U.S. patent application number 17/439380 was filed with the patent office on 2022-06-16 for interferent and baseline drift correcting sensor system.
This patent application is currently assigned to Sumitomo Chemical Co., Ltd.. The applicant listed for this patent is Sumitomo Chemical Co., Ltd.. Invention is credited to Robert Archer, Pascal Cachelin, Nicholas Dartnell, Daniel Tobjork.
Application Number | 20220187265 17/439380 |
Document ID | / |
Family ID | 1000006229355 |
Filed Date | 2022-06-16 |
United States Patent
Application |
20220187265 |
Kind Code |
A1 |
Tobjork; Daniel ; et
al. |
June 16, 2022 |
INTERFERENT AND BASELINE DRIFT CORRECTING SENSOR SYSTEM
Abstract
A sensor system that removes responses from an interferent
and/or corrects for baseline drift of a sensor to determine a
presence, a concentration or a change in concentration of a target
material in a gaseous environment. Fluid flowing into the system
may be directed by a valve arrangement to either a first fluid flow
path or a second fluid flow path. The target material may be
absorbed by a filter material in the first fluid flow path. Fluid
flowing along the second gas flow path passes directly to the
sensor. Responses of the sensor to fluids from the first and second
fluid flow paths may be used to determine a presence, concentration
or change in concentration of the target material.
Inventors: |
Tobjork; Daniel;
(Cambridgeshire, GB) ; Dartnell; Nicholas;
(Cambridgeshire, GB) ; Cachelin; Pascal;
(Cambridgeshire, GB) ; Archer; Robert;
(Cambridgeshire, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sumitomo Chemical Co., Ltd. |
Tokyo |
|
JP |
|
|
Assignee: |
Sumitomo Chemical Co., Ltd.
Tokyo
JP
|
Family ID: |
1000006229355 |
Appl. No.: |
17/439380 |
Filed: |
March 16, 2020 |
PCT Filed: |
March 16, 2020 |
PCT NO: |
PCT/GB2020/050667 |
371 Date: |
September 14, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01N 33/0031 20130101;
G01N 33/0047 20130101; G01N 33/0014 20130101 |
International
Class: |
G01N 33/00 20060101
G01N033/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 14, 2019 |
GB |
1903473.5 |
Claims
1. A sensor system configured to determine a presence, a
concentration or a change in concentration of a target material in
a gaseous or liquid environment, comprising: a sensor configured to
respond to the target material; an inlet configured to draw gas
from an environment into the apparatus; and a valve arrangement
configured to direct fluid drawn from the environment to a first
fluid flow path in fluid communication with the sensor or to a
second fluid flow path in fluid communication with the sensor.
2. The system according to claim 1, wherein the first fluid flow
path is disposed between the sensor and a first valve of the valve
assembly and the second fluid flow path is disposed between the
sensor and a second valve of the valve assembly.
3. The system according to claim 1 wherein the first and second
fluid flow paths are disposed between the sensor and a three-way
valve of the valve assembly.
4. The system according to claim 1, wherein the system further
comprises a third fluid flow path in fluid communication with the
sensor and disposed between a valve of the valve arrangement and
the sensor.
5. The system according to claim 1, wherein a water reservoir in
fluid communication with the first fluid flow path is disposed in
fluid communication with the first fluid flow path between the
valve assembly and the sensor.
6. The system according to claim 5, wherein the water reservoir is
in fluid communication with the second fluid flow path.
7. The system according to claim 6, wherein a saturated salt
solution is disposed in the water reservoir.
8. The system according to claim 6 wherein a desiccant is disposed
between the inlet and the valve assembly.
9. The system according to claim 6 wherein a desiccant is disposed
in the second fluid flow path.
10. The system according to claim 1, wherein the sensor is a thin
film transistor.
11. The system according to claim 1, wherein a filter material for
removing the target material from the fluid is disposed in the
first fluid flow path.
12. The system according to claim 11, wherein the filter material
is a desiccant filter material.
13. The system according to claim 11, wherein the filter material
comprises silica gel.
14. The system according to claim 11, wherein the filter material
is a molecular sieve.
15. The system according to claim 1 wherein the system is a gas
sensor system and the sensor is a gas sensor.
16. A kit for forming the sensor system according to claim 1,
comprising a sensor, a fluid inlet, a first fluid flow path, a
second fluid flow path and at least one valve for forming the valve
arrangement.
17. (canceled)
18. A method of determining a presence, concentration or change in
concentration of a target material in a gaseous or liquid
environment, the method comprising: measuring, in either order, a
first response and a second response of a sensor of a sensor system
wherein the sensor is configured to respond to the target material
and wherein the sensor system comprises: the sensor; an inlet
configured to draw gas from an environment into the apparatus; and
a valve arrangement configured to direct fluid drawn from the
environment to a first fluid flow path in fluid communication with
the sensor or to a second fluid flow path in fluid communication
with the sensor, wherein the first response is a response of the
sensor to fluid from the first flow path which has been treated to
remove the target material from the fluid and the second response
is a response of the sensor to fluid from the second flow path
which has not been treated to remove the target material from the
fluid; and subtracting the first sensor measurement or a derivative
thereof from the second sensor measurement or a derivative
thereof.
19. The method according to claim 18, wherein a filter material for
removing the target material from the fluid is disposed in the
first fluid flow path.
20. The method according to claim 18, wherein the first sensor
measurement is generated by exposing the sensor to a sample from
the fluid environment which has been exposed to a desiccant filter
material and rehydrated.
21. (canceled)
22. The method according to claim 18, wherein the target material
is 1-methylcyclopropene.
23-34. (canceled)
Description
BACKGROUND
[0001] Embodiments of the present disclosure relate to apparatus
and methods for sensing a target gas in an environment. More
particularly, but not by way of limitation, a gas sensor system is
provided that corrects/removes effects of interferent and/or
corrects baseline drift. Some embodiments of the present disclosure
relate to apparatus and methods for sensing a polar gas, e.g.
1-methylcyclopropene (1-MCP).
