Design of interdigitated transducers for acoustofluidic applications

Abstract

Interdigitated transducers (IDTs) were originally designed as delay lines for radars. Half a century later, they have found new life as actuators for microfluidic systems. By generating strong acoustic fields, they trigger nonlinear effects that enable pumping and mixing of fluids, and moving particles without contact. However, the transition from signal processing to actuators comes with a range of challenges concerning power density and spatial resolution that have spurred exciting developments in solid-state acoustics and especially in IDT design. Assuming some familiarity with acoustofluidics, this paper aims to provide a tutorial for IDT design and characterization for the purpose of acoustofluidic actuation. It is targeted at a diverse audience of researchers in various fields, including fluid mechanics, acoustics, and microelectronics.

Aerosol jet printing of surface acoustic wave microfluidic devices

“…6 . Other factors, such as mass loading, frequency, capacitance, and inductance, can also influence the measured displacement 48 , 81 , 85 , 86 . Although the cleanroom fabricated device shows the best performance, the performance of the silver nanowire printed device is still favorable.…”

“…The fabrication process often requires several steps, including photolithography, metal evaporation, and chemical lift-off techniques. Photolithography processes add a layer of complexity due to the high-resolution masks that are required to fabricate the microscale interdigital transducer finger widths, which are typically proportional to 1/4 th the wavelength of the resonant frequency of the SAW 46 – 48 . Metal evaporation techniques coupled with the photolithography process also require cleanroom access and are expensive in terms of the cost of use, materials, and high-vacuum equipment itself.…”

Recent progress on acoustofluidic manipulation of cells and particles

“…Factors contributing to diffraction include scattering by the electrodes within the IDT, the ratio of the IDT aperture to the acoustic field wavelength, and the propagation distance [34,72,73]. Each finger electrode acts as a scattering source for the acoustic wave, and high-frequency IDTs, which contain a larger number of finger electrodes than low-frequency IDTs, are more susceptible to diffraction [74,75]. To inhibit diffraction-induced peripheral vortices, one conventional solution is to widen the aperture, thus generating broader areas where the acoustic radiation force is dominant.…”

Wave-based sensor responses with embedded electrode layouts

“…The circular layout has the potential to generate waves in a larger area of the piezoelectric substrate and can be extended in multi-axial sensing. Lastly, the slanted type features a varying finger spacing across the electrode's length, enabling the sensor to operate in a wide frequency range 1 . All the layouts are designed with a 2.5 mm delay line (distance between input and output electrodes), 50 µm spacing, 6 input pairs, 3 output pairs, and 0.5 metallization ratio.…”

“…Acoustic wave-based piezoelectric sensors have emerged over the decades in multiple disciplines as an ideal candidate for structural health monitoring (SHM) methods because of their adjustable frequency range, easy processability, and wireless capability [1][2][3][4] . Evaluation of strain concentrations during the additive manufacturing process demands a micro-sized sensor that can detect meaningful information wirelessly to ensure quality.…”