Dear Adrian,

Can you comment on the merits of harvesting energy with soft materials in general?

Hi Lihua,

There are no commercialized electrodes for DE transducers per se, but there are commercialized DE actuators. These actuators generally makes use of carbon grease as compliant electrodes. There are other candidates like metallic powder, and carbon nanotubes.

We really welcome newcomers to this field, and any interesting ideas should be actively shared between researchers. Do feel free to share your thoughts on this topic, if you have any.

Best,

Adrian

Hi, Adrian

interesting topic. I currently works on harvesting vibration energy via piezoelectric transduction. I first saw your idea in this year's SPIE NDE conference at San Deigo. seems the mechanism is similar to electrostatic generator.

Is there any commercialized elastomer transducer with flexible and durable electrodes avaliable in the market. or you just made the electrodes yourself in the labratory. I have interest to try this new material for energy harvesting purpose.

Thanks

Yes Keith, I do agree with your observations.
Dissipation mechanisms are very complex topics, especially for deformable
polymers. Added to the complexity is the mechanisms are vastly varied
between polymers of different molecular structures, and also dependent on
various ambient factors like temperature, humidity and chemical composition.
Its non-determinstic behavior is compounded by the fact that input
variables like mechanical stress, electric field, excitation frequency and
material properties may further modify their dissipation characteristics.

Having said that, we really seek like-minded researchers who
are interested in electromechanical dissipation. Only through better
understanding of these effects, that we may design materials that minimize
them, thereby improving the conversion efficiency by a quantum leap.

Adrian

Hi Adrian,

Thanks

Dear Zhuangjian,

Let us begin by discussing the dissipative mechanisms in dielectric elastomers.

Dielectric elastomers are
electromechanically-coupled systems that dissipates energy in two major ways -
mechanically and electrically. Subject to a mechanical force, the
deformation relaxes to a equilibrium state after some time tau_v. This
process is known as viscoelastic relxation, and tau_v is the viscoelastic
relaxation time. Subject to an electric field, the dipoles relaxes and
orientates towards the direction of the field after some time tau_e. This
process is known as dielectric relaxation, and tau_e is the dielectric
relaxation time. Furthermore, if the electric field is sustained long
enough or if the electric field is sufficiently high, charges may begin to leak
through the dielectric. This process is known as current leakage, and the
product of the resistivity and capacitance of the DE gives some kind of
"RC" time constant, or the characteristic time where current leakage
builds up to a stable magnitude.

Some experiments on typical DE materials like VHB
acrylic elastomer and silicone elastomers have shown that tau_v is in the order
of 10^2 seconds, tau_e is in the 10^-6 seconds, and RC time is about 10^3
seconds. This will determine the rate of operation whereby loss will be
significant or may be avoided.

Experiments specifically performed to determine
dissipative processes in DE are limited, yet essential to provide guidance for
optimal operation of DE actuators and generators. I certainly hope more
work can be done in this aspect.

Adrian

References

R. Palakodeti & M. R. Kessler, Mater. Lett. 60, 3437-3440, 2006. (On DEA viscoelasticity, efficiency with dependence on prestrain & frequency)

J. S. Plante & S. Dubowsky, Sens. Actuators A 137, 96-109, 2007. (On major dissipative mechanisms - viscoelasticity & current leakage, experiments & modelling)

T. A. Gisby, S. Q. Xie, E. P. Calius & I. A. Anderson, EAPAD Proc. SPIE 7642, 764213, 2010. (An experiment to measure leakage current with applied field)

X. Zhao, S. J. A. Koh & Z. Suo, Int. J. Appl. Mech. 3, 203-217, 2011. (A theory of viscoelastic dissipation in DEs)

Hi Adrain,

Thank you for posting this interesting thread. The dielectric elastomer is great promise as actuator materials in converting mechanical to electrical energy.

One quick question, is there any research work about the energy of conversion is strain rate or loading rate dependence in using DEG? As you said, Motion-based energy harvesting is the process of converting dissipated mechanical energy into electrical energy. Sources of mechanical energy include the ocean waves, wind, human motion, vehicular traffic, and vibrations in buildings and bridges. This source of energy is dynamic loading, the materials properties could be changed when the strain is higher.

Interesting topic here, Adrian.

As you pointed out, most experimental studies have focused on VHB and silicone, and neither material is designed specifically for DEGs. Dissipative processes such as viscoelasticity and current leakage have been shown to affect the performance of these DEs and thus limit their application. Viscous losses reduce the useful mechanical input work while current leakage may result in a lower voltage boost across the generator. In particular, current leakage in dielectrics is a complex phenomenon; for example, the nature of the conduction mechanisms appears to be elusive in many cases.

Understanding the impact of these dissipative mechanisms on the performance of a DEG is a challenging issue.

Hi Xiaodong,

Soft materials are capable of converting mechanical to electrical energy in several ways, I shall just touch on the conversion process of a deformable capacitor (also known as a dielectric elastomer). A dielectric elastomer (DE) consists of a thin membrane of polymer (for instance, rubber), sandwiched between compliant electrodes (for instance carbon grease). The DE is first pre-stretched and pre-charged with a small electric field. After which, the DE is mechanically relaxed. When it is relaxed in the open-circuit condition, the electrodes are separated, separating the unlike charges, and squeezing the like charges closer together. This action increases the potential difference between the electrodes, thereby boosting the voltage. When it is relaxed in the closed-circuit condition, the charges are pumped to an external circuit, creating a current that powers a electrical load.

The generated electrical energy may be used to directly power a load, or be stored in a battery or capacitor.

The paper by Pelrine et. al. addresses the basic mechanisms of energy conversion (first attached paper in original post), my papers illustrate that the energy density of conversion for soft materials may be orders of magnitude higher than existing technologies like piezoelectrics and EM generators (next two papers). The final two papers by a New Zealand Group (headed by Prof. Iain Anderson) introduces a creative circuit design that allows a DE generator to boost voltage from Volts to kilo-Volts.

Adrian, this is a very interesting topic. I would like to know how biological soft materials do energy harvesting and how to store it? Do you know any papers? Thanks.