Hual-Te Chien

The influence of piezoelectricity on free and reflected waves from fluid‐loaded anisotropic plates

A unified analytical treatment is presented supported by extensive numerical illustrations of the interactions of ultrasonic waves with piezoelectric anisotropic plates. The plates are allowed to possess up to monoclinic anisotropic symmetry and associated piezoelectric coupling. The plates are also assumed to be immersed in water and subjected to incident acoustic beams at arbitrary polar and azimuthal angles. Simple analytical expressions for the reflection and transmission coefficients are derived, from which all propagation characteristics are identified. Such expressions contain, as a by‐product, the secular equation for the propagation of free harmonic waves on the piezoelectric plates. This equation is written in simple and completely separate terms pertaining to symmetric and antisymmetric modes. It is found that piezoelectric coupling, as well as water, influence both types of modes. Higher symmetry, such as orthotropic, transverse isotropic, and cubic, are contained implicitly in this analysis. ...

An in-line ultrasonic viscometer

An in-line viscometer is valuable to the control of a flow process, particularly a non-Newtonian flow because its viscosity is shear-rate dependent and thus requires continuous monitoring. Currently available in-line viscometers are mostly of the probe design [1] and may obstruct the flow pattern, causing plugging problem in flows with suspended particles. A probe-type viscometer generally measures a response of fluid density-viscosity product. To separate mass loading and viscous effects, Kim and Bau [2] used a dual-probe design based on torsional wave speed and attenuation measurements. However, no commercial system has been developed from their concept. Another limitation of existing probe-type viscometers is the range of application, primarily in the low-viscosity range.

Millimeter-wave scattering from neutral and charged water droplets

We investigated 94 GHz millimeter-wave (MMW) scattering from neutral and charged water mist produced in the laboratory with an ultrasonic atomizer. Diffusion charging of the mist was accomplished with a negative ion generator (NIG). We observed increased forward- and backscattering of MMW from charged mist, as compared to MMW scattering from an uncharged mist. In order to interpret the experimental results, we developed a model based on classical electrodynamics theory of scattering from a dielectric sphere with diffusion-deposited mobile surface charge. In this approach, scattering and extinction cross-sections are calculated for a charged Rayleigh particle with effective dielectric constant consisting of the volume dielectric function of the neutral sphere and surface dielectric function due to the oscillation of the surface charge in the presence of applied electric field. For small droplets with radius smaller than 100 nm, this model predicts increased MMW scattering from charged mist, which is qualitatively consistent with the experimental observations. The objective of this work is to develop indirect remote sensing of radioactive gases via their charging action on atmospheric humid air.

Wave propagation interaction with free and fluid‐loaded piezoelectric substrates

A unified analytical treatment is presented that is supported with numerical illustrations of the interactions of ultrasonic waves with piezoelectric anisotropic half‐space substrates. The solids are allowed to possess up to monoclinic anisotropic symmetry and associated piezoelectric coupling. The solids are also assumed to be loaded with water and subjected to incident acoustic beams at arbitrary polar and azimuthal angles. Simple analytical expressions for the reflection and transmission coefficients are derived from which all propagation characteristics are identified. Such expressions contain, as a by‐product, the secular equation for the propagation of free harmonic waves on the piezoelectric substrate. It is found that piezoelectric coupling, as well as water, influence both types of modes. Higher symmetry, such as orthotropic, transverse isotropic, and cubic, are contained implicitly in this analysis. This paper also demonstrates that the motion of the surface and SH modes uncouple for propagation...

Measurement of shear impedances of viscoelastic fluids

Shear-wave reflection coefficients from a solid/fluid interface are derived for non-Newtonian fluids that can be described by Maxwell, Voigt, and power-law fluid models. Based on model calculations, we have identified the measurable effects on the reflection coefficients due to fluid non-Newtonian behavior. The models are used to interpret the viscosity data obtained by a technique based on shear impedance measurement.

