Abstract-Carbon nanotubes (CNTs) have been researched extensively for gas-sensing applications due to their unique electrical, chemical, and structural properties. Single-walled carbon nanotubes (SWNTs) have been predominantly used due to their superior electrical conductivity and higher sensitivity relative to multiwalled CNTs. This paper presents the design and characterization of a novel planar sensor fabricated on paper substrate to detect small concentrations of ammonia gas, using the shift in resonance frequency of a patch antenna as the discriminator. We have investigated three main design issues in depth. First, functionalization of the SWNTs with a polymer is studied in order to enhance the gas detection sensitivity. Second, a thin film of the functionalized SWNT is characterized to create a surface impedance model for the explanation and prediction of the resonance shift due to different gas concentrations. Finally, as a proof of concept, functionalized SWNTs are integrated into a patch antenna design and the return loss is measured in a closed-system environment to show high sensitivity for low concentrations of ammonia gas. The proposed antenna-based wireless gas sensor can be utilized in several applications, given its small form factor, light weight, and little to no power requirements.Index Terms-Carbon nanotubes (CNTs), gas sensors, inkjet printing, passive detection, poly(m-aminobenzene sulfonic acid) single-walled carbon nanotube (PABS-SWNT), power scavenging, wireless sensor node.
Abstract-Light-weight antenna arrays require utilizing the same antenna aperture to provide multiple functions (e.g., communications and radar) in separate frequency bands. In this paper, we present a novel antenna element design for a dual-band array, comprising interleaved printed dipoles spaced to avoid grating lobes in each band. The folded dipoles are designed to be resonant at octave-separated frequency bands (1 and 2 GHz), and inkjet-printed on photographic paper. Each dipole is gap-fed by voltage induced electromagnetically from a microstrip line on the other side of the substrate. This nested element configuration shows excellent corroboration between simulated and measured data, with 10-dB return loss bandwidth of at least 5% for each band and interchannel isolation better than 15 dB. The measured element gain is 5.3 to 7 dBi in the two bands, with cross-polarization less than 25 dBi. A large array containing 39 printed dipoles has been fabricated on paper, with each dipole individually fed to facilitate independent beam control. Measurements on the array reveal broadside gain of 12 to 17 dBi in each band with low cross-polarization.Index Terms-Dual band antenna, dual frequency, inkjet printing, multifunctional antennas, nested antennas, phased array, printed dipole, shared aperture design.
Ultra wideband (UWB) Doppler radar has many biomedical applications, including remote diagnosis of cardiovascular disease, triage and real-time personnel tracking in rescue missions. It uses narrow pulses to probe the human body and detect tiny cardiopulmonary movements by spectral analysis of the backscattered electromagnetic (EM) field. With the help of super-resolution spectral algorithms, UWB radar is capable of increased accuracy for estimating vital signs such as heart and respiration rates in adverse signal-to-noise conditions. A major challenge for biomedical radar systems is detecting the heartbeat of a subject with high accuracy, because of minute thorax motion (less than 0.5 mm) caused by the heartbeat. The problem becomes compounded by EM clutter and noise in the environment. In this paper, we introduce a new algorithm based on the state space method (SSM) for the extraction of cardiac and respiration rates from UWB radar measurements. SSM produces range-dependent system poles that can be classified parametrically with spectral peaks at the cardiac and respiratory frequencies. It is shown that SSM produces accurate estimates of the vital signs without producing harmonics and inter-modulation products that plague signal resolution in widely used FFT spectrograms.
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