Medical device design for IoT: Meeting FDA guidelines

In the past few years, the market for IoT devices has exploded, opening up a whole new world of possibilities for telehealth and medical applications. Advancements in sensor design, battery life and wireless networking technologies have allowed everything from insulin pumps to pacemakers to be connected to the internet. To successfully launch a new medical product in the IoT market, manufacturers need to understand the regulations that ensure medical device designs are reliable, safe, and secure.

The FDA recently released guidelines pertaining to wireless medical device design, development, testing and use. We’ll address a few of their recommendations here.

Selection and performance of wireless technology

Prior to selecting a wireless technology, medical device manufacturer should consider if their intended product and use case is suited for a wireless environment. Assuming that it is, the FDA recommends:

* Choosing an appropriate wireless technology (e.g., WMTS, IEEE 802.11) and RF frequency of operation for the intended application.

* Considering risks such as data corruption or loss and interference from simultaneous transmitters in a given location, which can increase latency and transmitted signal error rates

* Considering backups as a mitigation in the event that the RF wireless link is lost or corrupted

The choice of wireless technology will depend on a number of factors, including range, battery life, data sampling rate, coexistence and operating spectrum, just to name a few. Of course, the actual application of the medical device is also important. Some frequently monitored human biological signals and their associated sample rates are listed in the table below. (*See Figure 1)

The optimal wireless technology can be determined through careful analysis of the product requirements and environmental limitations. Personal heath devices usually operate in the 2.4GHz industrial, scientific, and medical (ISM) radio band, which includes Bluetooth, Wi-Fi and ZigBee. Refer to the table below for some frequently used wireless standards for medical devices.

Depending on how much data is being transferred, which medical device is talking, and where it’s been transferred to, a mesh network of medical devices or a gateway device may be used.

Pre-certified wireless SoC modules are quite ubiquitous, enabling medical device OEMs to achieve a quick time to market. Nuvation design partner Texas Instruments offers various wireless SoC modules that have been pre-certified for medical applications, using standards such as Wi-Fi, Bluetooth, Sub-GHz and ZigBee. (See Figure 2).

Wireless SoC OEMs provide documentation in support of the regulatory status of their SoC modules (e.g. FCC/Industry Canada for North America and CE for Europe). A statement is usually found on the datasheet or product specification. When using pre-certified wireless modules designers need to pay close attention to the constraints under which the module passed regulatory approval. For example a specific type of antenna may be required, there may be a recommended printed circuit board placement or other layout guidelines, or required values for any external components. Any deviation can impact whether a pre-certification credit can be claimed, which may result in expensive regulatory testing and delays in product launch.

Wireless coexistence

The FDA recommends taking into account other wireless technologies and users that might be expected to be in the vicinity of the wireless medical device. Coexistence will be dependent on frequency, space and time. The likelihood of coexistence of medical devices is increased if the separation of channels between wireless networks is increased (frequency), the signal-to-interference ratio (SIR) of the intended received signal is increased (space) and the overall channel occupancy of the wireless channel is decreased (time). The designer should consider situations where multiple devices will be in close proximity, such as in a hospital.

Designers should also select a wireless technology that has coexistence features built in. Bluetooth, for example, uses Adaptive Frequency Hopping (AFH) to facilitate coexistence with Wi-Fi devices. Texas Instruments has a proprietary wireless audio technology that uses built-in adaptive frequency-hopping algorithms to minimizing interference.

EMC of the wireless technology

The FDA recommends:

* EMC should be an integral part of the development, design, testing and performance

* Conformance to the IEC 60601-1-2 standard or other appropriate standards

Best practices for EMC compliance include things like good enclosure design, thorough signal integrity analysis and the use of shielded connectors. At Nuvation we conduct Design for EMC Compliance reviews as part of the design risk mitigation.

There are many regulatory organizations and associated standards for medical devices, depending on the technology and application. Some of the common ones for IoT devices are listed in the table on the left. (See Figure 3)

Information for proper set-up and operation

The FDA recommends providing users with the specific RF wireless technology type (e.g., IEEE 802.11b), characteristics of the modulation and effective radiated RF power, and a warning label. While this seems straightforward, products can fail certification because manufacturers fail to adhere to documentation requirements as outlined in the medical standards.

Of course, there is much more involved with meeting the FDA requirements and successful medical product development. Nuvation has delivered many electronic product designs for various medical and IoT applications, with clients including Abbott Laboratories, Boston Scientific, PediaVision and Numera.