A fundamental challenge for surface acoustic wave (SAW) temperature sensors is the detection of small temperature changes on non-planar, often curved, surfaces. In this work, we present a new design methodology for SAW devices based on flexible substrate and bimorph material/structures, which can maximize the temperature coefficient of frequency (TCF). We performed finite element analysis simulations and obtained theoretical TCF values for SAW sensors made of ZnO thin films (~5 μm thick) coated aluminum (Al) foil and Al plate substrates with thicknesses varied from 1 to 1600 μm. Based on the simulation results, SAW devices with selected Al foil or plate thicknesses were fabricated. The experimentally measured TCF values were in excellent agreements with the simulation results. A normalized wavelength parameter (e.g., the ratio between wavelength and sample thickness, λ/h) was applied to successfully describe changes in the TCF values, and the TCF readings of the ZnO/Al SAW devices showed dramatic increases when the normalized wavelength λ/h was larger than 1. Using this design approach, we obtained the highest reported TCF value of −760 ppm/K for a SAW device made of ZnO thin film coated on Al foils (50 μm thick), thereby enabling low cost temperature sensor applications to be realized on flexible substrates.
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Shear horizontal surface acoustic waves (SH-SAWs) have been regarded as good candidates for liquid sensing applications but are inefficient in fluid manipulation due to a minimal fluid coupling between the fluid and acoustic waves. However, in this letter, a vertical jetting function was realized using the SH-SAW generated from a 36° Y-X LiTaO3 SAW device. The jetting of the droplet induced by the SH-SAWs was observed nearly along the vertical direction, and the aspect ratio of the liquid beam is proportional to the applied power before breaking up, which is dramatically different from those generated from the conventional Rayleigh SAWs. By conducting theoretical simulation and experimental investigation on the SH-SAWs systematically, we concluded that the wave/energy pressure dissipated into the sessile droplets causes this vertical ejection on the device surface.
This document may differ from the final, published version of the research and has been made available online in accordance with publisher policies. To read and/or cite from the published version of the research, please visit the publisher's website (a subscription may be required.)IEEE/OSA Journal of Lightwave Technology 1 Abstract-In this paper, we investigate a nonlinear compensation technique with two different architectures using direct modulation (DM) and external modulation (EM) techniques, termed as DM based frequency dithering (DMFD) and EM based frequency dithering (EMFD). We show that DMFD and EMFD methods operate substantially different in radio-over-fiber (RoF) system by optimizing the dithering technique relative to the LTE technology. The proposed techniques is only applicable if the condition of {f L < f d < f RF } is met, where f L represents the dithering boundary limit of 14 MHz, f d is DMFD signal frequency and f RF is the RoF carrier frequency. Analysis of the optical launch power for DMFD and EMFD methods reveal that the stimulated Brillouin scattering (SBS) threshold is above ~6 dBm for the LTE-RoF system. In addition, we also unveil that DMFD and EMFD methods do not introduce additional distortion for the linear and optimum optical launch power regions, which are frequency chirp driven regions. If the given condition is met, the proposed method improves the LTERoF system without any shortcoming. Finally, at 10 dBm launch power, DMFD and EMFD methods exhibits an average signal-tonoise ratio (SNR) gain of ~5.95 dB and ~7.71 dB, respectively. Index Terms-Long Term Evolution (LTE); Radio-over-fiber (RoF); Nonlinear Compensation; Optical OFDM (OOFDM) I. INTRODUCTIONThe actively growing end user subscriptions with bandwidth hungry, high specification, real-time, and delay-sensitive applications have been driving the mobile communications technology to continuously progress forward. The 3 rd generation partnership program (3GPP) established a standard known as the LTE to support the rapidly evolving mobile communication requirements [1].In the radio access network of LTE, eNodeB (eNB) functions as the base station (BS) similar to the global system Manuscript received April 29, 2013 for mobile communications (GSM) and universal mobile telecommunication system (UMTS) BSs. However, the eNB provides the real-time operation via a 2-node architecture, without an external central controller. The 2-node architecture is achievable because the eNB architecture is designed with built-in central controller with a radio access network, and such evolution leads to costly infrastructure expansion. In addition, the vastly allocated spectrums for LTE in urban locations throughout the world are either 2.6 GHz or 1.8 GHz [2] where the drawback is the excessive loss on the wireless propagation. As a result the eNB cell radius is limited to 1 km in urban operating conditions [3]. The throughput for the user equipment (UE) at the cell edge is <20 Mb/s from the maximum of 100 Mb/s owing to the deteriorating SNR, thu...
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