The multinational electronics company Xiaomi announced the development of a new power transmission system that can charge a cellphone from across a room without any wires or charging pads.
The Mi Air Charge Technology, still in development, is capable of providing 5 watts of power to a device around 16 feet away. Transmission is unaffected by physical objects between transmission and receiving points.
As a company blog posted on its web site stated today, “The core technology of Xiaomi’s remote charging lies in space positioning and energy transmission.”
The charging base is composed of an array of 144 antennas that utilize beamforming to send millimeter-wide waves directly to a cellphone or other device.
Beamforming creates wireless signals that are aimed towards a specific device to achieve a faster, more reliable and more direct connection. Traditional wireless signals disperse waves to reach multiple devices over a wide area.
Devices such as smartphones capture the waves and convert them into power. Beacon antennas on the devices to be charged emit low-power signals allowing the charging station to pinpoint their location. A 14-antenna receiving array captures and converts the waves into power.
Miami says it hopes to soon broaden the reach of Mi Air Charge Technology.
“In the near future,” Xiaomi says, its “self-developed space isolation charging technology will also be able to work with smart watches, bracelets and other wearable devices.”
“Soon our living room devices, including speakers, desk lamps and other small smart home products, will all be built upon a wireless power supply design, completely free of wires, making our living rooms truly wireless,” Xiaomi says.
The concept of modern wireless charging was introduced in 2009 as Palm Inc. unveiled its wireless Touchstone charger for use with its popular Palm personal digital assistant. Those devices were the first widely used handheld computers and helped usher in cellphone technology.
A technology similar to Mi Air Charge was introduced in 2015 by tech firm Energous, which claimed its WattUp technology could charge phones up to 15 feet away. It used a combination of radio frequency and Bluetooth connections to identify and contact receiving-chip embedded devices to be charged. Its prototypes did not exceed 70 percent efficiency and the product was never brought to market.
The first known use of wireless power transfer technology was 127 years ago as inventors M. Hutin and M. Le-Blanc introduced an electric vehicle. But competitor combustion engines gained wide acceptance and electric vehicles, especially cars, would not gain serious attention until more than a century later.
Xiaomi is noted for its highly regarded Mi series cellphones. In 2014, its Xiaomi Mi 3 held the title as the fastest Android smartphone. And while the Apple iPhone 12 boasted a groundbreaking 15-watt MagSafe wireless charging staton last year that could fully charge a phone in a half hour, Xiaomi at the same time unveiled an 80-watt that could complete the job in 19 minutes.
The Mi Air Charge Technology is not expected to be available before 2022.
reference link: blog.mi.com/en/2021/01/29/forg … r-charge-technology/
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From electromagnetic engineering to wireless power transmission and energy harvesting – Alexandru Takacs
Wireless power transmission and energy harvesting
In 1864, J.C. Maxwell unified the electromagnetic theory by introducing a set of differential equations known as ‘Maxwell equations’. Maxwell’s work was groundbreaking and represents a milestone in the development of electromagnetic physics.
His results have been made possible as a result of 200 years of research performed by talented Scientists including, but not limited to, Coulomb, Ampère, Faraday, Lenz, Œrsted, Gauss, and Huygens. Maxwell’s equations explained most of the known electromagnetic phenomena and introduced the idea that electromagnetic waves should exist. Some years later, in 1887, Heinrich Hertz experimentally proved the existence of electromagnetic waves. The Hertz experiment opened the way for the use of such waves to transfer/transmit ‘something’ from one point to other without the use of wires.
Two talented scientists and inspired inventors explored two different and apparently opposite research directions:
- (i) the use of the electromagnetic waves to transmit information (Marconi’s approach, which opened the way for radio communications, a better alternative to the telegraph);
- (ii) the use of electromagnetic waves to transmit energy (Tesla’s approach, which opened the way for wireless power transmission/transfer, or WPT, as an alternative to the wired grid used for electricity distribution).
Marconi’s approach was easier to implement and important advances were rapidly obtained in the field. The 20th century confirmed the ‘supremacy’ of the Marconi approach (wireless communications) over Tesla’s approach (WPT), with several notable exceptions:
- (i) the technology of induction cooking, based on power transmission in the near-field region by using the magnetic field, was first introduced in a World Fair at Chicago in 1933 and was then developed at large scale starting from 1970;
- (ii) the birth of the RFID technology in 1950 as a consequence of an espionage affair (Russians spied on the American embassy in Moscow by using a rudimentary RFID technology),
- (iii) the Brown experiments (1960-1980) that demonstrated that is possible to transmit energy at a distance, in the far-field region, by using RF and microwave waves.
At the beginning of the 21st century, WPT research once again raised interest through a focus on new fields of applications: wireless charging of various electronics devices (smartphones, laptops, electronic bio-implants, etc), wireless charging of electric cars, implementation of battery-less systems (including, but not limited to: wireless sensors, active tags, cyber-physical systems, etc.). Figure 4 shown the photos of several WPT demonstrators and products illustrating the historical evolution of WPT concepts and research.
Wireless power transmission for batteryless applications
Wireless power transmission for batteryless tags, wireless sensing devices, and indoor localization and tracking systems
In the last decade, RF power transmission has regained particular interest thanks to the large-scale deployment of wireless electronic systems used in Internet of Things scenarios (IoTs), where wireless sensors and tags are used in many applications, such as patient in-home health monitoring48, structural health monitoring49, automobile/aircraft health monitoring50, etc.
