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{{Short description|Type of spray nozzle}}
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[[File:Microspray Focused Ultrasonic Nozzle.JPG|thumb|PictureRendering of an ultrasonic nozzle]]
'''Ultrasonic nozzles''' are a type of [[spray nozzle]] that usesuse high frequency [[vibration|vibrations]] produced by [[Piezoelectricity|piezoelectric]] transducers[[transducer]]s acting upon the nozzle tip that will create [[capillary waves]] in a liquid film. Once the [[amplitude]] of the capillary waves reaches a critical height (due to the power level supplied by the generator), they become too tall to support themselves and tiny droplets fall off the tip of each wave resulting in [[Aerosol|atomization]].<ref name="Lang 1962 6">{{cite journal|last=Lang|first=Robert|title=Ultrasonic Atomization of Liquids|journal=The Journal of the Acoustical Society of America|year=1962|volume=34|issue=1|page=6|doi=10.1121/1.1909020|bibcode = 1962ASAJ...34....6L }}</ref>
 
The primary factors influencing the initial droplet size produced are [[frequency]] of vibration, [[surface tension]], and [[viscosity]] of the liquid. Frequencies are commonly in the range of 20–180&nbsp;kHz, beyond the range of human hearing, where the highest frequencies produce the smallest drop size.<ref>{{cite book|last=Berger|first=Harvey|title=Ultrasonic Liquid Atomization Theory and Application|year=1998|publisher=Partridge Hill Publishers|location=Hyde Park, NY|isbn=978-0-9637801-5-7|page=44}}</ref>
 
== History==
 
In 1962 Dr. Robert Lang followed up on this work, essentially proving a correlation between his atomized droplet size relative to [[Rayleigh scattering|Rayleigh's]] liquid wavelength.<ref name="Lang 1962 6"/> Ultrasonic nozzles were first commercialized by Dr. [[Harvey L. Berger]].
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== Applications==
Subsequent uses of the technology include coating blood collection tubes, spraying flux onto printed circuit boards, coating implantable drug eluting [[stent]]s and balloon/catheters, [[Floatfloat glass]] manufacturing coatings,<ref>{{cite journal|last=Davis|first=Nancy|title=Ultrasonic Spray for Glass Manufacturing|journal=Glass Magazine|date=Feb 2005|url=http://www.sono-tek.com/wp-content/uploads/2012/01/Ultrasonic_Spray_for_Glass_Manufacturing.pdf}}</ref> anti-microbial coatings onto food,<ref>{{cite news|last=DiNapoli|first=Jessica|title=Sono-Tek targets food safety|url=http://www.recordonline.com/apps/pbcs.dll/article?AID=/20131010/BIZ/310100335/0/SEARCH|newspaper=Times Herald-Record|date=2013-10-10}}</ref> precision semiconductor coatings and alternative energy coatings for solar cell and fuel cell manufacturing, among others.
[[File:Patrick Teppor and PEM active layer deposition by ultrasonic spraying.jpg|thumb|PEM active layer deposition by ultrasonic spraying. Ultrasonic spraying first creates tiny droplets that deposit on the surface of the Nafion membrane, creating a uniform layer of platinum-carbon catalyst]]
 
===Drug eluting stents and drug-coated balloons===
[[Pharmaceuticals]] such as [[Sirolimus]] (Rapamycinalso called rapamycin) and Paclitaxel used with or without an excipient[[paclitaxel]] isare coated on the surface of drug eluting stents (DES) and drug-coated balloons (DCB). These devices benefit greatly from ultrasonic spray nozzles for their ability to apply coatings with little to no loss. Medical devices such as DES and DCB because of their small size, require very narrow spray patterns, a low-velocity atomized spray and low-pressure air because of their small size.<ref name="Drug Eluting Stents">{{cite web|last=Berger|first=Harvey|title=Director of Technology|url=http://www.emdt.co.uk/article/using-ultrasonic-spray-nozzles-coat-drug-eluting-stents|work=European Medical Device Technology|accessdateaccess-date=7 February 2014}}</ref>
 
