Wireless Recharging/Transmission Technology
Table of content
I. Abstract 3
II. Introduction 3
III. CurrentStatus of the Technology 6
IV. EconomicPotentialof the Technology 8
V. CurrentPlayersin the WPT 9
VI. Advantages and Hurdles 10
VII. Conclusion 12
VIII. Reference 13
Today we are surrounded by electronic gadgets and many of them run on electricity from battery as
source. Battery makes these electronic gadgets mobile which makes it easy to carry around
anywhere we want. But when the power lever of the battery runs low we need to run towards the
nearest wired power source to recharge the battery. Now imagine a way through which we can
recharge the battery without the wire-recharger. This is possible now through the use of charge pump
technology. This technology uses a wireless charger which converts the RF/Microwave frequency
waves into DC signal and this energy can be stored in the battery. This term paper focuses on the
modalities and technological aspects of the technology. Then we will look into the existing products
which already incorporates this technology also some other research areas where electricity can be
transmitted wireless. This term paper will end with the future scope of this technology.
We are using electricity for more than a century now and all these years electricity is transmitted
through wire cables to commercial and home units. We also use various electronic gadgets which
uses electricity through wire cables. Is it possible to done away with wire cables altogether and have
free electricity transmission without the physical connection? It is possible through wireless
transmission of electricity. The first concept that electricity can be transmitted without wire was
demonstrated by Nikola Tesla in 1893 during which he demonstrated the wireless illumination of
phosphorescent lamps at world exposition in Chicago. This feat was possible because of electro
dynamic induction. Induction is the prime principal used to transmit electricity for shorter distances.
Other means like R/F energy is used for short range electricity transmission. For far range electricity
transmission microwaves and laser as medium can be used which is currently in research stage. The
short range electricity transmission can be used to light electric gadgets and also to change batteries
wirelessly. Long range electricity transmission can light an entire city. The main advantage of this
transmission technique is that we can totally do away with wires which will help us to bring the
electricity to nook and corner of the world. Efficiency is the main criteria for this technology. R/F
energy transmission is having the least efficiency ratio and induction charger is having the most
History of Wireless transmission Technology
In 1820 Andre Ampere develops Ampere’s law proving that electric current in a metal conductor
produces a magnetic field around it.
In 1931 Michael Faraday develops faraday’s law describing that a magnetic field is induced when a
metal is subjected to time varying magnetic field flux.
In 1983 Nikola Tesla demonstrates the wireless illumination of lamps thus proving the possibility of
wireless power transmission.
In 1897 Tesla got the first patent registered for wireless transmission.
In 1964 William brown demonstrated a model helicopter flown with a beam of microwave sent from
In 1973 world’s first RFID system was demonstrated in Los Alamos National lab.
In 2008 Intel reproduces Tesla’s 1894 electrodynamics induction and wirelessly powered a bulb with
75% energy efficiency.
In 2010 Haier Group debuts world’s first completely wireless LCD television based on Tesla’s
electrodynamics induction process.
Techniques of Wireless Electricity Transmission
Wireless energy transmission or wireless power transmission (WPT) is different from wireless
information transmission; here the electric power is transmitted to a receiver through the use of radio,
Laser or a microwave waves. The efficiency or transmission ratio becomes the critical parameter
against which various methods are calibrated. In short wireless power transmission is defined as the
process through which energy/electricity can be transferred to the conductor without any physical
means of contact.
We will look into the various technologies in detail now-
a) Inductive Charging: Induction is the production of electricity across a conductor situated in a
changing magnetic field moving or a conductor moving through a changing magnetic field.
When a conductor is subjected through a changing magnetic field a current is induced in the
conductor and this current can be stored or used. The transfer of energy takes place by
electromagnetic coupling through a process known as mutual induction. This process works
only in short distances and can be used to run electric gadgets. The basic wireless changer
consists of the units which produces the changing magnetic field in varying degree. These
chargers are now commercially available and this can be used to charge any device which
uses a battery. Like cell phones, lap tops etc.
