Ultrasonic antifouling: Difference between revisions
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'''Ultrasonic antifouling''' is a technology that uses high frequency sound ([[ultrasound]]) to prevent or reduce [[biofouling]] on underwater structures, surfaces, and medium. Ultrasound is just high frequency sound (which humans can not hear). Ultrasound has the same physical properties as human-audible sound. The method has two primary forms: sub-cavitation intensity and cavitation intensity. Sub-cavitation methods create high frequency vibrations, whilst cavitation methods cause more destructive microscopic pressure changes. Both methods are shown to inhibit or prevent [[biofouling]] by algae and other single-celled organisms. |
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{{Short description|Uses high frequency sound to prevent or reduce biofouling on underwater structures}} |
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'''Ultrasonic antifouling''' is a technology that uses high frequency sound ([[ultrasound]]) to prevent or reduce [[biofouling]] on underwater structures, surfaces, and medium. Ultrasound is just high frequency sound (which humans can not hear). Ultrasound has the same physical properties as human-audible sound. The method has two primary forms: sub-cavitation intensity and [[cavitation]] intensity. Sub-cavitation methods create high frequency vibrations, whilst cavitation methods cause more destructive microscopic pressure changes. Both methods inhibit or prevent [[biofouling]] by [[algae]] and other [[Microorganism|single-celled organisms]]. |
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== |
==Background== |
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[[Ultrasound]] was discovered in 1794 when Italian physiologist and biologist [[Lazzaro Spallanzani|Lazzarro Spallanzani]] discovered that [[Bat|bats]] navigate through the reflection of high frequency sounds.<ref>{{Cite web|last=|first=|date=21 October 2014|title=The History of Ultrasound|url=https://ultrasoundschoolsguide.com/history-of-ultrasound/|archive-url=|archive-date=|access-date=20 January 2021|website=Ultrasound Schools Guide}}</ref> Ultrasonic antifouling is believed to have been discovered by the [[US Navy]] in the 1950s{{Citation needed|date=January 2021|reason=This is often claimed, and the reference to the US Navy provides some credibility to the claim, but such a claim requires an original source citation}}. During [[sonar]] tests on submarines, it is said that the areas surrounding the sonar transducers had less fouling than the rest of the hull {{Citation needed|date=January 2021|reason=This is often claimed, and the reference to the US Navy provides some credibility to the claim, but such a claim requires an original source citation}}. |
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This term comprises at least two topics: [[ultrasonic]] (ultrasound) and [[Biofouling|antifouling]] (biofouling): |
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[[Antifouling]] (the removal of [[biofouling]]) has been attempted since ancient times, initially using wax, tar or asphalt. Copper and lead sheathings were later introduced by [[Phoenicia|Phoenicians]] and [[Carthaginians]]."<ref name=":0">{{Cite journal|author-link=DOI: 10.1039/C5TB00232J (Review Article) J. Mater. Chem. B, 2015, 3, 6547–6570|date=2015|title=Non-toxic, non-biocide-release antifouling coatings based on molecular structure design for marine applications|url=https://pubs.rsc.org/en/content/articlehtml/2015/tb/c5tb00232j|archive-url=|archive-date=|access-date=20 January 2021|journal=Journal of Materials Chemistry B|doi=10.1039/C5TB00232J|last1=Nurioglu|first1=Ayda G.|last2=Esteves|first2=A. Catarina C.|last3=De With|first3=Gijsbertus|volume=3|issue=32|pages=6547–6570|pmid=32262791 |doi-access=free}}</ref> The [[Cutty Sark]] is one example of such [[copper sheathing]], available to view in [[Greenwich, England]]. |
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# [[Ultrasound]] has been known about since 1794 when an Italian physiologist and biologist named Lazzarro Spallanzani discovered that bats navigate in the dark through the reflection of high frequency sounds. <ref>{{Cite web|last=|first=|date=|title=The History of Ultrasound|url=https://ultrasoundschoolsguide.com/history-of-ultrasound/|url-status=live|archive-url=|archive-date=|access-date=20 January 2021|website=Ultrasound Schools Guide}}</ref> Ultrasonic antifouling is believed to have been discovered by the [[US Navy]] in the 1950s {{Citation needed|date=January 2021|reason=This is often claimed, and the reference to the US Navy provides some credibility to the claim, but such a claim requires an original source citation}}. During [[sonar]] tests on submarines, it is said that the areas surrounding the sonar transducers were cleaner of fouling than the rest of the hull {{Citation needed|date=January 2021|reason=This is often claimed, and the reference to the US Navy provides some credibility to the claim, but such a claim requires an original source citation}}. |
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# [[Antifouling]] (the removal of [[biofouling]]) has been a desire of sailors for what feels like forever. "Coating technology has been applied to ships and vessels since very ancient times, either to protect the wood from shipworms or to prevent fouling. The first materials to be used were natural products like waxes, tar or asphalt. Later on, copper and lead sheathings were introduced by the [[Phoenicia|Phoenicians]] and [[Carthaginians]]."<ref name=":0">{{Cite web|last=|first=|author-link=DOI: 10.1039/C5TB00232J (Review Article) J. Mater. Chem. B, 2015, 3, 6547-6570|date=2015|title=Non-toxic, non-biocide-release antifouling coatings based on molecular structure design for marine applications|url=https://pubs.rsc.org/en/content/articlehtml/2015/tb/c5tb00232j|url-status=live|archive-url=|archive-date=|access-date=20 January 2021|website=The Royal Society of Chemistry}}</ref> There is the oft quoted example of how the British Royal Navy recognised the benefit of copper sheathing on their wooden hulls to prevent worms and other organisms deteriorating their boats <ref>{{Cite web|last=|first=|date=20 January 2021|title=A Copper Bottomed Guarantee|url=https://dreamsails.co/ultrasonic-antifouling-everything-you-need-to-know/#Royal_Navy_Copper_Sheathing|url-status=live|archive-url=|archive-date=|access-date=21 January 2021|website=Dream Sails}}</ref> The [[Cutty Sark]] is one example of such copper sheathing, available to view in Greenwich, England. |