[0002] Thin film transistors (TFTs) have been previously used as
gas sensors. For example, such use of thin film transistors as gas
sensors is described in Feng et al, "Unencapsulated Air-stable
Organic Field Effect Transistor by All Solution Processes for Low
Power Vapor Sensing" Scientific Reports 6:20671 DOI:
10.1038/srep20671 and Besar et al, "Printable ammonia sensor based
on organic field effect transistor", Organic Electronics, Volume
15, Issue 11, November 2014, Pages 3221-3230. In thin film
transistor gas sensors, a semiconducting layer is in electrical
contact with source and drain electrodes and a gate dielectric is
disposed between the semiconducting layer and a gate electrode.
Interaction of a target material with the TFT gas sensor may alter
the drain current of the TFT gas sensor.
[0003] Ethylene produced by plants can accelerate ripening of
climacteric fruit, the opening of flowers, and the shedding of
plant leaves. 1-methylcyclopropene (1-MCP) is known for use in
inhibiting such processes.
[0004] It may be desirable to determine the presence and/or
concentration of certain materials in a gaseous environment.
However, a gas sensor used for this purpose may respond to one or
more materials in the environment other than the target material;
the concentration of background materials in the environment that
the gas sensor responds to may change over time; or the response of
the gas sensor to a target or background material may change as the
gas sensor ages.
SUMMARY
[0005] In some embodiments there is provided apparatus configured
to determine a presence, a concentration or a change in
concentration of a target material in an environment, e.g. a liquid
or gaseous environment. The apparatus may contain a sensor, e.g. a
gas sensor, configured to respond to the target material. The
apparatus may contain a fluid inlet, e.g. a liquid or gas inlet,
configured to draw liquid or gas from an environment into the
apparatus. The apparatus may contain a valve arrangement configured
to direct fluid drawn from the environment to a first fluid flow
path in fluid communication with the sensor or to a second fluid
flow path in fluid communication with the gas sensor.
[0006] Optionally, the first fluid flow path is disposed between
the gas sensor and a first valve of the valve assembly and the
second fluid flow path is disposed between the gas sensor and a
second valve of the valve assembly.
[0007] Optionally, the first and second fluid flow paths are
disposed between the sensor and a three-way valve of the valve
assembly.
[0008] Optionally, the apparatus further has a third fluid flow
path in fluid communication with the sensor and disposed between a
valve of the valve arrangement and the sensor.
[0009] Optionally, in the case where the fluid is a gas, a
humidification stage, e.g. comprising or consisting of a water
reservoir, in fluid communication with the first fluid flow path is
disposed in fluid communication with the first fluid flow path
between the valve assembly and the sensor. Optionally, the
humidification stage, e.g. the water reservoir, is in fluid
communication with the first and second fluid flow paths.
Optionally, a saturated salt solution is disposed in the water
reservoir. A desiccant may be disposed in a dehumidification stage
for dehumidification of gas drawn into the apparatus, the
dehydrated gas being subsequently rehydrated at the humidification
stage. Optionally, the dehumidification stage is disposed between
the inlet and the valve assembly. Optionally, the desiccant is
disposed in the second fluid flow path.
[0010] Optionally, the sensor is a thin film transistor.
[0011] In some embodiments there is provided a method of
determining a presence, concentration or change in concentration of
a target material in an environment, e.g. a liquid or gaseous
environment. The process may include measuring, in either order, a
first response and a second response of a sensor of the sensor
apparatus. The first response may be a response of the sensor to
gas from the first flow path which has been treated to remove the
target material from the fluid. The second response may be a
response of the sensor to gas from the second flow path which has
not been treated to remove the target material from the fluid. The
method may include subtracting the first sensor measurement or a
derivative thereof from the second sensor measurement or a
derivative thereof.
[0012] Optionally, a filter material for removing the target
material from the fluid is disposed in the first fluid flow
path.
[0013] In some embodiments, the filter material is a molecular
sieve.
[0014] In some embodiments, the filter material is a desiccant
filter material, optionally silica gel.
[0015] Optionally, the first sensor measurement is generated by
exposing the sensor to a sample from the environment which has been
exposed to the desiccant filter material and rehydrated.
[0016] Optionally, the system is a gas sensor system, the sensor is
a gas sensor and the environment from which the fluid is drawn is a
gaseous environment.
[0017] Optionally, the target material is an alkene, optionally
ethylene or 1-methylcyclopropene.
[0018] Optionally, the first and second sensor measurements or
derivatives thereof are a selected from a change in resistance of
the sensor; or, in the case of a TFT sensor, a change in drain
current of the sensor; and a change in dI/dt wherein I is drain
current and t is time.
[0019] In some embodiments there is provided a method of
withdrawing 1-methylcyclopropene from a gaseous environment in
which the environment is contacted with silica gel.
[0020] In some embodiments there is provided method of determining
a presence, a concentration or a change in concentration of a
target material, e.g. a target gas, in an environment. The method
may include measuring a rate of change in drain current or
resistance of a TFT gas sensor upon exposure to the environment for
a time period. The method may include determining, from the rate of
change, a presence, a concentration of a change in concentration of
the target material at a point during the time period.
[0021] Optionally, the method includes determining dI/dt for the
time period wherein I is drain current and t is time; identifying
dI/dt peaks; and determining, from the dI/dt peaks, a presence, a
concentration or a change in concentration of the target material
at the point during the time period. Optionally, the gas is
1-methylcyclopropene.
[0022] In some embodiments, the present disclosure provides a
method of determining a presence, concentration or change in
concentration of a target material in a gas, the method
comprising:
[0023] dehumidifying the gas;
[0024] rehumidifying the dehumidified gas; and
[0025] measuring a response of a gas sensor configured to detect
the target material.
[0026] Optionally, the gas is rehumidified to within a
predetermined range.
[0027] Optionally, the gas is dehumidified by bringing it into
contact with a molecular sieve or a solid metal salt.
[0028] Optionally, the gas is rehumidified by a saturated salt
solution.
[0029] Optionally, the target gas is an alkene.
[0030] Optionally, the target gas is 1-methylcyclopropene or
ethylene.
[0031] According to some embodiments, the present disclosure
provides a gas sensor apparatus configured to determine a presence,
a concentration or a change in concentration of a target material
in a gaseous environment, comprising:
[0032] a dehumidification stage configured to dehumidify gas drawn
into the apparatus from an inlet;
[0033] a gas sensor; and
[0034] a rehumidification stage disposed between and in fluid
communication with the dehumidification stage and the gas sensor,
the rehumidification stage being configured to rehumidify the
dehumidified gas.
