Biomedical Engineering Reference
In-Depth Information
S
p
ark Ga
p
R charge
HV
Sour ce
Transmission
Line 1
L
Bypass
Transmission
Line 2
Wideband Antenna
Figure 4.23
A beefed-up indirect-injection ESD test can serve as the basis for wideband assess-
ment of a device's susceptibility to radiated EMI. The transmission lines of a Blumlein pulse gener-
ator are charged by a high-voltage power supply via R
charge
. When a certain voltage is developed
across the transmission line, the spark gap triggers, causing a very fast pulse to be delivered to a
wideband antenna.
Applied at the input of the
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flyback driver, 12 V should produce 15 to 20 kV dc at the
output of the
flyback's tripler. This high voltage is used to charge two transmission line
capacitors Z1 and Z2 which are etched on a double-sided 0.4-mm-thick copper-clad PCB
as shown in Figure 4.25. The TEM horn antenna is formed from two truncated triangular
pieces of single-sided PCB and edge-soldered to the Blumlein generator board. The spark
gap is simply a copper or bronze U shape with a bolt and nuts that permit the discharge
gap width to be adjusted.
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Susceptibility to Conducted Electromagnetic Interference
EMI susceptibility tests for medical devices conducted according to IEC-61000-4-6
involve injecting RF voltages onto the power line and bulk RF currents into other signal
cables. A current probe is clamped around the entire cable bundle, and radio-frequency
Warning!
This is a dangerous device! It produces high voltages that can cause very
painful or lethal electrical shocks. In operation, the spark gap produces signi
cant levels
of ultraviolet radiation, which must be shielded to prevent eye damage. In addition, spark
discharges can ignite
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flammable or volatile atmospheres. Finally, the EMI levels gener-
ated by this circuit are certainly above what the FCC likes to see dumped into the atmos-
phere. Thus, this generator should only be operated inside a properly shielded room.
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