The authors are grateful to the University of California and the NANO3 facility at UC San Diego for provision of funds and facilities in support of this work. This work was performed in part at the San Diego Nanotechnology Infrastructure (SDNI) of UCSD, a member of the National Nanotechnology Coordinated Infrastructure, which is supported by the National Science Foundation (Grant ECCS&#8722;1542148). The work presented here was generously supported by a research grant from the W.M. Keck Foundation. The authors are also grateful for the support of this work by the Office of Naval Research (via Grant 12368098).

1. Thickness mode transducer fabrication via DC sputtering
<ol>
	<li>Wafer preparation
	<ol>
		<li>Place a 100 mm 128YX LN wafer in a clean glass dish of at least 125 mm diameter. Sonicate the wafer in at least 200 mL of acetone for 5 min.</li>
		<li>Repeat sonication with isopropyl alcohol and again with deionized water for 5 min each.</li>
		<li>Remove visible water from the surface using dry nitrogen.</li>
		<li>Completely remove water from the surface by placing the wafer on a hotplate at 100 &#176;C for 5 min. Ensure that there is a sheet of aluminum foil on the hotplate as this helps in dissipation of charge buildup on the wafer.</li>
	</ol>
	</li>
	<li>Electrode deposition
	<ol>
		<li>Place the wafer in the vacuum chamber of the sputter deposition system and pump down the chamber to 5 x 10-6 mTorr. Set the argon pressure to 2.3 mTorr and the rotation speed to 13 rpm. 
		NOTE: If parameters for the speci&#64257;c instrument being used have been established that result in high quality &#64257;lms, then use those instead.</li>
		<li>Deposit 5&#8722;10 nm of titanium at 1.2&#8722;1.6 A/s. 
		NOTE: Before beginning this process with the intended wafer, test the deposition rate with the plasma power set to 200 W and depositing for 1 min. Then measure the height of the layer with a pro&#64257;lometer. Do this separately for each metal. Set the power according to this test in order to achieve the stated deposition rate.</li>
		<li>Deposit 1-1.2 &#181;m of gold at 7&#8722;9 A/s. 
		NOTE: Deposition at a higher rate due to increased plasma power or increased argon partial pressure may reduce &#64257;lm quality.</li>
		<li>Remove the wafer and repeat steps 1.2.1&#8722;1.2.3 for the second side of the wafer.</li>
	</ol>
	</li>
	<li>Dicing
	<ol>
		<li>Use a dicing saw to dice the entire wafer as needed. 
		NOTE: A protective resist can be applied on the substrate prior to dicing, and the system (Table of Materials) used here applies a UV curable &#64257;lm just before the samples are loaded on the dicing stage. It is found that dicing the samples with an automated dicing saw does not compromise the integrity of the samples. Hand-scribe dicing of LN is possible, though tedious and prone to inconsistencies.</li>
	</ol>
	</li>
</ol>
2. Making electrical and mechanical contact with the transducer
NOTE: Several methods are described below (steps 2.1&#8722;2.4), and it is highlighted later in the protocol which method is most appropriate for each subsequent step.
<ol>
	<li>Place a diced transducer &#64258;at on a magnetic steel plate. Mount one pogo-probe in contact with the plate and another pogo-probe in contact with the top surface of the transducer. Hereafter this will be referred to as pogo-plate contact.</li>
	<li>Place the transducer between two pogo-probes. Hereafter referred to as pogo-pogo contact.</li>
	<li>Solder wire to each face of the transducer. Hereafter referred to as solder contact.</li>
	<li>Assemble a custom transducer holder.
	<ol>
		<li>Order the custom printed circuit boards (PCBs) whose Gerber &#64257;les have been provided.</li>
		<li>Solder two surface mount spring contacts(Table of Materials) to each custom PCB. Press &#64257;t the spikes into the plated holes on the custom PCBs such that they point away from each other.</li>
		<li>Connect the two custom PCBs with board spacers and screws so that the contacts are just in contact with each other. Adjust the spacing with plastic washers if necessary.</li>
		<li>Slide a 3 mm x 10 mm transducer in between the inner pair of contacts. Clip the outer contacts so they do not short the circuit. 
		NOTE: Figure 1 shows the entire assembly.</li>
	</ol>
	</li>
</ol>
3. Resonance frequency identi&#64257;cation via impedance analysis
<ol>
	<li>Ensure that a port calibration has been performed according to the manufacturer&#8217;s instructions for the speci&#64257;c contact method being used.</li>
	<li>Connect a transducer to the open port of the network analyzer (Table of Materials) with one of the contact methods described in steps 2.1&#8722;2.4. 
	NOTE: It can be instructive to repeat this analysis with multiple electrical contact methods and compare the results.</li>
	<li>Select the re&#64258;ection coefficient parameter, s11, via the user interface of the network analyzer, choose the frequency range of interest, and perform the frequency sweep. 
	NOTE: s11 is the input re&#64258;ection coefficient and has a minimum value at the resonance frequency of operation. For a typical 500 &#181;m thick 128YX LN wafer, the primary resonance frequency will be near 7 MHz and the second harmonic will be near 21 MHz, as illustrated in Figure 2. The impedance plot in frequency space displayed on the instrument will exhibit local minima at the resonance frequencies.</li>
	<li>Export the data by selecting Save/Recall | Save Trace Data on the user interface for closer inspection using data processing software to identify the precise minima locations.</li>
</ol>
4. Vibration characterization via LDV
<ol>
	<li>Place a transducer in pogo-plate contact on the LDV stage. Connect the pogo-probe leads to the signal generator. Ensure that the objective in use is selected in the acquisition software (Table of Materials) and focus the microscope on the surface of the transducer.</li>
	<li>De&#64257;ne the scan points by selecting De&#64257;ne scan points or proceed to step 4.3 if performing a continuous scan.</li>
	<li>Select the Settings option and under the General tab, select either the FFT or Time option depending on whether the scan is being performed in frequency or time domain.&#160;Select the number of averages in this section. 
	NOTE: The number of averages affects scan time. Five averages for the transducers described in this protocol have shown to give sufficient signal/noise ratio.</li>
	<li>In the Channel tab, make sure that the Active boxes are checked, which correspond to the reference and re&#64258;ected signal from the transducer. Adjust the reference and incident channels by selecting a voltage value from the drop-down menu in order to obtain maximum signal strength from the substrate.</li>
	<li>In the Generator tab, if the measurement is carried out under single frequency signal, select Sine from the Waveform pull down list; if it is under a band signal, select MultiCarrierCW.</li>
