Download harnessing free energy from radio transmissions

HARNESSING NO-COST ENERGY FROM RADIO
TRANSMISSIONS
Saptarshi Bandyopadhyay
Indian Institute of Technology Bombay
Powai, Mumbai
(Stream EB, Application No. 516435)
The idea that forms the basis of this project is to trap the energy carried by radio wave
broadcasts that is unused by the receiver and store this energy for later use. This
results in a no-cost source of energy transmitted via radio waves.
Origin of Idea:
The idea originated in the summer of 2006 when I was working on a research project at
the Giant Meterwave Radio Telescope (GMRT) facility near Pune. In the course of my
work I encountered the massive amount of radio noise termed Radio Frequency
Interference (RFI) which frequently plays havoc with data collected by the radio
telescopes. This has a detrimental effect on observations but reduction of such noise is
not undertaken. Hence I attempted to utilize this radio noise productively.
Motivation:
In the present urban scenario, extensive radio signals are broadcast by major radio
stations operating in metropolitan cities.
Back of the envelope calculations yield the following results:
Each radio station transmits 10 to 30 Kilowatts of power.
An ordinary handheld radio receiver requires about 1 microwatt of power for
normal performance.
Given the above facts, even if the entire population of a city of 10 million had
their radios playing, the amount of power used would still fail to exceed 50100 watts. The remainder of the energy goes unutilized.
The aim of this project is to tap into this energy and make it a viable zero-cost power
source.
Yet another significant source of radio noise is telecommunication. Today when mobile
communication holds sway over the populace, mobile antennae are erected almost
every kilometer apart. These antennae transmit about 1 kilowatt of power.
Modus operandi:
The following is a brief outline of my attempt to harness the unutilized energy transmitted
via radio waves I constructed several antennae to measure the amount of power received.
Results show that this value is low. However since this energy is available free of
cost I judged the effort to tap it as being worthwhile.
I have to make either passive or semi-active circuits (output greater than input
from battery) to rectify the alternating signals received from the radio waves.
The energy output by the circuit in the form of a rectified DC signals needs to be
stored for future use.
On successful completion of the above, other ideas like addition of power from
different antennae could be implemented.
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Progress to date:
Monopole antenna for 93.5FM (λ = 3.20m)
The theory of monopole antennas states that the length of the monopole antenna must
be λ/4 (about 80cm in this case) for the antenna to get impedance matched with the
surroundings at that wavelength. However this applies only to the ideal situation where
the ground plane extends infinitely. The aluminum plate used as the ground plane in my
experiments in the laboratory measured 70.3 ( ± 0.1 )cm × 70.5 ( ± 0.1) cm. Hence the
length of the monopole used was 93.7( ± 1 )cm. The reason for such a large relative
error in the measurement of the length of the monopole, which is an aluminum rod of
diameter 6mm, is because the shape is rather crooked; hence precision in length
measurement reduces.
Image of monopole antenna in laboratory
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Network analyzer showing impedance matching of antenna
The impedance matching of the monopole is seen through the network analyzer. It is
seen that the standing wave ratio is good in the range of measurements. Hence there
are fewer reflections in the circuit and most of the power is transferred.
Measurements were then carried out using the spectrum analyzer. As the results show,
many peaks are obtained in the 90 MHz to 95 MHz band. Each of these peaks gives
above 100 nanowatts (at 300 micro volts) of power. When integrated over the entire
spectrum, power received is approximately 2 to 3 microwatts at voltages of about 10 to
12 millivolts. All these are received purely in the form of alternating signals, which are
actually the carrier waves for the actual data transmitted. I got access to these
instruments in Prof. Girish Kumar’s lab in Electrical Department, IITB.
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Table of signal strengths at different wavelengths
FREQUENCY
STRENGTH
90.96MHz
-59.3dBm
92.4MHz
-52.1dBm
93.48MHz
-53.4dBm
96.0MHz
-71.0dBm
98.28MHz
-66.8dBm
100.4MHz
-74.0dBm
Decibels milli (dBm) is the unit used to measure the power carried by radio signals. Its
relationship with the Watt is:
1 dBm = 10 X log10 [1 Watt/ 10-3 Watt]
Spectrum analyzer showing frequency distribution of radio signals received
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Monopole antenna for mobile frequencies (800 to 900MHz)
An antenna was then built for wavelengths in the mobile range from 800MHz to 1GHz, in
the form of a 10.1 ( ±0.1 )cm copper wire and the same ground plane previously used.
Initially the same ratio as previously was used for computing the length of the monopole
(9cm) for the wavelength of 33cm (900MHz). However there was some impedance
mismatch seen in the network analyzer, which I conclude was due to the change in ratio
of the ground plane size to the monopole length. The new length was a little larger than
the one previously calculated. The impedance matching of the monopole antenna is as
shown in the network analyzer.
Mobile monopole antenna
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Network analyzer showing impedance matching of antenna
Then some measurements were carried out with the spectrum analyzer. As seen in the
image below, the mobile antenna appears to give certain ranges in which strong signals
are received. Hence I attempted to find the average strength of these signals.