Fig 1:Induction based wireless charger.
b) Evanescent Wave Coupling: This concept works on the principle that if both the coils of the
gadget and the transmitter to resonate at the same frequency then electricity can be induced
in them. One good point to be noted is that this process can be carried out even if distance
between the conductor coil and the transmitter coil is high and even multiple devices can be
powered through this process till they share the same frequency. This wave coupler can
power all electric devices in a home. The efficiency of this process depends on the distance
between the transmitter and the conductor coil. The efficiency is highest when both the
couples are tight and with increase in distance the magnetic energy is lost between the coils
and efficiency reduces. This technology is not commercially available yet but the future is
bright as lots of research is going on.
Fig 2: Evanescent Wave Coupling
c) Capacitive Induction: Capacitive Induction or Capacitive coupling is an electric field created
through differential capacities between two electrodes using high frequency AC current. The
alternative current produces a changing electric field which induces a current in the
electrodes. This effect is knows as Tesla effect.
d) Far Field Electricity Transmission: All the above stated technologies are used to transmit
power wireless through a small distance often in centimetre or in inches. But there are ways
to transmit power to large distances. This can be achieved using the radio or microwave
power transmission. The main criterion here is also the efficiency. If we can transmit large
power efficiently over large distance then this technology could be used widely. First we look
at Radio/Microwave power transmission.
I. Radio/Microwave Power transmission: The basic step up for this process is three
components like a transmitter, Antenna and a charge pump to power some power units. The
transmitter is used to transmit high frequency radio/microwave energy. The frequency is
usually between 900 to 1200 MHz range. The transmitted radio frequency (RF) is captured
using an antenna. The energy captured through antenna is fed to a charge pump which will
convert this energy into DC current which can be used to run gadgets. The main component
here is the charge pump. At the heart of the charge pump consists of capacitors which will be
charged by the received RF. This stored in the capacitor can be converted to DC current.
Usually this current is stored in a battery and then this battery is used to run electronic
components. The main disadvantage with this type of power transmission is its efficiency is
very less. Lots of energy is lost in the transmission of RF. Only a small fraction is trapped by
the antenna placed at a distant. The efficiency can be slightly bettered through the use of
microwave as it can be transmitted in a line. But still its efficiency is way behind the
conventional transmission. In conventional power transmission the loss is around 6 %( in
USA) but with the current wireless transmission technology efficiency is less than 80-90% and
this is for inductive power transmission. For RF power transmission is less than 10%. But still
this is one technology which can transmit power to great distance.
II. Laser Power Transmission: Similar to RF power transmission we can use LASER to
transmit power to large distance. Since laser is a concentrated beam of light with very high
energy this can be used to transmit power with an efficiency of 40-45%. Some of the
advantage of using Laser over RF power transmission is that Laser has more energy
transmission capacity. It does not interfere with the existing radio frequency usage systems
like mobile phone transmission. It does have adverse human effects unless someone comes
into the line of sight of laser. One main advantage over RF power transmission is we have
control over the direction of the power transmission as in RF power transmission it is
omnipresent and laser can be transmitted in any particular direction which we want.
III. CurrentStatus of the Technology
The induction based wireless chargers are already available in the market. Some companies are
already marketing their products with wireless charger. The induction based chargers have achieved
efficiency between 80 to 90%. The evanescent wave coupling is still in research stage, but once this
technology is viable then all electronic component in a home can be charged with a single transmitter
placed centrally in a home. In far field electricity transmission the technology can transmit power but it
is not economically viable due to less efficiency and high input cost.
Fig 3: Dell Laptop with wireless charger. Dell Latitude model.
Above picture shows the Dell Latitude series laptop which uses world’s first wireless recharging pad
to charges its batteries. The battery of the laptop is connected to an induction coil and this laptop is
placed on the charging pad which has coils made inside. When power is connected to the charger
due to mutual induction the battery of the laptop is charged. The time it takes to charge this laptop is
same as the time it takes with the wired charger.
