“Protective shields activated” for data transmission
Testing of shield attenuation and electromagnetic compatibility on cables for medical devices
Shield attenuation describes the effectiveness of the cable’s shield against interfering signals. Rather like a Faraday cage, the shield protects the elements that lie beneath the shield against external electromagnetic influences to ensure EMC.
To test shield attenuation, Leoni fits a 3 m-long cable in the test set-up with a plug at one end and a terminating resistor at the other and feeds it into a measuring tube. Power is then fed into the cable. Energy now escapes from the cable shield and spreads out. The shielding and measuring tube are short-circuited at the end near the transmitter, while overlap of the wave running back and forth is measured at the opposite end. Shield attenuation should be understood as the logarithmic relationship between the power fed in and the power now measured.
Shield attenuation is measured based on the frequency, but remains largely constant on cables as of a few 10 MHz. As the wavelength at lower frequencies would be too long for the electrical measuring equipment, shield performance is determined from the transfer impedance at max. 100 MHz.