April 2012, Scientific American

The race is on to develop advanced new multifunctional

biomimetic jellyfish robots. What does this hold for the

future of aquatic engineering?

By Jacie Sales

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AQUATIC SCIENCE

Scientific American, April 2012

It turns out that one of the features that makes

jellyfish swimming so efficient and that consequently

pushes scientific study of the jellyfish is its propulsion

frequency. Namely, if the jellyfish contracts its bell at

resonant frequency, the amplitude of oscillation increases

by 40% and the energy cost is reduced by 35% of the to-

tal cycle cost. [12] Clearly, this swimming feature offers

great potential for energy efficient systems and incites

exploration into the physiology and mechanics surround-

ing the unique frequency pattern.

Dissecting Efficiency

Physiologically, the jellyfish is in effect a

stretchy bag of fluid. Resembling a thick-walled para-

chute, the body, or bell, of the jellyfish is made almost

completely of water and consists of three layers: the outer

epidermis layer, the middle mesoglea (jelly) layer, and

the inner gastrodermis layer. [5] (See Figure 1) Spanning

a surprisingly wide range of tissue properties, the meso-

glea consists of several different fiber types and func-

tional patterns and divides into two general layers. The

stiff outer layer of the mesoglea, a mucopolysaccharide

matrix reinforced by both thick (1.5-1.8 μm) and thin (6-

15 nm) elastic fibers, maintains the stiffness and shape

vital for energy storage within the bell. [7] On the other

hand, the inner mesoglea consists of eight triangular

cross-sectional regions which lower stiffness, thus allow-

ing the bell to fold during contraction.

Ground-breaking research into the biomechanics

and locomotion of jellyfish is fueling the development of

aquatic vehicles and biomimetic robots capable of swim-

ming with drastically reduced energy costs and multiple

degrees of freedom. Though this research is not the first

in biologically-inspired robotics, it is proving to be some

of the most fruitful and scientifically rewarding. Already

teams around the world have produced state-of-the-art

designs and sub aquatic devices, and the jellyfish studies

are rapidly gathering momentum and new insights. With

countless applications and the incorporation of many new

technologies, this “jelly rush” is paving the way not only

for the future of energy efficiency, but also for the entire

field of aquatic engineering. The secret resides in the

unique—though easily overlooked—undulating motion

of the swimming jellyfish.

To the naked eye, there isn’t much to jellyfish

movement. It is driven by repeated cycles of pulsations

of the umbrella-shaped bell. These pulsations squeeze

the volume of water within the cavity, and since water is

effectively incompressible, the water is ejected through

the bell opening, creating the driving propulsion—simple

fluid mechanics. Yet if it’s so simple, why study jelly-

fish at all? Granted it may be intriguing and strangely re-

laxing to stare at a swimming jellyfish in an aquarium or

on the nature channel, but how can such seemingly sim-

ple motion be so scientifically enlightening?

DISSECTING EFFICIENCY p.2

Physiology and muscle synchro-nization shape the jellyfish’s smooth swimming style.

RESONATING EFFECTS p.3

Maximum efficiency is achieved when the bell contracts at reso-nance frequency.

RINGS OF POWER p.3

The unique vortex wake pattern provides an extra push for in-creased thrust and acceleration.

DAWN OF THE AGE OF ROBOTS p.4

New biomimetic designs usher in waves of aquatic advancement.

HE JELLYFISH: A 500 MILLION YEAR OLD, SPINLESS, SACK OF JELLY. Take it

out of water and it collapses into a quivering blob with all the menace of a jello-mold. Yet

believe it or not, within this absurdly simple creature lies the answers to some of man’s most pondered

problems.

