GB2624464A

GB2624464A - Sensor

Info

Publication number: GB2624464A
Application number: GB2217388.4A
Authority: GB
Inventors: Ejaz Huq Syed; Yasser Al Aioubi Mohamad
Original assignee: Oxford Healthtech Ltd
Current assignee: Oxford Healthtech Ltd
Priority date: 2022-11-21
Filing date: 2022-11-21
Publication date: 2024-05-22
Also published as: GB202217388D0; WO2024110497A1

Abstract

A device configured to detect the presence of a solvent, the device comprising: a solvent responsive switch 102 with power supply 104, comprising: a set of two electrodes 106a,106b; an electrically conductive element 108 configured to move from a first configurational state to a second configurational state responsive to the presence or absence of solvent, wherein, in the first configurational state, the electrically conductive element is in electrical contact with said electrodes so as to close the solvent responsive switch (Fig.1B), and wherein, in the second configurational state, the electrically conductive element is electrically disconnected from said electrodes so as to open the solvent responsive switch (Fig.1A). A solvent absorbent element 110 is arranged relative to the conductive element 108, such that, if the solvent absorbent element 110 expands in the presence of its solvent, it will shift the conductive element 108 towards, and into contact with the electrodes 106a, 106b to close the switch 102.

Description

SENSOR

Field of the Invention

The present invention relates to a device for detecting the presence of a solvent and method for detecting the presence of a solvent.

Background

Water and other chemical leaks are a common and undesirable problem. If a water leak is present within a building and left undetected, damage may be caused before the leak can be fixed. Similar problems arise for other chemical leaks, which may also be dangerous to human or animal life. There is a need for a detector that at least partially solves these problems.

Summary of the Invention

According to a first aspect of the present invention, there is provided a device configured to detect the presence of a solvent, the device comprising: a solvent responsive switch, comprising: a set of two electrodes; an electrically conductive element configured to move from a first configurational state to a second configurational state responsive to the presence or absence of solvent, wherein, in the first configurational state, the electrically conductive element is in electrical contact with said electrodes so as to close the solvent responsive switch, and wherein, in the second configurational state, the electrically conductive element is electrically disconnected from said electrodes so as to open the solvent responsive switch.

Optionally, the device further comprises a solvent absorbent element configured to expand in the presence of the solvent, and wherein, said expansion of the solvent absorbent element effects movement of the electrically conductive element between the configurational states.

A housing may define an enclosure for containing the solvent absorbent element and the electrically conductive element and, the electrically conductive element may be slidably movable within the enclosure between the configurational states.

The solvent absorbent element may be seated on a shelf above a base of the housing from which solvent is able to ingress.

The electrically conductive element may be a film, which in the first configurational state, is in physical contact with and extends between the two electrodes. and wherein, the electrically conductive element may transition to the second configurational state by the expansion of the solvent absorbent element rupturing the film.

The electrically conductive element may be resiliently shaped to define an enclosure for containing the solvent absorbent element, and expansion of the solvent absorbent element may cause the shape of the electrically conductive element to change so that physical contact is made between the electrically conductive element and the electrodes.

The electrically conductive element may comprise a base portion and side wall portions extending from the base portion, and expansion of the solvent absorbent element may cause the side wall portions to pivot outwardly about the base portion so that physical contact is made between the side wall portions and the electrodes.

The electrically conductive element may define a split housing, comprising a first and a second part, for containing the solvent absorbent element and the device may further comprise: a biasing element configured to urge the first and second parts of the split housing together into the first configurational state. Expansion of the solvent absorbent element may cause the first and second part of the split housing to physically separate from one another, thereby transitioning from the first to the second configurational state.

The device may further comprise a first and a second housing respectively defining an enclosure for containing a solvent absorbent element. The electrically conductive element may comprise a first portion forming part of the first housing and a second portion forming part of the second housing. The first and second housings are arranged such that the first and second portions of the conductive element oppose one another and expansion of the solvent absorbent element may cause the first and second portions of the electrically conductive elements to make physical contact with one another. Expansion of the solvent absorbent element may cause the first and/or second portion of the electrically conductive element to bow into physical contact with one another.

The electrically conductive element may be provided as a coating which at least partially covers the solvent absorbent element, and expansion of the solvent absorbent element may cause the coating to make contact with the two electrodes.

The solvent absorbent element may comprise polydimethylsiloxane (PDMS) and the solvent may be any one or more of acetone, methyl ethyl ketone, toluene or hexane; or the solvent absorbent element may comprise any one or mixture of: polyimide P84®, Matrimid®, polyethylenimine (PEI), polyacrylonitrile (PAN), polysulfone (PES), poly(ethersulfone) (PSF), PEBAX®, poly(1-trimethylsilyI-1-propyne) (PTMSP) and the solvent may be any one or mixture of: hexane, toluene, dichloromethane, ethyl acetate, methyl ethyl ketone, acetone, isopropanol, ethanol, methanol and water.

The solvent absorbent element may comprise a super absorbent polymer, SAP. A SAP is a water-absorbing polymer which can absorb aqueous solutions through hydrogen bonding with water molecules. In deionized and distilled water, a SAP may absorb 300 times its weight (from 30 to 60 times its own volume) and become up to 99.9% liquid, and when put into a 0.9% saline solution the absorbency drops to approximately 50 times its weight. That is, the presence of valence cations in solution impedes the polymer's ability to bond with the water molecule. A SAP is any water-absorbing polymer that is able to absorb greater than lOg of water per 1g of SAP (10g/g) and retain that absorbed water under pressure (> 0.67g/cm2).

The SAP may comprise a particle having dimensions of around 0.5mm to 5mm, or the SAP comprises a film having a thickness of around 0.1mm to 1mm.

The solvent responsive element may be configured to move in the presence of the solvent to effect movement of the electrically conductive element between the configurational states.

Optionally, the device includes a housing that defines an enclosure for containing the solvent responsive element and the electrically conductive element. The electrically conductive element is then arranged on the solvent responsive element, which is configured to be buoyant in the solvent so that, as solvent fills the enclosure, the solvent responsive element may move towards the electrodes, causing the electrically conductive element to make physical contact with the electrodes.

Optionally, the device includes a housing that defines an enclosure for containing the solvent responsive element and the electrically conductive element. The electrically conductive element is then arranged on the solvent responsive element, which is a film extending across the enclosure and impermeable to the solvent, so that, as solvent fills the enclosure, the film may be deflected towards the electrodes, causing the electrically conductive element to make physical contact with the electrodes.

The device may include a solvent responsive element configured to dissolve in the presence of the solvent. Dissolution of the solvent responsive element may cause (i.e., effect) movement of the electrically conductive element between the configurational states.

The electrically conductive element may be a film, which in the first configurational state, is in physical contact with and extends between the two electrodes and which is supported by the solvent responsive element. The electrically conductive element may transition to the second configurational state as the support provided by the solvent responsive element is removed following its dissolution or partial dissolution.

