In this paper, a novel tomographic system for imaging the nonlinear parameter (B/A) of biological objects is described. This parameter is closely related to the detailed properties of tissue, and may well provide a new powerful tool for ultrasonic tissue characterization. In our new system, an impulsive, relatively high power (10 mW/cm2), low frequency pump wave is applied from the opposite direction of a cw low intensity probe wave of high frequency (5 MHz) so that the phase of the probe wave is modulated sequentially by the product of the nonlinear parameter (B/A) along the beam (x axis) and the pressure of the impulsive pump wave. This modulated probe wave is detected and demodulated to derive the distribution of (B/A) along the x axis. Many responses are averaged to increase the S/N ratio. Inverse or other filtering operations are applied to widen the frequency bandwidth of the pump wave. The entire system is realized in hardware. The counterbeam orientation makes the imaging system compact, with easy access to many parts of the human body. Its resolution is two times that of the perpendicular system proposed previously by us and the attenuation of the pump wave can also be compensated for easily. A practical system aimed at breast and liver diagnosis is described. The principle of the method and the system construction are described. B/A images of several objects are given.
An attractive future application of superconducting cavities is a TeV energy superconducting linear collider (TESLA). Large merits of TESLA comparing to normal conducting linear collider are to loose alignment tolerance and less wake field due to the lower frequency (1.3GH.z). The final focus also is easy by the large electron/positron population in bunches. TESLA demands up-grading field gradients of over 25 MV/m. KEK has started R&D on 1.3GHz niobium superconducting cavities since 1990. So far seven single cell cavities and two 9-cell cavities have been fabricated and tested. Parallel to them, input coupler design and niobium material study are being conducted. This paper reports the present status of KEK's efforts for TESLA.
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