Energy harvesting powers battery-free environmental sensors -

Energy harvesting powers battery-free environmental sensors

Acceptability of Internet of Things (IoT) has grown tremendously worldwide, however the rate of this progress is posing challenges to its experts, who are expressing concerns/fears about its future. It has been estimated that by 2025, devices connected to the IoT network may exceed the remarkable figure of 75 billion units. This gives credence to the professionals’ worries and the need to be adequately prepared so that the gains achieved will not vanish.

Already, IoT specialists foresee a scenario where a plethora of electronic devices communicate through a common interface, typically represented by a wireless connection to the cloud. The number of devices connected to the IoT network is continuously growing, as a result, new sensor technologies will be required to support the demand for data generated by the explosive growth of connected devices. This will be the next challenges for IoT.

“I believe that the next challenges for IoT will be focused around identifying which devices will be part of the IoT.  Just because it is technically possible to design a smart device doesn’t necessarily mean that there is value to having every device connected to the IoT”, said Greg Rice, Technical Marketing Manager, ON Semiconductor.

Connected devices and sensors will play an important role in several areas, including automotive, industrial automation, smart homes, consumer computing, agriculture and mobile health. Sensed, collected and aggregated data will grow exponentially, leading to an estimated traffic of 125 exabytes of data per day in 2025. Managing these large amounts of data generated by devices connected to IoT will be a tough challenge.

Expatiating on the challenges and proffering a way forward, Rice stated that, “If every bit of data that is generated at the edge of the IoT is sent through the cloud, this could create congestion in networking infrastructure. It might be more efficient to perform some basic data analysis and aggregation at the edge of the IoT, rather than sending everything through the cloud to the core of the network”.

Energy harvesting

Energy harvesting will be crucial to face the challenges offered by the exponential growth of IoT devices. Rice believes that the challenges with energy harvesting are centered around the efficiency of power harvesting, and the reliability of the devices that are powered through energy harvesting”. Devices for energy harvesting operate with very small amounts of power, their design is many times a trade-off between technical performance and reduced power consumption. “A challenge with devices designed to operate through energy harvesting is finding the right balance of these tradeoffs in the design process”, Rice highlighted.

Another relevant challenge is the source of power for energy harvesting. During daylight hours, a solar powered device can operate efficiently by exploiting the available sunlight. However, the same cannot be said for its operation at night. Similarly, devices that use RF power for energy harvesting must be in the presence of an RF field with a certain signal strength. In case more RF fields are deployed to support energy harvesting devices, the associated health risks shall be carefully evaluated.

Battery-free sensors

ON Semiconductors has designed an innovative wireless and battery-free suite of sensors for the IoT network. The Smart Passive Sensors™ (SPS) device family enables the monitoring of temperature, pressure, moisture or proximity at the network edge. Since environmental sensors are often deployed in remote locations or on a wide area such as a factory or a building, changing a battery frequently is not an economically viable operation. Energy harvesting, particularly RF power for SPS sensors, is able to meet this requirement. As shown in Figure 1, each SPS sensor is a battery-free and microprocessor-free RFID sensor tag with an antenna block for wireless communication, through industry-standard UHF Gen 2 protocol, with an RFID reader. When a SPS sensor is interrogated by an RF reader, it uses the energy received from the signal, providing a fast and accurate reading from the sensor.

Figure 1: SPS sensor functional block

“This sensor network is designed to work using RF energy harvesting. There is a central sensor hub which transmits RF power through a connected antenna. The individual sensor nodes are wireless and battery free, and they operate by converting the energy in the surrounding RF field into a power source for the electronics on the sensor nodes”, explained Rice.

As shown in Figure 2, each sensor hub integrates two key blocks: the reader module and the processing module. The reader module performs protocol specific functions to communicate with sensors and expose raw sensor data (EPC, Temp, RSSI, Code, etc.) to the processing module. The processing module aggregates and formats sensor data for additional analysis. The sensor hub connectivity capabilities include WiFi, Ethernet, Bluetooth, and other protocols suitable for sending sensor data to the cloud for further analysis, analytics, and decisions.

Figure 2: sensor hub block diagram

The overall sensor IoT architecture is shown in Figure 3. The sensor hub collects data from multiple sensors and communicates with other connected devices through the cloud to enable IoT in new applications and scenarios.

Figure 3: the sensor IoT architecture

At the heart of the sensing block is the Magnus-S2© Sensor IC from RF Micron, a UHF RFID chip that is powered by RF energy harvesting from the UHF reader. The Magnus−S2 utilizes the patented self−tuning Chameleon engine that adapts the RF front−end to optimize performance in various environmental conditions. These sensor tags function in either the FCC defined UHF band or the ETSI UHF band. The small form factor and battery−free capabilities of Smart Passive Sensors allow them to be designed into applications where size and accessibility are at a premium.

The SPS device family includes:

  • Temperature sensors, designed for passive sensing of temperature on metal, non-metal and ceramic surfaces. Applications include predictive maintenance in industries and data centers;
  • Moisture sensors, designed for passive sensing of moisture on various surfaces or finished goods made of plastics, wood, ceramic, soil, and plaster. Applications include moisture level or leak detection and quality control in different industrial contexts;
  • Fluid-level sensors designed for passive sensing of fluid through thin surfaces such as plastics.


The number of devices connected to the IoT network is constantly growing, with applications involving all sectors of technology. The success and expansion of the IoT sector strictly depends on the characteristics and performance of the sensors involved. New sensor technologies are needed to complement traditional sensor networks. A battery-free, wireless sensor with cloud connectivity enables enhanced monitoring of environmental conditions in different applications such as data centers, industrial predictive maintenance, construction and power, cold chain, digital farming and smart healthcare.

>> This article was originally published on our sister site, Power Electronics News.


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