Apparatus and method for estimating body temperature

1 . An apparatus for estimating body temperature, the apparatus comprising:

a first temperature sensor configured to measure a skin surface temperature at a measurement point of a user;

a thermally conductive material on the first temperature sensor;

a second temperature sensor configured to measure a surface temperature of the thermally conductive material; and

a processor configured to:

calculate skin heat flux based on the skin surface temperature and the surface temperature of the thermally conductive material,

estimate an amount of heat that is released from a body of the user based on at least one of a heart rate, an age, a stature, and a weight of the user, estimate a centroid temperature at the measurement point of the user based on the skin surface temperature at the measurement point, and the calculated skin heat flux, and the estimated amount of heat that is released from the body of the user, and

estimate a core body temperature of the user based on the estimated centroid temperature at the measurement point.

2 . The apparatus of claim 1 , wherein at least one of the first temperature sensor and the second temperature sensor is a thermistor.

3 . The apparatus of claim 1 , wherein the processor is further configured to calculate the skin heat flux by subtracting the surface temperature of the thermally conductive material, from the skin surface temperature at the measurement point of the user.

4 . The apparatus of claim 1 , further comprising a photoplethysmography (PPG) sensor configured to measure a PPG signal from the user,

wherein the processor is further configured to estimate blood pressure of the user based on the measured PPG signal, estimate a blood flow rate of the user based on the estimated blood pressure, and estimate the centroid temperature at the measurement point of the user further based on the blood flow rate of the user.

5 . The apparatus of claim 1 , wherein the processor is further configured to estimate the centroid temperature at the measurement point of the user based further on thermal conductivity of a skin tissue of the user, and a radius of a body part at the measurement point of the user.

6 . The apparatus of claim 1 , wherein the measurement point is located at a wrist of the user, and the processor is further configured to estimate the core body temperature based on a length of an arm of the user, the centroid temperature of the wrist, a heat flux in the wrist, an arterial blood pressure, and a blood flow rate.

7 . The apparatus of claim 6 , wherein the processor is further configured to calculate the heat flux in the wrist based on a convection coefficient of blood, a mean temperature of blood, and a temperature of a blood vessel wall.

8 . The apparatus of claim 1 , further comprising a display configured to provide the user with the estimated core body temperature of the user.

9 . The apparatus of claim 1 , wherein the measurement point is a first measurement point, and the apparatus further comprises a third temperature sensor configured to measure a skin surface temperature at a second measurement point of the user,

wherein the processor is further configured to estimate the core body temperature further based on the skin surface temperature at the second measurement point of the user.

10 . The apparatus of claim 1 , wherein the processor is further configured to estimate the core body temperature further based on an ambient air temperature.

11 . A wearable device configured to be worn around a wrist of a user, the wearable device comprising:

a first contact-type temperature sensor and a second contact-type temperature sensor that are disposed apart from each other, via a thermally conductive layer provided between the first contact-type temperature sensor and the second contact-type temperature sensor; and

a processor configured to:

control the first contact-type temperature sensor to measure a skin surface temperature of the wrist;

control the second contact-type temperature sensor to measure a temperature of the thermally conductive layer;

calculate a skin heat flux based on change between the skin surface temperature of the wrist and the temperature of the thermally conductive layer;

calculate a heat flux in the wrist based on a convection coefficient of blood, a mean temperature of blood, and a temperature of a blood vessel wall;

estimate a centroid temperature of the wrist based on the skin surface temperature of the wrist and the skin heat flux; and

estimate a core body temperature of the user based on the centroid temperature of the wrist, and a length of an arm of the user.

12 . A method of estimating body temperature, the method comprising:

measuring, using a first temperature sensor, a skin surface temperature at a measurement point of a user;

measuring, using a second temperature sensor, a surface temperature of a thermally conductive material, the thermally conductive material being on the first temperature sensor;

calculating a skin heat flux based on the skin surface temperature and the surface temperature of the thermally conductive material;

estimating a centroid temperature at the measurement point based on the skin surface temperature at the measurement point, and the calculated skin heat flux, wherein the estimating of the centroid temperature at the measurement point comprises estimating an amount of heat that is released from a body of the user based on at least one of a heart rate, an age, a stature, and a weight of the user; and

estimating a core body temperature of the user based on the estimated centroid temperature at the measurement point.

13 . The method of claim 12 ,

wherein the calculating the skin heat flux comprises calculating the skin heat flux by subtracting the surface temperature of the thermally conductive material from the skin surface temperature.

14 . The method of claim 12 , wherein the estimating of the centroid temperature at the measurement point comprises:

measuring a photoplethysmography (PPG) signal from the user,

estimating blood pressure of the user based on the measured PPG signal;

estimating a blood flow rate based on the estimated blood pressure of the user, and

estimating the centroid temperature further based on the blood flow rate.

15 . The method of claim 12 , wherein the estimating the centroid temperature at the measurement point comprises estimating the centroid temperature at the measurement point based further on thermal conductivity of a skin tissue of the user and a radius of a body part at the measurement point of the user.

16 . The method of claim 12 , wherein the measurement point is located at a wrist of the user, and the estimating the core body temperature of the user comprises estimating the centroid temperature of the wrist based on a length of an arm of the user, the centroid temperature of the wrist, a heat flux in the wrist, an arterial blood pressure, and a blood flow rate.

17 . The method of claim 16 , wherein the estimating the core body temperature of the user comprises calculating the heat flux in the wrist based on a convection coefficient of blood, a mean temperature of blood, and a temperature of a blood vessel wall.

18 . A wearable device configured to be worn around a wrist of a user, the wearable device comprising:

a first temperature sensor configured to measure a skin surface temperature at a measurement point of a user;

a thermally conductive material on the first temperature sensor;

a second temperature sensor configured to measure a surface temperature of the thermally conductive material;

a photoplethysmography (PPG) sensor configured to measure a PPG signal from the user; and

a processor configured to:

calculate skin heat flux based on the skin surface temperature and the surface temperature of the thermally conductive material,

calculate a heat flux in the wrist based on a convection coefficient of blood, a mean temperature of blood, and a temperature of a blood vessel wall,

estimate blood pressure of the user based on the measured PPG signal,

estimate a blood flow rate of the user based on the estimated blood pressure,

estimate a centroid temperature at the measurement point of the user based on the skin surface temperature, the skin heat flux, and the blood flow rate, and

estimate a core body temperature of the user based on the centroid temperature at the measurement point.

19 . The wearable device of claim 18 ,

wherein the processor is further configured to calculate the skin heat flux by subtracting the surface temperature of the thermally conductive material, from the skin surface temperature at the measurement point of the user.