Constant-power versus constant-voltage actuation in frequency sweeps for acoustofluidic applications

TL;DR

This paper compares constant-power, constant-voltage, and constant-voltage across the transducer methods in frequency sweeps for acoustofluidic devices, highlighting the most reliable approach for resonance characterization.

Contribution

It introduces a systematic comparison of three actuation methods, demonstrating that constant power dissipation provides the most accurate resonance detection.

Findings

Constant power dissipation reveals true resonance frequencies.

Constant voltage across the transducer favors low-impedance resonances.

Constant voltage input is affected by amplifier and wiring impedance.

Abstract

Supplying a piezoelectric transducer with constant voltage or constant power during a frequency sweep can lead to different results in the determination of the acoustofluidic resonance frequencies, which are observed when studying the acoustophoretic displacements and velocities of particles suspended in a liquid-filled microchannel. In this work, three cases are considered: (1) Constant input voltage into the power amplifier, (2) constant voltage across the piezoelectric transducer, and (3) constant average power dissipation in the transducer. For each case, the measured and the simulated responses are compared, and good agreement is obtained. It is shown that Case 1, the simplest and most frequently used approach, is largely affected by the impedance of the used amplifier and wiring, so it is therefore not suitable for a reproducible characterization of the intrinsic properties of the acoustofluidic device. Case 2 strongly favors resonances at frequencies yielding the lowest impedance of the piezoelectric transducer, so small details in the acoustic response at frequencies far from the transducer resonance can easily be missed. Case 3 provides the most reliable approach, revealing both the resonant frequency, where the power-efficiency is the highest, as well as other secondary resonances across the spectrum.