Energy Harvesting and Potential University of Rhode Island Biomedical Engineering Andrew Seitler

Sources Energy can be Harvested Thermoelectric – Body heat Photovoltaic – Light (Artificial and Solar) Electrostatic – Electric Potential change Electromagnetic – Vibration

Thermoelectric Energy Heat Transfer is the transfer of thermal energy from a hot mass to a cooler mass. The human body generates constant heat Sleeping 250 Btu/hr (75 watts) Awake 400 Btu/hr (120 watts) Light work/exercise 650 Btu/hr (190 watts) Heavy work/exercise 2400 Btu/hr (700 watts) Majority of Heat escapes through the head λ thermal conductivity σ electrical conductivity S, Seebeck Coefficient

Thermoelectric energy transfer

Photovoltaic Energy Any light source can be used to generate energy even at small invisible amounts. Artificial Lights generate a constant 60 Hz signal along with a small amount of photons. The sun generates energy commonly called solar radiation, easily transferred by heat; far more efficiently harvested by photovoltaic. Photovoltaic devices are made of silicon and convert solar radiation directly into energy or electrical current. h, Planck's constant Φ, work function f, frequency

Electrostatic Energy Stationary or slow moving electric charges Electric charges are constantly changing on the human body. Contact with objects that have a higher or lower charge cause electric charges to transfer. Neurons and electrical impulses Special vibrating piezoelectric devices can be tuned to pick up these changes. Q, Electrical Charges R, distance between charges Ε0,Permittivity Constant

Electromagnetic Energy Motors are designed to turn when current is applied; they allow for current generation when they are turned. Piezoelectric devices create vibrations or can be used to vibrate and generate energy based on frequencies readily available. Mass driven magnets Human motion Walking Exercising

Piezoelectric Energy Transfer

Ambient Energy in Environment Human created ambient energy Radio Towers Cell phone Towers Television Stations Solar Radiation Creation of Heat Photon vibrations High Energy Radiation

Current Devices Currently energy harvesting used for sensors. Mostly military use for listening devices Piezoelectric’s currently in use Radioisotopes Vibrations Charged Battery Coupled Capacitors

Challenges from different Sources Energy Source Challenge Estimated Power (in 1 cm3 or 1 cm 2) Light Conform to small surface area 10µW – 15mW (outdoors: 0.15mW-15mW) (indoors: <10µW) Vibrations Variability of Vibration 1µW – 200 µW (Piezoelectric: 200µW) (Electrostatic: 50µW-100 µW) (Electromagnetic: <1µW) Thermal Small thermal gradients 15µW (10 degree C gradient)

Future Possibilities Smaller Devices Energy Farming becomes more efficient Piezoelectric devices can automatically tune Possibility to listen to and transfer energy from High energy electromagnetic radiation. Heat from current devices transfer to power themselves. Reduce need for batteries

Works Cited http://spectrum.ieee.org/semiconductors/de vices/wireless-sensors-that-live-forever http://spectrum.ieee.org/energy/renewables /putting-wireless-power-to-work http://earth2tech.com/2008/12/17/chip- companies-eye-energy-harvesting/