Potassium-sodium niobate lead-free piezoelectric materials: past, present, and future of phase boundaries.

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

The recent introduction of surface acoustic wave (SAW) technology onto lab-on-a-chip platforms has opened a new frontier in microfluidics. The advantages provided by such SAW microfluidics are numerous: simple fabrication, high biocompatibility, fast fluid actuation, versatility, compact and inexpensive devices and accessories, contact-free particle manipulation, and compatibility with other microfluidic components. We believe that these advantages enable SAW microfluidics to play a significant role in a variety of applications in biology, chemistry, engineering and medicine. In this review article, we discuss the theory underpinning SAWs and their interactions with particles and the contacting fluids in which they are suspended. We then review the SAW-enabled microfluidic devices demonstrated to date, starting with devices that accomplish fluid mixing and transport through the use of travelling SAW; we follow that by reviewing the more recent innovations achieved with standing SAW that enable such actions as particle/cell focusing, sorting and patterning. Finally, we look forward and appraise where the discipline of SAW microfluidics could go next.

Surface acoustic wave microfluidics

This paper reviews recent developments of ultrasonic motors using piezoelectric resonant vibrations. Following the historical background, ultrasonic motors using standing and traveling waves are introduced. Driving principles and motor characteristics are explained in comparison with conventional electromagnetic motors. After a brief discussion on speed and thrust calculation, finally, reliability issues of ultrasonic motors are described.

/pdf/piezoelectric-ultrasonic-motors-overview-vhj6r1ou7e.pdf

Piezoelectric ultrasonic motors: overview

Fluid manipulations at the microscale and beyond are powerfully enabled through the use of 10–1,000-MHz acoustic waves. A superior alternative in many cases to other microfluidic actuation techniques, such high-frequency acoustics is almost universally produced by surface acoustic wave devices that employ electromechanical transduction in wafer-scale or thin-film piezoelectric media to generate the kinetic energy needed to transport and manipulate fluids placed in adjacent microfluidic structures. These waves are responsible for a diverse range of complex fluid transport phenomena—from interfacial fluid vibration and drop and confined fluid transport to jetting and atomization—underlying a flourishing research literature spanning fundamental fluid physics to chip-scale engineering applications. We highlight some of this literature to provide the reader with a historical basis, routes for more detailed study, and an impression of the field's future directions.

https://users.monash.edu/~lyeo/Dr_Leslie_Yeo/Surface_Acoustic_Wave_Microfluidics_files/annurev-fluid-010313-141418.pdf

Surface Acoustic Wave Microfluidics

An ultrasonic motor is proposed which uses two piezoelectric elements in the stator. One element is used to generate a vibration polarized with respect to the direction of motion of the rotor or the slider. The other one generates a vibration perpendicular to the motion of the rotor. By imaging the ratio of the vibration amplitudes and the phase, the Lissajous figure of the particle on the stator surface can be controlled easily. This makes it possible to operate the motor stably, even at low speed. >

Ultrasonic motors

An application of a surface acoustic wave device for miniaturization of ultrasonic atomizers and for functional system construction is proposed. Actually, ultrasonic atomizers are rather smaller than those produced by other methods, so that nebulizers that are handy to carry use ultrasonic vibration. However, they are too large for a pocket or a catheter. A fine mist has been obtained with the first trial of a surface acoustic wave atomizing device whose dimensions are pocket size. There is a possibility of this functional device being reduced to a system of millimetre size. The atomizer consists of a vibrator, a cover and a tube. The vibrator and cover material are 127.8° Y-cut LiNbO3 to generate a Rayleigh wave, a kind of surface acoustic wave. The Rayleigh wave is the driving force of the pumping and atomizing effects. The pumping effect is caused by the wave motion of the elastic material and viscosity of the fluid, like an ultrasonic motor. The atomizing rate varies according to the driving voltage. The maximum rate is about 0.6 ml min−1 at around 10 MHz. The linear mean diameter is 19 μm and the Sauter's mean diameter is 34 μm. A smaller device that operates at 47 MHz is also demonstrated.

Surface acoustic wave atomizer

To measure the characteristics of ultrasonic motors, such as the maximum torque, torque-speed relationship and the frictional coefficient at the contact surface, a method in which the torque is calculated from the transient responses is proposed. The rise curve that is the transitional change in the rotor speed soon after turning on the motor gives the load characteristics, while the fall curve that is the decay of the rotor speed after turning off the motor yields the frictional coefficient of the contact surface. This method requires only a short time (the transient time of the motor) to complete the measurement. The relations between the transient responses, the load characteristics and the frictional force are analyzed, and the method is applied to a hybrid transducer type rotary motor and a traveling wave type linear motor. >

An estimation of load characteristics of an ultrasonic motor by measuring transient responses

The first success in the operation of an ultrasonic linear motor at HF band driving frequency using the Rayleigh wave is described. The substrate material is a 127.8/spl deg/ Y-cut LiNbO/sub 3/ wafer whose diameter is three inches. Four interdigital transducers (IDT's) are arranged to excite x- and y-propagation waves in both directions. The dimensions of the IDT are 25 mm aperture size, 400 /spl mu/m pitch, 100 /spl mu/m strip width, and 10 pairs. The operation area is about 25 mm square, The driving frequency is about 9.6 MHz in the x direction and about 9.1 MHz in the y direction. The most important point of the success is the shape of the contact surface and slider materials. For the contact materials, small balls about 1 mm in diameter are introduced to obtain sufficient contact pressure around 100 MPa. The use of ruby balls, steel balls, and tungsten carbide balls is investigated. Each slider has three balls to enable stable contact at three points. The maximum transfer speed is about 20 cm/s. The transfer speed is controllable by changing the driving voltage.

Ultrasonic linear motor using surface acoustic waves

An ultrasonic motor using bending vibrations of a short cylinder with free-free ends is proposed, and its performance and efficiency are discussed. The motor is small in size and realizes a high mechanical output of more than 1 W. The general principle of the motor, which uses traveling waves, is as follows. When a traveling wave propagates along an elastic object, particles at the surface move elliptically. A movable object (a slider or a rotor) pressed to the elastic object may be caused to move due to the frictional forces between it and the surface. A motor based on this principal has been constructed and studied. The vibration mode used is found to have an undesirable radial component, which restricts the efficiency of the motor to about 10% at best. A large amount of the energy supplied is lost by the slippage owing to the existence of the undesirable component. It is concluded that to derive larger output power, the frictional material needs to be carefully chosen. >

Minoru Kurosawa

Papers

Ultrasonic motors

Surface acoustic wave atomizer

An estimation of load characteristics of an ultrasonic motor by measuring transient responses

Ultrasonic linear motor using surface acoustic waves

An ultrasonic motor using bending vibrations of a short cylinder