Scannable sensors are ready to bring contactless data transfer to implantable and wearable devices

There’s no question that cell phones have made our lives more convenient. Whether our phones are used for making calls, uploading photos and streaming music, we rely on our smart phones for dynamic data transfer. In the last few years, Near Field Communications (NFC) technology has become available in an increasing number of smart phones while being touted as for its potential to eliminate cash and physical credit card transactions. Consumers simply tap their phone on a retailer’s terminal to make an instant payment and exchange other data. NFC is finding uses in transit systems, retail chains and even amusement parks.

While NFC hasn’t completely replaced the wallet or purse, IHS expects global shipments of cellphones with NFC technology will reach 1.2 billion units by 2018. ( IHS also notes, however, that the NFC ecosystem rollout has been slow. As the NFC infrastructure slowly expands, it is being integrated into devices in the industrial, white goods, and gaming markets.

NFC technology uses magnetic induction to fill the physical space between two closely spaced devices in order to exchange data, usually in the 13.56 MHz band. There are two types of NFC devices: Active devices have their own power source can read information from an NFC tag and respond to other devices, and passive NFC devices, which lack the power source and can only send data. Since the data being exchanged is often sensitive – credit card numbers and medical data, for example – NFC encrypts the data and sends it over a unique, secure channel.

An ideal technology for medicine
The medical market is particularly poised to take advantage of NFC thanks to smart sensors that can measure physical conditions of patients and wirelessly transmit that data to a nearby Android phone or monitoring device using a readily available WLAN or other mobile network to medical professionals for monitoring and evaluation. Many field trials of NFC sensors in wearables and implantable devices have begun. Secure data transfer is just one of characteristics of NFC technology that make it attractive for medical uses. Another attribute is its use of the 13.56 frequency band. The frequency is compatible with human tissue for potential use in implantable devices, is universally available, and it is accredited worldwide, including for medical use. In fact, NFC radio technology piggybacks on a lot of existing technologies, making potential implementation easy.

“You can overlay the radio with existing sensors or existing devices … and make it essentially an NFC sensor,” says John Peeters, founder and president of Gentag, Inc., which specializes in custom NFC sensors and tags. “So any existing sensor or device out there could be made compatible with this technology, or you can take the chip and create a new generation of very low cost, very low power sensors.”

As the Internet of Things (IoT) and wearable medical devices progress, designers can also take advantage of NFC’s low power requirement for applications that demand long battery lifetimes or even devices without batteries. NFC sensors are essentially RFID tags which rely on energy harvested from the reader. This battery-free (passive) operation is important for wearable devices because the thickness of the device could determine whether a patient will wear it. Anything thicker than a normal Band Aid can be uncomfortable for the patient. For implantable medical devices such as a blood glucose sensor, battery-free operation could mean a single implant can last for many years. “In an NFC-enabled sensor, this harvested power can also be used to power a sensor,” says Oluf Alminde, senior marketing manager, power & wireless at ams AG. Because the lifetime of the tag is theoretically unlimited and requires no wired connection, the sensor tags can be embedded for a variety of applications.” Passive NFC sensors also eliminate issues related to battery disposal.

Figure 1. Block diagram of SL13A NFC-enabled sensor from ams

Although passive NFC sensor-based solutions are optimal for healthcare applications, there are situations when passive technology is not possible. For instance, noise may complicate the design, or more likely, the power available on the chip may not be sufficient to power the sensor. In that case, Alminde says, “it is possible to add a small supplemental power supply in the form of a capacitor that is charged before the measurement, and from which power is drawn during the measurement.”

Standard or custom solution
A designer looking to integrate NFC-enabled sensors into a medical device can find both standard solutions or vendors that specialize in custom implementations. Austria-based ams, for instance offers both ISO-15693-compliant tags for NFC and HF RFID readers and an EPC Gen 2 Class 3 tag for RFID readers. Each features an on-board temperature sensor, an interface to an external sensor, and can operate in passive mode. Be sure to let the vendor know the range requirements and the type of sensor that will be required for the job. Says Alminde, “Sometimes (the customers) have their own sensors or some ideas about their sensors, so is this a type of sensor that can actually can be integrated onto the silicon. Or, do we need to have it externally connected to the chip so the chip would have the front end for the sensor but not necessarily the sensor itself on the silicon.”

In other instances, a company may want its own custom chip with its own unique IDs. It is possible to build on the standard NFC communications and libraries and then integrate a specially designed ASIC built for a specific sensor. Gentag, for instance, can provide the custom ASIC and sensor tag as well as the reader. In fact, it can develop the entire sensor network for disposable diagnostics and even its own smart phones which don’t have the features of a commercially available smart phone but which offer special apps that allow home health care workers to monitor their patients. “Rather than being a ‘one shoe fits all’ technology, we see the market emerging as a customization solution for a very big company,” says John Peeters.

A promising prognosis
As NFC sensor-based devices continue to penetrate the healthcare market, the technology is also evolving for more widespread adoption. NFC is often perceived as being able to read across small distances of a few centimeters, but given the right components in the radio, antenna and power, Gentag’s Peeters asserts that ISO-15693, a part of most NFC radios, has up to an 80 cm read distance. And, companies that develop readers continue their work toward expanding read distances for future applications. They are also working around the remaining barriers that pertain to cell phones themselves, such as the locks that the phone companies have on some subcomponents of NFC. As these issues are addressed, more consumers own smart phones with NFC capabilities, and the Internet of Things (IoT) becomes more ubiquitous, even more possibilities for patient monitoring and better outcomes will result. “NFC is an ideal tech for IoT and uses in medical applications,” says Peeters. “Our expectation is this technology will be everywhere very soon."