This article reviews acoustic microfiuidics: the use of acoustic fields, principally ultrasonics, for application in microfiuidics. Although acoustics is a classical field, its promising, and indeed perplexing, capabilities in powerfully manipulating both fluids and particles within those fluids on the microscale to nanoscale has revived interest in it. The bewildering state of the literature and ample jargon from decades of research is reorganized and presented in the context of models derived from first principles. This hopefully will make the area accessible for researchers with experience in materials science, fluid mechanics, or dynamics. The abundance of interesting phenomena arising from nonlinear interactions in ultrasound that easily appear at these small scales is considered, especially in surface acoustic wave devices that are simple to fabricate with planar lithography techniques common in microfluidics, along with the many applications in microfluidics and nanofluidics that appear through the literature.

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Microscale acoustofluidics: Microfluidics driven via acoustics and ultrasonics

https://www.repository.cam.ac.uk/bitstream/1810/264501/1/Fu_et_al-2017-Progress_in_Material_Science-VoR.pdf

Advances in piezoelectric thin films for acoustic biosensors, acoustofluidics and lab-on-chip applications

We report the use of focused surface acoustic waves (SAWs) generated on 128° rotated Y-cut X-propagating lithium niobate (LiNbO3) for enhancing the actuation of fluids and the manipulation of particle suspensions at microscale dimensions. In particular, we demonstrate increased efficiency and speed in carrying out particle concentration/separation and in generating intense micromixing in microliter drops within which acoustic streaming is induced due to the focused SAW beneath the drop. Concentric circular and elliptical single-phase unidirectional transducers (SPUDTs) were used to focus the SAW. We benchmark our results against a straight SPUDT which does not cause focusing of the SAW. Due to the increased wave intensity and asymmetry of the wave, we found both circular and elliptical SPUDTs concentrate particles in under 1 s, which is one order of magnitude faster than the straight SPUDT and several orders of magnitude faster than conventional microscale devices. The concentric circular SPUDT was found ...

/pdf/particle-concentration-and-mixing-in-microdrops-driven-by-2rlmbke5ff.pdf

Particle concentration and mixing in microdrops driven by focused surface acoustic waves

This book gives the fundamental principles and device design techniques for surface acoustic wave filters. It covers the devices in widespread use today: bandpass and pulse compression filters, correlators and non-linear convolvers and resonators. The newest technologies for low bandpass filters are fully covered such as unidirectional transducers, resonators in impedance element filters, resonators in double-mode surface acoustic wave filters and transverse-coupled resonators using waveguides.The book covers the theory of acoustic wave physics, the piezoelectric effect, electrostatics at a surface, effective permittivity, piezoelectric SAW excitation and reception, and the SAW element factor. These are the main requirements for developing quasi-static theory, which gives a basis for the non-reflective transducers in transversal bandpass filters and interdigital pulse compression filters. It is also needed for the reflective transducers used in the newer devices. It is a thorough revision of a classic on surface acoustic wave filters first published in 1985 and still in print. It uniquely combines easy-to-understand principles with practical design techniques for all the devices in widespread use today. It includes complete coverage of all the latest devices which are key to mobile phones, TVs and radar systems; and, a new foreword by Sir Eric Albert Ash.

Surface Acoustic Wave Filters: With Applications to Electronic Communications and Signal Processing

Background and History. Resonator and Filter Topologies. Baw Device Basics. Design and Fabrication of BAW Devices. FBAR Resonators and Filters. Comparison with SAW Devices. Films Deposition for BAW Devices. Characterization of BAW Devices. Monolithic Integration. System-in-Package (SiP) Integration. Index.

RF bulk acoustic wave filters for communications

This paper discusses the application of Love mode propagating on Cu-grating/rotated YX-LiNbO3-substrate structure to the development of ultra-wideband and low-loss RF surface acoustic wave (SAW) filters. Theoretical analysis suggested that high performance resonators with very small capacitance ratio would be realised using Cu gratings with a thickness of several percent of wavelength. It was also suggested that in particular, on 15°YX-LiNbO3-substrate structure, the spurious response due to Rayleigh mode could effectively be suppressed. An IDT-type one-port SAW resonator and a ladder-type SAW filter were fabricated on the Cu-grating/15°YX-LiNbO3-substrate structure, and their high performances are demonstrated with discussion.

