- Table 3. Transmitter rankings. Multi-Position Ranking Transmitter ID UUT 1 UUT 2 UUT 3 UUT 4 UUT 5 UUT 6 UUT 7 UUT 8 Average difference by Rx 1 2 3 4 5 6 7 8 1 2 4 5 7 3 8 6 Center-Position Only Ranking Phone 1 Ranking Phone 2 Ranking Phone 1 Ranking Phone 2 Ranking 2 5 1 3 7 4 6 8 1.25 2 1 3 6 4 8 2 7 5 Average Difference by Tx 0.50 1.00 3.00 1.00 1.50 2.50 1.00 2.50 Standby Power W Range 130mW to 810mW UUT 7 UUT 4 UUT 1 0.2 0.4 mW FIG 11 Sample of common wireless transmitters in 2021. 0.6 0.8 1 24-h period. However, it is well within reach to reduce quiescent power by 50%. Looking at seven popular wireless transmitters introduced in 2021, we observed a narrower standby power range of 130-810 mW, with the median value (after removing the 810 mW outlier) of 210 mW (Figure 11). This is up from the 180 mW median value we saw in the first experiment (Figure 9). Cutting standby power to 100 mW would save 2.6 Wh over a 24-h period. Conclusion As a result of the efforts by the WPC Energy Star Task force to develop and validate a fair and repeatable test, we are disappointed to conclude that we were not able to meet the goal of proposing an efficiency-test protocol for the U.S. Environmental Protection Agency (EPA) that could rank Qi wireless power transmitters based on power-transfer efficiency. We hope the industry and academic institutions will continue to research this problem and discover alternative approaches to solving this need. The following bullets summarize our top findings. ■ Wireless power systems for consumer applications have entered mass-adoption. Energy savings improvement programs that target these systems will provide a meaningful societal benefit. ■ Because of receiver-transmitter interaction, it is not possible to quantify or rank a stand-alone wireless power transmitter based on efficiency. ■ A more narrowly defined receiver specification will help measure and help the industry improve wireless power system efficiency. ■ It is possible to quantify and rank the power-transfer efficiency of a transmitter-receiver pair if the receiver design is fixed and the x-, y-, and z-coordinates are carefully controlled. ■ The test receiver in an efficiency test protocol must present a real-world load-resistance profile. September 2022 z IEEE POWER ELECTRONICS MAGAZINE 63 Transmitter