Apparatus and method for generating a motional signature indicative of motion of moving parts of a target machine

1. An apparatus comprising:

receiving circuitry configured to receive a signal formed from a plurality of multipath signal components, including a first set of multipath signal components that have been subjected to modulation by interaction with at least one moving part of a target machine, the first set of multipath signal components having time varying signal paths due to the interaction with said at least one moving part;

evaluation circuitry configured to generate, for at least one property of the received signal, an evaluation signal;

modification circuitry configured to produce a modified evaluation signal by applying a removal operation to at least partially remove from said evaluation signal a contribution to that evaluation signal from the plurality of multipath signal components whose associated signal paths are non-time-varying; and

processing circuitry configured to perform one or more processing operations on the modified evaluation signal to produce a motional signature indicative of the motion of said at least one moving part.

2. The apparatus as claimed in claim 1 , wherein the evaluation circuitry is arranged to generate the evaluation signal to be indicative of variation between values of said at least one property of the received signal and corresponding values of said at least one property of a further signal.

3. The apparatus as claimed in claim 2 , wherein:

the receiving circuitry comprises a first receiving circuit configured to receive said signal and a second receiving circuit, separated from the first receiving circuit, configured to receive said further signal, said further signal also formed from a plurality of multipath signal components, including a second set of multipath signal components that have been subjected to modulation by interaction with said at least one moving part.

4. The apparatus as claimed in claim 3 , wherein the first receiving circuit and the second receiving circuit are separated by a distance sufficient to ensure a difference between said signal and said further signal.

5. The apparatus as claimed in claim 2 , further comprising:

reference signal generation circuitry configured to generate a reference signal used as said further signal.

6. The apparatus as claimed in claim 2 , wherein said at least one property of the received signal comprises an amplitude and the evaluation circuitry is arranged to generate said evaluation signal having a signal value indicating a ratio of the amplitudes of the received signal and the further signal.

7. The apparatus as claimed in claim 2 , wherein said at least one property of the received signal comprises a phase and the evaluation circuitry is arranged to generate said evaluation signal having a signal value indicating a difference of the phases of the received signal and the further signal.

8. The apparatus as claimed in claim 2 , wherein the evaluation circuitry comprises phase and/or gain detector circuitry arranged to receive as inputs both the received signal and the further signal.

9. The apparatus as claimed in claim 1 , wherein said modification circuitry comprises AC coupling circuitry.

10. Theme apparatus as claimed in claim 9 , wherein said AC coupling circuitry comprises capacitor circuitry located in series between an input and an output of the modification circuitry.

11. The apparatus as claimed in claim 1 , wherein the modification circuitry is incorporated within the processing circuitry and applies a DC filtering operation on the evaluation signal after digitization of the evaluation signal.

12. The apparatus as claimed in claim 1 , wherein the first set of multipath signal components have cyclical time varying signal paths due to the interaction with said at least one moving part, which causes said first set of multipath signal components to contribute a cyclical variation to the values of said at least one property of the received signal.

13. The apparatus as claimed in claim 1 , wherein said processing circuitry is arranged to perform one or more filtering operations to generate said motional signature from the modified evaluation signal.

14. The apparatus as claimed in claim 1 , wherein the processing circuitry is arranged to generate said motional signature in at least one of a frequency domain and a time domain.

15. The apparatus as claimed in claim 1 , wherein the received signal is an electromagnetic signal.

16. The apparatus as claimed in claim 15 , wherein the received electromagnetic signal is an RF signal.

17. A method of generating a motional signature indicative of motion of at least one moving part of a target machine, comprising:

transmitting, by a transmitter, within an environment containing said target machine, a signal;

receiving a signal that is a version of the transmitted signal formed from a plurality of multipath signal components, including a set of multipath signal components that have been subjected to modulation by interaction with said at least one moving part, the set of multipath signal components having time varying signal paths due to the interaction with said at least one moving part;

generating, for at least one property of the received signal, an evaluation signal;

producing a modified evaluation signal by applying a removal operation to at least partially remove from said evaluation signal a contribution to that evaluation signal from the plurality of multipath signal components whose associated signal paths are non-time-varying; and

performing one or more processing operations on the modified evaluation signal to produce said motional signature.

18. The method as claimed in claim 17 , wherein:

said receiving, generating, producing and performing steps are performed within detector circuitry; and

said detector circuitry is placed closer to the target machine than the transmitter used to transmit said signal.

19. The method as claimed in claim 18 , wherein the transmitter is located relative to the detector circuitry so as to reduce a contribution to the received signal from the plurality of multipath signal components that are not in said set of multipath signal components.

20. The method as claimed in claim 17 , wherein the transmitted signal has a carrier frequency selected having regard to at least one property of said at least one moving part.

21. The method as claimed in claim 17 , wherein:

said transmitting step comprises transmitting a series of signals having different carrier frequencies; and

said receiving, generating, producing and performing steps are performed for each of a series of received signals corresponding to the series of transmitted signals, to produce said motional signature for each of the different carrier frequencies.

22. The method as claimed in claim 21 , wherein:

said receiving, generating, producing and performing steps are performed within detector circuitry; and

said transmitting step is arranged to switch between the signals in said series of transmitted signals under control of the detector circuitry.

23. An apparatus comprising:

means for receiving a signal formed from a plurality of multipath signal components, including a set of multipath signal components that have been subjected to modulation by interaction with at least one moving part of a target machine, the set of multipath signal components having time varying signal paths due to the interaction with said at least one moving part;

means for generating, for at least one property of the received signal, an evaluation signal;

means for producing a modified evaluation signal by applying a removal operation to at least partially remove from said evaluation signal a contribution to that evaluation signal from the plurality of multipath signal components whose associated signal paths are non-time-varying; and

means for performing one or more processing operations on the modified evaluation signal to produce a motional signature indicative of the motion of said at least one moving part.