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ACD
D-DOT SENSOR (Ground Plane)
 These ACD (Asymptotic
Conical Dipole) sensors are mounted on a conducting surface and
used to measure the normal component of the displacement current
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Click here for 
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The asymptotic cone design exhibits less capacitance than the
HSD design and extends the upper frequency limit for the same
value of equivalent area (Aeq). The ACD sensor is also used to
measure the time rate of change of source charge density, qs,
in both EMP and lightning experiments. (Data Sheet 1117 describes
HSD type qs sensors). EG&G developed a shape for the sensing element
which optimizes the bandwidth and pulse response of these sensors.
The ACD design uses a thin dielectric cylinder to support and
align the sensing element.