U.S. patent application number 15/382632 was filed with the patent office on 2017-04-06 for temperature sensor structure.
The applicant listed for this patent is Cambridge Temperature Concepts Limited. Invention is credited to Shamus Husheer.
Application Number | 20170095158 15/382632 |
Document ID | / |
Family ID | 39865895 |
Filed Date | 2017-04-06 |
United States Patent
Application |
20170095158 |
Kind Code |
A1 |
Husheer; Shamus |
April 6, 2017 |
Temperature Sensor Structure
Abstract
A device for measuring temperature includes first and second
temperature sensors enclosed in a first material having one or more
material components, a contact surface for contacting a body whose
temperature is to be measured, at least part of the contact surface
being parallel to a lateral direction. The first and second
temperature sensors are arranged at different depths from the
contact surface and the net thermal conductivity across the device
from the contact surface through the first and second temperature
sensors is greater than the net lateral thermal conductivity of the
device through the first and second temperature sensors.
Inventors: |
Husheer; Shamus; (Cambridge,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Cambridge Temperature Concepts Limited |
Cambridge |
|
GB |
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|
Family ID: |
39865895 |
Appl. No.: |
15/382632 |
Filed: |
December 17, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13061191 |
Mar 21, 2011 |
9562811 |
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PCT/EP2009/061096 |
Aug 27, 2009 |
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15382632 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 2562/0271 20130101;
G01K 1/14 20130101; G01K 1/16 20130101; G01K 13/002 20130101; A61B
2562/043 20130101; G01K 1/165 20130101; G01K 7/42 20130101; A61B
5/01 20130101 |
International
Class: |
A61B 5/01 20060101
A61B005/01; G01K 7/42 20060101 G01K007/42; G01K 1/16 20060101
G01K001/16; G01K 13/00 20060101 G01K013/00; G01K 1/14 20060101
G01K001/14 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 28, 2008 |
GB |
0815694.5 |
Claims
1. A device for measuring temperature comprising: first and second
temperature sensors mounted on a circuit board and enclosed in a
material comprising a first material component and a second
material component, the first and second temperature sensors being
embedded in the first material component and the second material
component at least partially enclosing the first material component
and having a lower thermal conductivity than the first material
component; and a contact surface for contacting a body whose
temperature is to be measured; wherein the first and second
temperature sensors are arranged at different depths from the
contact surface and the net thermal conductivity across the device
from the contact surface through the first and second temperature
sensors is greater than the net thermal conductivity of the device
in lateral directions parallel to the contact surface; wherein the
circuit board extends substantially across the first material
component between the first and second temperature sensors, the
circuit board and first material component having substantially the
same thermal conductivity of at least 0.5 W/mK.
2. A device as claimed in claim 1, wherein the first material
component has a greater thermal conductivity than the second
material component by a factor of at least 4.
3. A device as claimed in claim 1, wherein the second material
component completely encloses the first material component.
4. A device as claimed in claim 3, wherein the second material
component is thicker over the lateral extremities of the first
material component than over the contact surface and its opposing
surface.
5. A device as claimed in claim 1, wherein the first material
component is substantially disc-shaped and the plane of the disc is
substantially parallel to the contact surface.
6. A device as claimed in claim 5, wherein the second material
component forms a ring-shaped annulus about the disc-shaped first
material, the plane of the ring being substantially coincident with
the plane of the disc.
7. A device as claimed in claim 1, wherein each depth is a distance
from the contact surface to the respective temperature sensor along
an axis substantially perpendicular to the contact surface.
8. A device as claimed in claim 1, wherein each depth is a thermal
depth defined by the net thermal conductance from the contact
surface to the respective temperature sensor.
9. A device as claimed in claim 8, wherein the first and second
temperature sensors are at the same distance from the contact
surface along an axis substantially perpendicular to the contact
surface.
10. A device as claimed in claim 1, wherein a surface of the first
material component provides at least part of said contact
surface.
11. A device as claimed in claim 1, wherein the first material
component comprises at least first and second material parts having
different thermal conductivities, the first temperature sensor
being embedded in the first material part and the second
temperature sensor being embedded in the second material part.
12. A device as claimed in claim 11, wherein at least part of the
contact surface is provided by the first and second material
parts.
13. A device as claimed in claim 1, wherein the net thermal
conductivity across the device is lowest in the lateral
directions.
14. A device as claimed in claim 1, wherein the first material
component is a thermally conductive polymer.
