Analyte in soil and other medium sensor arrangement

Abstract

A sensor for sensing the type and concentration of an analyte within a medium is disclosed. The sensor comprises a porous body located, in use, in fluid communication with the medium containing at least one analyte and dissolved organic compounds. The porous body is transmissive to ultraviolet radiation and there are at least two ultraviolet radiation transmitters and at least one ultraviolet radiation receiver, each transmitter and the or each receiver operating at different wavelengths, each transmitter and the or each receiver located adjacent to the porous body, wherein each transmitter and receiver are orientated such that each transmitter and receiver respectively sends and receives ultraviolet radiation through at least a portion of the porous body, such that at least two characteristics of the ultraviolet radiation received at the or each ultraviolet radiation receiver are respectively indicative of the concentration of the analyte and the dissolved organic compounds within the porous body at the known temperature and known moisture content of the medium.

Description

ANALYTE IN SOIL AND OTHER MEDIUM SENSOR ARRANGEMENTPRIORITY DOCUMENT

[0001] The present application claims priority from Australian Provisional Patent Application No. 2023900739 titled “ANALYTE IN SOIL AND OTHER MEDIUM SENSOR ARRANGEMENT” and filed on 17 March 2023, the content of which is hereby incorporated by reference in its entirety.FIELD OF THE DISCLOSURE

[0002] Aspects of the disclosure relate to detecting analytes, particularly nitrates, in soil and other mediums.BACKGROUND

[0003] Methods and apparatus for detecting analytes in soils and other mediums are replete with sensor devices that measure biological or chemical reactions by generating signals proportional to the analyte concentration in the tested medium.

[0004] One particular analyte of interest is nitrates (NOs ) and nitrites (NO2 ). Inorganic fertilisers, in particular nitrogen-based fertilisers, are commonly used in agriculture. Adding too much fertiliser to the soil is inefficient and costly and causes environmental pollution. Determining the concentration of an analyte such as nitrates in the crop soil assists in assessing the effectiveness of the fertiliser added to the soil over time and can have a bearing on the future need to add more or less fertiliser to the soil.

[0005] A particularly unwanted consequence of fertiliser use is that nitrates and nitrites enter the environment because too much fertiliser has been added to the fields of various crops. The crop roots mostly absorb nitrates and nitrites and enter the food chain. However, nitrate ions can be harmful to humans and animals if they exceed known levels in water and foods. Although every country is cognizant of this issue, they all have different acceptable levels of concentration of nitrates in mg per litre in potable water and in foodstuffs.

[0006] Nitrates are not the only potentially harmful analyte; others are phosphate, mercury, cadmium, dioxin, zinc, polychlorinated biphenyl (PCB), arsenic, chlorinated hydrocarbons, lead, and many others. Some of them accumulate in humans and animals over time until their toxicity becomes an adverse health or well-being issue. However, some analytes are beneficial to crop growth, so there is a need to measure those as well to determine whether enough of the analyte is in the soil at a particular time when crop growth is needed. Depending on their concentration, some analytes act as plant nutrients, includingnitrogen, phosphorus, potassium, calcium, magnesium, sulphur, boron, chloride, manganese, nickel, copper, zinc, molybdenum, iron, hydrogen, carbon, and oxygen.

[0007] Soil provides a typically unrecognized source of potentially adverse contaminants and components to humans and animals. Humans may be exposed directly by, for example, airborne dust and children incur greater exposures per unit of body weight. In addition, epidemiologic studies of hazardous- waste sites show soil as a route of exposure to contaminates and components of the soil that are potentially adverse to the human and animal population.

[0008] One known measurement technique for determining the concentration of analytes in soil involves the extraction of a sample of the soil so that a laboratory can perform the measurement, which is typically a destructive process. The measurement result is typically provided days and sometimes weeks after the soil sample was taken. Any delay in receiving the measurement result may be critical to the farmer’s decision to irrigate or fertilise more or less in the period subsequent to the sample being taken. Even the measurement techniques using on-site assay arrangements require appropriate quantities of aqueous solutions and portable and rugged testing equipment. In some cases, mechanical mixing, heating and ultra-sound are applied to the sample to accelerate the extraction of relevant soil nutrients and even then, a need to use solvents to further isolate and extract selected nutrients, including nitrates.

[0009] An example of an on-site measurement technique for nitrate presence in a soil sample using an ion-selective sensor. In one example, the sensor is a polymer such as poly (3,4-ethylenedioxythiophene) (PEDOT). PEDOT is a conjugated polymer that carries positive charges and is based on poly thiophene. A PEDOT-based sensor is useable as a nitrate sensor to detect nitrate in water, and either an immersion or inline configuration, in which nitrate ion uptake leads to oxidation of PEDOT and a change of its optical properties. For example, a single-mode fibre is coated at its tip with PEDOT, and the PEDOT membrane undergoes chemical oxidation and reduction (redox). The change in optical properties due to redox switching varies with the intensity of light back-reflected by the fibre coated with PEDOT. Oxidation demonstrates a linear response to the uptake of nitrate ions in concentrations ranging between 0.2 and 40 parts per million (ppm). Such a sensor is only useful in a liquid such as water and does not operate in granular mediums such as soil.

