A circular disk resonator is used to study the gas sensing properties of carbon nanotubes. It detects the presence of gases based on the change in the dielectric constant rather than electrical conductivity of single walled carbon nanotubes (SWNTs) upon gas exposure. A conducting circular disk is coated with electric arc prepared SWNTs and degassed by heating under a high vacuum. It exhibits noticeable shifts in resonant frequency to both polar $({\mathrm{NH}}_3$ and CO) and nonpolar gases (He, Ar, ${\mathrm{N}}_2,$ and ${\mathrm{O}}_2\mathrm{).}$ Gas concentrations as low as 100 ppm can be detected using this sensor configuration.

We present the design and development of highly sensitive and fast-responsive microwave resonant sensors for monitoring the presence of ammonia gas. The sensor consists of a circular disk electromagnetic resonant circuit coated with either single- or multiwalled carbon nanotubes that are highly sensitive to adsorbed gas molecules. Upon exposure to ammonia, the electrical resonant frequency of the sensor exhibits a dramatic downshift of 4.375 MHz. The recovery and response times of these sensors are nominally 10 min. This technology is suitable for designing remote sensor systems to monitor gases inside sealed opaque packages and environmental conditions that do not allow physical wire connections.

This article reviews the state-of-the-art millimeter-wave (mm-wave) power amplifiers (PAs), focusing on broadband design techniques. An overview of the main solid-state technologies is provided, including Si, gallium arsenide (GaAs), GaN, and other III-V materials, and both field-effect and bipolar transistors. The most popular broadband design techniques are introduced, before critically comparing through the most relevant design examples found in the scientific literature. Given the wide breadth of applications that are foreseen to exploit the mm-wave spectrum, this contribution will represent a valuable guide for designers who need a single reference before adventuring in the challenging task of the mm-wave PA design.

We present the design and development of a novel antenna that effectively radiates at three frequency bands to harvest RF energy from cellular network frequency bands (900 MHz and 1900 MHz) and Wi-Fi sources (2.4 GHz) available in ambience. The antenna is designed using the combination of three different design techniques including composite right/left hand transmission line (CRLH). In addition, a high efficiency, sensitive triple-band rectifier is also proposed in this work. The rectifier provides a maximum conversion efficiency of 80%, 46% and 42% at 940MHz, 1.95GHz and 2.44 GHz, respectively. The experimental results demonstrate that the proposed triple-band RF energy harvesting system can collect 6.6 times more power than the single 900MHz band one and 3.4 times more power than three individual bands combined.

We present the development of a device-level linearization technique and its applications in broadband power amplifiers (PAs). The proposed topology firstly combines derivative transconductance superposition method and gate capacitance compensation technique, and creates a "sweet region" for suppressing third-order intermodulation (IM3) without the penalty of large power consumption. The effectiveness of the proposed technique has been demonstrated through a fully integrated distributed amplifier. The experimental results in 0.18-mum RF CMOS technology show that IM3 is improved by 11 dB. The achievable power-added efficiency is up to 25%, which is the highest among the broadband CMOS PAs reported thus far. The amplifier achieves a measured 3-dB bandwidth of 3.7-8.8 GHz, and a gain of 8.24 dB. The amplifier only consumes 154-mW dc power, and the measured saturation power (P_sat) is 19 dBm.

A fully integrated 60 GHz power amplifier using a standard 90 nm CMOS process is presented. The power amplifier consists of six 2-stage power amplifiers, three 2-way Wilkinson power splitters for parallel amplification, and three 2-way Wilkinson power combiners to combine the output power. The power amplifier achieves again of +20 dB, a P _1dB of +18 dBm and a P _sat of +20 dBm with 1.2 V supply.