam is formed; (2) wave beam signals yS(n) of a reference radio station and wave beam signals y1(n), ..., yJ(n) of J interference radio stations are input into an instant ICA (independent composition analysis) blind source separation module, then output signals p0(n), p1(n), ..., pJ(n) of the blind source separation are sent to an ambiguity-resolving processing module, and obtaining the signal q(n) of the reference radio station; (3) yl(n) is input into a plurality FIR (finite impulse response) filters of a spatial domain-fast time domain module, two-dimensional self-adaptive filtering processing is carried out through a multi-dimensional spatial domain-fast time domain algorithm, and a monitoring channel signal z(n) is output and obtained; and (4) based on the signal q(n) of the reference radio station and the monitoring channel signal z(n), a time delay Doppler plane of a target is calculated. According to the invention, the sequence ambiguity problem of output signals of the blind source separation method is solved, and the reliable reference radio station direct wave recovery is ensured.

The invention provides a rapid backward projection imaging method based on offline projection, and a rapid time-domain imaging idea based on an offline projection method is provided aimed at solving the problem that a time-domain algorithm is high is computational complexity and long in time consumption. Aimed at an application scene determined according to the geometric relation of imaging and known in advance, an offline calculation manner is used to calculate and store variables needed in the backward projection algorithm in advance, the flexibility and high precision of the time-domain algorithm are maintained, and in the imaging process, the calculation steps can be reduced substantially and time consumption of imaging is reduced.