Position sensing system

Abstract

An anatomical position sensing system (,) using one or more substantially spherical transponders for measuring relative positions and distances. Transponders (P) and (S) are capable of receiving and transmitting RF signals, and communicating between themselves and with a separate CPU (,). The CPU (,) is controlled by an operator at an operator control panel (,), interacts with an alarm (,) for providing audible alerts to the operator, and a display for displaying information to the operator. The CPU (,) controls a broadband antenna (,) to transmit, at a frequency f,, a low-frequency RF power signal (,) across a wide field to energize the transponders (P) and (S). Directional components (,) and (,) intercept and energize the transponders (P) and (S). Once energized, transponder (P) transmits a range signal in all directions including component (,) at a very high RF frequency f,, extending from transponder (P) to transponder (S). Upon receipt of the range signal (,), transponder (S) emits a data signal at a very high RF frequency f,in all directions, including component (,), which is directed at the antenna (,). The distance (D) is determined by measuring the attenuation of the range signal (,) as it is received by transponder (S). Transponder (S) then modulates the value of the strength of the incoming range signal (,) onto the data signal. The CPU (,) computes the distance (D) from the incoming data signal (,) from a lookup table derived from a sequence of calibration steps prior to beginning normal operation.