Wireless charging: The coil strikes back

    According to the current hot trend of drone development, whether it is delivering packages, monitoring farms, or catching criminals, this small and flexible aircraft seems to be able to do it in the future. However, this guy is not without shortcomings, the most annoying of which is the problem of insufficient battery life. Most drones currently on the market can stay in the air for no more than 30 minutes on a single charge, after which the battery needs to be replaced or connected to a power source for charging.

DHL uses drones to deliver packages

    However, Joshua Smith, a computer scientist at the University of Washington, is trying to change this embarrassing situation of drones. In May of this year, Joshua's own Wibotic company was established to solve the charging problem of automated products including drones and ground robots. He hopes to abandon the physical connection method. When the battery of the robot or drone is low, the power can be replenished within a range of about half a meter from the charging device; LaserMotive, a startup company also from Seattle, is even more ambitious. The company is currently developing a system that can use lasers and photovoltaic cells to charge drones in flight.

    In fact, the idea of ​​transmitting electrical energy wirelessly has existed for more than a century. In 1893, Nikola Tesla, one of the advocates of industrial-grade electricity applications, demonstrated the "stunt" of "lighting up a light in the next room" at the Columbian Exposition held in Chicago that year. However, compared with Tesla's long-cherished ambition, this little trick of "lighting up a light bulb" seems to be not worth mentioning at all. According to his idea, in the future, electricity can be transmitted to all parts of the world by "broadcasting" using towers and balloons. Tesla even successfully applied for investment from JPMorgan Chase for the first experiment.

Nikola Tesla

    Unfortunately, as most physicists predicted at the time, Tesla's "wireless power transmission" experiment ultimately failed. Although Tesla's paranoia and love of the limelight were once criticized, it is undeniable that some reliable ways to achieve long-distance power transmission are currently gaining more and more attention. For example, the wireless charging technology pioneered by Tesla has been realized on mobile phones, and researchers are even developing similar wirelessly powered kitchen appliances, military equipment such as head-up displays, and medical devices such as heart pumps and electroencephalograms. According to IHS, a well-known market research organization, the current annual sales of such equipment is around US$500 million, and this number will increase 30 times in the next 10 years.

Standard Issues

    Putting aside the "laser power generation" mentioned by LaserMotive, there is a most basic physical principle behind the current mainstream wireless charging technology - induction. The alternating current through the primary coil generates a vibrating induced magnetic field, and in this magnetic field, an induced current is generated in the secondary coil close to the primary. If the two coils are close to each other and the winding direction of the wires is consistent, then almost no energy will be lost in the electromagnetic induction process; but if the two coils are separated by only a few millimeters, or one of the coils is arbitrarily swung, the efficiency of power transmission will drop significantly.

Coupled induction principle

    At present, all electric toothbrush products on the market use the above-mentioned coupled inductive wireless charging technology. However, if it is to be used on a drone, it means that the aircraft needs to hover in a fixed position above the charging device for a long time, which is obviously not very practical.

    The solution provided by Wibotic is to adjust the vibration frequency of the circuits in the energy transmitter and the energy receiver to be consistent, or to make them resonate at a specific frequency, so as to achieve efficient transmission of electric energy. This induction method allows the distance between the energy transmitter and the receiver to be kept about the diameter of the coil. In addition to charging drones, the charging device built based on this principle can be made into a bowl shape or embedded under the desktop to power smart watches, laptops and other products.

    Like electromagnetic induction, the idea of ​​generating current through magnetic field resonance was put into practice by Tesla in his demonstration in 1893. However, in order to generate induced current at a specific distance, the entire system was specially optimized. However, the resonance induction technology that has evolved to this day can automatically change the electrification characteristics of its internal circuits as the situation changes. Therefore, Wibotic said that even if the drone shakes violently or in strong winds, it will not affect the charging efficiency of the system. Philips has previously demonstrated a food processor with wireless charging function, which relies on a coil embedded in the kitchen stove for power supply and is not affected by splashing juice, dirt, etc.

    Regardless of whether wireless charging technology can be as highly developed as Liu Cixin described in The Three-Body Problem, it is essential to at least establish a unified industry standard. However, since the emergence of wireless charging technology in 1890, two groups of scholars, led by Tesla who preferred to use alternating current and Edison who advocated direct current, have been arguing endlessly. For consumer products, three major technical standards have been derived so far.

