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Table 1 Overview of alternative sources of energy to replace batteries

From: RF power harvesting: a review on designing methodologies and applications

Source

Power density

Harvesting tech.

Advantages

Disadvantages

Solar

Indoor: 10 µW/cm2

Outdoor: 10 mW/cm2

Photovoltaic

High power density

Mature

Not always available

Required exposure to light (not implantable)

Expensive

Vibration

Human: 4 µW/cm2

Industrial: 100 µW/cm2

Piezoelectric

Electrostatic

Electromagnetic

Implantable

High efficiency

Not always available

Material physical limitation

Thermal

Human: 30 µW/cm2

Industrial: 1–10 mW/cm2

Thermoelectric

Pyroelectric

High power density

Implantable

Not always available

Excess heat

RF

GSM: 0.1 µW/cm2

WI-FI: 1 mW/cm2

Antenna

Always available

Implantable

Low density

Efficiency inversely proportional to distance