Gustavo P. Rehder

A conductive polymer based electronic nose for early detection of Penicillium digitatum in post-harvest oranges.

We describe the construction of an electronic nose, comprising four chemiresistive sensors formed by the deposition of thin conductive polymer films onto interdigitated electrodes, attached to a personal computer via a data acquisition board. This e-nose was used to detect biodeterioration of oranges colonized by Penicillium digitatum. Significant responses were obtained after only 24 h of incubation i.e. at an early stage of biodeterioration, enabling remedial measures to be taken in storage facilities and efficiently distinguishing between good and poor quality fruits. The instrument has a very low analysis time of 40 s.

Compact and Broadband Millimeter-Wave Electrically Tunable Phase Shifter Combining Slow-Wave Effect With Liquid Crystal Technology

Based on a CMOS slow-wave coplanar-waveguide transmission-line topology, a novel compact millimeter-wave phase shifter is presented. The tunability is accomplished by using a liquid crystal (LC) material as a tunable dielectric between the coplanar signal strip and the shielding plane of the slow-wave transmission line. The device tunability is considerably enhanced by moving the free-standing signal strip with the application of a bias voltage. Combining the miniaturizing benefits of the slow-wave effect with the continuous tuning of LC material, the proposed device occupies only 0.38 mm2 and exhibits high performance. The phase shifter was characterized up to 45 GHz for a maximum bias voltage of 20 V without significant power consumption. The reproducible measurements show a figure-of-merit (ratio between the maximum phase shift and the maximum insertion loss) of 51°/dB at 45 GHz.

Modeling and Characterization of Slow-Wave Microstrip Lines on Metallic-Nanowire- Filled-Membrane Substrate

In this paper, a physical model of the slow-wave (SW) microstrip lines based on a metallic-nanowire-filled-membrane substrate is presented for the first time. The model properly predicts the behavior of the SW transmission lines as shown by the experimental results. Two sets of transmission lines differing in oxide thickness with various widths were fabricated and characterized up to 70 GHz. The electrical model is valid for both oxide thicknesses and microstrips width. High-quality factors are obtained, above 40 from 30 GHz up to 70 GHz, paving the way for further designs of passive circuits, like power dividers or hybrid couplers, with good performance.

Slow-wave microstrip line on nanowire-based alumina membrane

This paper proposes a new technology for slow wave microstrip lines based on a low-cost metallic-nanowire-filled-membrane substrate (MnM-substrate). These transmission lines can operate from RF to millimeter-wave frequencies. The MnM-substrate consists in a dielectric material containing vertical metallic nanowires connected to a bottom ground plane. The innovative concept of the slow-wave microstrip lines on MnM-substrate is presented, as well as the electromagnetic considerations, fabrication process, and measurement results. Initial results show high relative dielectric constants (up to 43). Hence, it is possible to reach high-quality factor transmission lines within a great range of impedances, from 20 to 100 Ω, without critical dimensions.

Optical humidity Sensor using Polypyrrole (PPy)

In previous works it was demonstrated that the electrical resistivity of Polypyrrole (PPY) changes when exposed to different organic solvents which allowed the development of applications in gas sensors [1,2]. Also, is well known that optical gas sensors have several advantages over conventional electronic ones like high sensitivity, reduced signal-to-noise ratio, and compatibility with combustible gases. The optical properties of polymer materials have became of great importance in modern optical design of polymer based optical sensors and devices. Thin polymer films appear in an ample spectrum of applications such as photonics, data storage, communications and sensor devices [3]. In this work an optical sensor for the detection of water vapor using Polypyrrole (PPY) as active material is proposed. As a first step in studying polypyrrole for this application, the refractive index of this material was measured after the films were exposed to water vapor, and the results showed a variation of the refractive indices of the polymer in the wavelength of 632.8 nm. Finally, an optical device was fabricated using integrated optics technology over silicon, which uses polypyrrole as active layer for sensing. The results of the characterization of this optical device showed that for relative humidity concentrations above a specific value (~70%) the optical power at the output of the device decays to insignificant values, which allows for the device to be used as an optical switch.

