Battery-free, wireless, and electricity-driven soft swimmer for water quality and virus monitoring

Miniaturized mobile electronic system is an effective candidate for in situ exploration of confined spaces. However, realizing such system still faces challenges in powering issue, untethered mobility, wireless data acquisition, sensing versatility, and integration in small scales. Here, we report a battery-free, wireless, and miniaturized soft electromagnetic swimmer (SES) electronic system that achieves multiple monitoring capability in confined water environments. Through radio frequency powering, the battery-free SES system demonstrates untethered motions in confined spaces with considerable moving speed under resonance. This system adopts soft electronic technologies to integrate thin multifunctional bio/chemical sensors and wireless data acquisition module, and performs real-time water quality and virus contamination detection with demonstrated promising limits of detection and high sensitivity. All sensing data are transmitted synchronously and displayed on a smartphone graphical user interface via near-field communication. Overall, this wireless smart system demonstrates broad potential for confined space exploration, ranging from pathogen detection to pollution investigation.


Supplementary Tables
Summary of the mass and dimensions of individual SES system accessories.

Fig. S2 .
Fig. S2.Fabrication process of the flexible circuit copper electrode.Photolithography and wet etching are used to pattern 18-μm-thick copper electrodes on a 12.5-μm-thick polyimide substrate.

Fig. S3 .
Fig. S3.Flexibility characterization of wireless power and communication modules.(A-D) Flexible receiver and NFC electrodes.(E-H) Modules on flat and curved surfaces.(I-K) Small resonant frequency drifts demonstrate stable wireless operation during bending.

Fig. S4 .
Fig. S4.Wireless SES' navigation in a closed-loop pipe.(A) The swimmer completes two laps around the circular channel through untethered, multi-turn steering.(B) The moving angles versus the time during the two laps.

Fig. S5 .
Fig. S5.Controllable path steering of the upgraded SES in confined spaces.(A) The coordinate location and steering path.(B) The direction steering during the motion.When the RF coil was directly above the two receiver antennas, the swimmer swam forward.When the RF coil was above one of the antennas, the swimmer turned to the left and to the right.

Fig. S6 .
Fig. S6.Actuation coil magnetic field simulation.(A) Position of the magnets in relation to the actuation coil.(B) Plot of normalized flux versus distance between magnet and coil.(C) FEA simulation results of the actuation coil's magnetic field strength distribution at different distances.

Fig. S7 .
Fig. S7.Continuous tail undulation of SES in water for efficient swimming.

Fig. S8 .
Fig. S8.Floating performance of the aerogel silicone foam.(A) A pure PDMS support and an aerogel PDMS foam support fall into the water.The pure PDMS support sinks to the bottom, yet the aerogel PDMS foam support floats.(B) The aerogel silicone foam support floats from the bottom to the surface of the water.

Fig. S9 .
Fig. S9.Centroid and center of mass simulations.(A) Coordinate axes applied on the SES system from the top view and side views.(B) Centroid and center of mass positions for 8 mm tail SES system.(C) Centroid and center of mass positions for varied tail lengths.

Fig. S10 .
Fig. S10.Soft tails with different lengths.(A) Designs of tail lengths of 3 mm, 8 mm, 13 mm, 18 mm and 23 mm.Tail length is defined as the distance between the magnet center and the tail end.(B) Photograph of the fabricated tails.

Fig. S11 .
Fig. S11.Tail thickness and flexibility.(A) The swimmer tail thickness is 0.6mm.(B) Curling the swimmer tail with a round straw.(C) Twisting the swimmer tail.

Fig
Fig. S12.FEA simulation analysis of the SES' resonant frequencies and vibration modes in air.(A) Schematic of the vibration modes' top view (left) and section view (right) along the white dashed line.(B) Resonant frequencies corresponding to vibration mode 1-3.

Fig
Fig. S13.FEA simulation analysis of the SES' resonant frequencies and vibration modes in water.Schematic of the resonant mode 1 (top) and resonant 2 (bottom) for the swimmer with different tail length.

Fig. S14 .
Fig. S14.Rear view of tail beating behavior during one actuation cycle.

Fig. S16 .
Fig. S16.Displacement per cycle versus input voltage for an 8mm tail swimmer at 15Hz.(A) 0.8 mm displacement per cycle at 300mV input voltage.(B) 1.8 mm displacement per cycle at 500mV input voltage.(C) 2.2 mm displacement per cycle at 700mV input voltage.

Fig. S17 .
Fig. S17.Integrated sensor design.(A) Design of the integrated sensor with a SARS-CoV-2 senor, a Cl -senor and a NH4 + sensor.(B) Photograph of the fabricated sensor electrodes.

Fig. S22 .
Fig. S22.Front-and back-view of the SES monitoring system.

Table S2 :
Information summary of SES in this work and animals that swim in a similar manner.

Table S3 :
Coordinates of the centroid and center of mass for the SES system.

Table S4 :
Material parameters used in the dynamic simulation.

Table S5 :
Comparison with other existing actuation approaches.