WO2017174977A1 - Caractérisation de particules - Google Patents

Caractérisation de particules Download PDF

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Publication number
WO2017174977A1
WO2017174977A1 PCT/GB2017/050943 GB2017050943W WO2017174977A1 WO 2017174977 A1 WO2017174977 A1 WO 2017174977A1 GB 2017050943 W GB2017050943 W GB 2017050943W WO 2017174977 A1 WO2017174977 A1 WO 2017174977A1
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Prior art keywords
radiation
particle
probe volume
single particle
beams
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PCT/GB2017/050943
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English (en)
Inventor
Odd Ketil Andersen
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Particulate As
Samuels, Adrian James
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Publication of WO2017174977A1 publication Critical patent/WO2017174977A1/fr

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/10—Investigating individual particles
    • G01N15/14—Optical investigation techniques, e.g. flow cytometry
    • G01N15/1434—Optical arrangements
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/18—Water
    • G01N33/1826—Organic contamination in water
    • G01N33/1833—Oil in water
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/10—Investigating individual particles
    • G01N15/14—Optical investigation techniques, e.g. flow cytometry
    • G01N15/1456—Optical investigation techniques, e.g. flow cytometry without spatial resolution of the texture or inner structure of the particle, e.g. processing of pulse signals
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/10—Investigating individual particles
    • G01N2015/1027—Determining speed or velocity of a particle
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/10—Investigating individual particles
    • G01N15/14—Optical investigation techniques, e.g. flow cytometry
    • G01N15/1434—Optical arrangements
    • G01N2015/1447—Spatial selection
    • G01N2015/145—Spatial selection by pattern of light, e.g. fringe pattern
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/10—Investigating individual particles
    • G01N15/14—Optical investigation techniques, e.g. flow cytometry
    • G01N15/1434—Optical arrangements
    • G01N2015/1454—Optical arrangements using phase shift or interference, e.g. for improving contrast
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/10—Investigating individual particles
    • G01N15/14—Optical investigation techniques, e.g. flow cytometry
    • G01N2015/1486—Counting the particles
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
    • G01N21/64—Fluorescence; Phosphorescence
    • G01N2021/6417—Spectrofluorimetric devices
    • G01N2021/6421—Measuring at two or more wavelengths
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
    • G01N21/64—Fluorescence; Phosphorescence
    • G01N21/6486—Measuring fluorescence of biological material, e.g. DNA, RNA, cells
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
    • G01N21/65—Raman scattering
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2201/00—Features of devices classified in G01N21/00
    • G01N2201/02—Mechanical
    • G01N2201/021—Special mounting in general
    • G01N2201/0212—Liquid borne; swimming apparatus
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2201/00—Features of devices classified in G01N21/00
    • G01N2201/02—Mechanical
    • G01N2201/021—Special mounting in general
    • G01N2201/0216—Vehicle borne
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2201/00—Features of devices classified in G01N21/00
    • G01N2201/02—Mechanical
    • G01N2201/021—Special mounting in general
    • G01N2201/0218—Submersible, submarine
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
    • G01P5/00—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft
    • G01P5/26—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft by measuring the direct influence of the streaming fluid on the properties of a detecting optical wave

Definitions

  • Particle characterisation This invention relates to apparatus and methods for characterising particles in an aquatic mass.
  • the characterisation of particles is important in many applications. For example, there are many circumstances in which it is necessary to monitor the extent of pollution in an ocean or other body of water. In the event of an oil spill, it is desirable to be able to measure the extent of the spill, and/or to monitor the effect of the use of chemicals (e.g. dispersants) on spills to determine the fate of the oil. It may also be necessary to monitor particles in discharges, for example, drilling mud from drilling operations or produced water from oil production, as well as the discharge of ballast water, which might be a major pathway for introducing species to new environments. Ballast water may be checked to ensure that particles are removed according to protocol, and remaining particles are not alive. This is important to ensure agreement with regulations regarding discharges before water is discharged into an ocean. As another example, there is a need to monitor algae in coastal regions. Many coastal regions are affected by harmful algal blooms (HABs), which are caused by blooms of microscopic algae that may be toxic to humans, fish, birds and other life in and near oceans.
  • Many particles of interest exhibit fluorescence (i.e. the emission of radiation in response to stimulating radiation).
  • Known methods of monitoring particles include exciting fluorescence in particles in a body of water, and then studying the spectral properties of the emitted radiation to try to characterise the particles. This method can give a reasonable indication of particles in a body of water if the majority of particles emitting radiation are of the same type.
  • the water contains not only the particles of interest, but many other particle types. For example, in a region where it is desired to monitor oil contamination, there may also be algal particles. It is also possible that the water contains dissolved organic matter. Consequently, the measured fluorescence signal is the sum of many individual particle fluorescence signals, emitted by many different particle types.
  • the Applicant has identified a need for an improved method and apparatus for the characterisation of particles in an aquatic mass which contains a mixture of different particle types.
