Resolution of direct space charge distribution measurement methods

Spatial resolution is a key parameter for the measurement of any distribution. In the case of space charge distribution measurements, it is difficult to compare technique performances since each technique has its own resolution definition most of the time. In this paper the resolution, in terms of position accuracy and charge discernment, is determined on the basis of a unique definition for the thermal, the pressure-wave- propagation and the electro-acoustic methods and their derived techniques. It is shown that spatial resolution is similar throughout the sample in the case of the pressure- wave-propagation or the electro-acoustic methods, except if attenuation and dispersion of elastic waves are important, but decreases as the charge position inside the sample in the case of thermal method. Elastic wave methods are therefore preferable for a given signal to noise ratio as soon as the sample thickness is larger than twice the sound velocity times the excitation rise time.