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EMC in Medical Applications

EMC in Medical Applications

In today’s world, all electrical and electronic devices employ very high frequency switching circuits that generate unwanted high frequency electrical signals or noise that can cause Electromagnetic Interference (EMI) with nearby devices. EMI can disrupt the intended operation of a device and cause disturbance or malfunction. 

Electromagnetic interference (EMI) filters reduce electrical noise and prevent interference with other devices. This makes electromagnetic interference (EMI) filters crucial for a wide range of equipment and devices. While EMI filters are present in all modern electronics, their function is particularly critical in the medical industry.

Why Is It Critical to Utilize an EMI Filter in Medical Devices?

Life-sustaining devices constantly function in the close vicinity of one another. It is critical that they work uninterrupted and as intended. If a medical device stops functioning, the consequences can be fatal. Often, the most vital  equipment and devices have the greater susceptibility to interference. For example, defibrillators and magnetic resonance imaging (MRI) are two of the greatest sources of electrical noise in medical settings and are also highly vulnerable to any external noise. Global medical directives such as UL 60601-1, IEC 60601-1 and CISPR 11 are aimed at curbing these interference issues and ensure that products pose no safety hazard to patients.

Using a well-designed filter minimizes product malfunctions and reduces potential risk to the patient. 

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Unique Requirements for Medical Applications

To meet medical EMC directives, equipment must be able to effectively attenuate noise signals while meeting low leakage allowances. 

Why is low leakage critical in medical applications?  

Leakage current, which is common in most electrical and electronic equipment, usually flows to ground through a ground conductor (earth/ground leakage). Some leakage current can also flow through the equipment enclosure creating an electrical charge (touch current) under normal condition. Medical devices are mostly connected to patients and some of these connections can be electrically conductive giving path to the leakage current to enter the patient's body (patient leakage).

Higher amount of leakage current to the human body can result in an electric shock. If the device is connected to the patient intravenously or to the heart this current can induce ventricular fibrillation which can be fatal. This can happen due to high patient leakage or inadvertent diverting of touch / earth leakage to the patient due to errors, physical contacts, fault conditions or bad grounding. High leakage can damage patient implants (pacemaker, heart pumps) and trip GFCI causing disruption to other medical devices. This can pose serious risks to short-term and long-term health and life of the patient. 

IEC 60601-1 Compliance

The International Electrotechnical Commission (IEC) standardized their compliance criteria with IEC 60601. Medical devices must meet these requirements for commercialization. Manufacturers design their products to meet these standards. The IEC standard covers emissions (CISPR 11), immunity and safety requirements. In its simplest form, the rule states that emissions from accredited medical devices must not harm humans or other devices.

EMI filters themselves do not have to comply with IEC 606011 requirements. They can, however, help medical devices comply with the emissions requirements by bringing emissions below CISPR 11 limits. EMI filter manufacturers like Astrodyne TDI have decades of experience in designing filter solutions for medical applications to help medical equipment manufacturers achieve CISPR 11 / IEC 60601-1 compliance.

Line to Ground (Y-) Capacitors and Compliance

As mentioned above, leakage current is a critical safety parameter in medical applications. The leakage current is caused by (Y) capacitors connected between line and ground (direct leakage) and by various insulations and dielectrics in the equipment (stray / parasitic leakage). The medical directive limits the total allowed leakage current for different applications (devices and equipment) that come in direct contact with the patient. These are:

Patient Devices CF - Cardiac floating / conductive intracardiac connection

Patient Devices BF - Body floating / conductive body connection 

Patient Devices B - Body / non-conductive physically connection

In Type B, applied parts (in contact with the patient) may be connected to earth, while Type BF and CF are 'floating' and must be separated from earth.

The normal condition leakage current limits of each type are as follows:

Leakage Type

Type CF

Type BF

Type B

Patient Leakage

10uA

100uA

100uA

Enclosure Leakage

100uA

100uA

100uA

Earth/Ground Leakage

500uA

500uA

500uA


Considering that there are many unavoidable sources of leakage current in medical equipment, the available leakage current for filters is almost zero which translates to no Y-capacitors. Line to ground (Y) capacitors are a key component of any filter circuit. Bigger Y-capacitors help the filter’s insertion loss/EMC performance however they also result in higher leakage current. This creates a unique challenge for an EMI filter designer. If Y-capacitor value is reduced to meet leakage current limits, the insertion loss performance suffers as well and, in many instances, this can result in equipment failing the emissions test. To make this up, Y-capacitor value must be optimized, and other components must be adjusted which can lead to customization or fully custom design. One EMI filter feature that is very useful in medical applications is the option of adjustable/selectable Y-capacitors (0 / 0.1nF / 0.22nF/ 0.33nF / 0.47nF / 0.68nF / 1.0nF etc). 

Adjusting selectable Y-capacitors allows users to find an optimized value which greatly helps in insertion loss - leakage current optimization.

Advantages of Working With Astrodyne TDI

Astrodyne TDI has extensive experience in working with medical device manufacturers, providing high-quality, high reliability power supplies and EMI filters solutions for over 50 years. Astrodyne TDI has also been providing EMI filters for a wide range of applications, including medical, commercial, appliance, industrial and military. Our EMI filter solutions can help in improving the EMI performance of your devices and in meeting the relevant EMC standards.

We offer both off-the-shelf and custom EMI filters. We closely work with you to determine the ideal EMI filtering solutions for your applications. We offer a wide range of filter types, from small IEC inlets, power entry modules and single-phase options to high current three-phase filters. We have full engineering and design expertise for developing custom EMI solutions to help your equipment meet applicable EMI requirements, if necessary.

At Astrodyne TDI, we understand EMI. Our 3 in-house pre-compliance labs globally help us test OEM equipment and create a baseline measurement. Our advanced filter design capability and thousands of standard products / designs help us quickly select a standard solution, customize a design or build a custom. The equipment is retested to ensure compliance with at least 6-8dB margin. Our agency approved in-house safety lab allows us to test and certify our new filter designs to relevant safety standards for US (UL 60939), Canada (CSA C22.2) and Europe (EN 60939-3). 

Partnering with us ensures you get an excellent product and shorten your product design and compliance cycle. Medical device manufacturers enjoy many benefits when they work with Astrodyne TDI:

  • Free pre-compliance testing

  • No-cost samples for testing

  • Quick turnaround

  • Customization availability

  • Engineering support

  • Selectable Y-caps

Order EMI Filters From Astrodyne TDI

Customers will find Astrodyne TDI's designs and filter solutions outside the medical field as well. Our EMI filters are present aboard aircraft and Navy ships and also in electric car chargers and high-end appliances.

Start your EMC-compliant medical devices designs with Astrodyne TDI by shopping our selection of medical-grade EMI filters and Medical Power Supplies today. Contact us online for more information.   
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