| 摘要 |
PURPOSE:To maintain an S/N ratio at almost the same value as in the past along with a decrease in erroneous measurement in the direction of blood stream by expanding a limit of a maximum Doppler frequency, measurable without uncertainty, more than several times than that in the past. CONSTITUTION:An average phase difference DELTAthetaG and a phase difference DELTADELTAthetaof the difference are determined from a transmission frequency f0 and a larger transmission frequency f0<1>. Among the results, the phase difference DELTADELTAtheta of the difference is large in error at a low S/N ratio. But, as a rough phase difference is determined, the phase difference DELTADELTAtheta of the difference will not exceed + or -pieven when the phase difference exceeds + or -pi between the respective transmission frequencies and a reception frequency. Thus, +2pi is added to the average phase difference DELTAthetaG using the value to correct the aliasing of the phase difference DELTAthetaG. Moreover, a correction error preventing processing is performed to correct a wrong direction of speed. |