  • a method of characterising individual particles in an aquatic mass comprising: generating an interference pattern in the aquatic mass by overlapping two beams of electromagnetic radiation, wherein the interference pattern is generated in a probe volume defined by a region of overlap of the two beams;
  • the invention extends to an apparatus for characterising individual particles in an aquatic mass, the apparatus comprising:
  • a source of electromagnetic radiation arranged to generate an interference pattern in the aquatic mass by overlapping two beams of electromagnetic radiation, wherein the interference pattern is generated in a probe volume defined by a region of overlap of the two beams, thereby to illuminate a single particle in the probe volume to cause said single particle to emit radiation;
  • a detector arranged to detect the radiation emitted by the single particle; and processing means configured to use spectral data derived from the detected radiation to determine a property of the single particle.
  • the invention enables more detailed and more useful information to be obtained about particles in an aquatic mass because the particles are characterised individually.
  • the prior art only allows the determination of bulk properties of large numbers of particles in water, e.g. the bulk properties of many thousands of particles, which may provide less information and/or less useful information.
  • the measured signal of radiation emitted from particles is the sum of many individual particle signals, which includes not only signals from the particles of interest, but also signals from other particles, e.g. dissolved organic matter, that may not be of interest. The signals from particles that are not of interest may therefore obscure the signals of interest.
  • the ability to look at individual particles arises from the use of an interference pattern in a probe volume.
  • the probe volume may be very small, and the length scale of the interference pattern (e.g. fringe width) may be very small, allowing the interference pattern to illuminate one particle at a time.
  • the probe volume has a maximum dimension that is smaller than a mean separation between particles in the aquatic mass.
  • the maximum dimension of the probe volume may be, for example, less than half of the mean particle separation, less than one fifth of the mean particle separation, or less than one tenth of the mean particle separation.
  • the method comprises illuminating just one particle of interest at a time.
  • the detected radiation may be emitted and/or scattered by more than one particle in the probe volume.
  • the method comprises the step of discarding or disregarding spectral data corresponding to radiation detected when more than one particle is
  • characterising individual particles refers to determining a property of a single particle, i.e. so that individual properties of individual particles may be determined separately.
  • the method comprises determining at least one property of the particle other than its velocity, speed, or direction of motion. It will be appreciated that a property of the particle may be determined from spectral data that is characteristic of (e.g. unique to) to the single particle that is illuminated.
  • the spectral data may comprise an emission spectrum, e.g. a fluorescence emission spectrum.
  • the emission spectrum may be a full spectrum (i.e. having sufficient resolution to determine a detailed fluorescence spectrum of the particle).
  • the spectral data may comprise values indicative of the amount of radiation falling within predefined wavelength bands, e.g. a few wavelength bands. This may be considered equivalent to an emission spectrum having very coarse resolution but which may be sufficient to identify particles of interest in some applications.
  • spectral data may be acquired by integrating the detected radiation over time, e.g. for the duration of the particle's passage through the probe volume. This allows a more reliable measurement to be obtained than might be achievable using only an instantaneous measurement.
  • the spectrum of the radiation that is emitted by a particle may be indicative of a kind of fluorescence by the particle.
  • the spectrum of fluorescence radiation emitted by a particle may depend on the substance the particle is made from.
  • the particle size can be determined for very small particles, e.g. down to sizes in the region of 3 ⁇ - 5 ⁇ .
  • Raman scattering involves inelastic scattering of photons when they interact with molecular vibrations or other excitations in the particle, resulting in the energy of the scattered photons being shifted relative to the incident photons. This shift in energy, and thus in wavelength, gives information about the vibrational modes in the particle, and thus provides information about the particle properties.
  • Measurement of radiation from Raman scattering requires a larger particle than fluorescence measurements, but the information obtained can be more diagnostic (i.e. it contains more useful information for determining particle properties and dinstinguishing particles).
  • Any suitable radiation of any suitable wavelength may be used to induce Raman scattering, e.g. laser radiation.
  • the radiation may be the same radiation that is used to generate the interference pattern. In that case, the wavelength of the exciting radiation would be the same as the radiation used for inducing
  • a different wavelength of radiation may be used, in which case an additional source of electromagnetic radiation is used.
  • An additional detector may be provided, e.g. to detect the Raman scattered radiation if a different wavelength radiation is used.
  • Using an additional source having a different wavelength from that used for inducing fluorescence is advantageous as it can prevent the fluorescence signal masking the Raman scattering signal.
  • the radiation used to induce Raman scattering is the same radiation that is used to generate the interference pattern, as discussed previously the length scale of the probe volume and the interference fringes means that typically only one particle will be illuminated at a time. This means that it is possible to detect Raman- scattered radiation from one particle at a time, thus allowing the determination of the properties of a single particle via Raman spectroscopy.
  • the radiation from the additional source may be used to illuminate a probe volume by overlapping two beams of the radiation.
