Ambient backscatter

Ambient backscatter{{cite book | chapter-url=https://dl.acm.org/doi/10.1145/2486001.2486015 | doi=10.1145/2486001.2486015 | chapter=Ambient backscatter: Wireless communication out of thin air | title=Proceedings of the ACM SIGCOMM 2013 conference on SIGCOMM | date=2013 | last1=Liu | first1=Vincent | last2=Parks | first2=Aaron | last3=Talla | first3=Vamsi | last4=Gollakota | first4=Shyamnath | last5=Wetherall | first5=David | last6=Smith | first6=Joshua R. | pages=39–50 | isbn=978-1-4503-2056-6 }} uses existing radio frequency signals, such as radio, television and mobile telephony, to transmit data without a battery or power grid connection. Each such device uses an antenna to pick up an existing signal and convert it into tens to hundreds of microwatts of electricity.{{cite web|url=http://www.kurzweilai.net/battery-free-short-range-wireless-communication-between-devices |title=Battery-free short-range wireless communication between devices |publisher=KurzweilAI |date= |accessdate=2013-08-15}} It uses that power to modify and reflect the signal with encoded data. Antennas on other devices, in turn, detect that signal and can respond accordingly.

Initial implementations can communicate over several feet of distance, even if the transmission towers are up to {{convert|10.5|km}} away. Transmission rates were 1k bits per second between devices situated {{convert|0.45|m}} apart inside and {{convert|0.75|m}} apart outside, sufficient to handle text messages or other small data sets. Circuit sizes can be as small as 1 sq. mm. Later implementation uses Wi-Fi,{{Cite web|title=WiFi Backscatter|url=https://iotwifi.cs.washington.edu/|access-date=2020-11-20|website=iotwifi.cs.washington.edu}} Bluetooth,{{Cite journal|last1=Ensworth|first1=Joshua F.|last2=Reynolds|first2=Matthew S.|date=September 2017|title=BLE-Backscatter: Ultralow-Power IoT Nodes Compatible With Bluetooth 4.0 Low Energy (BLE) Smartphones and Tablets|url=https://ieeexplore.ieee.org/document/7898833|journal=IEEE Transactions on Microwave Theory and Techniques|volume=65|issue=9|pages=3360–3368|doi=10.1109/TMTT.2017.2687866|bibcode=2017ITMTT..65.3360E |s2cid=44760506 |issn=0018-9480}} FM radio{{Cite web|title=FM Backscatter|url=https://smartcities.cs.washington.edu/|access-date=2020-11-20|website=smartcities.cs.washington.edu}} and LoRa transmissions.{{Cite web|title=Long-Range Backscatter|url=https://longrange.cs.washington.edu/|access-date=2020-11-20|website=longrange.cs.washington.edu}}{{Cite book|last1=Peng|first1=Yao|last2=Shangguan|first2=Longfei|last3=Hu|first3=Yue|last4=Qian|first4=Yujie|last5=Lin|first5=Xianshang|last6=Chen|first6=Xiaojiang|last7=Fang|first7=Dingyi|last8=Jamieson|first8=Kyle|title=Proceedings of the 2018 Conference of the ACM Special Interest Group on Data Communication |chapter=PLoRa |date=2018-08-07|series=SIGCOMM '18|location=Budapest, Hungary|publisher=Association for Computing Machinery|pages=147–160|doi=10.1145/3230543.3230567|isbn=978-1-4503-5567-4|doi-access=free}} There exists technology to extend backscatter communication range up-to 3.4 kilometers while consuming 70 μW power at the backscatter tag.{{Cite book|last1=Varshney|first1=Ambuj|last2=Pérez-Penichet|first2=Carlos|last3=Rohner|first3=Christian|last4=Voigt|first4=Thiemo|title=Proceedings of the 15th ACM Conference on Embedded Network Sensor Systems |chapter=LoRea |date=2017-11-06|chapter-url=https://doi.org/10.1145/3131672.3136996|series=SenSys '17|location=New York, NY, USA|publisher=Association for Computing Machinery|pages=1–2|doi=10.1145/3131672.3136996|isbn=978-1-4503-5459-2|s2cid=3938018 }}

This approach would let mobile and other devices communicate without being turned on.{{Cite web|last=Georgia Institute of Technology|title=Backscatter breakthrough runs near-zero-power IoT communicators at 5G speeds everywhere|url=https://techxplore.com/news/2021-06-backscatter-breakthrough-near-zero-power-iot-5g.html|access-date=2021-06-27|website=techxplore.com|language=en}} It would also allow unpowered sensors to communicate, allowing them to function in places where external power cannot be conveniently supplied.{{cite web|url=http://www.gizmag.com/ambient-backscatter-unpowered-communication/28709/ |title=Ambient backscatter tech allows devices to communicate, sans batteries |publisher=Gizmag.com |date= 15 August 2013|accessdate=2013-08-15}}

In 2021, researchers integrated RF backscatter with Li-Fi to achieve greater range via PassiveLiFi.{{Cite web|title=IoT Devices Will No Longer Need to Rely on Batteries to Operate|url=https://www.hackster.io/news/iot-devices-will-no-longer-need-to-rely-on-batteries-to-operate-ef02b6ed3b08|access-date=2021-11-27|website=Hackster.io|language=en}}