What exactly is the "passive Internet of Things "?

Si Gyeongmin

Dec 15, 2021

What is the passive Internet of Things?


Passive Internet of Things, as the name suggests, is the Internet of Things without a "source".


"Source" means power and energy source. The passive optical network (PON) and passive wavelength division (WDM) that we often talk about all involve "passive". To put it bluntly, passive means no external power supply and no battery.


The passive Internet of Things is not a passive network, but a passive end node.


In other words, there is no change in the network, and the terminal node devices connected to the network do not have a power cord or a built-in battery.


So here comes the problem. For terminal node devices, there are sensors that need to generate data, chips that need calculations, and modules that need to send and receive signals. Without power, who will provide the energy for work?


In fact, the so-called "passive" does not mean that the terminal node does not use electricity, but is a way of obtaining electricity (energy).


The "passive Internet of Things" that everyone is currently discussing mainly refers to the Internet of Things based on wireless electromagnetic energy capture technology.


In other words, it refers to the Internet of Things technology in which the Internet of Things terminal captures and collects energy by collecting radio waves emitted from the network side.


In fact, RFID is a kind of passive Internet of Things.


The principle of RFID is very simple. When the tag is close to the reader, it receives the radio frequency signal sent by the reader, generates an induced current, and obtains energy. With this little energy, the tag sends information to achieve communication with the reader.


Now, on the basis of RFID, the passive Internet of Things hopes to further extend, expand the passive interconnection based on Wi-Fi, Bluetooth, 3G, 4G, and even 5G communication technology.


Technical Challenges of Passive IoT


Everyone knows that RFID is a very mature technology. The most important reason why RFID can work normally is that the distance between the tag and the reader is very close.


The farther the distance, the lower the density of electromagnetic energy, the more difficult it is to obtain energy.


RFID belongs to inductive coupling. The shape of the antenna is a coil. The transmission of electromagnetic energy is completed in the induction field area and the distance is very short.


The working distance of Wi-Fi and Bluetooth is far greater than that of RFID, and that of 3G/4G/5G is farther. This is not an induction field, but a radiation field.


The antenna technology used in the radiation field is mainly a dipole antenna or a microstrip antenna. It is extremely difficult to use these antennas to complete the transmission of electromagnetic energy in the radiation field.


In the past, this was unthinkable. Now, with the advancement of semiconductor technology, the power consumption of terminal chips has been reduced to mW or even lower, coupled with the continuous upgrading of energy conversion technology, has made the energy capture and use of long-distance communication technology a possibility.


Characteristics of Passive IoT


Energy shock


The energy of passive IoT nodes is no longer a single static trend from high to low. Since the energy comes from the environment, it will present a dynamic state of high and low.


Node imbalance


There is randomness and instability in energy acquisition in passive IoT nodes, and the energy distribution in the entire network may be uneven, which will also cause differences in each node.


Energy constraints


Passive IoT obtains energy in different ways, and the collected environmental energy is very weak, generally in the nanowatt (nW) to microwatt (μW) level, and is affected by the node's power storage capacity.


Connection vulnerability


The network connectivity of the passive Internet of Things is directly affected by the energy of each node. When the energy of some nodes is below a certain level, these nodes become isolated nodes, causing the network to be disconnected. Due to the turbulence of energy, the connectivity of the network is fragile, intermittently, and it is difficult to maintain continuous connectivity.


The meaning of passive IoT


The biggest advantage of the passive Internet of Things is that it does not require batteries at all.


NB-IoT changes the battery every 10 years (ideally), and the passive IoT is not needed for life. This not only reduces the labor cost of battery replacement, but also reduces the cost of battery components.


Second, no battery is needed, which is conducive to environmental protection. Although a single battery is very small, it has a scale of hundreds of billions, and its environmental impact cannot be underestimated.


Third, without a battery, the volume of the terminal can be further reduced. For example, like RFID, it is a small patch, which will greatly benefit the terminal design.


All in all, the passive Internet of Things is a very good development idea. However, it may take a long time for us to really get this path through.


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