  • a coherent (e.g. monochromatic) additional light source may be used so that an additional interference pattern is generated in the probe volume.
  • the two beams may be non-coherent such that a further fringe pattern is not produced.
  • the invention provides a method of characterising individual particles in an aquatic mass, the method comprising:
  • the invention extends to an apparatus for characterising individual particles in an aquatic mass, the apparatus comprising:
  • a source of electromagnetic radiation arranged to overlap two beams of electromagnetic radiation to illuminate a probe volume defined by a region of overlap of the two beams, thereby to illuminate a single particle in the probe volume to cause said single particle to scatter radiation via Raman scattering;
  • a detector arranged to detect the radiation scattered via Raman scattering by the single particle
  • processing means configured to use spectral data derived from the detected radiation to determine a property of the single particle.
  • the beams of radiation may be coherent so that an interference pattern is generated in the probe volume.
  • the apparatus preferably comprises a Laser Doppler Velocimeter arranged to determine a speed of the particle using Laser Doppler Velocimetry (LDV).
  • LDV Laser Doppler Velocimetry
  • the particle will tend to scatter more light to the detector than when it is in a region of destructive interference, i.e. a dark region of the interference pattern.
  • the detected radiation will vary in intensity.
  • the interference pattern is a sinusoidally varying fringe pattern
  • the intensity of detected radiation will also be sinusoidally varying.
  • the frequency of variation in intensity will depend on the speed of the particle and the fringe separation.
  • the speed of the particle perpendicular to the fringes may thus be related to the fringe spacing and the frequency of variation in the intensity of the detected radiation.
  • the apparatus may be mounted on a moving vehicle, e.g. an autonomous underwater vehicle (AUV), or a remotely operated vehicle (ROV).
  • AAV autonomous underwater vehicle
  • ROV remotely operated vehicle
  • the apparatus may be advantageously positioned and configured so that the interference pattern comprises fringes aligned substantially perpendicular to a direction of propulsion of the vehicle. It is also preferred that the probe volume is sufficiently far from the vehicle to be in a region of laminar flow of the water. In that situation, the flow of particles relative to the vehicle will be substantially perpendicular to the fringe direction, allowing the particle speed relative to the vehicle to be more accurately determined.
  • the method may also comprise counting particles, e.g. counting the number of particles illuminated by the interference pattern in a time period. Particle counting may be used to determine a particle density and thereby to determine a particle flow rate in the aquatic mass.
  • the variation in the signal corresponding to the intensity of the detected radiation may be also be used to determine the reliability of the data collected.
  • the recorded intensity of the scattered radiation may vary according to the brightness of the fringes as the particle moves through the interference pattern, e.g. exhibiting a number of peaks corresponding to the number of fringes that the particle has moved through.
  • the interference pattern may have, for example, between five and ten fringes. If a particle passes close to the centre of the probe volume, the recorded scattered radiation may exhibit several peaks, e.g. five or more peaks. In contrast, if the particle passes close to the edge of the probe volume, there might be only one or two peaks.
  • the reliability of the data may be greater if the particle has passed near the centre of the probe volume, as there is more scattered and/or emitted radiation that can be collected and used.
  • data corresponding to a particle may be discarded if the recorded intensity of the scattered radiation exhibits fewer than a threshold number of peaks.
  • the threshold number may be, for example, three, four, five, six, or more than six. It will be understood, therefore, that the actual sampling volume in which particles may be characterised may be smaller than the probe volume, as data
  • the size and shape of the actual sampling volume may be dynamically determined depending on, for example, particle and flow characteristics, the laser properties, and the threshold number of peaks.
  • particle means any individual piece of matter or material, e.g. a piece of particulate matter or a droplet.
  • the particle may be an algae particle.
  • the algae particle may emit radiation by fluorescence due to the presence of chlorophyll a in the algae.
  • an algae particle may emit radiation by fluorescence due to phycocyanine, for example in blue-green algae.
  • an algae particle may emit radiation by fluorescence due to the presence of phycoerythrin, e.g. in red algae.
  • the particle may be a droplet.
  • the particle may be an oil droplet.
  • the oil droplet may emit radiation by fluorescence due to the presence of polycyclic aromatic hydrocarbons (PAH) in the oil droplet.
  • PAH polycyclic aromatic hydrocarbons
  • the particle may be coated in oil or organic matter that emits fluorescence radiation, thereby causing the particle (e.g. which may be a particle comprising inert matter coated by organic matter) to emit fluorescence radiation.
  • the interference pattern may be generated by any source of electromagnetic radiation but a laser is used.
  • the interference pattern is created using two beams from a single electromagnetic radiation source.
  • the electromagnetic radiation source may be arranged (e.g. using optical components) to provide two separate radiation beams directed so that they overlap to define the probe volume, thereby generating an interference pattern.
  • the distance of the probe volume from the apparatus may be chosen depending on the type of particles to be characterised and the situation in which the apparatus is used.
