Learn the benefits of using a pre-certified radio frequency (RF) module in the design phase when building a new IoT application, and learn the implications in EMC and Radio certifications.
The Internet of Things (IoT) is revolutionizing the quantity and manner in which we exchange and store information.
Historically, people exchanged information through reading and speaking. Today and in the future, machines will increasingly handle information management.
The size of these machines has been drastically reduced, from room-sized computers to pocket-sized devices with even greater computing power.
The future is promising with the widespread adoption of 5G technology, which enables high data transfer rates and low latency.
Additionally, shifting processing capacity closer to data sources, such as sensors, enhances real-time applications and supports increasingly advanced use cases.
Some IoT nodes use wired communication mediums like Ethernet or CAN. However, scalability and adaptability necessitate low-cost deployment and maintenance solutions.
Therefore, wireless communications are the most cost-effective option for IoT networks. Compared to wired networks, wireless systems are easier to install, access, and monitor, and they are also simpler to scale, making them ideal for rapidly expanding networks.
When designing a new IoT electronic system, system architects must choose a radio protocol from options like ZigBee, Wi-Fi, Bluetooth, and LoRa.
The choice depends on factors such as the coverage area, number of nodes, speed, latency, transmission power, and the battery life of the IoT nodes.
Once the protocol is chosen, the second big question is: should I develop all the electronics by myself? Or should I use a pre-existing module that seems to be plug-and play?
This article aims to clarify the advantages and disadvantages of using existing RF modules and their impact on the development and certification roadmaps.
REGULATORY COMPLIANCE
Every product entering a new market, such as the EU or USA, must comply with various regulations, including chemical safety and electromagnetic interference (EMI).
These requirements depend on the geographic regions where the products are sold, their regulatory agencies, and the product type. Each country has its regulatory framework governing RF technologies to avoid interference and ensure safe operation.
In the United States, the Federal Communications Commission (FCC) oversees this, while Europe follows the Radio Equipment Directive (RED).
Manufacturers need to take care of three aspects related to the electronics of their products:
- Safety: manufacturers need to guarantee the health and safety of people, animals, and properties.
- Electromagnetic Compatibility (EMC): electronic products must not generate electromagnetic disturbances above the limit, and they must allow other equipment to operate properly.
- Efficient use of the spectrum: electronic products using radio communications must make an efficient use of the radio spectrum, respecting the designated frequency bands.
The requirements related to Radio Frequency are very strict, so manufacturers will not get approval if the device transmits energy “just a little bit” over the limits.
They need to prove that the new product is clearly not emitting in unexpected bands, that the emissions are within the accepted transmission power, and that the product is not a hazard for the user.
USING AN EXISTING RF MODULE OR BUILDING A NEW ONE
Designers building a new application need to face the decision of using an existing module or designing a new one. Considering just the design stage, using an existing module brings the advantages of:
- Fast development of software, since the hardware platform is available at an early stage
- The hardware is validated, so fewer hardware re-spins are needed
- Support from an existing community, making development easier
On the other hand, using an existing module has disadvantages. Naming some of them:
- Limited customization, which means the modules are not suitable for all kinds of applications
- Modules are big, taking up considerable amount of the board space
- The modules might have more functionalities than needed, provoking excessive power consumption.
For most of the applications like industrial or home automations, space and power are not a limiting factor, so the disadvantages of using an existing module are less important than the benefits. It is then the most convenient approach to make a fast development.
Small companies or startups do not have in-house knowledge of antenna engineering or specialized equipment such as vector network analyzers (VNA), spectrum analyzers (SA) or RF design and simulation software tools.
Using a module reduces the need for all of them, giving manufacturers the chance of launching and validating new applications fast.
SELECTING A MODULE — CERTIFICATES
There are many existing modules in the market and not all of them have gone through the same levels of quality control and development stages.
Pre-certified RF modules are wireless communication modules that have passed some regulation tests before being sold to manufacturers.
To reduce the development time, it is better to choose a module that has gone through an intensive certification process like those in Reference 1.
While this is an advantage compared to building everything from scratch, manufacturers still need to do their work to have a complete certificated product.
Manufacturers should check all the documentation provided by the module manufacturer to avoid possible surprises.
Certificates are linked to specific components such as the hardware version, software version, or the test conditions. Therefore, if any of those changes, the validity of the performed tests is at risk.
Here is a non-exhaustive list of things to consider when selecting a module:
- Market certification: EU (CE), US (FCC)… the certification should be aligned with the intended manufacturer market. For example, FCC certifications are not valid in the EU market.
- Hardware version: the hardware version that has been certified should be the same as the one that will be installed in the new product during the whole lifecycle of the product.
- Software version: during the certification tests, the modules run a specific version of software (firmware). Changes in this software should not impact the result of the tests.
Having these certificates is very useful to have a baseline of some key metrics such as output power, frequency bands, and distance to the limits for new tests.
So, even if they do not exempt manufacturers from testing their products, these certificates are useful to interpret results and build the technical file of them.
COMPLIANCE WITH A PRE-CERTIFIED MODULE
While using products that are already certified brings benefits in the product development phases, that does not mean that certification efforts are eliminated.
The responsibility for the final product lies with the product manufacturer. Electronic products are complex, with power supplies, analog and digital circuits, and integrating communication capabilities with RF modules.
Then, manufacturers cannot underestimate the steps needed to comply with the legal requirements and need to consider compliance of the whole product in the planning phase.
There are many factors that can affect the results of the EMC and radiation tests, provoking that the emissions and the radio measurements measured on the full product differ from the ones obtained by the module manufacturer.
Manufacturers should take care of the following aspects:
Mechanical Enclosures
Metallic enclosures can have resonant effects at certain frequencies due to their physical dimensions, shape, and openings. If these resonances overlap with the frequency band of the RF module, it can modify the radiation
pattern of the module.
Antenna Type and Position
Some of the RF modules have an external antenna that can be customized, changing its gain and direction depending on the application. Furthermore, the properties of the RF link can be affected by the position of the antenna
in relation to other board components or conductive surfaces.
Printed Circuit Board (PCB) Design
The board stackup, the ground planes position and extension, and the position of other board components in relation to the RF module can significantly impact the behavior of the radiation pattern.
When the RF modules are certified, they are being tested with the minimum number of components, so the two boards will significantly differ from each other.
Software
Software configuration related to output power, frequency, modulation schemes, and bandwidth selection will affect the radio frequency behavior. Manufacturers need a careful development of software, both for production and for the certification tests, to ensure that the emissions are within the limits.
CONCLUSION
Using a pre-certified module to build a new IoT electronic system reduces development time and the need for highly experienced designers or advanced design and simulation tools.
However, it does not exempt manufacturers from meeting legal requirements. The new system often differs significantly from the unit certified by the module manufacturer, necessitating full testing to ensure compliance.
REFERENCES
1. ESP32 certificates (https://www.espressif.com/en/support/documents/certificates)
2. Modular Transmitter Integration Guide Guidance for Host Product Manufacturers
