Controlling surface acoustic wave atomization for high rates or fine particles via distinct broad- and narrow-film regimes enabled by an external capillary feed

Surface acoustic wave atomization holds immense potential for microfluidics and drug delivery, yet its commercial viability is throttled by a critical trade-off: high power inputs required for high throughputs inevitably lead to thermal failure. In this study, we present a breakthrough solution driven by logical progression from engineering optimization to physical discovery. First, we optimize the liquid delivery by replacing complex, active microfluidic channels with a simple, passive external supply using wetting paper strips. This low-cost, high-efficiency approach effectively decouples the liquid reservoir from the acoustic source. Second, this robust liquid management solves the thermal crisis and uncovers two distinct fluid dynamic regimes previously masked by device failure: the broad-film regime and the narrow-film regime. Third, we characterize the distinct performance advantages unlocked by these regimes: the broad-film regime utilizes thin-film lubrication physics to produce remarkably fine aerosols (0.7 μm), while the narrow-film regime leverages violent liquid column breakup to achieve record-breaking throughputs (1.1 ml/min). This study transforms structural optimization into a fundamental control strategy, offering a versatile platform for both precision nanomedicine and high-flux coating applications.