the deposit 52 and the body member 23 which could be caused by conductive glue filling the pinholes the application of insulating film 48 has been found to reduce the incidence of rejection of specimen units from a 50 percent rate of rejection found to exist where no insulating film is used to a negligible percentage when constructed as described the electrical connection of the other ends of gold wires 50 and 54 to coaxial wires 38 and 40 is facilitated in any suitable manner the particular arrangement shown in fig2 includes provision of a pair of terminal pins 58 and 60 projecting through perforated terminal pin mounting stock 62 which in turn is secured to the rear face of specimen unit 22 by adhesive tape not shown gold wires 50 and 54 are connected to the end of the pins projecting from the front side as shown in the drawing of the terminal pin mounting stock and the center conductors of coaxial wires 38 and 40 are connected to the pin ends projecting from the rear side the body of test specimen 22 is returned to electrical ground by a suitable ground connection 64 the outer conductors of coaxial wires 38 and 40 and the faraday cage 36 are returned to ground too reference is now made to fig3.