# FAQs – Measuring Magnetic and Electric Fields The output of these sensors depends on their physical dimensions which are calibrated at the factory at the point of production. Therefore, these sensors do not need to be re-calibrated unless their physical form is altered, for example, through damage.

Using a Prodyn B-DOT or D-DOT sensor is the best way to measure a pulsed electromagnetic field because they have been specifically designed to have a frequency response which minimizes distortion to the pulse. Using an ordinary antenna or “homemade” sensor will not provide the predictability over frequency that is required to provide accurate results.

The sensors are passive devices, therefore, a power source is not required.

The voltage output from a D-DOT is given by the expression: ..where E0  is the permittivity of free space 8.854 × 10-12

Since a D-DOT responds to the rate of change of the electric displacement vector, the peak voltage will occur when the differential is a maximum. Therefore, we need first to calculate the maximum value of the differential.

D = field x E0 x sin(ωt) therefore, dD/dt = field  x  E0 x ω cos(ωt)

The maximum value of the differential will occur when cos(ωt) = 1.

Therefore, the maximum value of the differential = field x E0 x ω

Hence the peak voltage Vmax = AeqR x field x E0 x ω (see output voltage equation above)

For example:

A continuous wave environment with a 50V/m peak field at 1MHz the output from an AD-70 D-DOT means:

….therefore Vmax = 1×10-3 x 100 x 50 x 8.854×10-12 x 2π x 106=  278μV

When using an oscilloscope or spectrum analyser, a load of 50Ω should be presented.  A spectrum analyser would normally present this impedance anyway.

When using a passive integrator, a load of 1MΩ should be presented.

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