	<li>Change the bandwidth and FFT lines in the Frequency tab to adjust the scan resolution for a frequency domain scan. Similarly, change the Sample Frequency in the Time tab when performing time domain measurements. 
	NOTE: The bandwidth typically used is 40 MHz and the number of FFT lines is 32,000. The presentation software (Table of Materials) can be used to process and analyze the data obtained from the scan. A typical displacement spectrum is provided in Figure 3.</li>
</ol>
5. Fluid supply
<ol>
	<li>Obtain a 25 mm long, 1 mm diameter wick composed of a bundle of &#64257;bers of a hydrophilic polymer designed to transport aqueous liquid across its length such as those available for plug-in air fresheners.&#160;Trim one end such that an off center point is formed.</li>
	<li>Insert the wick into a syringe tip with an inner diameter that provides a snug &#64257;t and a length that allows the wick to extend 1&#8722;2 mm beyond each end. Lock the tip onto a syringe with the desired capacity (1&#8722;10 mL).</li>
	<li>Mount the wick/syringe assembly such that the wick is 10&#176;&#8722;90&#176; from horizontal (depending on the desired atomization rate, which also depends on the applied voltage) and the tip of the wick is just in contact with the edge of the transducer as shown in Figure 1C.</li>
	<li>Fill the syringe with water and apply a continuous voltage signal (starting with 20 Vpp) at the resonance frequency determined using the impedance analyzer. Adjust the voltage level until the liquid is atomized continuously without the device &#64258;ooding or drying out.</li>
</ol>
6. Dynamics observation via high-speed imaging
<ol>
	<li>Rigidly mount a high-speed camera horizontally on an optical table, place a transducer in either pogo-pogo contact or pogo-plate contact on an x-y-z stage near the focal length of the camera, and position a diffuse light source at least one focal length on the opposite side of the transducer from the camera.</li>
	<li>For pogo-pogo contact, position the &#64258;uid supply so that it does not block the camera view or the light source. For pogo-plate contact, apply &#64258;uid directly to the substrate with a pipette.</li>
	<li>Adjust the camera focus and the x-y-z position to bring the &#64258;uid sample into sharp focus.</li>
	<li>Estimate the frequency of the speci&#64257;c phenomenon to be studied based on literature. Choose a frame rate at least twice as large as this frequency according to the Nyquist rate in order to avoid aliasing. 
	NOTE: For example, consider capillary waves that occur on a sessile drop at a range of frequencies. Cameras limited in spatial resolution can only distinguish waves with a minimum amplitude. In this case the minimum amplitude occurs around 4 kHz so a frame rate of 8,000 frames per second (fps) is chosen.</li>
	<li>Adjust the light intensity, the camera shutter, or both in order to optimize contrast between the &#64258;uid and the background. 
	NOTE: An opaque dye can be added to the &#64258;uid in order to increase the contrast.</li>
	<li>Connect alligator clips from the ampli&#64257;ed signal generator to the pogo-probes leads.</li>
	<li>Capture video in the camera software simultaneously with actuation via the voltage signal either by manually triggering both at the same time or by connecting a trigger output from the signal generator to the camera. 
	NOTE: The typical frame rate used is 8,000 fps and a CF4 objective is used.</li>
	<li>Save only the frames containing the phenomenon to avoid wasted storage, which is particularly relevant at large frame rates, to produce a result as shown in Figure 4. 
	NOTE: Make sure to save the &#64257;le in a format that is compatible with the image processing software of choice so that useful data can be extracted.</li>
</ol>
7. Droplet size measurement via laser scattering analysis
<ol>
	<li>The laser scattering system (Table of Materials) has a module that transmits the laser and one that receives the scattered laser signal. Position the modules along the rail provided with the system, with a 20&#8722;25 cm gap between them.</li>
	<li>Rigidly mount a platform in this gap such that, when the transducer and &#64258;uid supply assemblies are placed on it, atomized mist will be ejected into the laser beam path. Facilitate this alignment by turning on the laser beam via&#160;selecting Tools | Laser Control... | Laser on as a visual indicator.</li>
	<li>Fix the transducer holder to the platform and &#64257;x the &#64258;uid supply assembly to an articulated arm (Table of Materials). Position the &#64258;uid supply assembly so that the tip of the wick is just in contact with the edge of the transducer.</li>
	<li>Create a standard operating procedure (SOP) in the software by clicking the New SOP icon. Con&#64257;gure the SOP with the following settings: template = Default continuous, sampling period (s) = 0.1, under Data handling, click Edit... and set Spray pro&#64257;le | Path length (mm) to 20.0, click Alarms to uncheck Use default values and set Min transmission (%) to 5 and 1 and set Min scattering to 50 and 10. Leave all other settings as defaults. 
	NOTE: Consult the software manual that came with the instrument.</li>
	<li>Start the measurement within the software by clicking Measure | Start SOP and selecting the SOP created in step 7.4. Wait for background calibrations to complete. Fill the &#64258;uid supply reservoir, the syringe, with water up to the desired level and note the volume. Turn on the voltage signal to begin atomizing the &#64258;uid. Start the stopwatch and start the measurement by clicking Start.</li>
	<li>The software generates a size distribution based on the scattered laser signal at the receiver due to Mie theory and a multiple scattering algorithm. Once the desired volume of &#64258;uid has been atomized, turn off the voltage signal, stop the stopwatch, and record the &#64257;nal volume, and stop recording data by clicking Stop. 
	NOTE: The laser scattering system is capable of measuring as little as 1 &#956;L of fluid and does not have an upper limit for fluid volume. The atomization &#64258;ow rate can simply be calculated by dividing the volume by the time duration.</li>
	<li>In the measurement histogram, select the portion of the data during which the atomization was occurring as expected and the signal at the receiver was strong enough to be statistically significant. Click Average | Ok to generate a distribution based on the selected data. 
	NOTE: All measurements with this technique are statistical averages and thus, if there are too few droplets, then the scattered signal will be weak, and the measurement will be statistically insigni&#64257;cant.</li>
	<li>Save the average distribution&#160;by selecting the window and clicking Edit | Copy text then pasting the result in a text &#64257;le and saving with an appropriate name. 
	NOTE: This distribution data can now be used with other software (e.g., MATLAB) to create the plot in Figure 5.</li>
</ol>

