Dual-Use Strain Sensors for Acoustic Emission and Quasi-Static Bending Measurements.

In this paper, a MEMS piezoresistive ultrathin silicon membrane-based strain sensor is presented. The sensor's ability to capture an acoustic emission signal is demonstrated using a Hsu-Nielsen source, and shows comparable frequency content to a commercial piezoceramic ultrasonic transducer. To the authors' knowledge, this makes the developed sensor the first known piezoresistive strain sensor which is capable of recording low-energy acoustic emissions. The improvements to the nondestructive evaluation and structural health monitoring arise from the sensor's low minimum detectable strain and wide-frequency bandwidth, which are generated from the improved fabrication process that permits crystalline semiconductor membranes and advanced polymers to be co-processed, thus enabling a dual-use application of both acoustic emission and static strain sensing. The sensor's ability to document quasi-static bending is also demonstrated and compared with an ultrasonic transducer, which provides no significant response. This dual-use application is proposed to effectively combine the uses of both strain and ultrasonic transducer sensor types within one sensor, making it a novel and useful method for nondestructive evaluations. The potential benefits include an enhanced sensitivity, a reduced sensor size, a lower cost, and a reduced instrumentation complexity.

Simplified weighting function for high dynamic range video frame formation.

High dynamic range imagery has matured from a laboratory demonstration to an integrated capability in consumer-level cameras. However, high dynamic range video has lagged in development despite the introduction of several different frame formation methodologies and system architectures. The most common formation methodology involves the calculation of a high dynamic range image from a series of rapidly bracketed frames at varying exposure levels, then through the use of a radiometric calibration, recombined utilizing a weighted maximum likelihood estimator. The ideal weighting scheme to minimize the error on final image formation has been investigated by several authors. A new nonrecursive, simplified weighting scheme is proposed that utilized only knowledge of the optical attenuation, integration time, and sensor gain. A method is developed to test the various weighting schemes for their resilience to error with limited available exposures over a wide range of exposure value offsets, a common scenario for multi-imager-based high dynamic range video systems.