Patent ID: 7780590

Claim:
A method of adding or removing fluid from an implanted gastric band system through an access port, comprising: providing an external locator comprising a radio frequency transmitter/receiver for sending an interrogation signal and receiving a response; maneuvering the external locator outside a patient within whom has been implanted a fluid-actuated gastric band system having a fluid access port, the fluid access port including a radio frequency receiver/transmitter; sending an interrogation signal from the external locator to stimulate the access port receiver/transmitter to generate a response signal; adjusting the position of the external locator until the response signal indicates that a reference point on the external locator is positioned over an entrance point on the patient's body directly over the access port; passing a hypodermic needle through the entrance point and into the access port; and introducing fluid to or removing fluid from the access port using the needle, wherein the external locator includes an antenna array with an array face having four or more antennae mounted on a planar mounting element in a diamond pattern with each of the antenna being a predetermined distance from the center of the diamond pattern, the array operable by the radio frequency transmitter for transmitting the interrogation signal and receiving the response signal, and wherein the antenna array generates a difference signal for each opposing pair of the antennae based on the response signal.