DESCRIPTION OF THE DRAWINGS
[0035] The disclosed technology and accompanying figures describe
some implementations of the disclosed technology.
[0036] FIG. 1 illustrates gas sensor apparatus according to some
embodiments having first and second gas flow paths in which a
target material is removed and is not removed, respectively, from
gas entering the apparatus before reaching a gas sensor;
[0037] FIG. 2 illustrates a process according to some embodiments
for determining the presence, concentration or change in
concentration of a target gas in an environment using measurements
of a gas sensor apparatus in a first and second state;
[0038] FIG. 3 illustrates a process according to some embodiments
for determining the presence, concentration or change in
concentration of a target gas in an environment using measurements
of a gas sensor apparatus in a first state, a second state and a
closed state;
[0039] FIG. 4 illustrates gas sensor apparatus according to some
embodiments in which desiccated gas is rehydrated before reaching a
gas sensor;
[0040] FIG. 5 illustrates gas sensor apparatus according to some
embodiments in which desiccated and untreated gas are both exposed
to water before reaching a gas sensor;
[0041] FIG. 6 illustrates gas sensor apparatus according to some
embodiments in which gas entering the apparatus is dehumidified
before being separated into first and second gas flow paths and
subsequently rehumidified before reaching a gas sensor;
[0042] FIG. 7 illustrates gas sensor apparatus according to some
embodiments in which gas entering the apparatus is separated into
first and second gas flow paths in which gas in one or both gas
flow paths is dehumidified and subsequently rehumidified before
reaching a gas sensor;
[0043] FIG. 8 illustrate gas sensor apparatus according to some
embodiments in which gas entering the apparatus is dehumidified and
subsequently rehumidified;
[0044] FIG. 9 illustrates a bottom gate, bottom contact TFT sensor
according to some embodiments;
[0045] FIG. 10 illustrates a bottom gate, top contact TFT sensor
according to some embodiments;
[0046] FIG. 11 illustrates a top gate, bottom contact TFT sensor
according to some embodiments;
[0047] FIG. 12 illustrates a top gate, top contact TFT sensor
according to some embodiments; and
[0048] FIG. 13A is a graph of average resistance change vs. time
for OTFT gas sensor for which background has been subtracted
according to some embodiments;
[0049] FIG. 13B is a graph of average resistance change vs
theoretical (assumed) 1-MCP concentration for the data of FIG.
13A;
[0050] FIG. 14 is a graph of average resistance change vs
theoretical 1-MCP concentration after 5 and 20 minutes exposure of
an OTFT gas sensor, for which background has been subtracted
according to some embodiments;
[0051] FIG. 15A is a graph of current vs. time upon exposure to
1-MCP of multiple OTFT gas sensors having the same structure but
formed in different batches;
[0052] FIG. 15B is a graph of response of the gas sensors of FIG.
15A vs. 1-MCP concentration;
[0053] FIG. 16A is a graph of dI/dt vs time upon exposure to 1-MCP
of multiple OTFT gas sensors having the same structure but formed
in different batches;
[0054] FIG. 16B is a graph of dI/dt vs. 1-MCP concentration for the
of the gas sensors of FIG. 16A;
[0055] FIG. 17A is a graph of humidity of an output gas following
humidification only of an input gas; and
[0056] FIG. 17B is a graph of humidity of an output gas following
dehumidification and rehumidification of an input gas.
[0057] The drawings are not drawn to scale and have various
viewpoints and perspectives. The drawings are some implementations
and examples. Additionally, some components and/or operations may
be separated into different blocks or combined into a single block
for the purposes of discussion of some of the embodiments of the
disclosed technology. Moreover, while the technology is amenable to
various modifications and alternative forms, specific embodiments
have been shown by way of example in the drawings and are described
in detail below. The intention, however, is not to limit the
technology to the particular implementations described. On the
contrary, the technology is intended to cover all modifications,
equivalents, and alternatives falling within the scope of the
technology as defined by the appended claims.
DETAILED DESCRIPTION
[0058] Unless the context clearly requires otherwise, throughout
the description and the claims, the words "comprise," "comprising,"
and the like are to be construed in an inclusive sense, as opposed
to an exclusive or exhaustive sense; that is to say, in the sense
of "including, but not limited to." As used herein, the terms
"connected," "coupled," or any variant thereof means any connection
or coupling, either direct or indirect, between two or more
elements; the coupling or connection between the elements can be
physical, logical, electromagnetic, or a combination thereof.
Additionally, the words "herein," "above," "below," and words of
similar import, when used in this application, refer to this
application as a whole and not to any particular portions of this
application. Where the context permits, words in the Detailed
Description using the singular or plural number may also include
the plural or singular number respectively. The word "or," in
reference to a list of two or more items, covers all of the
following interpretations of the word: any of the items in the
list, all of the items in the list, and any combination of the
items in the list.
[0059] As used herein, by a material "over" a layer is meant that
the material is in direct contact with the layer or is spaced apart
therefrom by one or more intervening layers.
[0060] As used herein, by a material "on" a layer is meant that the
material is in direct contact with that layer.
[0061] A layer "between" two other layers as described herein may
be in direct contact with each of the two layers it is between or
may be spaced apart from one or both of the two other layers by one
or more intervening layers.
[0062] The teachings of the technology provided herein can be
applied to other systems, not necessarily the system described
below. The elements and acts of the various examples described
below can be combined to provide further implementations of the
technology. Some alternative implementations of the technology may
include not only additional elements to those implementations noted
below, but also may include fewer elements.
[0063] These and other changes can be made to the technology in
light of the following detailed description. While the description
describes certain examples of the technology, and describes the
best mode contemplated, no matter how detailed the description
appears, the technology can be practiced in many ways. Details of
the system may vary considerably in its specific implementation,
while still being encompassed by the technology disclosed herein.
As noted above, particular terminology used when describing certain
features or aspects of the technology should not be taken to imply
that the terminology is being redefined herein to be restricted to
any specific characteristics, features, or aspects of the
technology with which that terminology is associated. In general,
the terms used in the following claims should not be construed to
limit the technology to the specific examples disclosed in the
specification, unless the Detailed Description section explicitly
defines such terms. Accordingly, the actual scope of the technology
encompasses not only the disclosed examples, but also all
equivalent ways of practicing or implementing the technology under
the claims.
