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Wind dispersal of battery-free wireless devices

Nature volume 603, pages 427–433 (2022)Cite this article

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Abstract

Plants cover a large fraction of the Earth’s land mass despite most species having limited to no mobility. To transport their propagules, many plants have evolved mechanisms to disperse their seeds using the wind1,2,3,4. A dandelion seed, for example, has a bristly filament structure that decreases its terminal velocity and helps orient the seed as it wafts to the ground5. Inspired by this, we demonstrate wind dispersal of battery-free wireless sensing devices. Our millimetre-scale devices weigh 30 milligrams and are designed on a flexible substrate using programmable, off-the-shelf parts to enable scalability and flexibility for various sensing and computing applications. The system is powered using lightweight solar cells and an energy harvesting circuit that is robust to low and variable light conditions, and has a backscatter communication link that enables data transmission. To achieve the wide-area dispersal and upright landing that is necessary for solar power harvesting, we developed dandelion-inspired, thin-film porous structures that achieve a terminal velocity of 0.87 ± 0.02 metres per second and aerodynamic stability with a probability of upright landing of over 95%. Our results in outdoor environments demonstrate that these devices can travel 50–100 metres in gentle to moderate breeze. Finally, in natural systems, variance in individual seed morphology causes some seeds to fall closer and others to travel farther. We adopt a similar approach and show how we can modulate the porosity and diameter of the structures to achieve dispersal variation across devices.

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Fig. 1: Wind-dispersed battery-free wireless devices.
Fig. 2: Wind-dispersal mechanism.
Fig. 3: Battery-free wireless sensor.
Fig. 4: Outdoor evaluation.

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Data availability

All data needed to evaluate the conclusions of the paper are available in the paper or in the Extended Data and Supplementary Information.

Code availability

Source code is available on a public GitHub repository for download: https://github.com/uw-x/wind_dispersal/.

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Acknowledgements

We thank S. Kaplan and J. Smith for feedback on the manuscript and K. Johnson, V. Arroyos and B. Nguyen for help with experiments. This research is funded by Moore Inventor Fellow award #10617 and grant FA9550-14-1-0398 from the US Air Force Office of Scientific Research. S.G. is also funded by the National Science Foundation.

Author information

Authors and Affiliations

  1. Paul G. Allen School of Computer Science and Engineering, University of Washington, Seattle, WA, USA

    Vikram Iyer & Shyamnath Gollakota

  2. Department of Electrical and Computer Engineering, University of Washington, Seattle, WA, USA

    Hans Gaensbauer & Shyamnath Gollakota

  3. Department of Biology, University of Washington, Seattle, WA, USA

    Thomas L. Daniel

Authors
  1. Vikram Iyer
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  2. Hans Gaensbauer
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  3. Thomas L. Daniel
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  4. Shyamnath Gollakota
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Contributions

V.I. designed and fabricated the hardware and performed experiments. S.G. and V.I. designed the overall system, experiments and evaluation. T.D. advised on the design and characterization of the drag-enhancing structures. H.G. implemented the backscatter code and sensor release mechanism used for outdoor testing. V.I. and S.G. wrote the manuscript; T.D. edited the manuscript. S.G. and V.I conceptualized the work.

Corresponding authors

Correspondence to Vikram Iyer or Shyamnath Gollakota.

Ethics declarations

Competing interests

S.G. is a co-founder of Jeeva Wireless, Wavely Diagnostics, and Sound Life Sciences.

Peer review

Peer review information

Nature thanks Elizabeth Farrell Helbing and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data figures and tables

Extended Data Fig. 1 Effect of outer ring on terminal velocity.

a, Terminal velocities of 26% fill structures with different diameters using a 30-mg payload. b, Terminal velocities of 55% fill structures with different diameters with and without an outer ring using a 30-mg payload.

Extended Data Fig. 2 Additional fill patterns.

Additional fill patterns used to vary porosity. Changes include concentric circles connecting horizontal spokes extending out from the centre with various spacings, as well as additional cuts in the concentric circles between spokes.

Extended Data Fig. 3 Fabrication process.

Fabrication process used to produce the curved drag enhancing structures.

Extended Data Fig. 4 SX1276 receiver on–off keying packet structure.

a, Packet structure for the SX1276 receiver operating in on–off keying mode. b, Minimal packet structure used for testing the lower bit rates of 1.5 and 4.8 kbps. CRC, cyclic redundancy check.

Extended Data Fig. 5 Supporting transmissions from multiple devices.

a, Natural variance of start-up time for outdoor measurements. b, Two waveforms recorded under similar light conditions show that natural variation in start-up time and time between packets reduces the probability of collisions. c, Addition of a random delay between each packet to reduce collisions. d, Network simulation of up to 1,000 nodes each transmit 100 packets. Node start and inter-packet transmission times are normally distributed based on power-harvesting data (N = 100 packets per node × 10 repetitions = 1,000). e, Network simulation with normally distributed start-up time assuming 1.4 klx followed by fixed 10-s delay between packets (N = 1000). f, Result of applying pseudorandom delays of up to 8 packet lengths with random start times assuming 1.4 klx (N = 1,000). The plot shows that this approach can support large networks where the data are transmitted at rates less than once every 10 s.

Extended Data Fig. 6 Additional power harvesting results.

a, Cold-start time required to charge the storage capacitor from zero to the time at which it can backscatter its first packet; measured using indoor LED lights (N ≥ 5, error bars = ±σ). b, Throughput of the sensor device after start up at different illumination levels indoors (N ≥ 5, error bars = ±σ). c, Measurements of power harvested at different light levels outdoors from our solar cells. (N ≥ 3, error bars = ±σ).

Extended Data Fig. 7 Drone mechanism to drop the sensors.

a, Small quadrotor with the mechanism used to drop devices from altitudes over 5 m outdoors. b, Drop mechanism consisting of a solenoid that can be wirelessly triggered by a Bluetooth transmission. Upon triggering, the supercapacitor keeps the solenoid retracted for a few seconds allowing the wire holding the sensor in place to fall freely. Because our evaluation requires tracking each individual structure, the drone attachment currently drops a single device. It can be extended to drop multiple devices simultaneously using a similar mechanism.

Extended Data Fig. 8 Sensor calibration set-up using a weather station.

a, Picture of weather station used for reference temperature, humidity, solar radiation and pressure measurements, and placement of the test wireless sensor node. b, Correlation of small onboard light sensor readings with reference solar radiation data. c, Correlation of small, onboard temperature sensor (HDC2010) readings with reference solar radiation data. d, Correlation of onboard temperature sensor temperature sensor (BME280) readings with reference solar radiation data.

Extended Data Fig. 9 Prototype full-duplex cancellation of our narrowband signals.

a, Full-duplex cancellation block diagram. b, Results of applying full-duplex cancellation to reduce transmitter interference for backscatter.

Extended Data Table 1 Sensor power measurements and part numbers
Full size table

Supplementary information

Supplementary Information

This file contains three Supplementary Tables and their accompanying legends; and the legends for Supplementary Videos 1–6.

Supplementary Video 1

Vertical wind tunnel test.

Supplementary Video 2

Effect of outer ring.

Supplementary Video 3

Effect of stiffness.

Supplementary Video 4

Unstable descent of solid discs.

Supplementary Video 5

Self-righting behaviour.

Supplementary Video 6

Outdoor wind dispersal.

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Iyer, V., Gaensbauer, H., Daniel, T.L. et al. Wind dispersal of battery-free wireless devices. Nature 603, 427–433 (2022). https://doi.org/10.1038/s41586-021-04363-9

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