This robot can also dive and come back to the surface. Faster flapping results in strong downward waves that push the robot upward, while slower flapping creates weaker upward waves that allow it to move further down. (Real manta rays sink when they slow down.) It also proved he could take a load from the bottom of a tank and bring it to the surface.
Eating on the go
Because manta rays are essentially giant moving water filters, researchers at MIT looked to them and other mobula rays (a group that includes manta rays and devil rays) for inspiration in figuring out possible improvements to industrial water filters.
Manta rays feed by leaving their mouths open while they swim. On the underside of both sides of a manta ray's mouth are structures known as mouth plates, which look something like a dashboard air conditioner. When water enters the mouth, plankton particles too large to pass through the plates bounce further down into the manta's body cavity and eventually into the stomach. Gills absorb oxygen from the water that spouts out, allowing the manta ray to breathe.
The MIT team was particularly interested in mobula rays because they thought the animals had struck an ideal balance between letting in water quickly enough to breathe and maintaining highly selective structures that prevent most plankton from escaping into the water. To create a filter as close to a mobula beam as possible, the team 3D printed plates that were then glued together to create narrow gaps between them. Particles that do not pass flow into a waste reservoir.
When pumping slowly, water and smaller particles flowed out of the filter. When the pumping was accelerated, the water created a vortex in each orifice that allowed water, but not particles, to pass through. The team realized that this is how mobula rays are such successful filter feeders. They need to know the right speed to swim so that they can breathe and still get an optimal amount of plankton in their mouths.
The team believes that incorporating vortex action “will extend the traditional design of [industrial] filters,” as they said in a study recently published in PNAS.
Manta rays may look alien, but there's nothing sci-fi about the way they use physics to their advantage, from powerful swimming to efficient (and simultaneous) eating and breathing. Sometimes nature comes along with the most ingenious technical upgrades.
Scientific Progress, 2024. DOI: 10.1126/sciadv.adq4222
PNAS, 2024. DOI: 10.1073/pnas.241001812
