Scanning Electrical Mobility Spectrometer

The measurement of particle size distributions using electrical mobility can be accelerated significantly by an alternate mode of operating mobility instruments. Rather than changing the electric field in discrete steps to select particles in a given mobility range, the electric field can be scanned continuously. The particles are classified in a time-varying electric field, but for an exponential ramp in the field strength there remains a one-to-one correspondence between the time a particle enters the classifier and the time it leaves. By this method, complete scans of mobility with as many as 100 mobility measurements have been made in 30 seconds using a differential mobility classifier with a condensation nuclei counter as a detector.