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Pressure/acoustic sensors based on a hollow-core photonic bandgap fiber (HC-PBF) with thin outer-cladding and a fiber-tip micro-cavity with ultra-thin graphene diaphragm are reported. The HC-PBF sensor demonstrates a normalized acoustic responsivity of~25 dB higher than standard single mode fiber while the fiber-tip sensor has a record high pressure responsivity of well over 1000 nm/kPa.
As the use of ultrasonic transducers has increased so has the need to measure and characterize their pressure fields. Currently available hydrophones are limited by long scan times, and multiple source pulses to measure large area fields. Using a 2D capacitive micro-machined ultrasonic transducer (CMUT) array and associated electronics we are able to improve on these limitations. The CMUT inherently...
We measure the effects of a weak language model, estimated from as little as 100k words of text, on unsupervised acoustic model training and then explore the best method of using word confidences to estimate n-gram counts for unsupervised language model training. Even with 100k words of text and 10 hours of training data, unsupervised acoustic modeling is robust, with 50% of the gain recovered when...
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