15. A device as claimed in claim 1, wherein, in use, a surface of
the first material component remote from said contact surface is
exposed.
16. A device as claimed in claim 15, wherein said remote surface
supports a thin layer having a higher thermal conductivity than the
first material.
17. A device as claimed in claim 1, wherein the first material
component has a thermal conductivity of 3 W/mK.
18. A device as claimed in claim 1, wherein the first material
component has a greater thermal conductivity than the second
material component by a factor of at least 10.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to a device for measuring
temperature, particularly the temperature of an animal or human
body.
[0002] Sensors for measuring temperature are well known and include
thermistors, thermocouples and semiconductor-based electronic
sensors. If correctly calibrated, such sensors can provide an
indication of the temperature of an object in the region from which
the sensor takes its inputs. For example, a thermistor placed in
direct contact with an object will give an indication of the
temperature of that part of the object with which the sensor is in
contact.
[0003] Often, an object does not have a uniform temperature and its
measured temperature varies throughout its volume. For example, the
temperature of an animal or human typically varies from its core
body temperature to skin temperature. Skin temperature can vary
considerably with environmental conditions and it is therefore the
core body temperature which is typically more important for medical
and diagnostic applications. However, it is not always possible or
convenient to measure core body temperature directly by invasive
means. It is preferable to make one or more measurements of an
easily accessible part of the body (such as skin temperature) and
estimate core body temperature from those measurements.
[0004] US Patent Application No. 2007/0282218 discloses a device
for measuring the local temperature of an external surface of a
body using at least two temperature sensors separated by an
insulating layer. The measurements may be used to calculate core
body temperature by correcting for a difference between core body
temperature and local temperature. Algorithms for performing such a
correction in dependence on known thermal characteristics of the
body are well known in the art (for example, see "Computation of
mean body temperature from rectal and skin temperatures", Journal
Applied Physiology 31: 484-489, 1971).
[0005] An example of a conventional device 12 for measuring the
temperature of a body 11 is shown in FIG. 1. Temperature sensors 13
and 14 are arranged at different distances from the external
surface 18 of body 11 in material 15, and are separated by a
thermally-insulating barrier 16. The effect of thermally-insulating
barrier 16 is to cause temperature sensors 13 and 14 to attain
different equilibrium temperatures at different rates, such that a
measurement of the temperature of body 11 can be estimated from the
heat flow across the device between the first and second
sensors.
[0006] Conventional devices measure the heat flow from the subject
body into the device and require that the temperature sensors are
accurately positioned so as to properly capture the flow of heat
across the device. The accuracy of such devices is therefore
heavily dependent on the accuracy of placement of the sensors of
the device. Furthermore, the devices are readily influenced by
other sources of heat in their environment.
[0007] There is therefore a need for a device for measuring
temperature whose accuracy is less dependent on the accuracy of
placement of its temperature sensors and the proximity of other
sources of heat in its environment.
SUMMARY OF THE INVENTION
[0008] According to a first aspect of the present invention there
is provided a device for measuring temperature comprising: first
and second temperature sensors enclosed in a first material having
one or more material components; a contact surface for contacting a
body whose temperature is to be measured, at least part of the
contact surface being parallel to a lateral direction; wherein the
first and second temperature sensors are arranged at different
depths from the contact surface and the net thermal conductivity
across the device from the contact surface through the first and
second temperature sensors is greater than the net lateral thermal
conductivity of the device through the first and second temperature
sensors.
[0009] Suitably, said first material has an anisotropic thermal
conductivity. Preferably the thermal conductivity of the first
material has an anisotropy ratio of at least 2. Preferably the
first material has a maximum thermal conductivity of at least 0.5
W/m K.
[0010] Optionally, the device further comprises a second material
at least partially enclosing the first material and having a lower
thermal conductivity in the lateral direction than the first
material. Preferably the first material has a greater thermal
conductivity than the second material in the lateral direction by a
factor of at least 4.
[0011] According to a second aspect of the present invention there
is provided a device for measuring temperature comprising: a first
material having one or more material components; first and second
temperature sensors embedded in the first material; a second
material at least partially enclosing the first material and having
a lower thermal conductivity than the first material; and a contact
surface for contacting a body whose temperature is to be measured,
at least part of the contact surface being parallel to a lateral
direction; wherein the first and second temperature sensors are
arranged at different depths from the contact surface and the first
and second materials are arranged such that the net thermal
conductivity across the device from the contact surface through the
first and second temperature sensors is greater than the net
lateral thermal conductivity of the device through the first and
second temperature sensors.
