Detector systems

1. A detection system comprising a plurality of magnetic field generators and a plurality of magnetic field detectors located adjacent to a detection area, and a control system arranged to generate magnetic field using the generators, and, for each of the generators, to make measurements of the magnetic field generated using each of the detectors, a processor arranged to process the measurements to generate a plurality of sets of data characterizing the detection area as an object moves through the detection area and to combine the sets of data to form a resultant data set, wherein said resultant data set is representative of a planar image, and a displacement sensor arranged to detect a displacement of a part of the object away from a reference position, wherein the processor is arranged to correct for the displacement when combining the sets of data and wherein said correction shifts a detected feature back to the reference position.

2. A detection system according to claim 1 which is a security detection system in which the generators and detectors are mounted on support means arranged to allow a person to walk through the imaging area.

3. A detection system according to claim 1 further comprising a movement sensor arranged to measure changes of position of at least a part of an object relative to the generators and detectors and to use the changes of position when combining the sets of data.

4. A detection system according to claim 3 wherein the data sets are combined to form a combined data set that includes data for each element in a plane of elements, wherein the data for each element includes data from each data set.

5. A detection system according to claim 1 wherein the processor is arranged to combine the sets of data to produce a tomographic data set representing the object.

6. A system according to claim 1 wherein the reference position is a position relative to at least a part of the object and the displacement is a displacement relative to at least a part of the object.

7. A system according to claim 1 wherein the detectors comprise detector coils, and the control system is arranged to make the measurements by detecting electrical signals induced in the detector coils.

8. A system according to claim 1 wherein the generators comprise generator coils and the control system is arranged to generate the magnetic field by generating an electric current in the generator coils.

9. A system according to claim 1 wherein at least one of the generators is arranged to operate also as a detector.

10. A system according to claim 1 wherein at least some of the generators or detectors are arranged in a planar array.

11. A system according to claim 1 wherein the generators and the detectors are located in a floor or wall structure or building furniture.

12. A method of analyzing an object comprising providing a plurality of magnetic field generators and a plurality of magnetic field detectors located around a detection area, generating magnetic field using each of the generators, for each of the generators, making measurements of the magnetic field produced using each of the detectors, processing the measurements to generate a plurality of sets of data characterizing the detection area as an object moves through the detection area and to combine the sets of data to form a resultant data set, wherein said resultant data set is representative of a planar image, detecting a displacement of a part of the object away from a reference position, and correcting for the displacement when combining the sets of data, wherein said correction shifts a detected feature back to the reference position.

13. A method according to claim 12 in which the generators and detectors are mounted on support means arranged to allow a person to walk through the detection area.

14. A method according to claim 12 further comprising measuring changes of position of at least a part of an object relative to the generators and detectors and using the changes of position when combining the sets of data.

15. A method according to claim 12 further comprising combining the sets of data to produce a tomographic data set representing the object.

16. A method according to claim 12 wherein the reference position is a position relative to at least a part of the object and the displacement is a displacement relative to at least a part of the object.

17. A method according to claim 12 wherein the generators comprise generator coils and the magnetic fields are generated by generating electric current in the generator coils.

18. A method according to any of claim 12 wherein the detectors comprise detector coils and the magnetic fields are measured by measuring induced signals in the detector coils.