[0064] To reduce the number of claims, certain aspects of the
technology are presented below in certain claim forms, but the
applicant contemplates the various aspects of the technology in any
number of claim forms. For example, while some aspect of the
technology may be recited as a computer-readable medium claim,
other aspects may likewise be embodied as a computer-readable
medium claim, or in other forms, such as being embodied in a
means-plus-function claim.
[0065] In the following description, for the purposes of
explanation, numerous specific details are set forth in order to
provide a thorough understanding of implementations of the
disclosed technology. It will be apparent, however, to one skilled
in the art that embodiments of the disclosed technology may be
practiced without some of these specific details.
[0066] The techniques introduced here can be embodied as
special-purpose hardware (e.g., circuitry), as programmable
circuitry appropriately programmed with software and/or firmware,
or as a combination of special-purpose and programmable circuitry.
Hence, embodiments may include a machine-readable medium having
stored thereon instructions which may be used to program a computer
(or other electronic devices) to perform a process. The
machine-readable medium may include, but is not limited to, floppy
diskettes, optical disks, compact disc read-only memories
(CD-ROMs), magneto-optical disks, ROMs, random access memories
(RAMs), erasable programmable read-only memories (EPROMs),
electrically erasable programmable read-only memories (EEPROMs),
magnetic or optical cards, flash memory, or other type of
media/machine-readable medium suitable for storing electronic
instructions. The machine-readable medium includes non-transitory
medium, where non-transitory excludes propagation signals. For
example, a processor can be connected to a non-transitory
computer-readable medium that stores instructions for executing
instructions by the processor.
[0067] Sensors such as gas, liquid or particulate sensors may
suffer from drift, i.e. the signal produced may change over time
without any change in the environment (e.g. composition of the
environment or changes in pressure or temperature). This may limit
the lifetime of the sensor and/or accuracy of its measurements. The
present inventors have found that changes arising for such drift
may be compensated for using gas sensor apparatus and methods as
described herein.
[0068] FIG. 1 illustrates gas sensor apparatus 100 according to
some embodiments of the present disclosure. Although the apparatus
is described herein with reference to gas sensor apparatus, it will
be understood that the apparatus may be, e.g. for use in detection
of a target material in a liquid. Although the apparatus is
described herein with reference to apparatus containing a gas
sensor configured to detect a target gas, it will be understood
that the target material may be a liquid target material or a
particulate material contained within a fluid and the sensor may be
selected accordingly.
[0069] The apparatus has a first gas flow path 110 between a first
valve 115 and a gas sensor 150 and a second gas flow path 120
between a second valve 125 and the gas sensor 150. FIG. 1
illustrates apparatus having a valve assembly of a first and second
valve, e.g. a first and second two-way valve. In other embodiments,
the valve assembly may comprise or consist of a single three way
valve may be used to direct flow of gas from the atmosphere to the
first or second gas flow path.
[0070] It will be understood that a "valve" as used herein means
any apparatus configured to allow or block gas flow through the
valve and may be manually operable (e.g. by way of a manually
operable tap) and/or may be electromechanical, e.g. a solenoid
valve, controllable by a controller, e.g. a programmable
controller.
[0071] With reference to FIG. 2, in use of the apparatus gas from
an atmosphere is drawn into the apparatus by any method known to
the skilled person, e.g. by use of one or more pumps (not shown).
The responses of the gas sensor 150 are measured in a first state
of the apparatus in which gas reaches the gas sensor from the first
flow path 110 only (e.g. while the first valve 115 is open and the
second valve 125 is closed) to give a first gas sensor measurement
and for gas reaching the gas sensor in a second state of the
apparatus in which gas reaches the gas sensor from the second flow
path 120 only (e.g. while the second valve 125 is open and the
first valve 115 is closed) to give a second gas sensor measurement.
The gas sensor may be sealed from gas communication with any gas
other than that from the first or second gas flow paths. The
apparatus state may be alternated between the first and second
states.
[0072] In some embodiments, the apparatus may be configured to
exhaust gas out of the apparatus after exposure of the gas sensor
150 to gas from one of the first and second gas flow paths and
before exposure to gas from the other of the first and second gas
flow paths.
[0073] Gas flowing along the second gas flow path 120 may reach the
gas sensor 150 substantially unchanged from its composition in the
environment from which it was drawn.
[0074] Gas flowing along the first gas flow path 110 may pass
through or over a filter material in a filter region or stage of
the first gas flow path 110 between the first valve 115 and the gas
sensor 150. The filter material may be disposed in a chamber 130
having an inlet and outlet in fluid communication with the first
gas flow path. The chamber may be removable and/or may have a
sealable opening, e.g. for replacement of the filter material
therein.
[0075] The filter material may adsorb or absorb the target
material. The filter material may react with the target material.
In some embodiments, the filter material selectively removes only
the target material from the gas it is exposed to. It will be
understood that the filter material is selected according to the
target material. In some embodiments, the filter material
selectively removes the target material and one or more further
materials from the gas it is exposed to. The filter material may be
a desiccant, e.g. silica gel, which removes water in addition to
the target material. The present inventors have found that silica
gel may be used to withdraw both water and 1-MCP from an
environment.
[0076] In some embodiments, the filter material is a molecular
sieve. The average pore size of the molecular sieve may be selected
according to the target material. In the case of a volatile organic
compound, e.g. 1-MCP, the molecular sieve optionally has a pore
size of at least 4 .ANG., optionally at least 5 .ANG. or 10
.ANG..
[0077] In some embodiments, the filter material is active
carbon.
[0078] Filtering of the target material has been described above
with reference to a filter material. In other embodiments, a filter
device, e.g. a mesh or HEPA filter for a particulate target
material or a scrubber for a target compound, may be used.
[0079] The presence, concentration or a change in concentration of
the target material may be determined by subtracting the first gas
sensor measurement or a derivative thereof from the second gas
sensor measurement or a derivative thereof. This determination may
be made without needing a separate background reading.
[0080] The apparatus may be cycled between first and second states
to allow for changes in the gas, such as changes in humidity, e.g.
due to temperature or pressure changes, to be taken into
account.
