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What you will learn:
- Wireless sensor networks used for energy harvesting.
- How energy harvesting best serves nanoelectric applications.
- An overview of a wireless energy harvesting switch.
Energy harvesting (WSN) based wireless sensor networks are the result of activating WSN nodes with the ability to extract energy from the surrounding environment. There is no single wireless technology or standard that WSN operates on. However, many wireless standards contribute to the success of WSN systems. The most popular of these are the Bluetooth, ultra-wideband (UWB) and Zigbee wireless standards according to IEEE 802.15.4.
What is a WSN?
The main component of any WSN network is a WSN transceiver. The transceiver houses both the RF transmitter and the RF receiver. The WSN transceiver complies with all WSN wireless standards, one of which is IEEE 802.15.4
Down IQ PMIC
Power management ICs (PMICs) typically incorporate several of the following: low-dropout (LDO) regulators, DC-DC regulators, sequencers, load switches, supervisors, load switches, power ICs self-test (BIST), as well as logic components in a single integrated circuit. These devices are easily configurable with hardware and serial communications.
A PMIC must handle loads ranging from microamps to hundreds of milliamps and must be able to distribute power to devices used in an energy harvesting system. The PMIC will provide efficient system management for loads ranging from fractions of microamps to a few hundred milliamps. It will typically operate on a 2.2-5V input range.
If an energy harvesting network becomes too active, excess nodes should be kept in standby mode until needed for coverage and connectivity, especially if other nearby system nodes fail.
Some energy harvesting systems can draw all of their energy from the surrounding environment, usually light or vibrational energy. Such devices could serve as platforms for running environmental sensors or other types of sensors in remote locations.
Nanoelectric applications can make the most of energy harvesting as the primary power source. Applications include smart homes, smart thermostats, smart locks, smart doors and windows, and even fitness bands, sports watches, and activity trackers.
Hard-to-reach remote applications will really benefit from energy harvesting. Instead of sending a technician out every month or year to replace batteries, these types of applications will now run battery-free and last virtually forever.
Most energy harvesting components, such as solar panels or piezoelectric devices, can only produce a few milliwatts (one thousandth of a watt) or even a few microwatts (one millionth of a watt) per hour. Although small, such quantities, when accumulated, can power small systems due to recent improvements in microcontrollers and low-power transmitters. By using such self-powered systems, sensor networks could be set up where it was not possible to do so before, due to the inability to supply power (by replacing batteries or by running a power line) to the sensors.
Even medical devices implantable in the human body can use energy harvesting techniques. These types of applications run at low data rates and low duty cycles while operating on average nano power.
Sources such as light, electromagnetic (EM) waves, vibration on bridges, or even heat generated by the human body are viable energy sources. Light produces by far the most energy per unit area. Solar harvesting applications can sometimes use low IQ buck converter in design as well.
Solar energy harvest
So how can designers use solar power to transmit via radio?
If we have solar cells that receive sunlight and they are arranged in series to create a higher voltage, we still won’t have enough power in those cells. The solution is to store this energy in something like a capacitor. This way we can now use a nanopower, low-IQdc-dc buck converter to create a center rail needed to power a radio IC (see picture).
Wireless switch using energy harvesting
The switch of this design is constructed like a linear dynamo and will transform its mechanical energy into electrical energy. This electrical energy is recovered optimally.
Since the switch is cordless and cableless, it increases flexibility and availability where mechanical vibration or a chemically aggressive environment can render cables impractical.
Kinetic energy is the energy generated by the motion of an object. In this case, the object is a magnet in the switch that moves back and forth inside a coil. It changes the magnetic field and induces a voltage in this coil. This principle is well known as electromagnetic induction or Faraday’s law.
Energy harvesting switches are ideal when reduced maintenance and installation costs, increased flexibility and system availability are required and when wiring would be impossible. These switches are a potential solution especially in explosion proof applications. Indeed, their inherent low-power operating characteristics allow the design to avoid the use of intrinsically safe barriers, encapsulation, or other costly protection methods.
This type of design targets applications that require start-stop signals for machine start and stop control, presence and position sensing, counting, alarm signaling, and other desired digital inputs. .
In this example, a buck converter regulates the rectified and doubled signal coming from the switch, feeding the output voltage to a 32-bit, 2.4 GHz Arm Cortex-M3 multi-protocol wireless MCU with 128 KB of flash memory. A voltage doubler is used at the input of the buck converter to charge the capacitors from the output voltage of the switch and switch these loads so that exactly twice the voltage is produced at the output compared to the ‘Entrance. All these devices consume very little IQ.
Engineers have harvested energy for hundreds of years, first with water and windmills, then hydroelectric dams, solar panels and geothermal power plants. Now, in today’s advanced electronic environment, engineers can use tiny solar panels and thermoelectric generators to access energy from seemingly insignificant temperature differences – piezoelectric devices that convert small mechanical vibrations energy to create electricity.
The amount of power can be low (measured in microwatts) and devices typically do not generate electricity 24/7. But the ambient energy sources they use, including light, heat differentials, vibrating beams, transmitted RF signals and others, provide this small amount of energy for free. Low quiescent currents help make this possible.
An introduction to wireless sensor networksUniversity of Southern California
“A 1.1 nW Energy Harvesting System with 544 pW Quiescent Power for Next-Generation Implants,” US National Library of Medicine, NIH