An instrument sterile drape includes a plastic sheet and an instrument sterile adapter (ISA) coupled to the plastic sheet. The ISA includes bottom and top plates located on opposite sides of the plastic sheet plate and joined together. A passage in the bottom plate allows an instrument carriage flux connection to pass through the plastic sheet and the bottom plate to be adjacent to the top plate. The top plate includes a signal transmission area that will be adjacent to an upper surface of the flux connection of the instrument carriage. A flux connector may close an opening in the signal transmission area of the top plate and provide a path for an electrical or optical signal. The signal transmission area of the top plate may be thinned to allow an RFID sensor to be closer to an RFID device in a surgical instrument attached to the instrument sterile adapter.