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==Theory== |
==Theory== |
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=== Ultrasound === |
=== Ultrasound === |
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[[File:Sound and ultrasound.jpg|thumb|Range of sound frequencies including audible and inaudible sound]] |
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Ultrasound (ultrasonic) is just sound at a high frequency such that human's can not normally hear it.<ref>{{Cite web|last=|first=|date=20 January 2021|title=Sound & Ultra-sound (Ultrasonics)|url=https://dreamsails.co/ultrasonic-antifouling-everything-you-need-to-know/#Sound_and_Ultrasound|url-status=live|archive-url=|archive-date=|access-date=20 January 2021|website=Dream Sails ~ Ultrasonic Antifouling ~ Everything You Need to Know}}</ref> There is nothing different about ultrasound compared to sound than its frequency. |
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Ultrasound (ultrasonic) is sound at a frequency high enough that humans can not hear it. Sound has a [[frequency]] (low to high) and an [[Intensity (physics)|intensity]] (quiet to loud). |
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Ultrasound is used to clean jewellery, weld rubber, treat [[Abscess|abscesses]], and [[sonography]]. These applications rely on the interaction of sound with the media through which the sound travels. In maritime applications, ultrasound is the key ingredient in [[sonar]]; sonar relies on sound at frequences ranging from [[Infrasound|infrasonic]] to ultrasonic. |
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=== Biofilm === |
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It is the intensity of sound that causes the impact on media. [https://www.youtube.com/watch?v=8NW8buaT_e0&feature=youtu.be Ultrasound can be so gentle as to blow out a candle]<ref>{{Cite web|last=|first=|date=20 January 2021|title=Ultrasonic Candle Blow Out|url=https://www.youtube.com/watch?v=8NW8buaT_e0&feature=emb_logo|url-status=live|archive-url=|archive-date=|access-date=20 January 2021|website=YouTube}}</ref> or so intense as to fuse together materials,<ref>{{Cite web|last=|first=|date=20 January 2021|title=SharperTek Ultrasonic Plastic Welder for Strap and Velcro Welding|url=https://www.youtube.com/watch?v=rixDo08gZHc&feature=emb_logo|url-status=live|archive-url=|archive-date=|access-date=20 January 2021|website=YouTube}}</ref> and more. There is therefore, clearly, a difference between the sound in [[sonography]] and [[ultrasonic welding]]. Indeed, bats use ultrasound and these clearly are not of a high power. |
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The three main stages are formation of a conditioning [[biofilm]], microfouling and macrofouling. A [[biofilm]] is the accretion of single-celled organisms on a surface. This creates a habitat that enables other organisms to establish themselves. The conditioning film collects living and dead bacteria, creating the so-called primary film.<ref name=":0" /> |
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=== |
=== Ultrasonic antifouling === |
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The two approaches to ultrasonic antifouling are: |
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Biofouling starts small; it's a small issue which could simply be wiped away with a soft cloth, but quickly worsens as the habitat created by one organism permits, attracts, or otherwise leads to another [https://pubs.rsc.org/en/content/articlehtml/2015/tb/c5tb00232j "The fouling process starts from the moment the surface is immersed in water and takes place in three main stages: formation of a conditioning film, microfouling and macrofouling"]<ref name=":0" /> "The combination of the conditioning film and the slime of living and dead bacteria cells generates the first stage of microfouling, so-called the primary film."<ref name=":0" /> |
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[[File:Ultrasonic Antifouling (boat).jpg|thumb|A boat hull in the water surrounded by bio-organisms]] |
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[[File:Ultrasonic Antifouling (boat) - Control box & Transducer.jpg|thumb|Section through a boat hull showing the control box and transducer against the hull.]] |
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[[File:Ultrasonic Antifouling - Side profile, dispersal of biofouling.jpg|thumb|Ultrasound vibrates the hull (or other attached object) surface to inhibit the first stage of fouling thereby cutting the entire upper food chain and fouling process at source.]] |
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'''Cavitation:''' Ultrasound of high enough intensity causes water to boil, creating [[cavitation]]. This physically annihilates living organizsm and the supporting biofilm. One concern is to the potential effect on the hull. Cavitation<ref>{{Cite web|url=https://h2obiosonic.com/docs/H2OBIOSONIC%20Ultrasonication%20Acoustic%20Cavitation%20Effect.pdf|title="Acoustic Cavitation Explained – H2oBioSonic"}}</ref> can be predicted mathematically through the calculation of [[acoustic pressure]]. Where this pressure is low enough, the liquid can reach its [[Boiling point#Relation between the normal boiling point and the vapor pressure of liquids|vaporisation pressure]]. This results in localised vaporisation, forming small bubbles; these collapse quickly and with tremendous energy and turbulence, generating heat on the order of {{Convert|5000|K|abbr=on}} and pressures of the order of several [[Standard atmosphere (unit)|atmospheres]].<ref>Environmental Health Perspectives, Vol 64, pp. 233–252, 1985. "[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1568618/ Free radical generation by ultrasound in aqueous and nonaqueous solutions]. P. Riesz, D. Berdahl, and CL Christman</ref> Such systems are more appropriate where power consumption is not a factor, and the surfaces-to-be-protected can tolerate the forces involved. |
