Design and Assessment of an Ultrasonic Pollination System for Greenhouse Tomatoes

This work presents the design and the first quantitative greenhouse assessment of an ultrasonic device that pollinates tomato flowers without physical contact. Greenhouse tomato production relies on commercial bumblebee hives, which entail recurring costs, management and regulatory constraints, and biosecurity risks. A portable handheld airborne ultrasonic device integrating two synchronized open-hardware phased-array modules (2 × 256 elements, 40 kHz carrier) was developed, with electronic phase control for focal-point steering and amplitude modulation (20 Hz–1 kHz) to excite floral vibrations. A coupled finite-element/boundary-element model indicated that reducing the acoustic wavelength toward millimeter-scale floral dimensions increases acoustic–structure coupling. Performance was evaluated in a greenhouse on 102 tomato plants divided into three groups (untreated controls, a commercial vibrating wand, and ultrasonic actuation) at operating distances of 0.1–0.3 m, using a single module aimed by one operator. Focused ultrasound produced sound pressure levels of 155–160 dB (RMS, re 20 µPa) at the focal point, and ultrasonic pollination consistently achieved fruit-set rates above 90% (up to 96.5%), approaching the commercial vibrating wand (94%), whereas untreated controls remained at 53–65%. Under the greenhouse conditions and working distances tested, focused, modulated airborne ultrasound may therefore offer a promising non-contact alternative to contact-based pollination. Occlusion sensitivity, acoustic attenuation, and operator exposure remain to be addressed.