AMS Sees Potential Medical Applications for Its HF Data-logging RFID Chip

By Claire Swedberg

The semiconductor company says medical equipment providers are studying the SL13A IC for use in a device to track a patient's blood glucose levels.

Semiconductor firm AMS is marketing a sensor-supporting passive high-frequency (HF) RFID chip that could be used to monitor the health of individuals diagnosed with such conditions as diabetes, when implanted under their skin. The company is also marketing a passive ultrahigh-frequency (UHF) version that could be employed to track temperatures or conditions around goods such as perishable foods and pharmaceuticals in transit. The UHF-based model was initially created in 2009 by integrated circuit manufacturer IDS Microchip, to measure temperatures and then transmit the collected data to a reader, according to Oluf Alminde, the senior marketing manager of AMS' power and wireless business unit, and previously IDS' product marketing director. More recently, IDS began developing an HF version. Medical applications were not initially a target for either version of the technology, however.

In November 2012, IDS Microchip was acquired by AMS, which has now begun marketing the sensor-supporting chips as part of its own portfolio. Since that acquisition, AMS reports, multiple medical companies have been testing biomedical applications involving its HF chip, while logistics firms worldwide are testing the UHF version. In addition, a New Jersey-based packaging products company is marketing a battery-assisted passive (BAP) tag made with the UHF chip, allowing its customers to track the temperatures of goods in transit.

The SL13A demo kit includes the HF RFID chip with an integrated temperature sensor, as well as a dipole antenna and a battery holder.

As IDS Microchip was developing an RFID-enabled data-logger chip with a built-in temperature sensor, the initial application involved the cold-chain transportation of perishable goods. The result was the SL900A chip, which IDS launched in March 2011 (see RFID News Roundup: IDS Microchip Releases New EPC-based Sensory Tag Chip). The company then began marketing a tag reference design using the chip in June 2012 (see RFID News Roundup: Blue Spark Technologies, IDS Microchip Codevelop EPC Gen 2 BAP RFID Sensors). The SL900A chip can operate in a fully passive UHF (EPC Gen 2) mode and, when not being read, uses a battery to enable the collection and storage of sensor data. In addition, IDS developed the SL13A chip, an HF version of the IC that complies with the ISO 15693 standard and can be used with or without a battery. Near Field Communication (NFC) standards published by the NFC Forum support only HF tags compliant with the ISO 14443 A and B standards, not ISO 15693. However, NFC-enabled Android-based phones running a special application, such as STMicroelectronics' NfcV-reader application—available for free on Google Play—are capable of reading tags complying with ISO 15693, including those made with the SL13A chip.

As IDS was developing the HF chip, Alminde says, the company "started seeing interest from the medical field." For medical equipment providers, he notes, the HF data-logger provides numerous advantages. Such a data-logger would not require users to purchase dedicated RFID readers, for example, since a growing number of cell phones have built-in NFC readers that—assuming they are running NfcV or a similar app—could read sensor data on the SL13A chip. The phone could then use a cellular or Wi-Fi Internet connection to automatically forward that information to physicians or other interested parties.

The most common potential use case, Alminde says, is for diabetic patients, who must monitor their blood's glucose level on a regular basis—sometimes twice daily—traditionally requiring that they prick a finger each time to draw blood. They must then be able to visually check the results and call a health-care provider if they determine that a problem exists.

For the diabetic application, a tag made with the SL13A chip would be integrated with a glucose sensor. The chip measures approximately 2 millimeters by 2 millimeters (0.08 inch by 0.08 inch) and is about 0.75 millimeter (0.03 inch) in thickness, though it could be thinned further for use with specific inlays. The glucose sensor, which would be powered by the passive tag when being read, would add to the size. Such an implantable device has yet to be developed, Alminde says, so it is unknown how big it would need to be, nor whether it would prove practical. However, he adds, the goal would be to design the glucose-measuring tag so that it could be implanted in a user just below the skin. The user could then launch a phone app to be used with the NFC technology, placing the phone against the area of the skin under which the tag was implanted. The interrogator would provide sufficient power, through its transmission, to prompt the chip to broadcast back its own unique identifier, along with the glucose level being measured at that time. This could make it possible for health-care providers to collect data regarding a particular patient without requiring a phone call or office visit with that individual. If someone wanted the tag to store a history of glucose levels even when not being interrogated, a battery would be required. To date, however, no medical device manufacturer has expressed an interest in developing a battery-powered version for implantation within a patient, Alminde indicates.

The needs of the cold chain market are very different, Alminde says. In this case, he explains, end users often already have a UHF RFID reader on hand and want the longer read range of a UHF transmission, and are thus less interested in the HF version. The tag can be larger than the HF model, and can incorporate temperature sensors or other devices, such as a moisture sensor. While the UHF model of the chip is being used or tested by several companies in the supply chain industry, some construction businesses are also testing the tag.

For example, a UHF tag made with the SL900A chip could be placed within wet cement and, when interrogated, transmit data indicating whether the cement at that location had dried sufficiently for further construction to proceed. The tag's chip can make some calculations as well; for example, it can determine any change in an item's shelf life, based on the temperatures to which that product has been exposed, and thus transmit a new expiration date that could then be viewed on a handheld's screen. In addition, the SL900A chip can include alarm functionality, by which an alert would be sounded in the event that the reader interrogated a tag for which the temperature had exceeded acceptable limits. If sensor data is being collected and stored on the tag when that tag is not being interrogated, Alminde adds, a battery would be required.

What's more, the UHF version could be employed by the automotive industry, in order to track the temperatures of automotive components, or monitor tire pressure.

AMS is offering the SL13A IC in the form of an RFID chip with an integrated temperature sensor and 8 kilobits of EEPROM memory. Similarly, AMS offers the SL900A chip with an integrated temperature sensor and 9 kilobits of EEPROM. Either chip can operate in fully passive mode or BAP mode (1.5 volts or 3 volts). The SL13A version costs $2.59 apiece, while the SL900A is priced at $3.63 each.

The company also sells a demonstration kit consisting of a complete tag in the form of a printed circuit board with either the SL13A or SL900A chip, as well as a dipole antenna, a replaceable 3-volt coin battery and software to be loaded onto a handheld EPC Gen 2 UHF reader or an NFC-enabled phone, for use in capturing and storing sensor data. Both the SL900A demo kit and the SL13A demo kit are available at AMS' Web site for $55 apiece. According to Alminde, the company has already sold a large quantity of these kits.