In my previous article I was reviewing wireless coexistence testing which generally focuses on the mutual effects of coexisting radio systems while using a shared frequency spectrum for their intended transmission and reception.
More specifically, the coexistence evaluation assesses the ability of the equipment under test (EUT) to perform its intended radio operation in the electromagnetic (EM) environments in which it will be used.
As stated, the wireless coexistence is of particular importance for radio communication use in critical systems that serve health & safety related applications, e.g. for wireless medical devices.
In this article I want to review another test discipline that is essential for the safe and effective use of medical devices: Electromagnetic compatibility (EMC) testing.
EMC is defined as the ability of equipment or a system to function satisfactorily in its EM environment without introducing intolerable EM disturbances to anything in that environment [1]. In accordance with the definition, EMC test disciplines can be grouped into immunity and emission testing.
Since our focus is the safe and effective operation of medical devices the EMC immunity testing shall be given special attention in the following review.
While the wireless coexistence testing is only applicable to medical devices with a radio function, i.e. wireless medical devices, EMC immunity testing looks at the effects of EM disturbances on the medical device whether it uses radio frequency (RF) energy for its function or not.
The widely accepted international standard for the EMC assessment of medical devices is IEC 60601-1-2 Edition 4.1 (2020-09).
In line with the EMC definition provided above, IEC 60601-1-2 applies to the basic safety and essential performance of medical electrical equipment (ME equipment) or medical electrical systems (ME systems) in the presence of EM disturbances and to EM disturbances emitted by ME equipment and ME systems [2].
The tests for emitted EM disturbances within IEC 60601-1-2 are conducted emissions, radiated emissions, harmonic distortion, voltage fluctuation and flicker.
Let us now concentrate on the EMC immunity testing of medical devices.
Within IEC 60601-1-2 the EUT performance in the presence of EM disturbances is evaluated as immunity to:
The immunity to PROXIMITY FIELDS FROM WIRELESS COMMUNICATION EQUIPMENT needs special consideration due to the continuous evolution of radio technologies. In particular, the enablement of new radio technologies, frequency bands and transmitter power levels to boost network capacity and data throughput in the radio communication space, is by far outpacing the cadence of IEC 60601-1-2 standard updates.
Consequently, Edition 4.1 of IEC 60601-1-2 as published in 2020, is only providing test frequencies and test levels for representative examples of radio communication technologies to verify the immunity to PROXIMITY FIELDS FROM RF WIRELESS COMMUNICATION EQUIPMENT.
However, the risk management process of IEC 60601-1-2 requires device manufacturers to study the state of the art of radio communication technologies when defining an inclusive test plan for immunity to PROXIMITY FIELDS FROM RF WIRELESS COMMUNICATION EQUIPMENT in the environment of intended use.
Likewise, Edition 4.1 of IEC 60601-1-2 is defining induction cooking appliances, electronic article surveillance systems and radio-frequency identification readers as representative sources of magnetic field disturbance to verify the immunity to PROXIMITY MAGNETIC FIELDS.
Again, manufacturers should review additional technologies that might present a risk to the medical device for inclusion in their test plan for immunity to PROXIMITY MAGNETIC FIELDS.
IEC 60601-1-2 is referencing the basic EMC standards IEC 61000-4-3 and IEC 61000-4-39 defining the testing and measurement techniques for immunity to RADIATED RF EM FIELDS, PROXIMITY FIELDS FROM RF WIRELESS COMMUNICATIONS EQUIPMENT and PROXIMITY MAGNETIC FIELDS.
Testing the immunity to RADIATED RF EM FIELDS is applying the test methodology specified in IEC 61000-4-3, which is designed to assess the immunity to EM fields from RF sources not in close proximity to the EUT.
While particular considerations are devoted to the protection against intended emissions from radio communication transmitters, IEC 61000-4-3 also considers radiation caused by the operation of devices such as welders, thyristors, fluorescent lights, switches operating inductive loads, etc.
IEC 61000-4-3 has defined EM radiation environments as moderate, with test level class 2 (3 V/m), and as severe, with test level class 3 (10 V/m), assuming a minimum separation distance of 1 m between the field generating source and the EUT.
These immunity test levels are applied by IEC 60601-1-2 for environments specified as professional healthcare facility and home healthcare. Test levels, frequency range and modulation as guided by IEC 61000-4-3 are adopted.
The test methodology as specified in IEC 61000-4-3 is not optimal for testing the effects of RF wireless communication equipment in close proximity to medical devices.
As a result, IEC 60601-1-2 Edition 4.0 has introduced additional requirements to test for immunity to PROXIMITY FIELDS FROM RF WIRELESS COMMUNICATIONS EQUIPMENT assuming a separation distance of 0.3 m between the wireless communication devices and the EUT. Discrete test frequencies, immunity test levels and appropriate modulations for different radio communication technologies have been defined.