<ol><li>Wood, R. W., Loomis, A. L. XXXVIII.physical and biological effects of high-frequency sound-waves of great intensity. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aWood%2C+RW+%22The+London%2C+Edinburgh%2C+and+Dublin+Philosophical+Magazine+and+Journal+of+Science%22">The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science</a>. 4 (22), 417-436 (1927).</li>
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<li>Wang, J., Hu, H., Ye, A., Chen, J., Zhang, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Experimental+investigation+of+surface+acoustic+wave+atomization%5BTitle%5D)+AND+%22Sensors+and+Actuators+A%3A+Physical%22%5BJournal%5D)">Experimental investigation of surface acoustic wave atomization.</a> Sensors and Actuators A: Physical. 238, 1-7 (2016).</li>
<li>James, A., Vukasinovic, B., Smith, M. K., Glezer, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Vibration-induced+drop+atomization+and+bursting%5BTitle%5D)+AND+%22Journal+of+Fluid+Mechanics%22%5BJournal%5D)">Vibration-induced drop atomization and bursting.</a> Journal of Fluid Mechanics. 476, 1-28 (2003).</li>
<li>Randall, C. A., Kim, N., Kucera, J. P., Cao, W., Shrout, T. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Intrinsic+and+extrinsic+size+effects+in+fine-grained+morphotropic-phase-boundary+lead+zirconate+titanate+ceramics%5BTitle%5D)+AND+%22Journal+of+the+American+Ceramic+Society%22%5BJournal%5D)">Intrinsic and extrinsic size effects in fine-grained morphotropic-phase-boundary lead zirconate titanate ceramics.</a> Journal of the American Ceramic Society. 81 (3), 677-688 (1998).</li>
<li>Tsai, S. C., Lin, S. K., Mao, R. W., Tsai, C. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Ejection+of+uniform+micrometer-sized+droplets+from+Faraday+waves+on+a+millimeter-sized+water+drop%5BTitle%5D)+AND+%22Physical+Review+Letters%22%5BJournal%5D)">Ejection of uniform micrometer-sized droplets from Faraday waves on a millimeter-sized water drop.</a> Physical Review Letters. 108 (15), 154501(2012).</li>
<li>Jeng, Y. R., Su, C. C., Feng, G. H., Peng, Y. Y., Chien, G. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+PZT-driven+atomizer+based+on+a+vibrating+flexible+membrane+and+a+micro-machined+trumpet-shaped+nozzle+array%5BTitle%5D)+AND+%22Microsystem+Technologies%22%5BJournal%5D)">A PZT-driven atomizer based on a vibrating flexible membrane and a micro-machined trumpet-shaped nozzle array.</a> Microsystem Technologies. 15 (6), 865-873 (2009).</li>
<li>Lupascu, D., Rödel, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Fatigue+in+bulk+lead+zirconate+titanate+actuator+materials%5BTitle%5D)+AND+%22Advanced+Engineering+Materials%22%5BJournal%5D)">Fatigue in bulk lead zirconate titanate actuator materials.</a> Advanced Engineering Materials. 7 (10), 882-898 (2005).</li>
<li>Kawamata, A., Hosaka, H., Morita, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Non-hysteresis+and+perfect+linear+piezoelectric+performance+of+a+multilayered+lithium+niobate+actuator%5BTitle%5D)+AND+%22Sensors+and+Actuators+A%3A+Physical%22%5BJournal%5D)">Non-hysteresis and perfect linear piezoelectric performance of a multilayered lithium niobate actuator.</a> Sensors and Actuators A: Physical. 135 (2), 782-786 (2007).</li>
<li>Qi, A., Yeo, L., Friend, J., Ho, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((The+Extraction+of+Liquid%2C+Protein+Molecules+and+Yeast+Cells+from+Paper+Through+Surface+Acoustic+Wave+Atomization%5BTitle%5D)+AND+%22Lab+on+a+Chip%22%5BJournal%5D)">The Extraction of Liquid, Protein Molecules and Yeast Cells from Paper Through Surface Acoustic Wave Atomization.</a> Lab on a Chip. 10 (4), 470-476 (2010).</li>
<li>Collignon, S., Manor, O., Friend, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Improving+and+Predicting+Fluid+Atomization+via+Hysteresis-Free+Thickness+Vibration+of+Lithium+Niobate%5BTitle%5D)+AND+%22Advanced+Functional+Materials%22%5BJournal%5D)">Improving and Predicting Fluid Atomization via Hysteresis-Free Thickness Vibration of Lithium Niobate.</a> Advanced Functional Materials. 28 (8), 1704359(2018).</li>
<li>Lawson, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((The+vibration+of+piezoelectric+plates%5BTitle%5D)+AND+%22Physical+Review%22%5BJournal%5D)">The vibration of piezoelectric plates.</a> Physical Review. 62 (1-2), 71(1942).</li>
<li>Fukushima, Y., Nishizawa, O., Sato, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+performance+study+of+a+laser+doppler+vibrometer+for+measuring+waveforms+from+piezoelectric+transducers%5BTitle%5D)+AND+%22IEEE+Transactions+on+Ultrasonics%2C+Ferroelectrics%2C+and+Frequency+Control%22%5BJournal%5D)">A performance study of a laser doppler vibrometer for measuring waveforms from piezoelectric transducers.</a> IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control. 56 (7), 1442-1450 (2009).</li>
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The authors have nothing to disclose.