https://iopscience.iop.org/article/10.1143/JJAP.43.3063/pdf

Ultra-Wideband Surface Acoustic Wave Devices Using Cu-Grating/Rotated-YX-LiNbO3-Substrate Structure

In this paper, we describe possible configurations for tunable filters based on RF surface or bulk acoustic wave (SAW/BAW) technologies. The frequency tuning is made possible by variable capacitors (VCs) connected to SAW/BAW resonators in the ladder-type filter configuration. First, it is shown that the passband edges can be controlled by one VC connected to each resonator. Second, it is discussed that the width and location of a passband can be controlled flexibly by two VCs connected to each resonator both in parallel and in series. Finally, the SAW filters with the proposed configuration are fabricated on a Cu-grating/15°YX-LiNbO3 substrate structure, and the tuning capability is demonstrated.

https://iopscience.iop.org/article/10.1143/JJAP.49.07HD24/pdf

Tunable Radio-Frequency Filters Using Acoustic Wave Resonators and Variable Capacitors

This paper discusses a technique to suppress spurious transverse mode responses appearing in ultra-wideband SAW resonators fabricated on a Cu- grating/15degYX-LiNbO3 structure. The basic idea of the technique is inserting length- and width-weighted dummy electrodes between a bus-bar and interdigital electrodes. For practical device design, an analysis was made to show how the profile (field distribution) of both dominant and spurious transverse modes depends on the length and width (equivalent to SAW velocity) of the dummy electrodes. IDT-type SAW resonators were fabricated on a Cu- grating/15degYX-LiNbO3 structure using the length- and width-weighted dummy electrodes. The experimental results were in good agreement with the theoretical analysis and prediction, showing that the proposed technique is effective in suppressing the spurious responses caused by the transverse modes.

Suppression of Transverse Mode Responses in Ultra-Wideband SAW Resonators Fabricated on a Cu-Grating/15°YX-LiNbO 3 Structure

The paper discusses the application of Love mode propagating on Cu-grating/rotated YX-LiNbO/sub 3/-substrate structure to the development of ultra-wideband and low-loss RF SAW filters. Theoretical analysis suggests that high performance resonators with very small capacitance ratio may be realised using Cu gratings of the thickness of several percent of wavelength. It was also suggested that, in particular, on a 15/spl deg/YX-LiNbO/sub 3/-substrate structure, the spurious response due to the Rayleigh mode could effectively be suppressed. IDT-type one-port SAW resonators and ladder-type SAW filters were fabricated on the Cu-grating/15/spl deg/YX-LiNbO/sub 3/-substrate structure, and their high performances are demonstrated by discussion.

Wideband Love wave filters operating in GHz range on Cu-grating/rotated-YX-LiNbO/sub 3/-substrate structure

Diamond has the highest known SAW phase velocity, sufficient for applications in the gigahertz range. However, although numerous studies have demonstrated SAW devices on polycrystalline diamond thin films, all have had much larger propagation loss than single-crystal materials such as LiNbO3. Hence, in this study, we fabricated and characterized one-port SAW resonators on single-crystal diamond substrates synthesized using a high-pressure and high-temperature method to identify and minimize sources of propagation loss. A series of one-port resonators were fabricated with the interdigital transducer/ AlN/diamond structure and their characteristics were measured. The device with the best performance exhibited a resonance frequency f of 5.3 GHz, and the equivalent circuit model gave a quality factor Q of 5509. Thus, a large fQ product of approximately 2.9 × 1013 was obtained, and the propagation loss was found to be only 0.006 dB/wavelength. These excellent properties are attributed mainly to the reduction of scattering loss in a substrate using a single-crystal diamond, which originated from the grain boundary of diamond and the surface roughness of the AlN thin film and the diamond substrate. These results show that single-crystal diamond SAW resonators have great potential for use in low-noise super-high-frequency oscillators.

Tatsuya Omori

Papers

Ultra-Wideband Surface Acoustic Wave Devices Using Cu-Grating/Rotated-YX-LiNbO3-Substrate Structure

Tunable Radio-Frequency Filters Using Acoustic Wave Resonators and Variable Capacitors

Suppression of Transverse Mode Responses in Ultra-Wideband SAW Resonators Fabricated on a Cu-Grating/15°YX-LiNbO 3 Structure

Wideband Love wave filters operating in GHz range on Cu-grating/rotated-YX-LiNbO/sub 3/-substrate structure

Low propagation loss in a one-port SAW resonator fabricated on single-crystal diamond for super-high-frequency applications