[0012] The second material may completely enclose the first
material. Preferably the second material is thicker over the
lateral extremities of the first material than over the contact
surface and its opposing surface. Preferably the first material is
substantially disc-shaped and the plane of the disc is
substantially parallel with the lateral direction. Preferably the
second material forms a ring-shaped annulus about the disc-shaped
first material, the plane of the ring being substantially
coincident with the plane of the disc.
[0013] Each depth may be a distance from the contact surface to the
respective temperature sensor along an axis substantially
perpendicular to the contact surface. Alternatively, each depth is
a thermal depth defined by the net thermal conductance from the
contact surface to the respective temperature sensor. The first and
second temperature sensors may be at the same distance from the
contact surface along an axis substantially perpendicular to the
contact surface.
[0014] Preferably a surface of the first material provides at least
part of said contact surface.
[0015] Optionally, the first material comprises at least first and
second material components having different thermal conductivities,
the first temperature sensor being embedded in the first material
component and the second temperature sensor being embedded in the
second material component. Preferably at least part of the contact
surface is provided by the first and second material
components.
[0016] Preferably the net thermal conductivity across the device is
lowest in the lateral direction. Preferably the first material is a
thermally conductive polymer.
[0017] Optionally, the contact surface supports a thin layer having
a higher thermal conductivity than the first material. Preferably,
in use, a surface of the first material remote from said contact
surface is exposed. Optionally, said remote surface supports a thin
layer having a higher thermal conductivity than the first
material.
DESCRIPTION OF THE DRAWINGS
[0018] The present invention will now be described by way of
example with reference to the accompanying drawings, in which:
[0019] FIG. 1 is a diagram of a prior art device for measuring heat
flow from a body.
[0020] FIG. 2 is schematic diagram of a temperature measuring
device in accordance with a first embodiment of the present
invention.
[0021] FIG. 3 is a schematic diagram of a temperature measuring
device in accordance with a second embodiment of the present
invention.
[0022] FIG. 4 is a schematic diagram of a temperature measuring
device in accordance with a third embodiment of the present
invention.
DETAILED DESCRIPTION OF THE DRAWINGS
[0023] The following description is presented to enable any person
skilled in the art to make and use the invention, and is provided
in the context of a particular application. Various modifications
to the disclosed embodiments will be readily apparent to those
skilled in the art.
[0024] The general principles defined herein may be applied to
other embodiments and applications without departing from the
spirit and scope of the present invention. Thus, the present
invention is not intended to be limited to the embodiments shown,
but is to be accorded the widest scope consistent with the
principles and features disclosed herein.
[0025] The present invention provides an improved device for
measuring temperature and heat flow into or out of a subject body.
The device is particularly suitable for measuring the temperature
of a human or animal body. A measure of the heat flow from a body
combined with a measure of the temperature at the surface of that
body allows the calculation of an estimate of a temperature within
the body, if one knows something of the thermal characteristics of
the body.
[0026] For example, the core body temperature (Tcore) of a human or
animal may be estimated from a first temperature T1 taken at a
first point (such as at the skin) and a second temperature T2
measured at a second point related to the first point by a known
thermal transfer function. As is well known in the art, these
parameters allow the calculation of the heat flowing out of the
skin in this region and can be used to estimate core body
temperature Tcore by:
Tcore=T1+A(T2-T1)
[0027] Parameter A is typically an empirically determined
coefficient which depends upon the thermal characteristics of the
device (the thermal transfer function) and the body tissue.
Including higher order terms can further improve the accuracy of
this estimate. The thermal characteristics of the device can be
straightforwardly selected by design and measured precisely in the
laboratory.
[0028] FIG. 2 shows a device 28 in accordance with a first aspect
of the present invention. Temperature sensors 22 and 23 are mounted
on PCB 24, which may or may not extend across the diameter of
material component 25 in which it is embedded. PCB 24 is chosen to
have a similar thermal conductivity to material 25 such that the
effect of its presence on the flow of heat to the first and second
temperature sensors 22, 23 is minimised. Indeed, PCB 24 may be
omitted if there is some other means of connection to the sensors,
in which case material 25 extends between sensors 22 and 23.
Material 25 is partially enclosed by material 26, which has a lower
thermal conductivity than material 25.
