We are in the age of an AI (artificial intelligence) explosion. Everything — from your refrigerator to your dog’s bowl — will become part of the AI neuron network. Worldwide revenues for the AI market, including software, hardware, and services, are forecast to grow 16.4 percent year over year in 2021 to $327.5 billion, and by 2024 the market is expected to break the $500 billion mark.

While these numbers are impressive, AI will only reach its full potential when it can be fed with a constant stream of data from a plentitude of diverse sources. In order to gather data at a rate that enables high value AI output, you need a ubiquitous sensor network in place. Sensors are the neurons that fire the AI synapses. These synergies are imperative to the frequency and quality of the output.

Over the past few years sensors have begun to make their mark as the framework of the IoT. In 2022, motion sensors are expected to account for 8.35 percent of the global IoT-enabled sensors market. Total revenue generated by the enabled sensors market is estimated to reach $56 billion in 2022.

Sensor networks need to continue to expand in order to be able to truly support the adoption and fulfillment of high value AI. However, scalable expansion of sensor networks is being stifled by the restrictions of placement due to needing access to power. So how can we “keep the lights on and the neurons firing?”

Historically, sensors are powered by wires and/or batteries. However, both these options have limitations. Wires can be expensive to run and often restrictive — with limits in cable length and potential for breakage points. Batteries have limited life; they need to be replaced on a regular basis and are thrown away when spent. In short, they are not dependable for the time cycles required; they are a repetitive cost, and they are environmentally unsustainable.

An Alternative to Traditional Power

A substitute for wires and batteries is energy harvesting (capturing available energy). Or wireless charging (generating energy to wirelessly power a device), which is the process where energy is derived from predictable external energy sources, captured, and stored for applications including small wireless autonomous devices like those used in wireless sensor networks.

There are many methods of wireless charging, which we’ll briefly take a look at:

  • Vibration is the concept of converting vibration energy to electrical energy. This method is only ideal for machinery that vibrates.

  • UV/IR energy must have direct line of sight between the transmitter and the receiver for it to work properly, any obstructions result in no power reaching the receiver.

  • Qi is inductive charging and offers watts of power, but is only for applications where the transmitter and receiver are a few millimeters apart; device alignment is quite restrictive.

  • Solar and wind, in most cases, must be outdoors and therefore can be costly to build and can also be a bit limited in its capabilities.

  • Radio frequency (RF) does not require direct line of sight, can deliver power into waterproof enclosures, is low power (μW to mW) and is more versatile than the processes previously mentioned.

Wireless Sensor Networks

RF wireless power technology is unique because it uses radio frequency electromagnetic waves rather than magnetic fields to charge a device. An RF transmitter uses electronics to generate an RF signal. The RF signal is sent to an antenna, which transmits the RF waves to a receiver embedded within a device, which picks them up using an antenna. They are then converted into usable DC using an embedded chip. This powers the device or recharges the battery. The transfer of RF wireless power can be described in the far-field using the well-known Friis Equation. The equation shows us how the transmitted power, types of antennas, and frequency of the RF signal impact the received power at different distances.

Figure 2. PowerSpot transmitter. (Courtesy of Powercast)

RF wireless power can be implemented as a charging spot where multiple devices can simultaneously be powered; as an RF beam that can be sent directly toward a particular device several meters away from the transmitter; or as a focused spot directly in front of the transmitter. Because it is a two-sided system (transmit and receive), a solution can be engineered for most applications. One big advantage of RF wireless power is that it can be implemented in a variety of different environments and configurations, for example, large-scale facilities such as hotels, office complexes, and campuses. Most times there are unoccupied areas of a hotel, office complex, or campus, which do not need lights on or the temperature systems to be running at a steady state. The ability to change these conditions (not having lights on in certain unoccupied rooms and not having the AC or heating system kick on or running less often) can create eco-friendly facilities, enhancing the user experience and providing significant cost savings.

Typically, sensor networks are only integrated when the building is designed, or during a large-scale remodel effort, due to the complexity of implementation. However, wireless sensor networks (WSNs) using RF wireless power make implementation much easier. No need to run wires, no need to consider battery issues. A WSN enables unrestricted, spatially dispersed, and dedicated sensors for monitoring and reporting the physical conditions of the environment and organizing the collected data at a centralized location.

Today, WSNs still primarily rely on battery power, which as noted, is not entirely reliable or preferable. But, the introduction of WSN tech’s ‘cut the cords’ mentality allows for sensing to take place out of sight and in hard-to-reach places. Integrating energy harvesting takes WSN versatility a step farther by removing human interaction after installation so that these systems can reliably operate continuously without the need for maintenance. Furthermore, while energy harvesting does add an initial upfront cost, the economic ROI from greater control is rapid, and the freedom from future maintenance (battery replacement) and disposal have a compounding effect.

Outside of environmental monitoring and control, other ways this technology can be applied include battery-free personal temperature scanning systems designed to help with COVID-19 protocols, battery-free sensing in hazardous material chambers or storage containers where it’s dangerous for individuals to be around, and even vaccine temperature tracking using existing RFID equipment — a common practice in most medical settings.

Figure 3. Battery-less RFID temperature scanner. (Courtesy of Powercast)

Demand for WSNs

As demand for AI increases, so will the demand for WSNs. Research projects that the global wireless sensor network market is expected to grow at a CAGR (compound annual growth rate) exceeding 14 percent over the forecast period. Its size can balloon to $1.5 billion by 2022. WSNs are beneficial for many reasons: they are flexible and adaptable, are scalable, and can accommodate new devices at any time, and can help with cost savings since there are no wiring costs.

The need for WSNs will be seen across all areas of business — from retail to warehouses, manufacturing facilities and beyond. Even public spaces are utilizing WSNs in traffic lights, bus stops, highways, crosswalks, and so on. Office buildings are using WSNs to monitor employees’ locations as well as asset tracking to see where laptops are located within a building. From smart thermostats, locks, blinds, lights, and plugs, it seems as though everything is connected these days, and as we see more smart devices pop up we’ll see even larger inquiries for WSNs. They will be the backbone of the smart cities of tomorrow.

RF Wireless Power

While there are several options for over-the-air power, RF is among the most dependable and scalable forms of wireless power transfer for both indoor and outdoor environments. In general, wireless power is more reliable than energy harvesting, as it’s identifiable and predictable. It’s also easy to integrate RF wireless charging technology as it’s not restricted by movement or exact placement, allowing it to accommodate devices that induction cannot.

Wireless power is the enabling technology of tomorrow. It will give us the flexibility to deploy WSNs in a manner whereby we can make tomorrow smarter, safer, greener, and better.

This article was written by Charlie Goetz, Chief Executive Officer, Powercast (Pittsburgh, PA). For more information, contact Mr. Goetz at This email address is being protected from spambots. You need JavaScript enabled to view it.; or visit here .


Sensor Technology Magazine

This article first appeared in the June, 2021 issue of Sensor Technology Magazine.

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