RF energy harvesting system basics-Radio Frequency harvesting

This article covers RF energy harvesting system basics. This radio frequency harvesting is useful to charge the battery. It covers RF energy harvesting system block diagram with components.

The concept is related to converting ambient energy present in the air into electrical energy. Following are the typical energy harvesting schemes available today. It operates in milliwatt and microwatt power levels.
•  Solar energy
•  Mechanical energy
•  Thermal energy
•  Radio Frequency energy
•  Electromagnetic energy
•  Biochemical energy
•  Radioactive energy etc.

This technology uses intermediate stages of power conditioning, storage batteries or storage capacitors to conserve harvested energy from environment.

Let us understand radio frequency harvesting. This type of energy harvesting utilizes radiations from RF sources such as TV and radio broadcasting transmitter stations, cellular base stations, communication satellites etc.

Radio Frequency waves used in this RF energy harvesting system is part of electromagnetic spectrum. Maximum power available in RF energy harvesting is 0.7 µWatt for 2.4GHz and about 1 µWatt for 900 MHz frequency theoretically. This can be achieved with free space distance of about 40meters.

RF energy harvesting system Block Diagram with Components

RF energy harvesting system

The figure-1 depicts block diagram of RF energy harvesting system. It consists of following modules. It converts RF energy to DC energy hence it is also referred as RF to DC converter. Figure also mentions discrete circuit components used in these modules.
• Antenna
• Matching Network
• Voltage multiple one or more (i.e. rectifier circuit)
• Energy storage circuits

Antenna: This device picks up RF radiations from various sources available in the free space. The picked up RF energy later is guided to the rest of the modules using transmission line or guided structures. Antenna converts electromagnetic energy picked up into elecrical signals. Refer types of antenna.

Matching Network: It is used to couple maximum RF energy into the circuit. The circuit is made of capacitor and inductor components.

Voltage multiplier: Figure mentions voltage multiplier or rectifier made of diodes and capacitors. Higher are these stages higher is the voltage at the load and lesser is the current. But higher number of stages result into increase in charging delay before it goes for energy storage. Refer halfwave and full wave rectifier circuits.

Energy storage: The DC power obtained from the previous module is stored either in the capacitor or passed to the battery in order to conserve for later use.

Advantages of RF energy harvesting

Following are the benefits or advantages of RF energy harvesting:
• Works in dark locations also.
• Provides power on demand and even in mobility conditions.
• Provides tracking capabilities.
• Can benefits in electric tariffs.
• Can work as secondary battery while on travel

Other energy harvesting techniques

Refer Energy Harvesting Methods which describes types and basics of energy harvesting techniques and energy harvesting materials. The energy harvesting techniques include thermoelectric energy harvesting, photovoltaic energy harvesting, piezoelectric energy harvesting, pyroelectric energy harvesting, rf or wireless or electromagnetic energy harvesting, wind energy harvesting, vibration energy harvesting etc.

RF and Wireless Terminologies