A 900-MHz radio-frequency energy harvester is designed and implemented for remotely powered devices. An efficient power path structure with adaptive control is proposed to maintain close-to-optimal power conversion efficiency. The control circuit consumes low power by adopting a novel open-loop asynchronous implementation and duty-cycled operation. A startup circuit is also presented. Measurement results show minimum input available power for startup of 17 dBm. With input available power of 12 dBm and load resistance of 144 , the measured output power is 27.8 , giving an output voltage of 2 V. This corresponds to an end-to-end power conversion efficiency of 44.1%. The harvester consumes quiescent current of 1.56 at output voltage of 2 V.Index Terms-DC-DC boost converter, energy harvesting, full-bridge differential rectifier, passively powered device, power conversion efficiency, radio-frequency energy harvesting, remotely powered device, wireless sensor network, wireless sensor node. 1549-8328

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Two approaches to detect defects on printed circuit board had been evaluated. One is the direct comparison of the tested image with a template image. Before the comparison, we adopted an interpolation method to reconstruct the test image such that the orientation and position of components shown on the test image are the same as those on the template image. The second approach is using image features to detect and classify defects. We proposed a two steps inspection scheme. The inspection system is divided into the screening stage and the classification stage. The object of the screen stage is to quickly screen out most normal components to reduce overall processing time. Only one image feature is used as the screen index. At the classification stage, the neural networks were adopted to integrate all image feature information available to more precisely classify those fail to pass the screening test.

This article tries to disclose true parity relationships between gold and silver prices using fractional cointegration analysis. Both gold-silver and silver-gold parities are slow-adjustment long-memory processes with a time-varying risk premium. Information exposed by the parities is extremely useful in relatively long-run spread trading in the precious metal markets. Significant riskless profits could be earned based on the general ECMs' forecasting of the changes of the futures and cash spreads between gold and silver. The performance problem of gold and silver markets as a whole, therefore, is obvious.

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