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Carbon-nanotube ͑CNT͒-based strain sensors have the potential to overcome some of the limitations in small-scale force/displacement sensing technologies due to their small size and high sensitivity to strain. A better understanding of the dominant and limiting causes of high strain sensitivity is needed to enable the design and manufacture of high-performance sensor systems. This paper presents the theoretical framework that makes it possible to predict the strain sensitivity of a carbon nanotube based on it chiral indices ͑n , m͒. This framework is extended to capture the behavior of sensors composed of multiple CNTs in a parallel resistor network. This framework has been used to predict that a parallel resistor network of more than 100 randomly selected CNTs should have a gauge factor of approximately 78.5Ϯ 0.4. This is within the experimental error of the measured gauge factor of 75Ϯ 5 for such CNT resistor networks.

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A summary of recent research in micropositioning and nanopositioning is presented. The work is classified into five groups by actuation approach, including piezoelectric, magnetic, electrostatic, thermal, and electrochemical microactuators. A consistent set of measurable, key characteristics are proposed: degrees of freedom, range, resolution, range-to-resolution ratio, footprint, force, natural frequency, and bandwidth. Values of the key characteristics are listed in tables. The results demonstrate the boundaries of current knowledge and the advantages of each actuation approach. This is the first time this information has been compiled in this growing field and it is summarized in such a way as to be useful to readers. There are 82 references cited in this review article.