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=== Ultrasonic Antifouling === |
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In the references here, there are at least two views about sound used in ultrasonic antifouling: |
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'''Sub-cavitation:''' The sound vibrates the surfaces (e.g. hull, sea chests, water coolers) to which the transducer is attached. The vibrations prevent the cyprid stage of the biofouling species from attaching themselves permanently to the substrate by disrupting the [[Van der Waals force|Van Der Waals Force]] that allow their [[Microvillus|microvilli]] to hold themselves to the surface .<ref name="Cyprid" /> |
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# '''Cavitation''' intensity power antifouling: The ultrasound is of such a high intensity that the water boils with [[cavitation]]. The biofilm and organisms are annihilated. This type has been shown to remove established marine biofouling. With these high intensities of ultrasound there can be concerns as to the effect on the hull, not just the water and biofilm touching the hull. Acoustic cavitation<ref>[https://h2obiosonic.com/docs/H2OBIOSONIC%20Ultrasonication%20Acoustic%20Cavitation%20Effect.pdf "Acoustic Cavitation Explained - H2oBioSonic"]</ref> can be predicted theoretically through the calculation of [[acoustic pressure]] and where this pressure is low enough, the liquid can reach its [[Boiling point#Relation between the normal boiling point and the vapor pressure of liquids|vaporisation pressure]]. This results in localised vaporisation of the liquid, forming small bubbles; these collapse quickly and with tremendous energy and turbulence, generating heat on the order of 5000[[Kelvin|K]] and pressures of the order of several atmospheres.<ref>Environmental Health Perspectives, Vol 64, pp. 233-252, 1985. "[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1568618/ Free radical generation by ultrasound in aqueous and nonaqueous solutions]. P. Riesz, D. Berdahl, and CL Christman</ref> Such systems are more appropriate where power consumption, and the surfaces-to-be-protected can tolerate highly destructive cavitation. |
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# '''Sub-cavitation''' intensity power antifouling: The ultrasound causes vibration in the surfaces (e.g. hull, propeller shafts, rudders, sea chests, water coolers) to which the transducer is attached. At lower intensity levels, the rapid vibrations, creates small movements of the surrounding water, making it extremely difficult for marine life to firmly attach to a surface, and even to exist and function. This type works best to maintain a clean hull; such as inhibiting the settlement of barnacle [[cyprid]]s.<ref name="Cyprid" /> The disturbance of this first stage "[[biofilm]]" with even a subtle intensity of ultrasound reduces or removes the entire sequence of upper stages which are the cause of so much trouble for the boat owner. For sailing yachts, where power is a limited resource, especially when not connected to shore power, such low power systems are more appropriate. |
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Different [[frequencies]] and intensities (or power) of ultrasonic waves have varying effects on marine life, such as [[barnacle]]s,<ref name="Cyprid">{{Cite journal|last1=Guo|first1=S. F.|last2=Lee|first2=H. P.|last3=Chaw|first3=K. C.|last4=Miklas|first4=J.|last5=Teo|first5=S. L. M.|last6=Dickinson|first6=G. H.|last7=Birch|first7=W. R.|last8=Khoo|first8=B. C.|year=2011|title=Effect of ultrasound on cyprids and juvenile barnacles|journal=Biofouling|volume=27|issue=2|pages=185–192|doi=10.1080/08927014.2010.551535|pmid=21271409|s2cid=36405913 }}</ref> mussels and algae. |
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== Components == |
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Commercial ultrasonic systems have been used to control [[algal blooms]] in ponds, harbours and reservoirs.<ref>[http://www.lgsonic.com/cases/blue-green-algae-harbour "LG Sonic Tholen harbour"]</ref> In controlling the algae, the first stage in the [[Biofouling|fouling sequence]] is halted, acting as a prevention, rather than a cure as with traditional [[anti-fouling paint]]. |
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The two main components of an ultrasonic antifouling system are: |
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* '''[[Transducer]]''': The speaker or transducer takes an electrical signal and vibrates the medium in which it is located at the frequencies in the signal. The transducer is in direct contact with the hull or other surfaces, causing them to propagate the sound. Hull materials such as concrete and wood do not provide good antifouling since they contain many voids that dissipate/absorb the sound. |
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* '''Control Unit:''' The sound source and amplifier that provides the signals and power to each transducer. A single control box might control multiple transducers with either the same signal or varied signals. |
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== The Appeal of Ultrasonic Antifouling == |
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The main reason ultrasonic antifouling has so much interest is: |
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==Applications== |
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* It offers '''continuous stable protection''' instead of gradually wearing out as do antfouling coatings and paints |
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Commercial systems are available in a wide range of energies and configurations. All use ceramic [[Piezoelectric transducers#Transducers|piezoelectric transducers]] as the sound source. Dedicated systems support: |