In order to increase the energy autonomy of such wireless sensors and tags, two scenarios are usually considered:
i. Wireless Power Transmission (WPT), where the wireless powering is carried out using dedicated RF sources.
This scenario is useful for the 3D indoor localization of objects with passive (or batteryless) Radio-Frequency IDentification (RFID) tags .
Indeed, WPT can be used to supply power to low-cost, maintenance-free, autonomous tags. The main advantage of WPT is the control of the whole transmission chain. As the user sets the frequency and the amount of the transmitted power, the system’s efficiency can be accurately estimated for such a scenario;
ii. Energy Harvesting (EH), where the ambient RF energy is harvested. In this scenario, the frequency and the power generated by RF sources (from, e.g., Television, GSM, or Wi-Fi networks) are not under the users’ control. Furthermore, the low ambient RF power densities make energy harvesting very difficult to exploit in practice.
In these two scenarios, rectennas are usually designed for harvesting the available electromagnetic energy and to supply power to DC-to-DC boost converters and power
management units of passive (batteryless) and wireless sensors. The block diagram of standard rectennas is shown in Figure 7. It is composed of two main passive devices: the antenna and the rectifier.
The antenna captures the ambient electromagnetic energy and converts it into a guided RF signal. The antenna radiation efficiency drives the RF-to-DC efficiency of the rectenna and, consequently, it must be maximized. Furthermore, the size of the antenna must be as small as possible in order to be embedded in most systems in use nowadays. For a given bandwidth, the best trade-off has to be found between size and radiation efficiency of the antenna.
The rectifier converts the guided RF signal into the DC power for supplying DC-to-DC boost converters and electronic devices, such as sensors. The key component is the non-linear device (e.g., Schottky diode or transistor) used to convert the RF signal into a DC voltage.
This device is carefully selected in this study in order to rectify low-power signals. Moreover, the rectifying process generates undesirable harmonics at the input and output ports of the non-linear device. At the input port, a matching circuit/band-pass filter is usually placed to prevent these harmonics from being re-radiated by the antenna and to maximize the energy transfer. In addition, the harmonics generated at the output port are low-pass filtered along with the fundamental harmonic. The load (that is, the DC-to-DC boost converter and sensing device) is then supplied with the required DC power to operate.
In December 2015 we were contacted by a Toulouse start-up, Uwinloc51, that began developing an innovative system for indoor localization. The Uwinloc system was revolutionary because they proposed the first battery-less tag for tracking a large volume of assets. The basic principle of such a system, shown in Figure 8, is to use a minimized number of synchronized UWB beacons to precisely localize UWB baterryless tags powered wirelessly by a WPT far-field technique. A system of synchronous UWB beacons assures the precise localization of battery-less UWB tags. The tags are equipped with rectennas and receive the energy wirelessly from the beacons that also transmit a RF energy/power in an ISM frequency band.
After signing an NDA (Non-Disclosure Agreement), we started to work together with Uwinloc as part of a collaboration project52 funded by Uwinloc (from June 2016 to April 2017). Following the design requirements provided by Uwinloc, we proposed innovative rectenna and rectifier topologies and we quantified the main limitation of such WPT systems.
We still collaborate with Uwinloc beyond the end of this first research project. At the end of 2017, we were awarded a research grant (OPTENLOC53) co-funded by Région Occitanie (in the frame of GRAINE call) and by Uwinloc. As part of this ongoing OPTENLOC project (started in January 2018) the research focus shifted from the optimization of the WPT receiver side (i.e., the design and the optimization of the rectenna and its optimal integration with the electronics of the UWB tag) to the optimization of the overall WPT system, including both the Tx (RF sources) and Rx (the rectennas integrated into the battery-less tag) parts of the system. Thus, our ongoing research is focused on:
- (i) the optimal integration of the UHF rectenna into the UWB batteryless tag. The tag should be as compact as possible, low profile, and insensitive to its environment. The size of the UHF antenna has to be further miniaturized and integrated on the same PCB as the UWB antenna. There are very few published results54,55,56 concerning the integration of the UWB and UHF antennas and basically two solutions can be envisaged : (1) two separate antennas (one for UHF and one for UWB) or (2) a single multiband antenna covering both the UHF and UWB frequency bands. The first solution is less compact while the second one can be more compact but requires the use of diplexer systems. The final choice should be a best trade-off between antagonist criteria concerning the compactness, the losses, and the intrinsic antenna/antennas performances (gain, efficiency, input impedances, etc.).
- (ii) the characterization and the modeling of a propagation channel for at least several typical indoor locations.
- (iii) the development of methodologies and strategies to find : (1) the minimum number of RF sources for a given indoor location and (ii) the best-site implantation of the UHF RF sources, at least for typical indoor locations.
- (iv) the development of a phasing/time delay command system for the RF sources in order to increase, on demand, the amount of RF energy available in some particular location where the UWB don’t have enough energy to communicate with the beacon. Basically, the RF power radiated by the RF sources is regulated, but it is possible to control the relative phase or the time delay (if waveform pulses are used) between the RF sources in order to improve the power density of the electromagnetic waves in targeted location.
An overview of the state of the art in the field of the far-field WPT57 demonstrates that this topic is intensively addressed by the scientific community. Progress has been made in the development of innovative solutions for implementing the basic parts of such a system. To the best of my knowledge, there are no published results concerning a complete far-field WPT system for tags localization. This full-system approach forms the core of the ongoing research performed together with our industrial partner (Uwinloc) as part of the OPTENLOC project.
reference link : https://hal.laas.fr/tel-02503585/document