Online Electro-mechanical Impedance-based Structural Tamper Detection

Tools that provide evidence of whether or not the structure of a container have been tampered with are important for a number of applications. The problem of providing evidence of tamper has many similarities with the structural health monitoring (SHM) problem. As a result, techniques developed by the structural health monitoring community have potential to help address the problem of determining whether or not a structure has been tampered with by an adversary. The difference between SHM and detecting structural tampering is that the former deals with structures damaged by environmental and\or loads effects, while the latter deals with damage intentionally induced in a structure. Detecting structural tampering is complicated by the fact that a determined attacker can adopt a series of measures to recover the status ante quo. The challenge is to find unique features which are irreversibly modified during the attack despite attempts by the attacker to return the structure to its nominal initial condition. Furthermore, these features cannot be overly sensitive to benign environmental changes that cannot be accounted for. The authors explore the use of impedance-based online structure tampering detection technique. The variations of the impedance signature are monitored near one of the bolts used to seal a lid to the top of a box in order to assess if the structure has been tempered with. This study is performed by applying high-frequency structural excitations through surface-bonded piezoelectric transducers, and measuring the output impedances. For the specific problem under investigation, the challenge is represented by the need to separate a tampering attack not only from environmental modifications, but also from any damage's onset and evolution which the structure can experience throughout its life.