The dimensions and aspect ratio of a transducer affects the vibration modes it produces. Because the lateral dimensions are &#64257;nite, there are always lateral modes in addition to the desired thickness modes. The above LDV methods can be used to determine dominant modes in the desired frequency range for a given transducer. A square with dimensions below 10 mm typically gives a close approximation to a thickness mode. Three by ten millimeter rectangles also work well. Movie 1 and Movie 2</str...

Ultrasound atomization has been studied for almost a century and although there are many applications, there are limitations in understanding the underlying physics. The &#64257;rst description of the phenomenon was made by Wood and Loomis in 19271, and since then there have been developments in the &#64257;eld for applications ranging from delivering aerosolized pharmaceutical &#64258;uids2 to fuel injection3. Although the phenomenon works well in these applications, the underlying physics is not well understood4,5,6.
A key limitation in the &#64257;eld of ultrasonic atomization is the choice of material used, lead zirconate titanate (PZT), a hysteretic material prone to heating7 and lead contamination with elemental lead available from the inter-grain boundaries8,9. Grain size and mechanical and electronic properties of grain boundaries also limit the frequency at which PZT can operate10. By contrast, lithium niobate is both lead-free and exhibits no hysteresis11, and can be used to atomize &#64258;uids an order of magnitude more efficiently than commercial atomizers12. The traditional cut of lithium niobate used for operation in the thickness mode is the 36-degree Y-rotated cut, but the 127.86-degree Y-rotated, X-propagating cut (128YX), typically used for surface acoustic wave generation, has been shown to have a higher surface displacement amplitude in comparison with the 36-degree cut13 when operated in resonance and low loss. It has also been shown that thickness mode operation offers an order of magnitude improvement in atomizer efficiency over other modes of vibration13, even when using LN.
The resonance frequency of a piezoelectric device operating in the thickness mode is governed by its thickness t: the wavelength &#955; = 2t/n where n = 1, 2,... is the number of anti-nodes. For a 500 &#181;m thick substrate, this corresponds to a wavelength of 1 mm for the fundamental mode, which can then be used to calculate the fundamental resonance frequency, f = v/&#955; if the wave speed, v, is known. The speed of sound through the thickness of 128YX LN is approximately 7,000 m/s, and so f = 7 MHz. Unlike other forms of vibration, particularly surface-bound modes, it is straightforward to excite higher-order thickness mode harmonics to much higher frequencies, here to 250 MHz or more, though only the odd-numbered modes may be excited by uniform electric &#64257;elds14. Consequently, the second harmonic (n = 2) near 14 MHz cannot be excited, but the third harmonic at 21 MHz (n = 3) can. Fabrication of efficient thickness mode devices requires depositing electrodes onto opposing faces of the transducer. We use direct current (DC) sputtering to accomplish this, but electron-beam deposition and other methods could be used. Impedance analysis is useful to characterize the devices, particularly in &#64257;nding the resonance frequencies and electromechanical coupling at these frequencies. Laser Doppler vibrometry (LDV) is useful to determine the output vibration amplitude and velocity without contact or calibration15, and, via scanning, the LDV provides the spatial distribution of surface deformation, revealing the mode of vibration associated with a given frequency. Finally, for the purposes of studying atomization and &#64258;uid dynamics, high-speed imaging can be employed as a technique to study the development of capillary waves on the surface of a sessile drop16,17. In atomization, like many other acoustofluidic phenomena, small droplets are produced at a rapid rate, over 1 kHz in a given location, too quickly for high-speed cameras to observe with sufficient &#64257;delity and &#64257;eld of view to provide useful information over a sufficiently large droplet sample size. Laser scattering may be used for this purpose, passing the droplets through an expanded laser beam to (Mie) scatter some of the light in re&#64258;ection and refraction to produce a characteristic signal that may be used to statistically estimate the droplet size distribution.
It is straightforward to fabricate piezoelectric thickness mode transducers, but the techniques required in device and atomization characterization have not been clearly stated in the literature to date, hampering progress in the discipline. In order for a thickness mode transducer to be effective in an atomization device, it must be mechanically isolated so that its vibration is not damped and it must have a continuous &#64258;uid supply with a &#64258;ow rate equal to the atomization rate so that neither desiccation nor &#64258;ooding occur. These two practical considerations have not been thoroughly covered in the literature because their solutions are the result of engineering techniques rather than pure scienti&#64257;c novelty, but they are nonetheless critical to studying the phenomenon. We present a transducer holder assembly and a liquid wicking system as solutions. This protocol offers a systematic approach to atomizer fabrication and characterization for facilitating further research in fundamental physics and myriad applications.