[0010] Other measurement arrangements may also include optical sensors, which are used to irradiate a soil sample, wherein reflections from the sample are detected and measured. Examples of a housing having one or more optical sources include xenon and deuterium lamps that generate and guide transmission of ultraviolet light sources in the range 240 nm to 400 nm and have a Full Width Half Magnitude (FWHM) in the range of 10 nm to 20 nm. Additionally, the housing includes electronic control circuits that perform a method of driving the radiation sources so as to pulse them sequentially. The housings for those types of radiation sources are large (2,000 cm3), require voltages greater than 400volts, take time to warm up to an operating temperature and need bandpass filters, and consequently have a high cost to purchase and maintain and are used only on extracted samples of soil and cannot be used in-situ.

[0011] Yet another arrangement is the use of a soil solution sampler to collect fluid from the surrounding soil. Still, it requires a reservoir of sample solution, a pump, a measurement cell through which the solution flows, and different calibrations to accommodate different soil types.

[0012] A yet further sensor type requires exposure of the soil to an exposed gate of an ion-sensitive field-effect transistor (ISFET) and a solid-state reference electrode, which is electrically coupled with the ISFET sensor to facilitate the detection of analytes via the ion transfer from the soil to the device. The effectiveness of such a sensor relies greatly on the robustness of the ISFET, its resistance to corrosive elements in the soil, temperature sensitivity and stability over time.

[0013] Accordingly, a need exists for analyte detection and measurement in non-laboratory settings.BRIEF DESCRIPTION OF ASPECTS

[0014] Sensor arrangements and sensors that use UV-C to detect an analyte, such as nitrates, that infiltrate a porous body, used in situ in a medium, are disclosed.

[0015] In an aspect, disclosed herein is a sensor arrangement for sensing the type and concentration of an analyte within a medium comprising a porous body located, in use, in fluid communication with the medium containing at least one analyte and dissolved organic compounds, such that within the porous body, there is a state of hydraulic equilibrium between the fluid in the porous body and the fluid in the medium at a known temperature and known moisture content of the medium, wherein the porous body is transmissive to ultraviolet radiation and there are at least two ultraviolet radiation transmitters and at least one ultraviolet radiation receiver, each transmitter and the or each receiver operating at different wavelengths, each transmitter and each receiver located adjacent to the porous body, wherein each transmitter and receiver are orientated such that each transmitter and receiver respectively sends and receives ultraviolet radiation through at least a portion of the porous body, such that at least two characteristics of the ultraviolet radiation received at the or each ultraviolet radiation receiver are respectively indicative of the concentration of the analyte and the dissolved organic compounds within the porous body at the known temperature and known moisture content of the medium.

[0016] In an aspect, the sensor arrangement comprises a porous body located, in use, in fluid communication with the medium. Within the porous body, there is a state of hydraulic equilibrium between the solution in the porous body and the solution in the medium at a known temperature and known moisture content of the medium, wherein the porous body is transmissive to ultraviolet radiation.There are at least two ultraviolet radiation transmitters, and the output of each ultraviolet radiation transmitter is beam split to provide ultraviolet radiation that is received by an ultraviolet radiation intensity sensor that monitors the intensity output of each ultraviolet radiation transmitter.

[0017] In an aspect, there is a pair of an ultraviolet radiation transmitter and an ultraviolet radiation receiver, each located adjacent to the porous body, to respectively send and receive ultraviolet radiation through at least a portion of the porous body, such that at least two characteristics of the ultraviolet radiation received at the ultraviolet radiation receiver is indicative of the type and concentration of the analyte within the porous body at the known temperature and known moisture content of the medium.

[0018] In an aspect, the analyte concentration in the sample solution within the porous body is due to the difference in the ultraviolet radiation at the receiver compared with the ultraviolet radiation transmitted as detected.

[0019] In another embodiment, wherein each of the two pairs of an ultraviolet radiation transmitter and an ultraviolet radiation receiver operates at different frequencies or across two different or overlapping bands of frequencies.

[0020] In an aspect, the ultraviolet radiation is ultraviolet C radiation to detect the concentration of analytes that absorb wavelengths in the UV-C band. In certain embodiments, the transmitters transmit at wavelengths of 200-300 nm.

[0021] In an aspect, an ultraviolet radiation transmitter transmits a wavelength of 220 -240 nm for nitrate detection, and another ultraviolet radiation transmitter transmits a wavelength of 260-280 nm to correct for the presence of dissolved organic substances.

[0022] In an aspect, the porous body is porous fused silica material, wherein there are no spatial rearrangements of silica particles over time. Changes in pore spacing over time could otherwise adversely affect the determination of the analyte concentration over time.

[0023] In an aspect, the porous silica material has a determined purity.

[0024] In an aspect, the analyte is nitrate.

[0025] In a further aspect, a sensor arrangement further comprises a longitudinal housing body supporting two or more spaced sensors for sensing the type and concentration of an analyte within a medium at two or more spaced apart locations within the medium. For example, the two or more sensors in the sensor arrangement are positioned along the longitudinal length of the sensor body, where there is a longitudinal spacing between sensors.

[0026] In an aspect, the sensor arrangement further comprises an arrangement to measure soil water, soil salinity (total soil ion content) and / or soil temperature within a sphere of influence within the medium adjacent to the porous body.

[0027] Some embodiments described herein may be implemented using programmatic elements, often called modules or components, although other names may be used. Such programmatic elements may include a program, a subroutine, a portion of a program, a software component or a hardware component capable of performing one or more stated tasks or functions.

