Sensor calibration considering subject-dependent variables and/or body positions

1. A method of calibrating a sensor associated with a subject, comprising:

producing, by the sensor, a sensor vector {right arrow over (V)} associated with a body acceleration of the subject relative to a gravity vector;

calibrating the sensor vector {right arrow over (V)}, including:

processing the sensor vector {right arrow over (V)} with the subject at a first elevation angle relative to a reference to produce a first calibrated sensor vector {right arrow over (V)} S , wherein the processing of the sensor vector includes:

determining an angle α and applying rotational matrix R 1 to the sensor vector {right arrow over (V)}, wherein the rotational matrix R 1 is an XY rotation for α° around a Z axis,

determining an angle β and applying rotational matrix R 3 to the sensor vector {right arrow over (V)}, wherein the rotational matrix R 3 is a YZ rotation for β° around an X axis,

obtaining user input on an orientation of the sensor with reference to a midline of the body and determining an ideal upright sensor vector {right arrow over (V)} u ,

determining rotational matrix R s by the product of the rotational matrix R 3 and the rotational matrix R 1 , wherein the rotational matrix R s , is an intermediate rotational matrix,

applying the rotational matrix R s rotation to the ideal upright sensor vector {right arrow over (V)} u to obtain a rotated ideal upright sensor vector {right arrow over (V′ u )}, and

determining an angle ζ using {right arrow over (V′ u )} and applying the rotational matrix R 2 to the sensor vector {right arrow over (V)} to obtain the first calibrated sensor vector {right arrow over (V)} S wherein the rotational matrix R 2 includes an XY rotation for ζ° around the Z axis;

determining a second elevation angle η associated with elevation of the subject relative to the reference, wherein the determining of the second elevation angle η includes:

determining an angle δ and rotational matrix R y , wherein the rotational matrix R y is an XZ rotation for δ° around a Y axis,

applying the rotational matrix R y rotation to the sensor vector {right arrow over (V)} to obtain {right arrow over (XY)}, wherein {right arrow over (XY)} is the rotated vector on an XY plane,

determining an angle γ using reference to {right arrow over (XY)} and an ideal gravity vector on supine {right arrow over (G)} s , and

obtaining the sensor elevation angle η as a function of γ;

determining rotational matrix R x , by rotating an YZ plane of the sensor vector {right arrow over (V)} for η° around the X axis;

calculating a second calibrated sensor vector {right arrow over (V)} Sη as a function of R x , and the first calibrated sensor vector {right arrow over (V)} S ; and

determining a physiological or physical assessment of the subject using the second calibrated sensor vector {right arrow over (V)} sη .

2. The method of claim 1 , wherein:

the angle α is an arccosine of ratio of a y component to a magnitude in an XY plane of the sensor vector {right arrow over (V)};

the angle β is a function of arccosine of a ratio of the magnitude in the XY plane to an overall magnitude of the sensor vector {right arrow over (V)}; and

the angle ζ is an arccosine of the ratio of a y component to the magnitude in the XY plane of the rotated ideal upright sensor vector {right arrow over (V′)} u .

3. The method of claim 1 , wherein

the angle δ is an arccosine of the ratio of the magnitude in the XY plane to an overall magnitude of the sensor vector {right arrow over (V)}; and

the angle γ is an arccosine of the ratio of a dot product of {right arrow over (XY)} and {right arrow over (G)} s to the magnitude of {right arrow over (XY)}.

4. The method of claim 1 , wherein the determination of the second elevation angle η includes receiving an input of a body elevation angle ε of the subject.

5. A system to calibrate a sensor associated with a subject, comprising:

a processor; and

a memory device coupled to the processor, wherein the memory device includes an application that, when executed by the processor, causes the processor to:

determine a sensor vector {right arrow over (V)} associated with body acceleration of the subject relative to a gravity vector;

calibrate the sensor vector {right arrow over (V)}, including:

processing the sensor vector {right arrow over (V)} with the subject at a first elevation angle relative to a reference to produce a first calibrated sensor vector {right arrow over (V)} s , wherein the processing of the sensor vector includes:

determining an angle α and applying rotational matrix R 1 to the sensor vector {right arrow over (V)}, wherein the rotational matrix R 1 is an XY rotation for α° around a Z axis,

determining an angle β and applying rotational matrix R 3 to the sensor vector {right arrow over (V)}, wherein the rotational matrix R 3 is a YZ rotation for β° around an X axis,

obtaining user input on an orientation of the sensor with reference to a midline of the body and determining an ideal upright sensor vector {right arrow over (V)} u ,

determining rotational matrix R s by the product of the rotational matrix R 3 and the rotational matrix R 1 , wherein the rotational matrix R s , is an intermediate rotational matrix,

applying the rotational matrix R s rotation to the ideal upright sensor vector {right arrow over (V)} u , to obtain a rotated ideal upright sensor vector {right arrow over (V′ u )}, and

determining an angle ζ using {right arrow over (V′ u )} and applying rotational matrix R 2 to the sensor vector {right arrow over (V)} to obtain the first calibrated sensor vector {right arrow over (V)} S , wherein the rotational matrix R 2 includes an XY rotation for ζ° around the Z axis;

determining a second elevation angle η associated with elevation of the subject relative to the reference, wherein the determining of the second elevation angle η includes:

determining an angle δ and rotational matrix R y , wherein the rotational matrix R y is an XZ rotation for δ° around a Y axis,

applying the rotational matrix R y rotation to the sensor vector {right arrow over (V)} to obtain {right arrow over (XY)}, wherein {right arrow over (XY)} is the rotated vector on an XY plane,

determining an angle γ using reference to {right arrow over (XY)} and an ideal gravity vector on supine {right arrow over (G)} S , and

obtaining the sensor elevation angle η as a function of γ;

determining rotational matrix R x , by rotating an YZ plane of the sensor vector {right arrow over (V)} for η° around the X axis;

calculating a second calibrated sensor vector {right arrow over (V)} Sη as a function of R x , and the first calibrated sensor vector {right arrow over (V)} S ; and

determine a physiological or physical assessment of the subject using the second calibrated sensor vector {right arrow over (V)} sη .