[0081] In some embodiments, the apparatus may be held in a second
state for longer than the first state. Optionally, the apparatus is
held in the second state for at least 60% or at least 70% of the
time during which gas sensor measurements are made. The second
state may be interspersed with periodic, and relatively short,
changes to the first state to allow for a background measurement.
In this way, near-continuous monitoring of a target material in an
environment with accurate adjustments due to any changes in the
background measurement (e.g. due to changes in the environment
and/or the gas sensor) may be achieved.
[0082] In some embodiments, the apparatus may be held in a first
state for longer than the second state, for example if the gas
sensor degrades in the presence of the target material, e.g. due to
poisoning of an active material of the gas sensor by the target
material or if the gas sensor responds relatively rapidly when
exposed to the target material but recovers to a baseline state
relatively slowly after exposure. Optionally according to these
embodiments, the apparatus is held in the second state for at least
80% or at least 90% of the time during which gas sensor
measurements are made. By limiting exposure of the gas sensor to
the target material, the lifetime of the gas sensor may be extended
and/or accuracy of measurements may be maintained over a longer
period.
[0083] The method described herein may allow for changes in
responsiveness of the gas sensor over time to be taken into
account, e.g. due to ageing of the gas sensor; changes in the
composition of the atmosphere such as changes in humidity over
time; and/or changes in environmental conditions such as changes in
atmospheric temperature or pressure. In this way, environmental
changes over time may be taken into account, e.g. over the course
of a day, such as changes between morning, afternoon, evening and
night or over a longer period such as seasonal changes over the
course of a year.
[0084] With reference to FIG. 3, following admission of gas into
one of the first and second gas flow paths, the apparatus may be
placed in a closed state by closing it off from the external
environment for a period of time, e.g. by closing both the first
and second valves, before admission of gas into the other of the
first and second gas flow paths. Closing off the apparatus from the
external environment may be done if concentration of the target gas
varies with time. The period of closed time may be selected
according to a length of time the gas sensor takes to provide a
signal with a sufficiently large signal-to-noise ratio in response
to exposure to gas from the first or second flow path.
[0085] The apparatus may be cycled between the first state; a
closed state following the first state; a second state; and a
closed state following the second state. Gas in the apparatus may
be removed therefrom, e.g. by a pump or by displacement with a gas
that the gas sensor is not responsive to, between the first state
and the second state.
[0086] The apparatus may be held in the first state, second state,
or a closed state following the first or second state, for a
predetermined period. The predetermined period may depend on, for
example, an estimated concentration of the target material and/or
responsiveness of the gas sensor to the target material.
[0087] By setting the apparatus to a closed state, the amount of
target material that the gas sensor is exposed to and/or length of
time that the gas sensor is exposed to the target material may be
limited. This may extend lifetime of the gas sensor.
[0088] A measurement of a response of gas sensor 150 to gas from
the first flow path is described herein as a "first gas sensor
measurement" and a measurement of a response of gas sensor 150 to
gas from the second flow path is described hereinafter as a "second
gas sensor measurement". It will be understood that the first and
second gas sensor measurements may be taken in any order.
[0089] In some embodiments, the apparatus may be configured to
direct gas from the first flow path and/or from the second flow
path to a return loop (not shown) following exposure of the gas
sensor to the gas for repeating measurement of the response of the
gas sensor to the gas. Recycling the gas and repeating the
measurement may occur while the apparatus is in a closed state in
which the apparatus is closed off from the external environment,
e.g. the first and second valves are closed.
[0090] The amount of the filter material and/or surface area of the
filter material in fluid communication with gas flowing along the
first gas flow path may be selected according to parameters
including one or more of: the rate at which the target gas is
withdrawn from the environment; the flow rate of the gas; and the
target material absorption capacity per unit mass of filter at the
environmental conditions. In the case where the filter material is
a desiccant, the amount and/or surface area of the filter material
may be selected, at least in part, according to the humidity of the
environment.
[0091] With reference to FIG. 4, in the case where the filter
material is a desiccant, a humidification stage, e.g. comprising or
consisting of a water reservoir 140, may be disposed in the first
gas flow path between the filter region and the gas sensor 150. Gas
flowing along the first gas flow path may pass through or over
water disposed in the water reservoir. The water content of
desiccated gas flowing along the first gas flow path may thereby be
returned to a level which is the same as or similar to water
content of the gas in the environment from which it was drawn. The
water disposed in the reservoir may have a salt dissolved therein.
The water may be a saturated salt solution. The humidification
stage may comprise a gel humidifier. The gel may or may not contain
a salt. The humidity of the gas may be set to a predetermined level
or range as described in, for example, L. B.
[0092] Rockland, Anal. Chem. 1960, 32, 10, 1375. "Saturated Salt
Solutions for Static Control of Relative Humidity between 5.degree.
and 40.degree. C." or L. Greenspan, Journal of Research of the
National Bureau of Standards-A. Physics and Chemistry Vol. 81 A,
No. 1, 1977. "Humidity Fixed Points of Binary Saturated Aqueous
Solutions", the contents of which are incorporated herein by
reference. The predetermined humidity level or range may be
selected to maximise lifetime of the gas sensor. For example, the
predetermined humidity level or range may be below a threshold
humidity at which condensation forms on the gas sensor. A preferred
humidity of a gas reaching the gas sensor is in the range of 60-95%
in the case where the sensor is an organic thin film transistor and
the target material is 1-methylcyclopropene.
[0093] If the gas sensor is not sensitive to water then the water
source may be omitted from the apparatus.
[0094] FIG. 5 illustrates gas sensor apparatus according to some
embodiments of the present disclosure. The apparatus is as
described with reference to FIG. 4 except that the water source 140
is disposed such that all gas flowing through the apparatus comes
into fluid communication with water from the water source before
reaching the gas sensor 150. By exposing gas from both the first
and second gas flow paths to water from a common water reservoir
140, gas reaching gas sensor 150 from both gas flow paths may have
the same water content. The water content of the gas reaching the
gas sensor may be controlled and/or set to a predetermined value as
described with reference to FIG. 4. Any response of the gas sensor
150 to water vapour may consequently be eliminated when the second
gas sensor measurement is subtracted from the first gas sensor
measurement.
[0095] FIGS. 1, 4 and 5 illustrate gas sensor apparatus in which
gas flowing along the second gas flow path reaches the gas sensor
150 substantially unchanged from gas in the environment.
