An Impedance-Loaded Surface Acoustic Wave Corrosion Sensor for Infrastructure Monitoring.

Passive surface acoustic wave (SAW) devices are attractive candidates for continuous wireless monitoring of corrosion in large infrastructures. However, acoustic loss in the aqueous medium and limited read range usually create challenges in their widespread use for monitoring large systems such as oil and gas (O&G) pipelines, aircraft, and processing plants. This paper presents the investigation of impedance-loaded reflective delay line (IL-RDL) SAW devices for monitoring metal corrosion under O&G pipeline-relevant conditions.

Investigation of Goubau Wave Propagation on Large Pipes for Sensing Applications.

We examine the application of guided waves on a single conductor (Goubau waves) for sensing. In particular, the use of such waves to remotely interrogate surface acoustic wave (SAW) sensors mounted on large-radius conductors (pipes) is considered. Experimental results using a small-radius (0.

Zeolitic imidazolate framework-coated acoustic sensors for room temperature detection of carbon dioxide and methane.

The integration of nanoporous materials such as metal organic frameworks (MOFs) with sensitive transducers can result in robust sensing platforms for monitoring gases and chemical vapors for a range of applications. Here, we report on an integration of the zeolitic imidazolate framework - 8 (ZIF-8) MOF with surface acoustic wave (SAW) and thickness shear mode quartz crystal microbalance (QCM) devices to monitor carbon dioxide (CO2) and methane (CH4) under ambient conditions. The MOF was directly coated on the Y-Z LiNbO3 SAW delay lines (operating frequency, f0 = 436 MHz) and AT-cut quartz TSM resonators (resonant frequency, f0 = 9 MHz) and the devices were tested for various gases in N2 under ambient conditions.

SAW Sensors for Chemical Vapors and Gases.

Surface acoustic wave (SAW) technology provides a sensitive platform for sensing chemicals in gaseous and fluidic states with the inherent advantages of passive and wireless operation. In this review, we provide a general overview on the fundamental aspects and some major advances of Rayleigh wave-based SAW sensors in sensing chemicals in a gaseous phase. In particular, we review the progress in general understanding of the SAW chemical sensing mechanism, optimization of the sensor characteristics, and the development of the sensors operational at different conditions.

Robust ultrasonic damage detection under complex environmental conditions using singular value decomposition.

Guided wave ultrasonics is an attractive monitoring technique for damage diagnosis in large-scale plate and pipe structures. Damage can be detected by comparing incoming records with baseline records collected on intact structure. However, during long-term monitoring, environmental and operational conditions often vary significantly and produce large changes in the ultrasonic signals, thereby challenging the baseline comparison based damage detection.

Surface acoustic wave devices for harsh environment wireless sensing.

Langasite surface acoustic wave devices can be used to implement harsh-environment wireless sensing of gas concentration and temperature. This paper reviews prior work on the development of langasite surface acoustic wave devices, followed by a report of recent progress toward the implementation of oxygen gas sensors. Resistive metal oxide films can be used as the oxygen sensing film, although development of an adherent barrier layer will be necessary with the sensing layers studied here to prevent interaction with the langasite substrate.

Langasite surface acoustic wave gas sensors: modeling and verification.

We report finite element simulations of the effect of conductive sensing layers on the surface wave velocity of langasite substrates. The simulations include both the mechanical and electrical influences of the conducting sensing layer. We show that three-dimensional simulations are necessary because of the out-of-plane displacements of the commonly used (0, 138.

Langasite surface acoustic wave sensors: fabrication and testing.

We report on the development of harsh-environment surface acoustic wave sensors for wired and wireless operation. Surface acoustic wave devices with an interdigitated transducer emitter and multiple reflectors were fabricated on langasite substrates. Both wired and wireless temperature sensing was demonstrated using radar-mode (pulse) detection.

Generation and detection of guided waves using PZT wafer transducers.

We report here the use of finite element simulation and experiments to further explore the operation of the wafer transducer. We have separately modeled the emission and detection processes. In particular, we have calculated the wave velocities and the received voltage signals due to A0 and S0 modes at an output transducer as a function of pulse center frequency.

Fibroblast growth and H-7 protein kinase inhibitor response monitored in microimpedance sensor arrays.

Functional genomic studies and drug candidate testing both require high throughput, parallel experimentation strategies to screen for variable cellular behaviors. In this article we describe the use of an impedance sensing electrode array that is capable of sensing cell "presence" as well as the extent of cell (focal) attachment to the substrate. The signals provided by mouse fibroblasts on a sensing structure containing four different sized electrodes are reported.

MEMS ultrasonic transducers for the testing of solids.

Arrays of capacitive diaphragm ultrasonic transducers could potentially be used for non-destructive ultrasonic testing and structural monitoring. In this paper, we consider the efficiency of coupling of these transducers to solid media. We show that efficient coupling can be realized by using a silicone coating as a coupling medium.

Electrical characterization of coupled and uncoupled MEMS ultrasonic transducers.

We report electrical characterization of micromachined polysilicon capacitive diaphragms for use as ultrasonic transducers. Admittance measurements yield insight into the resonant behavior and also the damping resulting from ultrasonic radiation and frictional forces caused by the etch release holes. Unbonded transducers exhibit sharp resonances with Q values that increase with decreasing air pressure.