[0029] Device 28 is configured such that material 25 provides a
contact surface 27 that is adapted to contact the body whose
temperature is to be measured (such as the skin of a human).
Surface 27 will be referred to herein as the contact surface, and
the opposing surface of a device in accordance with the present
invention, out of which heat from the body flows, will be referred
to as the outer surface. Surface 27 may support an adhesive or
other means for attaching the device to the surface of a subject
body.
[0030] In accordance with the present invention, sensors 22 and 23
are situated at different distances from contact surface 27 such
that the sensors are at different distances from body 21 (the
source of heat). Preferably sensors 22 and 23 lie on a common axis
perpendicular to contact surface 27. This configuration assumes
that the vector describing the heat gradient close to the surface
of body 21 is normal to that surface.
[0031] It is preferable that material 26 does not extend completely
over the contact or outer surfaces of the device. It is
advantageous if a surface of material 25 forms at least part of
contact surface 27 such that the material contacts body 21 in use,
and that a surface of material 25 forms at least part of outer
surface 27 such that the material is exposed to the environment,
allowing heat to flow through the device and out of that surface.
Material 26 may enclose material 25 completely, but in this
embodiment, it is preferably that material 26 is thinner over the
outer and/or contact surface, or be doped in those regions with a
more conductive material (such as a metal) so as to increase its
conductivity.
[0032] One or both of the contact and outer surfaces may support a
thin layer (typically less than 1 mm thick) of an additional
material (not shown in the figures). This additional material may
have a high thermal conductivity (for example, greater than that of
material 25 and preferably at least 10 W/mK) so as to efficiently
couple (a) the contact surface to the body whose temperature is
being measured, and/or (b) the outer surface to the ambient
environment. Alternatively, if the additional material is
sufficiently thin (preferably less than 0.25 mm), it may have a low
thermal conductivity (possibly lower than 1 W/mK) and act as a
protective layer for the respective surface, or means for
supporting (for example) an adhesive layer.
[0033] By adjusting the extent to which insulating material 26
extends over the outer surface of the device, the rates at which
the sensors reach their equilibrium temperatures can be varied. It
is envisaged that the extent to which the insulating material
extends over the outer surface is selected empirically, taking into
account the typical range of temperatures expected of the body and
environment.
[0034] The arrangement of material components 25 and 26 is chosen
such that an axis of greatest thermal conductivity across the
device is defined. In the embodiment shown in FIG. 2, the axis of
greatest thermal conductivity is roughly perpendicular to contact
surface 27, through material 25. This is because material 26, which
has a lower thermal conductivity, reduces the net thermal
conductivity in the directions parallel to contact surface 27 (i.e.
laterally). The axis of greatest thermal conductivity is preferably
coincident with the direction of heat flow out of body 21. In other
words, the direction of the vector describing the flow of heat from
body 21 is chosen to be coincident with the direction of highest
thermal conductivity of the device when the device is placed in
position on the body. In contrast with conventional device
configurations, the arrangement of the present invention helps to
minimise the leakage of heat to the sensors from the lateral
extremities of the device and ensure that it is the heat flow from
the core of the body that is measured.
[0035] It is advantageous if the thermal conductivity of material
26 is at least 4 times smaller than that of material 25, and
preferably at least 10 times smaller. Material 25 preferably has a
thermal conductivity of at least 0.5 W/mK. It is particularly
advantageous if material 25 is a thermoconductive polymer, such as
D8102 manufactured by Cool Polymers which has a thermal
conductivity of 3 W/mK. Material 26 is preferably a thermoplastic,
such as polyvinyl chloride (PVC) or polyurethane (PU).
[0036] Preferably material 25 is substantially disc-shaped having
greater extent parallel to surface 27 than normal to surface 27.
For example, an appropriate diameter for a patch for the human body
is approximately 15 mm, with the two parts of material 25 being
approximately 2.5 mm and separated by a PCB disc also 15 mm in
diameter and 1 mm thick. Preferably material 26 forms a ring-shaped
annulus about material 25, and in the present example is preferably
a coating approximately 1 mm thick over material 25.
[0037] A device as shown in FIG. 2 may be conveniently manufactured
by over-molding the temperature sensors with a thermally conductive
polymer, and then over-molding the resulting article with a
thermally insulating polymer predominantly in a ring laterally
about the disc. In embodiments in which the sensors are mounted on
a circuit board, the device may be constructed with a temperature
sensor on each side of a printed circuit board. A first
over-molding may then be performed using a polymer with thermal
characteristics similar to or more conductive than those of the
circuit board, and a second over-molding performed using a
substantially more insulating polymer. If polymer 25 in which the
PCB is embedded is particularly electrically conductive, a thin
electrically-insulating layer or film may be employed between the
PCB and the conductive polymer.