[0028] Analyte concentration and other measurements (including but not limited to: dissolved organic compounds, soil moisture, temperature and concentration of salts) can be triggered to occur at the same point in time when, for example, the Field Capacity of the soil has been reached after a rainfall or irrigation event. When Field Capacity has been reached, soil water and nutrient movement become negligible, consequently, the steady state depth position of nitrate in the soil profile can be determined. Yet further, in one arrangement, measurements can be triggered or programmed to occur during the soil drying to determine the plant analyte uptake rate determined.

[0029] As used herein, a module or component can exist on a hardware component independently of other modules / components, or a module / component can be a shared element or process of other modules / components, programs or machines. A module or component may reside on one machine, such as on a client or a computer server, or a module / component may be distributed amongst multiple machines, such as on multiple clients or computer server machines. Any system described may be implemented in whole or in part on a computer server or as part of a network service. Alternatively, a system described herein may be implemented on a local computer, computer processor, computer terminal, or server in whole or part. In either case, implementation of the system provided for in this application may require the use of memory, processors and network resources (including data ports, and signal lines (optical, electrical and other communication modalities), unless stated otherwise. Each program executed on a processor changes the state of the processor and makes it perform an action that is, in some cases, unique for the operation of the processor when performing the actions defined by the program. The changed state of the computer interacts with peripherals, and those actions may be unique to the peripheral.

[0030] Some embodiments described herein may generally require computers and computer processors, including processing and memory resources. For example, systems described herein may be implemented on a server or network service. Such computer servers may connect and be used by users over networks such as the Internet or by a combination of networks, such as cellular networks and the Internet. Alternatively, one or more embodiments described herein may be implemented locally, in whole or in part, on computing machines such as desktops, cellular phones, personal digital assistances or laptopcomputers. Thus, memory, processing and network resources may all be used in connection with the establishment, use or performance of any embodiment of a method or system described herein (specifically including the performance of embodiments of a method or implementation of a system).

[0031] Furthermore, some embodiments described herein may be implemented using instructions that are executable by one or more processors. These instructions may be carried on a computer -readable medium. Machines that may be shown in the figures provide examples of processing resources and computer-readable mediums on which instructions for implementing embodiments can be carried out and executed. In particular, the numerous machines associated with one or more embodiments include a processor(s) and various forms of memory for holding data and instructions. Examples of computer- readable mediums include permanent memory storage devices, such as hard drives on personal computers or computer servers. Other examples of computer storage mediums include portable storage units, such as CD or DVD units, flash memory (such as carried on many cell phones and personal digital assistants (PDAs), and magnetic memory. Computers, terminals, and network-enabled devices (e.g. mobile devices such as cell phones) are all examples of processors and devices. Instructions are usually stored on transitory and non-transitory computer-readable mediums, including RAM, ROM and EPROM devices.

[0032] The present disclosure can be implemented in numerous ways, including as a process, an apparatus, a system, or a computer-readable medium such as a computer -readable storage medium or a computer network wherein program instructions and digital data files are sent over wireless, optical, or electronic communication links. It should be noted that the order of the steps of disclosed processes may be altered within the scope of the disclosure.

[0033] Details concerning computers, computer networking, software programming, telecommunications and the like may at times not be illustrated explicitly as such was not considered necessary to obtain a complete understanding nor to limit a person skilled in the art of performing the embodiments, are considered present nevertheless as such are considered to be within the skills of persons of ordinary skill in the art.

[0034] The brief description is provided to introduce a simplified selection of concepts described below in the detailed description of embodiments. The summary does not intend to identify any or all of the claimed subject matter's key or essential features.

[0035] It will be appreciated by those skilled in the art that this disclosure is not restricted in its use to the particular application, or applications described. Neither is the present disclosure restricted in its preferred embodiment with regard to the particular elements and features described or depicted herein. It will be appreciated that the disclosure is not limited to the embodiment or embodiments disclosed but iscapable of numerous rearrangements, modifications and substitutions without departing from the scope as set forth and would be understood by the person or team having skill in the art.BRIEF DESCRIPTION OF THE FIGURES

[0036] Figure 1 depicts an embodiment of a sensor arrangement for sensing the type and concentration of an analyte within a medium;

[0037] Figure 2 depicts an embodiment of the housing of a sensor arrangement as disclosed in US5418466;

[0038] Figure 3 depicts an embodiment of the housing of a sensor arrangement as disclosed in US 10060873;

[0039] Figure 4 depicts an embodiment of a sensor arrangement for sensing the type and concentration of an analyte within a medium;

[0040] Figure 5 depicts a functional block diagram of an embodiment of a sensor arrangement;

[0041] Figure 6 depicts an example of a UV radiation transmitter element;

[0042] Figure 7 depicts multiple versions of the encapsulation of UV radiation transmitter elements;

[0043] Figure 8 depicts an example of a UV receiver element that is uncapped;

[0044] Figure 9 depicts an example of a UV receiver element that is capped;

[0045] Figure 10 depicts an example of a perspective and top view of a porous body (which is not the shape described in this specification);

[0046] Figure 11 depicts a graphical representation of the absorbance of UV-C wavelengths by an analyte such as nitrate;

[0047] Figure 12 depicts a visual and numerical visualisation of the nitrate nitrogen values for soils; and

[0048] Figure 13 depicts an example of a fleshy root yield versus nitrate concentration in the soil.DETAILED DESCRIPTION OF EMBODIMENTS

[0049] In general, sensors have a wide range of applications that aim to improve the quantity and quality of information available on which to base decisions. The range of sensor use includes but is not restricted to environmental monitoring, potentially dangerous element detection in solids and liquids, food safety, and many more.

