Toward a low-cost disdrometer: simulating the collision of raindrops with a cantilever piezo film

Raindrop size distribution (DSD) is the key factor to derive reliable rainfall estimates. It is strongly related to a number of integral rainfall parameters, including rain intensity (R), rain water content (W) and radar echo (Z). Disdrometers are the senors commonly used to measure DSD based upon microwave or laser technologies; such as JWD (Joss-Waldvogel Disdrometer), Parsivel and 2DVD (Two-Dimensional Video Disdrometer). These sensors have different strengths and weakness, and they are relatively expensive. This hinders the possibility to have a large-scale and high-density observation of DSD. In this work, our goal is to explore the possibility to develop a lightweight and low-cost disdrometer with high accuracy.

We start with establish a model that can well simulate the signal reaction of a single drop falling on a cantilever piezo film. A series of experiments were conducted to test the reaction of drops with different sizes (diameters ranging from 2 - 4 mm) and as drops falling onto different locations of the film. We then modelled the collision by assuming the piezo film to be a damped cantilever beam and drop force to be a step force; and the drop force is derived based upon the measurement of the deflection of beam end, which is further used to fit the damp ratio. Preliminary results suggest that the signal reaction of a single drop hits can be well simulated based upon the proposed model under current experimental setting. More experiments and simulations are currently undergoing to explore the capacity of the proposed model with different drop falling velocity, size and position, as well as its reaction of multiple drops.