  • the distance may also be chosen to optimise the amount of light received by the detector. For example, if the beams are directed so that they overlap close to the apparatus, more of the scattered and/or emitted radiation may be received by the detector. This is because of two factors. First, light from the probe volume will be incident on the detector over a greater area which allows for more sensitive measurements from a detector having a given sensitivity per unit detection surface area. Second, there is a reduced amount of absorption by the water (e.g. sea water) if the light only travels a short distance through the water. Accordingly, if the probe volume is far away from the apparatus, there may be reduced sensitivity.
  • water e.g. sea water
  • the distance of the probe volume from the apparatus there are additional factors that may be used to determine the distance of the probe volume from the apparatus. For example, if the probe volume is close to the apparatus (e.g. close to an optical arrangement for directing light onto the detector), good spatial resolution may be obtained for small particles. If the probe volume is farther away, good spatial resolution may be obtained for medium and large particles. If the apparatus is mounted on a moving under water vehicle (e.g. an AUV), there may be turbulence in the water around the vehicle when it is moving, with a region of laminar flow farther away from the vehicle. In the region of laminar flow, the particles may all move with approximately the same speed, while in the turbulence, the particle may have many different speeds. The distance to the probe beam may be advantageously chosen so that it is outside the turbulence and in the laminar flow, which may yield better results for the particle characterisation.
  • a moving under water vehicle e.g. an AUV
  • electromagnetic radiation may comprise the Laser Doppler Velocimeter laser. It will be appreciated that this advantageously obviates the need to provide two separate electromagnetic sources, e.g. two separate lasers, as the LDV laser can be used for both purposes.
  • the apparatus in addition to the source of electromagnetic radiation which illuminates the particle to cause it to emit radiation, the apparatus comprises a further electromagnetic radiation source.
  • the source of electromagnetic radiation and the further electromagnetic radiation source preferably have different wavelengths. This is advantageous as the wavelengths may, for example, be chosen so that the source of electromagnetic radiation has a wavelength that is optimal for inducing the particle to emit light, while the further electromagnetic radiation source has a wavelength optimal for scattering by the particle.
  • the type of electromagnetic radiation source e.g. the type of laser, may be selected so as to provide a wavelength suitable for exciting fluorescence in a particle.
  • the radiation source may be selected to have a wavelength to excite fluorescence in a particular particle type of interest, or a particular particle type that is expected to be seen in an aquatic mass.
  • the radiation source may emit radiation in the blue-violet frequency region of the visible spectrum; for example, the radiation emitted by the electromagnetic radiation source may have a wavelength between 300 nm and 500 nm.
  • the radiation source comprises a blue laser.
  • a blue laser may refer to a laser having a wavelength spectrum covering part of the short wavelength end of the visible spectrum, e.g. part of the blue to violet spectrum.
  • a 405 nm laser may be used.
  • a 405nm laser is particularly advantageous for several reasons. Suitable 405nm lasers produce a strong (i.e. intense) beam which is suitable for use in the sea.
  • the wavelength spectrum of a 405nm laser falls within the range of wavelength absorbed by many different of particles of interest (e.g. different algae species) to produce detectable fluorescence. In particular, chlorophyll a absorbs 405nm radiation strongly.
  • suitable dichroic mirrors are readily available to separate to the LDV Doppler signal and the fluorescence signal.
  • other wavelengths may be used.
  • the radiation source's wavelength may fall outside of the visible spectrum. However, preferably the wavelength is a visible wavelength. This may be better from a health and safety viewpoint, e.g. to satisfy safety regulations relating to open radiation sources. In addition, it facilitates the alignment of the apparatus (e.g. optical components) which may be more easily achieved if the radiation is visible.
  • the wavelength of a radiation source may refer to a peak or central wavelength of the spectrum of the radiation emitted by the source.
  • Additional radiation sources may be used to induce the particle to emit or scatter radiation, e.g. to enhance fluorescence from the particle, or to characterise the particle using Raman scattering.
  • the additional radiation sources may have a different wavelength. For example, if a main laser of 405 nm is used to excite fluorescence in polycyclic aromatic hydrocarbons (PAH) at 405 nm, normally PAH structures comprising four or more ring structures will be excited. Naphthalene absorbs predominantly at 266 nm, so an additional laser may be provided to excite smaller ring structures. Similarly, other particles will have characteristic absorption frequencies and so additional lasers may be selected with suitable frequencies to excite the desired particles.
  • PAH polycyclic aromatic hydrocarbons
  • the detected radiation is separated according to its wavelength.
  • the detected radiation may be separated into two portions.
  • a first portion of the separated radiation may comprise radiation that is below a threshold wavelength.
  • the first portion may correspond to scattered radiation, which is likely to be of approximately the same wavelength as the incident radiation.
  • a second portion of the separated radiation may comprise radiation that is above the threshold wavelength.
  • the second portion may correspond to emitted radiation, as emitted radiation is typically of lower energy (i.e. longer wavelength) than the radiation that excites the emission.
