GB2468522A

GB2468522A - Breath analyser

Info

Publication number: GB2468522A
Application number: GB0904277A
Authority: GB
Inventors: Per Holmberg
Original assignee: Autoliv Development AB
Current assignee: Autoliv Development AB
Priority date: 2009-03-12
Filing date: 2009-03-12
Publication date: 2010-09-15
Anticipated expiration: 2029-03-12
Also published as: GB2468522B; GB0904277D0

Abstract

A breath analyser, for instance for measuring alcohol in breath, comprises a housing (2) in which is located; a cavity (3) defining a flow path in direct communication with the exterior of the housing at two ends, the internal surface of which includes at least one window (6) transmissive to radiation and at least one mirror portion reflective to radiation (7); a radiation source (5) that emits radiation into the cavity via the window; and a radiation sensor (5) that detects the radiation after it has been reflected from the reflective portion back through the window. The cavity may be provided with two or more reflective portions (7, 8) and with a separate radiation entry and exit window.

Description

Title: A Breath Analyser

Description of Invention

THIS INVENTION relates to a breath analyser, and in particular concerns a analyser for use in analysing volatile elements within the expired breath of a test subject.

It is often desirable to analyse the breath exhaled by a person to test whether the breath contains certain substances. The most common example of this is to test the content of alcohol in a subject's breath, to determine whether the subject is likely to have consumed too much alcohol to perform certain tasks such as driving a motor car or operating machinery.

In recent years, it has become common practice for law enforcement officers to analyse the breath of a motorist or potential motorist who may have consumed an excessive quantity of alcohol, or the breath of an individual present at the scene of a crash or other accident. Hand-held analysers have been developed for this purpose. it has also been proposed to incorporate analysers into motor vehicles, for instance built into the dashboard of a vehicle, to analyse the breath of an occupant of the driver's seat. If a determination is made that an occupant of the driver's seat has a high concentration of alcohol in his/her exhaled breath, a warning may be provided, or indeed the vehicle may be immobilised.

For both of these purposes, a compact, re-usable analyser is required.

Many hand-held or vehicle-mounted analysers include a passage extending all the way through the analyser, with expired breath being directed into the passage for analysis. An example of this is the analyser shown in US5942755, which includes a generally cylindrical gas transit passage having source and detection modules provided on opposite sides of the passage.

Infrared radiation is emitted by the source module and this radiation passes into the passage through a first window, passes directly across the centre of the passage and exits the passage through a second window which is substéntially opposite the first window. A detection module, which is provided behind the second window, analyses the radiation to determine whether the absorption spectrum exhibited by the radiation indicates a high content of alcohol in gases in the passage.

lt is an object of the present invention to provide an improved analyser of this type.

Accordingly, one aspect of the present invention provides a breath analyser comprising: a radiation source for emitting radiation; a radiation sensor for sensing radiation emitted by the radiation source; and a housing having a cavity passing therethrough, the cavity having two ends which are both in direct communication with the exterior of the housing, so as to define a flow path through the housing, and an internal surface which substantially surrounds the flow path, the internal surface comprising at least one window which is substantially transmissive to the radiation emitted by the radiation source and at least one reflection portion which is substantially reflective to the radiation emitted by the radiation source, wherein the radiation source and the radiation sensor are located within the housing so that radiation from the radiation source may be emitted into the cavity through the at least one window, the emitted radiation being reflected by the at least one reflection portion, so that the path of the radiation is deflected, and subsequently exiting the cavity through the at least one window so as to impinge on the radiation sensor.

Advantageously, at least two reflection portions are provided, and wherein the emitted radiation is reflected by each of the at least two reflection portions.

Preferably, the cross-section of the cavity defines a central point, and wherein the radiation from the radiation source enters the cavity through the at Feast one window in a direction which does not pass through the central point.

Conveniently, the reflection portions are separated from one another.

Advantageously, a single window is provided through which the radiation both enters and exits the cavity.

Preferably, two windows are provided, the radiation entering the cavity through a first window and exiting the cavity through a second window.

Conveniently, the at least one reflection portion comprises a region of a continuous reflection surface.

Advantageously, the path described by the radiation within the cavity lies substantially in a single plane.

Preferably, the path described by the radiation within the passage crosses with itself.

Conveniently, the cross-sectional shape of the cavity comprises rounded internal surfaces.