<table><tbody><tr><td>Amplifier</td><td>Amplifier Research, Souderton, PA, USA</td><td>5U1000</td><td></td></tr><tr><td>Articulating arm</td><td>Fisso, Zurich, Switzerland</td><td></td><td></td></tr><tr><td>CF4 Objective</td><td>Edmund Optics, Barrington, NJ, USA</td><td></td><td>Objective used for high speed imaging</td></tr><tr><td>Dicing saw</td><td>Disco, Tokyo, Japan</td><td>Disco Automatic Dicing Saw 3220</td><td></td></tr><tr><td>Fiber Fragrance Diffuser Wick</td><td>Weihai Industry Co., Ltd., Weihai, Shandong, China</td><td>https://www.weihaisz.com/Fiber-Fragrance-Diffuser-Wick_p216.html</td><td></td></tr><tr><td>High Speed Camera</td><td>Photron, San Diego, USA</td><td>Fastcam Mini</td><td></td></tr><tr><td>Laser Doppler Vibrometer</td><td>Polytec, Waldbronn, Germany</td><td>UHF120</td><td>Non-contact laser doppler vibrometer</td></tr><tr><td>Laser Scattering Droplet size measurement system</td><td>Malvern Panalytical, Malvern, UK</td><td>STP5315</td><td></td></tr><tr><td>Lithium niobate substrate</td><td>PMOptics,Burlington, MA, USA</td><td>PWLN-431232</td><td>4&amp;rdquo; double-side polished 0.5 mm thick 128&amp;deg;Y-rotated cut lithium niobate</td></tr><tr><td>Luer-lock syringes</td><td>Becton Dickingson, New Jersey, USA</td><td></td><td></td></tr><tr><td>Nano3 cleanroom facility</td><td>UCSD, La Jolla, CA, USA</td><td></td><td>Fabrication process is performed in it.</td></tr><tr><td>Network Analyzer</td><td>Keysight Technologies, Santa Rosa, CA, USA</td><td>5061B</td><td></td></tr><tr><td>Oscilloscope</td><td>Keysight Technologies, Santa Rosa, CA, USA</td><td>InfiniiVision 2000 X-Series</td><td></td></tr><tr><td>PSV Acquistion Software</td><td>Polytec, Waldbronn, Germany</td><td>Version 9.4</td><td>LDV Software</td></tr><tr><td>PSV Presentation Software</td><td>Polytec, Waldbronn, Germany</td><td>Version 9.4</td><td>LDV Software</td></tr><tr><td>Signal generator</td><td>NF Corporation, Yokohama, Japan</td><td>WF1967 multifunction generator</td><td></td></tr><tr><td>Single Post Connector</td><td>DigiKey, Thief River Falls, MN</td><td>ED1179-ND</td><td></td></tr><tr><td>Sputter deposition</td><td>Denton Vacuum, NJ, USA</td><td>Denton 18</td><td>Denton Discovery 18 Sputter System</td></tr><tr><td>Surface Mount Spring Contacts</td><td>DigiKey, Thief River Falls, MN</td><td>70AAJ-2-M0GCT-ND</td><td></td></tr><tr><td>Teflon wafer dipper</td><td>ShapeMaster, Ogden, IL, USA</td><td>SM4WD1</td><td>Wafer Dipper 4&quot;</td></tr><tr><td>XYZ Stage</td><td>Thor Labs, Newton, New Jersey, USA</td><td>MT3</td><td>Optical table stages</td></tr></tbody></table>

fabrication and characterization of thickness mode piezoelectric devices for atomization and acoustofluidics

We present a technique to fabricate simple thickness mode piezoelectric devices using lithium niobate (LN). Such devices have been shown to atomize liquid more efficiently, in terms of &#64258;ow rate per power input, than those that rely on Rayleigh waves and other modes of vibration in LN or lead zirconate titanate (PZT). The complete device is composed of a transducer, a transducer holder, and a &#64258;uid supply system. The fundamentals of acoustic liquid atomization are not well known, so techniques to characterize the devices and to study the phenomena are also described. Laser Doppler vibrometry (LDV) provides vibration information essential in comparing acoustic transducers and, in this case, indicates whether a device will perform well in thickness vibration. It can also be used to &#64257;nd the resonance frequency of the device, though this information is obtained more quickly via impedance analysis. Continuous &#64258;uid atomization, as an example application, requires careful &#64258;uid flow control, and we present such a method with high-speed imaging and droplet size distribution measurements via laser scattering.

Thickness mode piezoelectric devices were fabricated from 128YX lithium niobate. Figure 1 shows a complete assembly to hold the transducer in place with a custom transducer holder used with the passive &#64258;uid delivery system developed for continuous atomization. The characterization steps for these devices include determination of the resonant frequency and harmonics using an impedance analyzer (Figure 2). The fundamental frequency of the devices was found ...

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Fabrication and Characterization of Thickness Mode Piezoelectric Devices for Atomization and Acoustofluidics

Fabrication of piezoelectric thickness mode transducers via direct current sputtering of plate electrodes on lithium niobate is described. Additionally, reliable operation is achieved with a transducer holder and &#64258;uid supply system and characterization is demonstrated via impedance analysis, laser doppler vibrometry, high-speed imaging, and droplet size distribution using laser scattering.