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*It is fitted on the '''inside of a boat hull''' and therefore requires no external access, dry docking or lifting of the boat |
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*It is '''modular and scalable''' to all sizes of boats. Each transducer has a defined radius of influence e.g. 10m radius (300m^2) and can be positioned to ensure complete coverage, or even extra coverage of different surfaces. |
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* The '''power consumption''' is appropriate to the vessel size: small vessels which rely on stored battery power only require a few transducers, whilst commercial vessels which require many more transducers or higher power transducers have onboard generators. Small vessels may even use wind and solar energy to power such systems. |
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*It has a '''low single cost''' compared to the annual repeated costs of antifouling paints. |
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* Above all, it is [[sustainable|'''sustainable''']]: fit once, can be of low power consumption, and no polluting chemicals ([[Biocide|biocides]]) are used in operating. |
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* Ship hull protection (to prevent fouling, increase speed and reduce fuel costs) |
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== Components of an Ultrasonic Antifouling System == |
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* Heat exchanger protection (to extend operational cycles between cleaning) |
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There are two main components of an ultrasonic antifouling system: |
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* Water intakes (to prevent blockages) |
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[[File:Installed ultrasonic transducer.tif|thumb|Installed ultrasonic transducer]] |
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* Fuel tanks (to prevent diesel contamination) |
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* Offshore structures (such as wind farms, oil and gas installations etc.) |
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* HVAC Cooling Towers to reduce or eliminate chemical dosing treatments |
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===Algae control=== |
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# '''[[Transducer]]''', or in human audible terms, a [[Loudspeaker|speaker]]. A speaker, like a transducer, is just a device that takes an electrical control signal and vibrates the medium in which it is located. Thus, a speaker normally vibrates the air in order to propagate sound such as music or voices. The term transducer is used in more engineering based discussion, and in this case since the medium is water (sea water) then the vibration from the transducer propagates through the water. The transducer is in such firm and direct contact with the hull or other surfaces that it causes them to propagate the (ultra)sound. Hull materials such as concrete and wood do not provide good antifouling since they contain many voids which dissipate and absorb the sound. "The transducers are directly fixed to the inside of the boat hull"<ref name=":1">{{Cite web|last=|first=|date=|title=Ultrasonic Marine Anti-fouling System|url=https://www.ultrasonicmarine.co.uk/|url-status=live|archive-url=|archive-date=|access-date=20 January 2021|website=Ultrasonic Marine}}</ref> with a firm bond to the inside surface of the boat hull or attached to other items such as propeller shafts, sea chests, pipework etc., such that the ultrasound radiates from the surface of the item to be protected from fouling. An [https://www.ultrasonicmarine.co.uk/ installed transducer is shown in the images on this page], |
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'''Ultrasonic algae control''' is a commercial technology that has been claimed to control the blooming of [[cyanobacteria]], [[algae]], and [[biofouling]] in [[lakes]], and [[reservoirs]], by using pulsed [[ultrasound]].<ref>{{cite news|title=Soundwaves kill algae in reservoir|url=https://www.stuff.co.nz/taranaki-daily-news/67743363/soundwaves-kill-algae-in-reservoir|last=Utiger|first=Taryn|publisher=Stuff (company)|date=14 April 2015}}</ref><ref>{{cite news|title=Literature Review of the Effects of Ultrasonic Waves on Cyanobacteria, Other Aquatic Organisms, and Water Quality|url=https://dnr.wi.gov/files/PDF/pubs/ss/SS0595.pdf|publisher=Wisconsin DNR.Gov}}</ref> The duration of such treatment is supposed to take up to several months, depending on the water volume and algae species. Despite the experimental demonstration of certain bioeffects in small samples under controlled laboratory and sonication conditions, there is no scientific foundation for outdoors ultrasonic algae control. |
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# '''Control box''', or in music terms the sound source and amplifier, provides the signals and power to each transducer. A control box might control multiple transducers with either the same signal or a variation, depending on the control box, "Each system includes a Control Box with status LEDs and 1 to 4 Transducer units".<ref name=":1" /> The control box is positioned in any convenient location such that power is easily connected and future access is possible. |
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It has been speculated that ultrasound produced at the resonance frequencies of cells or their membranes may cause them to rupture. |
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Between the two is often standard single-core 'satellite' cable. |
