With the advent of the era of the Internet of Things (IoT), the emphasis for product development has been on adding connectivity, as well as the new features and services it supports. This often means adding one or more radios to a product to provide a wireless connectivity solution. From lights to laptops, from HVAC systems to appliances, products are integrating radio technologies to communicate with each other, the IoT and consumers. Correspondingly, more manufacturers now have to be concerned about radio compliance in addition to electromagnetic compatibility (EMC) issues.
EMC testing is concerned with preventing unexpected electrical interactions directly between products, as well as between the products and the environment in which they operate. Electronic products generate electromagnetic fields unintentionally during normal operation and can cause interference to radio services of all kinds. In some cases, they can affect each other directly in unexpected ways.
In this context, EMC testing takes two forms:
1) emissions testing, which measures the electromagnetic fields generated by the product to ensure they remain below acceptable levels to minimize the possibility of interference; and
2) immunity testing, which subjects products to electrical disturbances typical for its intended environment, in an effort to determine if the product can be affected by EMC disturbance in a significant way. Putting a radio into a product adds new considerations to product compliance and EMC testing.
Basic EMC Considerations
Even without an integrated radio, electronic products are subject to EMC requirements in many parts of the world. The applicable requirements vary by geographical region but are usually a mix of emissions and immunity requirements. In the U.S., the Federal Communications Commission (FCC) requires most electronic devices operating above 9 kHz to meet the requirements of Code of Federal Regulations Title 47 “Telecommunications” Part 15 Subpart B, which contains limits for electromagnetic emissions from both the product enclosure and power lines. Canada has similar emissions requirements for various product types in their series of Interference-Causing Equipment Standards (ICES).
Other economies, such as the European Union (EU), require both emissions and immunity testing. There are many different EMC compliance standards in the EU. Which one to apply depends on the product type, but usually includes immunity to surges, interference on the power lines, radiated interference, electro-static discharge (ESD), ambient magnetic fields, and even how the product performs during a blackout or brownout. Medical devices in the U.S., Canada, the EU and other economies are often required to meet the EMC requirements contained in IEC 60601-1-2, which contains testing of both emissions and immunity similar to that found in the EU standards.
Emissions testing for non-radio products usually takes about one day at a test lab and requires one or more samples configured to operate normally for the duration of the test. Emissions scans can take anywhere from a few minutes to several hours each, and the product needs to operate normally while the scan is running, so it may be necessary to configure the product to operate repetitively when it may not do so in everyday use. All required equipment and power supplies should be provided so that all I/O ports are populated, as the lab may not have appropriate equipment on hand to exercise the product. It always helps to provide clear and concise operating instructions as well, rather than a large manual.
Immunity testing usually takes two to four days per operating mode, and some of the tests can run for hours. The same setup considerations apply as for emissions, with the additional requirement to specify product performance criteria during the immunity testing, so that lab personnel can determine if the product has been affected by the EMC disturbance.
For some immunity tests, such as radiated and line-conducted radiofrequency immunity, where a disturbance is applied to the product in steps across a frequency range, a full product operating cycle must be observed while the disturbance is applied for three seconds per frequency. If the product operating cycle is longer than three seconds, it either must be modified to be three seconds or less for the purposes of testing, or the test dwell time must be lengthened. Since some immunity testing like surges and ESD can be destructive, multiple samples may be needed. For both emissions and immunity testing, special software may be required to meet these configuration requirements.
Radio-Specific Regulatory Issues
Radio regulatory compliance presents its own set of challenges, above and beyond typical EMC issues. In many regions such as the U.S. and Canada, radios require certification and special labeling, adding cost and time to the approval process compared to the usual Supplier’s Declaration of Conformity. In the EU, the requirements of the Radio Equipment Directive (RED) must be met instead of those found in the EMC Directive. For some radios with restrictions on usage in the EU, obtaining a CE Mark may involve more than just issuing a Declaration of Conformity and may even require a review of the product’s technical compliance documentation by a Notified Body.
Since frequency allocations vary by country, a radio can be legal for operation in one country but not another. This can lead to multiple versions of the same radio or multiple product versions containing different radios.
In addition, and unrelated to regulatory approvals, some kinds of radios like WiFi and Bluetooth also require registration and approval by relevant industry associations in order to legally use the WiFi, Bluetooth, or other trademarked industry logos. The difference from the regulatory approval process is the focus on the interoperability of radios of the same type rather than on meeting regulatory requirements, so that consumers know that, when they buy it, it will work with other radios of the same type.
Testing requirements increase as well when a radio is added to a device. Radio frequency (RF) exposure is a concern and testing or calculations may be needed to show compliance with exposure limits. Devices used within 20 cm of the human body may also require specific absorption rate (SAR) RF exposure testing, where a robotic arm with a field probe maps the intensity of the electric field at typical usage distances in order to demonstrate that the product isn’t coupling too much energy to the body when in use.
Compared to non-radio devices, devices with integrated radios are also subject to expanded emissions testing requirements, usually requiring testing of multiple channels across the band of operation, and across wider frequency ranges that usually extend up to the 10th harmonic of the radio operating frequency. Radios like WiFi that have multiple modulation types and data rates must show compliance in all operating modes, resulting in a testing cycle that can last anywhere from one or two days to several weeks, depending on the type of radio and the implementation.
