FEAT RE FEA ATURE
THE ININTERNET of TH NGS SUPPLEME HINGI
MENT
THERE’S POWER IN THE AIR: tte life s a im ct o th succe s o Io ces. H re tro the real of the I ternet of Thi gs
THERE’S POWER IN THE AIR: Wireless battery charging for the IoT
Battey life has a huge impact on the success of IoT devices. Here Tony Armstrong, director of m rketing for th Power by Linear Group at Analog Devices explores the current capabi ties for power transm sion withi
recto
of marketing for the Power by Linear Group at Analog Devices explores the current capabilities for power transmission within the realms of the Internet of Things
T
he term “Internet of Things” (IoT) refers to the ongoing trend to
connect not only people and computers, but all sorts of “things” to the Internet and each other. By way of example, consider if you will applications such as industrial manufacturing facilities or large infrastructure proj
ojects where
connecting more sensors (or actuators) in more places can increase efficiency, improve safety and enable entirely new business models. This increased level of data exchange is also commonly referred to as Industry 4.0.
Traditionally, the various types of sensors used in such factories were connected by wires to their power sources. However; going forward, rather than the challenge and expense of running cables all around a facility, it is now possible to install reliable,
industrial-strength wireless sensors that can operate for years on a small battery, or even harvested energy fromsources such as light, vibration or temperature gradients. It is also possible to use a combination of a rechargeable battery and multiple ambient energy sources too. State-of-the-art and off-the-shelf energy harvesting (EH) technologies, for example in vibration energy harvesting and indoor or wearable photovoltaic cells, yield power levels in the order of milliwatts under typical operating
conditions. While such power levels may appear restrictive, the operation of harvesting elements such as wireless sensor nodes over a number of years can mean that the technologies are broadly comparable to long-life primary batteries, both in terms of energy provision and the cost per energy unit provided. Although primary batteries claimto be able to provide up to 10 years of life, this greatly depends on both the level of power pulled out of it and the frequency with which it occurs.
Systems incorporating EH capabilities will typically be able to recharge after
S4 S4 DECEMBER JANUAR 201 ECEMBER/JANUARY 2018 | ELEC ELECTRONICS / ELECTRONICS ELECTRONICS
depletion, something that systems powered by primary batteries cannot do. Nevertheless, most implementations will use an ambient energy source as the primary power source, but will
supplement it with a primary battery that can be switched on if the ambient energy source goes away or is disrupted. This can be thought of as a “battery life extender” capability, giving the systema long working life – approaching that of the working life of the battery which is usually about 12 Thionyl Chloride
chemistry. Moreover, years for Lithium
due to intrinsic safety concerns, some rechargeable batteries cannot be charged by wires but require being charged via wireless power transfer techniques. In many of these applications a connector for charging purposes is difficult or impossible to use. For
,
example, some products require sealed enclosures to protect sensitive electronics fromharsh environments. Other products may simply be too small to include a connector, and in products where the battery-powered application includes movement or rotation, then it is virtually impossible to have charging with wires. Therefore, what alternative method can be employed to deal with these circumstances? Well, it is clearly one which eliminates the connector and would be wireless charging capable. A wireless charging solution adds value,
reliability and robustness in those applications where connectors cannot.
WIRELESS POWER TRANSMISSION Wireless power is a good solution in those instances where an ohmic
WIRELESS POWER ANSMISSION
connector cannot be used. So what is it? Simply put, wireless power transmission is the transmission of electrical energy froma power source to an electrical load through electrical insulator(s). There are a few challenges involved in transferring power in this manner. When an electrical current flows through a conductor, a magnetic field is generated. Specifically, when an alternating current is flowing through a conductor, a time varying magnetic field is generated in the vicinity of the conductor And if another
.
conductor is placed in this magnetic field, an alternating current is induced in this second conductor.
The magnetic field intensity is Figure 1: Figure 1:
Wireless power transfer from a primary transmit coil (Tx
Wireless power transfer from a primary transmit coil (Tx) to a secondary rreceive coil (Rx),
Tx) to a secondar
eceive coil (Rx), including the LT
including the LTC4120L C4120
proportional to the magnitude of the current flowing in the conductor. Energy is transferred froma conductor that produces the fields (the primary) to any conductor on which the fields impinge (the secondary) via the magnetic coupling defined above. In a loosely coupled system, where the coupling coefficient is low, a high frequency current does not pass for long distances along a conductor but rapidly loses energy because of the impedance
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