Development of MEMS varactor for selectable-band patch filter

The use of MEMS as tuning elements is interesting for their higher performance in terms of loss and nonlinearity. Here, MEMS varactors are integrated to a patch filter through a flip-chip process in order to change the filter center frequency. The selected frequencies are the ones assigned to WiMAX frequency bands at 2.5 GHz and 3.5 GHz.

Wood identification by a portable low-cost polymer-based electronic nose

The rapid and reliable identification of woods is a difficult task, yet extremely necessary for the control of illegal logging or trade of protected species. In this paper we describe a portable low-cost electronic nose based on conductive polymers, capable of distinguishing pairs of similar-looking woods, aiming to help wood traders to comply with the determinations of the United Nations (UN) Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Examples of woods with CITES restrictions are (i) mahogany (Swietenia macrophylla) and Spanish-cedar (Cedrela fissilis), and (ii) Brazilian walnut (Ocotea porosa) and black-cinnamon (Ocotea catharinensis). The e-nose consists of an array of four different gas sensors fabricated by the deposition of thin doped conductive polymer films onto the surface of interdigitated metallic electrodes. The electrical conductance responses of the sensors upon exposure to the volatile compounds emitted by the wood specimens, after scratching their surface, were evaluated by principal component analysis (PCA). The data can be processed on small computers or even on smart phones. The analysis time is only 10–15 min. Leave-one-out analysis gave a classification hit rate of 100% for group (i) and 94% for group (ii). Hence, this is an extremely viable method for standard control use in remote places such as roads in the Amazon forest, which are sometimes hundreds of miles away from urban centers, where conventional analyses could be performed.

60 GHz antennas on silicon with embedded cavity-backed structure

In this paper a new silicon-based antenna structure with an embedded back cavity is presented. The basic antenna with an optimized geometry has good impedance matching with return loss of -40 dB at the resonant frequency of 60 GHz and a gain of 7.6 dBi. A multi-layer structure can be realized that can lead toward the design of electromagnetic bandgap (EBG) layers inside the antenna to obtain desirable radiation characteristics. An example of such a structure is illustrated with a U-form uniplanar periodic structure under the radiating element that increases its gain by about 0.7 dBi at 60 GHz.

Metallic nanowire filled membrane for slow wave microstrip transmission lines

A new concept of slow wave microstrip transmission lines (SW μTL) dedicated to mmW and sub-mmW applications (100 GHz and further) is described herein. The microstrip is deposited on a specific substrate consisting in a metallic nanowires-filled membrane (MnM) of alumina covered with a thin top layer of silicon oxide. The slow wave effect is obtained thanks to metallic nanowires that capture the electric field while the magnetic field can extend in the whole substrate. Despite of the strong miniaturization expected, such SW μTLs should reach a quality factor five times higher than the one obtained with a conventional microstrip line (without nanowires). Such SW μTL can act as interconnecting paths if the MnM substrate is used as a 3D-interposer.

MEMS-based incandescent microlamps for integrated optics applications

In this work we present the fabrication and operation of incandescent microlamps for integrated optics applications. This microlamp emits white and infrared light from a chromium resistor embedded in a free-standing silicon oxynitride (SiOxNy) cantilever that can be coupled to an optical waveguide. In fact, the chromium resistor is sandwiched between layers of SiOxNy that isolate it from the atmosphere, while electric current heats the resistor to incandescent temperatures. The same SiOxNy material used in the microlamp fabrication is also used to produce the optical waveguides to allow a monolithic integration of light source and optical circuit. Front-side bulk micromachining of the silicon substrate in potassium hydroxide (KOH) solution is used to fabricate the cantilevers that thermally isolate the resistors from the substrate, thus reducing the heat transfer and the current required to light the lamp.