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2.10 Device Level Energy Issues 99
Considering this approach of looking at energy consumption for one measurement
instead of average power consumption, it results that, today:
• Sending 100 bits of data consumes about 5 μJ,
• Measuring acceleration consumes about 50 μJ,
• Making a complete measurement: measure + conversion + emission
consume 250–500 μJ.
Therefore, with 100 μW harvested continuously, it is possible to perform a
complete measurement every 1–10 seconds. This duty cycle can be sufficient
for many applications. For other applications, basic functions’ power consumptions
are expected to be reduced by 10 to 100 within 10 years; which
will enable continuous running mode of EH-powered IoT devices.
Even though many developments have been performed over the last 10
years, energy harvesting — except PV cells — is still an emerging technology
that has not yet been adopted by industry. Nevertheless, further improvements
of present technologies should enable the needs of IoT to be met.
An example of interoperable wireless standard that enables switches, gateways
and sensors from different manufacturers to combine seamlessly and
wireless communicates with all major wired bus systems such as KNX, LON,
BACnet or TCP/IP is presented in [120].
The energy harvesting wireless sensor solution is able to generate a signal
from an extremely small amount of energy. From just 50 μWs a standard
energy harvesting wireless module can easily transmit a signal 300 meters (in
a free field).
2.10.3 Future Trends and Recommendations
In the future, the number and types of IoT devices will increase, therefore
inter-operability between devices will be essential. More computation and
yet less power and lower cost requirements will have to be met. Technology
integration will be an enabler along with the development of even lower power
technology and improvement of battery efficiency. The power consumption
of computers over the last 60 years was analysed in [133] and the authors
concluded that electrical efficiency of computation has doubled roughly every
year and a half. A similar trend can be expected for embedded computing using
similar technology over the next 10 years. This would lead to a reduction by