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Cavitation: Ultrasound of high enough intensity causes water to boil, creating [[cavitation]]. This physically annhilates 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.
Cavitation: Ultrasound of high enough intensity causes water to boil, creating [[cavitation]]. This physically annhilates 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.


Sub-cavitation: The sound vibrates the surfaces (e.g. hull, propeller shafts, rudders, sea chests, water coolers) to which the transducer is attached. The rapid vibrations disrupt the cyprid stage of the biofouling species from being able to permanently attach themselves to the substrate by disrupting the [[Van der Waals force|Van Der Waals]] forces that keep the [[Microvillus|microvilli]] of the cyprid in contact with the surface. This form of ultrasonic antifouling such as that employed by Ultraguard branded products can keep a clean surface free from biofouling but it can't remove well established mature biofouling.
Sub-cavitation: The sound vibrates the surfaces (e.g. hull, propeller shafts, rudders, sea chests, water coolers) to which the transducer is attached. The rapid vibrations create small movements of the surrounding water, largely preventing marine life from attaching. This type can maintain a hull that is already clean.<ref name="Cyprid" /> A first stage "[[biofilm]]" can be disrupted with even a low intensity ultrasound, preventing the larger stages from developing.


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|doi=10.1080/08927014.2010.551535|pmid=21271409}}</ref> mussels and algae.
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|doi=10.1080/08927014.2010.551535|pmid=21271409}}</ref> mussels and algae.
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Commercial ultrasonic systems have been used to control [[algal blooms]] in ponds, harbours and reservoirs.<ref>{{Cite web|url=https://www.lgsonic.com/cases/|title=Cases|website=LG Sonic}}</ref> In controlling the algae, the first stage in the [[Biofouling|fouling sequence]] is halted, acting as a prevention, rather than a cure.
Commercial ultrasonic systems have been used to control [[algal blooms]] in ponds, harbours and reservoirs.<ref>{{Cite web|url=https://www.lgsonic.com/cases/|title=Cases|website=LG Sonic}}</ref> In controlling the algae, the first stage in the [[Biofouling|fouling sequence]] is halted, acting as a prevention, rather than a cure.


== Components ==
[[
[[File:Castor Ultraguard 09.2021 (3).jpg|thumb|An Ultraguard ultrasonic antifouling transducer attached to the hull of a tug]]
]]
[[File:UG-06 Inside 2.jpg|thumb|The inside of an Ultraguard UG-06 ultrasonic antifouling system control unit]]
<ref></ref>== Components ==
The two main components of an ultrasonic antifouling system are:
The two main components of an ultrasonic antifouling system are:
[[File:Installed ultrasonic transducer.tif|thumb|Installed ultrasonic transducer]]
[[File:Installed ultrasonic transducer.tif|thumb|Installed ultrasonic transducer]]
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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.
* [[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.
* Control box: 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==
==Applications==

Revision as of 13:28, 22 July 2022

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

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

Ultrasound

Range of sound frequencies including audible and inaudible sound

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

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 the primary film.[2]

Ultrasonic antifouling

The two approaches to ultrasonic antifouling are:

Cavitation: Ultrasound of high enough intensity causes water to boil, creating cavitation. This physically annhilates 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, propeller shafts, rudders, sea chests, water coolers) to which the transducer is attached. The rapid vibrations create small movements of the surrounding water, largely preventing marine life from attaching. This type can maintain a hull that is already clean.[5] A first stage "biofilm" can be disrupted with even a low intensity ultrasound, preventing the larger stages from developing.

Different frequencies and intensities (or power) of ultrasonic waves have varying effects on marine life, such as barnacles,[5] mussels and algae.

Commercial ultrasonic systems have been used to control algal blooms in ponds, harbours and reservoirs.[6] In controlling the algae, the first stage in the fouling sequence is halted, acting as a prevention, rather than a cure.

Components

The two main components of an ultrasonic antifouling system are:

Installed ultrasonic transducer
  • 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 box: 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

Commercial systems are available in a wide range of energies and configurations. All use ceramic piezoelectric transducers as the sound source. Dedicated systems support:

  • Pool cleaning (to reduce chemicals necessary to prevent algae blooms)
  • 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
  • Propeller shaft/Propeller

Most systems are controlled by variable-frequency drive units, which run random frequencies in the ultrasonic spectrum of 20–45 kHz over an operational cycle. Intelligent systems target specific frequencies, as well as manage power consumption, protect batteries and power supplies and come with options such as remote monitoring, alarm systems and daylight sensors.[citation needed]

Limitations

Required tuning

Ultimate effectiveness is a function of the frequencies used, sound intensity, transducer location, water temperature and salinity, and marine organisms, requiring trial and error before optimal antifouling is achieved.

Hull materials

Ultrasonic systems are ineffective on wooden-hulled vessels, or vessels made from ferro-cement. Vessels with foam or wood-core composite hulls require modification at transducer sites. Ultrasonic systems work with reduced effectiveness on vibration isolated fittings, such as sterndrives. This is because the hull must pass the ultrasound waves from the transducer inside the hull to the water, and these materials dampen the wave amplitude.

References

  1. ^ "The History of Ultrasound". Ultrasound Schools Guide. Retrieved 20 January 2021.{{cite web}}: CS1 maint: url-status (link)
  2. ^ a b "Non-toxic, non-biocide-release antifouling coatings based on molecular structure design for marine applications". The Royal Society of Chemistry. 2015. Retrieved 20 January 2021.{{cite web}}: CS1 maint: url-status (link)
  3. ^ ""Acoustic Cavitation Explained - H2oBioSonic"" (PDF).
  4. ^ 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
  5. ^ 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. doi:10.1080/08927014.2010.551535. PMID 21271409.
  6. ^ "Cases". LG Sonic.