In 2009 Haier announced world’s first wireless LED TV. The figure of the TV is given below.
Fig 4: Haier’s world’s first Wireless LCD TV.
In near future we can expect such technology to be incorporated into many more gadgets like I-Pod,
TV Remote, LCD TV, Lamps to run on induction based electricity transmission. We don’t need to
worry about charging our gadgets. The battery level of these components will be always at optimal
In the realm of science fiction there are ideas and concepts where scientists and visionaries see this
concept being used for applications outside of this world. There is a concept of solar power satellite.
This concept is given another name as space based solar power where the solar radiation is
converted into electricity and beamed to earth for use here. Even though this idea is not yet in
practical application, some countries are active in research and development of this unique concept
like Japan in 2009 announced plan to orbit low earth satellites which will collect solar radiation and
transmit power back to earth through microwave. The first prototype will be operational in the year
2030. European space agency plans to put solar collecting small satellites in deep space to study
various ways solar energy can be captured and stored with degree of efficiency.
Fig 5: Artistic concept of solar satellite
The above picture is a conceptualization of a solar powered satellite which will capture the falling
solar radiation and transmit it back to earth as a powerful microwave radiation. This radiation will be
pin pointed to a collection station where it will be converted to electricity. This is where the Japan is
currently working on.
IV. EconomicPotentialof the Technology
This technology is already being used commercial as seen in the figure given couple of pages above.
Some companies have started to sell induction based charger to charger small battery operated
gadgets like TV remote, i-Pod, cell phones etc. Dell started to use wireless charger with their model
back in 2008.Evanescent coupling devices could possibly power all electric appliances in a home. A
transmitting device fitted centrally in a home can power all electric devices within a specified distance
Researchers at Korea Advanced Institute of Science and Technology (KAIST) has developed an
electric bus which drives power beneath the road surface where non-contact magnetic charging unit is
placed which the bus picks up as it moves along and gets itself recharged. This technology
demonstrator just gives us a glimpse of the future it holds. The experiment was a huge success;
researchers were able to transmit up to 60% of power from the coupling to the charging circuit in the
Aviation sector is one area where there is huge potential for practical application of this technology.
Experiments were carried out successfully to fly air craft with power beamed from the ground to the
air craft. World’s first fuel less aircraft was flown in Canada in 1987 with microwave energy beamed
from the ground. This program was called stationary high altitude relay platform, in short SHARP.
Recently NASA test flown an aircraft power by Laser beam sent from ground from its Dryden centre.
The power beamed to the aircraft is stored is a high power battery which deliver power to the motors
which fly these aircraft.
In 1975 NASA successfully demonstrated the microwave wireless power transmission of 30Kw power
over a distance of 1.6 Kms. The receiver transferred the power at 82% efficiency which was
remarkable. If this technology can be implemented then remote villages can receive power wireless
from distant transmission station and power can be made available to villages.
V. CurrentPlayersin the WPT
Some companies are active in Wireless power transmission technology. For eg
DELL- Dell has started giving the option of having wireless chargers in there customization option to
Palm Inc- This smart phone company announced in 2009 to launch touch stone models of phones
with wireless charger as its standard accessory.
Hughes Electronics- This Company in collaboration with General motors introduced a battery
operated car with the option of recharging it wireless. The car is named General Motors EV1 electric
Evatran Company- A subsidiary of MTC Transformers began development of ‘plug less power’ in
2009. This is based on inductive charging system which will power electric car through wireless
Toshiba- They released a wireless powered television which was first in the world to have a powering
mechanism of that kind.
Wireless Power Consortium- An alliance of 20 firms had formed this group to device open source
standard for wireless charging technology. Some bug tickets include Philips, Sanyo, Nokia, Texas
Instruments, research in Motion, Duracell, and Energizer etc. Their draft version is ready as of July
2010. Some companies like Samsung electronics and Ericson are associates of this group who will
contribute standards to be part of this alliance.