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The center frequencies of the ultrasound pulses used in academic studies lie between 20 kHz and 2.5 MHz.<ref>{{cite book|vauthors=Kotopoulis S, Schommartz A, Postema M|title=2008 IEEE Ultrasonics Symposium |chapter=Safety radius for algae eradication at 200 kHz – 2.5 MHz |year=2008 |pages=1706–1709|doi=10.1109/ULTSYM.2008.0417|isbn=978-1-4244-2428-3 |s2cid=21382938 |url=https://hal.archives-ouvertes.fr/hal-03193318/file/P2D050-03.pdf |chapter-url=https://hal.science/hal-03193318}}</ref> The [[acoustic power|acoustic powers]], [[acoustic pressure|pressures]], and [[acoustic intensity|intensities]] applied vary from low, not affecting humans, |
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<ref>{{cite journal|title=Evaluation of Power Ultrasonic Effects on Algae Cells at a Small Pilot Scale|vauthors=Wu X, Mason TJ| journal=Water|volume=9|number=7|page=470|date=June 2017|doi=10.3390/w9070470|doi-access=free}}</ref><ref>{{cite journal|url=http://suslick.scs.illinois.edu/documents/philtrans99335.pdf|vauthors=Suslick JS, Didenko Y, Fang MM, Hyeon T, Kolbeck KJ, McNamara WB, Wong M| title=Acoustic cavitation and its chemical consequences| journal=Phil. Trans. R. Soc. Lond. A|date=1999|volume=357|issue=1751|pages=335–353|doi=10.1098/rsta.1999.0330|bibcode=1999RSPTA.357..335S|s2cid=12355231}}</ref> |
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to high, unsafe for swimmers.<ref>{{cite journal|title=Ultrasound and swimmer safety|vauthors=Postema M, Schommartz A|journal=Fortschritte der Akustik: DAGA 2008, 34. Deutsche Jahrestagung für Akustik, 10.-13. März 2008 in Dresden, Deutsche Gesellschaft für Akustik, Mar 2008, Dresden, Germany|series=Fortschritte der Akustik |pages=467–468|year=2008|url=https://hal.science/hal-03195585}}</ref> |
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According to research at the [[University of Hull]], [[ultrasound]]-assisted gas release from [[blue-green algae]] cells may take place from [[nitrogen]]-containing cells, but only under very specific short-distance conditions, which are not representative for intended outdoors applications.<ref>{{cite journal|vauthors=Kotopoulis S, Schommartz A, Postema M|title=Sonic cracking of blue-green algae|journal=Applied Acoustics|year=2009|volume=70|issue=10|pages=1306–1312|doi=10.1016/j.apacoust.2009.02.003|s2cid=110406431 |url=https://hal.archives-ouvertes.fr/hal-03193313/document}}</ref> In addition, a study by [[Wageningen University]] on several algae species concluded that most claims on outdoors ultrasonic algae control are unsubstantiated.<ref>{{cite journal|title=Beating the blues: Is there any music in fighting cyanobacteria with ultrasound?|vauthors=Lürling M, Tolman Y|journal=Water Research|volume=66|issue=1|year=2014|pages=361–373|doi=10.1016/j.watres.2014.08.043|pmid=25240117 |bibcode=2014WatRe..66..361L }}</ref> |
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==Modern usage== |
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Modern commercial systems are available in a wide range of powers and installation variants, however all use similar ceramic [[Piezoelectric transducers#Transducers|piezoelectric transducer]] as the ultrasound source. There are dedicated systems for: |
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* Pool cleaning (to reduce chemicals necessary to prevent algae blooms) |
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* Ship hull protection (to prevent fouling, increasing speed and reducing fuel costs) |
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* Heat exchanger protection (to extend operational cycles between cleaning) |
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* Seachest / water intakes (to prevent blockages by marine growth) <ref>[https://sonihull.com/what-are-you-protecting/box-coolers-seachests-pipework/ "Box Coolers, Seachests & Pipework"]</ref> |
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* Fuel tank protection (to stop algae growth and prevent diesel contamination) |
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* Protection of offshore structures (such as wind farms, oil & gas installations etc.) |
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* HVAC Cooling Towers to reduce or eliminate chemical dosing treatment |
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* Propeller Shafts and Propellers <ref>[https://sonihull.com/what-are-you-protecting/propeller-shafts-propellers/ "Propeller shafts & propellers"]</ref> |
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However, most of these systems are controlled by fairly simple variable-frequency drive units, which run random frequencies in the ultrasonic spectrum of 20–45 kHz over an operational cycle. |
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Intelligent systems will target specific frequencies, as well as manage power consumption, protect batteries & power supplies and come with various other features and options such as remote monitoring, alarm systems and daylight sensors. Several companies have patents on their intelligent systems {{Citation needed|date=January 2021|reason=The patents should be shown or exact patent numbers listed.}} |
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Some systems will actually automatically calibrate after installation and target the ideal frequency range for the substrate to maximize effectiveness.<ref>[https://cleanahull.com "CleanAHull.com"]</ref><ref>[https://hullsonic.com.au "HullSonic.com.au – Ultrasonic Antifouling"]</ref> |
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==Limitations== |
==Limitations== |
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=== |
=== Surface Cleaning === |
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Ultrasonic antifouling systems are generally only capable of maintaining a clean surface. They can't clean a surface that already has a well established and mature biofouling infestation. To this end, they are a preventative measure with the goal of an ultrasonic antifouling system being to maintain the protected surface as close to its optimum clean state as possible. |
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Ultrasonic anti-fouling may be considered a complete replacement for traditional anti-fouling paints; as well as a preventive measure to deter marine growth from a surface. There is so much latitude in the installation of an ultrasonic antifouling system from: |