  • the threshold may be chosen so that the detected radiation is separated into (i) predominantly emitted radiation and (ii) predominantly scattered radiation.
  • the detected radiation may thereby be split into a portion for spectral analysis (e.g.
  • the detected radiation may be split into more than two portions according to more than one threshold wavelength, e.g. into scattered radiation, emission from a first particle type having a characteristic range of frequencies, and emission from a second particle type having a different characteristic range of frequencies.
  • Any suitable means e.g. optical component(s), may be used to separate the radiation.
  • a dichroic mirror or filter may be used.
  • the radiation may be separated so as to send emitted radiation (e.g. fluorescence signals) to a spectrometer and to send scattered radiation an LDV processing engine, or other speed, velocity, and/or direction analysis engine.
  • a threshold wavelength (e.g. a single threshold wavelength in a case where the radiation is separated into two portions) may be slightly above the wavelength of the electromagnetic source. For example, it may be between 5 and 10 nm above. As an example, for a 405 nm radiation source, the threshold may be 410 nm. This may help to avoid any of the 405nm radiation entering into the spectrometer. It is undesirable for 405nm radiation to enter the spectrometer as it may cause backscattering and obscure the radiation of interest (i.e. the fluorescence radiation), as the 405nm radiation may be significantly more intense than the fluorescence radiation.
  • the size of the probe volume will be determined by the characteristics of the radiation sources or lasers and/or any optical components used to focus the radiation, e.g. laser beam width, radiation wavelength, focal length of optical components.
  • the size of the probe volume may be on the scale of tens of microns, e.g. between 50 ⁇ and 100 ⁇ , or between 20 ⁇ and 200 ⁇ .
  • the probe volume may be around 200 ⁇ in length, around 50 ⁇ in width and around 50 ⁇ in depth.
  • the characteristic length scale of the interference pattern e.g. the fringe spacing
  • the characteristic length scale, e.g. fringe spacing depends on the wavelength of the radiation.
  • the characteristic length scale, e.g. fringe spacing may be on the order of microns, e.g. between 5 ⁇ and 10 ⁇ , or between 2 ⁇ and 20 ⁇ , although it will be understood that the length scale/fringe spacing may be larger or smaller than this.
  • Any suitable detector may be used to detect the emitted and/or scattered radiation.
  • photomultiplier tubes may be used.
  • a charge coupled device may be used.
  • a linear photo diode array may be used.
  • a high resolution e.g. 1-2 nm
  • Lower resolution but higher sensitivity improves the chance of detecting fluorescence radiation for a particle. Accordingly, it may be necessary to balance resolution and sensitivity.
  • a charge coupled device may give better resolution, but may have reduced sensitivity. If its sensitivity is sufficiently high, a charge coupled device is preferable for the detector.
  • the method of the invention may be applied on test samples that have been collected from an aquatic mass, e.g. in a laboratory setting. However, preferably the method is applied in situ in ambient water, e.g. in an aquatic mass where particles of interest are found.
  • the apparatus may be mounted on a moving vehicle. In other embodiments, the apparatus is fixed at a location in an aquatic mass, e.g. at a monitoring station in an ocean.
  • the method may be applied "in line", for example, in discharge outlets. For example, oil droplet concentration or type may be measured in produced water discharges.
  • the method may be used for characterisation of ballast water, for example to determine the size of particles present to ensure agreement with regulations before discharging the water.
  • the method may be used to detect changes in water mass characteristics (e.g. which may be characterised by changes in algal composition). As another example, it may be used to detect oil droplets from leaks or spills, e.g. to measure the extent of a spill. It may be used to document the effects of the use of chemicals on spills, for example during clean-up operations. It may be used to validate distribution models for produced water and drilling mud.
  • water mass characteristics e.g. which may be characterised by changes in algal composition
  • oil droplets from leaks or spills e.g. to measure the extent of a spill. It may be used to document the effects of the use of chemicals on spills, for example during clean-up operations. It may be used to validate distribution models for produced water and drilling mud.
  • the method may comprise carrying out a spectral analysis of the radiation to obtain the spectral data.
  • the method may comprise determining the spectral components of detected radiation.
  • the method may comprise comparing the spectral data with recorded spectral data in a database, and/or reviewing of the spectral data by an operator. This may enable the processing means or an operator to identify or characterise a particle based on the comparison of the spectral data with recorded spectral data.
  • the spectral data may be used to create a record, e.g. database files, of spectral data corresponding to particular particles or particle types. These records may then be used subsequently to identify particles. It will be understood that different algal species have different fluorescence spectra, and that some spectra are easier to distinguish/identify than others.
  • the recorded data may added to the database to build up a library of different recorded spectra, irrespective of whether a particle or particle type has been identified as corresponding to the data.
  • the data added to the database may include and/or be grouped according to the results of data analysis, e.g. multivariate analysis. Such data may be used subsequently to help distinguish spectra and/or to identify particles.
