Electromagnetic Sensor Arrays—Theoretical Studies

Eddy current probes have been used for decades to detect flaws in metal objects. These probes are unusually sensitive to changes in the proximity distance to the test surface, and special techniques must be used to suppress this proximity signal when searching for flaws. More recently this proximity effect of a test coil has been recognized as useful for robotic sensing, and several sensors of this type are on the market. However, recent scientific advances in the design of eddy current flaw detection probes have not yet been applied to eddy current robotic sensors. A similar situation exists in connection with capacitive sensors, which were initially applied as intruder sensors, and more recently to a small degree, as robotic proximity sensors. A common criticism of these circuit-type sensors is that they do not provide sufficient spatial selectivity to be useful in robotic applications. However, recent studies of flaw detection probes have shown that desirable detection properties can be designed into the probe by using spatial frequency analysis to determine the optimum probe geometry for the task at hand. In this approach the probe is treated as a spatial filter, much like optical signal processing components, but in this case the electromagnetic field is nonradiating (or quasistatic). The purpose of this research is to develop a conceptual base and associated technology for electromagnetic sensor arrays applied to automated manufacturing, maintenance, and NDE. This paper discusses concepts and theory, while the experimental system and measurements are presented in a companion paper [1].</p

Electromagnetic Sensor Arrays—Theoretical Studies

Eddy current probes have been used for decades to detect flaws in metal objects. These probes are unusually sensitive to changes in the proximity distance to the test surface, and special techniques must be used to suppress this proximity signal when searching for flaws. More recently this proximity effect of a test coil has been recognized as useful for robotic sensing, and several sensors of this type are on the market. However, recent scientific advances in the design of eddy current flaw detection probes have not yet been applied to eddy current robotic sensors. A similar situation exists in connection with capacitive sensors, which were initially applied as intruder sensors, and more recently to a small degree, as robotic proximity sensors. A common criticism of these circuit-type sensors is that they do not provide sufficient spatial selectivity to be useful in robotic applications. However, recent studies of flaw detection probes have shown that desirable detection properties can be designed into the probe by using spatial frequency analysis to determine the optimum probe geometry for the task at hand. In this approach the probe is treated as a spatial filter, much like optical signal processing components, but in this case the electromagnetic field is nonradiating (or quasistatic). The purpose of this research is to develop a conceptual base and associated technology for electromagnetic sensor arrays applied to automated manufacturing, maintenance, and NDE. This paper discusses concepts and theory, while the experimental system and measurements are presented in a companion paper [1]

Interoperable conditional access with video selective encryption for portable devices

The pay-TV industry seeks to extend its reach to portable display devices. At the same time, it seeks to ensure a horizontal market by making interoperable the Conditional Access Systems (CASs) employed to protect content. To achieve interoperability for such devices, this paper proposes a form of selective encryption for video that allows simultaneous distribution of a small percentage of video data on a per-CAS basis, allowing sharing of the unencrypted video between the CASs. The bitrate overhead for each additional CAS enabled is found to be on average 7.41 %, whereas the computational overhead amounts to no more than 40 ms for the benchmark sequences tested. Adaptation of CAS to transparent encryption of scalable video is also demonstrated in this paper