The following solvent responsive element and solvent pairings are possible. The solvent responsive element comprises polyethylene, and the solvent comprises any one or more of: a hydrocarbon; or a halogenated hydrocarbon. The solvent responsive element comprises polybutadiene and the solvent comprises any one or more of: a hydrocarbon, Tetrahydrofuran or a ketone. The solvent responsive element comprises polyacrylate and the solvent comprises any one or more of: an aromatic hydrocarbon, a chlorinated hydrocarbon, Tetrahydrofuran, an ester or 2-Butanone. The solvent responsive element comprises polyacrylamide and the solvent comprises water. The solvent responsive element comprises poly(vinyl) ether and the solvent comprises a halogenated hydrocarbon, 2-Butanone or butanol. The solvent responsive element comprises poly(vinyl) alcohol and the solvent comprises a glycol or N, N-Dimethylformamide. The solvent responsive element comprises poly (vinyl acetate)and the solvent comprises an aromatic hydrocarbon, a chlorinated hydrocarbon, Tetrahydrofuran, an ester or N, NDimethylformamide. The solvent responsive element comprises poly (vinyl chloride)and the solvent comprises Tetrahydrofuran, Dimethly sulfoxide or N, N-Dimethylformamide. The solvent responsive element comprises poly (vinylidene chloride) and the solvent comprises Tetrahydrofuran, dioxane or N, N-Dimethylformamide. The solvent responsive element comprises polyacrylonitrile and the solvent comprises Dimethly sulfoxide or N, N-Dimethylformamide. The solvent responsive element comprises polyurethane and the solvent comprises an aromatic hydrocarbon, Tetrahydrofuran or N, NDimethylformamide. Or, the solvent responsive element comprises polyurea, and the solvent comprises a phenol or formic acid.

The electrically conductive element may be configured to at least partially dissolve in the presence of the solvent and this dissolution of the electrically conductive element causes the movement of the electrically conductive element from the first to the second configurational state.

The following electrically conductive element and solvent pairings are possible. The electrically conductive element comprises aluminium and the solvent comprises any one or more of sodium hydroxide, potassium hydroxide or hydrochloric acid. The electrically conductive element comprises copper and the solvent comprises any one or more of nitric acid or sulphuric acid. The electrically conductive element comprises gold and the solvent comprises hydrochloric acid, nitric acid or a mixture thereof. Or, the electrically conductive element comprises silver and the solvent comprises any one or more of hydrochloric acid or nitric acid According to a third aspect of the present invention, there is provided a device configured to detect the presence of a solvent, the device comprising: a transmitter and receiver; and a solvent absorbent element arranged in a radiation path between the transmitter and receiver, wherein, the solvent absorbent element is configured to expand in the presence of the solvent in order to change the radiation path between the transmitter and receiver and cause the intensity of radiation received by the receiver to change by a predetermined threshold, said threshold being indicative of the device being in the presence of the solvent.

According to a third aspect of the present invention, there is provided a method of detecting the presence of a solvent using a device according to any one of the preceding claims, the method comprising: determining that the solvent is present conditional upon whether an electrical current is able to pass through the solvent responsive switch in the device.

The method may, in response to said determining step, comprise triggering any or more of: sounding an alarm; switching on a light element; and transmitting an RE signal from an RF antenna to a remote device.

Brief Description of the Drawings

Some embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which: Figures 1 and 2 are schematic illustrations of solvent detectors having a solvent responsive electrical switch; Figures 3 to 12 are schematic illustrations of solvent responsive electrical switches; Figure 13 is a schematic illustration of a solvent detector having an optical transmitter and receiver; and Figure 14 is a schematic illustration of a matrix arrangement of solvent responsive electrical switches.

Detailed Description

Proposed herein is a device adapted to detect the presence of a solvent by monitoring whether an electrical current is able to pass through a solvent responsive electrical switch in the device, which is configured to switch between an open and a closed state, dependent on the presence/absence of solvent.

The solvent responsive switch includes: a set of two electrodes and an electrically conductive element configured to move from a first configurational state to a second configurational state in response to the switch being in the presence or absence of solvent. In the first configurational state (i.e., when the switch is closed), the electrically conductive element is in electrical contact with the electrodes to close to switch, whereas in the second configurational state (i.e., when the switch is open), the electrically conductive element is electrically disconnected from the set of electrodes.

The solvent responsive switch may further include a solvent absorbent element configured to expand in the presence of the solvent and shrink in the (relative) absence of the solvent (e.g., as the solvent absorbent element dries). The solvent responsive switch is structured such that switching between the open and closed states is caused by changes in the volume of the solvent absorbent element. Example devices are described below, in particular in Figures 1A, 1B, 2, 3A, 3B, 4, 5A, 5B, 6A, 6B, 7A and 7B.

The solvent responsive switch may include a solvent responsive element (which could be the solvent absorbent element). The solvent responsive switch is structured so that in response to being in the presence of the solvent, the solvent responsive element is able to move the electrically conductive element in order to effect switching of the solvent responsive switch. Example devices are described below, in particular in Figures 1A, 1B, 2, 3A, 33, 5A, 5B, 6A, 6B, 7A, 7B, 8A, 8B, 9A, 93, 10A, 103, 11A and 113.

The solvent responsive switch may include an electrically conductive element that is configured to at least partially dissolve in the presence of its solvent. The dissolution of the conductive element causes the element to switch between configurational states (i.e., from closed to open). An example device is shown in Figures 12A and 12B.

Also proposed herein is a device adapted to detect the presence of a solvent by monitoring the change of a radiative signal (e.g., light) between a transmitter and receiver. The device includes a solvent absorbent element, which is disposed in a radiation path between the transmitter and receiver. As the solvent absorbent element expands and shrinks in the presence and (relative) absence of solvent, the radiation path (e.g., its length) between the transmitter and receiver changes, which affects the light intensity measurable at the receiver. A threshold increase in measured light intensity by the receiver is considered indicative of the device being in the presence of its solvent. Example devices are described below, in particular in Figure 13A and 133.

Referring to Figure 1A and Figure 1B, a solvent detector 100, comprising a solvent responsive electrical switch 102 in an open configuration (Figure 1A) and a closed configuration (Figure 13), is shown. The detector 100 further comprises a power supply 104 to provide electrical power to the solvent responsive switch 102. The power supply 104 may be mains supply, or a local energy storage device (e.g., a battery).

As shown in Figures 1A and 1B, the switch 102 comprises: two spaced electrodes 106a, 106b; a movable, electrically conductive element 108 vertically spaced from the electrodes 106a, 106b; and a solvent absorbent element 110 arranged relative to the conductive element 108, such that, if the solvent absorbent element 110 expands in the presence of its solvent, it 110 will shift the conductive element 108 towards, and into contact with the electrodes 106a, 106b in order to close the switch 102. The switch 102 therefore closes in the presence of its solvent.

In the specific example illustrated, the conductive element 108 rests or sits on top of the solvent absorbent element 110 and both are located within an enclosure of a housing 112.

This couples their movement, meaning that as the solvent absorbent element 110 moves upwards or downwards within the housing 112 during expansion and shrinking, the conductive element 108 correspondingly moves upwards or downwards. In the example shown, the conductive element 108 is forced to protrude out from the opening 114 to make contact with the electrodes 106a, 106b, although this is not essential.

In an alternative example (not shown), the conductive element 108 is arranged to be vertically offset from the solvent absorbent element 110. For example, the conductive element 108 may be seated on a shelf that extends inwardly from the enclosure inner walls. As such, the solvent absorbent element 110 and conductive element 108 may be coupled or decoupled, depending on whether they 110, 108 are in contact or not. The working principle of the switch however remains the same as illustrated example. The conductive element 108 may also be slidably engaged with the enclosure walls (not shown).