6. The system of claim 5 , wherein:

the angle α is an arccosine of ratio of a y component to a magnitude in an XY plane of the sensor vector {right arrow over (V)};

the angle β is a function of arccosine of a ratio of the magnitude in the XY plane to an overall magnitude of the sensor vector {right arrow over (V)}; and

the angle ζ is an arccosine of the ratio of a y component to the magnitude in the XY plane of the rotated ideal upright sensor vector {right arrow over (V′ u )}.

7. The system of claim 5 , wherein

the angle ζ is an arccosine of the ratio of the magnitude in the XY plane to an overall magnitude of the sensor vector {right arrow over (V)}; and

the angle γ is an arccosine of the ratio of a dot product of {right arrow over (XY)} and {right arrow over (G)} s to the magnitude of {right arrow over (XY)}.

8. The system of claim 5 , wherein the determination of the second elevation angle η includes receiving an input of a body elevation angle ε of the subject.

9. A sensor device, comprising:

one or more sensors;

a structure configured to support the one or more sensors for attachment to the subject;

a processor; and

a memory device coupled to the processor, wherein the memory device includes an application that, when executed by the processor, causes the processor to:

determine a sensor vector {right arrow over (V)} associated with body acceleration of the subject relative to a gravity vector;

calibrate the sensor vector {right arrow over (V)}, including:

calibrating the sensor vector {right arrow over (V)} with the subject at a first elevation angle relative to a reference to produce a first calibrated sensor vector {right arrow over (V)} s , wherein the processing of the sensor vector includes:

determining an angle α and applying rotational matrix R 1 to the sensor vector {right arrow over (V)}, wherein the rotational matrix R 1 is an XY rotation for α° around a Z axis,

determining an angle β and applying rotational matrix R 3 to the sensor vector {right arrow over (V)}, wherein the rotational matrix R 3 is a YZ rotation for β° around an X axis,

obtaining user input on an orientation of the sensor with reference to a midline of the body and determining an ideal upright sensor vector {right arrow over (V)} u ,

determining rotational matrix R s by the product of the rotational matrix R 3 and the rotational matrix R 1 , wherein the rotational matrix R s , is an intermediate rotational matrix,

applying the rotational matrix R s rotation to the ideal upright sensor vector {right arrow over (V)} u to obtain a rotated ideal upright sensor vector {right arrow over (V′ u )}, and

determining an angle ζ using {right arrow over (V′ u )} and applying rotational matrix R 2 to the sensor vector {right arrow over (V)} to obtain the first calibrated sensor vector {right arrow over (V)} S , wherein the rotational matrix R 2 includes an XY rotation for ζ° around the Z axis;

determining a second elevation angle η associated with elevation of the subject relative to the reference, wherein the determining of the second elevation angle η includes:

determining an angle δ and rotational matrix R y , wherein the rotational matrix R y is an XZ rotation for δ° around a Y axis,

applying the rotational matrix R y rotation to the sensor vector {right arrow over (V)} to obtain {right arrow over (XY)}, wherein {right arrow over (XY)} is the rotated vector on an XY plane,

determining an angle γ using reference to {right arrow over (XY)} and an ideal gravity vector on supine {right arrow over (G)} s , and

obtaining the sensor elevation angle η as a function of γ;

determining rotational matrix R x by rotating an YZ plane of the sensor vector {right arrow over (V)} for η° around the X axis;

calculating a second calibrated sensor vector {right arrow over (V)} Sη as a function of R x and the first calibrated sensor vector {right arrow over (V)} S ; and

determine a physiological or physical assessment of the subject using the second calibrated sensor vector {right arrow over (V)} sη .

10. The sensor device of claim 9 , wherein:

the angle α is an arccosine of ratio of a y component to a magnitude in an XY plane of the sensor vector {right arrow over (V)};

the angle β is a function of arccosine of a ratio of the magnitude in the XY plane to an overall magnitude of the sensor vector {right arrow over (V)}; and

the angle ζ is an arccosine of the ratio of a y component to the magnitude in the XY plane of the rotated ideal upright sensor vector {right arrow over (V′ u )}.

11. The sensor device of claim 9 , wherein

the angle δ is an arccosine of the ratio of the magnitude in the XY plane to an overall magnitude of the sensor vector {right arrow over (V)}; and

the angle γ is an arccosine of the ratio of a dot product of {right arrow over (XY)} and {right arrow over (G)} s to the magnitude of {right arrow over (XY)}.

12. The sensor device of claim 9 , wherein the determination of the second elevation angle η includes receiving an input of a body elevation angle ε of the subject.

13. The sensor device of claim 9 , wherein the structure comprises a patch form factor.

14. The sensor device of claim 13 , wherein the structure comprises an adhesive configured to be removably attached to the subject.

15. The sensor device of claim 9 , wherein the structure comprises an adhesive configured to be removably attached to the subject.

16. The sensor device of claim 9 , further comprising a wireless transmitter configured to store or transmit the determined second elevation angle η.