New-Tech Europe | June 2017

Medical Devices Special Edition

processing capability. For instance, the Nordic nRF51822 uses an ultra-low-power consumption ARM Cortex M0 core for maximum power efficiency, while the nRF52832 has a Cortex M4 to support a broader variety of applications. For a majority of wearable applications, an SoC design will provide the best power efficiency, ease of integration and development cost. As a single chip design, SoC devices also lend themselves to small form factor, thin and light wearables. With its ultra-low power consumption, widespread compatibility, and ease of implementation using SoC modules, it's no wonder Bluetooth Smart is the number one wireless protocol for wearable devices today. NFC While Bluetooth Smart is undeniably important for wearables, it's not the only game in town. Near- Field Communication(NFC) plays an important role as another, often complementary wireless communication protocol. Unlike Bluetooth which allows devices up to 30 feet away to connect, NFC requires devices to be within 10cm or even less - practically touching. On the surface, NFC's limited range seems like a drawback, but in fact it's key to its success. By requiring devices to be in extremely close proximity, NFC inherently makes sure that the right devices are connected. Whereas Bluetooth has a complicated pairing process involving selecting the right device and entering passcodes, NFC connections are "tap and go". Users simply tap the devices together

connection, transmit a message, and close the connection in tens of milliseconds. This fast messaging doesn't just make for responsive devices, but also helps Bluetooth Smart minimize power consumption by maximizing the time the radio is turned off. Combined with a peak transmit power of about 15mA, this allows extremely efficient power usage, and there are Bluetooth Smart devices which can last months or even years off coin cell batteries. Security is essential for medical applications and Bluetooth Smart doesn't disappoint. It uses robust, 128-bit AES-CCM encryption, and Elliptic curve Diffie-Hellman key generation for protection against eavesdropping. Implementing Bluetooth Smart can be done using network processors, HCI modules, or SoC chips. Network processors, also known as connectivity ICs, are Bluetooth radio modules with low power MCUs which implement the Bluetooth stack, minimizing the load on the host processor. This makes them appropriate for devices with a low power MCU. HCI modules are bare-bones Bluetooth radio modules which implement physical and link layer, and rely on the host system to implement the upper layers of the Bluetooth stack. HCI modules are appropriate for devices which have a powerful host processor with the resources to run the Bluetooth stack in addition to application logic. SoC chips combine Bluetooth radios with relatively powerful MCUs which can run the entire Bluetooth stack along with application logic all on the same chip. These can range in their

and a connection is automatically established, messages transmitted, and the connection closed. The quick and intuitive usage of NFC makes it particularly attractive for elderly populations as well as hospital staff, as it means equipment can be deployed with minimal training. The quick tap and go connections used by NFC are also well suited for clinical settings where multiple devices might need to be read by a centralized smartphone or other NFC reader. With Bluetooth, a connection would have to be manually setup for each separate device sequentially, but with NFC, each device is simply tapped as it needs to be read, without having to wade through a list of possibly dozens of devices in the vicinity. NFC's other main draw is its extremely attractive power consumption characteristics. NFC devices can often be passively powered - meaning the NFC device is powered by the RF field generated by the NFC reader. The amount of power generated is small, with a typical figure of 4mA at 3.3V, but it's enough to power simple sensor readings. Without the need for a battery, incredibly small and thin form factors can be made, making NFC an ideal technology for skin patch sensors, implantables, or clothing. Because of its need for close proximity between devices, NFC provides a basic yet effective form of physical security and authentication, and greatly reduces the possibility of Man-in-the-Middle attacks. Like Bluetooth Smart, NFC also supports AES encryption, and Diffie-Hellman key exchange if an additional level

44 l New-Tech Magazine Europe