The skilled reader will appreciate that the conductive element 108 may or may not protrude from the opening 114 in either the open or closed states. The determining factor is the placement of the electrodes 106a, 106b relative to the protruding part of the conductive element 108. For example, if the electrodes 106a, 106b are placed on top of the housing 112, the conductive element 108 will not protrude when contact is established.

The moveable conductive element 108 may be a thin film or a thin metal plate (thickness < 5mm), or a conductive pad having appreciable thickness (thickness > 5mm).

The housing is formed from a material that is unaffected by the solvent (e.g., a suitable plastic unreactive and/or insoluble in the solvent).

A characteristic volume of absorbed solvent is required to cause sufficient expansion of the solvent absorbent element 110 to effect the switching described above. This characteristic volume can be tuned according to required sensitivity of the detector. For example, a relatively sensitive detector can be constructed by decreasing the vertical spacing between electrodes 106a, 106b and opening 114. A less sensitive detector (which could be useful for eliminating false-positives from condensation, or detecting larger solvent leaks) can be constructed by increasing that spacing.

There are, however, other ways to control the characteristic volume. In general, the characteristic volume depends on a number of interrelated parameters, including, for example: * the expansion coefficient of the solvent absorbent element 110 (i.e., the ratio of element 110 volume increase relative to the volume of absorbed solvent). As the expansion coefficient increases the characteristic volume decreases; and * the vertical distance that the electrical conductive element 108 requires shifting in order to contact the electrodes 106a, 106b. As this distance increases, the characteristic volume increases.

If the solvent absorbent element 110 and conductive element 108 are initially vertically separated, the characteristic volume further depends on the vertical distance that the solvent absorbent element 110 requires shifting to contact the electrically conductive element 108. As this distance increases, the characteristic volume increases.

In Figures 1A and 1B, the moveable conductive element 108 defines one or more apertures, which allow solvent ingress into the enclosure. In a specific example, the conductive element 108 is a mesh (e.g., metallic). These apertures however, are optional (See, Figure 2). The conductive element 108 may be square, rectangular, circular or any other shape in cross section.

Turning to Figure 2, another example solvent detector 200 is shown. The solvent detector 200 is the same as the solvent detector 100 of Figures 1A and 1B except the electrically moveable conductive element 208 of Figure 2 does not define an aperture and instead solvent ingress to the enclosure is via a network of capillaries 204. The network of capillaries 204 are shown as forming part of the base of the housing 112, however, the capillaries 204 could additionally, or alternatively, be arranged along the side walls of the housing 112 (not shown).

As solvent enters the enclosure via surface tension (i.e., not necessarily aided by gravity), the solvent detector 200 in Figure 2 is particularly useful for detecting the presence of solvent on surfaces and determining the source of a leak more effectively (i.e., solvent is not required to drip from the source into the detector from above).

The network of capillaries may be integral to the housing 112 (e.g., thin tubular holes made to the housing base) or created as an insert that is affixed to the housing base. The insert may be formed of any material (e.g., a metal, plastic or glass) and optionally provided with a coating to encourage wetting and capillary action. For example, if the capillaries are initially hydrophobic and the solvent is water, the capillaries are provided with a hydrophilic coating to facilitate ingress of water.

In some examples (not illustrated in Figures 1A, 1B or 2), the device includes both the network of capillaries 204 and an electrically conductive element 108 with apertures (e.g., mesh). This increases the overall number of entry points for solvent ingress into the enclosure, which reduces the time to switch the solvent responsive switch and detect, for

example, a leak.

Figures 3A and 3B show another example of a solvent detector 300, comprising a solvent-responsive electrical switch 102 in an open and closed configuration respectively. The solvent detector 300 differs from the solvent detectors 100, 200 of Figures 1 and 2 in that the movable, electrically conductive element 308 is resiliently shaped to define an open-ended enclosure that contains the solvent absorbent element 110. The moveable, electrically conductive element 308 therefore functions as both an electrical contact (moveable to open and close the switch) and a housing for the solvent absorbent element 110.

More specifically, the electrically conductive element 308 comprises a base portion 312 and a side wall portion 310 extending at an obtuse angle from the base portion 312. The side wall(s) 310 are flexible enough (e.g., made from a resilient material and/or thin enough) so that expansion of the solvent absorbent element 110, contained by element 308, causes wall portions 310 to pivot outwardly (i.e., move) about the base portion 312.

As the conductive element 308 is resilient, the side walls 310 spring back to the open configuration after the solvent absorbent element 110 dries and shrinks in size. The switch 102 therefore is urged closed in the presence of (enough) solvent and urged open as the solvent absorbent element 110 dries (i.e., in the absence of that solvent).

As with Figures 1A, 1B and 2, there is a characteristic volume of solvent required to effect the switching between the open/closed configurations. This characteristic volume can be set according to operational needs (e.g., sensitivity requirements). In general, the characteristic volume depends on a number of interrelated parameters, including, for

example:

* the angle that side wall 310 is required to traverse to make contact with electrodes 106a, 106b. As the angle increases, the characteristic volume to effect switching increases. This angle depends on: o the difference between the lateral spacing of electrodes 106a, 106b and the lateral extent (i.e., width) of base portion 312; and o the vertical offset between the base portion 312 and the electrodes 106a, 106b.

* whether the solvent absorbent element 110 contacts the sidewall portions 308 when dry. If the solvent absorbent element 110, when dry, is sized such that it already contacts the side walls 308, the characteristic volume is less than if the solvent absorbent element 110 requires expansion to establish this contact; * the expansion coefficient of the solvent absorbent element 110 (i.e., ratio of element 110 volume increase relative to the volume of absorbed solvent). As the expansion coefficient increases the characteristic volume decreases; and * the compressibility of the solvent absorbent element 110 relative to the flexibility of the side walls 310. As the solvent absorbent element 110 becomes more rigid (compared with the side walls 310), then the characteristic volume decreases.

In the example shown in Figures 3A and 38, the solvent absorbent element 110 is specially adapted in shape to more effectively engage with, and move the side walls 310 of the electrically conductive element 308 towards electrodes 106a, 106b. The solvent absorbent element 110 is shown as a ball, but the skilled reader will understand that other shapes and forms of the solvent absorbent element 110 are entirely possible. The solvent absorbent element 110 may even be in powder form (e.g., an assembly of those shapes).

Referring now to Figures 4A and 48, another example of a solvent detector 400 is shown, comprising a solvent-responsive electrical switch 402 in an open and closed configuration respectively.

Unlike Figures 1A, 1B, 2, 3A and 3B, the solvent responsive switch 402 in Figures 4A and 4B is in an open configuration when the solvent absorbent element 110 is in the presence of its solvent (i.e., when wet) and in a closed configuration when the solvent absorbent element 110 is in the absence of its solvent (i.e., when dry or not sufficiently wet).

The switch 402 comprises a split housing for containing the solvent absorbent element 110. The split housing comprises two electrodes 406a, 406b, each having an inwardly facing protruding portion 408a, 408b, biased towards one another by a restoring element 410. In Figures 4A and 4B, the restoring element 410 is a pair of opposing springs, which are affixed to the outwardly facing sides of the electrodes 406a, 406b. The spring constant of the springs may be in the range 0.5 to 5 N/mm The restoring element 410 is therefore in a state of compression in both the open and closed configurations.

In other examples (not shown), the restoring element 410 is affixed between the inwardly facing sides (but not the inwardly facing protruding portions 408a, 408b) of the electrodes 406a, 406b. In such examples, the restoring element 410 is under tension in the open and closed configuration and electrically insulating to prevent current passing between electrodes 406a, 406b.

