A new sensor structure for the measurement of an electromagnetic pulse

Harry Diamond Laboratories (HDL), Woodbridge, VA, currently uses groundplane version electric- and magnetic-field sensors to measure the electric and magnetic fields produced during a simulated high-altitude electromagnetic pulse (HEMP). These sensors are also used for the measurement of such pulsed fields in the vicinity of metallic enclosures. A new sensor structure has been developed to measure the electric and magnetic fields accurately. The authors have recently fabricated and mounted a hollow metallic cylinder behind the sensor's 0.218-m (8 1/2 in) ground plane to house a fiber-optic transmitter, amplifiers, and other equipment necessary for data collection. The presence of this metallic cylinder increases (“enhances”) the amplitude of a signal when measured with this new sensor structure geometry (“sensor/cylinder”). The electric- and magnetic-field enhancements caused by the presence of this metallic cylinder were measured in both the frequency and time domains. The enhancement was also calculated numerically using a three-dimensional finite-difference code. To eliminate unwanted field coupling to the sensor's coaxial signal cable, the output of the sensor is transmitted through fiber-optic cables to remotely located recording equipment. In the frequency domain, the enhancements for both the electric and magnetic field were determined using a large transverse electromagnetic (TEM) cell. In the time domain, the enhancements were determined by comparing simulated HEMP fields measured with this sensor/cylinder to those measured with miniature electric- and magnetic-field sensors. The degree of enhancement of this sensor/cylinder will vary as a function of distance when the sensor/cylinder is placed next to a conducting object, such as a metallic shelter. These enhancements were also determined using miniature electric- and magnetic-field sensors.