Fig. 1: Ultrasonic moisture extraction concept and a high-efficiency extractor prototype.

a The ultrasonic extractor comprises a PZT-crystal piezoelectric transducer and a stainless-steel (SS) porous membrane through which the desorbed water is extracted from a sorbent material under vibrational actuation. The black dashed box shows the transducer structure, including an Ag-coated PZT ring topped with a thin layer of water-resistant resin attached to the SS membrane and encased in a silicone elastomeric ring. The red dashed box shows the structure of the micro-machined nozzles on the SS membrane, which assist in directing the flow of water out of the device. b The diagram of the system assembly and sorption/desorption stages of the moisture harvesting process utilizing a sorbent material and a micro-actuator. The top Ag layer and the SS membrane are connected to the electrode wires. c A CAD model of the system custom-designed to collect the moisture extracted from the sorbent by the actuator. d A photograph of the FDM-printed device prototypes with hydrogel sorbents in the process of moisture harvesting from ambient air. The inset shows a close-up view of the collected water droplets on the glass enclosure. e Efficiency values of the moisture extraction achieved in this study compared with the state-of-the-art literature data (here, s = short actuation period; l= long actuation period; s_m = multiple repetitive cycles of short actuation periods). Scale bars: 50 µm (a); 15 mm (d).