Although the restoring element 410 is shown as an opposing spring pair, the restoring element 410 may instead be a single spring that biases one electrode 406a, 406b towards the other 406b, 406a, or it may be a plurality of opposing spring pairs.

In the presence of solvent, the solvent absorbent element 110 expands to engage with the electrodes 406a, 406b, urging them apart from one another. Eventually, the force urging the electrodes 406a, 406b apart overcomes the restoring force of the restoring element 410, and the switch 402 opens.

Conversely, in the absence of solvent (e.g., as the solvent absorbent element 110 dries), the solvent absorbent element 110 shrinks and the force it exerts urging the electrodes 406a, 406b apart decreases. This may be a gradual decrease Of the solvent absorbent element 110 remains engaged with the electrodes 406a, 406b) or sudden (when the solvent absorbent element 110 loses contact with electrodes 406a, 406b). Eventually, the restoring force of the restoring element 110 overcomes the force urging the electrodes 406a, 406b apart and the inwardly facing protruding portions 408a, 408b of electrode 406a, 406b are forced back into contact with one another. The switch 402 therefore closes As above, there is a characteristic volume of solvent required to effect switching, which can be tuned according to operational needs. In general, the characteristic volume depends on a number of interrelated parameters, including, for example: * whether the solvent absorbent element 110 contacts the inwardly facing walls of the electrodes 406a, 406b when dry. If the solvent absorbent element 110 is sized such that it already contacts the inwardly facing walls of the electrodes 406a, 406b when dry, the characteristic volume is less than if the solvent absorbent element 110 needs to expand to establish this contact; * the expansion coefficient of the solvent absorbent element 110 (i.e., ratio of element 110 volume increase relative to the volume of absorbed solvent). As the expansion coefficient increases the characteristic volume decreases; and * the compressibility of the solvent absorbent element 110 relative to the stiffness of the restoring element(s) 410 (i.e., their spring constant). As the solvent absorbent element 110 becomes less compressible compared to the restoring element, the characteristic volume decreases.

The solvent sensitivity of the switch shown in Figures 4A and 4B can therefore be controlled by selecting the stiffness of the restoring element(s) 410 (i.e., spring stiffness). This is advantageous compared to some of the other illustrated examples described, where structural changes to the switch are required to control solvent sensitivity.

Turning back to Figures 4A, 4B, the restoring element 410 is shown as part of the electrical circuit, which connects power supply 104 to the electrodes 406a, 406b. This is, however, only an illustrative example. In some examples, the restoring element 410 does not form part of the circuit. The solvent absorbent element 110 is also shown as being specially adapted in shape (e.g., shaped as a ball) to more effectively engage with and move the inwardly facing sides of the electrodes 406a, 406b apart. However, other shapes and forms (e.g., a powder) of the solvent absorbent element 110 are possible.

Figures 5A and 5B show another example of a solvent detector 500, comprising a solvent-responsive electrical switch 502 in an open and closed configuration respectively.

The solvent responsive electrical switch 502 comprises two spaced, flexible conductive elements 506a, 506b, which are arranged to oppose one another. The conductive elements 506a, 506b respectively form part of a housing 512 defining an enclosure that carries the solvent absorbent element 110. The conductive elements 506a, 506b may be spaced laterally or vertically. Electrodes 506a, 506b form another part of the housing 512.

Each housing 512 may be open-ended or closed. A closed housing 512 comprises a base portion, a lid portion and side walls that extend between the base and lid portions to provide the enclosure. An open-ended housing 512 differs from a closed housing 512 in that at least one of the base, lid or side walls is omitted. The conductive elements 506a, 506b may be any of the base portion, lid portion or side wall of an open-ended or closed housing 512.

In Figures 5A and 5B, one of the side walls is shown to include perforations 514. The perforations 514 allow solvent ingress into the enclosure. There are, however, other ways to facilitate solvent ingress into the enclosure, as the skilled reader will appreciate.

For example, the housing 512 may be lidless and solvent may enter the enclosure through that open end. In another example, the base portion or side walls may include a network of capillaries (e.g., as shown in Figure 2), a solvent permeable membrane, a solvent porous membrane, or the like.

In a specific example, the lid portion of the housing comprises a solvent porous layer and the base portion of the housing comprises the conductive elements. The conductive elements may be described as a membrane or film.

As solvent ingresses the enclosure, the solvent absorbent element 110 expands to engage against the conductive elements 506a, 506b, which, in response, bows outwardly. Upon continued bowing, the conductive elements 506a, 506b eventually establish contact to close the switch 502 (Figure 5B).

The other parts of the housing 512 (e.g., sidewalls, lid or base) are, preferably, although not necessarily, more rigid than the conductive element 506a, 506b to maximise this bowing movement. That is, a rigid wall (or lid/base as the case may be) opposing the conductive elements 506a, 506b is effective at reducing the characteristic volume required to switch the switch 502. This improves the sensitivity of the device 500.

As above, there is a characteristic volume of solvent required to effect switching, which can be tuned according to operational needs. In general, the characteristic volume depends on a number of interrelated parameters, including, for example: * whether the solvent absorbent element 110 contacts the conductive elements 506a, 506b (and opposing walls) when dry. If so, the characteristic volume is less than if the solvent absorbent element 110 needs to expand to establish this contact; * as noted above, the difference in stiffness between the conductive elements 506a, 506b and the wall (or base/lid as the case may be) opposing the conductive elements 506a, 506b. As this difference increases, the conductive elements 506a, 506b bows out more (for the same solvent absorbent element expansion), thereby reducing the characteristic volume; * the expansion coefficient of the solvent absorbent element 110 (i.e., ratio of element 110 volume increase relative to the volume of absorbed solvent). As the expansion coefficient increases the characteristic volume decreases; and * the lateral spacing of the conductive elements 506a, 506b prior to bowing. As the lateral spacing increases, the characteristic volume increases since greater bowing is required to establish contact between conductive elements 506a, 506b.

Figure 6a and 6b show another example of a solvent responsive electrical switch 602 for a solvent detector in an open and closed configuration respectively.

The solvent responsive electrical switch 602 differs from the switches 102, 202 of Figures 1A, 1B, and 2in that the movable, electrically conductive element 108, 208 is provided as a coating 608 on the solvent absorbent element 110. The coating 608 covers a part of the solvent absorbent element 110 so that solvent can reach the solvent absorbent element 110.

In the presence of solvent, the solvent absorbent element 110 expands. The coating 608 arranged around the solvent absorbent element 110 correspondingly moves towards and eventually contacts electrodes 106a, 106b to close the switch 602 (Figure 6B). The solvent absorbent element 110 may be spherical in shape, although this is not essential.

Other shapes and forms of the solvent absorbent element 110 are possible.

In some examples, the electrically conductive coating 608 is flexible (e.g., a polymer matrix metal composite (PMMC)) so that the coating 608 can stretch as the solvent absorbent element 110 expands. However, the coating 608 may also be rigid, provided the uncoated parts of the solvent absorbent 110 have sufficient flexibility to accommodate for the strain during expansion In a specific example, the coating 608 is a thin metallic film (e.g., of copper) In Figures 6A and 6B, an aperture 612 is provided in the base of the housing 112 to facilitate solvent ingress. This aperture 612 is, however, optional: for example, it can be replaced by the network of capillaries 204, shown in Figure 2 or removed entirely from the switch 602. As above, the network of capillaries 204 may be provided with a coating to encourage wetting and capillary action. For example, if the capillaries comprise a material that is hydrophobic and the solvent is water, the capillaries can be provided with a hydrophilic coating to facilitate ingress of water.

