A Tunable EMI Notch Filter for AM Radio in Electrical Vehicles

Electromagnetic interference (EMI) generated by electric vehicles (EVs) increasingly disrupts amplitude modulation (AM) radio reception, prompting some automakers to remove AM radios entirely. This trend raises public safety concerns, as AM radio plays a critical role in disseminating emergency alerts. Traditional EMI mitigation techniques, such as low-pass filters (LPFs), often involve tradeoffs in size, weight, and performance, making them impractical for EV applications. This article presents a two-stage tunable notch filter (NF) designed specifically for electromagnetic compatibility (EMC) applications in the 540–750 kHz range, where, as reported, AM radio in EVs is most vulnerable. This is a first prototype that combines continuous tuning via core saturation (tunable inductor) and dielectric biasing (tunable capacitor) for AM-band narrowband EMI mitigation in EVs. The filter’s resonant frequency can be dynamically tuned in real time to match varying EMC conditions. The proposed tunable NF achieves up to 60 dB attenuation with 50/50 Ω terminating impedances, and real-world testing against emissions from a dc/dc GaN converter demonstrates up to 30 dB EMI suppression of I _DM current. This attenuation is comparable to a conventional LPF while reducing the inductance value by a factor of 33, significantly reducing size and weight. This compact and tunable NF offers a viable alternative to bulky LPFs for narrowband EMI mitigation, and supports the preservation of AM radio functionality.