===Fuel cells===
Research has shown that ultrasonic nozzles can be effectively used to manufacture [[Protonproton exchange membrane fuel cell]]s. The inks typically used are a [[platinum]]-[[carbon]] suspension, whereinwhere the platinum acts as a catalyst inside the cell. Traditional methods to apply the catalyst to the [[proton exchange membrane]] typically involve [[screen printing]] or doctor-blades. However, thisthese methodmethods can haveresult in undesirable cell performance due to the tendency of the catalyst to form agglomerations resulting in non-uniform gas flow in the cell and prohibiting the catalyst from being fully exposed and, running the risk that the solvent or carrier liquid may be absorbed into the membrane, both of which impeded proton exchange efficiency.<ref>{{cite journal|last=Wheeler|first=D|author2=Sverdrup, G. |title=Status of Manufacturing: Polymer Electrolyte Membrane (PEM) Fuel Cells|journal=Technical Report|date=March 2008|volume=NREL/TP-560-41655|page=6|url=http://www.nrel.gov/docs/fy08osti/41655.pdf|doi=10.2172/924988}}</ref> When ultrasonic nozzles are used, the spray can be made to be as dry as necessary by the nature of the small and uniform droplet size, by varying the distance the droplets travel and by applying low heat to the substrate such that the droplets dry in the air before reaching the substrate. Process engineers have finer control over these types of variables as opposed to other technologies. Additionally, because the ultrasonic nozzle imparts energy to the suspension just prior to and during atomization, possible agglomerates in the suspension are broken up resulting in [[Homogeneity and heterogeneity|homogenous]] distribution of the catalyst, resulting in higher efficiency of the catalyst and in turn, the fuel cell.<ref>{{cite journalconference|last=Engle|first=Robb|title=MAXIMIZING THE USE OF PLATINUM CATALYST BY ULTRASONIC SPRAY APPLICATION|journalconference=Proceedings of Asme 2011 5Th International Conference on Energy Sustainability & 9Th Fuel Cell Science, Engineering and Technology Conference|date=2011-08-08|volume=ESFUELCELL2011-54369|pages=637–644|doi=10.1115/FuelCell2011-54369|isbn=978-0-7918-5469-3|url=http://www.sono-tek.com/wp-content/uploads/2012/01/ASME_Journal_of_Fuel-Cell_Science.pdf}}</ref><ref>{{cite journal|last=Millington|first=Ben|author2=Vincent Whipple |author3=Bruno G Pollet |title=A novel method for preparing proton exchange membrane fuel cell electrodes by the ultrasonic-spray technique|journal=Journal of Power Sources|date=2011-10-15|volume=196|issue=20|pages=8500–8508|doi=10.1016/j.jpowsour.2011.06.024|bibcode = 2011JPS...196.8500M }}</ref>▼
 
▲Research has shown that ultrasonic nozzles can be effectively used to manufacture [[Proton exchange membrane fuel cell]]s. The inks typically used are a [[platinum]]-[[carbon]] suspension, wherein the platinum acts as a catalyst inside the cell. Traditional methods to apply the catalyst to the [[proton exchange membrane]] typically involve [[screen printing]] or doctor-blades. However, this method can have undesirable cell performance due to the tendency of the catalyst to form agglomerations resulting in non-uniform gas flow in the cell and prohibiting the catalyst from being fully exposed and running the risk that the solvent or carrier liquid may be absorbed into the membrane, both of which impeded proton exchange efficiency.<ref>{{cite journal|last=Wheeler|first=D|author2=Sverdrup, G. |title=Status of Manufacturing: Polymer Electrolyte Membrane (PEM) Fuel Cells|journal=Technical Report|date=March 2008|volume=NREL/TP-560-41655|page=6|url=http://www.nrel.gov/docs/fy08osti/41655.pdf|doi=10.2172/924988}}</ref> When ultrasonic nozzles are used, the spray can be made to be as dry as necessary by the nature of the small and uniform droplet size, by varying the distance the droplets travel and by applying low heat to the substrate such that the droplets dry in the air before reaching the substrate. Process engineers have finer control over these types of variables as opposed to other technologies. Additionally, because the ultrasonic nozzle imparts energy to the suspension just prior to and during atomization, possible agglomerates in the suspension are broken up resulting in homogenous distribution of the catalyst, resulting in higher efficiency of the catalyst and in turn, the fuel cell.<ref>{{cite journal|last=Engle|first=Robb|title=MAXIMIZING THE USE OF PLATINUM CATALYST BY ULTRASONIC SPRAY APPLICATION|journal=Proceedings of Asme 2011 5Th International Conference on Energy Sustainability & 9Th Fuel Cell Science, Engineering and Technology Conference|date=2011-08-08|volume=ESFUELCELL2011-54369|url=http://www.sono-tek.com/wp-content/uploads/2012/01/ASME_Journal_of_Fuel-Cell_Science.pdf}}</ref><ref>{{cite journal|last=Millington|first=Ben|author2=Vincent Whipple |author3=Bruno G Pollet |title=A novel method for preparing proton exchange membrane fuel cell electrodes by the ultrasonic-spray technique|journal=Journal of Power Sources|date=2011-10-15|volume=196|issue=20|pages=8500–8508|doi=10.1016/j.jpowsour.2011.06.024|bibcode = 2011JPS...196.8500M }}</ref>
 