  • the apparatus may comprise a user interface.
  • the user interface may allow an operator to view spectral data or data relating to particles in the aquatic mass.
  • the user interface may allow the operator to view data embodying the characterisation of particles, e.g. data indicating a particle's material or size. It may also allow the operator to view data indicating to a particle's velocity, speed or direction of motion, or data indicating a particle density or flow rate in the aquatic mass.
  • the user interface may allow an operator to select what data to display.
  • the user interface may be capable of displaying data in real time, e.g. spectral data or data indicating the properties of particles, as it is received, or shortly after it is received. It may also allow an operator to view stored data, e.g.
  • data collected on an AUV may be stored for later retrieval and analysis, while data on an ROV following a ship may transmit recorded data in real time for real time analysis.
  • Figure 1 shows a Laser Doppler Velocimeter used in embodiments of the present invention
  • Figure 2 shows a close-up view of a probe volume formed by an intersection of two laser beams produced by the Laser Doppler Velocimeter of Figure 1 ;
  • Figure 3 shows an absorption spectrum of chlorophyll a
  • Figure 4 shows a fluorescence emission spectrum of chlorophyll a
  • Figure 5 shows four detected radiation spectra 68, 70, 72, 74 obtained in accordance with the method of the present invention.
  • Figure 6 shows a graph of fluorescence signals observed from single algae cells in a sample of tetraselmis sp in water.
  • Figure 7 shows the Laser Doppler Velocimeter of Figure 1 with a dichroic mirror for separating the received radiation that is scattered or emitted from particles in the probe volume according to its wavelength;
  • Figure 8 shows the variation with time of the light intensity scattered from a particle in a probe volume of the Laser Doppler Velocimeter of Figure 1 ;
  • Figure 9 shows the light intensity of Figure 8 filtered using a bandpass filter to remove the Gaussian envelope
  • Figure 10 shows a schematic representation of signal and data handling according to embodiments of the present invention.
  • Figure 1 shows a Laser Doppler Velocimeter 2 used in embodiments of the present invention for characterising individual particles in an aquatic mass.
  • the Laser Doppler Velocimeter 2 comprises a housing 4 containing a laser 6.
  • the laser 6 is used to produce two beams 10, 12 of coherent laser light at 405 nm.
  • the beams 10, 12 are directed by additional optical components (not shown) through holes 13 at the edge of the lens 8 so that the beams overlap to define a probe volume 14.
  • the overlap of the beams in the probe volume 14 is shown in Figure 2, which magnifies the region in the dotted circle 16.
  • the first beam 10 and second beam 12 are directed to overlap to define the probe volume 14.
  • an interference pattern 22 is created.
  • the interference pattern 22 consists of interference fringes localised in the probe volume.
  • the Laser Doppler Velocimeter 2 is disposed in an aquatic mass 24, e.g. an ocean. Particles 26 in the aquatic mass move through the probe volume 14, due to the flow of the aquatic mass 24 in which the particles 26 are suspended. The particles 26 therefore move through the probe volume 14. Due to the size of the probe volume 14, typically only one particle 26 is in the probe volume at a time. If data should be recorded indicating that more than one particle 26 is in the probe volume 14, that data may be discarded.
  • the presence of more than one particle 26 in the probe volume 14 occurs very infrequently.
  • a particle enters the probe volume 14, it is illuminated by the interference fringes.
  • the particle may scatter and/or emit radiation.
  • radiation 28 that is emitted and/or scattered by a particle 26 is coupled in to one or more optical fibres 30 by the centre portion of the lens 8 and optical components 31.
  • the optical components 31 are represented schematically by a lens, but it will be appreciated that the optical components may comprise any number of optical components possibly including, but not limited to, one or more lenses, diffraction gratings, mirrors, etc.
  • the radiation 28 is then transmitted via the optical fibre(s) 30 to one or more detectors, as described further below with reference to Figure 7.
  • a particle may scatter and/or emit radiation.
  • the radiation emitted or scattered will depend on the type of particle.
  • algae particles containing chlorophyll a are described.
  • other particles may be characterised.
  • other types of algae particles or oil droplets containing polycyclic aromatic hydrocarbons may be characterised.
  • Figure 3 shows an absorption spectrum of chlorophyll a. There is an absorption peak 32 at approximately 400 nm.
  • energy from the radiation is absorbed by the particle 26. This is because the wavelength of the laser beams 10, 12 coincides with the absorption band 34 of chlorophyll a. The absorbed energy is them re-emitted via fluorescence.
  • Figure 4 shows a fluorescence emission spectrum of chlorophyll a.
  • the emitted fluorescence radiation falls within a band 36 of approximately 600 nm to 750 nm, i.e. the emitted radiation is generally of a longer wavelength than the incident radiation from laser beams 10, 12.
  • radiation that is scattered from the particle 26 is approximately the same wavelength as the incident radiation from laser beams 10, 12.
