Ultrasonic trapping of small particles by sharp edges vibrating in a flexural mode

Abstract

Ultrasonic trapping of small particles by sharp edges vibrating in a flexural mode is reported. Two rectangular metal plates with a sharp edge are mechanically excited to vibrate in a flexural mode by the piezoelectric rings which are pressed between them by a bolt structure. Small particles such as mint seeds and flying color seeds can be attracted to the sharp edges of the plates. Relationship between input power applied to the piezoelectric rings and the number of trapped particles is experimentally investigated for mint seeds and flying color seeds in water and air. The result shows that for a given type of particle, there exists an input power at which the number of trapped particles is a maximum. Mechanism analysis shows that nodes or antinodes of acoustic pressure of the sound field near the sharp edges are responsible for the trapping.

Microscale acoustofluidics: Microfluidics driven via acoustics and ultrasonics

“…Employing lab-fabricated, focusing ultrasonic transducers from Y-cut LN in thickness-mode operation at 23-37 MHz, they were able to trap and retain oleic acid drops of around 125 m diameter in water in a region of a few hundred microns in size. Hu et al (2004) presented a simple arrangement to trap individual particles, brine shrimp, thyme, salt crystals, and similar objects with a size of around 50-900 m, in the pressure node between vibrating, tapered beams while operating in air or water. This route came about from the group's work in acoustic levitation, and indeed the literature in that area, for example, Hertz (1995), is worth consulting in considering new ideas for trapping particles with acoustics.…”

“…Circumventing the limitations of current microfluidics technology is indeed critical to delivering on its idyllic promises (Ho et al, 2011), from handheld medical diagnostic devices for the rapid detection of single molecules associated with heart disease (Gerszten and Wang, 2008), cancer (Lu et al, 2005), and physiological fluid chemistry (Craighead, 2006), to water purification (Shannon et al, 2008) and polymerase chain reaction on a chip (Huang et al, 2006). Fortunately, acoustic wave technology at the microscale to nanoscale is helping to make these things reality, as will be shown, and furthermore promises to allow researchers to produce and exploit interesting physical phenomena seen at the microscale-to-nanometer scale.…”

Ultrasonic microfluidic transportation based on a twisted bundle of thin metal wires

“…The length of the metal wire bundle immersed in water was about 3 mm. When a driving voltage with a frequency close to the resonance frequency was applied to the ultrasonic transducer, the thickness mode vibration could be excited in the transducer [13][14][15]. This resulted in an ultrasonic vibration in the thin metal wires.…”

“…Ten copper wires with a diameter of 199 m each form the bundle, and the bundle length is 38 mm beyond the stainless steel plates. The ultrasonic transducer has a sandwich structure with a multi-layer piezoelectric vibrator at the center, which is formed by four piezoelectric rings (C203, Fuji Ceramics, Japan) [13][14][15]. The outer diameter, inner diameter and thickness of each piezoelectric ring are 20, 12 and 2.4 mm, respectively.…”

Acoustophoretic cell and particle trapping on microfluidic sharp edges

“…In literature, particle attraction to oscillating structures has previously been observed in centimeter-scaled setups: The attraction of ∼ 1 mm particles to oscillating sharp edges (Hu et al 2004), rods (Liu and Hu 2009), and needles (Hu et al 2007) was reported in the kHz range. In these cases, the described physical effects were also based on acoustic radiation forces, yet with a different structural setup and physical modeling.…”