T

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April 2012, Scientific American

Adding to this folding pattern is the peculiar jel-

lyfish musculature. Unlike fish or even squids, jellyfish

have only one set of swimming muscles, which are an-

tagonized only by the elasticity of the bell. When motor

neurons around the edges of the

mesoglea muscle sheet synapse

it creates a muscle action poten-

tial, staggered in the circumfer-

ential direction. This reinforces

the efficient tendency of the

mesoglea to fold first near the

joints and later between the

joints, extending the radial fi-

bers. [7] Additionally, the ve-

lum muscles, a separate group

from the bell contraction mus-

cles, are responsible for thrust

and turning. By contracting dur-

ing the jet stroke, they create a

nozzle and consequently in-

crease the velocity of the flow

out of the bell along with the to-

tal forward thrust. The radial muscles of the velum con-

tract asymmetrically, pointing the nozzle off-axis to al-

low the jellyfish to turn. [7] The total effect of this pre-

cise orchestration between turning and contracting mus-

cles combined with the jellyfish’s unique physiology

shapes its system of free, smooth swim.

Resonating Effects

While the distinctive musculature of the jellyfish

generates propulsion, the real question, energy efficiency,

is shaped almost exclusively by frequency. Swimming

requires the jellyfish muscles to generate enough force to

expel the water from within the bell. Since the force of

the jet equals the mass of water times acceleration, the

jellyfish generates more thrust by expelling a greater vol-

ume of water and thus jetting greater mass. Similarly,

the jellyfish increases acceleration by squeezing the bell

more rapidly. These optimal swim styles coalesce to

form the remarkably efficient resonant swim gait. In this

gait the jellyfish bell contracts at resonant frequency,

which entails beginning the next pulse just as the bell

reaches its maximum extension after refilling. [7] The

key to the added efficiency: effective use of maximum

extension. Larger than the resting diameter, the maxi-

mum extension achieved during the resonant gait pro-

vides the jellyfish with an extra volume of water for the

subsequent jet. Since thrust pro-

duction of the system is propor-

tional to the mass of the water

ejected during contraction, the

additional volume can be used by

the jellyfish to increase its for-

ward acceleration while simulta-

neously reducing the overall en-

ergetic cost. The obvious advan-

tage of this doubly cost-effective

super-gait makes the jellyfish the

ruling king of undersea energy

conservation.

Rings of Power

As if the jellyfish did not

have enough energy-saving

tricks, one more bonus swim

phenomenon—vortex rings—proffers an even higher

level of propulsive efficiency. When the jellyfish bell

contracts, it produces a high pressure in the subumbrellar

chamber. This pressure generates the expulsion of fluid,

which results in vortex rings, doughnut-shaped swirls of

water that basically push the jellyfish forward. More

specifically, the sudden ejection of a jet during swim-

ming causes a roll-up of the jet layer. This roll-up cre-

ates a pulsed series of vortex rings, or toroids, which

propagates down-stream under its own self-induced ve-

locity. Vortexes merge in a laterally oriented vortex su-

perstructure that induces flow both toward the subum-

brellar surface and downstream. The rings then pass se-

quentially down the length of the jellyfish, accelerating

additional ambient fluid and thus augmenting the total

propulsive thrust. [1] So even without trying, a byprod-

uct of the jellyfish’s standard swimming is an added driv-

ing force propelling the animal forward at virtually no

cost. With this simple yet highly effective propulsion,

the jellyfish cannot help but be the quintessential model

of efficiency and a very attractive paradigm to research-

ers developing aquatic vehicles and biomimetic robots.

JELLY LAYERS including the epidermis, the

mesoglea jelly, and the gastrodermis.

http://www.cabrillo.edu/~jcarothers/lab/notes/radiata/VISUALS/images/MainFrame_clip_image005.png