    [1] Qi is a wireless charging standard launched by the Wireless Power Consortium (WPC), the world's first organization to promote the standardization of wireless charging technology. There are nearly 200 technology companies among the WPC members. This standard allows the maximum output power of wireless charging devices to not exceed 5W, which is generally used by mobile phone manufacturers. Currently, there are 12 car models that provide wireless charging devices that meet the Qi standard, and a total of 80 different models of smartphones can be adapted. In addition, some models of modular desks and bedside lamps sold by IKEA have built-in Qi standard wireless chargers.

    [2] The PMA standard, launched by the Power Matters Alliance, is a direct competitor to Qi and focuses on the fast food market. Currently, hundreds of McDonald’s and Starbucks chains across the United States have begun to provide consumers with wireless chargers that comply with the PMA standard;

    [3] The Wireless Power Consortium (A4WP) has launched the Rezence standard. It allows multiple devices to be charged simultaneously and is more flexible in terms of the position and angle of the devices. Its charging capacity and time are also more in line with consumer expectations, and the maximum transmission power does not exceed 50W. Although there are currently no electronic products that are compatible with the Rezence standard, Intel has stated that it will integrate this technology into the next generation of microprocessor chips developed for tablets and laptops, and a large number of new products will be launched as early as next year.

    In early June this year, PMA and A4WP officially announced their merger, and will work to integrate magnetic resonance and magnetic induction technologies to create a more unified wireless charging standard. Obviously, the Qi standard of the WPC Alliance will be severely impacted. However, the Apple Watch smartwatch launched by Apple this year uses a "self-developed" wireless charging device that does not meet any standard on the market.

Apple, which has always been different, has brought its own wireless charging standard this time

    However, for ordinary consumers, the battle for industry standards for wireless charging technology actually has more advantages than disadvantages, because mobile phones and other electronic products that can adapt to two or even multiple standards are bound to become the mainstream of the market.

    Alex Gruzen, founder of wireless charging equipment company WiTricity (one of the initiators of the A4WP Alliance), believes that who wins or loses is not the key, and Intel's participation will have a positive impact on the entire industry. Alex said that in 2003, when Intel decided to integrate wireless network functions into its own processor products, no one expected that a revolution about "Wi-Fi" would start. Therefore, wireless charging technology is currently in the same period of change, and everything is possible in the future.

Tesla’s Exception

    As wireless charging technology is gaining popularity in the field of consumer electronics, the automotive industry is also paying more and more attention to this new technology, and the popularity of electric vehicles has also opened up new market opportunities for wireless charging technology. However, car companies, which have always been cautious, do not want to get involved in similar "standard wars", so the Society of Automotive Engineers (SAE), after consulting with car manufacturers, wireless charging technology companies and power suppliers in detail, established the industry standard for future automotive wireless charging services, namely, output power ≤ 20kW and operating frequency 85kHz.

    The first batch of models equipped with wireless chargers that meet this standard are expected to be launched in 2017 or 2018. Interestingly, Tesla Motors, named after the physicist "Tesla", does not seem to be interested in wireless charging technology. In particular, CEO Elon Musk believes that compared with super charging stations, wireless charging technology is an "inefficient and low-energy" charging method, but the latter not only has a maximum output power of 6 times that of the former, but has also taken root in thousands of regions around the world.

Road with wireless charging function

    However, whether it is plug-in or wireless, fixed electric vehicle charging stations still cannot meet the ambitions of some companies. Recently, Qualcomm and German automaker Daimler aim to revolutionize the way traditional electric vehicles are charged. It even hopes to integrate wireless chargers and roads in the future. In this way, automobile OEMs that have mastered this technology will obviously leave most of their competitors behind, because as the most expensive component of electric vehicles, the battery life of lithium batteries will directly affect the sales of the models. At present, in parts of South Korea, Italy, the United Kingdom and California, many electric buses can be recharged through wireless charging equipment buried underground.

summary:

    The large-scale application of wireless charging technology can not only change the iteration mode of consumer electronic products, but also have an unprecedented impact on the automotive industry. Once car companies cut the capacity of on-board batteries by half, they can save tens of thousands of dollars in costs without affecting the battery life, which is also very beneficial to consumers and may even give birth to a new car purchase/leasing model.

    Although Tesla failed to realize his long-cherished wish of transmitting electricity between continents through broadcasting, his "little trick" may have a more far-reaching impact on the progress of human society: the maturity of wireless charging technology has driven the healthy development of electric vehicles, which means fresher air and a more livable living environment.