How to Solve EMI Noise in Medical Cables?

Many medical devices rely on cable and other interconnectors, but unlike the cables used in communication networks, medical cables have unique technical requirements. Medical cables must be extremely flexible and able to withstand repeated bending, and also meet strict regulatory safety guidelines. So, how can we solve the EMI noise in medical cables during use?

Selective filtering circuit for hospital cables

EMI problems can be solved by finding the frequency of interfering noise and adding a selective filtering circuit to the instrument circuit board, or by adding a filter to the connector in the medical cable bundle. Thin film capacitors and resistors can eliminate unwanted signal noise by grounding near the noise source. However, medical cables and connectors must be small enough to limit the performance of coaxial filter circuits if they are too large, which will have a certain impact on the effectiveness of anti-electromagnetic interference.

Overall shielding of hospital cables

When it comes to isolating interfering electromagnetic waves from complex external environments, using braided shields on hospital cables has always been one of the mainstream methods. The industry generally recognizes that braiding is usually the best shielding solution, which can easily provide a level of up to 85dB isolation from external noise.

To reduce the number of lines entering and leaving the system, medical devices can use hybrid cables and connectors to combine power, signals, and triggers into one connector and cable system. However, it is important to note that on the inside of the connector, one side has power pins and the other has signal pins. More importantly, the cable from each metal circular connector to the main interface connector is a hidden braided shield layer. The shield must be kept 360 degrees sealed from the metal connector to each smaller circular connector. If there are gaps or the shield layer is not connected, the cable becomes an antenna at the open loop, and EMI will leak into the instrument rack in the ICU unit, affecting the instrument. Thickness of braiding, selection of metal material, type of braiding, and uniform plating of external shielding can be used to adjust EMI shielding effectiveness. In this regard, equipment designers should communicate with cable designers in advance to select appropriate shielding effectiveness.

Simplify the internal wiring of hospital cables

Many cable designs support the highest-speed digital processing system, which is required for real-time imaging or active subcutaneous examination. It is similar to the "hot line" used by telephone companies, which can significantly improve their shielding effectiveness. Each set of high-speed digital wires is wrapped with a "leakage" wire. Twisted pair cables can handle signals in the high-gigabit/second range, while shielded cables can quickly return to the signal source signal and can eliminate potential EMI noise and additional fluctuations caused by the high speed of the signal. At the same time, medical cables also need to install a lightweight overall cover for protection, so in most cases, choosing aluminum foil shielding will be more common because it can ensure that the cable has small and flexible characteristics while still increasing the EMI protection of the sheath.

Conductive coating and shrinkage sleeve for hospital cables

For some EMI cable applications, another solution is to use special sheaths made of polyolefin heat shrink tubing.

As medical technology continues to innovate and change, how to achieve appropriate electromagnetic shielding while effectively protecting hospital cables is a challenge for every designer, and the solutions are not static.