We present a technique to fabricate simple thickness mode piezoelectric devices using lithium niobate (LN). Such devices have been shown to atomize liquid ...

fabrication-characterization-thickness-mode-piezoelectric-devices-for

Research

JoVE Journal

Engineering

6.8K Views.  University of California San Diego. Deze technieken kunnen worden gebruikt om vragen te beantwoorden over resonantiefrequentie, opwinding in de trillingsmodus, trillingsamplitude en hoe transducers met deze kenmerken als verstuivers presteren. Met informatie die door deze analyses wordt verstrekt, is het mogelijk om de effecten van onafhankelijke variabelen en experimenten met thickness mode transducers rigoureus te kwantificeren. Deze techniek maakt de ontwikkeling mogelijk van apparaten die kunnen worden gebruikt om geneesmid...

Video: Fabrication and Characterization of Thickness Mode Piezoelectric Devices for Atomization and Acoustofluidics

Fabrication, Operation and Flow Visualization in Surface-acoustic-wave-driven Acoustic-counterflow Microfluidics

Surface acoustic waves (SAWs) can be used to drive liquids in portable microfluidic chips via the acoustic counterflow phenomenon. In this video we present the fabrication protocol for a multilayered SAW acoustic counterflow device. The device is fabricated starting from a lithium niobate (LN) substrate onto which two interdigital transducers (IDTs) and appropriate markers are patterned. A polydimethylsiloxane (PDMS) channel cast on an SU8 master mold is finally bonded on the patterned substrate. Following the fabrication procedure, we show the techniques that allow the characterization and operation of the acoustic counterflow device in order to pump fluids through the PDMS channel grid. We finally present the procedure to visualize liquid flow in the channels. The protocol is used to show on-chip fluid pumping under different flow regimes such as laminar flow and more complicated dynamics characterized by vortices and particle accumulation domains.

In this video we first describe fabrication and operation procedures of a surface acoustic wave (SAW) acoustic counterflow device. We then demonstrate an experimental setup that allows for both qualitative flow visualization and quantitative analysis of complex flows within the SAW pumping device.

Surface acoustic waves (SAWs) can be used to drive liquids in portable microfluidic chips via the acoustic counterflow phenomenon. In this video we ...

Fabrication and Testing of Microfluidic Optomechanical Oscillators

Cavity optomechanics experiments that parametrically couple the phonon modes and photon modes have been investigated in various optical systems including microresonators. However, because of the increased acoustic radiative losses during direct liquid immersion of optomechanical devices, almost all published optomechanical experiments have been performed in solid phase. This paper discusses a recently introduced hollow microfluidic optomechanical resonator. Detailed methodology is provided to fabricate these ultra-high-Q microfluidic resonators, perform optomechanical testing, and measure radiation pressure-driven breathing mode and SBS-driven whispering gallery mode parametric vibrations. By confining liquids inside the capillary resonator, high mechanical- and optical- quality factors are simultaneously maintained.

Parametric optomechanical excitations have recently been experimentally demonstrated in microfluidic optomechanical resonators by means of optical radiation pressure and stimulated Brillouin scattering. This paper describes the fabrication of these microfluidic resonators along with methodologies for generating and verifying optomechanical oscillations.

Cavity optomechanics experiments that parametrically couple the phonon modes and photon modes have been investigated in various optical systems including ...

Experiments on Ultrasonic Lubrication Using a Piezoelectrically-assisted Tribometer and Optical Profilometer

Friction and wear are detrimental to engineered systems. Ultrasonic lubrication is achieved when the interface between two sliding surfaces is vibrated at a frequency above the acoustic range (20 kHz). As a solid-state technology, ultrasonic lubrication can be used where conventional lubricants are unfeasible or undesirable. Further, ultrasonic lubrication allows for electrical modulation of the effective friction coefficient between two sliding surfaces. This property enables adaptive systems that modify their frictional state and associated dynamic response as the operating conditions change. Surface wear can also be reduced through ultrasonic lubrication. We developed a protocol to investigate the dependence of friction force reduction and wear reduction on the linear sliding velocity between ultrasonically lubricated surfaces. A pin-on-disc tribometer was built which differs from commercial units in that a piezoelectric stack is used to vibrate the pin at 22 kHz normal to the rotating disc surface. Friction and wear metrics including effective friction force, volume loss, and surface roughness are measured without and with ultrasonic vibrations at a constant pressure of 1 to 4 MPa and three different sliding velocities: 20.3, 40.6, and 87 mm/sec. An optical profilometer is utilized to characterize the wear surfaces. The effective friction force is reduced by 62% at 20.3 mm/sec. Consistently with existing theories for ultrasonic lubrication, the percent reduction in friction force diminishes with increasing speed, down to 29% friction force reduction at 87 mm/sec. Wear reduction remains essentially constant (49%) at the three speeds considered.

We present a protocol for using a piezoelectrically-assisted tribometer and optical profilometer to investigate the dependence of ultrasonic wear and friction reduction on linear velocity, contact pressure, and surface properties.

Friction and wear are detrimental to engineered systems. Ultrasonic lubrication is achieved when the interface between two sliding surfaces is vibrated at ...