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=== Hull materials === |
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* the frequencies used, |
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Ultrasonic systems are ineffective on wooden-hulled vessels, or vessels made from ferro-cement as these materials dampen the vibrations from the transducers. Composite hulls with a sandwich construction may also require modification to form monolithic plinths of solid material at each transducer location. |
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* the intensity of the ultrasound, |
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* the location of each transducer, |
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* the water temperature and salinity, as well as |
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* the type of organisms in the water, |
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that some trial and error might be required before complete antifouling is achieved. |
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In review of the effectiveness of installation on a 34 foot sailing yacht "... |
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=== Established Methods === |
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There is a large vested interest from boat yards and boat maintenance companies to sell and provide the current antifouling paints and coatings which are required each annum rather than the single-install ultrasonic antifouling systems. Ultrasonic antifouling systems are now cost competitive, thanks to production efficiencies and established designed, that they out perform the cost of antifouling coatings, and indeed are a DIY option for the average sailor who is accustomised to performing their own repairs and installs. |
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=== Hull Materials === |
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Ultrasonic systems cannot work on wooden-hulled vessels, or vessels made from ferro-cement. Vessels with foam or wooden cored composite hulls will require modification to the hull in the specific locations that the transducers are to be installed. Ultrasonic systems will work with reduced effectiveness on vibration isolated fittings, such as sterndrives. This is because the hull must pass the ultrasound waves from the transducer located inside the hull through to the water, and these materials act to dampen the amplitude of ultrasonic waves. |
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==Applications== |
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Sites and structures using ultrasonic antifouling include: |
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* 34 foot sailing yacht hull <ref>{{Cite web|last=|first=|date=2016|title=This is How You Sonic - Cruising World Magazine|url=https://2def3001-f970-4e96-b00e-a5919154cc20.filesusr.com/ugd/1604ca_675a813ff4ef4d5795ec6964ed16afd8.pdf|url-status=live|archive-url=|archive-date=|access-date=21 January 2021|website=Ultrasonic Marine}}</ref> |
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*HVAC Cooling Tower full scale trial results<ref>[http://h2obiosonic.com/docs/HVAC-Trial-2015.pdf "H2oBioSonic HVAC Trial Results, Joshua David"]</ref> |
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* Tholen Harbour, the Netherlands<ref>[http://www.lgsonic.com/cases/blue-green-algae-harbour/ "LG Sonic Tholen Harbour"]</ref> |
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* Longham lakes, UK<ref>[http://www.lgsonic.com/cases/water-treatment-plants/blue-green-algae-successfully-monitored-controlled-using-ultrasound-new-mpc-buoy/ "LG Sonic reservoir test"]</ref> |
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* 3x MOD Mk IV LCVP landing craft trial<ref>[http://www.ultrasonic-antifouling.com/testimonials/ministry-of-defence-lcvp-mkiv-landing-craft/ "Ultrasonic Antifouling LTD testimonials page"]</ref> |
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* Kippari magazine test boat<ref>[http://onlinemagazine.cbfnet.co.uk/sonic-shield-intelligent-antifouling/sonic-shield-kippari/ "CMS Marine magazine review"]</ref> |
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* Moody 36 ‘Dalriada’<ref>[http://onlinemagazine.cbfnet.co.uk/sonic-shield-intelligent-antifouling/cms-marine-sonic-shield-review/ "CMS Magazine review"]</ref> |
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* Alloy Yachts ‘Mondango 3’<ref>[https://cleanahull.com/ultrasonic-antifouling/ultrasonic-antifouling-testimonials/ "Ultrasonic Antifouling Testimonials - CleanAHull.com"]</ref> |
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* Dredgers<ref>[https://sonihull.com/case-studies/ "Ultrasonic Antifouling Case Studies - Sonihull.com"]</ref> |
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*Coast Guard & Patrol Boats <ref>[https://sonihull.com/case-studies/lsc-keeps-dutch-patrol-boats-clear/ "LSC Keeps Dutch Patrol Boats Clear - Sonihull.com"]</ref> |
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* Propeller Shafts & Propellers <ref>[https://sonihull.com/what-are-you-protecting/propeller-shafts-propellers/ "Protecting Propeller Shafts & Propellers - Sonihull.com"]</ref> |
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==References== |
==References== |
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Latest revision as of 11:03, 4 December 2024
Ultrasonic antifouling is a technology that uses high frequency sound (ultrasound) to prevent or reduce biofouling on underwater structures, surfaces, and medium. Ultrasound is just high frequency sound (which humans can not hear). Ultrasound has the same physical properties as human-audible sound. The method has two primary forms: sub-cavitation intensity and cavitation intensity. Sub-cavitation methods create high frequency vibrations, whilst cavitation methods cause more destructive microscopic pressure changes. Both methods inhibit or prevent biofouling by algae and other single-celled organisms.
