A blue room. Fiberglass cones. A deafening silence within. There’s no mistaking an anechoic chamber. Altyor has one at its Saint-Cyr-en-Val site. It is about 40m² and 4m high.
Baptiste Didé, electronic engineer at Altyor, introduces us to the components of a tool he uses daily.
What is an anechoic chamber?
It is a compartment used to test electronic products in isolation from the outside world and vice versa. This means that measurements are not affected by fields radiated outside the chamber, nor are the surroundings affected by strong fields emitted from inside the chamber. This “quarantining” is possible owing to the metal frame. Inside, there are also specific cone-shaped insulators to eliminate reflection, i.e. to prevent waves from bouncing off the walls like billiard balls. As such, a directional field to or from the antenna is created.
What is the purpose of an anechoic chamber?
An anechoic chamber is used for three purposes:
- to perform EMC (electromagnetic compatibility) testing and therefore measure whether the product’s radiation falls within the standards template so as not to interfere with other products during its actual use
- to verify the product’s immunity so that it is not interfered with in the presence of other products
- to measure the radio performance of the product
What tools are needed, in addition to the chamber?
Various types of antennas are required. They differ according to their transmission power and the frequency range. In terms of power, at ALTYOR we can measure 3V per meter from 80 Mhz. As regards frequency range, we can extend the signal from 30 Mhz to 18 Ghz, which allows for wide range coverage. As such, all far fields, whether sub-GHz frequencies such as LoRa, Sigfox and EnOcean or above GHz frequencies, Wi-Fi, Bluetooth, 2G and 4G, can be measured.
The antenna is connected by cables to instruments outside the chamber so as not to interfere with the measurements. There is a spectrum analyzer, amplifiers/generators, attenuators, etc.
How does it work?
The product is measured in different positions (usually X, Y, Z) to obtain a graphical representation of the received power.
If you wanted your product to emit an omnidirectional signal, i.e. with optimal power in all directions, the diagram will show a single central lobe.
You may, however, also want to produce a directional signal but with a higher power (like a TV antenna), in which case the diagram will show a main lobe elongated towards the desired direction.
Here are two diagrams of products coming out of this chamber:
Are your anechoic chamber results certifying?
For a new product, our results will in fact constitute pre-certification that will allow the customer to apply for certification at a laboratory knowing that their product meets the standards on the tested parts. This avoids often long and costly back and forths with labs. It can take one or two months or more to set a date.
During product upgrades or investigations, the anechoic chamber can be used to test the alteration, by comparison, before returning to the laboratory.
What is the cost of an anechoic chamber?
The cost of a chamber depends on its surface area, ranging from 20,000 euros to millions of euros. The larger and higher the chamber, the more you can test in standard conditions (at 10 m for a height of 1 to 4 m). At Altyor, we can carry out tests at a height of 3 m and 1.30 m, which is quite impressive. Laboratories have huge chambers. The largest in the world is in California – it is 80.4 m long, 76.2 m wide and 21.3 m high.
At what point in the development process should these tests be carried out?
For pre-certification in view of certification, they should be carried out with final products with the real materials. As such, you have to wait for the first products of the pre-series.
However, in the case of investigation, you can already start with functional prototypes with mechanics. The tests will obviously have to be confirmed with final products, as many things can interfere with the product.
What things can interfere with a product’s radiation?
There are factors that are internal to the product and also external factors. This is why radiation simulations that can be done during product design in no way replace a real-life chamber test with a final product.
First of all, the components (and their materials) placed next to the antenna and the type of power supply can interfere with the RF (radio frequency) operation of the product. Moreover, paint – for example, black paint – may be loaded with carbon and may change the radiation of the product. What’s more, its immediate environment and its installation environment has to be taken into account. For example, we know that home automation products, such as NodOn products, will be embedded in a wall, so the possibility of a concrete wall or a plasterboard wall has to be taken into account. The environment of the skin, for smart bracelets for example, also influences the radiation.
How then can the signal be improved?
The RF signal can be improved by means of capacitors and inductors. Mechanics also play a big role, as does battery placement. Our feedback, mechanical/electronic design and chamber tests allow us to improve product performance.
Find out more about smart product pre-certification and certification:
If you have questions or need further information, please contact us at: moc.r1620308315oytla1620308315@ssen1620308315isub1620308315