Changing the channel of operation, output power, modulation used, data rates, and any other parameter that needs to be varied during testing almost always requires special software. There are some exceptions, such as the EU WiFi standard ETSI EN 300 328, which specifies testing in normal operating modes. But in most cases it is necessary to provide both normal operating modes as well as test modes that allow varying the parameters mentioned, including turning on and off, hopping on a frequency hopping radio like Bluetooth, and providing continuous or nearly continuous transmission modes to support some tests, even if the radio does not typically operate that way.
EMC immunity testing also changes when a radio is added to a product. In addition to observing basic product functionality during testing, EU standards for radio EMC also require that the quality of the radio link be monitored during the EMC disturbances. In many cases, a test is performed with the radio idle to see if the EMC disturbance can cause it to unexpectedly transmit. This presents unique challenges for manufacturers, who generally must provide custom test software solutions that establish and maintain a continuous or repetitive RF link between the transmitter and receiver, and that also allow the quality of that link to be monitored during testing. Often, such software needs to be expressly crafted for the various anticipated testing scenarios.
Radio EMC testing requires significant preparation to determine the required test modes and provide software that can support testing when a manufacturer arrives at the lab. Otherwise, the project will experience delays as the issues are worked through during lab testing time. This is especially true for medical devices containing radios. In situations where the radio supports the essential performance of the medical device, U.S. Food and Drug Administration (FDA) regulations generally require wireless coexistence testing to ANSI C63.27 to determine the potential impact on patient safety attributable to degradation of the radio link due to nearby radios. The FDA will also expect evidence in the hazard analysis and risk management file that confirms the evaluation of radio operation. In such cases, performance of the radio during the EMC testing will be relevant for the medical device as well.
At least one sample is needed for radio EMC testing, but it is acceptable to provide as many as are needed to cover all the necessary test modes and to replace any samples damaged during testing. It is not necessary to perform all testing on the same sample.
Radio Modules
Some of the challenges presented by integrating a radio into a product can be mitigated by use of a pre-approved radio module. Regulations in the U.S. and Canada allow certification of radio circuit boards with built-in antennas that can be integrated into host products with proper labeling and user instructions and without the need to perform additional certifications, so long as any restrictions on usage documented in the modular certification are respected. Only full radio implementations with antennas can be modules, and reference designs are not allowed for certification.
In the EU, technically pre-approved radio modules do not exist; however some radio manufacturers pre-test modular configurations to demonstrate that the radio is likely to be able to comply when placed inside a host product. Care should be taken when reviewing a Declaration of Conformity for a radio module, as not all requirements may have been tested due to the open board nature of the module (ESD, for example).
However, use of a pre-approved module does not solve all the compliance issues. In both the EU and in North America, manufacturers who integrate radio modules into their products are still responsible for compliance of the host device with the module installed. Therefore, before declaring conformity, it is important to evaluate compliance of the host product with the module installed. Depending on the nature of the module and its intended usage, additional certifications may be needed for legal distribution in the U.S. and Canada in cases where the certification restrictions of the module are not met (for example modification of an antenna or use within 20 cm of the human body).
In the EU, the technical documentation for the host product supporting the Declaration of Conformity should include documentation supporting compliance of the radio module in the host. This means that either it needs to be obtained from the radio module manufacturer or it may be necessary to construct from scratch a full set of compliance documentation including test reports.
Even in cases where the documentation can be obtained, testing of the radio module by itself may not be representative of performance in a host product. Therefore, the required risk assessment of non-compliance under the RED would need to determine whether there are any gaps in compliance documentation that need to be filled. For example, operation in a host may degrade antenna performance. And, though it may be easier to meet output power requirements in such a case, the antenna performance may be degraded to the point that the receiver no longer meets applicable requirements.
In other cases, interactions between the host circuitry and the radio circuitry can cause unexpected intermodulation products or can provide resonant antennas for signals that did not have one prior to combining the two devices. For these reasons, the FCC urges final integrators of radio modules to consider doing some amount of radio testing in the host product. Similar testing may also be useful for closing gaps in technical documentation for the EU Declaration of Conformity. At the very least, the host must be tested for non-radio compliance with the radio installed. Anticipating these needs in advance helps to more effectively manage product deployment schedules, thereby avoiding unnecessary delays from sourcing test software from the module manufacturer.
Pre-approved radio modules sometimes need testing for other reasons. They may be pre-approved in the U.S. and Canada, or Japan or Korea, but not other regions. Each region may have different restrictions attached to the certification. Some countries require in-country testing, or don’t have modular approval programs and therefore require testing of each radio in each host prior to selling in that country.
In other cases, it may be possible to leverage FCC certifications and testing or EU test reports and Declarations of Conformity. But local representation, certification fees, or paperwork may still be required to approve the radio. Even planning the label can take on a new dimension, as most regulators require a mark or ID number for a radio which may not have appeared on the product label in the past.
Conclusion
Taking advantage of experts with EMC and radio testing and knowledge can make the development of any connected device easier. Independent third-party testing groups can function as a second set of eyes to help ensure a product’s safety and performance. Additionally, third-party groups often have experts on hand who know the space, are familiar with regulatory requirements, and have experience that may help educate manufacturers on the requirements, indirectly aiding in the testing and development of products.
Connected products offer exciting, new opportunities throughout multiple industries. The new considerations that come with this pioneering technology must be understood, considered and implemented, not just for required legal purposes, but for ensuring a quality product that meets customer demand. That can make all the difference when it comes to a product’s (and a brand’s) success.