Background
[edit]Ultrasound was discovered in 1794 when Italian physiologist and biologist Lazzarro Spallanzani discovered that bats navigate through the reflection of high frequency sounds.[1] Ultrasonic antifouling is believed to have been discovered by the US Navy in the 1950s[citation needed]. During sonar tests on submarines, it is said that the areas surrounding the sonar transducers had less fouling than the rest of the hull [citation needed].
Antifouling (the removal of biofouling) has been attempted since ancient times, initially using wax, tar or asphalt. Copper and lead sheathings were later introduced by Phoenicians and Carthaginians."[2] The Cutty Sark is one example of such copper sheathing, available to view in Greenwich, England.
Theory
[edit]Ultrasound
[edit]
Ultrasound (ultrasonic) is sound at a frequency high enough that humans can not hear it. Sound has a frequency (low to high) and an intensity (quiet to loud).
Ultrasound is used to clean jewellery, weld rubber, treat abscesses, and sonography. These applications rely on the interaction of sound with the media through which the sound travels. In maritime applications, ultrasound is the key ingredient in sonar; sonar relies on sound at frequences ranging from infrasonic to ultrasonic.
Biofilm
[edit]The three main stages are formation of a conditioning biofilm, microfouling and macrofouling. A biofilm is the accretion of single-celled organisms on a surface. This creates a habitat that enables other organisms to establish themselves. The conditioning film collects living and dead bacteria, creating the so-called primary film.[2]
Ultrasonic antifouling
[edit]The two approaches to ultrasonic antifouling are:
Cavitation: Ultrasound of high enough intensity causes water to boil, creating cavitation. This physically annihilates living organizsm and the supporting biofilm. One concern is to the potential effect on the hull. Cavitation[3] can be predicted mathematically through the calculation of acoustic pressure. Where this pressure is low enough, the liquid can reach its vaporisation pressure. This results in localised vaporisation, forming small bubbles; these collapse quickly and with tremendous energy and turbulence, generating heat on the order of 5,000 K (4,730 °C; 8,540 °F) and pressures of the order of several atmospheres.[4] Such systems are more appropriate where power consumption is not a factor, and the surfaces-to-be-protected can tolerate the forces involved.
Sub-cavitation: The sound vibrates the surfaces (e.g. hull, sea chests, water coolers) to which the transducer is attached. The vibrations prevent the cyprid stage of the biofouling species from attaching themselves permanently to the substrate by disrupting the Van Der Waals Force that allow their microvilli to hold themselves to the surface .[5]
Different frequencies and intensities (or power) of ultrasonic waves have varying effects on marine life, such as barnacles,[5] mussels and algae.
Components
[edit]The two main components of an ultrasonic antifouling system are:
- Transducer: The speaker or transducer takes an electrical signal and vibrates the medium in which it is located at the frequencies in the signal. The transducer is in direct contact with the hull or other surfaces, causing them to propagate the sound. Hull materials such as concrete and wood do not provide good antifouling since they contain many voids that dissipate/absorb the sound.
- Control Unit: The sound source and amplifier that provides the signals and power to each transducer. A single control box might control multiple transducers with either the same signal or varied signals.
Applications
[edit]Commercial systems are available in a wide range of energies and configurations. All use ceramic piezoelectric transducers as the sound source. Dedicated systems support:
- Ship hull protection (to prevent fouling, increase speed and reduce fuel costs)
- Heat exchanger protection (to extend operational cycles between cleaning)
- Water intakes (to prevent blockages)
- Fuel tanks (to prevent diesel contamination)
- Offshore structures (such as wind farms, oil and gas installations etc.)