The preferred antenna distance of 3 m for testing per IEC 61000-4-3 is maintained as well as an allowed reduction of the test distance to a minimum of 1 m, e.g. to achieve the immunity test levels. Also, the IEC 61000-4-3 concept of a uniform field area (UFA), which ensures that the field strength variations are acceptable small, is applied.
IEC 60601-1-2 requires that ME equipment and ME systems that intentionally receive RF electromagnetic energy for the purpose of their operation shall be tested at the frequency of reception.
Thus, there are no receiver exclusion bands allowed as e.g. permitted by the radio EMC standards EN 301 489-1/52. This is to allow the assessment of the basic safety and essential performance of an intentional receiver when an ambient signal is in the passband. It is understood that the receiver might not achieve normal reception during the test.
The evaluation of the immunity to PROXIMITY MAGNETIC FIELDS is assuming devices predominantly emitting magnetic fields in the frequency range 9 kHz to 13.56 MHz being operated in close proximity to medical devices. Close proximity per IEC 61000-4-39 refers to a separation distances <= 500 mm between the transmitter antenna and the EUT for magnetic fields with a frequency < 26 MHz.
Per IEC 60601-1-2 measurements should only be performed if:
a) the ME Equipment or ME System contains magnetically sensitive components or circuitry within the enclosure or as part of an attached accessory and
b) a separation distance of 0.15 m cannot be ensured between magnetically sensitive components or circuitry to the specified field sources during intended use.
If a) and b) are true, the manufacturer may determine that the risk of exposure to interfering signals is acceptable. In that case immunity to PROXIMITY MAGNETIC FIELDS is not required, otherwise testing per IEC 61000-4-39 shall be performed.
The test distance per IEC 61000-4-39 is defined as 50 mm.
The two large regulatory schemes that are regulating EMC testing for medical devices are the Medical Devices Regulation (MDR) in Europe and the Food and Drug Administration (FDA) in the USA.
For the MDR testing should be performed per IEC 60601-1-2 (state of the art) in the lack of harmonised standards.
The FDA has IEC 60601-1-2 Edition 4.1 (2020-09) listed as Recognised Consensus Standard [3]. It also lists AIM 7351731 Rev. 3.00 (2021-06-04) for EM immunity testing at radio frequency identification (RFID) readers.
At TÜV SÜD we have assessed the state of art radio communication technologies to augment the existing test specifications for enclosure port immunity to PROXIMITY FIELDS FROM RF WIRELESS COMMUNICATIONS EQUIPMENT.
We have added test frequencies and immunity test levels to table 9 of IEC 60601-1-2 for additional frequency bands and user equipment (UE) power classes for LTE and 5G NR as well as the frequency extension for Wi-Fi 6E (5925 – 7125 MHz).
For 5G NR all frequency bands currently operated in the EU and the USA are included in frequency ranges
FR1 (410 – 7125 MHz) and FR2-1 (24.25 – 52.6 GHz).
Our augmented table 9 is based on the following formula to calculate the immunity test levels of the assumed radio communication services for free-space propagation in the far field:
E= 6/d* √P (E.1)
where E is the immunity test level [V/m], P is the maximum EIRP [W] and d is the distance [m]
Our test program is based on an assumed minimum separation distance of 0.3 m between the RF wireless communication UE and the sensible medical device during their intended use. We have also defined appropriate modulation schemes and duty cycle configurations. We use signal generators to provide the interferer signals determined in a stable manner.
The 1 m antenna distance allowed by IEC 61000-4-3 is exercised where needed to implement the required immunity test levels, e.g. for 5G NR FR2-1 UEs which are allowed to use a significantly higher equivalent isotropically radiated power (EIRP) utilising higher gain antennas.
Based on FDA feedback we have also implemented immunity testing against magnetic fields in the kHz range as emitted by wireless power transfer (WPT) technology for portable electronic devices. This is complementing the testing against disturbance generated by induction cooking appliances, electronic article surveillance and RFID readers as specified in IEC 60601-1-2.
This immunity to PROXIMITY MAGNETIC FIELDS is performed as ad hoc testing, usually with real UEs (WPT charging pods).
Please get in contact with TÜV SÜD if you need to discuss the test frequencies, immunity test levels, modulations and duty cycle configurations we defined for radiated RF immunity to LTE, 5G NR (FR1 and FR2-1), Wi-Fi 6E and WPT disturbances.
[1] IEC 60050 International Electrotechnical Vocabulary (IEV)
[2] IEC 60601-1-2 Edition 4.1 (2020-09)
[3] Recognised Consensus Standards: Medical Devices (fda.gov)
TÜV SÜD's certification and testing services are independent of each other and do not impact one another. Our certification services are delivered by TÜV SÜD's recognised Certification Bodies, while our testing services are conducted through TÜV SÜD Testing Labs.
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