Abstract: A method and apparatus for determining planar impedance tomography of a sample comprising a measurement head unit comprising an impedance sensor; a three-axis actuator assembly, coupled to the measurement head unit, for positioning the impedance sensor relative to a sample; a controller, coupled to the three-axis actuator assembly, for controlling the three-axis actuator assembly to position the impedance sensor at a plurality of locations relative to the sample; and an impedance analyzer, coupled to the impedance sensor, for determining an impedance value at each location in the plurality of locations.

Abstract: A preferred composite which is useful at temperatures in excess of about 0.degree. C. comprising a ceramic matrix and 40-60% on volume basis of coated and uncoated fibers embedded in the matrix generally parallel to each other and in a controlled arrangement; the matrix is selected from the group consisting essentially of silicon nitride, silicon carbide and zirconium titanate; the fibers are silicon carbides fibers 5-20 microns thick; the coating on the coated fibers is boron nitride 0.1-0.3 microns thick; cross-section of the composite contains about one half, on volume basis, of uncoated fibers in one band extending from one side edge of the cross-section to the opposite side edge; the composite having unexpectedly improved strength and/or toughness compared to a composite composed of only coated or only uncoated fibers.