[0096] In other embodiments, the filter material disposed in the
first gas flow path may selectively remove the target material and
one or more further materials from the gas it is exposed to, and a
further, different, filter material for selectively removing only
the one or more further materials from the gas may be disposed in
the second gas flow path. For example, a desiccant filter material
for withdrawing water and the target material may be disposed in
the first gas flow path and a further desiccant material for
withdrawing only water from the target material may be disposed in
the second gas flow path. In some embodiments, the gases may reach
the gas sensor in a desiccated state. Desiccation of gases reaching
the gas sensor may eliminate any response of the gas sensor due to
water.
[0097] In some embodiments, two or more different filter materials
are disposed in the first gas flow path wherein the different
filter materials have different rates of absorption and/or
different absorption capacities (measured as grams of target
material that the filter material can absorb per gram of filter
material) for a material in the gas drawn from the environment. In
some embodiments, a first filter material may absorb the target
material at a faster rate and/or to a greater capacity than a
second filter material and the second filter material may absorb a
non-target material (e.g. water) at a faster rate and/or to a
greater capacity than the first filter material.
[0098] In some embodiments, a material other than the target
material, e.g. water, may be removed by a suitable filter material
before gas drawn from the environment reaches the valve
arrangement. In some embodiments, a desiccant is disposed at the
entrance to, or in, the gas inlet. In some embodiments, desiccated
gases may be rehydrated before reaching the gas sensor, e.g. by
exposure to a water reservoir as shown in FIG. 4.
[0099] FIG. 6 illustrates a gas sensor apparatus as illustrated in
FIG. 5 and further comprising a dehumidification stage 160. The
dehumidification stage may comprise a chamber comprising a
desiccant disposed between or at the gas inlet and the valve
assembly. Accordingly, an input gas is dehumidified by the
desiccant in dehumidification stage 160 and subsequently
rehumidified by water in reservoir 140. The extent of
rehumidification may be controlled by, without limitation, a
saturated salt solution or gel humidifier as described with
reference to FIG. 4.
[0100] The present inventors have found that dehumidification of an
input gas from an atmosphere followed by rehumidification of the
dehumidified gas may result in less variation in humidity of the
rehumidified output gas (arising from, e.g., variations in humidity
of the input gas) than an output gas which has been subjected to
only one of dehumidification and humidification.
[0101] The desiccant disposed in chamber 160 may selectively remove
water only from the gas. In some embodiments, the desiccant is a
molecular sieve which may have a size selected to remove water but
not a target material, e.g. a molecular sieve having a pore size of
less than 4 .ANG., e.g. 3 .ANG. if the target gas is an organic
compound such as an alkene, e.g. 1-MCP or ethylene; an alcohol,
e.g. ethanol; or CO2. The desiccant may be a solid state salt. The
salt may be an ammonium, alkali, alkali earth or transition metal
salt. The salt may be, without limitation, a halide, hydroxide,
sulfate, acetate, dichromate, formate or nitrate. Exemplary salts
include, without limitation, NH.sub.4NO.sub.3,
(NH.sub.4).sub.2SO.sub.4, LiCl, NaCl, MgCl.sub.2, KCl, KOH, KBr,
KI, NaBr, Mg(NO.sub.3).sub.2, NaNO.sub.3, KNO.sub.3, sodium or
potassium acetate, sodium or potassium dichromate, calcium formate
and copper sulfate.
[0102] FIG. 7 illustrates a gas sensor apparatus as described with
reference to FIG. 6 except that the dehumidification stage 160 is
disposed in the second gas flow path 120, i.e. between the valve
assembly and the gas sensor 150. Gas flowing in the first gas flow
path 110 may or may not be dehumidified by the filter material
disposed in the first gas flow path.
[0103] It will be appreciated that the filter material for removal
of the target material according to these embodiments may or may
not also remove water. It will be appreciated that dehumidification
and rehumidification of an input gas to control humidity of an
output gas may be used in arrangements other than those having
first and second gas flow paths as described in FIGS. 1-7.
[0104] FIG. 8 illustrates gas sensor apparatus according to some
embodiments of the present disclosure. The apparatus comprises a
dehumidification stage 160 for dehumidification of a gas drawn into
the apparatus, a gas sensor 150 and a rehumidification stage 140
disposed in a fluid flow path between the dehumidification stage
and the gas sensor 150. The apparatus may contain a single gas flow
path between an inlet of the apparatus and the gas sensor, as
illustrated in FIG. 8. The apparatus may contain two or more gas
flow paths between an inlet of the apparatus and the gas sensor.
Dehumidification and rehumidification may be achieved as described
anywhere herein, e.g. with respect to FIGS. 4, 5, 6 and 7.
[0105] FIGS. 1, 4, 5, 6 and 7 illustrate gas sensor apparatus
having a valve assembly comprising two-way valves. In other
embodiments, the valve assembly may comprise or consist of a 3-way
valve.
[0106] FIGS. 1, 4, 5, 6 and 7 illustrate gas sensor apparatus
having first and second gas flow paths between a valve arrangement
and a gas sensor. In other embodiments, the gas sensor apparatus
may have one or more further gas flow paths between the valve
arrangement and the gas sensor, e.g. a third gas flow path between
a third valve and the gas sensor. In some embodiments, the second
gas flow path may not contain any filter material for withdrawing
any material in the gas; and the first and third gas flow paths may
contain a material for removal of different materials or different
combinations of materials from the gas. This may be particularly
advantageous if the gas sensor is responsive to both the target
material and one or more other materials in the environment, e.g.
water.
[0107] If the gas sensor is responsive to both the target material
and another material in the gas, e.g. water, then the first gas
flow path may contain a material for withdrawing both of these
materials from the gas and the third gas flow path may contain a
material for withdrawing only one of these materials from the gas.
The responses of the gas sensor to gases from the first and third
gas flow paths may be used to determine the response due to the
target material and the response due to the other material that the
gas sensor is responsive to. If the gas sensor is responsive to
water, this arrangement may eliminate the need to rehydrate gas
reaching the gas sensor if a filter material which withdraws both
the target material and water from the gas is used.
