God said there should be a network, the Internet of Things, and the interconnection of all things, so that sensors attached to various objects can transmit data to the network. However, God also encountered technical problems: WiFi, Bluetooth, ZigBee and other mainstream wireless networking methods now consume too much power. The devices using these technologies can only run with battery power. If they are used in real IoT devices, their size, cost and maintenance are under pressure.
Asymmetric power consumption requirements at the receiver/transmitter
The so-called radio communication requires that both sides have the ability to send and receive information, that is, it must include two parts: transmission and reception. The power consumption of the accepted chips can be reduced to a very low level thanks to the progress of semiconductor process.
However, the transmitting part has always been high, because the energy required for transmitting signals is just so much (if the signal is too weak, others will not receive it) - the power consumption of normal wifi routes for sending RF is about 0.1W. When the mobile phone sends WiFi, for the sake of battery and heat, it will be controlled at about 25mW (finally know why the mobile phone hot spot signal is so weak, and why the mobile phone is still so hot).
A blessing in disguise, "passive" RF chip
The power consumption at the signal transmitting end is still high, which in turn is a condition that can be used well: our usual wifi, bluetooth and even visible light are radio waves with different frequencies, and regular radio signals can transmit information, so that they are energy themselves and can be converted into electricity after being absorbed (like solar panels basking in the sun).
This also lays a physical foundation for the passive transmission technology ("passive" power supply) mentioned below - as long as the energy consumption of the signal transmitting chip is low enough and the energy absorbed from the signal radio, the chip can send another signal even without batteries.
Apple Pay
In fact, we already have a similar technology - Backscatter Communication, which is loosely defined as passive communication technology, The RFID technology has long been integrated into bus cards and meal cards.
Recently, the NFC used for Apple Pay, Samsung Smart Pay and other functions is the version of RFID radio frequency technology running at 13.56MHz with transmission distance less than 10cm. As long as the signal strength provided by the transmitter is enough, the chip without its own power supply can also send signals for communication.
"Dilemma" of Solar Flashlight
In "Domestic Lingling Paint", Still photo of solar flashlight
Although the power consumption of passive RF devices is low, the transmission distance, speed and frequency band of the signals they send are far from the lowest level WiFi required by Marlowe. In addition, they can only absorb radio in a specific frequency band, and a large amount of visible light (corresponding to solar panels), radio and television signals, radio signals and WiFi signals in the air are "wasted".
There have also been studies before, trying to let passive communication equipment absorb radio, television and WiFi signals for power supply, but the results are relatively sad, the transmission speed is only 1Kbps (0.125KB/s, well, it is no different from the network disconnection...), the transmission distance is good, and it can still be about 0.6m, but it seems that there is no egg use.
In addition, the WiFi signal was simply converted into electricity, and then another wireless signal with different frequencies was used for transmission （ WiFi in the environment becomes Radio of another frequency...) , and common devices such as mobile phones can't receive . The situation is quite like a "solar flashlight", absorbing strong and warm sunlight, but only the light of the flashlight is transformed 。
A breakthrough is coming?
The signal at the bottom of the above figure called WiLab_0000 is the passive Wi Fi signal
On February 24, computer scientists and engineers at the University of Washington announced that the power consumption of their passive Wi Fi (Passive Wi Fi) system had been reduced to one ten thousandth of that of traditional Wi Fi, and this time, after absorbing radio energy, they sent out pure WiFi signals!!!!!!
What a passive Wi Fi device looks like
The system can send 802.11b standard WiFi signals, which can be directly recognized by mobile phones, tablets and other devices. Its limit speed is up to 11Mbps (1375KB/S), and the transmission distance is up to 30 meters. The power consumption is 14.5 μ W at 1Mbps and 59.2 μ W (0.0000592 W) at 11Mbps.
This power consumption is so outrageous that it is only one ten thousandth of the traditional WiFi, and even thousands of times more than Bluetooth and ZigBee (the most promising low-power transmission technology in smart homes). Engineers and computer geeks are simply moved to kneel down.
They tried to commercialize this technology through a company called Jeeva Wireless, and the product is expected to be available in two to three years. In addition, the University of Washington was engaged in the technology of charging mobile phones with WiFi signals last year. Although the visible light used for solar energy and solar energy is radio waves, and not as mature as the technology of solar panels, at least it can be used without light
However, I have heard about the device that converts the signal in the environment into electricity and then pushes the Bluetooth chip to work before, but it failed in the end. So we have to wait for the real machine to run out of the laboratory before we can really confirm the delay (￣Д￣) dealer
