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Top 5 things to know about wireless power design

Technology News |
By eeNews Europe

When designing a wireless power system, the key considerations that impact the design are typically user experience, efficiency, power levels, standards, component selection/availability and cost. A well-designed system can provide a variety of benefits from improved features (e.g. a smartphone that no longer needs to be plugged in) to enabling new technologies (e.g. a sensor hub placed inside of a radioactive environment that is inaccessible by wires and unsafe for human interaction). Wireless power systems utilizing magnetic field coupling have been around since the late 1800s, but recent advances in components, chips, and system architectures allow engineers to readily implement wireless power into their devices to improve user experience. So, let’s examine the top five things to know about wireless power design.

#1: User Experience

How users interact with a device is one of the most fundamental questions every good engineer asks at the start of a project. Do your customers require rapid charging? Alignment flexibility? Low heating? Long-distance charging? High power? Multiple receivers per each transmitter? Small form factors?

All of these options are achievable but often times come with a tradeoff. For example, high power and low heating don’t always go hand-in-hand. Distance and efficiency are fundamentally opposed. A firm understanding of what your users require and how to prioritize those needs is an essential first step in designing a wireless power system for your device.

#2: Efficiency

Of any metric that can be used to gauge the performance of a wireless power system, efficiency is king. Inherently efficient systems can provide greater distance, more orientation flexibility, lower heating, smaller sizes and a lower drain on the power source. The three main blocks of the wireless power system largely govern efficiency as follows:



Figure 1: The three blocks of a wireless power system.

If all three blocks operate at their lowest estimated efficiency (i.e., 80%, 70% and 80%; see Figure), the overall system efficiency would be approximately 45%. For a 5W device, it would take 11W of transmitted power in order to provide full charging to the device and roughly 6W would be dissipated into the device itself (as heat) and into the surrounding environment, including the air, furniture, and human tissue. At low power levels, this may be safe and acceptable. At higher power levels, like for electric vehicle recharging where 5kW is a typical lower end charge level, 6kW would be lost into the transmitter, car, and surrounding environment and would pose serious heating and safety problems.

In the case where all three blocks of the wireless power system operate at their highest estimated efficiency (i.e., 95%, 90% and 95%), the overall system efficiency would be approximately 82%. In this case, a 5W device would only require approximately 6W from the transmitter and only 1W would be lost to inefficiencies. In order to increase system efficiency, designers should focus on high efficiency components and increased coupling between the transmitter and receiver.

#3: Power Levels

Wireless power systems using magnetic field coupling can be implemented for devices from milliwatts to kilowatts. For microwatt devices, energy harvesting or RF wireless power may be a more attractive option to explore. The power requirements for your device will dictate your component selection, companies with whom you can partner on design, and sizes.

#4: Standards & Regulatory

Multiple standards currently exist for wireless re-charging of electronic devices, including Alliance For Wireless Power (A4WP), Power Matters Alliance (PMA) and Wireless Power Consortium (WPC). The standards organizations exist to provide a platform for interoperability between transmitters and receivers while providing guidelines on innovation of products and components that meet regulatory requirements.

If your device requires interoperability (will users want to recharge it at the airport or their local coffee shop?), you should focus your design around a standard. Generally speaking, A4WP has the most technologically advance solution for “loosely coupled” systems and WPC has the most readily available development tools and components, but is a “tightly coupled” system (at least for the time being). PMA is merged with A4WP and provides the “tightly coupled” technology to that shared standard.

If your device does not require interoperability and users will always use one transmitter type for their device, you have the flexibility to develop a proprietary, closed solution. It may still make sense to use off-the-shelf components and technology from the standards organizations as your starting point for ease of development and availability of resources, but you do not need to focus on meeting the full standard specification. If your device meets your requirements and stays within regulatory limits, you will have a winning design.

#5: Component Selection

Since efficiency is king and components dictate efficiency, it is essential to know about your options when selecting components. There are a number of component companies developing high efficiency, cutting edge components in the wireless power space. For example, Efficient Power Conversion Corp has developed eGAN transistors with high efficiency switching to yield high performance power amplifiers. On the antenna side, NuCurrent has developed antenna structures that yield high efficiency, highly scalable, and small antennas. Meanwhile, IC companies like IDT, Broadcom, Texas Instruments and others are developing ICs that can support multiple standards, various power levels, and small form factors. Options abound and if you are new to wireless power designs, one of the best places to start is working with a component vendor or design consultant who understands the wireless power landscape and can help fast-track your design needs and introductions to strategic development partners.

About the Author

Dr. Vinit Singh is CTO of NuCurrent, a leading developer of high-efficiency antennas for wireless power applications. Compliant across Alliance for Wireless Power (A4WP), Wireless Power Consortium (Qi) and Power Matters Alliance (PMA) standards, NuCurrent works closely with electronic device OEMs and integrators to custom-design, rapid-prototype and integrate the optimal antenna for a broad range of applications.


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