Capacitive Coupling to Mains Voltage Using a Foil Probe

This multisim circuit is based on experiments performed in my kitchen using my battery powered DSO138 scope and some aluminium foil to capacitativily couple to mains voltage. The foil forms a cylindrical capacitor around the live wire (with the wire insulation as the dielectric). The combination of a series capacitance with the scopes input impedance forms a high pass filter with a corner frequncy much higher than 50Hz. There is high attenuation of the observed p2p signal on the scope. The size of the signal seen on the scope increased for the larger pieces of foil used (larger coupling capacitance). The signal size also depended on how well coupled the ground probe was to earth. For the same size piece of foil, when the ground probe was held in my hand the observed signals were always greater then when the ground probe was left un-connected on the worksurface.