RF-based energy harvesting involves capturing ambient radio frequency (RF) energy from sources like cell phones, WiFi networks, and television broadcasts. This energy can then be converted into direct current (DC) power to charge or operate low-power electronic devices without needing batteries. For example, one system harvests RF energy from nearby iPhones using an RF receiver and converts it to power tiny wireless sensor nodes for applications like health monitoring. This technology could eliminate the need for batteries in many small devices.

1. RF-based Energy Harvesting
Catching a Wave

2. • No matter how smart and fast your devices would be, the biggest issue is always with the battery
technology.
• Whenever you go to buy any electronic gadget — smartphone, laptop, or any wearable — the most
important specification isn’t its processor speed or its camera quality but its Battery Backup, which
is not getting better any time soon.
• What if you could eliminate the very thing entirely?
Statement
(C) Jitendra Adhikari, 2016
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3. Radio frequency (RF) is any of the electromagnetic wave frequencies that lie in the range extending from around 3 kHz to
300 GHz, which include those frequencies used for communications or radar signals. RF usually refers to electrical rather
than mechanical oscillations. However, mechanical RF systems do exist.
Radio Frequency (RF) communications is based on laws of physics that describe the behavior of electromagnetic energy
waves.
RF communication works by creating electromagnetic waves at a source and being able to pick up those electromagnetic
waves at a particular destination. These electromagnetic waves travel through the air at near the speed of light. The
wavelength of an electromagnetic signal is inversely proportional to the frequency; the higher the frequency, the shorter
the wavelength.
Imagine an RF transmitter wiggling an electron in one location. This wiggling electron causes a ripple effect, somewhat
akin to dropping a pebble in a pond. The effect is an electromagnetic (EM) wave that travels out from the initial location
resulting in electrons wiggling in remote locations. An RF receiver can detect this remote electron wiggling.
Frequency is measured in Hertz (cycles per second) and radio frequencies are measured in kilohertz (KHz or thousands of
cycles per second), megahertz (MHz or millions of cycles per second) and gigahertz (GHz or billions of cycles per second).
Higher frequencies result in shorter wavelengths. The wavelength for a 900 MHz device is longer than that of a 2.4 GHz
device.
In general, signals with longer wavelengths travel a greater distance and penetrate through, and around objects better
than signals with shorter wavelengths.
Intro to Radio Frequency (RF)
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The Idea
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Nikola Tesla
Wardenclyffe Tower, also known as the
Tesla Tower, was an early wireless
transmission station designed and built by
Nikola Tesla.
Tesla intended to transmit messages,
telephony and even facsimile images
across the Atlantic to England and to
ships at sea based on his theories of using
the Earth to conduct the signals.
• Inventor
• Electrical engineer
• Mechanical
engineer
• Physicist
• Futurist
Best known for his
contributions to
the design of the
modern alternating
current (AC)
electricity supply
system.

5. 5
Free Energy - Nikola Tesla
(C) Jitendra Adhikari, 2016
https://youtu.be/qdIAwcgtqac

6. The basics of RF Harvesting
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7. RF energy is currently broadcasted from billions of radio transmitters around the world, including mobile
telephones, handheld radios, mobile base stations, and television/radio broadcast stations.
The ability to harvest RF energy, from ambient or dedicated sources, enables wireless charging and/or usage of low-
power devices and has resulting benefits.
Battery-based systems can be trickled charged to eliminate battery replacement or extend the operating life of
systems using disposable batteries. Battery-free devices can be designed to operate upon demand or when
sufficient charge is accumulated.
In both cases, these devices can be free of connectors, cables, and battery access panels, and have freedom of
placement and mobility during charging and usage.
RF Source
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8. RF energy harvesting devices, such as Powercast’s Powerharvester® receivers, convert RF energy into DC power.
These components are easily added to circuit board designs and work with standard or custom antennas.
Improving the RF sensitivity allows for RF-to-DC power conversion at greater distances from an RF energy source.
However, as the range increases the available power and rate of charge decreases.
An important performance aspect of an RF energy harvester is the ability to maintain RF-to-DC conversion
efficiency over a wide range of operating conditions, including variations of input power and output load
resistance.
RF energy-harvesting circuits that can accommodate multi-band or wideband frequency ranges, and automatic
frequency tuning, will further increase the power output, potentially expand mobility options, and simplify
installation.
RF Harvesting Receivers
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9. Powercast’s Powerharvester
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10. 10
A tiny computer
A team of researchers from the University of Washington’s
Sensor Lab and the Delft University of Technology has
developed a new gadget that doesn’t need a battery or any
external power source to keep it powered; rather it works on
radio waves.
The device sucks radio waves out of the air and then converts
them into electricity.
Dubbed Wireless Identification and Sensing Platform (WISP), the device is a combination sensor and computing chip that
uses a standard off-the-shelf RFID (Radio Frequency Identification) reader to suck in radio waves and convert them into
electricity.
The discovery could highly transform the Internet of Things (IoT) world as the WISP is even more low maintenance compared
to Bluetooth Low Energy sensor chips being used today.
The next step in making the WISP usability even more convenient and easy is to create module (Wisent) that would allow for
wireless programming of the WISP. With the help of Wisent, the WISP can be programmed wirelessly and uses the very same
radio waves to communicate.
(C) Jitendra Adhikari, 2016

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RF energy can be used to charge or operate a wide range of low-power devices. At close range to a low-power
transmitter, this energy can be used to trickle charge a number of devices including GPS tracking tags, wearable
medical sensors, and consumer electronics such as e-book readers and headsets.
At longer range the power can be used for battery-based or battery-free remote sensors for control and building
automation, structural monitoring, and industrial control. Depending on the power requirements and system
operation, power can be sent continuously, on a scheduled basis, or on-demand.
Imagine a mobile phone powering a battery-less, body-worn sensor that sends data to the phone via a commonly
used protocol such as Wi-Fi or Bluetooth. This data can be displayed locally on the handset or transmitted by the
phone to a monitoring service.
Typical Applications
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12. 12
Powercast P2110 Harvests Ambient RF
Energy from iPhone
(C) Jitendra Adhikari, 2016
https://youtu.be/uox8Rmm9_c4

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