Meaning
The intensity of unintentional electromagnetic radiation emitted by a device must remain below strict regulatory limits to prevent interference. Measuring the spurious field strength allows certification laboratories to determine if the device complies with electromagnetic compatibility standards. This metric is expressed in microvolts per meter at a defined measurement distance.
Measurement Protocol
Testing takes place in a calibrated anechoic chamber equipped with a rotating tabletop and a height-adjustable antenna. The device under test operates at its maximum output power while the receiver sweeps across the specified frequency range. Recording the highest spurious field strength ensures that even the most fleeting emission spikes are captured for compliance analysis.
Shielding Necessity
Inadequate shielding of high-speed digital lines or sub-harmonics from internal clocks can lead to excessive radiated emissions. When the spurious field strength exceeds the legal limit, the product cannot receive market authorization. Adding metal shielding cans over the noisy integrated circuits is a common method used to block these unwanted radiated fields.
Design Verification
Engineers use electromagnetic simulation tools early in the design cycle to identify potential leakage points in the enclosure. They optimize the ground plane and add decoupling capacitors to high-speed signal lines to suppress emissions at their source. Physical prototyping and pre-compliance testing help to confirm that the changes are effective before committing to expensive production tooling.
This iterative process reduces the risk of failing the final regulatory testing and ensures a smoother path to product release, saving development time and resources.