In order that the present invention may be more readily understood, embodiments thereof will now be described, by way of example, with reference to the accompanying figure, which shows a schematic view of an analyser embodying the present invention.

Referring to the figure, a hand-held analyser 1 comprises an outer housing 2, which in the depicted embodiment is generally oblong. A gas transit passage 3 is defined in the housing, passing substantially entirely through the housing and having respective first and second open ends. In preferred embodiments of the invention! the open ends do not have filters or other obstructive objects which would impede the flow of gas between the ambient air and the interior of the passage 3, or accumulate deposits which may have an impeding or contaminating effect.

The passage 3 is defined by an interior surface 4, which is generally square or rectangular in crosssection, although the invention is not, of course, limited to this shape.

Mounted within the housing 1, near to or adjacent the passage 3, is a combined transmitter and receiver unit 5. The unit 5 includes a transmitter which is operable to emit radiation, preferably in the infrared (lR) portion of the electromagnetic spectrum, and also includes a receiver which is operable to receive and detect incoming radiation, preferably in the same wavelength range as the emitted radiation.

A window portion 6 of the surface 4 defining the passage 3, which is approximately in the middle of one of the sides of the passage 3 and near to or adjacent the transmitter and receiver unit 5, is substantially transmissive to radiation in the wavelength range emitted by the transmitter and receiver 5.

However, the remaining parts of the surface 4 of the passage 3 are substantially reflective to the radiation emitted by the transmitter.

In a preferred embodiment of the invention, the transmitter and receiver unit 5 is configured so that radiation emitted from the receiver is directed through the window portion 6 in a direction which is generally perpendicular to the longitudinal axis of the passage 3, and is also generally perpendicular to the part of the interior surface 4 which contains the window portion 6.

Use of the analyser 1 will now be described. Once the analyser has been switched on, a subject is invited to exhale towards or into the passage 3.

Radiation is limited by the transmitter, as described above. The radiation strikes a region 7 of the waIl 4 of the passage directly opposite the transmitter and (as this region will be substantially reflected to the radiation) is reflected directly back across the interior of the passage 3. The radiation will pass through the window portion 6, and can be detected and analysed by the receiver.

It will be understood that, because of the internal reflection of the radiation, the length of the paths travelled by the radiation within the passage 3 will be relatively great, which will increase the accuracy of protection of substances contained within the exhaled breath.

Preferably, before the testing of a subject's breath, a calibration procedure is carried out, in which the passage 3 is filled with clean air and radiation is emitted by the transmitter, reflected from the first and second portions 7,8 of the interior wall 4 of the passage 3 and then detected by the receiver 5.

It is anticipated that a heating arrangement may need to be provided to heat the interior reflective surfaces of the passage 3, to avoid the formation of condensation.

In further embodiments of the invention, the transmitter and receiver unit 5 is configured so that radiation emitted from the receiver is directed through the window portion 6 in a direction which is generally perpendicular to the longitudinal axis of the passage 3, but which subtends an angle of around 300 with an imaginary line connecting the transmitter and receiver 5 to the central longitudinal axis of the passage 3.

Radiation is emitted by the transmitter, as described above and initially strikes a first region 7 of the wall 4 of the passage 3, and is reflected back into the interior of the passage 3. It will be understood that the first region 7 is spaced apart from the window portion 7 by around 120° (i.e. one third) of the circumference of the interior surface of the passage.

Following reflection from the first portion 7, the radiation strikes a second portion 8 of the wall 4 of the passage 3. Once again, the radiation will be reflected by the second portion 8 back into the interior of the passage 3. It will also be understood that the second portion 8 is spaced apart from both the window portion 6 and the first portion 7 by approximately 120° of the circumference of the interior surface of the passage 3.

Following this second reflection, the radiation is directed towards, and passes through, the window portion 6. The radiation is detected and analysed by the receiver. The path of the radiation within the passage therefore approximately describes an equilateral triangle, in a plane that is substantially perpendicular to the longitudinal axis of the passage.

It will be understood that, because of the multiple internal reflections of the radiation, the length of the path travelled by the radiation within the passage 3 will be relatively great. For the detection of carbon dioxide or water vapour in the expired breath of a subject using IR radiation (which, as a skilled person will appreciate, may be used to determine the degree of dilution of the subject's breath by ambient air), a path length of around 10 centimetres is required. For the detection of alcohol in expired breath, a path length of approximately 15 to 20 centimetres is generally required. If the radius of the passage 3 shown in figure 1 is 3.6 centimetres, the distance travelled by the radiation within the passage 3 will be approximately 20 centimetres. A relatively long path length can therefore be defined within a flow passage having a relatively small radius.

