WO2011042679A1

WO2011042679A1 - Breath sensor

Info

Publication number: WO2011042679A1
Application number: PCT/GB2009/051349
Authority: WO
Inventors: Hans Graan
Original assignee: Autoliv Development Ab; Beattie, Alex
Priority date: 2009-10-09
Filing date: 2009-10-09
Publication date: 2011-04-14
Also published as: EP2486403A1; EP2486403B1

Abstract

A sensor comprising: a body comprising a lid and a base, the lid and base being formed from one or more materials having low thermal conductivity, the lid and base being fitted together to define an enclosure which is substantially enclosed;thin reflective layers or coatings formed on respective inner surfaces of the lid and base, the layers or coatings on the lid and base being in conductive contact with one another; a substrate on which the body is mounted, the substrate defining at least one region which is conductive to heat or current;a source of heat or current provided outside the enclosure and connected to provide current or heat to the at least one region of the substrate;a conductor protruding from the body to contact the at least one region of the substrate, to transmit heat or current from the at least one region to the reflective layers or coatings formed on the lid and the base; and a connection between the conductor and the at least one region of the substrate, the connection allowing conduction of heat or current and also allowing for variations in distance between the components of the body and the substrate arising from thermal expansion.

Description

BREATH SENSOR

Description of Invention

THIS INVENTION relates to a sensor, and in particular concerns a sensor for determining, through analysis of the breath of a subject, whether the subject is likely to have taken or consumed one or more substances, such as alcohol, which might impair the subject's ability to drive a motor vehicle.

In many countries it is illegal to carry out certain activities, such as driving a motor vehicle or operating machinery, whilst under the influence of

intoxicating substances such as alcohol. One convenient method of determining whether a subject is or maybe over the prescribed legal limit for any such substance is to analyse the exhaled breath of the subject. Many different types of breath analyser have been developed for this purpose, but most types of analyser comprise a substantially enclosed chamber into which a subject exhaled breath is directed and stored. A beam of light, for instance infrared light, is then directed through the sample chamber, and is absorbed by a detector. The presence of certain traces of substances within the exhaled breath can be analysed through investigating the regions of the light spectrum which are absorbed as the light passes through the exhaled breath.

It is often desirable for the analyser to be as small as possible, for instance if they are to be used in hand-held devices as used by the police, or for sensors which are to be installed in a vehicle dashboard to determine if an occupant or the driver maybe over the prescribed legal limit for alcohol/drugs. For this reason sensors are often arranged so that the beam of light is reflected multiple times within the chamber, so that the beam of light passes through the sample of exhaled breath several times. This can give the beam of light a relatively long effective path length through the exhaled breath, without correspondingly increasing the size of the sample chamber.

The internal surfaces of sample chambers are therefore often made to be reflective. However, exhaled breath is often at an elevated temperature when compared to the ambient air, and as freshly-exhaled breath is directed into a sample chamber condensation can often form on the reflective surfaces. This will reduce the reflectivity of the surfaces, so that reduced intensity of light reaches the detector. Clearly, this will reduce the consistency and reliability of the detector.

To overcome this difficulty, it has previously been proposed to heat the internal reflective surfaces of a sample chamber to at least around 34°C, to avoid the formation of condensation. To achieve this, a wire may be wrapped around the exterior of the sample chamber, and a current passed through the wire so that the temperature of the wire rises through resistive heating, thus heating the sample chamber and the reflective surfaces. An example of such an arrangement is shown in US5222389.

It is an object of the present invention to provide an improved sensor/analyser of this type.

Accordingly, one aspect of the present invention provides a sensor

comprising: a body comprising a lid and a base, the lid and base being formed from one or more materials having low thermal conductivity, the lid and base being fitted together to define an enclosure which is substantially enclosed; thin reflective layers or coatings formed on respective inner surfaces of the lid and base, the layers or coatings on the lid and base being in conductive contact with one another; a substrate on which the body is mounted, the substrate defining at least one region which is conductive to heat or current; a source of heat or current provided outside the enclosure and connected to provide current or heat to the at least one region of the substrate; a conductor protruding from the body to contact the at least one region of the substrate, to transmit heat or current from the at least one region to the reflective layers or coatings formed on the lid and the base; and a connection between the conductor and the at least one region of the substrate, the connection allowing conduction of heat or current and also allowing for variations in distance between the components of the body and the substrate arising from thermal expansion.

Advantageously, two regions which are conductive to heat or current are provided on the substrate, and two conductors protrude from the body to contact the respective regions of the substrate, to transmit heat or current from the regions to the reflective layers or coatings formed on the lid and the base.

