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Wireless Charging Design in Wearables Using Simulation

Working for ANSYS gives me incredible opportunities to work with innovative companies and learn about the latest technologies that are being developed to improve our lives. One of the intriguing companies I have had the pleasure to work with is RF2ANTENNA. RF2ANTENNA works on developing innovative and easy-to-integrate products for specific applications in wireless communications and wireless charging, with the goal of improving the efficiency of IoT devices with affordable solutions. Their core competency is in providing solutions to radiation problems in mobile products. The ANSYS Startup Program has given them the opportunity to take their work to the next level.

Until recently, every device had to have a plug-in for the power source and other inputs and outputs, such as audio, video, network, etc. With advances in wireless communications, most of the plug-ins other than the one for the power source have disappeared over the last 10 years. Recent advances in wireless charging, however, are paving the way for new devices that have no visible ports or connectors. Many cell phone OEMs have already incorporated wireless charging into their designs. The real value of wireless charging, however, is when it is used on devices that cannot be removed, such as wearable electronics. In wireless charging designs for wearables, the coil designs must be customized to meet the needs of each device. In this blog, I will be talking about how RF2ANTENNA designed and optimized a wireless charging system using ANSYS tools. Contour plots of efficiency vs. different capacitor values

Power Transfer in Wireless Charging

A wireless charging system consists of coupled coils and charging circuits. There are different algorithms and techniques for wireless charging, but our focus here is mainly on optimizing power transfer from the source to the device that is being charged wirelessly. The efficiency of this power transfer directly affects the charging time and energy use regardless of the algorithms.

Leveraging ANSYS Simulation Software

Without going into the details of the coil designs, RF2ANTENNA engineers used ANSYS Maxwell 3D to extract the circuit values for the “wireless coupling mechanism.” They then used ANSYS Nexxim to optimize the circuit and the coils for the charging efficiency (the power delivered divided by the power received) by changing the values of the tuning capacitors (CS and CL) as shown in the CL versus CS plot. Since this was a wearable application, they also used ANSYS HFSS to plot the electric field strength on the human body (due to the charging current) using ANSYS’ human body model. Electric field distribution on the human body model due to the current on the charging device as simulated in ANSYS HFSS

This work could have been done experimentally, of course, but that would involve building different sized coils and setting up a complex measurement system. Electric field distribution is very difficult to obtain experimentally, as it would require detailed models and precise measurement capabilities. The electric field distribution can be used to understand the human body’s exposure to electric fields associated with such wirelessly charged wearable devices.

ANSYS Maxwell 3D and ANSYS Nexxim helped RF2ANTENNA engineers to design the coils that were needed to optimize the efficiency of the charging mechanism. Without these tools, they would not be able to achieve the same quality of design using traditional measurement setups.

Looking to the Future

RF2ANTENNA will continue its efforts to create customized designs in the fields of wireless charging and antennas for mobile devices using ANSYS products. Their goal is to release their first product (which will be an antenna) for wireless communications this year. This product will enable IoT devices to communicate better with more range, so it can be used in RFID and mesh radio applications.

To learn how you can use simulation, check out the ANSYS Startup Program.