Fabrication and Operation of Acoustofluidic Devices Supporting Bulk Acoustic Standing Waves for Sheathless Focusing of Particles

Acoustophoresis refers to the displacement of suspended objects in response to directional forces from sound energy. Given that the suspended objects must be smaller than the incident wavelength of sound and the width of the fluidic channels are typically tens to hundreds of micrometers across, acoustofluidic devices typically use ultrasonic waves generated from a piezoelectric transducer pulsating at high frequencies (in the megahertz range). At characteristic frequencies that depend on the geometry of the device, it is possible to induce the formation of standing waves that can focus particles along desired fluidic streamlines within a bulk flow. Here, we describe a method for the fabrication of acoustophoretic devices from common materials and clean room equipment. We show representative results for the focusing of particles with positive or negative acoustic contrast factors, which move towards the pressure nodes or antinodes of the standing waves, respectively. These devices offer enormous practical utility for precisely positioning large numbers of microscopic entities (e.g., cells) in stationary or flowing fluids for applications ranging from cytometry to assembly.

Acoustofluidic devices use ultrasonic waves within microfluidic channels to manipulate, concentrate and isolate suspended micro and nanoscopic entities. This protocol describes the fabrication and operation of such a device supporting bulk acoustic standing waves to focus particles in a central streamline without the aid of sheath fluids.

Acoustophoresis refers to the displacement of suspended objects in response to directional forces from sound energy. Given that the suspended objects must ...

A Microfluidic Platform for Precision Small-volume Sample Processing and Its Use to Size Separate Biological Particles with an Acoustic Microdevice

A major advantage of microfluidic devices is the ability to manipulate small sample volumes, thus reducing reagent waste and preserving precious sample. However, to achieve robust sample manipulation it is necessary to address device integration with the macroscale environment. To realize repeatable, sensitive particle separation with microfluidic devices, this protocol presents a complete automated and integrated microfluidic platform that enables precise processing of 0.15&#8211;1.5 ml samples using microfluidic devices. Important aspects of this system include modular device layout and robust fixtures resulting in reliable and flexible world to chip connections, and fully-automated fluid handling which accomplishes closed-loop sample collection, system cleaning and priming steps to ensure repeatable operation. Different microfluidic devices can be used interchangeably with this architecture. Here we incorporate an acoustofluidic device, detail its characterization, performance optimization, and demonstrate its use for size-separation of biological samples. By using real-time feedback during separation experiments, sample collection is optimized to conserve and concentrate sample. Although requiring the integration of multiple pieces of equipment, advantages of this architecture include the ability to process unknown samples with no additional system optimization, ease of device replacement, and precise, robust sample processing.

This protocol describes a system architecture for performing automated small volume (0.15&#8211;1.5 ml) particle separations using a microfluidic device, and discusses methods to optimize acoustofluidic device performance and operation.

A major advantage of microfluidic devices is the ability to manipulate small sample volumes, thus reducing reagent waste and preserving precious sample. ...

Bioengineering

A Polymer-based Piezoelectric Vibration Energy Harvester with a 3D Meshed-Core Structure

In this study, we fabricated a flexible 3D mesh structure with periodic voids by using a 3D lithography method and applying it to a vibration energy harvester to lower resonance frequency and increase output power. The fabrication process is mainly divided into two parts: three-dimensional photolithography for processing a 3D mesh structure, and a bonding process of piezoelectric films and the mesh structure. With the fabricated flexible mesh structure, we achieved the reduction of resonance frequency and improvement of output power, simultaneously. From the results of the vibration tests, the meshed-core-type vibration energy harvester (VEH) exhibited 42.6% higher output voltage than the solid-core-type VEH. In addition, the meshed-core-type VEH yielded 18.7 Hz of resonance frequency, 15.8% lower than the solid-core-type VEH, and 24.6 &#956;W of output power, 68.5% higher than the solid-core-type VEH. The advantage of the proposed method is that a complex and flexible structure with voids in three dimensions can be relatively easily fabricated in a short time by the inclined exposure method. As it is possible to lower the resonance frequency of the VEH by the mesh structure, use in low-frequency applications, such as wearable devices and house appliances, can be expected in the future.

In this study, we fabricated a flexible 3D mesh structure and applied it to the elastic layer of a bimorph cantilever-type vibration energy harvester for the purpose of lowering resonance frequency and increasing output power.

In this study, we fabricated a flexible 3D mesh structure with periodic voids by using a 3D lithography method and applying it to a vibration energy ...

Fabrication of Nanoheight Channels Incorporating Surface Acoustic Wave Actuation via Lithium Niobate for Acoustic Nanofluidics

Controlled nanoscale manipulation of fluids is known to be exceptionally difficult due to the dominance of surface and viscous forces. Megahertz-order surface acoustic wave (SAW) devices generate tremendous acceleration on their surface, up to 108 m/s2, in turn responsible for many of the observed effects that have come to define acoustofluidics: acoustic streaming and acoustic radiation forces. These effects have been used for particle, cell, and fluid manipulation at the microscale, although more recently SAW has been used to produce similar phenomena at the nanoscale through an entirely different set of mechanisms. Controllable nanoscale fluid manipulation offers a broad range of opportunities in ultrafast fluid pumping and biomacromolecule dynamics useful for physical and biological applications. Here, we demonstrate nanoscale-height channel fabrication via room-temperature lithium niobate (LN) bonding integrated with a SAW device. We describe the entire experimental process including nano-height channel fabrication via dry etching, plasma-activated bonding on lithium niobate, the appropriate optical setup for subsequent imaging, and SAW actuation. We show representative results for fluid capillary filling and fluid draining in a nanoscale channel induced by SAW. This procedure offers a practical protocol for nanoscale channel fabrication and integration with SAW devices useful to build upon for future nanofluidics applications.

