The invention provides a sensor assembly which can sense human tissue in a protected area of a machine. An emitter plate and a plurality of sensor plates are disposed co-planar to each other and adjacent to the protected area of the machine. An electric field is generated between the emitter plate and the sensor plates and directed towards the protected area. The sensor plates produce electrical signals corresponding to the electric field received at the sensor plate. The electrical signals are amplified, measures, and analyzed to determine if human tissue is within the protected area. If human tissue is detected, a machine interface circuit will shut down the machine to prevent injury.