ELECTROMAGNETIC COMPATIBILITY AND MEDICAL DEVICES - Design and Development of Medical Electronic Instrumentation - page 178

Semi Anechoic Chamber

EUT

Nonconductive
Support Table with
Turntable (80 cm high)

Field Density
Probe

Antenna

Generator

Amplifier

Controller

Figure 4.21 Setup for assessing the susceptibility of a medical device to radiated emissions.
Testing is performed in a shielded enclosure with anechoic material placed throughout the enclosure
to minimize reflections. The transmit antenna is typically located 3 m from the device under test. An
isotropic field strength meter is placed inside the room to yield an indication of the field strength.

test is also exposed to a 3-V/m field of 900 MHz modulated with a 200-Hz square wave

and modulated with 50% duty cycle in both vertical and horizontal polarizations.
Sometimes, additional test and monitoring equipment is needed to generate test signals
and to evaluate the performance of the device under test. Figure 4.22 shows the experimen-
tal setup used to test the RFI susceptibility of a prototype implantable-device programmer.
The implantable device programmed by this device is meant to interact with the patient's
heart. Although the implantable device itself was not the subject of this speci

fi

c test, it had
to be in communication with the programmer so that the performance of the programmer
could be evaluated while being exposed to the 3-V/m RFI. In addition, since the program-
mer has an ECG input, a patient simulator had to be connected to the programmer during the
tests. The patient simulator as well as the implantable device were placed under an aluminum
foil shield. A shielded closed-circuit TV camera relayed the image from the programmer's
computer screen to those who were monitoring the device outside the shielded room.
Because of the amount of EMI generated, there is no easy legal way of conducting this test
outside a shielded room. As such, the common engineering practice is to apply good design
practice and then cross

fi

fi fingers when running the test at a quali fi ed facility. Design-lab testing