| 摘要 |
PURPOSE: To measure exact thickness of thin film such as thickness of artery wall by converting a complex electric signal received with a sensor to frequency spectrum using a personal computer(PC) and executing a specific signal processing. CONSTITUTION: An artery wall 2 has outer surface 3 and inner surface 4 and ultrasonic wave 5 transmitted from a sensor 6 is reflected at the outer surface 3 and the inner surface 4. This echo signal is received with the sensor 6 and the signal is processed with the PC 8. Firstly, the complex electric signal g(t) from the sensor 6 has a certain amplitude as a function of frequency which is converted to a frequency spectrum having a real part Re [G(f)] and an imaginary part Im [G(f)]. Then n-th absolute value of frequency spectrum|G(f)|<n> = Re[G(f)]<2> +Im[G(f)]<2> }<n/2> is calculated. Next, to separate the echo of the complex electric signal into an effective part and noise positioning at both sides, a logarithmic function of the calculated absolute value is calculated. By applying reverse conversion to the period signal of the effective part to determine an envelope, the distance is obtained from the time difference of the peak of the maximum amplitude.
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