1. Selective filtering circuit
EMI problems can be solved by finding out the frequency of interfering noise and adding selective filtering circuits to instrument circuit boards, or filters to connectors on medical cable wiring harnesses. Thin film capacitors and resistors can eliminate unwanted signal noise by grounding them near the noise source. However, the medical cables and connectors must be made small enough that if they are too large, they will limit the performance of the coaxial filtering circuit and thus have some impact on the effectiveness of EMI.
2. Overall shielding
The braided shielding on medical cable has been one of the main methods to isolate the interfered electromagnetic wave from the complex external environment. It is generally accepted in the industry that weaving is often the best masking solution, which can easily provide up to 85 dB of external noise isolation. To reduce the number of wires going in and out of the system, medical devices can use hybrid cables and connectors, combining power, signals, and triggers into a single connector and cable system. But notice that inside the connector, there is a power pin on one side and a signal pin on the other. But more importantly, the medical cable from each metal circular connector to the main interface connector is hidden by a braided shield.
Shielding must maintain a 360-degree seal from the metal connector to each smaller circular connector. If there is a gap or the shielding layer is not connected, the cable becomes an antenna at the open loop, and EMI will leak into the instrument rack of the ICU unit, affecting the instrument. Factors such as braided layer thickness, choice of metal material, braided layer type, and uniform coating outside the shield can be used to adjust EMI shielding effect. In this regard, equipment designers had better communicate with cable designers in advance to choose the appropriate shielding efficiency.
3. Simplify the wiring in cables
Many medical cables are designed to support the fastest digital processing systems needed, such as real-time imaging or active subcutaneous examination. Cables based on IEEE 1394, somewhat similar to the "firewire" used by telephone companies, could significantly improve shielding. Each set of high-speed digital wires is wrapped in a "drain" wire. Twisted-pair wires can handle signals in the high gigabit/s range, while scrambles can return signals quickly to the source and eliminate potential EMI noise and additional fluctuations due to extremely fast signal speeds. At the same time, medical cables also need to be protected by a lightweight overall shielding layer, so in most cases, aluminum foil shielding is relatively common, because it can ensure that the cable has the characteristics of small and soft, EMI protection efficiency of the sheath can still be improved.