[0050] One of the many applications of sensors is their use as devices for monitoring food traceability, quality, safety and nutritional value. Many of those types of sensors fall into the ‘single-shot’ analysis tools category, i.e. where cost-effective and disposable sensing platforms are required to test a sample and then dispose of the sensor.

[0051] Yet further, a sensor, when used for pollution and soil monitoring, is required to function for periods of a few hours to several days, to months and years. Such sensors can be termed ‘long-term monitoring’ analysis tools.

[0052] Whether it is long-term monitoring or single-shot analysis, sensors are devices that are usable in many different setups.

[0053] Sensors transduce one type of energy into another, for example, the transduction of electromagnetic energy into a current / voltage output, such as for example in an antenna. The variability of the output indicates one or more characteristics of the received electromagnetic energy. For example, the received power of the electromagnetic energy can be determined by analysis of the instantaneous amplitude of a current or voltage, and a temporal characteristic of the variability of the electromagnetic energy becomes a signal.

[0054] The electronic portion of a sensor arrangement processes the transduced signal and prepares it for storage and / or display. The electronic circuitry may also perform signal transmutation and conditioning, including amplification and converting signals from analogue into a digital form more suitable for storage and later analysis or display immediately or in the future.

[0055] The display unit of the sensor arrangement provides a human-readable version of one or more of the quantified processed signals. The display may consist of a human interface system, including a 2- dimensional light-emitting display device, such as a liquid crystal display which uses the individual lightemitting elements to create images comprising numbers or curves the user will be capable of understanding. A display may consist of a combination of hardware and software that generates visual representations of the output of the electronic portion of the sensor. The display can include numeric, graphic, tabular data or images.

[0056] There are static and dynamic attributes that a preferred sensor possesses. The optimisation of these properties is reflected in the performance of the sensor in different environments and conditions.

[0057] Selectivity is the ability of a sensor to detect a specific analyte in a sample containing other admixtures and contaminants.

[0058] Reproducibility is the ability of the sensor to generate identical responses for a duplicated experimental setup. The transducer's precision and accuracy and the sensor arrangement's electronics contribute to reproducibility.

[0059] Precision is the sensor’s ability to provide the same or very similar result each time a sample is measured for a particular analyte. Whereas the accuracy of a sensor is determined by the sensor’s capacity to provide a mean value close to the true value when the sample is measured more than once.

[0060] Stability is the degree of susceptibility of the sensor arrangement’s output to changes in disturbances in and about the sensing arrangement and how the sensor output changes even when conditions in the surrounding are constant. Disturbances can cause a drift in the output signals of a sensor under measurement, which translates into an error in the measured characteristic, such as the concentration of an analyte, and thus affect the sensor’s reproducibility and accuracy. Stability is a desirable feature for a sensor used for continuous monitoring over relatively long periods. In the field soil monitoring environment, a long period could be three to tens of days and even months so as to span a crop’s complete growth to harvest season. The uncorrected response of transducers and electronics, which are temperature-sensitive, may influence the stability of a sensor. Therefore, appropriate electronic tuning or correction measures are preferable to minimise or eliminate instability or maximise the stability of a sensor’s response to unwanted influences. Another factor that can influence the stability is the affinity of the sensor, which is the degree to which the analyte binds to the sensor. Another factor that can adversely affect the measurement stability is the sensor's physical degradation over time.

[0061] Sensitivity is a measure of the minimum amount of analyte that a sensor arrangement can detect and is sometimes referred to as a limit of detection (LOD). A sensor preferably detects analyte concentrations and confirms the presence of minimal traces of analytes in a sample.

[0062] Linearity is an attribute of the sensor arrangement that indicates the accuracy of the measured response (for a set of measurements with different concentrations of the analyte) to a straight line, mathematically represented as y=mc, where c is the concentration of the analyte, y is the output signal, and m is the sensitivity of the sensor. The linear range of a sensor arrangement is defined as the range of analyte concentrations for which the sensor response changes linearly with the concentration. The relationship can be determined by experimentation and with absolute measurement values determined using other methods, one or more of which may be laboratory-based.

[0063] Figures 1 and 4 each depict an embodiment of a sensor arrangement for sensing the type and concentration of an analyte within a medium. In the embodiments depicted, the sensor arrangement comprises a porous body 10 located, in use, in fluid communication with a medium, not explicitly depicted but implied as the sensor arrangement's immediate surroundings such that there is fluid communication between the porous inert body and the medium. In another example, the medium may be confined to a vessel containing a fluid, and the sensor arrangement and the integral porous body are submerged into the fluid within the vessel. In another example, the medium is a foodstuff, and the sensor arrangement and the integral porous inert body are adjacent and in fluid / moisture communication with the foodstuff. The porous body is inert to the medium that lies in or adjacent to a medium with which there is fluid communication during the sampling process. Also, the porous body is inert to one or more analytes and one or more dissolved organic substances within the medium.

[0064] Figures 1 and 4 depict sensor arrangement embodiments for use in a soil medium. However, those embodiments should not be considered the only sensor arrangement that uses a porous body and should not be limited when using the sensor in housings for insertion into a soil medium. The function of the sensor arrangement does not rely on the porous body being fully immersed or inserted within or in fluid communication with the medium to be tested. Hence, by way of example, the porous body is at least partially inserted into the medium.