We demonstrate fabrication of nanoheight channels with the integration of surface acoustic wave actuation devices upon lithium niobate for acoustic nanofluidics via liftoff photolithography, nano-depth reactive ion etching, and room-temperature plasma surface-activated multilayer bonding of single-crystal lithium niobate, a process similarly useful for bonding lithium niobate to oxides.

Controlled nanoscale manipulation of fluids is known to be exceptionally difficult due to the dominance of surface and viscous forces. Megahertz-order ...

Fabrication of Surface Acoustic Wave Devices on Lithium Niobate

Manipulation of fluids and particles by acoustic actuation at small scale is aiding the rapid growth of lab-on-a-chip applications. Megahertz-order surface acoustic wave (SAW) devices generate enormous accelerations on their surface, up to 108 m/s2, in turn responsible for many of the observed effects that have come to define acoustofluidics: acoustic streaming and acoustic radiation forces. These effects have been used for particle, cell, and fluid handling at the microscale&#8212;and even at the nanoscale. In this paper we explicitly demonstrate two major fabrication methods of SAW devices on lithium niobate: the details of lift-off and wet etching techniques are described step-by-step. Representative results for the electrode pattern deposited on the substrate as well as the performance of SAW generated on the surface are displayed in detail. Fabrication tricks and troubleshooting are covered as well. This procedure offers a practical protocol for high frequency SAW device fabrication and integration for future microfluidics applications.

Two fabrication techniques, lift-off and wet etching, are described in producing interdigital electrode transducers upon a piezoelectric substrate, lithium niobate, widely used to generate surface acoustic waves now finding broad utility in micro to nanoscale fluidics. The as-produced electrodes are shown to efficiently induce megahertz order Rayleigh surface acoustic waves.&#160;

Manipulation of fluids and particles by acoustic actuation at small scale is aiding the rapid growth of lab-on-a-chip applications. Megahertz-order ...

Epitaxial Nanostructured &alpha;-Quartz Films on Silicon: From the Material to New Devices

In this work, we show a detailed engineering route of the first piezoelectric nanostructured epitaxial quartz-based microcantilever. We will explain all the steps in the process starting from the material to the device fabrication. The epitaxial growth of &#945;-quartz film on SOI (100) substrate starts with the preparation of a strontium doped silica sol-gel and continues with the deposition of this gel into the SOI substrate in a thin film form using the dip-coating technique under atmospheric conditions at room temperature. Before crystallization of the gel film, nanostructuration is performed onto the film surface by nanoimprint lithography (NIL). Epitaxial film growth is reached at 1000 &#176;C, inducing a perfect crystallization of the patterned gel film. Fabrication of quartz crystal cantilever devices is a four-step process based on microfabrication techniques. The process starts with shaping the quartz surface, and then metal deposition for electrodes follows it. After removing the silicone, the cantilever is released from SOI substrate eliminating SiO2 between silicon and quartz. The device performance is analyzed by non-contact laser vibrometer (LDV) and atomic force microscopy (AFM). Among the different cantilever&#8217;s dimensions included in the fabricated chip, the nanostructured cantilever analyzed in this work exhibited a dimension of 40 &#181;m large and 100 &#181;m long and was fabricated with a 600 nm thick patterned quartz layer (nanopillar diameter and separation distance of 400 nm and 1 &#181;m, respectively) epitaxially grown on a 2 &#181;m thick Si device layer. The&#160;measured&#160;resonance frequency was&#160;267 kHz and the estimated quality factor, Q, of the whole mechanical structure was Q ~ 398 under low vacuum conditions. We observed the voltage-dependent linear displacement of cantilever with both techniques (i.e., AFM contact measurement and LDV). Therefore, proving that these devices can be activated through the indirect piezoelectric effect.

Epitaxial Nanostructured &#945;-Quartz Films on Silicon: From the Material to New Devices

This work presents a detailed protocol for the microfabrication of nanostructured &#945;-quartz cantilever on a Silicon-On-Insulator(SOI) technology substrate starting from the epitaxial growth of quartz film with the dip coating method and then nanostructuration of the thin film via nanoimprint lithography.

In this work, we show a detailed engineering route of the first piezoelectric nanostructured epitaxial quartz-based microcantilever. We will explain all ...

Fabrication of High-Quality Whispering Gallery Mode Microbubble Resonators

We demonstrate a robust and standardized method for the fabrication of high-quality factor (Q-factor) Whispering Gallery Mode (WGM) Microbubble resonators (MBRs) with a precision glass processing machine (PGP). Microbubble resonators are a unique class of WGM devices with integrated fluidic channels, making them ideal for diverse sensing applications. Herein, we show a standardized protocol to fabricate high-Q microbubble resonators through the optimization of key performance metrics, such as Q-factor and wall thickness. We also show methods to improve the sensitivity of the platform to refractive index changes and other sensing targets through Hydrofluoric acid (HF) wet etching. Lastly, a brief analysis of the resistance of microbubbles to fluid flow is discussed, showing that smaller-diameter microbubbles exhibit greater resistance to flow for analyte delivery - a factor that should be considered for analyte delivery. The implementation of this refined fabrication protocol not only increases the success rate of device production but also reduces fabrication time. Moreover, the protocol can be expanded to other techniques used to produce MBRs, such as CO2 laser-based methods.

Here, we demonstrate a robust and standardized protocol for fabricating high-quality factor (Q-factor) Whispering Gallery Mode (WGM) Microbubble resonators (MBRs) with a precision glass processing machine (PGP).

We demonstrate a robust and standardized method for the fabrication of high-quality factor (Q-factor) Whispering Gallery Mode (WGM) Microbubble resonators ...

Fabrication and Characterization of Thickness Mode Piezoelectric Devices for Atomization and Acoustofluidics

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