Medical Versus Regular EMI Filters

EMI shielding is common in all sorts of applications: telecommunications, consumer electronics, computers, industrial, military, and more. One of the most common and important implementations is in power. By the nature of their functions and designs, power sources and supplies commonly generate electromotive interference in the form of radio waves. Appropriate shielding protects devices from unwarranted EMI effects that could cause errors, generate operational problems, change data, or even damage sensitive equipment.

However, although EMI filtering is in wide use, it isn’t uniform in structure or application. What might serve in one industry won’t necessarily in another. For example, the medical industry and equipment require approaches that can support and satisfy the literal life-or-death nature of the applications. From sensitive measurements of physiological phenomena such as EKGs and EEGs, to accurate delivery of medicines, including equipment like X-rays and MRIs that use complex electromagnetic or radiological measurement techniques, and down to the storage, retrieval, and display of imaging data, even during surgeries, disruption from EMI is a significant concern in the use of medical technology.

Such devices—and their power supplies and, therefore, filters—come under the International Electrotechnical Commission set of standards broadly called IEC 60601. These are separate from the regulatory process and compliance that countries require from vendors to show the efficacy and soundness of medical devices.

Various parts of IEC 60601 apply to broad categories of medical devices, in medical settings, at homes, or in special environments like military or industrial facilities. The standards cover use of equipment by virtually anyone, whether used by medical personnel, industrial workers, or patients and their caregivers. Also, the standards have undergone multiple revisions, and so familiarity with the most recent is important.

The importance of the standards and adherence to them comes clearer when considering the wide variety of environments and conditions under which medical devices might operate. Engineers and designers can’t assume in advance the quality of power delivery to the location where a device is used. The source power may be noisy and dirty, subject to the unpredictable frequency variations, spikes, and voltage ripple. Power cables can act like antennas, increasing the susceptibility to EMI. There is also the possibility of electromagnetic noise from power lines, electrical devices that arc, wireless devices and other radio transmitters of many types, computers and networks, storms, utility switching, and changes in supply line loads.

To ensure the best and proper types of filtering, it’s important to work with an experienced and reputable vendor that not only has applicable lines of products, but the expertise to help designers find the components and assemblies that will address the specific needs of their applications.

Ohmite, for example, has decades of experience in the needs and requirements of the medical industry and a range of products for associated equipment and devices. Its AHM series of IEC 61010-1-compliant dual-stage filters with low leakage are for low impedance loads controlling pulsed, continuous and intermittent interference noise and where high levels of power mains-borne interference are present. Current ratings run from 1A to 50A. It too is intended for high performance medical applications with no leakage currents, for example medical equipment, diagnostic equipment, X-ray machines, or MRIs.

The AHM-L Series comprises medical dual-stage, low-frequency filters. It is intended for switched mode power supplies to reduce noise back into the mains with good attenuation of incoming interference as well in high performance medical applications with no leakage currents. Available in multiple sizes and compliant with IEC 61010-1, models come in different mounting styles, termination, and circuit configuration and current ratings from 1A to 50A.

The AFM series are single-phase, medical-grade, inlet-type EMI filters. For diagnostic equipment, medical equipment, and X-ray applications, handles currents from 1A to 15A and single-phase supplies up to 250VAC. Available in multiple sizes and compliant with IEC 61010-1, models come in different mounting styles (screw or snap-in), termination, and circuit configuration.

While descriptions and specs on Ohmite’s website will be helpful, they aren’t the only resource the company offers. Contact Ohmite and communicate with an expert who at no charge can help you specify the best type of filter for your application and requirements.