[0065] Figure 1 depicts a sensor housing 12 wherein the housing is shown as being cylindrical. However, the Figure is only a partial view of the housing. In one embodiment, the housing is of the type disclosed in US5418466, which is owned by the subject applicant and an embodiment of the arrangement therein is illustrated in Figure 2. In another embodiment, the housing is of the type disclosed in US 10060873, which is owned by the subject applicant and illustrated in Figure 3. The shape of the prepared opening and the sensor housing shape is best complementary to prevent preferential path flow, as disclosed in the respective patent specifications referred to in this paragraph. In an embodiment, an embodiment of a sensor arrangement disclosed in this specification can be added to the embodiments depicted in Fig 2 and Fig 3 at a location above or below one or more of the depicted capacitive sensor rings 50.

[0066] A suitable material for the porous body is shown in Figure 10, although the porous body is not necessarily of the form depicted in Figure 10. For the purpose of this disclosure, the porous body has the texture and solid nature depicted in Figure 10. The porous body, in use in an embodiment, is located in the sensor arrangement such that it is in fluid communication with a medium to be assessed, wherein there is a state of hydraulic equilibrium between the solution in the porous body and the solution in the medium. Fluid from the medium to be tested may contain one or more analytes that enter the porous body by infusion due to the differences in partial pressures in the medium, which are initially higher than the initially lower partial pressures in the porous body. When equilibrium has been achieved between thepartial pressures of fluids in the porous body and the medium, analyte testing can be undertaken since there will be a concentration of the analyte in the porous body that is the same as that in the medium.

[0067] Analyte concentration and other measurements (including but not limited to: dissolved organic compounds, soil moisture, temperature and concentration of salts) can be triggered to occur at the same point in time when, for example, the Field Capacity of the soil has been reached after a rainfall or irrigation event and after a fertilisation or fertigation event. Both such events include the application of at least one plant nutrient but typically a multiple plant nutrient compound in what is typically referred to as fertiliser. When Field Capacity has been reached, soil water and nutrient movement become negligible, consequently, the steady state depth position of nitrate in the soil profile can be determined. Yet further, in an arrangement, measurements can be triggered or programmed to occur during the soil drying process to determine the plant analyte uptake rate.

[0068] There is no fixed period or necessarily accurate predictable period for equilibrium to be reached when a sensor arrangement is first placed in fluid communication with the medium. By way of guidance, for equilibrium to be reached when the porous body is first placed into clay soil, the period is at least one hour; in sandy soil, the period is at least half an hour; in saturated soil, the period is at least 15 minutes. The longer the porous body is in fluid communication with its surroundings, the more likely the ebb and flow of fluids into and out of the porous body will match the moisture level in the medium. The terms moisture and fluid are sometimes interchangeably used in this specification. The periods indicated may also vary due to the chosen porosity of the porous body. The water infiltration capacity of soil is but one characteristic of soil that will also affect the moisture content of the soil.

[0069] A consequence of the changing level of moisture within a medium being measured is that the equilibrium condition may not be stable. That is, there may rarely be absolute equilibrium, such that the flow of fluid into and out of the porous body may never cease. So, any measurements taken using the method and means disclosed herein are subject to the realisation that they are never ideal. However, any variability of measurements due to the dynamic nature of the flow in and out of the porous body is a temporal feature. Thus, due to the slowness of that flow, it is very likely that any variation of the measurement will be within acceptable limits of accuracy. Thus, since the measurement can be made within fractions of a second using the method and means disclosed, that measurement will provide representative and, thus, useable results. This is only the case once the initial inflow of fluid into the porous body has occurred. Thus, it is reasonable that there is effectively a state of equilibrium between the fluid in the medium and the porous body after an initial equilibrium period. The porous body is inert to the analyte of interest and any dissolved organic compounds of interest within the soil’s moisture content. It may be that certain porous bodies are not totally inert to all analytes or all dissolved organic compounds as long as any reaction does not affect the concentration of the analytes and dissolved organic compounds of interest.

[0070] All of the indicated minimum periods provided above assume that the porosity of the porous body lies between 15 % and 40 % and that the higher the porosity of the porous body, the shorter the period to achieve equilibrium. The porous body can be manufactured to a predetermined porosity by creating smaller or larger pore sizes, for example, between 3 and 15 micrometres ( m) in the porous body. In an embodiment, the porous body is made from synthetic silica glass. The purity of the silica glass can be controlled at the time of manufacture, and the manufacturing process ensures that there are no analytes of relevance in the porous body. The higher the purity, the less likely any other factors need to be accounted for when measurements for the presence of analytes are made using the porous body in accordance with the disclosure within this specification.

[0071] The pore size of the porous body can be selected at the time of manufacture. Thus, it is possible to predetermine the particular pore size of a porous body during manufacture to suit a particular sensor arrangement for use in a particular medium. For example, the pore size can be greater for clay soils and smaller for sandy loam soils. The same principle applies to porous body pore size choice when the medium to be tested is a solid or liquid foodstuff or a fluid of a particular density or surface tension characteristic.

[0072] The porous body can also be manufactured into a shape that best fits the application. In Figure 1, the porous body is rectangular in cross-section and is formed into a longitudinal block. The porous body 10 is located within a sensor housing 12, within which are located sensor devices such as an Ultraviolet (UV) emitter 14 and receiver 16 elements (as also depicted in Figure 5). The longitudinal sensor housing can support two or more spaced Ultraviolet (UV) emitter 14 and receiver 16 elements. Those elements have active areas, as depicted in Figures 6, 7 (40), 8 (60), and 9 (70). The active area of the element is placed into contact with the porous body so that there is minimal space between them. An intermediate layer of a substance can eliminate airborne contaminants entering the open volume between the porous body and the active area of the element. There can be a structure to maintain the spatial relationship between the element and the porous body so that during transport and use, they are fixed in position relative to one another. The intermediate layer may also have adhesive properties and, if sufficiently strong, eliminate the need for a structure as described.