Spectrum analyzer showing frequency distribution of radio signals received
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Table of strengths of the signals
FREQUENCY RANGE
STRENGTH
870-920MHz
-63 to -55 dBm
943-975MHz
-62 to -52 dBm
992-1017MHz
-63 to -60 dBm
Active rectifier circuit for AC signals in millivolts (mV)
Half wave rectifier circuit by a single diode
The simplest half wave rectifier circuit is shown above. But for this rectifier to function,
the diode needs a threshold voltage of 0.7V. Since my signals will be having very low
wattage and voltage, I cannot use this rectifier directly.
Preliminary active circuit for rectification of signals
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The preliminary circuit made for the rectifier is as shown in the diagram. It is active and
rectifies the signal at much lower than its threshold voltage of the diode. The high pass
filter at the input allows only the signals of very high frequency (above 1MHz) to pass
through the circuit. But since the normal diodes frequency response is not good at such
high frequencies, I have to use the schottky diode in its place.
Another circuit that can be used is the precision full wave rectifier circuit. Although the
operational amplifiers need a ±5V supply, the current drained can be reduced by high
resistances.
Precision Full wave rectifier circuit
The rectified output signal compared to the input signal as seen in the CRO
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Results obtained from experiments:
The first conclusion from the 93.5FM antenna is that it is receiving power in
microwatts inside IITB. This is a good value since normal handheld quartz watches
work with micro watt of power. Also on approaching the transmission station at Tardeo,
about 30km from IITB, the power received should increase by the inverse square
relationship and taking into consideration factors like attenuation due to structures.
There I expect the antenna to sense power in watts, which means even
conventional rectifier circuits will work there.
Almost similar inference is derived from the mobile antenna. To increase responsiveness
and coverage of the mobiles, mobile companies have set up low power transmitting
towers after every few kilometers. In IITB, there is a set of antennae outside the main
gate and another set of antennae on the main building, barely 800m apart. This shows
there is significant attenuation of the signals in the city, largely because of
concrete structures.
The rectifiers are able to convert the low wattage, low voltage AC signals to DC. But they
are all active circuits. I think passive circuits are possible as they won’t be disobeying the
law of conservation of energy, when they will be storing the energy from the antenna.
Future plans:
I plan to evaluate the increase in the power absorbed by the antennae as I approach the
radio transmission station. The radio station transmits about 10 kilowatt of power. I
expect to tap approximately 1 Watt with the antenna within 100m of the transmission
tower. I also plan to find whether metallic objects like pillars, metal cupboards, metal
window frames etc can be easily impedance matched so that they too behave as
antennae and capture power. This is because any metallic object can behave as an
antenna in theory; hence availability of metal antennae is not subject to scarcity any
longer.
The crucial point of my future work will be making the circuit to be connected to the
antenna. It should preferably be passive or at least semi-active. The circuit will be in two
parts 1. To convert the AC signal at such high frequencies to a DC signal.
2. Storing of power received from the DC signal for later use.
Innovative component in the design:
The main advantage of this method of trapping energy is that it is completely free
of cost. This is basically a recycling of energy which would have otherwise gone
unused. The method is highly cost effective since it is not required to put up any
antennae. Any object that conducts can act as an antenna and can be used to harness
the energy. The only external input will be a small circuit, which is a small initial
investment, not more than Rs50. Once connected, it is a continuous source of energy,
with almost no maintenance costs.
This source of energy is completely environment-friendly and does not cause
pollution in any form, thermal, atmospheric or noise.
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The sole disadvantage is that there needs to be a continuous and strong source of
radio energy received by the antenna. There are AM radio stations which transmit all
over the country and hence no part of the country will be completely in a radio free zone.
However this concept will work best near the transmitters, in urban areas where there
are many radio stations broadcasting. Also a lot of communication is by means of radio;
hence the circuit can harness large amounts of energy within metropolitan cities or in
areas where there is a large concentration of radio waves.
A frequently asked question is if my harnessing the energy will decrease the range of the
transmission as there is a removal of some energy from it. The answer is NO for the
following reason: As aforementioned, assume the transmitter transmits 10 kilowatts of
power but only about 100 watts of it is used by all the radios tuned in to it. A major part
of the remaining energy is sent into outer space, and another significant proportion is
earthed by all the metallic conducting pillars in buildings, bridges, light posts etc. My
circuit will be attached to such elements and will be trapping the energy which they are
earthing and thereby wasting. There is no necessity to erect any new antenna for
this purpose; hence I will not be in any way reducing the range or the strength of
the radio signals when I use my circuit, but turn it to advantageous use.
Future scope for implementation:
Anyone receiving a lot of radio energy can use this method to trap some energy,
especially people living close to radio transmitting towers. It can also be used for a large
number of practical purposes, like running watches, streetlights, signals, etc.
This method can be used for powering in areas where wiring is too expensive or not
possible at all. Future age satellites and space vehicles could use it as a primary source
of energy or at least as a reserve source if their solar cells malfunction. As humanity
explores reaches further from the sun, if we embark on long intergalactic space
missions, radio energy in the form of synchrotron radiation will become an important
source of energy, quite comparable to solar energy.
Conclusion:
Tapping of power from radio waves can provide a viable alternative to other energy
conversions. With this technology hopefully implemented someday in the future, it
provides a platform for man to tap energy out of the air, figuratively, which to date has
been done only in science fiction. This project is the beginning of another journey
whereby fantasies in the realm of science are transformed into fact for the good of our
world.
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