OFF-AXIS ELECTROMAGNETIC SENSOR
A sensing system includes an off-axis coil in which wire is wound in loops about a roll axis and at an angle to the roll axis. In particular, the loops define respective areas that have a normal direction at a non-zero angle relative to the roll axis. A field generator can generate a variable magnetic field through the coil, and sensor logic can be coupled to the coil and configured to determine a measurement of a roll angle of the coil about the first axis using an electrical signal induced in the coil.
1 . A sensing system comprising:
a first coil including wire that is wound in a plurality of loops around a first axis, wherein
each of the loops defines an area that has a first normal direction at a non-zero, first angle relative to the first axis.
2 . The sensing system of claim 1 , wherein the first angle exceeds 5°.
3 . The sensing system of claim 1 , wherein each of the loops includes a first part in which the wire is directed at an angle down the first axis and a second part in which the wire is wound at an angle up the first axis.
4 . The sensing system of claim 1 , further comprising:
a second coil including wire that is wound in a plurality of loops around the first axis, wherein the loops in the second coil define respective areas that have a second normal direction at a non-zero, second angle relative to the first normal direction.
5 . The sensing system of claim 4 , wherein the second angle is about 90°.
6 . The sensing system of claim 4 , wherein the first coil and the second coil are substantially identical, and the second coil has a yaw orientation that is rotated by 180° from an orientation of the first coil.
7 . The sensing system of claim 1 , further comprising:
a field generator configured to generate a varying magnetic field through the first coil; and
sensor logic coupled to receive an induced signal from the first coil, wherein the sensor logic is configured to use the signal in determining a roll angle of the sensor about the first axis.
8 . A sensing system comprising:
a first coil including wire that is wound in a plurality of loops about a first axis, wherein the loops define respective areas that have a first normal direction at a non-zero angle relative to the first axis; and
sensor logic coupled to the first coil and configured to use an electrical signal induced in the coil in determining a measurement of a roll angle about the first axis.
9 . The sensing system of claim 8 , further comprising:
a second coil including wire that is wound in a plurality of loops around the first axis, wherein the loops in the second coil define respective areas that have a second normal direction at a non-zero angle relative to the first normal direction.
10 . The sensing system of claim 9 , wherein the non-zero angle between the first normal direction and the second normal direction is about 90°.
11 . The sensing system of claim 9 , wherein the first coil and the second coil are substantially identical, and the second coil has a yaw orientation that is rotated by 180° from an orientation of the first coil.
12 . The sensing system of claim 8 , further comprising:
a field generator configured to generate a varying magnetic field through the first coil; and
sensor logic coupled to receive an induced signal from the first coil, wherein the sensor logic is configured to determine from the signal a roll angle of the sensor about the first axis.
13 . A medical system comprising:
an instrument;
a first coil in the instrument, the first coil including wire that is wound in a plurality of loops collectively defining a first core extending in a lengthwise direction of the instrument, wherein each of the loops defines an area that has a first normal direction at a non-zero, first angle relative to the lengthwise direction;
a sensing element providing an indication of a pointing direction of the instrument; and
sensor logic coupled to receive an induced signal from the first coil, wherein the sensor logic is configured to determine a roll angle of the instrument from the induced signal and the indication of the pointing direction from the sensing element.
14 . The system of claim 13 , wherein each of the loops in the first coil includes a first part in which the wire is directed at an angle down the first core and a second part in which the wire is wound at an angle up the first core.
15 . The system of claim 13 , wherein the sensing element comprises a second coil.
16 . The system of claim 15 , further comprising a field generator configured to generate a varying magnetic field through the first coil and the second coil.
17 . The system of claim 15 , wherein the second coil defines an area having a second normal direction that is along the lengthwise direction of the lumen.
18 . The system of claim 15 , wherein the second coil is a helical coil.
19 . The system of claim 13 , wherein the instrument comprises a catheter.
20 . The system of claim 13 , wherein the instrument comprises a probe, and
wherein the system further comprises a second instrument defining a lumen sized to guide the probe.
21 . The system of claim 20 , wherein the sensing element is positioned at least partially in a wall of the second instrument.
22 . The system of claim 20 , wherein the second instrument comprises a catheter.
23 . The system of claim 20 , wherein the second instrument comprises at least one of an endoscope, a bronchoscope, and a cannula.