[0073] Figure 4 depicts a variation of the mode or transmission and reception of UV-C radiation, in that there are one or more UV transmission elements radiating electromagnetic energy into the porous body and one or more UV receiver elements for receiving the reflected UV-C electromagnetic energy. The possibility of a UV radiation receiver being used to detect two different UV-C radiation wavelengths is not shown. Thus, just one UV radiation receiver is used in a switched mode. The active period and any blank period between the reception of one and then another wavelength of radiation is a matter of choice by one of skill in the art or determined by reasonable experimentation once the appropriate positioning of the UV radiation receiver in the arrangement is settled.

[0074] The signal received by a receiver element will be indicative of the absorption of the analyte of interest. It is a property of the porous body that some of the incident electromagnetic energy will be reflected. The principles described in this disclosure regarding the measurement and quantification of the absorption of a desired analyte apply equally to this embodiment.

[0075] It is a mechanical and electronic decision to provide complementary electrically conductive plugs and socket connectors (both not depicted) to the respective inputs and outputs of the UV emitter and receiver to allow the measurement frame (including the porous body) to be readily removed from the sensor separate from the associated processing electronics modules 18 to which the Ultraviolet (UV) emitter 14 and receiver 16 elements are electrically connected, in use. Appropriate sealing of the junction between the mounting frame and the sensor housing 20 is required to isolate the processing electronics modules from whichever medium and its associated fluids and moisture the sensor arrangement is located in fluid communication with. Providing a removable mounting frame also provides for the swapping in of a mounting frame that includes a porous body of different porosity that permits the same sensor housing to be used in, for example, different soil types where a particular porosity of the porous body is advantageous or more suited. Further, the longitudinal sensor housing can support two or more spaced sensors for sensing the type and concentration of an analyte within a medium.

[0076] A porous body made of porous silica made from spherical, high-purity glass silica grains has some of the following properties, including heat and thermal shock resistance, for example, the ability to remain stable and not degrade physically or chemically in temperatures up to 1000°C and resistance to oxidized environments; low thermal conductivity and correspondingly low thermal expansion rate and thus physically stable in all of the mediums anticipated to be worked with; and resistance to acid and alkali environments. Also, the porous body is ideally homogenous, of uniform density and inert so that no re-arrangements of the grains can occur.

[0077] The porous body has other properties, one of which is that the porous body is transmissive to ultraviolet radiation. Thus, the porous body is transmissive to electromagnetic (EM) energy, and the frequency / wavelength of EM energy that is transmitted without change includes Ultraviolet (UV) radiation. The spectrum of UV wavelength ranges from 400 nm, known as the beginning of the UV-A range that extends down to 315 nm, 316 nm to 280 nm, known as the UV-B range; 280 nm to 200 nm, known as the UV-C range, and the range 200 nm to 100 nm is known as the UV-vacuum range. There is an inverse relationship between EM wavelength and frequency, so as the wavelength decreases, the corresponding frequency increases.

[0078] For the purpose of detecting analytes and, in particular, nitrites and nitrates, the UV-C range is most useful. Nitrate and nitrite are inorganic compounds and also polyatomic ions. Nitrate comprises one atom of nitrogen (N) and three atoms of oxygen (0); nitrate’s chemical symbol is NO3. Nitrate is notnormally dangerous to the health of humans unless it is reduced to nitrite (NO2) in excessive amounts. Still, both are useful for plants to enhance their growth and disease resistance, and both occur naturally in soil, air, water, and the human body. The choice to use UV-C radiation is made since it is known that nitrate and nitrite absorb some UV-C radiation. In particular, at 220-240 nm but not at 260-280 nm and follows Beer’s law with linear behaviour to 11 mg nitrogen / litre of solution. Since dissolved organic matter may also absorb at 220-240 nm, it is possible to distinguish between the absorbance of nitrate and the other organic matter in water by making a co-measurement of the sample’s absorbance at 260-280 nm. A correction factor can then be used to determine the actual nitrate concentration. The higher the absorbance of UV radiation, the higher the concentration of the nitrate analyte, (see Figure 11) the exact correlation factor has to be determined experimentally using the final measurement apparatus.

[0079] The mentioned further measurement can be achieved by switching the UV emitter's and receiver's operating frequency (tuned) or simultaneously using two emitters (14 and 14a, as depicted in Figure 5) and two receivers (16 and 16a, as depicted in Figure 5) which form two transmitter and receiver pairs operating at 220 nm and the other at 275 nm respectively. When using the two different UV-C wavelengths, the difference between the two received signals can be used to determine the actual amount of nitrate in the solution within the porous body and, thus, the medium. An absorbance baseline is determined by the dissolved organic compounds (DOC) that can be determined using the 270 nm UV-C light. On top of this baseline, the nitrate analyte concentration will cause an additional absorbance to be measured using 220 nm UV-C light. The correction should be a simple subtraction: nitrate absorbance minus DOC absorbance = corrected nitrate absorbance.

