Patent ID: 7974680

Claim:
Assessment apparatus for determining a fingerprint signal of an interfering article in an energy field for a medical procedure, comprising: a set of one or more radiators, which is adapted to generate an energy field at at least one fundamental frequency; a receiving sensor, which is adapted to generate a first signal responsive to the energy field when an interfering article is at a first location relative to the receiving sensor, the first location being in a vicinity of the receiving sensor, the first signal defining a distorted signal, the receiving sensor being adapted to generate a second signal responsive to the energy field when the interfering article is at a second location relative to the receiving sensor, the second location not being in a vicinity of the receiving sensor such that the interfering article has substantially no effect on the second signal, the second signal defining a clean signal; and a control unit, which is adapted to: receive a first amplitude of the first signal and a second amplitude of the second signal from the receiving sensor, subtract the second amplitude of the second signal from the first amplitude of the first signal, in order to compute a fingerprint signal characteristic of the interfering article based on the clean signal and the distorted signal, and store, in a database, data indicative of the fingerprint signal, in association with an identity of the interfering article.