Squid-inspired soft superpropulsion

TL;DR

This paper introduces superpropulsion, a mechanism where squid-like compliant nozzles store and return energy during pulsed jets, significantly enhancing propulsion efficiency and reach.

Contribution

It reveals the biological basis of superpropulsion and demonstrates engineered nozzles that achieve over 300% impulse amplification through timing optimization.

Findings

Engineered nozzles with matched response times significantly increase impulse.

Superpropulsion enhances jet reach and plume dispersion.

Gains persist after miniaturization, applicable to soft robotics.

Abstract

Squid span four orders of magnitude in size yet rely on pulsed jets. We show that the funnel (siphon) is a compliant nozzle whose dilation and recoil lag mantle contraction, storing and returning energy within each pulse, a mechanism we term superpropulsion. Histology reveals a collagen sheath, and chromatophore tracking in two squid species quantifies a repeatable phase lag. Engineered nozzles, 3D fluid-structure simulations, and a reduced-order mathematical model predict > 300% impulse amplification when nozzle response time matches jet acceleration (tau/T = 0.2-0.4), overlapping in vivo timing. Tuned nozzles extend jet reach, enhance plume dispersion, and improve jet-driven boat transport, with gains persisting after 40x miniaturization. Superpropulsion recasts pulsed jets as impedance matching, with a soft nozzle acting as an elastic capacitor that passively shapes impulse delivery in soft robotic thrusters and fluidic actuators.