The analyser 1 may be configured so that a greater number of reflections occur before the radiation is detected. For instance, the radiation may describe a five-pointed "pentagram" pattern before being absorbed. For a flow passage having a radius of 3.6 centimetres, the total path length travelled by the radiation within the passage itself would be just over 34 centimetres. Generally, the path described by the radiation within the passage 3 may cross with itself, and this will assist in maximising the path length.

In preferred embodiments, however, the radiation is reflected by at least two reflection portions 7,8 provided on the interior of the passage 3. These reflection portions are preferably separated from one another, and may comprise separate distinct regions of reflective material or, as in the embodiment shown in figure 1, may be different portions of a continuous region of reflective material.

S

Preferably, the cross-section of the passage 3 defines a central point (e.g., for a cylindrical passage, the central point would be the centre of the cylinder in the plane of the radiation's path), and advantageously radiation is emitted into the passage in a direction which does not pass through the central point.

In the embodiment described above, a combined transmitter and receiver unit is provided. However, it should be appreciated that the transmitter and receiver may be provided as separate components, which need not be located in the same place. In embodiments of the invention, a first window is provided through which a transmitter may emit light into the passage, and a separate, second window is provided through which the radiation may pass in order to reach the receiver.

In the examples described above, the cross-sectional shape of the passage 3 is substantially square, rectangular or circular. However, it will be appreciated that any suitable shape of passage may be used. For instance, a hexagonal passage may be defined, with one face of the hexagon comprising a transmission window and the other five surfaces being reflective. Radiation may be emitted so as to bounce off each of the five surfaces before returning through the window for detection.

Whilst any shape or passage may be used, a generally circular passage, or at least a passage having rounded internal surfaces, is preferred, to allow for ease of cleaning the internal surfaces.

In the above embodiments, the path described by the radiation within the passage generally falls within a single plane. Whilst this is preferred, it should be appreciated that the radiation may describe any suitable path within the passage, and that this need not remain within a single plane. In embodiments of this type, the cross-sectional shape of the passage will not be constant along its length.

It will be appreciated that embodiments of the invention provide analysers which may lightly analyse a subject's breath, but which are more compact than conventional analysers.

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 breath analyser comprising: a radiation source for emitting radiation; a radiation sensor for sensing radiation emitted by the radiation source; and a housing having a cavity passing therethrough, the cavity having two ends which are both in direct communication with the exterior of the housing, so as to define a flow path through the housing, and an internal surface which substantially surroundsthe flow path, the internal surface comprising at least one window which is substantially transmissive to the radiation emitted by the radiation source and at least one reflection portion which is substantially reflective to the radiation emitted by the radiation source, wherein the radiation source and the radiation sensor are located within the housing so that radiation from the radiation source may be emitted into the cavity through the at least one window, the emitted radiation being reflected by the at least one reflection portion, so that the path of the radiation is deflected, and subsequently exiting the cavity through the at least one window so as to impinge on the radiation sensor.
2. A breath analyser according to claim 1, wherein at least two reflection portions are provided, and wherein the emitted radiation is reflected by each of the at least two reflection portions.
3. A breath analyser according to claim 2, wherein the cross-section of the cavity defines a central point, and wherein the radiation from the radiation source enters the cavity through the at least one window in a direction which does not pass through the central point.
4. A breath analyser according to claim 2 or 3, wherein the reflection portions are separated from one another.
5. A breath analyser according to any preceding claims, wherein a single window is provided through which the radiation both enters and exits the cavity.
6. A breath analyser according to any one of claims 1 to 4, wherein two windows are provided, the radiation entering the cavity through a first window and exiting the cavity through a second window.
7. A breath analyser according to any preceding claims, wherein the at least one reflection portion comprises a region of a continuous reflection surface.
8. A breath analyser according to any preceding claim, wherein the path described by the radiation within the cavity lies substantially in a single plane.
9. A breath analyser according to any preceding claim, wherein the path described by the radiation within the passage crosses with itself.
10. A breath analyser according to any preceding claim, wherein the cross-sectional shape of the cavity comprises rounded internal surfaces.