[0108] Subtraction of the first gas sensor measurement or a
derivative thereof (in which any target material has been absorbed
by the filter material) (from the second gas sensor measurement or
a derivative thereof (in which the target material has not been
removed from the gas reaching the gas sensor, e.g. in which the gas
is substantially unchanged from its composition in the external
environment), may provide a concentration value of the target
material or a value from which the concentration may be
derived.
[0109] A response of the gas sensor to known concentrations of the
target material may be measured for derivation of the concentration
value from the first and second gas sensor measurements.
[0110] The gas sensor apparatus may be in wired or wireless
communication with a processor configured to receive measurements
from the gas sensor. The processor may be configured to determine
the presence, concentration and/or change in concentration of the
target material from the received measurements.
[0111] The processor may be in wired or wireless communication with
a display, user interface or controller. In the case where the
target material is 1-MCP, the gas sensor apparatus may be
configured to send a signal to the display, user interface or
controller if 1-MCP concentration as determined from measurements
of the gas sensor apparatus falls below a threshold concentration.
The controller may be configured to activate a 1-MCP source for
release of 1-MCP into the environment upon receiving a signal from
the processor that 1-MCP concentration has fallen below a threshold
concentration.
[0112] The sensors described herein may be gas, liquid or
particulate sensors, preferably gas sensors, and may be selected
from any sensor known to the skilled person including, without
limitation, semiconductor sensors, e.g. semiconductor gas sensors;
photoionisation detectors; electrochemical sensors and IR sensors,
pellistors, optical particle monitors, quartz crystal microbalance
sensors, surface acoustic wave sensors (SAWS), cavity ring-down
spectroscopy (CRDS) sensors and biosensors. Semiconductor sensors
may comprise an organic semiconductor, an inorganic semiconductor
or a combination thereof. The organic semiconductor may be
polymeric or non-polymeric.
[0113] Exemplary semiconductor sensors are thin film transistor
sensors; vertical or horizontal chemiresistor sensors; and metal
oxide semiconductor sensors.
[0114] Metal oxide and photoionisation detectors may function most
effectively in a dry environment. Accordingly, in some embodiments
gas drawn into apparatus comprising a metal oxide sensor or
photoionisation detector may be dehumidified by at least one of a
material which removes water but not the target material and a
filter material which removes both of water and the filter
material, but not rehumidified before reaching the gas sensor.
[0115] Electrochemical sensors may provide more stable signals
and/or have longer lifetime if exposed non-continuously to a target
gas as described herein.
[0116] The first and second gas sensor measurements may be selected
according to the sensor type. In the case of a thin film transistor
sensor, the measurement or a derivative thereof may be one or more
of a change in drain current; a change in resistance; or a gradient
of a change over time, e.g. dI/dt in which I is drain current and t
is time.
[0117] FIGS. 9-12 describe various gas sensors. It will be
appreciated that the sensors according to these embodiments may
alternatively be used as liquid or particulate sensors.
[0118] FIG. 9 is a schematic illustration of a bottom contact
bottom gate TFT gas sensor suitable for gas sensor apparatus as
described herein. The bottom contact bottom gate TFT comprises a
gate electrode 203 over a substrate 201; source and drain
electrodes 207, 209; a dielectric layer 205 between the gate
electrode and the source and drain electrodes; and an semiconductor
layer 211 extending between the source and drain electrodes. The
semiconductor layer 211 may at least partially or completely cover
the source and drain electrodes.
[0119] FIG. 10 is a schematic illustration of a top-contact bottom
gate TFT gas sensor suitable for gas sensor apparatus as described
herein. The top-contact bottom gate TFT is as described with
reference to FIG. 9 except that the semiconductor layer 211 is
between the dielectric layer 205 and the source and drain
electrodes 207, 209.
[0120] FIG. 11 is a schematic illustration of a top gate, bottom
contact TFT gas sensor suitable for a gas sensor system as
described herein. The top gate bottom contact TFT comprises source
and drain electrodes 207, 209 on substrate 201; a semiconductor
layer 211; and a dielectric layer 205 between the gate electrode
203 and the semiconductor layer.
[0121] FIG. 12 is a schematic illustration of a top gate, top
contact TFT gas sensor suitable for gas sensor apparatus as
described herein. The top gate, top contact TFT is as described
with reference to FIG. 11 except that the semiconducting layer 211
is between the substrate 201 and the source and drain electrodes
207, 209.
[0122] The dielectric layer of a top-gate TFT gas sensor as
described herein may be a gas-permeable material, optionally an
organic material, which allows permeation of the gas to be sensed
through the dielectric layer to the semiconducting layer. The
top-gate top-contact TFT is as described with reference to FIG. 11
except that the semiconductor layer 211 is between the dielectric
layer 205 and the source and drain electrodes 207, 209.
[0123] The gate electrode of a top-gate TFT gas sensor as described
herein may be a gas-permeable material, optionally an organic
conducting material, and/or may be a patterned electrode defining
gaps through which gas may pass, e.g. a conductive strip having
fingers extending therefrom with a gap between adjacent fingers or
a patterned conductor having apertures formed therein.
[0124] The target material may be a volatile organic compound. It
will be understood that the target material may be an evaporated
organic compound which may have a boiling point at the pressure of
the environment, which is higher than the temperature of the
environment, e.g. an organic compound having a boiling point above
25.degree. C. at 1 atmosphere.
[0125] In some embodiments, the target material is an alkene. The
alkene may be an acyclic alkene, e.g. ethylene. The alkene may
comprise an alkene group substituted with an aromatic group, e.g.
styrene. The alkene may be cyclic, e.g. 1-MCP.
[0126] In some embodiments, the target material is an alkane, e.g.
methane.
[0127] In some embodiments, the target material is an ester. The
ester may be a C.sub.1-10 alkyl ester or C.sub.1-10 alkanoate
ester, optionally C.sub.1-10 alkyl-C.sub.1-10 alkanoate esters,
e.g. ethyl acetate; ethyl butanoate; ethyl hexanoate; propyl
acetate; butyl acetate; butyl butanoate; butyl hexanoate; pentyl
acetate; hexyl acetate; hexyl butanoate; hexyl hexanoate;
2-methylpropyl acetate; 2-methylbutyl acetate; ethyl
2-methylbutanoate; butyl 2-methylbutanoate; and hexyl
2-methylbutanoate.
