Force is All you Need? Rethinking Acoustic-Only Prediction of Mid-Air Haptics Perceived Strength

Mid-air haptic systems use focused ultrasound to create tactile sensations in free space. However, predicting and calibrating these systems according to human perception often requires complex multi-physics models or lengthy user studies. In this work, we address this challenge by conducting an extensive measurement campaign, capturing perceived intensity, acoustic pressure, and force across varying heights and device voltages. Using this data, we evaluate four linear models to predict perceived intensity, culminating in a model that combines normalized force and distance. This model achieves strong predictive accuracy, demonstrating that force is a practical and effective predictor of perceived intensity. Our findings show that force, measured using an affordable precision scale, offers a straightforward alternative to complex pressure-based approaches, providing an accessible framework for characterizing mid-air haptic systems. This approach enables efficient, perception-driven design and optimization of mid-air haptic applications.