Anechoic chamber offers isolated environment for performing some tests and measurements. On this post, you will find every aspect of anechoic chambers. If you want to contribute to this post, add your comment by using Submit Comment button at the end of this page. 

What is anechoic chamber? 

Let us start checking the definitions of these two words from Cambridge Dictionary:

anechoic: not able to send back an echo (= a sound that reflects off a surface)

chamber: a room used for a special or official purpose, or a group of people who form (part of) a parliament

According to dictionary, we can define anechoic chamber as a room which is not able to send back an echo and used for a special purpose.

More technically, an anechoic chamber is a room designed to completely absorb reflections of either sound or electromagnetic waves. Anechoic chambers are mostly isolated from waves entering from their surroundings.

What are the functions of an anechoic chamber? 

Anechoic chamber has two functions:

* To form a no reflection place

* To form isolated place

An anechoic chamber is used for either acoustic measurements or electromagnatic/RF measurements. Acoustic anechoic chambers do not allow reflection of sound waves inside the chamber and do not allow sound waves coming from outside. Electromagnetic/RF anechoic chambers do not allow reflection of electromagnetic waves inside the chamber and do not allow electromagnetic waves coming from outside. 

Why anechoic chamber is used? 

Main purpose is to create an reflection-free and noise-free test and measurement environment. Performing tests inside an anechoic chamber gives you much more reliable and accurate results when compared to testing outside. 

Acoustic and electromagnetic measurements are the measurements of the strengths of frequencies. But, when performing these measurements, how will you avoid reflections from other objects, interfering signals or noise? You have to use special materials that absorbs unwanted signals and shielding that prevents interfering signals or noise. 

Most of the acoustic, EMC, RF and antenna measurement standards require anechoic chamber to get accurate test results. Anechoic chambers are mostly used for product compliance tests and measurements. The product can be an audio device/component, electronic device/component/system, antenna or any product emits sound or electromagnetic wave. 

Which standards are used for anechoic chambers? 

Some of the anechoic chamber related standards are listed below.

Purpose of Anechoic Chamber Standard
Acoustics

ISO 3745

Acoustics

ISO 3741

Acoustics

ISO 3744

EMC

CISPR 16-1-4 (chamber requirements)

EMC CISPR 11 / EN 55011 (Industrial, Medical, Scientific)
EMC CISPR 12 (automotive)
EMC CISPR 14-1 / EN 55014-1
EMC CISPR 14-2 / EN 55014-2
EMC CISPR 24 (will be replaced by CISPR 35)
EMC CISPR 25 (automotive)
EMC CISPR 32 / EN 55032 (multimedia and IT equipments)
EMC CISPR 35 / EN 55035 (multimedia and IT equipments)
EMC CISPR 36 (new standard for automotive)
EMC IEC 60601-1-2 / EN 60601-1-2 (medical)
EMC ETSI EN 301 489-1 (radio devices and systems)
EMC UNECE R10 (Regulation 10) (automotive)
EMC RTCA DO-160 (avionics)
RF/Radio ETSI EN 300 328 (radio devices and systems)

The list includes both validation standards for compliance of anechoic chamber and test standards that anechoic chambers are referred. 

Which measurements are performed in anechoic chambers?

Anechoic chambers are used for these tests and measurements: 

Acoustics, ElectroMagnetic Compatibility (EMC), Radio Frequency (RF), Antenna, Microwave.   

Measurement distances in anechoic chambers

Most of the test standards specify the measurement distance between the tested product (EUT/DUT/AUT) and the antenna. The measurement distances are mostly 1 meter, 3 meter and 10 meter. Different test limits are applied for each measurement distances. 

Types of Anechoic Chambers

Depending on the application and measurement type, different types of anechoic chambers are used. Chamber types can be categorized into two:

1. Semi Anechoic Chamber (in which ground floor is reflective, thus it is called ‘semi anechoic’)

2. Fully Anechoic Chamber (all inner surfaces of the chamber are anechoic, thus it is called ‘fully anechoic’)

Product standards require anechoic chamber also defines the technical features of the anechoic chamber. For electronic products used in avionics, RTCA DO-160 standard defines the anechoic chamber parameters. For automotive, CISPR 12, CISPR 25 and CISPR 36 standards define the anechoic chamber parameters. For IT equipments, CISPR 32 refers to CISPR 16 compliany anechoic chambers. Same is for medical devices; IEC 60601-1-2 standard refers to CISPR 16 compliant anechoic chambers. If you are looking for anechoic chamber requirement of a specific product, firstly, you have to specify its applicable test or measurement standards. 

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