We report the first-ever direct detection of benzene in water at concentrations below 100 ppb (parts per billion) using acoustic wave (specifically, shear-horizontal surface acoustic wave, SH-SAW) sensors with plasticized polymer coatings. Two polymers and two plasticizers were studied as materials for sensor coatings. For each polymer-plasticizer combination, the influence of the mixing ratio of the blend on the sensitivity to benzene was measured and compared to commercially available polymers that were used for BTEX (benzene, toluene, ethylbenzene, and xylene) detection in previous work. After optimizing the coating parameters, the highest sensitivity and lowest detection limit for benzene were found for a 1.25 μm thick sensor coating of 17.5%-by-weight diisooctyl azelate-polystyrene on the tested acoustic wave device. The calculated detection limit was 45 ppb, with actual sensor responses to concentrations down to 65 ppb measured directly. Among the sensor coatings that showed good sensitivity to benzene, the best long-term stability was found for a 1.0 μm thick coating of 23% diisononyl cyclohexane-1,2-dicarboxylate-polystyrene, which was studied here because it is known to show no detectable leaching in water. The present work demonstrates that, by varying type of plasticizer, mixing ratio, and coating thickness, the mechanical and chemical properties of the coatings can be conveniently tailored to maximize analyte sorption and partial chemical selectivity for a given class of analytes as well as to minimize acoustic-wave attenuation in contact with an aqueous phase at the operating frequency of the sensor device.

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This paper presents the first demonstration of injection molding technology to enable large-scale mass manufacturing of high-performance tunable microwave filters to meet the growing needs of 5G small cell stations. This is the first time that a tunable filter satisfies all four of the following requirements simultaneously: low manufacturing cost, high quality factor, wide tuning range, and high power handling. Exhaustive research exists on the use of polymers for 3D microwave device manufacturing; nonetheless, mass-production technologies, such as injection molding, can provide low costs without compromising performance. The proposed bandpass filter implementation uses a tunable evanescent-mode cavity resonator injection molded with acrylonitrile-butadiene-styrene thermoplastic polymer. In addition, changing the critical gap size over the resonator's post through a commercial micro-actuator provides frequency tuning. The measured filter achieves an 86% tuning range from 2.8 -5.2 GHz with a state-of-the-art measured unloaded quality factor Q u of 1548 -2573. The filter has a measured insertion loss of 0.06 -0.1 dB with a fractional bandwidth from 7.6 -8.4 % across the entire tuning range. Moreover, for the first time in this manufacturing technology implementation, a bandpass filter is demonstrated with power handling capabilities beyond 100 W. The manufactured device demonstrates the significant potential of this technology for the scale-up manufacturing of reconfigurable high-Q RF filters without compromising performance.INDEX TERMS Evanescent-mode cavity filter, quality factor (Q), reconfigurable filter, tunable filter, injection molding, scale-up manufacturing method.

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