Game-Changing Thermal Energy Harvesting Power Cells for the IoT

March 08, 2018 by Paul Shepard

A new thermal energy harvesting technology was demonstrated publicly for the first time at this week's IEEE Applied Power Electronics Conference in San Antonio, Texas. Called the Evercell™ power cell (one of the Evergreen® technologies from The Face® Companies) the device employs a patented passive structure that operates according to known laws of physics captured and amplified in a previously unknown manner.

The Evercell™ thermal harvester demonstration unit pictured above is seen producing a constant output of about 200mV. Production Evercell™ thermal harvesters will be scaled up to deliver an output of 1.2Vdc.

It has long been held that segregating, isolating and directing accumulation of electrons at the atomic level required excitation by an infusion of energy - more energy than a resulting system would generate. The passive nature of the Evercell™ power cell provides a structural capacity for the accumulation of electric potential with no energy expending budget to overcome. Evercell™ is both a disruptive and a game-changing device.

Evercell™ is expected to be disruptive because the technology will enable the elimination of many of the small size (coin-cell type) batteries currently used in low-power wireless sensor and communication systems, among other applications. Coin cell batteries, for example, are increasingly onerous due to their use of toxic materials, the proper disposal of which presents increasing challenges, and the presence of which around small children is dangerous.

Evercell™ is game-changing because the technology will enable the development of completely new and novel applications that are not possible to design using batteries. Those applications are expected to include sensors embedded in structures such as concrete or airframes and other inhospitable environments to advanced wireless medical sensors and devices.

When the requirement to routinely change batteries is eliminated, applications that would have previously been restricted, or rendered impossible, by such a restriction become open to consideration.

Evercell™ operates on the nanometer scale and employs surface phenomena (differential work functions between opposing conductor surfaces) and quantum tunneling based on the proximity of the opposing conductor surfaces to harvest thermal energy, converting it to an electric potential through the accumulation of a charge at the surface of one of the opposing conductors.

The accumulated charge can then be selectively and/or controllably discharged through a load, thereby powering the load. Examples of expected performance for first-generation production devices include:

  • 5-µW device:
    • 34mm x 34mm x 1mm
    • 1.2V output
    • 4.2µA continuous current
  • 480-nW device:
    • 30mm x 30mm x 0.2mm
    • 1.2V output
    • 400nA continuous current
  • 960-nW device:
    • 50mm x 75mm x 0.1mm
    • 1.2V output
    • 800nA continuous current

Evercell™ employs a passive technique for harvesting thermal energy.  It has long been believed that control of electron migration at the atomic level, if implementable, may be effective in achieving the outcome realized by Evercell™.  Evercell™ achieves an outcome that Maxwell envisioned, but proved unable to implement in any practical manner, as his "theory" was constrained to an active scheme in which a required energy input negated any possible energy generation, resulting in a net negative. Evercell™ is a passive device.

Evercell™, in manner much different than conventional thermo-electric generators (TEGs) does not rely on significant, or even measurable, temperature differentials. The scale is vastly different since TEGs operate across a junction in a bulk of material while Evercell™ only operates at the surface boundaries, making Evercell™ work in environments in which the actual temperature differential is imperceptible.

Evercell™, in its ability to make advantageous use of quantum tunneling, provides a new and previously-untapped use of a known physical phenomenon that is also used in other well-known devices such as tunnel diodes, quantum computing platforms, and scanning tunneling microscopes.

Finally, Evercell™ is expected to be produced using conventional semiconductor fabrication equipment such as chemical vapor deposition (CVD), thermal or sputtering systems, reactive ion etching (RIE) systems, atomic layer deposition (ALD) systems, and plasma deposition systems.

That means that the production capacity to fabricate large numbers of Evercell™ devices already exists and should accelerate getting Evercell™ into the market in high volumes.

Key points about Evercell™ include:

  • Evercell™ produces a continuous output without a perceptible temperature differential (in essentially any environment above absolute zero).
  • Evercell™ is a passive solid state structure.
  • Evercell™ is scalable in its output and can be made in various form factors.
  • Evercell™ uses no toxic materials.
  • Evercell™ will provide a comparatively low-cost alternative (when mass-production is established).
  • Evercell™ leverages existing semiconductor manufacturing processes.