[0080] In an embodiment, the second pair of transmitter and receiver is used as a reference measurement to correct for any measurement drift over time. In an embodiment, not depicted, a beam splitter is located to separate the ultraviolet radiation of the at least two ultraviolet radiation transmitters. The radiation output of each ultraviolet radiation transmitter is beam split to provide ultraviolet radiation that is received by an ultraviolet receiver and if and when there is a variation in the level of received intensity and the variation is greater, on average, over a predetermined period, than a predetermined threshold then that condition can be recorded and reported by the triggering of a software sub-routine, which will alert the user of the circumstance.

[0081] Figure 5 depicts the associated processing electronics modules 18 to which the Ultraviolet (UV) emitters 14, 14a and (UV) receiver 16, 16a elements are electrically connected. The electronic module / s can be mounted on a dedicated printed circuit board or constructed of separate modules and appropriate interconnection to exchange data, signals and power. The power source or distribution of that power is not shown to unclutter the block diagrammatic depiction of the processing electronic modules.

[0082] A transmitter controller module 30 powers and receives the output of (UV) receivers 16, 16a which have received photons in the UV-C range, such as at about a predetermined wavelength of 220 nm for one of the receivers 16 and about 272 nm for the other receiver 16a.

[0083] A receiver module 32 drives the (UV) emitters 14, 14a with a suitable frequency to emit photons in the UV-C range, such as at about a predetermined wavelength of 220 nm for one of the emitters 14 and about 272 nm for the other emitter 14a.

[0084] A processor module 34 orchestrates the measurement method. In an embodiment, providing suitable frequencies to respective UV-C transmitter elements in timed intervals or pulsed over a predetermined period, receiving and transforming the signals received from the UV-C receivers, which may be primed for the reception as the processor is in control of the UV-C transmitters. The processor is adapted to receive other data, such as the temperature and moisture content of the medium, from an external source. The processor also performs calculations, uses look-up tables and provides data in a predetermined format that is representative of the analyte concentration, either with or without identifying the analyte. The processor module may also include one or more different types of data memory devices, Random Access Memory (RAM) for temporarily holding data, Electronic Programmable Read Only Memory (EPROM) for storing executable programs which perform one or more of the functions of the processor, wherein the data stored in devices which are transitory and non-transitory computer-readable mediums.

[0085] A communication module 36 receives data from the processor module and sends it to other modules within the sensor housing or external of the sensor housing via known wireless communication protocols. The communication module 36 is also adapted to receive data from external devices, wherein the data includes the temperature, moisture and salinity level of the medium at one or more locations along the sensor housing.

[0086] Figure 11 depicts a graph of absorbance against wavelength measured using an embodiment of the sensor arrangement disclosed herein. The greatest absorbance within the wavelength spectrum measured by the receiver element is at 221 nm, and a regression relationship at the absorbance wavelength has an r-squared value of 0.9936. The absorbances displayed at wavelengths below 221 nm are to be ignored since they represent the presence of non-nitrate ions and can be readily filtered out of the measurement results by tuning the receiver characteristics or applying an analogue or digital filter to the measurement signal.

[0087] When calibrating the sensor arrangement, it is also viable to use a standard addition method to determine the concentration of an analyte that is in a complex matrix, such as foodstuff-derived fluids, soil measurements, etc., using the method and apparatus disclosed herein.

[0088] Figure 6 depicts the Ultraviolet (UV) emitter 14 and receiver 16 elements on opposite sides of the rectangular cross-section porous body. If two UV emitter-receiver pairs are located adjacent to each other with respect to the porous body, there is a high likelihood that the sample measured will be the same.

[0089] The porous body 10 may have other shapes so as to maximize the area of exposure and thus maximize fluid communication into and out of the porous body or to accommodate additional UV emitter -receiver pairs.

[0090] When analyte measurements are made, it is advantageous that the medium's temperature and moisture and total ion content (soil salinity) content are known.

[0091] Reference is made to US5418466, titled “Moisture and salinity sensor and method of use”, which was owned by the subject applicant, discloses a method and means for measuring soil moisture that can be used in the same sensor housing as the sensor arrangement disclosed in this specification. The sensors and electronic circuits disclosed in US5418466 can be located in close proximity to the sensor arrangement disclosed in this specification, such that the soil moisture content of the soil in the vicinity of the sensor arrangement disclosed herein can be determined and the measurement data shared with the processor controlling the analyte measurement technique. The data can be in the form of a digital representation or an analogue representation. The process of adjustment can use a look-up table that includes known temperature against a known concentration adjustment factor, which is then applied to the measurement taken by the sensor arrangement. A linear or non-linear calibration equation can be used to adjust the absorbance of DOC and Analyte with temperature variation. As disclosed in US5418466, the moisture and salinity of the soil can also be provided for analysis and review, and the sensor housing depicted therein is useful for illustrating that the porous body and thermal sensor can be conveniently located between the pair of conductive capacitive sensor ring regions, with there being an aperture in the sensor housing to allow the porous body, and only the porous body to be exposed to the surrounding medium.

