Electrical impedance imaging

1. An apparatus for electrical impedance imaging, the apparatus comprising:

electrodes arranged on an electrode carrier in an arrangement comprising a unit of repetition that repeats over the electrode carrier and that has an angle of rotational symmetry less than 90°;

means for applying a first input electrical signal at a first input electrode pair of the electrodes;

means for detecting first output electrical signals at a first output electrode group of the electrodes;

means for applying a second input electrical signal at a second input electrode pair of the electrodes; and

means for detecting second output electrical signals at a second output electrode group of the electrodes;

wherein the second input electrode pair is aligned relative to the first input electrode pair at an angle of rotational displacement equal to one of the angles of rotational symmetry or a multiple of (one of) the angles of rotational symmetry.

2. An apparatus as claimed in claim 1 , wherein the unit of repetition overlaps from one repetition to another.

3. An apparatus as claimed in claim 1 , wherein the arrangement comprises one or more different units of repetition that each repeat over the electrode carrier and have angles of rotational symmetry less than 90°.

4. An apparatus as claimed in claim 1 , wherein the electrodes are arranged at one or more corners of each triangle of a tessellation of triangles.

5. An apparatus as claimed in claim 4 , wherein the triangles are equilateral triangles and wherein the triangles are of equal size.

6. An apparatus as claimed in claim 1 , comprising means for selecting a spacing of the electrodes of the first input electrode pair and a spacing of the electrodes of the second input electrode pair.

7. An apparatus as claimed in claim 1 , wherein the electrodes of the first input electrode pair and of the first output electrode group constitute a first electrode set having a first pattern, and the electrodes of the second input electrode pair and of the second output electrode group constitute a second electrode set having a second pattern, and wherein the second pattern is identical to the first pattern rotated by the angle of rotational displacement.

8. An apparatus as claimed in claim 7 , comprising means for selecting a number of electrodes in the first and second electrode sets and means for selecting the first pattern.

9. An apparatus as claimed in claim 8 , wherein a boundary of the first pattern is a hexagon, the hexagon having sides of length corresponding to a multiple of the length of a side of the equilateral triangles.

10. An apparatus as claimed in claim 9 , wherein the first input electrode pair comprises electrodes at opposite corners of the hexagon and the first output electrode group comprises all other electrodes of the first electrode set.

11. An apparatus as claimed in claim 1 , wherein the means for detecting the first output electrical signals is operable to detect the first output electrical signals at a plurality of combinations of electrodes of the first output electrode group, and the means for detecting the second output electrical signals is operable to detect the second output electrical signals at a plurality of combinations of electrodes of the second output electrode group.

12. An apparatus as claimed in claim 11 , comprising means for selecting a spacing of the electrodes of each of the combinations of electrodes.

13. An apparatus as claimed in claim 12 , wherein the plurality of combinations of electrodes of the first output electrode group are parallel to a line joining the electrodes of the first input electrode pair, and the plurality of combinations of electrodes of the second output electrode group are parallel to a line joining the electrodes of the second input electrode pair.

14. An apparatus as claimed in claim 13 , comprising means for applying a third input electrical signal at a third input electrode pair of the electrodes and means for detecting third output electrical signals at a third output electrode group of the electrodes, wherein the third input electrode pair is displaced from the first input electrode pair and the third output electrode group is displaced from the first output electrode group by a common distance and a common direction.

15. An apparatus as claimed in claim 1 , wherein the electrode carrier is at least part of a base of a receptacle for electrical impedance imaging of an object located within the receptacle, and wherein the receptacle comprises further electrodes arranged on a wall of the receptacle for electrical impedance imaging of an object located within the receptacle.

16. An apparatus as claimed in claim 15 , wherein the electrode carrier is rotatable relative to the wall.

17. An apparatus as claimed in claim 16 , comprising a spacing member for, spacing the object from the electrode carrier.

18. An apparatus as claimed in claim 17 , wherein the spacing member is electrically conductive and the spacing member has a conductivity less than or equal to the conductivity of the object.

19. A method of electrical impedance detection, comprising:

employing an electrode carrier having electrodes arranged on the electrode carrier in an arrangement comprising a unit of repetition that repeats over the electrode carrier and that has an angle of rotational symmetry less than 90°;

applying a first input electrical signal at a first input electrode pair of the electrodes;

detecting first output electrical signals at a first output electrode group of the electrodes;

applying a second input electrical signal at a second input electrode pair of the electrodes; and

detecting second output electrical signals at a second output electrode group of the electrodes;

wherein the second input electrode pair is aligned relative to the first input electrode pair at an angle of rotational displacement equal to one of the angles of rotational symmetry or a multiple of (one of) the angles of rotational symmetry.

20. An apparatus for electrical impedance imaging, the apparatus comprising:

electrodes arranged on an electrode carrier in an arrangement comprising a unit of repetition that repeats over the electrode carrier and that has an angle of rotational symmetry less than 90°; and

a controller configured to:

apply a first input electrical signal at a first input electrode pair of the electrodes;

detect first output electrical signals at a first output electrode group of the electrodes;

apply a second input electrical signal at a second input electrode pair of the electrodes; and

detect second output electrical signals at a second output electrode group of the electrodes;

wherein the second input electrode pair is aligned relative to the first input electrode pair at an angle of rotational displacement equal to one of the angles of rotational symmetry or a multiple of (one of) the angles of rotational symmetry.