As above, there is a characteristic volume of solvent required to effect switching, which can be tuned according to operational needs. In general, the characteristic volume depends on a number of interrelated parameters, including, for example: * the minimum distance that the coating 608 on the solvent absorbent element 110 requires shifting to contact the electrodes 106a, 106b. As this distance increases, the characteristic volume increases; and * the expansion coefficient of the solvent absorbent element 110 (i.e., ratio of element 110 volume increase relative to the volume of absorbed solvent). As the expansion coefficient increases the characteristic volume decreases.

Turning now to Figure 7A and 7B, an alternative example of solvent responsive switch 702 for a solvent detector is shown. Figure 7A shows the open configuration; Figure 7B shows the closed configuration.

The switch 702 comprises two spaced electrodes 106a, 106b; a flexible membrane 710; and a movable, electrically conductive element 108 mechanically coupled to the flexible membrane. The conductive element 108 is vertically spaced from the electrodes 106a, 106b so that, when the flexible membrane 710 shifts upwards, the conductive element 108 is able to establish electrical contact between the electrodes 106a, 106b to close the switch 702.

The switch 710 further comprises a housing 112 which defines an enclosure that the flexible membrane 710 spans across. The housing comprises a material (e.g., a plastic) that is not affected by the solvent. That is, the housing is immune to dissolution/reaction in the solvent. The flexible membrane 710 may be fixedly attached to the inwardly facing walls of the housing 112. The base of the housing 112 includes a network of capillaries 204 (as described above in relation to Figure 2) to allow solvent ingress to the housing 112. As above, the network of capillaries 204 may be provided with a coating to encourage wetting and capillary action. For example, if the capillaries comprise a material that is hydrophobic and the solvent is water, the capillaries can be provided with a hydrophilic coating to facilitate ingress of water.

The flexible membrane 710 is impervious to the solvent so that any solvent that enters the housing 112 collects beneath the membrane 710. As the housing continues to fill with solvent, the fluid level inside the housing rises and it first contacts the flexible membrane 710 and then shifts the membrane upwardly towards the electrodes 106a, 106b. The weight of the conductive element 108 resists this upward motion. The switch closes when the membrane 710 shifts the conductive element 108 upward enough for contact to be made with the electrodes 106a, 106b. This requires a characteristic volume of solvent.

In some examples (not shown), the flexible membrane 710 may bow upwardly about its attachment points with the housing 112, when the switch is in the closed state. The skilled reader will appreciate that the degree of bowing of the flexible membrane 710 in the open and closed states is not essential for the functioning of the switch.

In the absence of the solvent, the weight of the conductive element 108 maintains the vertical spacing between the electrodes 106a, 106b and the conductive element 108. In the open state, the flexible membrane 710 may generally bow downwardly although the skilled reader will understand that is not essential.

As has already been mentioned, a characteristic volume of solvent is required to effect switching. This characteristic volume can be tuned according to required sensitivity of the detector. The characteristic volume depends on a number of interrelated parameters, including, for example: * the vertical distance that the electrically conductive element 108 requires shifting to contact the electrodes 106a, 106b. As this distance increases, the characteristic volume increases. In turn, this vertical distance depends on: o the ratio of weight of the electrically conductive element 108 and the stiffness of the membrane 710. As this ratio increases, the membrane 710 bows downwardly to a greater extent, increasing the vertical distance between conductive element 108 and electrodes 106a, 106b; and a the thickness of the electrically conductive element 108; and 9 The dimensions of the enclosure (e.g., width, length).

The conductive element 108 may be fixedly attached to the membrane 710, although it is envisaged that, provided the element 108 is sufficiently heavy compared to the stiffness of the membrane 710, the downward deflection/bowing of the membrane 710 induced by its weight may be sufficient to hold the element 108 in the correct position (i.6 below the spacing between electrodes 106a, 106b) to allow switching.

In some examples, the conductive element 108 is integral with the membrane 710, e.g., as a conductive pad embedded within the membrane 710. In some examples, the flexible membrane 710 is intrinsically electrically conductive (e.g., the conductive element 108 is a portion of the membrane 710 embedded with conductive (e.g., metallic, carbon) particles). In such an example, the upward bowing of the membrane 710 allows contact to be made with electrodes 106a, 106b to close the switch.

Figure 8 is another example of a solvent responsive switch 802 for a solvent detector is shown. Figure 8A shows the switch 802 in an open state; Figure 8B shows the switch 802 in a closed state. Figure 8C shows a variant of the switch 802 in Figure 8A, having an aperture 804 in the housing 112 rather than a network of capillaries 204. As above, the network of capillaries 204 may be provided with a coating to encourage wetting and capillary action. For example, if the capillaries comprise a material that is hydrophobic and the solvent is water, the capillaries can be provided with a hydrophilic coating to facilitate ingress of water.

The switch 802 shown in Figures 8A and 8B differs from the switch 702 of Figure 7A and 7B in that the flexible membrane is replaced with buoyant element 810. As solvent enters the housing 112 via 204 and collects within the enclosure of the housing, the fluid level 814 inside the housing rises. The buoyant element 810 floats and hence shifts the conductive element 108 to which it is coupled towards the electrodes 106a, 106b as the fluid level 814 continues to rise. Eventually, the conductive element 108 is shifted upward enough to make contact with the electrodes 106a, 106b to close the switch 802. This requires a characteristic volume of solvent.

The conductive element 108 may be fixedly attached (e.g., glued) to the buoyant element 810. Alternatively, the conductive element 108 may be provided as an insert that is received by e.g., a recess in the buoyant element 810. In some examples, the buoyant element 810 is intrinsically electrically conductive (e.g., the conductive element 108 is a portion of the buoyant element 810 embedded with conductive (e.g., metallic, carbon) particles). In such an example, the switch closes after the conductive portion of the buoyant element 810 contacts electrodes 106a, 106b.

The characteristic volume required can be tuned according to required sensitivity of the detector. The characteristic volume depends on a number of interrelated parameters, including, for example: * the vertical distance that the electrically conductive element 108 requires shifting to contact the electrodes 106a, 106b. As this distance increases, the characteristic volume increases; and * The dimensions of the enclosure (e.g., width, length). As these dimensions increase, the characteristic volume increases.

Figures 9A and 9B show yet another example of a solvent responsive switch 902. Figure 9A shows the open configuration; Figure 9B shows the closed configuration.

The switch 902 differs from the switch 202 shown in Figure 2in that the solvent absorbent element 110 is vertically spaced from the base of the enclosure.

Unlike in Figure 2, where solvent may be immediately absorbed by element 110 upon ingress into the enclosure, in Figures 9A and 9B, the solvent absorbent element 110 is only able to absorb solvent after the fluid level of solvent rises high enough to contact the absorbent element 110. The characteristic volume to effecting switching is therefore greater in Figures 9A and 9B than in Figure 2, which can be useful depending on operational needs.

The solvent absorbent element 110 may be seated above the base of the enclosure on a shelf extending away from the enclosure walls (not shown). Alternatively, or in addition, the element 110 engages with the inwardly facing walls of the housing and is held above the base by friction.