Millimeter wave detection of nuclear radiation: An alternative detection mechanism

We present a nuclear radiation detection mechanism using millimeter waves as an alternative to conventional detection. It is based on the concept that nuclear radiation causes ionization of air and that if we place a dielectric material near the radiation source, it acts as a charge accumulator of the air ions. We have found that millimeter waves can interrogate the charge cloud on the dielectric material remotely. This concept was tested with a standoff millimeter wave system by monitoring the charge levels on a cardboard tube placed in an x-ray beam.

Method and apparatus for sizing and separating warp yarns using acoustical energy

A slashing process for preparing warp yarns for weaving operations including the steps of sizing and/or desizing the yarns in an acoustic resonance box and separating the yarns with a leasing apparatus comprised of a set of acoustically agitated lease rods. The sizing step includes immersing the yarns in a size solution contained in an acoustic resonance box. Acoustic transducers are positioned against the exterior of the box for generating an acoustic pressure field within the size solution. Ultrasonic waves that result from the acoustic pressure field continuously agitate the size solution to effect greater mixing and more uniform application and penetration of the size onto the yarns. The sized yarns are then separated by passing the warp yarns over and under lease rods. Electroacoustic transducers generate acoustic waves along the longitudinal axis of the lease rods, creating a shearing motion on the surface of the rods for splitting the yarns.

Passive Millimeter Wave Imaging and Spectroscopy System for Terrestrial Remote Sensing

We have built a passive millimeter wave imaging and spectroscopy system with a 15-channel filter bank in the 146-154 GHz band for terrestrial remote sensing. We had built the spectroscopy system first and have now retrofitted an imaging element to it as a single pixel imager. The imaging element consisted of a 15-cm-diameter imaging lens fed to a corrugated scalar horn. Image acquisition is carried out by scanning the lens with a 2-axis translation stage. A LabVIEW-based software program integrates the imaging and spectroscopy systems with online display of spectroscopic information while the system scans each pixel position. The software also allows for integrating the image intensity of all 15 channels to increase the signal-to-noise ratio by a factor of ~4 relative to single channel image. The integrated imaging and spectroscopy system produces essentially 4-D data in which spatial data are along 2 dimensions, spectral data are in the 3rd dimension, and time is the 4th dimension. The system performance was tested by collecting imaging and spectral data with a 7.5-cm-diameter and 1m long gas cell in which test chemicals were introduced against a liquid nitrogen background.

Critical issues in catalytic diesel reforming for solid oxide fuel cells

Developing low-cost diesel-reforming catalysts and improving fuel mixing prior to catalytic reforming were addressed as two critical issues under the current study. Ruthenium-doped lanthanum chromite and aluminite were explored as catalysts for the autothermal reforming of diesel fuel. Dodecane was used as a surrogate fuel. Both catalysts yielded nearly 20 moles of hydrogen per mole of dodecane at oxygen-to-carbon ratios of 0.5 and steam-to-carbon ratios of 2 at space velocities near 100,000/h−1. Both catalysts were shown to have good S tolerance when tested with a fuel mixture containing 50 parts per million S in the form of dibenzothiophene. Parallel to catalyst development, the impact of fuel mixing and vaporization through improved liquid injection also is under investigation.

Photoacoustic spectroscopy (PAS) system for remote detection of explosives, chemicals, and special nuclear materials

This paper describes a practical photoacoustic spectroscopy technique applied to remote sensing of chemicals in an open environment. A laboratory system that consists of a high-power CO2 laser and an open-field acoustic resonator is described. The acoustic resonator is a combination of a parabolic reflector and a narrow-band cylindrical acoustic resonator that resonates at the laser modulation frequency. The performance of the resonator is theoretically analyzed and experimentally verified. Significant improvement in signal-to-noise ratio has been achieved. Detection of gas-phase photoacoustic signals was demonstrated at a remote distance of several meters from the target. Potential applications to the detection of condensed-phase chemicals are discussed; the detection of the photoacoustic spectrum of trinitrotoluene (TNT) in an open environment is presented.