Circuit and Electromagnetic Modelling of a Low Cost Intentional Electromagnetic Interference Sensor J F Dawson, I D Flintoft, and L Dawson, Department of Electronics, University of York L Rebers, Dept of Electronics and Information Technology, University of Hannover Michael Camp, Juergen Schmitz, and Markus Jung, Rheinmetall Waffe Munition GmbH ABSTRACT The design of a low cost broadband Intentional Electromagnetic Interference (IEMI) detector and antenna to achieve a flat frequency response over a broad range is considered. SPICE simulation of the antenna, detector and low power log-amplifier circuit is used to predict the detector performance. The SPICE Antenna model is derived from numerical electromagnetic simulation. Simulations are compared with measured performance. INTRODUCTION The possible use of Intentional Electromagnetic Interference (IEMI) to disrupt critical infrastructure is becoming a significant concern [1]. One aspect of this threat is detecting the cause of a system failure. A failure due to IEMI may be blamed on faulty hardware or software, and much time and money may be wasted on searching for the cause, particularly if the failure is intermittent. It is therefore beneficial to consider how IEMI attacks may be detected. A number of IEMI detector systems have been developed previously such as those in references [2] and [3] which can detect IEMI. Although reference [4] describes a system that can determine the direction to the IEMI source, we have not been able to find references describing practical systems capable of determining the complete location of the source. In this paper, we describe a low cost detection system being developed as part of the STRUCTURES programme [5]. The STRUCTURES programme is one of several EU funded research programmes evaluating the effects of IEMI on critical infrastructure, including protection and detection. A complementary identification and location system is also being designed and a brief description is included in this paper for comparative purposes. DETECTOR DESIRABLES The three most important requirements for the detection system are the ability to detect an IEMI attack and generate an alarm, to send the received data for logging and post-processing, and to be cost- efficient. Additional features, such as locating and/or identifying the source of the attack, require designing a significantly more complex system, which is thus likely to be more expensive. Within the STRUCTURES project we are developing both, low- cost and high-performance detectors outlined in this paper. Detection of threat Clearly the first desirable property of a detector is that it can successfully detect the presence of an IEMI threat. False alarms should also be minimized. A field detector must have some means of discriminating between IEMI threats and other intentional or accidental sources such as mobile phones and electrostatic discharge. For simple detectors the discrimination between threat and other fields might be largely based on the level, though this can also be aided by ensuring that the detector is located away from expected transmitters such as mobile phones. A more complex system might be able to discriminate on the basis of frequency content and/or the time domain waveform. Similarly, a conducted interference detector must be able to differentiate between “normal” levels of transient and noise on a wire and that introduced by IEMI. Since most radiated IMEI sources are likely to use high gain antennas with narrow beam widths, it seems advantageous that a number of detectors are placed around any sensitive equipment, sufficiently close together that at least one detector will see the beam of any attack, even if it is slightly mis-directed. The susceptibility level of equipment used in industrial applications should be greater than 10 V/m and typical failure levels can be considerably higher and tend to increase with frequency [6] & [7]. Therefore, a detector should be sensitive to levels above 10 V/m and if the detector is placed between the source and equipment to be protected, it is likely to have an alarm threshold considerably greater than 10 V/m. Sources are available at ever increasing frequencies but their complexity increases with frequency. Although the majority of available sources operate below 3 GHz [8], detection at higher frequencies is desirable to allow for future developments. Communication and logging In order to allow notification of a threat and subsequent analysis (forensics) of the time, duration and number of attacks, some mechanism is required for the data from a number of sensors to be communicated to a local or remote monitoring and logging system, to send alerts and alarm indications (e.g. to a security office). Identification of threat Identification of the type of interfering signal is desirable, partly to discriminate between signals that may not be IEMI, such as a nearby mobile phone, and