In some examples, the conductive element 108 defines an opening 114 for solvent ingress to the enclosure 112 (as shown in Figures 1A and 1B). In a specific example, the conductive element 108 is a mesh or a thin film mesh (thickness less than 1mm).

The characteristic volume required to effect switching in Figures 9A and 9B depends on a number of interrelated parameters, including, for example: * the vertical distance that the electrically conductive element 108 requires shifting to contact the electrodes 106a, 106b. As this distance increases, the characteristic volume increases; * the vertical spacing of the solvent absorbent element 110 from the base As this spacing increases, the characteristic volume increases; * The dimensions of the enclosure (e.g., width, length). As these dimensions increase, the characteristic volume increases; and * the expansion coefficient of the solvent absorbent element 110 (i.e., the ratio of element 110 volume increase relative to the volume of absorbed solvent). As the expansion coefficient increases the characteristic volume decreases; In the alternative example shown in Figures 10A and 108, the moveable electrically conductive element 108 is replaced by a thin film 1008, which spans between electrodes 106a, 106b to close the switch 1002. In the presence of its solvent however, the solvent absorbent element 110 expands and ruptures the thin film (Figure 103), thereby irreversibly opening the switch 1002. The solvent absorbent element 110 is therefore responsive to effect switching in the presence of its solvent.

In an alternative example to that shown in Figures 10A and 103, as shown in Figures 11A and 113, the solvent absorbent element 110 is replaced with a solvent responsive element 1110 that dissolves (at least partially) in the presence of its solvent. In the closed state, the metallic thin film 1008 spans across the electrodes 106a, 106b. The film 1008 is however sufficiently thin that it is unable to support itself bridging the gap between the electrodes 106a, 106b. The solvent responsive element 1110 provides support to the thin film 1008 to prevent it collapsing under its own weight. However, in the presence of its solvent, the solvent responsive element 1110 dissolves and the thin film 208 breaks to irreversibly open the switch 1102.

In yet another example to that shown in Figures 10A and 10B, as shown in Figures 12A and 12B, the solvent absorbent element 110 is removed entirely and the conductive element 208, 1008 (which may be a thin film) itself constitutes a solvent responsive element. More particularly, the conductive element 208, 1008 is configured to dissolve (at least partially) in its solvent so that the switch 1202 opens in the presence of solvent. The conductive element 208 is sufficiently thick and the spacing between the electrodes 106a, 106b sufficiently small that the conductive element 208, 1008 is able to bridge the gap between electrodes 106a, 106b without breaking.

Comparing the examples shown in Figures 11 and 12, it is noted that polymers generally dissolve more slowly than metals because dissoiution is controlled by the movement of polymer chains: either their disentanglement or their diffusion across a boundary layer adjacent to the polymer-solvent interface. This movement is comparatively slow. This leads to a larger time delay in switching.

Any solvent which can either partially or fully dissolve a polymer or a metal can be detected by the switch shown in Figures 11 and 12. Example solvents include: water, alcohols, chlorine (e.g., hydrochloric acid), fluorine (e.g., hydrofluoric acid), sulphur (e.g., sulphuric acid), benzene, toluene, xylene or the like. A Table of solvents which are suitable for dissolving certain polymers is shown below. The skilled reader will appreciate that suitable blends of these polymers will also be dissolvable in the listed solvents.

Polymer Suitable solvent Polyethylene HC (hydrocarbon) and halogenated HC Polybutadiene HC, THF, ketones Polyacrylates Aromatic HC, chlorinated HC, THF, esters, ketones Polymethacrylates Aromatic HC, chlorinated HC, THF, esters, MEK Polyacrylamide Water Poly(vinyl) ethers Halogenated HC, MEK, butanol Poly (vinyl alcohol) Glycols, DMF Poly (vinyl acetate) Aromatic HC, chlorinated HC, THF, esters, DMF Poly (vinyl chloride) THF, DMF, DMSO Poly (vinylidene chloride) THF, dioxane, DMF Polyacrylonitrile DMF, DMSO Polyurethanes Aromatic HC, THF, DMF Polyureas Phenol, formic acid HC= hydrocarbon, THF= Tetrahydrofuran, MEK = 2-Butanone, DMF= N, ND imethylform am ide, DMSO= Dimethly sulfoxide A Table of solvents which are suitable for dissolving certain metals is shown below. The skilled reader will appreciate that suitable alloys of these metals will also be dissolvable in the listed solvents.

Metal Suitable solvent Aluminium Sodium hydroxide, potassium hydroxide, hydrochloric acid Copper Nitric acid, sulphuric acid Gold Mixture of hydrochloric acid and nitric acid Silver Hydrochloric acid, nitric acid In Figures 1 to 6 and 9 to 11, the solvent absorbent element 110 may be a super-absorbing polymer (SAP). A SAP is a water-absorbing polymers (classified as a hydrogel when mixed), which can absorb aqueous solutions through hydrogen bonding with water molecules. A SAP's ability to absorb water depends on the ionic concentration of the aqueous solution. In deionized and distilled water, a SAP may absorb 300 times its weight (from 30 to 60 times its own volume) and can become up to 99.9% liquid, and when put into a 0.9% saline solution the absorbency drops to approximately 50 times its weight. The presence of valence cations in the solution impedes the polymers ability to bond with the water molecule. A super-absorbing polymer is any water-absorbing polymer that is able to absorb greater than 10g of water per 1g of SAP (10g/g) and retain that absorbed water under pressure (> 0.67g/cm2). Some SAPs are able to absorb up to 800 times their weight. The SAP may be a particle, a plurality of particles (i.e., in powder form) or a film having a thickness of around 0.1mm to 1mm. Each SAP particle is between 0.1 to 5mm in size (e.g., diameter). As the SAP particles are small, the footprint of the switch may also advantageously be small. The solvent absorbent element 110 described above may also be referred to as a solvent responsive element.

Optionally, the expansion of the solvent absorbent element 110 is reversible. That is, after the solvent (e.g., water) is removed and/or the solvent absorbent element 110 dries, they 110 will shrink back to their original size (when dry). The switches described in Figures 1 to 6 and 9 therefore support multiple switching cycles.

An example SAP material is sodium polyacrylate with water as a solvent. Sodium polyacrylate is a network polymer comprising cross-linked polymer chains. Sodium polyacrylate absorbs water by osmosis. When in contact with water, there is a tendency for the sodium to distribute equally between the network polymer and the water. That is, some of the sodium atoms migrate from the network polymer to the water and are replaced with water molecules. Accordingly, the network polymer swells and the cross-links between polymer chains prevent dissolution. Sodium polyacrylate can absorb 800 times its weight of distilled water, and 300 times its weight in tap water (since tap water contains some sodium, calcium and other mineral salts).

Other SAP materials include: laponite (a synthetic clay) and clay-polymer hydrogels.

These swell in the presence of water. Further examples include, polyethylene oxide (PEO), laponitelPEO blends, sodium polyacrylate (PAAS) and laponite/PAAS blends.

The solvent absorbent element in Figures 1 to 6 and 9 may also be cellulosic or fibre-based, e.g., tissue paper, sponge, cotton, or fluff pulp. These materials do not absorb as much solvent as SAP materials but they have the advantage of being less solvent sensitive.

Although the solvent has been described as being water, any solvent can be detected (either as a vapour or as a liquid) by selection of a suitable material for the solvent absorbent element 110.

