EM Microelectronic’s Passive Sensor Chip Detects Moisture

By Claire Swedberg

The em|aura-sense, with capacitance for moisture or touch detection, can respond to a UHF RFID reader by storing sensor data or transmitting it back to the interrogator, enabling those with existing RFID inventory-counting systems to add the tags and gain additional data.

Automotive and healthcare companies are among those piloting a passive RFID sensor transponder that enables the detection of moisture without requiring a battery.  EM Microelectronic's em|aura-sense is a passive UHF RFID chip that can capture, store and send capacitive sensor data when interrogated. The system is suitable for green Internet of Things (IoT) deployments, the company says, since it provides intelligence when read without adding batteries to the waste stream once the tag is discarded.

The UHF RFID transponder is more cost-effective than battery-powered sensor tags, the semiconductor manufacturer reports. It uses the same Gen2v2 UHF standard as inventory-tracking RFID tags so that it can be easily built into solutions by systems integrators and operate with off-the-shelf UHF RFID readers, according to Pierre Muller, EM Microelectronic's RFID technical leader. The em|aura-sense chip is being built into  Avery Dennison's sensor labels, while it also operates with RFID inlays supplied by other manufacturers.

EM Microelectronic, part of the  Swatch Group, specializes in low-power ICs for battery-operated and in-field-powered applications, and it makes the ICs used in Swatch's watch products. The company has provided RFID chips for 30 years, first for animal identification, then serving the first mass deployment of passive UHF RFID with U.K. retailer  Marks & Spencer in 2005 (see  Marks & Spencer to Tag Items at 120 Stores and   Marks & Spencer Leads the Way). "We've always been in this space, with lots of custom development," Muller says, serving a wide variety of industries. "The common denominator is low power and differentiation."

The company also develops sensors, and it launched a battery-assisted sensing RFID tag approximately eight years ago that is still used—typically for smaller deployments to monitor cold food supply chains, for instance. However, for those who wish to have a wide-scale deployment of sensor measuring at a low cost, there have been limited options. "When you look at the IoT space, one of the main problems is maintenance of the sensor based on battery lifetime," Muller states. Users must keep track of battery life and replace the tag batteries.

EM Microelectronic considered solutions for companies whose deployments were wide-scale enough that they required millions of tags and could not track battery maintenance and cost. "We thought, 'Let's remove the battery,'" Muller recalls, adding that there is also a high cost for most sensor tags. Battery-assisted tags, he notes, can cost a few dollars per tag, as well as requiring maintenance if the battery fails, while the use of a battery introduces environmental issues when the product is discarded.

The em|aura-sense serves as a standard UHF RFID tag with an encoded unique ID, but it also provides an interface between the chip and moisture measurements, with a capacitance sensor on an inlay. The chip can then be used to detect changes in capacitance for humidity, moisture or touch. "Our first focus is on making it easy for a systems integrator to get reliable data," Muller explains.

The chip depends on power from an RFID interrogator to capture sensor data. There are three different modes in which the chip captures and shares sensor data. The Sense at Write mode enables users to leverage the interrogator's write mode as if writing data to the tag, but the interrogator can instead instruct the chip to capture sensor data and forward it to the interrogator. This typically requires the interrogation of tags one at a time. It can also be instructed by the reader to store that data instead of transmitting it, enabling a faster process. The data can then be captured at a later time, Muller says, though that can still be too slow for those interrogating numerous tags.

Sense at Select and Sense at Boot are two alternatives that enable the collection of tag IDs, using eXtended PC (XPC) (Words) W1 and W2 format to capture data via the TID memory. This method is a more efficient option involving the capturing of data, the company reports, even as a large number of tags are being interrogated for inventory purposes. When the chip is interrogated, it sends data in XPC Words 1 or 2. This process works well even in a noisy environment, Muller explains. EM Microelectronic intends for the chip to be operable in one of the three interrogation methods, with no customization required by an integrator. In fact, the chips can be added to an existing passive UHF RFID tracking system.

The chip's main benefit, Muller says, will be the cost-effectiveness of the application, which enables more wide-scale application and deployment. "The first focus is moisture sensing," he states, "and there are lots of different verticals where moisture sensing is of interest." One is the use of automotive tracking, for which passive sensor tags can be applied inside a car and at the manufacturing site, to test whether there is any leakage of water inside the vehicle. Another use case is in healthcare for adult diapers, for those in hospitals or the elderly. Because it operates with touch sensors, it can also detect information such as whether a door or latch is open or closed.

There are other passive UHF RFID sensor tags as well, including one from  Axzon (previously known as RF Micron) as part of its Smart Passive Sensing Technology. EM Microelectronic's focus is on providing simplicity with a standardized solution, Muller says, adding, "We want to offer something that is standard for any reader, making it very user-friendly for the systems integrator." The company has been working with  ISO's standards working group, as well as the  RAIN Consortium, to make the passive sensor capability standard within the UHF ISO 18000-6C standard. "We've been working with the ISO working group and RAIN Consortium on the standard," he states, "and we are in final review."

In the future, Muller reports, EM Microelectronic may opt to embed temperature sensors in its Augmented RFID product line. In the meantime, smart agriculture is another application for which multiple sensors in a field or greenhouse can enable the wireless tracking of moisture levels. A cost-effective tag is needed for such applications, he adds, without maintenance issues or battery replacement.