The Optimal Distance of the Electrode to the Lifting Film Surface when Lifting Dust Footwear Impressions Using an Electrostatic Dust Print Lifter.

Abstract

Footwear impressions are one of the valuable physical evidence encountered at crime scenes and its identification can facilitate narrowing down the suspects and establishing the identity of the criminals. The technique of electrostatic lifting (ESL) dust shoeprints at crime scenes is well established with scenes of crime examiners. And in the procedure, the recovery of the original item containing the impression should be made as good as it can and not damage the marks. In this study, the different particle sizes of SiO2 were used to simulate dust and light soil residues, comparing different particle sizes and electrode positions were used to compare the adsorption ability on the surface of electrostatic lifting film in high-voltage electrostatic field for the collection of shoeprints. The results indicated that lifting film in electrostatic field will be pressed down to the dust surface, the compaction and electrostatic adsorption force will vary with the distance between the high-voltage electrode and film surface. Reducing the distance can increase the electric field strength near the lifting film, and the adsorption capacity of Mylar aluminum-plating film to dusts can be improved significantly. Adsorption capacity of the lifting film was related to the size of dust particles and significantly improved with the increase of the particle charge. The optimum distance which can get the best adsorption capacity between the electrode and film surface is from 10 to 15mm.