Preferably, the connection comprises one or more quantities of flexible conductive material.

Conveniently, the flexible conductive material is formed from a non- conductive material having a plurality of grains or fibres of a conductive material embedded therein or coated on a surface thereof.

Advantageously, the connection comprises one or more strips of the flexible conductive material.

Preferably, the flexible conductive material comprises a polymeric material having a plurality of grains or fibres of a metal embedded therein or coated on a surface thereof. Conveniently, the conductor is provided on an extension of the lid which protrudes towards the substrate.

Advantageously, the sensor according to any preceding claim further comprising a source and a detector, the source emitting radiation which is reflected from the reflective layers or coatings formed on the inner surfaces of the lid and base before being absorbed by a detector.

Preferably, the lid and base are formed from one or more materials having low electrical conductivity.

In order that the present invention may be more readily understood, embodiments thereof will now be described, by way of example, in which:

Figure 1 shows a base of a sensor embodying the present invention;

Figure 2 shows a lid of a sensor embodying the present invention; and

Figure 3 shows the base and lid of figures 1 and 2 assembled to form a sensor.

Referring firstly to figure 1 , a base 1 of a sensor is shown. The base 1 is generally rectangular in shape, having opposing longer edges 2 and opposing shorter edges 3. The base 1 takes the form of a generally flat, planar bottom surface 4 surrounded by short upstanding walls 5 on all sides.

The base 1 is preferably provided with attachment means to allow the base 1 to be attached to a PCB 6. In the example shown in figure 1 , clips 7 are provided at each of the four corners of the base 1 . Each clip 7 protrudes substantially directly away from the plane of the bottom surface 4, extending away from the bottom surface 4 in the opposite direction to the direction in which the upstanding walls 5 extend. Each clip terminates at its distal end in an outwardly-flared detent 8.

In an embodiment, the PCB 6 to which the base 1 is to be attached is provided with four elongate slots 9, which are spaced apart with spacing corresponding to that of the clips 7. Each slot 9 has a width similar to the width of each clip 7, and a length which is slightly less than the distance between a back surface of the clip 7 (i.e. the surface of the clip 7 furthest from the detent 8) and the tip of the outwardly-flared detent 8. It will therefore be understood that, as the base 1 is pressed onto the PCB 6, one clip 7 will enter each of the slots 9, and will be able to fit through the slot 9 as the detent 8 will be deflected inwardly. When the detent 8 has passed through the slot 9, the detent 8 will spring outwardly, effectively locking the base 1 in place with respect to the PCB 6.

It will be understood that there are, of course, many other ways in which the base 1 may be attached to a PCB or other circuit board.

A pair of apertures 10 is provided at a first end of the bottom surface 4 of the base 1 . These apertures 10 are aligned with corresponding apertures (not shown) in the PCB 6, allowing parts of a source arrangement and a sensing arrangement respectively to protrude through the apertures 10, as will be described in more detail below.

Around mid-sections of the longer sides 2 of the base 1 , the upstanding walls 5 describe thinned portions 1 1 , with each thinned portion 1 1 having a protruding ridge 12 formed on an outer surface thereof. The base 1 is formed from one or more materials which has a low thermal conductivity and preferably also a high thermal capacity, for instance a plastics material.

A thin reflective coating or surface is formed on the bottom surface 4 of the base 1 . The coating or surface is conductive to heat and/or electricity, and is preferably formed from a metallic substance. In preferred embodiments of the invention, the coating or surface is formed from gold or a gold alloy.

In an embodiment, the layer or coating extends continuously to cover the internal surfaces of the upstanding walls 5 at the shorter edges 3 of the base 1 .

Turning to figure 2, a lid 13 is shown. The lid 13 takes a generally rectangular form, having opposing longer edges 14 and shorter edges 15, and the dimensions of the lid 13 correspond generally to the dimensions of the base 1 .

The lid 13 takes a similar form to the base 1 , having a generally flat, planar inner surface 16 and short upstanding walls 17 formed around all sides of the inner surface 16. In addition to the upstanding walls 17, the shorter edges 15 are provided with respective outwardly-flared protrusions 28, which extend away from the plane of the inner surface 16, over the outside of the upstanding walls 17, by a greater amount than the upstanding walls 17, and are also inclined outwardly. The outwardly-flared protrusions 28 are preferably substantially as wide as the shorter edges 15 of the lid 13, and have respective strips 18 of a flexible material provided on or near the free ends thereof. In preferred embodiments the flexible material is a polymer, and even more preferably is an elastomeric material. The flexible material has a plurality of filaments, specks or grains of a conductive material embedded therein, so that the flexible material is conductive to heat and/or electric current.

