ELECTRIC FIELD SENSOR (D-dot)
(FREE FIELD)
MODEL SD-20
DESCRIPTION
The PRODYN Model SD-20 sensor is equivalent to the AFWL Model HSD-2. This sensor produces
a voltage output in response to a time variant E-field. It is a lightweight device designed
for use in making free space measurements. For this type of measurement, the sensor should be
supported by dielectric materials and placed not closer than two sensor diameters from conduct-
ing surfaces.
The sensor consists of two conductive hemispherical shells mounted on opposite sides of a
conductive base plate by means of dielectric spacers. In an E-field, current is generated on
each shell and picked off each shell at four equally spaced points with four 200-ohms strip
lines. These are connected to the 100-ohm twinaxial output cable at the center of the sensor.
The equation pertinent to this device is:
Vo = R Aeq dD
dt
where
Vo = sensor output (volts)
R = sensor characteristic load impedance (100 ohms)
Aeq = sensor equivalent area (m2)
D = magnitude of electric displacement vector (D =e o E, in Coul/m2)
The sensor is a passive device, therefore, an external power source is not required.
The sensor is equipped for purging with a gas such as dry air, nitrogen, or SF
ELECTRICAL SPECIFICATIONS
Equivalent Area (Aeq) . . . . . . . . . . . . . . . . . . . 1x10-1m2
Frequency Response (3 dB Point) . . . . . . . . . .> 130 MHz
Risetime (t, 10-90) . . . . . . . . . . . . . . . . . . . . . . . .<2,7 ns
Maximum Output (peak) . . . . . . . . . . . . . . . . . . + 4 kv
Output Connector . . . . . . . . . . . . . . . . . . . . . . . 100 ohm Twinax (Modified GR-874)
PHYSICAL SPECIFICATIONS
Mass: 2.15 kg