For example: polydimethylsiloxane (PDMS) swells in: acetone (up to 95 by volume); methyl ethyl ketone (MEK) (up to 80% by volume); toluene (up to 150% by volume); and hexane (up to 180% by volume), within a 24 hour time period. Percentage values for swelling are calculated as: (Vs-Vd)/Vd, wherein Vd is the volume of the polymer, Vs is the volume of the swollen polymer.

Other polymers, such as polyimide P84®, Matrimie, polyethylenimine (PEI), polyacrylonitrile (PAN), polysulfone (PES), poly(ether-sulfone) (PSF), PEBAX®, poly(1-trimethylsily1-1-propyne) (PTMSP) swell in any one or more of the following: hexane, toluene, dichloromethane, ethyl acetate, methyl ethyl ketone, acetone, isopropanol, ethanol, methanol and water.

Turning to Figure 13A and 13B, a detector 1300 adapted to detect the presence (or absence) of a solvent is shown. The device 1300 includes: a transmitter 1302; a receiver 1304; a housing 1312; and a solvent absorbent element 1310 arranged in the housing and in a radiation path between the transmitter 1302 and receiver 1304. The housing 1312 defines an aperture 1314 to allow solvent ingress into the housing enclosure. In some examples, a network of capillaries 204 (as shown in Figure 2) is inserted into aperture 1314.

As the solvent absorbent element 1310 expands and shrinks in the presence and absence of solvent, the radiation path (e.g., its length) between the transmitter 1302 and receiver 1304 changes. The intensity of the radiation measurable at the receiver correspondingly changes. That is, as the solvent absorbent element 1310 expands, the radiation path decreases in length and a greater intensity is measured. The detector includes a controller with a processor to analyse the measured radiation intensifies. An increase in radiation intensity greater than a predetermined threshold is considered indicative of the device 1300 being in the presence of its solvent. The device 1300 may use a calibrated intensity value which corresponds to the expected light intensity when the element 1310 is dry to calculate this change.

The solvent absorbent element 1310 may be any of the example solvent absorbent elements described above. In a specific example, the radiation is light and the transmitter 1302 and receiver 1304 respectively comprise a light source (e.g., LED) and light sensor.

However, the radiation may instead be infrared with the transmitter and receiver being an infrared source (e.g., infrared LED) and an infrared sensor.

Any of the detectors described above may include a plurality of switches arranged in series, parallel and/or in a matrix (having m rows x n columns, where m and n are integers greater than or equal to 1). Such a matrix 1400, comprising three rows and three columns of wire 1404, is shown in Figure 14. A switch (denoted 100 in the Figure but which could be any of the switches described above) and a protective diode 1402 respectively connects each row to each column.

The skilled reader will appreciate that m and n may take any integer value (e.g., 5x10, 10x5, 20x20). The spacing between the rows and columns of the matrix arrangement 500 may be 5cm to 1m, specifically 10cm to 30cm, more specifically 15 to 20cm. The exact number and spacing between rows and columns is set according to the needs of the environment being monitored and the desired spatial sensitivity. In a specific example, the matrix may be up to several square metres in area, comprising up to 20 rows and columns, having a spacing of 15cm.

The working principle of selectively monitoring whether any given switch in the matrix is open or closed (i.e., determining if solvent absent/present) will now be described. The skilled reader will understand that the working principle extends to any dimension (m, n) of matrix.

If a potential difference V2 -Vi is applied across column 1 (Cl) and a potential difference V4-V3 is applied across row 1 (R1), then the potential difference across the switch that connects the column 1 and row 1 (denoted herein (1, 1)) is equal to V4-V1. A current may flow through column 1 (denoted 121), row 1 (denoted 143) and the switch 100 (denoted 141) from column 1 to row 1. The current measured in row 1 is the sum of 143 and 141.

As described above, the switch 100 may either be closed (allow current to pass through it) or open (prevent current passing through it) in the presence or absence of solvent. 141 is therefore equal to zero when the switch 100 is in the open configurational state, whereas 141 is non-zero when the switch 100 is in the closed configurational state. The measurable current that flows in row 1 therefore differs by 141 depending on whether the switch 100 is closed or open. By monitoring for this change in current, it can be determined whether a particular switch 100 in the matrix is in the presence or absence of solvent. This process can be repeated for each of the other switches (m, n).

Each switch in the matrix may be monitored periodically (e.g., every hour or once or day). In some examples, if solvent is detected by any one switch, neighbouring switches can be selected for monitoring to more rapidly determine the area where solvent may be present (i.e., the extent of the leak).

Any of the detectors described above may be printed on a substrate in a reel-to-reel (or roll-to-roll) process. For example, conductor tracks can be printed on the substrate, and the detectors subsequently connected thereto (e.g., via a pick and place process). The detectors may be placed at uniform intervals. In some examples, the detectors are provided on a PCB, which can be replaceably connected and disconnected. This is particularly advantageous where switching is irreversible (Figures 10 to 12).

The detectors may advantageously be small in size (e.g., less than few cubic mm). The detectors can be produced by MEMs technology, CNC machining, injection moulding or the like, which are processes known to the skilled reader.

Any of the detectors described above may further comprise a sensor panel having any one or more of the following auxiliary components: an alarm, light element (e.g., LED) and/or an RE antenna, which are activated (i.e., the alarm sounds, the light element is powered on and the RF transmits a signal) conditional on the solvent being detected.

The sensing panel comprises an electronic controller, which is configured to operate the auxiliary components in response to a switch in the detector being closed and/or opened and which is indicative of the device being the presence of solvent. For example, the alarm may be sounded responsive to the switch being closed, if the detector closes in the presence of solvent. Alternatively, the alarm may be sounded responsive to the switch being opened, if the detector opens in the presence of solvent.

The RFID of the RE antenna may be used to identify the RE antenna and correspondingly the detector location. The RE antenna may transmit a signal to a mobile or a laptop or a server (e.g., via WiFi or Bluetooth), which is monitoring the status of the sensing panel.

In some examples, the panel includes an optical transmitter and optical detector for monitoring whether the solvent absorbent element or solvent responsive element has expanded, dissolved or moved.

References to the relative terms such as vertical and lateral should be interpreted in light of the device orientation when in normal use.

The invention has been described in detail with reference to the examples. Modifications may, however, be made without departing from the scope of the invention as defined by the claims. Each feature disclosed or illustrated may be incorporated in the invention, whether alone or in any appropriate combination with any other feature disclosed or illustrated herein.

