Identifying of the Special Purpose Generator Pulses

Abstract

There are some suitable methods for the measurement of ultra-short solitary electromagnetic pulses (EMP) that are generated by high power microwave generators. The characteristics of EMPs are high power level (Pmax = 250MW) and very short time duration (tp2 ns). Special requirements for measurement methods have to be considered because of the speciflc EMPs properties. In the paper, two suitable methods for this application are presented. The flrst one, the calorimetric method, utilizes the thermal impacts of microwave absorption. The second method presented | the magneto-optic method | uses the Faraday's magneto-optic efiect as a sensor principle. A combined calorimetric sensor was realized and there were made some experimental EMP measurements with good results. The sensor utilizing the magneto-optic method is still in development. DOI: 10.2529/PIERS060901081439 In connection with the events of the last few years and with the increased number of terrorist activities, the problem of identifying and measuring the impact of electromagnetic weapons or other systems occurred. Among these weapons or systems there are also microwave sources which can reach extensive peak power of up to Pmax = 250MW. Solitary, in some cases several times repeated, pulses lasting from tp 2 ns cause the destruction of semiconductor junctions. The analysis of possible measuring methods convenient for the identiflcation and measurement of the ultra-short solitary electromagnetic (EM) pulses is presented in this paper; some of the methods were selected and used for practical measurement. 2. METHODS 2.1. Method Based on Faraday's Induction Law One group of methods is based on the application of Faraday's induction law where the pulse is located by sensor (coil with Ns = 1¥50 turns). The signal induced in the coil is led to the recording device, generally an oscilloscope. Due to safety requirements, the distance between the sensor and the oscilloscope is l = 50m. This parameter introduces quality decrease of the recorded information in the way of the signal amplitude reduction, change of the signal phase and the pulse prolongation. The elimination of this limitation is in Version I, depicted in Figure 1, made by backward correction exploiting the Laplace transform. Pulses up to limit pulse length Tmax = 1ns were measured by this method and magnetic ∞uxwas evaluated (4). Version II exploits the possibility of principal elimination of in∞uence of the transmitting line between the sensor and the measuring device by an analogue U/f. converter. Available measuring devices can achieve measured pulses with the limit length Tmax = 5ns. The solution in Version III is similar to Version II; the difierence is in the digital converter applied. By an available measuring devices application and fulfllled sampling theorem we can measure pulses with the limit length Tmax = 20ns. 2.2. Method Based on Faraday's Magneto-optic Efiect Version IV in Figure 1 is based on Faraday's magnetooptic efiect (4). The connection between the sensor and the measuring device is implemented in the optical wavelength. There are three basic types of the possible active sensors. The flrst type is a garnet with high Verdet constant, the second one is an optic flber and the third one is based on magneto-optic properties of ferromagnetic mono/multi thin fllm. Other types of Version IV sensors are based on the magneto-optic Kerr's efiects (MOKE), or surface MOKE (SMOKE) efiect. By an available measuring devices application we can measure pulses with the limit length Tmax = 0:1ns. The named methods indicate the electromagnetic parts of the wave | electric or magnetic. They don't express the power conditions of the electromagnetic wave. For some of the measurement it is essential to evaluate power ∞ow through the deflned area.