Although wireless charging pads are already available for smartphones, they can only work when the phone remains stationary. For cars, this kind of charging method is the same as charging a charging station for an hour or two, which is very inconvenient. Three years ago, Stanford University electrical engineer Shanhui Fan and his laboratory graduate student Sid Assawaworrarit created the first system to wirelessly charge objects in motion. However, this technology is too inefficient to be used outside the laboratory.
According to foreign media reports, Shanhui Fan and Sid Assawaworrarit recently demonstrated a new technology that can be promoted in the future to provide power for cars driving on highways. In the near term, the system will soon be able to wirelessly charge robots moving in warehouses and factory floors, allowing robots to work 24 hours a day without downtime.
The wireless charger transmits power by generating a magnetic field, and the magnetic field will oscillate at a certain frequency, causing resonance vibration in the coil of the receiving device. The problem is that if the distance between the power supply and the receiving device changes, even if the change is small, the resonance frequency will change.
Three years ago, the researchers made their first breakthrough and developed a wireless charger that can transmit power even if the distance from the receiving device changes. The researchers implemented this function by integrating an amplifier and a feedback resistor. When the distance between the charger and the moving object changes, the amplifier and the feedback resistor allow the system to automatically adjust the operating frequency. However, the initial system efficiency is insufficient and not practical. The amplifier itself needs to use a lot of power to achieve the amplification effect, resulting in the system can only transmit 10% of the power.
But in the new study, the researchers showed how to increase the wireless transmission efficiency of the system to 92%. Assawaworrarit explained that the key is to replace the original amplifier with a more efficient "switch mode" amplifier. This type of amplifier is not new, but the use conditions are very harsh, and only under very precise conditions can high-efficiency amplification effects be produced. After years of tinkering and additional theoretical work, researchers have designed effective circuit structures.
The new laboratory prototype system can wirelessly transmit 10 watts of power over a distance of 2 to 3 feet. Fan said there are no fundamental obstacles to expanding the system to transmit tens or hundreds of kilowatts of power required by a car. He said that the speed of the system is sufficient to provide power for a speeding car. This wireless power transmission technology can complete power transmission in a few milliseconds. Compared with the time required for a vehicle with a speed of 70 mph to pass through a 4-foot charging zone, it is simply not enough to hang teeth. However, the researchers say the only limiting factor is how quickly the car battery can absorb all the electricity.
Assawaworrarit said that wireless chargers do not pose a health risk because the magnetic fields generated by even the most powerful car wireless chargers are within the scope of existing safety guidelines. Although the magnetic field can indeed transmit electricity to people without any awareness.
Although it may take many years to embed wireless chargers on highways, robots and even drones may implement the technology first. Compared with a long highway, the cost of installing a charger on the ground or roof is much lower. Fan said that if you imagine a drone, you can dive down occasionally, hover over the roof, charge it quickly, and fly all day. (Yu Qiuyun)
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