Energy harvesting (EH) is the process of capturing and storing energy from external sources like solar, thermal, and kinetic energies for use in small, autonomous devices, potentially replacing batteries. This technology offers maintenance-free, environmentally friendly solutions with numerous applications, including in medical devices and remote sensing. Advances in materials and methods, such as piezoelectric and thermoelectric generators, enhance energy capture and efficiency, leading to new opportunities in various fields.

1. ENERGY HARVESTING BY
MICROMACHINES
CHANDAN KUMAR

2. WHY WE NEED ENERGY HARVESTING
• In modern days, the use of energy consumption increasing very rapidly.
Fossil fuels are finite and environmentally costly.
• Sustainable, environmental energy can be derived from nuclear fission or
captured from ambient sources. Large-scale ambient energy (eg. solar, wind
and tide), is widely available and large-scale technologies are being
developed to efficiently capture it.
• At the other end of the scale, there are small amounts of ‘wasted’ energy
that could be useful if captured. Recovering even a fraction of this energy
would have a significant economic and environmental impact. This is where
energy harvesting (EH) comes in.

3. INTRODUCTION
• Energy harvesting (also known as power harvesting or energy scavenging) is the process
by which energy is derived from external sources (e.g. solar power, thermal energy, wind
energy, salinity gradients, and kinetic energy), captured, and stored for small, wireless
autonomous devices, like the used in wearable electronics and wireless sensor network.
• EH also has the potential to replace batteries for small, low power electronic devices. This
has several benefits:
• Maintenance free – no need to replace batteries
• Environmentally friendly – disposal of batteries is tightly regulated because they contain
chemicals and metals that are harmful to the environment and hazardous to human
health
• Opens up new applications – such as deploying EH sensors to monitor remote or
underwater locations.

4. Where can energy be harvested?
• Energy is lost in every industrial process and everyday technology that you can think of,
eg:
• Power stations – nearly all of the world's electrical power is generated by heat engines.
These are gas or steam-powered turbines that convert heat to mechanical energy, which
is then converted to electricity. Approximately two-thirds of the energy input is not
converted to electrical power but lost as heat
• Computers and microwaves (in fact all our electronic gadgets) – lose energy through heat
and/or vibration

5. How can we harvest waste energy?
•
Different types of waste energy can be captured using different EH materials. The most
promising micro scale EH technologies in development include:
• Vibration, movement and sound can be captured and transformed into electrical power
using piezoelectric materials
• Heat can be captured and transformed into electrical power using
thermoelectric and pyro electric materials.

6. Types of energy harvesting material:
• Piezoelectric material- Mechanical stress ↔ electrical signal
• E.g. Battery-less remote control – the force used to press a button is sufficient to power
a wireless radio or infrared signal
• Thermoelectric material-Temperature differences across the material ↔ electric voltage
• E.g. Road transport – Cars and lorries equipped with a thermoelectric generators (TEG)
would have significant fuel savings (especially with the increasing cost of petrol). In 2009,
VW demonstrated this proof of concept . The thermoelectric generator of their prototype
car gained about 600W from running on a highway, reducing fuel consumption by 5% – it
is highly likely efficiency has improved significantly since then
• Pyro electric material.- Change in temperature ↔ electric charge
• E.g. The pyroelectric effect is used in some sensors, but it is still some way from
commercial energy harvesting applications.

7. MICROSTRUCTURED PIEZOELECTRIC SHOE POWER
GENERATOR OUTPERFORMS BATTERIES
• vibratory MEMS generators give out only microwatts of
electrical power.
• While this may be sufficient for emerging ultralow power sensors,
many current applications require mili watt power levels.
• Commercially available running sensors for shoes consume over
100 uW of electrical power and requirements for GPS locators are
even higher.
• Piezoelectric transducers generate electrical charge when
compressed. This makes piezoelectric materials especially
advantageous for power harvesting as they do not require bias
voltage for operation.
• In principle, a piezoelectric transducer together with two
rectifying diodes is sufficient for generating dc output voltage.

8. Continued….
• A significant challenge in harvesting piezoelectric energy is that piezoelectric
materials are optimal for generating high voltages but provide only a low current
output.
• The polymer used in the shoe transducer provides over 5 mJ of energy per step
but at voltages too large (>50 V) to be directly used in low power sensors.
• A breakthrough in piezoelectric power generation is the new voltage regulation
circuits that is developed at Louisiana Tech University that efficiently converts
the piezoelectric charge into a usable voltage.
• . A conversion circuit coverts the high voltage to a regulated 3 V output for
charging batteries or for directly powering electronics at better than 70%
conversion efficiency. Combined with the polymer transducer, the regulation
circuit gives time-averaged power of 2 mWper shoe during a regular walk.

9. New Applications for Energy Harvesting
• Medical and Fitness Devices:- RF is already being used experimentally to recharge the
batteries in pacemakers and implanted transcutaneous electrical nerve stimulation
(TENS) devices. The patient sits in a chair that contains a low-frequency RF source
whose output is received, rectified, and stored by the device.
• Researchers at MIT and Harvard have developed a chip that can be implanted into the
inner ear, with power provided by harvesting the energy in sound waves. The chip is
designed to monitor biological activity in the ears of people with hearing or balance
impairments.
• MEMS pyroelectric generator:- Oak Ridge National Laboratories has developed a
unique pyroelectric generator that can cool electronic devices, photocells, computers,
and even large waste-heat producing systems while generating electricity .

10. Conclusion:-
• Energy harvesting is useful in giving energy to low energy devices. EH also has the
potential to replace batteries for small, low power electronic devices. Benefits of EH:-
• Maintenance free – no need to replace batteries
• Environmentally friendly – disposal of batteries is tightly regulated because they contain
chemicals and metals that are harmful to the environment and hazardous to human health
• Opens up new applications – such as deploying EH sensors to monitor remote or
underwater locations.
• EH has also new applications in different sectors like medical fitness and solar field.