===Transparent conductive films===
Ultrasonic spray nozzle technology has been used to create films of [[indium tin oxide]] (ITO) in the formation of transparent conductive films (TCF).<ref>Z.B. Zhoua, R.Q. Cuia, Q.J. Panga, Y.D. Wanga, F.Y. Menga, T.T. Suna, Z.M. Dingb, X.B. Yub, 2001, "[http://www.sciencedirect.com/science/article/pii/S016943320000862X]," ''Preparation of indium tin oxide films and doped tin oxide films by an ultrasonic spray CVD process, Volume 172, Issues 3-4''</ref> ITO has excellent transparency and low sheet resistance, however it is a scarce material and prone to cracking, which does not make it a good candidate for the new flexible TCFs. Graphene on the other hand can be made into a flexible film, extremely conductive and has high transparency. Ag nanowires (AgNWs) when combined with Graphene hashave been reported to be a promising superior TCF alternative to ITO.<ref>Young Soo Yun, Do Hyeong Kim, Bona Kim, Hyun Ho Park, Hyoung-Joon Jin, 2012, "[http://www.sciencedirect.com/science/article/pii/S0379677912002056]," ''Transparent conducting films based on graphene oxide/silver nanowire hybrids with high flexibility, Synthetic Metals, Volume 162, Issues 15–16, Pages 1364–1368''</ref> Prior studies focus on spin and bar coating methods which are not suitable for large area TCFs. A multi-step process utilizing ultrasonic spray of graphene oxide and conventional spray of AgNWs followed by a [[hydrazine]] vapor reduction, followed by the application of [[polymethylmethacrylate]] (PMMA) topcoat resulted in a peelable TCF that can be scaled to a large size.<ref>Young-Hui Koa, Ju-Won Leeb, Won-Kook Choic, Sung-Ryong Kim, 2014, "[https://microspray.com/graphene-articles/]," ''Ultrasonic Sprayed Graphene Oxide and Air Sprayed Ag Nanowire for the Preparation of Flexible Transparent Conductive Films, The Chemical Society of Japan''</ref>
 
===Carbon nanotubes===
CNT thin films are used as alternative materials to create transparent conducting films (TCO layers)<ref name = "Chemical Engineering Science">{{cite journal|title=Insights into the physics of spray coating SWNT films|year=2010|last=Majumder|first=Mainak|journal=Chemical Engineering Science|volume=65|issue=6|pages=2000–2008|doi=10.1016/j.ces.2009.11.042|bibcode=2010ChEnS..65.2000M |display-authors=etal}}</ref> for touch panel displays or other glass substrates, as well as organic solar cell active layers.<ref name = "Solar Energy Materials & Solar Cells">{{cite journal|title=Ultrasonic spray deposition for production of organic solar cells|year=2009|last=Steirer|first=K. Xerxes|journal=Solar Energy Materials & Solar Cells|volume=93|issue=4|pages=447–453|doi=10.1016/j.solmat.2008.10.026|bibcode=2009SEMSC..93..447S |display-authors=etal}}</ref>
 
===Photoresist spray onto memsMEMs wafers===
[[Microelectromechanical systems]] (MEMs)<ref name="What are MEMs">{{cite web|title=Microelecromechanical Systems (MEMS)|url=http://www.csa.com/discoveryguides/mems/overview.php}}</ref> are small [[Microfabrication|microfabricated]] devices that combine electrical and mechanical components. Devices vary in size from below one [[micron]] to millimeters in size, functioning individually or in arrays to sense, control, and activate mechanical processes on the micro scale. Examples include pressure sensors, accelerometers, and microengines. Fabrication of MEMs involves depositing a uniform layer of [[photoresist]]<ref name="MEMs Lithography">{{cite web|title=Pattern Transfer|url=https://www.memsnet.org/mems/processes/lithography.html}}</ref> onto the Si wafer. Photoresist has traditionally been applied to wafers in IC manufacturing using a spin coating technique.<ref name="Spin Coating">{{cite web|title=Semiconductor Lithography (Photolithography) - The Basic Process|url=http://www.lithoguru.com/scientist/lithobasics.html}}</ref> In complex MEMs devices that have etched areas with high aspect ratios, it can be difficult to achieve uniform coverage along the top, side walls, and bottoms of deep grooves and trenches using spin coating techniques due to the high rate of spin needed to remove excess liquid. Ultrasonic spray techniques are used to spray uniform coatings of photoresist onto high aspect ratio MEMs devices and can minimize usage and overspray of photoresist.<ref name="Ultrasonic spray of photoresist">{{cite web|title=Process for Coating a Photoresist Composition onto a Substrate|url=httphttps://wwwpatents.google.com/patentspatent/US4996080}}</ref>
 
===Printed circuit boards===
The non-clogging nature of ultrasonic nozzles, the small and uniform droplet size created by them, and the fact that the spray plume can be shaped by tightly controlled air shaping devices makemakeS the application quite successful in [[wave soldering]] processes. The viscosity of nearly all fluxes on the market fit well within the capabilities of the technology. In [[soldering]], "no-clean" flux is highly preferred. But if excessive quantities are applied the process will result in corrosive residues on the bottom of the circuit assembly.<ref>{{cite web|last=Rathinavelu|first=Umadevi|title=Effect of No-Clean Flux Residues on the Performance of Acrylic Conformal Coating in Aggressive Environments|url=http://www.celcorr.com/Publications/Umadevi%201.pdf|publisher=IEEE}}</ref>
 
===Solar cells===
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== External links ==
* [https://books.google.com/books?id=k9mXGyFPFGoC&pg=PA537&dq=Ultrasonic+nozzle&hlpg=en&sa=X&ei=DoJaU-_EFIHx2wXLgoG4AQ&ved=0CFcQ6AEwBA#v=onepage&q=Ultrasonic%20nozzle&f=falsePA537 Further explanation of how an ultrasonic nozzle works]
 
[[Category:Fluid mechanics]]
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