- HVAC Cooling Towers to reduce or eliminate chemical dosing treatments
Algae control
[edit]Ultrasonic algae control is a commercial technology that has been claimed to control the blooming of cyanobacteria, algae, and biofouling in lakes, and reservoirs, by using pulsed ultrasound.[6][7] The duration of such treatment is supposed to take up to several months, depending on the water volume and algae species. Despite the experimental demonstration of certain bioeffects in small samples under controlled laboratory and sonication conditions, there is no scientific foundation for outdoors ultrasonic algae control.
It has been speculated that ultrasound produced at the resonance frequencies of cells or their membranes may cause them to rupture. The center frequencies of the ultrasound pulses used in academic studies lie between 20 kHz and 2.5 MHz.[8] The acoustic powers, pressures, and intensities applied vary from low, not affecting humans, [9][10] to high, unsafe for swimmers.[11]
According to research at the University of Hull, ultrasound-assisted gas release from blue-green algae cells may take place from nitrogen-containing cells, but only under very specific short-distance conditions, which are not representative for intended outdoors applications.[12] In addition, a study by Wageningen University on several algae species concluded that most claims on outdoors ultrasonic algae control are unsubstantiated.[13]
Limitations
[edit]Surface Cleaning
[edit]Ultrasonic antifouling systems are generally only capable of maintaining a clean surface. They can't clean a surface that already has a well established and mature biofouling infestation. To this end, they are a preventative measure with the goal of an ultrasonic antifouling system being to maintain the protected surface as close to its optimum clean state as possible.
Hull materials
[edit]Ultrasonic systems are ineffective on wooden-hulled vessels, or vessels made from ferro-cement as these materials dampen the vibrations from the transducers. Composite hulls with a sandwich construction may also require modification to form monolithic plinths of solid material at each transducer location.
References
[edit]- ^ "The History of Ultrasound". Ultrasound Schools Guide. 21 October 2014. Retrieved 20 January 2021.
- ^ a b Nurioglu, Ayda G.; Esteves, A. Catarina C.; De With, Gijsbertus (2015). "Non-toxic, non-biocide-release antifouling coatings based on molecular structure design for marine applications". Journal of Materials Chemistry B. 3 (32): 6547–6570. doi:10.1039/C5TB00232J. PMID 32262791. Retrieved 20 January 2021.
- ^ ""Acoustic Cavitation Explained – H2oBioSonic"" (PDF).
- ^ Environmental Health Perspectives, Vol 64, pp. 233–252, 1985. "Free radical generation by ultrasound in aqueous and nonaqueous solutions. P. Riesz, D. Berdahl, and CL Christman
- ^ a b Guo, S. F.; Lee, H. P.; Chaw, K. C.; Miklas, J.; Teo, S. L. M.; Dickinson, G. H.; Birch, W. R.; Khoo, B. C. (2011). "Effect of ultrasound on cyprids and juvenile barnacles". Biofouling. 27 (2): 185–192. doi:10.1080/08927014.2010.551535. PMID 21271409. S2CID 36405913.
- ^ Utiger, Taryn (14 April 2015). "Soundwaves kill algae in reservoir". Stuff (company).
- ^ "Literature Review of the Effects of Ultrasonic Waves on Cyanobacteria, Other Aquatic Organisms, and Water Quality" (PDF). Wisconsin DNR.Gov.
- ^ Kotopoulis S, Schommartz A, Postema M (2008). "Safety radius for algae eradication at 200 kHz – 2.5 MHz". 2008 IEEE Ultrasonics Symposium (PDF). pp. 1706–1709. doi:10.1109/ULTSYM.2008.0417. ISBN 978-1-4244-2428-3. S2CID 21382938.
- ^ Wu X, Mason TJ (June 2017). "Evaluation of Power Ultrasonic Effects on Algae Cells at a Small Pilot Scale". Water. 9 (7): 470. doi:10.3390/w9070470.
- ^ Suslick JS, Didenko Y, Fang MM, Hyeon T, Kolbeck KJ, McNamara WB, Wong M (1999). "Acoustic cavitation and its chemical consequences" (PDF). Phil. Trans. R. Soc. Lond. A. 357 (1751): 335–353. Bibcode:1999RSPTA.357..335S. doi:10.1098/rsta.1999.0330. S2CID 12355231.
- ^ Postema M, Schommartz A (2008). "Ultrasound and swimmer safety". Fortschritte der Akustik: DAGA 2008, 34. Deutsche Jahrestagung für Akustik, 10.-13. März 2008 in Dresden, Deutsche Gesellschaft für Akustik, Mar 2008, Dresden, Germany. Fortschritte der Akustik: 467–468.
- ^ Kotopoulis S, Schommartz A, Postema M (2009). "Sonic cracking of blue-green algae". Applied Acoustics. 70 (10): 1306–1312. doi:10.1016/j.apacoust.2009.02.003. S2CID 110406431.
- ^ Lürling M, Tolman Y (2014). "Beating the blues: Is there any music in fighting cyanobacteria with ultrasound?". Water Research. 66 (1): 361–373. Bibcode:2014WatRe..66..361L. doi:10.1016/j.watres.2014.08.043. PMID 25240117.