[0128] In some embodiments, the target material is a polar
compound. The target polar compound may be a hydrocarbon which does
not have a mirror plane bisecting a carbon-carbon bond of the
hydrocarbon. The target polar compound may have dipole moment of
greater than 0.2 Debyes optionally greater than 0.3 or 0.4 Debyes.
The target polar compound may be 1-MCP.
[0129] In some embodiments, the desiccant is silica gel and the
target polar compound is 1-MCP.
EXAMPLES
[0130] OTFT Gas Sensor
[0131] A PEN substrate was baked in a vacuum oven and then UV-ozone
treated for 30 seconds. Source and drain contacts were deposited
onto the substrate by thermal evaporation of 3 nm Cr followed by 40
nm Au through shadow masks with channel length of 125 .mu.m and a
channel width of 4 mm. Semiconducting Polymer 1, illustrated below,
was deposited over the substrate by spin coating from a 1% w/v
solution in 1,2,4-trimethylbenzene to a thickness of 40 nm and
dried at 100.degree. C. for 1 minute in air. The polymer dielectric
Teflon.RTM. AF2400 was spin coated from a 2.5% w/v solution in a
50:50 v/v blend of fluorinated solvents FC43 and FC85 to a 300 nm
thickness and dried at 80.degree. C. for 10 min, after a 5 minute
initial drying phase while spinning. The gate was formed by thermal
evaporation of Cr (3 nm) followed by Al (200 nm) through a shadow
mask to form a gate electrode having a comb structure with comb
fingers of 125 microns width and gaps of 125 microns between
fingers.
##STR00001##
[0132] Gas Sensor Measurements
[0133] The OTFT Gas Sensor was provided in an apparatus as
described in FIG. 5 containing a 40 ml or 100 ml vial filled with
silica gel pellets and a 20 ml vial containing water for gas to
flow over. 1-MCP was introduced into the apparatus by adding
cyclodextrin containing a known amount of 1-MCP (4.3 wt %) to
water. It was assumed that all 1-MCP was released by this process
to give an assumed (theoretical) concentration of 1-MCP.
[0134] Measurements were made according to steps (i)-(iv): [0135]
(i) The OTFT Gas Sensor was exposed for 1 hour to air from the
first gas flow path (i.e. with 1-MCP removed by the desiccant) and
a change in resistance was determined, from drain current at
Vd=Vg=-4V, to provide a baseline. [0136] (ii) The OTFT Gas Sensor
was then exposed for 20 minutes to air passing through the second
gas flow path with 1-MCP present at a theoretical concentration of
0.5 ppm. [0137] (iii) The OTFT was allowed to recover by exposure
to air from the first gas flow path for 2 hours. [0138] (v) Steps
(ii) and (iii) were repeated twice, in which the theoretical
concentrations of 1-MCP in the second and third iterations were 1
ppm and 4.5 ppm respectively.
[0139] The change in resistance of the OTFT Gas Sensor was measured
periodically throughout steps (ii)-(iv) and the background
measurement of (i) and (iii) was subtracted.
[0140] With reference to FIGS. 13A and 13B, the change in
resistance, following background subtraction, shows a linear
relationship with the theoretical 1-MCP concentration.
[0141] The response of the OTFT Gas Sensor was measured as
described above at different 1-MCP concentrations except that
exposure in step (ii) was for 5 minutes rather than 20 minutes.
[0142] With reference to FIG. 14, a stronger response (larger
signal to noise ratio) is achieved for longer exposure of the OTFT
Gas Sensor to 1-MCP.
[0143] Rate of Change Measurement
[0144] The sensitivity of a gas sensor to a target material can
vary between sensors made at different times, e.g. made in
different batches which may affect the accuracy of measurement.
[0145] Multiple OTFT Gas Sensors prepared as described above, but
in different batches, were exposed to increasing concentrations of
1-MCP with recovery periods of no 1-MCP exposure between each
exposure.
[0146] With reference to FIG. 15A, there is a significant variation
in measured drain current at Vds=Vg=-4V. As shown in FIG. 15B, this
variation results in relatively large error bars which increase as
the magnitude of the response increases.
[0147] The data from these multiple devices as rate of change of
drain current (dI/dt) vs time shows a much more uniform response
across the devices as compared to drain current vs. time, giving a
linear correlation with 1-MCP concentration with much smaller error
bars as shown in FIGS. 16A and 16B,
[0148] A rate of change of the gas sensor response to a change in
target material concentration can be considerably more significant
than other factors causing a change in the gas sensor response such
as changes in the background environment and/or ageing of the gas
sensor.
[0149] Consequently, a relatively large change in the rate of
change of response of the gas sensor may be attributed to a change
in concentration of a target material. By identifying the start of
this relatively large change, and subtracting it from the rate of
change prior to the start of this large change event, it may be
unnecessary to separately measure a response of the gas sensor to a
background environment and/or provide a control gas sensor.
[0150] The gas sensor apparatus and method as described herein may
be used in monitoring the concentration of a gas in an environment,
e.g. a concentration of 1-MCP in a location where harvested fruit
or plants are stored, such as a warehouse or store, or
concentration of 1-MCP during transportation of harvested fruit or
plants.
[0151] Humidity Control
[0152] Air having varying levels of humidity (input air) was
treated by either humidification only or dehumidification followed
by rehumidification to produce an output air.
[0153] Input air having a humidity of about 12% or about 90% was
passed at a fixed flow rate of 50 cm.sup.3/min and temperature of
5.degree. C. over a 30 ml vial containing dry LiCl salt for
dehumidification and subsequently over a 40 ml vial containing
about 30 ml of saturated NaCl solution for rehumidification. For
comparison, input air was treated in the same way but without
dehumidification.
[0154] With reference to FIG. 17A, changing input air from about
12% humidity to about 90% humidity is accompanied by an increase of
about 10% in humidity of the output air.
[0155] With reference to FIG. 17B, changing input air from about
12% humidity to about 90% humidity is accompanied by a much smaller
change in humidity (about 3%) of the output air. The gas sensor
apparatus and method as described herein may be used in monitoring
the concentration of a target material in an environment in which
the target material concentration is allowed to change naturally in
the environment or in which the target material is artificially
introduced or removed from the environment, e.g. introduction of
1-MCP into an environment, which may result in an irregular change
in concentration of the gas over time.
* * * * *