IAV GmbH- This German Company is working on chargers which can be implemented in the road
which would allow the car to be charged as it runs along the road surface.
VI. Advantages and Hurdles
If wireless recharging and transmission technology is applied in a large way, then we can do away
with costly grids and substations which provide us with power till now. Homes and cities can be
provided power wireless from a central transmission point which will cater to the needs of the
population within its reach. Battery operated devices will never run out of power if this technology is
implemented. When this technology is extended to cars then we can have cars that run non-stop with
full battery charge. We will never have to go to charging station or to any fuel station to get the tank
Future application of this technology is so immense that it is unwise not to invest in this area. As
mentioned above the experiments carried out with aircraft and public power transmission, if this
technology is implemented then aircraft can fly nonstop with no need to refuel. Remote corners of our
nation can be provided electricity with this technology. The future highway could have inductive coils
imbedded in the road which will provide continuous stream of electricity to the car. This technology
has a high efficiency of 80 to 90 % in some cases which is very encouraging. The potential for this
market is huge and estimated to be around 1 billion dollar per year market. Many companies are
researching in this area and standards have been put in place.
Hurdles for this technology-
a) Biological Drawbacks-
Some consider the usage of such high frequency radio and microwave to transmit power
could cause potential damage to living tissues. There is no concrete study to prove this, but
still many are wary about the prospect of being surrounded by high frequency waves. This
could be a hurdle to implement wireless transmission in large scale, but there are no known
aliments associated with induction based recharging techniques. If any life form comes in
between the line of sight of microwave and Laser signal then it can cause harm.
b) Economic cost-
The initial set up to transmit power to remote village is huge. Consider a village of 500 people;
it is not justified to invest 10-15 million dollars just to install the transmitting station to receive
the power. In house wireless power transmission like evanescent wave coupling is costly and
many people may be going for it.
c) Efficiency of current technology-
The maximum efficiency that can be achieved is around 92% with induction based wireless
charger. If wires chargers are used they can provide power to battery with much higher
efficiency. The wireless power transmission technique is also having very low efficiency
compared to the traditional or conventional way of power transmission. The transmission loss
in USA through conventional way is around 6%. All currently know wireless power
transmission technique has efficiency far less than this figure. In such situation the takers for
this technology will be less.
d) Resonance loss and atmosphere absorption loss-
Induction based power recharging technique has resonant loss which is unavoidable and may
produce excess heat. Sometimes the heat produced is so huge it may damage the
components permanently. If microwave or Radio waves are used to transmit power then there
could be some atmospheric absorption loss which cannot be done away with. One more
serious problem with Laser and Microwave based transmission technique is that they sent
signals in a particular direction and if there line if sight is broken or any obstruction come in
between then the power transmission will break.
e) Interference with existing network- Induction based recharging can cause resonance in
electric circuit which can cause motors and other such devices which will fluctuate will change
in resonance frequency. High frequency radio and microwave signal can interfere with the
existing mobile and radio signal which can play spoil sport.
Transmission of power without wire is not science fiction but a reality now. Without any physical
contacts we can transmit power to any distance and run appliances which can be controlled
independently. Many companies now have wireless chargers as part of their standard accessory.
When Nikola Tesla tried his induction coupling experiments the efficiency was in the range of 20%,
now the efficiency has increased to 80 to 90%. This is a very encouraging sign and academia and
industry recognize this change and trying to incorporate these solutions in everyday life. Some non-
profit organization like Japan’s space agency and European space agency is the process of
formulating a plan to send solar power satellite. May be in future the earth’s power requirement may
come from these satellites which can beam back power to earth. And one of the best advantage of
this technology would be we could get rid of all the cables line which stretch the face of our homes
and cities carrying power. Remote corners of our country can enjoy the benefits of electricity as this
technology can bring power to their footsteps. The future of wireless transmission/recharging
technology looks secured.
1) Wireless Electricity
4) Time line of Technology-
5) Wireless Technology
6) Espejel, J.D., “RF to DC power generation”, University of Maryland,
7) Wireless Charger