[0092] The determination of the temperature of a medium can be made in several ways. Since the measurement result is to be used by the sensor arrangement disclosed in this specification, it is advantageous if the data representative of the temperature is made available in either analogue or digital form. In one embodiment, the temperature is measured using a thermistor located on a signal processing board wherein the thermistor is in thermal contact with the inner wall of the sensor housing or a thermally conductive area installed in the wall of the housing, once in the soil comes into thermal contact with the sensor arrangement. Of course, where in this portion of the document, reference is made to the soil, the medium could also be other mediums, such as a foodstuff, or a body of grain, or ore. The temperature of the soil varies with depth, so multiple temperature sensors can be arrayed along the internal wall of thesensor housing, preferably located in proximity to the sensor arrangement so that temperature in the medium in the vicinity of both the temperature sensor and the sensor arrangement is substantially the same. However, that is not necessarily needed as the temperature profile is likely stable below a particular depth in the soil. For example, the soil measurement zone is the soil rhizosphere (where roots grow), however, soil temperature does vary diurnally and seasonally because of weather conditions, crop cover and soil moisture content. Variation of the temperature is less with greater soil depth. So, in use, the various sensors are at different depths relative to the surface of the medium when the housing is inserted into a prepared opening in the medium, for example, when inserted into the soil.

[0093] The embodiments described mostly refer to the use of the disclosed sensor arrangement in the soil. However, it is also possible that the medium is created by taking a sample of the substance to be tested and adding that to a known quantity of water (in an embodiment that water is filtered and possibly de-ionised) and the sensor arrangement, as disclosed herein, in a suitable housing is submerged within the aqueous solution of analytes and water. In this case, the temperature is still measured and used in the determination of the concentration of the analyte.

[0094] The most beneficial analyte measurements are possible when drainage in the soil of a growing crop is approaching the moisture Field Capacity point. This is when drainage has slowed to almost a standstill, and final nitrate re-positioning in the soil profile can be measured after rainfall or irrigation and, most usefully, after a fertilisation or fertigation event. Other measurements can be triggered during the dry down curve of soil moisture measuring nitrate use by plant uptake.

[0095] Figure 12 depicts a visual and numerical (mg / kg) visualisation of the nitrate nitrogen values for soils.

[0096] Figure 13 depicts an example of a fleshy root yield versus nitrate concentration in the soil.

[0097] The reference to any prior art in this specification is not, and is not to be taken as, an acknowledgement of any form of suggestion that such prior art forms part of the common general knowledge.

[0098] Throughout the specification and the claims that follow, unless the context requires otherwise, the words "comprise" and "include" and variations such as "comprising" and "including" will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers.

[0099] It will be appreciated by those skilled in the art that the disclosure described herein is not restricted in its use to the particular application described. Neither is the disclosure restricted in its preferred embodiment concerning the particular elements and features described or depicted herein. Itwill be appreciated that the scope of the disclosure is not limited to the embodiment or embodiments disclosed but is capable of numerous rearrangements, modifications, and substitutions without departing from the scope as set forth and defined by the claims.

Claims

CLAIMS1. A sensor for sensing the type and concentration of an analyte within a medium comprising: a porous body located, in use, in fluid communication with the medium containing at least one analyte and dissolved organic compounds, such that within the porous body, there is a state of hydraulic equilibrium between the fluid in the porous body and the fluid in the medium at a known temperature and known moisture content of the medium, wherein the porous body is transmissive to ultraviolet radiation and there are at least two ultraviolet radiation transmitters and at least one ultraviolet radiation receiver, each transmitter and the or each receiver operating at different wavelengths, each transmitter and the or each receiver located adjacent to the porous body, wherein each transmitter and receiver are orientated such that each transmitter and receiver respectively sends and receives ultraviolet radiation through at least a portion of the porous body, such that at least two characteristics of the ultraviolet radiation received at the or each ultraviolet radiation receiver are respectively indicative of the concentration of the analyte and the dissolved organic compounds within the porous body at the known temperature and known moisture content of the medium.

2. The sensor arrangement according to claim 1, wherein the concentration of the analyte in the fluid within the porous body is due to the absorption of one or a predetermined range of the ultraviolet radiation wavelengths as detected at a respective receiver.

3. The sensor arrangement according to either claim 1 or claim 2, wherein the dissolved organic compounds concentration in the sample solution within the porous body is due to the absorption of one or a predetermined range of the ultraviolet radiation wavelengths as detected at the respective receiver.

4. The sensor arrangement according to any one of claims 1 to 3, wherein ultraviolet radiation is ultraviolet C radiation to detect the concentration of analytes and the concentration of dissolved organic compounds that absorb wavelengths in the UV-C band.

5. The sensor arrangement according to claim 4, wherein one transmitter transmits at a wavelength of 220-240 nm and a second transmitter transmits at a wavelength of 260 to 280 nm.

6. The sensor arrangement according to any one of claims 1 to 5, wherein the porous body is porous silica material.

7. The sensor arrangement according to claim 6, wherein the porous silica material has a determined purity.

8. The sensor arrangement according to any one of claims 1 to 7, wherein the analyte is nitrate.

9. The sensor arrangement according to any one of claims 1 to 8, further comprising a longitudinal sensor housing supporting two or more spaced sensors for sensing the type and concentration of an analyte within the medium.

10. The sensor arrangement according to claim 9, wherein the two or more sensors in the sensor arrangement are positioned along the longitudinal length of the sensor housing, where there is a longitudinal spacing between sensors.

11. The sensor arrangement according to any one of claims 1 to 10, further comprising an arrangement to measure soil water, soil salinity (total soil ion content) and soil temperature within a sphere of influence within the medium adjacent to the porous body.

12. The sensor arrangement according to any one of claims 1 to 11, further comprising a beam splitter located so as to separate the ultraviolet radiation of the at least two ultraviolet radiation transmitters, and the radiation output of each ultraviolet radiation transmitter is beam split to provide ultraviolet radiation that is received by an ultraviolet radiation intensity sensor that monitors the intensity output of each ultraviolet radiation transmitter.

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