The Contrast Sensitivity Function
Prepared by Peter Wenderoth
Imagine that you are driving a car in a very thick fog. Objects which are normally easily seen, like black writing on a white billboard, will be hard to see because the black writing and the white background will both be greyish. That is the difference between whites and blacks - contrast - will be reduced
A high sensitivity vibrating reed magnetometer useful for measurements on very small ferromagnetic particles is described. The reed is made of gold wire (18 µm in diameter, 10 mm long). The mechanical vibrations of the reed are converted directly to an ac voltage by a piezoelectric ceramic. Using a lock-in amplifier magnetic moments as small as 10−9 Acm2 can be detected.
A very-high-sensitivity magnetometer is described in detail. The sensitivity of the apparatus is typically of the order of 10−9 A cm2/(Hz)1/2, so that changes in magnetic moment of 10−10 A cm2 can be detected. The magnetic moment can be calculated by simulation of the measurement system. An example of a hysteresis loop is shown. The size of the sample is determined by electron microscopy. The physical limits of the measurement system are worked out and discussed.