Wireless Power Transmission (WPT) How It Works Wireless Power Transmission (WPT) Janaya Walter

Overview Background Categories of WPT Near-field Techniques Far-field Techniques Advantages/Disadvantages and Applications Summary

Background WPT: transmission of electrical energy without the use of wires Requires transmitter (connected to a power source) and receiver Advantages: Useful for devices when wires are inconvenient, hazardous, impossible Protection to possible failures in the power source that can damage the device

Categories of WPT Non-Radiative (Near Field) Radiative (Far Field) Nonresonant Short Range (up to 1 antenna diameter) Resonant Mid Range (up to 10 times antenna diameter) Radiative (Far Field) Long Range (can reach up to several meters)

WPT Techniques Near-Field Techniques Far-Field Techniques Inductive Coupling Capacitive Coupling Magneto Dynamic Coupling Far-Field Techniques Microwaves RF Energy Lasers Ultrasonic Waves

Non-Resonant Inductive Coupling Current generated in a coil by magnetic field induces current in nearby coil Separation, alignment, size of coils determine efficiency of power transfer Involves base station (transmitter) with device placed on top coil diameter, D ReceiverCoil coil distance, z Transmitter Coil [1]

Non-Resonant Inductive Coupling Advantages High Efficiency (30-60% of power) Low heat generation Quick charging cycles Disadvantages Power transfer only up to a few centimeters Cannot pass through solid objects Cannot use device while charging More expensive than traditional charging

Qi Wireless Standard (2008) Inductive Coupling up to distances of 4 cm Generated Power: 5W delivered by low Qi Standard (i.e. mobile devices) 120W delivered by medium Qi Standard (i.e. laptops) Use of placement marks, grooves, or magnets for alignment Alignment between transmitter and receiver is key [2]

Qi Wireless Standard (2008) Mobile Devices (Nokia, LG, Samsung, iPhone) Qi “Hotspots” (Cafés, airports, etc.) Vehicles (personal or public) IKEA (i.e. lamps, tables) [2.5]

Resonant Inductive Coupling Induced current in primary coil still induces current in secondary coil Coils operate at identical resonant frequencies Primary coil induces high current amplification in secondary coil Provides greater allowable distance between coils [3]

Resonant Inductive Coupling Advantages Power transfer up to 10 times distance of Inductive Coupling Does not require exact precision between coils (as Inductive Coupling does) Low heat generation Disadvantages Low Efficiency (compared to non-resonant inductive coupling) Slower charging cycles (compared to non-resonant inductive coupling) Cannot pass through solid objects

Resonant Inductive Coupling Rezence (2012) WiPower (2004) PMA (2012) Open Dots (2015)

Radio Frequency Far Field Technique Advantages Transmitter emits electromagnetic waves (10MHz to 6GHz) Receiver “harvests” energy and converts into DC power Advantages Long-range transfer, No ‘line-of-sight’ system, High efficiency No risk to prolonged exposure (cannot cause radiation sickness) [6] Visible Spectrum

Powercast (2003) Far Field Radio Frequency Charging 1 W of power delivered up to 1.5 meter distance Transmits power to multiple devices at a time No charging mats or direct line-of-sight needed Obstruction does not affect power transfer Acts as ‘Wi-Fi system’ Efficiency up to 80 percent

Ultrasonic Waves Radiative (Far Field) Technique Transducer converts power source into sound energy (45-75 kHz) High frequency waves above hearing range (~20 kHz) Inaudible to people and animals “Light of Sight” system No power emitted if no receiver detected or beam is obstructed [4]

Ultrasonic Waves Advantages Disadvantages No risk to prolonged exposure (cannot penetrate skin or cause radiation sickness or genetic damage) No interference with communication systems (ideal for aircraft) Can charge multiple devices and when devices are in motion Disadvantages Currently only a prototype (uBeam - expected 2018) [5]

uBeam (2012) Far Field Ultrasonic Charging 1.5 W of power up to distances of 4 meters Line-of-sight technology allows “device in motion” charging Similar charging speed to traditional wired charging Less expensive than Inductive Coupling Slim and lightweight mobile device charging cases

Summary Technology Type Range Directivity Antenna Device Applications (Current or Future) Non-Resonant Inductive Coupling Near Field Short Low Wire Coils Mobile devices, electric tooth brushes, induction stove tops Resonant Inductive Coupling Mid Mobile Devices, Biomedical Implants, Electric Vehicles Capacitive Coupling Metal Plate Electrodes Mobile Devices, Smartcards Magnetodynamic Coupling N/A Rotating Magnets Electric Vehicles, Biomedical Implants Radio Frequency Waves Far Field Long High RF Antennas Solar Power Satellites, GPS Systems, RFID Tags, Biomedical Implants, Sensors Light Waves Lasers, photocells, lenses Drone Aircraft, Space Elevator Climbers Ultrasonic Waves Transducer Mobile Devices, Communication, drone aircraft

Summary Future? Increasing efficiency and maximum power transmission Lowering costs Exploring new techniques Proposed space-based wireless electricity system (JAXA; via Microwaves)

Questions?

References https://en.wikipedia.org/wiki/Wireless_power_transfer https://www.allaboutcircuits.com/technical-articles/introduction-to-wireless-power-transfer-wpt/ https://www.allaboutcircuits.com/news/new-technology-powers-drones-wirelessly/ http://iopscience.iop.org/article/10.1088/1742-6596/305/1/012088/pdf http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=7332954 http://www.inase.org/library/2015/zakynthos/bypaper/CIRCUITS/CIRCUITS-18.pdf https://www.engadget.com/2014/08/07/ubeam-wireless-charger-ultrasound/ https://ubeam.com/technology/ https://www.digikey.ca/en/articles/techzone/2016/aug/inductive-versus-resonant-wireless-charging https://en.wikipedia.org/wiki/Qi_(standard) http://opendotsalliance.org/about-us/history/ http://www.powercastco.com/company/about/

Image References [1] https://www.anandtech.com/show/9130/wireless-charging-standards-in-mobile/2 [2] http://www.qiwireless.com/wireless-power-consortium-extend-qi-standard-add-resonance-charging/ [2.5] http://blog.ravpower.com/2017/09/wireless-charging-technology-history-future/ [3] http://www.we-online.com/web/en/passive_components_custom_magnetics/blog_pbcm/blog_detail_ electronics_in_action_100415.php [4] http://www.bbc.co.uk/schools/gcsebitesize/science/edexcel/waves_earth/ultrasound_infrasoundrev1.shtml [5] https://www.engadget.com/2011/06/20/ubeam-developing-wi-fi-for-energy-to-enable-wireless-charging/ [6] https://draxe.com/electromagnetic-radiation/