Image Processing Reference
In-Depth Information
Energy
scavenging
Energy
storage
Energy
distribution
Concepts
Photovoltaic
Batteries
Microbatteries
Electromagnetic
coupling
Temperature gradient
Technologies
Human power
Wind/air flow
Microfuel cells
Ultracapacitors
RF radiation
Wired power grid
=
Commercial
availability
Pressure variations
Microheat engines
Acoustic waves
Vibrations
Radioactive power
sources
Optical
µW-kW
(m-mm)
50-3500 Ws/cm
3
10
m
-15m W/cm
3
Power levels
Electric field radiation
power level vs. range
Deficiencies
Reliability
Maintenance
General
industrial
applications
N/A
(only for special
single sensors)
Automation cell
power supply
many devices
Portable/mobile
user interfaces
FIGURE .
Overview of wireless power concepts and technologies; power levels, deficiencies, and remark for
general application in factory automation.
Fuel cells are potentially somewhat better, but even their realistic potential is little more than
Wh
cm
) and much development is still
requiredbeforetheycouldenvisionedtobeusedineverydayindustrialinstallations[].Anotherfact
is to be considered for fuel cells. Like human beings, they simply need air to breathe and evaporate
water, a challenge for IP housings.
Environmental energy sources also fail to meet the needs of general industry applications, due
to their unpredictable nature—both in terms of general usability without special engineering work
and reliability. Such solutions would also incur considerable engineering and design costs for every
single device. Nevertheless, for some niche applications, there are use cases, e.g., vibration or high
temperature monitoring (Figure .).
Regarding the energy distribution concepts, only magnetic coupling in the near field can trans-
fer enough power for general use. There are a number of possibilities to use magnetic coupling,
depending on the transmission distance, a wide range of applications and power levels can be covered
(mW at several meters of air gap up to tenth of kW at millimeters).
After a thorough evaluation of the various available options [,], it was concluded that the only
viable, generally applicable solution for factory automation is based on long-wave radio frequencies,
a form of inductive, magnetic coupling.
In Table ., a comparison for a special use case of a wireless proximity switch is summarized.
A figure of merit is defined, which summarizes the characteristic figures:
•
Energy amount over years (Wh)
•
Energy cost over years (USD)
•
Risk of developing such a supply (factor)
cm
/
(petrol energy density would be around Wh
/
The figure of merit is computed by dividing energy by cost and by risk according to Table ..
Inductive energy transfer at low frequencies of around kHz has clearly the highest figure of merit
regarding the intended application.
This is the so-called WISA-POWER approach. This wireless supply principle described below in
more detail provides power supply across a distance of a few meters with the help of magnetic fields