  • Figure 5 shows four detected radiation spectra 68, 70, 72, 74 obtained in accordance with the method of the present invention.
  • the first spectrum 68 is a spectrum obtained for a sample of crude oil droplets in water.
  • the spectrum 68 exhibits a peak 76 at around 560 nm resulting from fluorescence by polycyclic aromatic hydrocarbons (PAH).
  • the second spectrum 72 was obtained for a sample of isochrysis galbana (T. Iso) in water.
  • the third spectrum 74 was obtained for a sample of rhodomonas lens in water.
  • the fourth spectrum 76 was obtained for a sample of tetraselmis sp in water.
  • the second, third, and fourth spectra 70, 72, 74 each contain a peak 78 at approximately 680 nm resulting from fluorescence by chlorophyll A in the samples. All four of the spectra 68, 70, 72, 74 exhibit a peak 80 at approximately 460 nm, resulting from Raman scattering by the water molecules in the samples. It can thus be seen that the radiation detected in accordance with the method of the invention can be used to characterise particles according to fluorescence peaks present in the spectra.
  • Figure 6 shows a graph of fluorescence signals observed from single algae cells in a sample of tetraselmis sp in water.
  • Tetraselmis sp is an alga with particle size in the range of approximately 14 ⁇ to 23 ⁇ .
  • the graph shows the fluorescence signals obtain from 100 scans, where each scan records the radiation detected at the detector over a period of 1 ms. For ten of the scans, there is a peak in the detected radiation at 680 nm. This coincides with the wavelength of fluorescence from Chlorophyll A present in algae.
  • the measurement from a single particle is in the range of 50 to 80 counts, which corresponds to an energy range of 10 nW to 16 nW.
  • each of these peaks corresponds to a single algae cell passing through the probe volume. It can thus be seen that the method of the present invention allows the detection of fluorescence from individual particles such as single cells, thus allowing those particles to be characterised individually.
  • Figure 7 shows the Laser Doppler Velocimeter 2 of Figure 1 , and shows how the received radiation 28 is directed via one or more optical fibres 30 to the dichroic mirror 38.
  • the dichroic mirror 38 (here represented simply by a functional block) separates the radiation according to wavelength. Radiation that is above 410 nm is directed along a first optical fibre 40 towards a spectrometer 42.
  • the longer wavelength portion which passes along the fibre 40 contains
  • the spectrometer 42 is used to measure the spectral components of this radiation.
  • the spectrum of emitted radiation 28 can be used to determine the type of particle 26 that was in the probe volume 14. For example, if the florescence spectrum matches the characteristic fluorescence spectrum of chlorophyll a, it can be determined that an algae particle containing chlorophyll a is in the probe volume 14. Further information may be obtained from the spectrum. For example, depending on the intensity of the spectrum, the size of the particle 26 may be inferred.
  • the component of the received radiation that is below 410 nm is directed along a second optical fibre 44 towards an LDV processing engine 46, where the intensity of the radiation is measured and the speed of the particle 26 is inferred.
  • Such shorter wavelength component i.e. comprising wavelengths that are generally close to the wavelength of the incident radiation
  • Figure 8 shows the time variation in the intensity of radiation scattered from a particle moving through the probe volume 14. As the particle 26 moves through the probe volume 14, it is periodically illuminated by the interference fringes arising from constructive interference of the laser beams. This gives rise to a sinusoidal variation in the intensity of scattered light.
  • the profile of the light intensity has a Gaussian envelope, which arises because of the Gaussian profile of the laser beams 10, 12. Between the peaks in Figure 8, the light intensity does not fall close to zero. This is because, in the example shown, the particle size is comparable to the fringe width. In such a case, as the particle moves through the fringes, it is partially illuminated by the next fringe before it has completely moved out of the previous fringe. If the particle were much smaller than the fringe width, the intensity would fall much closer to zero as there would be times when the small particle is almost entirely within a region of destructive interference. Nonetheless the variation in intensity can still be used to determine the speed of the particle.
  • Figure 9 shows the light intensity profile of Figure 8 filtered using a bandpass filter to remove the Gaussian profile.
  • the intensity of scattered light depends on whether the particle is in a region of constructive interference or destructive interference
  • the frequency of the sinusoidal variation of measured scattered light intensity will depend on how quickly the particle is moving through the fringes.
  • the frequency f is calculated from the bandpass filtered light intensity profile (such as shown in Figure 9).
  • the frequency may be obtained from the sinusoidal profile using, for example, a Fast Fourier Transform.
  • the same laser it is particularly advantageous, as shown in the present embodiment, for the same laser to be used to provide the light scattered by the particle as well as to excite fluorescence in the particle.
  • information relating to both the speed of the particle and the fluorescence spectrum of the particle can be obtained using one laser.
  • two different lasers may be used as described earlier.
  • the lasers may be arranged so that they both focus on the same probe volume and produce separate interference patterns.
  • a different dichroic mirror may be used to separate the wavelength components into suitable bands.
