Biomedical Engineering Reference
In-Depth Information
footprinting (
Figure 5.6-3
), (2) device characterization,
fingerprinting (
Figure (5.6-4
), and
ad hoc
susceptibility
testing according to IEEE guidelines (Knudson and
Bulkeley, 1994).
Footprinting an area means performing a series of
spectrum/amplitude scans for electromagnetic radiation
in a defined or designated area. Footprinting is an ongoing
technique that defines electromagnetic radiation in a clin-
ical facility or facilities in a multibuilding campus. Foot-
printing is also done upon request from a department
experiencing performance degradation of clinical, di-
agnostic, or therapeutic devices when EMI is the suspect.
The procedure involves a series of 20-MHz-wide spec-
trum sweeps, beginning at 2 MHz and ending at 1 GHz
with antenna(s) in the horizontal plane. This procedure is
repeated with the antenna(s) vertically polarized. Tunable
standard antennas are adjusted for the correct resonant
length for the center of each 20-MHz window.
The footprinting procedures yield two results: An
overview of the radiated electromagnetic fields present at
a specified location in the environment and the ampli-
tudes and types of emission of those fields. Several in-
cident investigations have been successful using this
information. In cases where EMI has been site-originated,
the source has been removed and the problem has been
corrected. In some cases, the affected device required
maintenance to correct the problem. An added value of
footprinting is that the data obtained during the process
meets the basic requirements for a site search similar to
D
evice
U
nder
T
est
1-meter
distance
ANTENNAS
Selected and adjusted for frequency
range of emissions under
examination
TEST EQUIPMENT
CONFIGURED
FOR
FINGERPRINT
Figure 5.6-4 Fingerprinting.
CALIBRATED
ANTENNA SYSTEMS
the OATS procedure for fingerprinting individual devices.
The results of the footprinting scans are transferred to
a storage medium and filed. They form a comparison
database that is used to evaluate new devices before
introducing them into a specified area.
Biconical: Low Frequency Rod, Dipoles,
COMMUNICATIONS
SPECTRUM
ANALYZER
Fingerprinting
The process of fingerprinting a device has several steps.
Again, the spectrum analyzer and calibrated antenna
system are the primary tools used to analyze the device
under test (DUT) (see
Figure 5.6-4
). To minimize the
loss of information from the DUT due to masking by
other sources of electromagnetic radiation, areas within
the clinical physical plant should be tested using the
footprinting procedure until a relatively quiet area is
found.
For the fingerprinting procedure, as in the foot-
printing procedures, the standards antenna should be
located as far as possible from any conductive material.
The standards antenna should be located at a height
equal to the center of the DUT. Due to constantly
LAPTOP
COMPUTER
PRINTER
DATA
Archival
Storage
Figure 5.6-3 Typical equipment configuration for fingerprinting
and footprinting.
