Wireless Device Testing
Every radiofrequency (RF) wireless device, no matter what its function, must undergo a rigorous testing and certification process to ensure it meets guidelines set by FDA, the Federal Communications Commission (FCC), and international governing bodies such as the EU. It must not interfere with other wireless devices in the environment or allow those other devices to interfere with it.
Testing and certification typically requires four to six weeks, but manufacturers can take some simple steps beforehand to speed the process, cut costs, and avoid issues that can shut down production.
Designers and manufacturers must ensure their wireless medical devices function properly in environments where healthcare professionals and patients may also use other RF wireless technologies. According to FDA:
In the design, testing, and use of wireless medical devices, the correct, timely, and secure transmission of medical data and information is important for the safe and effective use of both wired and wireless medical devices and device systems. This is especially important for medical devices that perform critical functions such as those that are life-supporting or life-sustaining. For wirelessly enabled medical devices, risk management should include considerations for robust RF wireless design, testing, deployment, and maintenance throughout the life cycle of the product.
In plain English, devices must demonstrate electromagnetic compatibility (EMC). This means they do not emit levels of electromagnetic (EM) energy that causes electromagnetic interference (EMI) in other devices in the vicinity. There are different forms of EM energy that can cause EMI: conducted, radiated, and electrostatic discharge (ESD). A wireless device will be susceptible to EMI if the levels of EM energy exceed the EM immunity (resistance) in its intended operating environment.
These guidelines apply to all RF devices that will serve any kind of medical purpose, not just those intended for use in a hospital or physician’s office. There are three classifications of healthcare environments that cover a wide range of facilities and use cases a designer may not even realize qualify:
- Professional healthcare facility. This includes physician offices, dentist offices, limited care facilities, freestanding surgical centers, freestanding birthing centers, multiple treatment facilities, and hospitals (although RF wireless devices are not permitted to operate near high-frequency surgical equipment and the RF shield room of MRI machines).
- Home healthcare. The word “home” is a bit misleading because this category covers devices used in restaurants, shops, schools, churches, libraries, homes, vehicles, airports, other transportation centers, and hotels.
- Special environments. These include military areas; heavy industrial areas like power plants, factories, and mining operations; medical treatment areas with high-powered medical therapy equipment such as high-frequency surgical machines; and inside the RF shielded rooms of MRI machines.
The RF wireless testing process should include an analysis of the potential risks resulting from reasonably foreseeable EM disturbances. Consider all categories of EM phenomenon: conducted low-frequency, radiated low-frequency field, conducted high-frequency phenomena, radiated high-frequency field, ESD phenomena, and intentional EMI.
Additionally, the risk analysis should account for the physical, climatic, and use environments a device may be exposed to as it ages. Along with the normal wear and tear of pressing buttons and flipping switches hundreds of times, consider how extremes of temperature, supply voltage, shock, and vibration reduce immunity. What about the build-up of dust or condensation? How can even the cleaning process degrade immunity?
The most common wireless integration solution is to use certified modules. That’s a great choice, if available, because it can reduce the scope of the testing process. But it will not solve all problems, including some of the most common:
- Using an antenna different from the one referenced in the original certification
- Simultaneous transmissions when the module is “colocated” with another transmitter not specified on the FCC grant
RF wireless testing typically takes one to three weeks, plus an additional one to two weeks for achieving certifications. Manufacturers cannot expect their design and engineering teams to conduct RF wireless testing; they typically do not have the necessary expertise. Additionally, the designers may be in a different country than the manufacturing facility, which makes collaboration on testing difficult. That is why partnering with a third-party testing facility can make the process much less costly and time-consuming.
Whether a manufacturer conducts its testing in-house or partners with an outside laboratory, there are steps it can take beforehand to streamline the process and avoid issues that can cause significant production delays. The most important consideration is what type of wireless technology the device employs.
For instance, if the device leverages a cellular transmitter, the manufacturer should enable direct access to the antenna so the tester can bypass the over-the-air connection and just pop in a test SIM card.
If the device uses a wireless LAN connection, in addition to direct antenna access, the manufacturer should create a test mode that includes a random data set. This enables the tester to set power levels, channel, data rates, modulation, and all other criteria without having to connect to a wireless access point.
The release of Bluetooth Low Energy (LE) provides manufacturers with a more power- and application-friendly version of Bluetooth designed specifically for use in IoT devices and machines. Testing devices based on standard Bluetooth requires the creation of a test mode, but the requirements for Bluetooth LE devices are the same as for a wireless LAN.
You can significantly reduce the time and money you spend on laboratory testing and hasten time-to-market by helping your tester help you. Before sending the device to the lab, identify the operating environment and risk factors, and prepare the device ahead of time. That can mean the difference between making some final design tweaks or having to go back to the figurative and literal drawing board.
David Schramm, EMC/RF/SAR/HAC Manager at SGS.