“Data will be the next decade’s silicon,” says Dinesh Bharadia, an associate professor at UC San Diego in the Department of Electrical and Computer Engineering. Dinesh also has an affiliate appointment in the Department of Computer Science and Engineering and the Qualcomm Institute (QI). Now, he along with Nagarjun Bhat has published research on how a battery-less, fully passive sensing can be achieved at the RF frequency.
IoT Sensors can sense light, temperature, humidity, force, strain, etc. in distinct environments, but they remain battery-operated and costly today. Moreover, the lack of widespread adoption of these IoT sensors also hinders any progress towards battery-free, ubiquitous sensing.
Why this Renewed Focus on Fully-Passive Sensing?
As stated above, modern-day IoT sensors are costly due to the addition of a battery in sensor design. These sensors cannot work without battery power and that inflates the cost of these sensors. The high cost of sensors also means that it is not adopted widely and the price is not coming down any time soon. This begs the question, can there be fully passive sensors that can capture data such as changes in temperature, humidity, strain, and light and share the same with an integrated software system that can make sense of the data for broader end users?
The answer is why not. We already know about chipless RFID tags that are fabricated without an RFID chip and use plastic or conductive polymers or reflective materials that can reflect RF signals at certain RF frequencies and the RFID reader can read those signals. These tags are encoded with time domain and frequency domain encoding methods.
Then we have chipless RFID sensors that combine sensing materials such as graphene, paper, and metal oxides that can measure changes in temperature, humidity, and strain in an environment.
Additionally, the research published by Bhat and Bharadia at UC San Diego presents a fully passive, miniaturized RFID sensor in a “flexible form factor sensor interface titled ZenseTag that uses minimal electronics to read and communicate analog sensor data, directly at radio frequencies (RF).”
The sensor only uses the energy from harvested RF signals.
The sensors also work with a 15x10mm flexible PCB that connects sensors to a printed antenna and passive RFID ICs, which allows you to read the data through a GUI software system.
The invention of a Passive RFID Sensor pushes the global adoption of IoT Sensors which in turn facilitates more innovation and reduction in costs.
Benefits of Fully Passive Sensors in Various Applications
Batteryless sensors that support a small, lightweight design and can be integrated with a software solution offer many benefits in retail and food supply chains, cold chains and storage units, fashion retail, agriculture, construction, access control and security as well as event management.
Some of the benefits of passive sensors in various use cases are as follows:
1.In construction, passive sensors can measure strain at various construction projects including buildings, dams, and bridges. These RFID passive sensors can also be embedded with precast elements in construction and easily measure changes in strain, temperature, etc. ensuring early detection of cracks and failures in buildings, bridges, etc.
2. Similarly in the manufacturing industry, Passive Sensors offer a cost-effective way to measure failures of machines, and that helps with reducing downtime. These sensors help with detecting changes in temperature, humidity, and force and help predictive analytics algorithms to determine the next maintenance schedule for the machines at work.
3. Many tire manufacturing businesses also embed RFID sensor tags in their tires. The tag also provides a unique ID to the tire and ensures added visibility on the inventory floor. Tyre manufacturers can easily find the information on tire model no., size, and vehicle it is best suited to. Tyre RFID Sensors can also detect tire failure by measuring pressure, strain, and wear & tear, temperature, etc. while a vehicle is on the move.
4. Coming to access control and security, passive RFID sensors offer a cost-effective method for tracking people's movement and ensuring controlled access at security-risk venues, offices, and homes. These sensors can be integrated with concealed flooring at the entry and exit points and can detect the presence of an individual using light sensing and proximity sensing.
RFID-based access control with UHF Passive RFID tags and NFC cards is already a thing when it comes to security systems.
5. These passive sensors also find great applications in healthcare where access control, patient care, and storing medicines and vaccines at optimum temperature and humidity is crucial. These sensors can be fitted with medicine cabinets and can detect changes in the temperature within the cabinet.
6. These passive sensors can also be integrated with various appliances such as refrigerators and air conditions and can detect temperature and humidity and optimize operations accordingly. Refrigerators can adjust the temperature and help you keep your food fresh for many days.
7. In agriculture sector, humidity and temperature sensors play an important role and real-time sensing allows farmers to take appropriate measure and advance crop yield.
Avery Dennison’s Passive Sensors
Avery Dennison Smartrac has launched passive sensors that work on EPC UHF standards and utilize Axzon Magnus® S2 and S3 ICs.
The sensor by Avery Dennison costs a fraction of other sensors available in the market. It features a single-chip design with no batteries and low-cost construction. These UHF Passive Sensors by Avery Dennison Smartrac can be deployed in sensitive environments where an electric power source cannot be used.
Sensor Chip Capabilities
Axzon Magnus® S2 and S3 ICs have self-tuning capabilities and offer great performance in the presence of metals and liquids. The chip can easily adjust its internal variable capacitance to match the impedance of the antenna around metals and water.
How much the chip can adjust its capacitance forms the basis for moisture and high-dielectric material sensing capabilities.
Temperature Sensing Circuit
Temperature sensing is a function of the chip itself. The chip has a built-in temperature circuit that can detect the temperature of the silicon die and send that to the reader in digital value form.
Moisture Sensing
The Axzon Magnus® S2 and S3 ICs can measure the change in moisture as well by adjusting the internal capacitance as the detuning effect takes place due to moisture/water.
Proximity Sensing
The Sensor Chip can also measure proximity by adjusting the internal capacitance in the presence of detuning materials, including people, animals, and metals.
Pressure Sensing
A pressure sensor is designed using the same detuning principle by sandwiching a compressible material (foam or rubber) in between a sensor tag and a layer of metallic foil.
Passive Sensing is the Next Big Thing
Active sensors based on RFID and IoT technologies are costly and support a large form factor, which also hinders their integration with distinct small devices such as smartwatches or smart wristbands. This creates ample opportunities to develop passive sensors that are not only minuscule in size but also cost a lot less than an active sensor.
Passive sensing with chipless RFID and fully passive repurposed RFID tags is the next big thing. Real-time detection of changes in temperature, pressure, strain, humidity, light, proximity, etc. can be utilized in various applications in healthcare, manufacturing, construction, food retail, fashion and accessories, sports, etc. Moreover, integration of passive sensing will also boost global IoT adoption for sensing applications given the fact that adoption of IoT sensors with batteries is already low.
To conclude, RFID and IoT sensors play a crucial role in access control systems, event management, and warehouses. The advancement in battery-free sensors will allow users to streamline sensing applications at low costs.
Retail stores and healthcare will see the maximum adoption of these low-cost, RFID sensors, allowing for a fast, real-time data capture in food retail and supply chain, and while storing medicines and vaccines in optimum conditions.
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