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Scientific American, April 2012

pact microbots, an important factor when considering the

powering of the robotic system. Because the electromag-

netic structure of traditional motors is difficult to shrink,

other powering methods must be used, making simplicity

not just a benefit but a necessity. Another strongly

sought after characteristic of jellyfish swim is its multiple

degrees of freedom. This feature means that robots mod-

eled after jellyfish would be capable of walking and

swimming freely and smoothly in water or aqueous me-

dia, a great benefit for the potential jellyfish biomimetic

robot applications. Such constantly-growing applications

include pollution detection, video mapping, exploration

of unstructured underwater environments, and even

search and rescue missions for both civilian and military

purposes. The robots could also be very effectively used

for underwater surveillance since they would operate in-

cognito as real jellyfish. And as an added bonus, jelly-

fish have few natural predators. It would not be very

practical to dedicate time and money towards launching a

robot only to have it eaten by the first creature to come

swimming along. These and countless other advantages

and applications of the jellyfish model propel it to the

forefront of modern aquatic technology and make it the

superlative selection for biomimetic robotics. Armed

with the prized jellyfish blueprints, the only question re-

maining is how scientists will wield this powerful

weapon in the fight for underwater technological ad-

vancement.

Dawn of the Age of Robots

Biomimetics, the innovative offspring of engi-

neering and nature, is the well-established though ever-

expanding field that employs nature’s designs as engi-

neering models. After all, every species is a success

story, optimized by millions of years of natural selection.

Why not tap into the vast evolutionary goldmine? The

aim of biomimetics is to replicate biological systems us-

ing artificial materials, thereby enhancing the efficiency

of the overall engineering system. The first step in the

biomimetic process: find a biological design efficient

enough to produce noticeable technological results. This

is where the jellyfish comes into play. Simple, elegant,

and radically efficient, the jellyfish is the optimal candi-

date for biomimetic robots, a fact realized and utilized by

research teams around the world working on enhanced

underwater vehicles. So what makes a jellyfish robot so

superior to any other sea creature model? The most obvi-

ous advantage is the extreme energy efficiency offered

by the unique jellyfish swim style. The race for sustain-

able energy is underway, and in such times only energy-

saving designs are technologically competitive or even

viable. In this area jellyfish research offers not only in-

ventive robotics opportunities, but also insight into the

production and better use of energy. Additionally, the

simplicity of the jellyfish design allows for simple, com-

VORTEX RINGS created by jellyfish propulsion. (left) Medusa vortex wake visualized by injecting dye.

(right) Corresponding medusa vortex wake model. http://jeb.biologists.org/content/208/7/1257/F3.large.jpg

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April 2012, Scientific American 5

DESIGNS

Tak ing on the World One J e l lybot at a T i me The product of many different research teams working on jellyfish biomimetics: many different promising designs for jellyfish biomimetic robots. And while there is no clear winner, each de-sign offers a new insight and brings a new element to the table, from novel materials to innova-tive fuel sources. Every robot is unique and worth examination in painting the big picture of jel-lyfish biomimetics.

What’s new? Simple yet effective, Trijelly offers a new take on the definition of the optimal shape for a jellybot model. The primary feature of the Trijelly, as in-dicated by the name, is the triangular prism body, the purpose of which is to increase thrust by increasing volume change during contraction. The prototype also contains two pectoral fins, augmenting forward propulsion through the added push of flapping fins.

How does it work? Vinyl film encloses the front and back sides of the body, and two thin square plastic boards enclose the left and right sides. Driven by an actuator, when voltage is applied to Trijelly, the actuator shrinks. This causes the vinyl film to fold and the two plastic boards to compress the contents of the robot body cavity, producing the propulsive force. The actuator additionally powers the two pectoral fins, which flap to obtain fast forward swim speeds. [10] Overall experimental results of the prototype robot demonstrate great effi-ciency, increased swimming and floating speeds with increased voltage, and significant boosting of swim speeds thanks to the added thrust of the unique pectoral fin design.

Trijelly Jellybot With a Triangular Prism Body Shi et al., International Conference on Complex Medical Engineering

July 2010

TRIJELLY DESIGN with triangular prism body and two

pectoral fins. http://ieeexplore.ieee.org/stamp/stamp.j5558830&1

Driving Mechanism

Prototype

Scientific American, April 2012 6

DESIGNS

What’s new? With cutting edge materials, inventive tech-niques, and even a novel approach to input fre-quency, Bionicjelly strives for the maximum of biomimetic potential. The prototype uses ionic polymer metal composite (IPMC) actuators, ther-mally treated to imitate the curve of the jellyfish bell. Also, to utilize the efficiency of the jellyfish propulsion frequency, a bio-inspired signal was generated, almost exactly mimicking the real lo-comotion of a swimming jellyfish.