Legs 19 protrude from each corner of the lid 13, in a direction substantially directly away from the plane of the inner surface 16 thereof, in the same direction as the upstanding walls 17. Each leg 19 is able to deflect inwardly, and at its distal end, on an outer surface, each leg 19 terminates in a tapered surface 21 , which forms a point at the distal end and flares outwardly, terminating in a shoulder 20 which is formed on the outer surface of the leg 19 and faces towards the plane of the inner surface 16.

At a first end of the inner surface 16, an infrared (IR) source 22 is provided near the upstanding wall 17 on one side, and an IR receiver 23 is provided near the upstanding wall 17 on the other side. The IR source 22 and IR receiver 23 are separated by a baffle 24 which protrudes directly out of the inner surface 16, substantially perpendicular thereto, from the upstanding walls 5 at the first end around halfway to the central point of the inner surface 16.

At a second end of the lid 13, opposite from the first end, an inlet grille 25 is formed from a plurality of slots formed through the inner surface 16. Near the first end, an outlet grille 27 is formed from a series of further slots.

At around midway points of the longer edges 14, the upstanding walls 17 are provided with thinned portions 33, each of which includes an elongate slot 28 which is substantially parallel with the plane of the inner surface 16, and is of around the same size as the protrusion 12 that protrudes from each of the thinned portions 1 1 formed in the upstanding walls 5 of the base 1 . The inner surface 16 is provided with a thin conductive, reflective coating or layer, in the same manner as the bottom surface 4 of the base 1 . In embodiments of the invention, the reflective layer or coating extends continuously to cover the inner surfaces of the upstanding walls 17 formed at the shorter edges 15 of the lid 13. A conductive arrangement (not shown) is also provided to provide an electrically and/or thermally conductive path from each of the strips 18 of flexible material to the coating or layer formed on the inner surface 16 of the lid 13. For instance, one or more wires or regions of conductive material may be formed within each protrusion 28, or on an inner surface thereof, to provide this conductive arrangement.

To assemble the sensor, the lid 13 is placed over the base 1 , so that the legs 19 of the lid 13 pass through further slots 26 formed in the PCB 6. It will be understood that as the legs 19 pass through the further slots 26 they will be deflected inwardly, and will then spring outward so that the shoulder 20 in each leg 21 is abutted against the underside of the PCB 6, thus preventing the lid 13 from being pulled upward and removed from the PCB.

As this occurs, the thinned portions 1 1 ,33 of the upstanding walls 5,14 on the base 1 and lid 13 will slide over one another, and the projections 12 in the thinned portions 1 1 of the base 1 will slot into the slots 28 formed in the thinned portions 33 of the lid 13, further securing the lid 13 and base 1 to one another.

The coatings or layers formed on the bottom surface 4 of the base 1 , and on the inner surface 16 of the lid 13, will come into conductive contact with one another as the sensor is assembled. If the coatings or layers formed on the lid 13 and base 1 do not contact each other directly when the sensor is assembled (for instance, if the coatings or layers do not extend to cover the inner surfaces of the updating walls 5,17), then a conductive arrangement may be provided to allow this conductive contact, such as one or more wires or leads.

It will be appreciated that the base 1 and lid 13, when fitted together in this way, will produce a substantially enclosed interior space, which functions as a sample chamber during use of the sensor.

Use of the sensor will now be described.

The inner surfaces 4,16 of the base 1 and lid 13 will act as reflective surfaces during use of the sensor. It is therefore desirable, as discussed above, for these surfaces 4,16 to be heated, to avoid the formation of condensation on the surfaces 4,16 when they become exposed to exhaled breath. A heating arrangement is therefore provided to heat the surfaces 4,16.

In preferred embodiments the heating arrangement comprises a source of heat or current, which is provided outside the enclosure formed by the base 1 and lid 13. In one embodiment, a source of current (not shown) is provided, connected to conductive tracks on the PCB 6. The current source may be provided and mounted on the PCB 6, or indeed located away from the PCB 6. The current source is connected to one conductive region 29 on the PCB 6 (shown in figure 1) which is formed adjacent to one of the shorter edges 3 of the base 1 , and to a second conductive region which is formed adjacent the other short edge 3 of the base 1 . In preferred embodiments, one or both of the conductive regions 29 are elongate, parallel with the shorter edges 3, and formed to be approximately the same length as each of the shorter edges 3.