  • Figure 10 shows a schematic representation of the signal and data handling carried out in accordance with embodiments of the present invention.
  • the radiation 28 emitted and/or scattered from particles is separated by a dichroic mirror 38 into a first radiation component 48 (comprising radiation that is less than 410 nm in wavelength) and a second radiation component 50 (comprising radiation that is greater than 410 nm in wavelength) as previously described.
  • the first component 48 is detected by a detector measuring intensity, such as a photomultiplier tube, and the measured intensity is processed by the LDV processing engine 46 as described above to determine the speed of the particle.
  • the second component is directed to a spectrometer 42 which measures the spectrum of the radiation.
  • the data obtained from the LDV processing engine 46 and the spectrometer 42 are sent to a computer 52 for analysis and display.
  • the computer 52 comprises a processor 54 and a memory 56.
  • Stored in the memory is a database 58.
  • the memory 56 and therefore the database 58
  • the speed data and spectral data obtained by the LDV processing engine 46 and the spectrometer 42 are written to the database 58.
  • Positioning information 59 is also provided to the database 58, e.g. for mapping purposes.
  • Positioning data may include GPS (global positioning system) data and/or depth data (e.g. depth of an underwater vehicle below sea level).
  • GPS global positioning system
  • depth data e.g. depth of an underwater vehicle below sea level.
  • GPS global positioning system
  • depth data e.g. depth of an underwater vehicle below sea level.
  • an AUV may record GPS and depth data.
  • An ROV following a ship may record depth data, and acquire GPS data recorded on the ship.
  • the spectral data are compared with recorded spectral data in the database 58 to allow the particle 26 to be identified according to its emission spectrum. If the particle cannot be positively identified, the spectrum and/or a multivariate data analysis thereof may be recorded in the database for use in subsequent analysis or comparison.
  • the computer 52 provides a possibility for the comparison to be automatic, although the comparison may be initiated by an operator via a user interface 60 provided on the computer 52, e.g. by inputting an instruction to activate a comparison with data stored in the database (e.g. via a search of stored reference spectra).
  • the computer 52 also provides the option to display the recorded spectral data along with spectral data from the database 58 for a visual comparison by the operator.
  • the processor 54 is configured to carry out multivariate pattern recognition 62 to facilitate the comparison of the spectral data with recorded spectral data in the database 58.
  • information related to the identified spectrum is used in a further data analysis step 64 to present the data in a useful format (e.g. including a visual representation) in a 3D graphical information system (GIS) presentation 66 for the operator to study.
  • GIS graphical information system
  • the user interface 60 can be used to control the output on the 3D GIS presentation 66.
  • the user interface can get the GIS presentation 62 to display a continuous log of data obtained, or it can retrieve previously recorded data and/or reference data from the database for display, e.g. for comparison purposes.

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  • Life Sciences & Earth Sciences (AREA)
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  • Pathology (AREA)
  • Food Science & Technology (AREA)
  • Medicinal Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Dispersion Chemistry (AREA)
  • Investigating, Analyzing Materials By Fluorescence Or Luminescence (AREA)

Abstract

L'invention concerne un procédé et un appareil pour caractériser des particules individuelles dans une masse aquatique (24). Selon un premier aspect de l'invention, un motif d'interférence (22) est généré dans la masse aquatique (24) par chevauchement de deux faisceaux (10, 12) de rayonnement électromagnétique. La région de chevauchement délimite un volume de sonde (14) de telle sorte que le motif d'interférence (22) est généré dans le volume de sonde (14). Une particule unique (26) dans le volume de sonde est éclairée avec le motif d'interférence (22), amenant ladite particule unique (26) à émettre un rayonnement. Le rayonnement émis par la particule unique (26) est détecté, et des données spectrales dérivées du rayonnement détecté sont utilisées pour déterminer une propriété de la particule unique. Le rayonnement émis peut être une fluorescence. Selon un autre aspect de l'invention, un agencement similaire est utilisé pour éclairer une particule unique de telle sorte que la particule diffuse un rayonnement par diffusion Raman. Le rayonnement diffusé par effet Raman est détecté et utilisé pour déterminer une propriété de la particule unique (26).
PCT/GB2017/050943 2016-04-04 2017-04-04 Caractérisation de particules WO2017174977A1 (fr)

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Cited By (2)

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EP3745097A4 (fr) * 2018-01-23 2021-10-13 Kyocera Corporation Dispositif ainsi que procédé de mesure de fluide, et programme
US20210404942A1 (en) * 2018-10-25 2021-12-30 Plair Sa Method and device for detection and/or measurement of impurities in droplets

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Publication number Priority date Publication date Assignee Title
EP3745097A4 (fr) * 2018-01-23 2021-10-13 Kyocera Corporation Dispositif ainsi que procédé de mesure de fluide, et programme
US11226219B2 (en) 2018-01-23 2022-01-18 Kyocera Corporation Fluid measurement apparatus, fluid measurement method, and program
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