Claims

CLAIMS: 1. A device configured to detect the presence of a solvent, the device comprising: a solvent responsive switch, comprising: a set of two electrodes; an electrically conductive element configured to move from a first configurational state to a second configurational state responsive to the presence or absence of solvent, wherein, in the first configurational state, the electrically conductive element is in electrical contact with said electrodes so as to close the solvent responsive switch, and wherein, in the second configurational state, the electrically conductive element is electrically disconnected from said electrodes so as to open the solvent responsive switch 2. The device according to claim 1, further comprising: a solvent absorbent element configured to expand in the presence of the solvent, and wherein, said expansion of the solvent absorbent element effects movement of the electrically conductive element between the configurational states.3. The device according to claim 2, further comprising: a housing defining an enclosure for containing the solvent absorbent element and the electrically conductive element, wherein, the electrically conductive element is slidably movable within the enclosure between the configurational states.4. The device according to claim 3, wherein the solvent absorbent element is seated on a shelf above a base of the housing from which solvent is able to ingress.5. The device according to any preceding claim, wherein the electrically conductive element is a film, which in the first configurational state, is in physical contact with and extends between the two electrodes, and wherein, the electrically conductive element transitions to the second configurational state by the expansion of the solvent absorbent element rupturing the film.6. The device according to claim 2, wherein the electrically conductive element is resiliently shaped to define an enclosure for containing the solvent absorbent element, and wherein expansion of the solvent absorbent element causes the shape of the electrically conductive element to change so that physical contact is made between the electrically conductive element and the electrodes.7. The device according to claim 6, wherein the electrically conductive element comprises a base portion and side wall portions extending from the base portion, and wherein expansion of the solvent absorbent element causes the side wall portions to pivot outwardly about the base portion so that physical contact is made between the side wall portions and the electrodes.8. The device according to claim 2, wherein the electrically conductive element defines a split housing, comprising a first and a second part, for containing the solvent absorbent element, and the device further comprises: a biasing element configured to urge the first and second parts of the split housing together into the first configurational state; wherein expansion of the solvent absorbent element causes the first and second part of the split housing to physically separate from one another, thereby transitioning from the first to the second configurational state.9. The device according to claim 2, further comprising: a first and a second housing respectively defining an enclosure for containing a solvent absorbent element; wherein, the electrically conductive element comprises a first portion forming part of the first housing and a second portion forming part of the second housing, wherein the first and second housings are arranged such that the first and second portions of the conductive element oppose one another, and wherein expansion of the solvent absorbent element causes the first and second portions of the electrically conductive elements to make physical contact with one another.10. The device according to claim 9, wherein expansion of the solvent absorbent element causes the first and/or second portion of the electrically conductive element to bow into physical contact with one another.11. The device according to claim 2, wherein the electrically conductive element is provided as a coating which at least partially covers the solvent absorbent element, and wherein expansion of the solvent absorbent element causes said coating to make contact with the two electrodes.12. The device according to any preceding claim, wherein: the solvent absorbent element comprises polydimethylsiloxane (PDMS) and the solvent is any one or more of acetone, methyl ethyl ketone, toluene or hexane; or the solvent absorbent element comprises any one or mixture of: polyimide P84®, Matrimid", polyethylenimine (PEI), polyacrylonitrile (PAN), polysulfone (PES), poly(ether-sulfone) (PSF), PEBAX®, poly(1-trimethylsily1-1-propyne) (PTMSP) and the solvent is any one or mixture of: hexane, toluene, dichloromethane, ethyl acetate, methyl ethyl ketone, acetone, isopropanol, ethanol, methanol and water.13. The device according to any preceding claim, wherein the solvent absorbent element comprises a super absorbent polymer, SAP.14. The device according to claim 13, wherein the SAP comprises a particle having dimensions of around 0.5mm to 5mm, or the SAP comprises a film having a thickness of around 0.1mm to lmm.15. The device according to claim 1, further comprising: a solvent responsive element configured to move in the presence of the solvent to effect movement of the electrically conductive element between the configurational states.16. The device according to claim 15, further comprising a housing defining an enclosure for containing the solvent responsive element and the electrically conductive element, wherein, the electrically conductive element is arranged on the solvent responsive element, which is configured to be buoyant in the solvent so that, as solvent fills the enclosure, the solvent responsive element moves towards the electrodes, causing the electrically conductive element to make physical contact with the electrodes.17. The device according to claim 15, further comprising: a housing defining an enclosure for containing the solvent responsive element and the electrically conductive element, wherein, the electrically conductive element is arranged on the solvent responsive element, which is a film extending across the enclosure and impermeable to the solvent, so that, as solvent fills the enclosure, the film is deflected towards the electrodes, causing the electrically conductive element to make physical contact with the electrodes.18. The device according to claim 1, further comprising: a solvent responsive element configured to dissolve in the presence of the solvent, and wherein, said dissolution of the solvent responsive element effects movement of the electrically conductive element between the configurational states.19. The device according to claim 18, wherein the electrically conductive element is a film, which in the first configurational state, is in physical contact with and extends between the two electrodes and which is supported by the solvent responsive element, and wherein, the electrically conductive element transitions to the second configurational state as the support provided by the solvent responsive element is removed following its dissolution or partial dissolution.20. The device according to claim 19, wherein: the solvent responsive element comprises polyethylene and the solvent comprises any one or more of: a hydrocarbon; or a halogenated hydrocarbon; the solvent responsive element comprises polybutadiene and the solvent comprises any one or more of: a hydrocarbon, Tetrahydrofuran or a ketone; the solvent responsive element comprises polyacrylate and the solvent comprises any one or more of: an aromatic hydrocarbon, a chlorinated hydrocarbon, Tetrahydrofuran, an ester or 2-Butanone, the solvent responsive element comprises polyacrylamide and the solvent comprises water; the solvent responsive element comprises poly(vinyl) ether and the solvent comprises a halogenated hydrocarbon, 2-Butanone or butanol; the solvent responsive element comprises poly(vinyl) alcohol and the solvent comprises a glycol or N, N-Dimethylformamide; the solvent responsive element comprises poly (vinyl acetate)and the solvent comprises an aromatic hydrocarbon, a chlorinated hydrocarbon, Tetrahydrofuran, an ester or N, N-Dimethylformamide; the solvent responsive element comprises poly (vinyl chloride)and the solvent comprises Tetrahydrofuran, Dimethly sulfoxide or N, N-Dimethylformamide; the solvent responsive element comprises poly (vinylidene chloride) and the solvent comprises Tetrahydrofuran, dioxane or N, N-Dimethylformamide; the solvent responsive element comprises polyacrylonitrile and the solvent comprises Dimethly sulfoxide or N, N-Dimethylformamide; the solvent responsive element comprises polyurethane and the solvent comprises an aromatic hydrocarbon, Tetrahydrofuran or N, N-Dimethylformamide; or the solvent responsive element comprises polyurea and the solvent comprises a phenol or formic acid.21. The device according to claim 1, wherein the electrically conductive element is configured to at least partially dissolve in the presence of the solvent and said dissolution of the electrically conductive element effects the movement of the electrically conductive element from the first to the second configurational state.22. The device according to claim 21, including any one of the following features: i) the electrically conductive element comprises aluminium and the solvent comprises any one or more of sodium hydroxide, potassium hydroxide or hydrochloric acid; ii) the electrically conductive element comprises copper and the solvent comprises any one or more of nitric acid or sulphuric acid; Hi) the electrically conductive element comprises gold and the solvent comprises hydrochloric acid, nitric acid or a mixture thereof; or iv) the electrically conductive element comprises silver and the solvent comprises any one or more of hydrochloric acid or nitric acid.23. A device configured to detect the presence of a solvent, the device comprising: a transmitter and receiver; and a solvent absorbent element arranged in a radiation path between the transmitter and receiver, wherein, the solvent absorbent element is configured to expand in the presence of the solvent in order to change the radiation path between the transmitter and receiver and cause the intensity of radiation received by the receiver to change by a predetermined threshold, said threshold being indicative of the device being in the presence of the solvent.24. A method of detecting the presence of a solvent using a device according to any one of the preceding claims, the method comprising: determining that the solvent is present conditional upon whether an electrical current is able to pass through the solvent responsive switch in the device.25. The method according to any of the preceding claims, further comprising, in response to said determining step, triggering any or more of: sounding an alarm; switching on a light element; and transmitting an RF signal from an RF antenna to a remote device.