It will be appreciated that, when the lid 13 is secured to the PCB 6, the strips 18 of flexible material will come into electrical contact with the conductive regions 29. Components of the sensor will therefore form a conductive connection between the conductive regions 29, as electricity will be able to flow from one conductive region 29, through one of the strips 18 of flexible material to the conductive coatings formed on the main surface 4 of the base 1 and the inner surface 16 of the base 13. Electricity may then flow through the other one of the strips 18 of flexible material to the second conductive region.

It will therefore be understood that current may flow from the current source through the first conductive region 29, through the conductive coatings of the bottom surface 4 and inner surface 16, heating these surfaces through resistive heating, and to the second conductive region.

In automotive applications it may be expected that the temperature to which the sensor is exposed may vary between -40°C and + 85°C. A significant amount of thermal expansion/contraction is therefore to be expected.

However, due to the presence of the strips 18 of flexible material, a reliable electric connection may be maintained between the strips 18 and the conductive regions 29 on the PCB 6, even if the components of the sensor do expand and contract thermally.

In alternative embodiments, a source of heat may be provided, for instance a resistive heating coil, which transmits heat to the conductive regions 29 on the PCB 6. This heat will be conducted through these strips 18 of elastomeric material to the main surface 4 of the base 1 and the inner surface 16 of the lid 13, thus causing these surfaces 4,16 to heat up.

To use the sensor a subject is invited to exhale into the inlet grille 26. As this occurs, the enclosure formed within the sensor will partially fill with exhaled breath, and some of the air that was formerly inside the sensor will be driven out of the enclosure through the outlet grille 27.

The IR source 22, which is connected to a source connection 30 that protrudes through one of the apertures 10 formed through the main surface 4 of the base 1 , emits infrared light. This light is prevented from being transmitted directly to the IR sensor 23 by the baffle 24. The infrared light therefore travels across the length of the sensor and is reflected from the far wall (i.e. the wall formed at the short end of the sensor opposite the short end of which the IR source 22 and sensor 23 are provided), and is reflected to the IR sensor 23 (which is connected to a sensor connection 31 that protrudes through the other of the apertures 10 formed through the base 1). As this occurs, the infrared radiation will be reflected several times from the internal surfaces of the enclosure.

As is known in the art, the light received at the infrared sensor 23 will allow determinations to be made as to the concentration of volatile substances, such as alcohol, in the exhaled breath.

It will be appreciated that embodiments of the present invention provide a robust and practical sensor, which will perform well in significant temperature variations.

Although strips of flexible material are formed on the protrusions in the above description, other configurations of flexible material may be provided, for instance spaced apart balls or blobs. However, providing elongate strips allows relatively large contact areas without unduly increasing the size of the sensor. When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

CLAIMS:

1 . A sensor comprising:

a body comprising a lid and a base, the lid and base being formed from one or more materials having low thermal conductivity, the lid and base being fitted together to define an enclosure which is substantially enclosed; thin reflective layers or coatings formed on respective inner surfaces of the lid and base, the layers or coatings on the lid and base being in

conductive contact with one another;

a substrate on which the body is mounted, the substrate defining at least one region which is conductive to heat or current;

a source of heat or current provided outside the enclosure and connected to provide current or heat to the at least one region of the substrate;

a conductor protruding from the body to contact the at least one region of the substrate, to transmit heat or current from the at least one region to the reflective layers or coatings formed on the lid and the base; and

a connection between the conductor and the at least one region of the substrate, the connection allowing conduction of heat or current and also allowing for variations in distance between the components of the body and the substrate arising from thermal expansion.

2. A sensor according to any preceding claim, wherein two regions which are conductive to heat or current are provided on the substrate, and two conductors protrude from the body to contact the respective regions of the substrate, to transmit heat or current from the regions to the reflective layers or coatings formed on the lid and the base.

3. A sensor according to claim 1 or 2, wherein the connection comprises one or more quantities of flexible conductive material.

4. A sensor according to claim 3, wherein the flexible conductive material is formed from a non-conductive material having a plurality of grains or fibres of a conductive material embedded therein or coated on a surface thereof.

5. A sensor according to claim 3 or 4, wherein the connection comprises one or more strips of the flexible conductive material.

6. A sensor according to any one of claims 3 to 5, wherein the flexible conductive material comprises a polymeric material having a plurality of grains or fibres of a metal embedded therein or coated on a surface thereof.

7. A sensor according to any preceding claim wherein the conductor is provided on an extension of the lid which protrudes towards the substrate.

8. A sensor according to any preceding claim further comprising a source and a detector, the source emitting radiation which is reflected from the reflective layers or coatings formed on the inner surfaces of the lid and base before being absorbed by a detector.

9. A sensor according to any preceding claim, wherein the lid and base are formed from one or more materials having low electrical conductivity.