Off-axis electromagnetic sensor

Abstract

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.

What is claimed is: 
     
         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.