[0038] FIG. 3 shows a second embodiment of the present invention in
which sensors 22, 23 are mounted on a flexible printed circuit
board (PCB) 34. This has two advantages: firstly, device 38 can be
flexible, allowing contact surface to better conform to the
contours of the external surface of body 21; secondly, by arranging
the PCB to bend 180 degrees back upon itself (see FIG. 3), the
sensors can be positioned in material 25 such that only material 25
extends between the sensors and the flow of heat past the sensors
is not interrupted by the PCB.
[0039] FIG. 4 shows a third embodiment of the present invention in
which materials 25 and 26 of devices 28 and 38 are replaced by a
single material 45 having an anisotropic thermal conductivity.
Material 45 may comprise multiple material components arranged so
as to provide the anisotropic thermal conductivity. Sensors 22 and
23 are arranged in material 45 so as to lie substantially along the
axis of greatest thermal conductivity of the material and device
(indicated by the dashed lines in FIG. 4). Since it is typically
desired to capture the flow of heat in a normal direction out of
body 21, the axis of greatest thermal conductivity of material 45
will generally be substantially perpendicular to contact surface 27
of device 48.
[0040] It is advantageous if the axis of lowest thermal
conductivity of material 45 is substantially perpendicular to the
axis of greatest thermal conductivity so as to minimise the leakage
of heat to the sensors from the lateral portions of the device.
[0041] Suitable materials having anisotropic thermal conductivity
include thermally conductive polymers having substantially aligned
polymer chains and a material matrix of electrically conductive
components (such as metal fibres) aligned in a polymeric insulating
base material. Preferably material 45 is selected so as to have an
anisotropy ratio of at least 2: i.e. the thermal conductivity along
the axis of greatest thermal conductivity is at least twice that
along a substantially perpendicular axis of lowest thermal
conductivity. Most preferably the anisotropy ratio is at least 5.
Further advantageously, the thermal conductivity in all directions
perpendicular to the axis of greatest thermal conductivity is
substantially the same (preferably within 20%).
[0042] Contact surface 27 need not be perfectly flat and preferably
is adapted to conform to the external surface of the body whose
temperature is to be measured. If body 21 is a human or animal
body, it is advantageous if a device in accordance with the present
invention is flexible so as to allow the contact surface to
maintain a good contact with body 21 during movements of the human
or animal.
[0043] In the above embodiments, it is important that the
temperature sensors are at different depths from the contact
surface so that each sensor reaches a different equilibrium
temperature (as required by the above equation for estimating the
core temperature of a body). This depth may be the perpendicular
distance from the contact surface to the subject temperature
sensor. Alternatively, or additionally, the depth may be defined by
the "thermal depth" of the temperature sensor from the contact
surface. The thermal depth is the net thermal conductance of the
device from the contact surface to the subject temperature sensor
and varies with both the distance of the temperature sensor from
the contact surface and the thermal conductivity of the intervening
material(s).
[0044] By arranging for the thermal conductance from the contact
surface to be different for each temperature sensor, each
temperature sensor will equilibrate at a different temperature.
This can be straightforwardly achieved if material 25 comprises a
first material component in which a first temperature sensor is
enclosed and a second material component in which a second
temperature sensor is enclosed, the two material components having
different thermal conductivities. Most simply, material 25 can
comprise two halves: a first half of the first material component
containing the first temperature sensor and a second half of the
second material component containing the second temperature sensor,
with each material component extending between the respective
temperature sensor and the contact surface.
[0045] The term "perpendicular distance" as used herein shall be
taken to mean the distance from the specified point to the
specified surface along the line normal to that surface that passes
through that point.
[0046] The applicant hereby discloses in isolation each individual
feature described herein and any combination of two or more such
features, to the extent that such features or combinations are
capable of being carried out based on the present specification as
a whole in the light of the common general knowledge of a person
skilled in the art, irrespective of whether such features or
combinations of features solve any problems disclosed herein, and
without limitation to the scope of the claims. The applicant
indicates that aspects of the present invention may consist of any
such individual feature or combination of features. In view of the
foregoing description it will be evident to a person skilled in the
art that various modifications may be made within the scope of the
invention.
* * * * *