How does it work? First of all, what makes IPMC so advanced and functional is that it displays artificial muscle be-havior, a perfect material for modeling actual living systems. Under even low applied voltage, ion migration and electrostatic repulsion result in large bending deformation and consequent pro-pulsion. In addition, Bionicjelly’s bio-inspired electrical input signal with pulse-recovery process generates a much higher velocity and thrust in comparison with pure sinusoidal excitations with equal rms. [12] The combination of these two highly-efficient assets give Bionicjelly a fighting edge in the jellybot revolution.

Bionicjelly Jellybot Made of Ionic Polymer Sung-Weon Yeom et al., Chonnam University School of Mechanical Engineering

June 2010

BIONICJELLY PROTOTYPE components including IPMC actuator. http://iopscience.iop.org/0964-1726/18/8/08500

Testing Apparatus

Bio vs. Sinusoidal Signal

April 2012, Scientific American 7

Biomimetic robots are so innovative and effec-

tive because they combine the best of two worlds: engi-

neering and nature. As technologies progress, we can al-

ways look to biology to offer the simplest yet most effi-

cient designs. The jellyfish is the ultimate example of

this, and with its unique locomotion and energy efficient

propulsion, it paves the way for the future of aquatic

engineering.

DESIGNS

Hydrojelly Jellybot Fueled By Hydrogen Tadesse et al., Virginia Tech University

March 2012

What’s new? One of the most revolutionary designs of our time, Hydrojelly heralds in an age of life-like robots and infinite energy. Two features in particular give Hy-drojelly ascendancy over the many existing jellybot designs. First, this unique robot uses Shape Mem-ory Alloy (SMA), an alloy that returns to its original cold-forged shape when heated. And second, Hy-drojelly is the first underwater robot to use external hydrogen as its fuel source, the advantages of which are innumerable since a significant portion of water is hydrogen.

How does it work? Beneath the life-like Hydrojelly exterior, hydrogen and oxygen fuel meet in channels running over a platinum catalyst. The hydrogen-oxygen reaction produces heat, which carbon nanotubes conduct to the SMA; and since SMA material bends when heated, it contracts the outer umbrella of the robot, thus propelling it forward. [11] The SMA material then returns to its original shape, ready to contract again. In all, the process almost exactly mimics the swimming of a real jellyfish, a feat not easily accom-plished. Plus, hydrogen power means that Hydro-jelly regenerates fuel from its natural surroundings, thus theoretically never running out of energy.

LIFELIKE HYDROJELLY PROTOTYPE with sili-

con bell and SMA actuator. http://iopscience.iop.org/

0964-1726/21/4/045013/

Prototype

Hydrogen-Oxygen Reaction

Driving Mechanism

Carbon Nanotubes

A Novel Jellyfish-like Biomimetic Microbot. Shi et al. in IEEE, July 2010. http://ieeexplore.ieee.org/ stamp/stamp.jsptp=&arnumber=5558830 A Biomimetic Jellyfish Robot Based on IPMC. Yeom et al. in Smart Materials and Structures, Vol.18; 2009 http://iopscience.iop.org/ 0964-1726/ 18/ 8/5002 Vortex Rings in Bio-inspired and Biological Jet Propulsion. Krueger et al. In Advances in Science and Technology, Vol. 58, pages 237-247; 2008. http://sci.odu.edu/ biology/ directory/ bartol_pub/ Krueger_2008. Hydrogen-fuel-powered Biomimetic Jellyfish. Tadesse et al. in Smart Materials and Structures, Vol.21; March 2012; http://iopscience.iop.org/ 0964-1726/ 21/ 4/ 045013/