An example of wireless charging in IoT is digital door locks that recharge when closed. Wireless transmitters are located in the door frame and re-charge the bolting/communication mechanism anytime the door is closed. This replaces the need for changing batteries (a significant cost and environmental issue in hotels, for example) and enables a more seamless integration into homes, hotels and offices.
An example of wireless power in IoT is the electronic Smart Retail Label (“SRL”) and beaconing technology known as Powershelf. Battery free SRLs ensure accurate pricing and enable retailers to remotely change pricing on any SKU in the store in minutes. The system is powered by wireless power so it eliminates the need for battery disposal or paper price tags, creating significant cost reductions and an attractive carbon footprint friendly solution for retailers focused on environmental sustainability.
When designing in wireless charging/power, designers will have key considerations:
- Are interoperability standards important? Do you expect users to charge your devices at Starbucks? In their vehicle? If so, you will want to focus on wireless charging solutions that are standards compliant with at least one of the two leading standards, Wireless Power Consortium and AirFuel Alliance. If interoperability is very important, you can find multi-mode solutions that support all standards simultaneously.
Examples of products that benefit from interoperability: mobile phones, laptops, tablets (so you can charge at the coffee shop, home, rental car, airport, office, etc.). Examples of products that don’t benefit from interoperability: hearing aids, surgical tools, personal products (like some wearables, powered jewelry, etc.), specialty products (SCUBA watches) and non-consumer products (first responder radios, mobile phones/computers specialized for rugged worksites, remote sensors, etc.). Standards exist to support interoperability. Interoperability is only relevant if users will actual charge/power the product in diverse locations where wireless infrastructure is expected to be installed. If not, proprietary/non-standard wireless power systems can be a more efficient and cost effective option.
- Form factor is a major consideration. The largest components are the antennas and if you have a space constrained device, you will want to look for ultra-thin solutions. From embedded sensors to slim cell phones, space is a major constraint in many electronic devices.
- Power levels are essential to make sure your battery charge is adequate or your device is receiving enough direct power. There are a range of products from millwatt power levels up to 30 W+ coming to the market right now. Note that power and size go hand-in-hand – you can’t expect to get 30 W of wireless power with a device the size of a nickel.
- Orientation flexibility is important in selecting frequency of power transfer and if you require some positional freedom, you will likely be more well-suited with high frequency systems. Most high frequency systems today operate at 6.78 MHz, so there are components available for that frequency.
Higher efficiency, resonant systems allow greater distance of charging. However, component selection is critical because high frequency can be lost in the wrong components. GaN transistors like those from Efficient Power Conversion Corporation can help minimize switching losses in the power amplifier. Multi-layer, multi-turn antennas from NuCurrent can help minimize skin effects and proximity effects at high frequency and therefore have lower electrical series resistance and heat generation. Shielding materials customized for 6.78 MHz are also essential for appropriate shielding and minimizing losses due to eddy current buildup – your antenna provider should be able to provide the best materials for your application.
In particular, higher efficiency can be useful in applications where larger separation can be helpful. For example, sensors embedded in walls or in hazardous environments will need the wireless power to penetrate through walls or other material to activate the sensor. NuCurrent has transmitted power through 130-mm walls to 1-W loads – sufficient for many sensors in order to power them up and transmit data back to the source/reader through the wall.
- What other components are nearby to the wireless receiver? Shielding may be required to protect the components from EM fields. Shielding is generally required in any application where the wireless power system is surrounded by other electronics. Your antenna providers will help you understand the right application of shielding for you application.
Wireless charging and wireless power are enabling a whole new category of IoT devices and capabilities. If you are designing IoT devices make sure you are considering the potential of wireless power.
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