Gregory Kaduchak

Ultrasonic particle‐concentration for sheathless focusing of particles for analysis in a flow cytometer

The development of inexpensive small flow cytometers is recognized as an important goal for many applications ranging from medical uses in developing countries for disease diagnosis to use as an analytical platform in support of homeland defense. Although hydrodynamic focusing is highly effective at particle positioning, the use of sheath fluid increases assay cost and reduces instrument utility for field and autonomous remote operations.

Ultrasonic particle concentration in a line-driven cylindrical tube

Acoustic particle manipulation has many potential uses in flow cytometry and microfluidic array applications. Currently, most ultrasonic particle positioning devices utilize a quasi-one-dimensional geometry to set up the positioning field. A transducer fit with a quarter-wave matching layer, locally drives a cavity of width one-half wavelength. Particles within the cavity experience a time-averaged drift force that transports them to a nodal position. Present research investigates an acoustic particle-positioning device where the acoustic excitation is generated by the entire structure, as opposed to a localized transducer. The lowest-order structural modes of a long cylindrical glass tube driven by a piezoceramic with a line contact are tuned, via material properties and aspect ratio, to match resonant modes of the fluid-filled cavity. The cylindrical geometry eliminates the need for accurate alignment of a transducer/reflector system, in contrast to the case of planar or confocal fields. Experiments show that the lower energy density in the cavity, brought about through excitation of the whole cylindrical tube, results in reduced cavitation, convection, and thermal gradients. The effects of excitation and material parameters on concentration quality are theoretically evaluated, using two-dimensional elastodynamic equations describing the fluid-filled cylindrical shell with a line excitation.

High-frequency backscattering enhancements by thick finite cylindrical shells in water at oblique incidence: Experiments, interpretation, and calculations

Impulse response backscattering measurements are presented and interpreted for the scattering of obliquely incident plane waves by air-filled finite cylindrical shells immersed in water. The measurements were carried out to determine the conditions for significant enhancements of the backscattering by thick shells at large tilt angles. The shells investigated are made of stainless steel and are slender and have thickness to radius ratios of 7.6% and 16.3%. A broadband PVDF (polyvinylidene fluoride) sheet source is used to obtain the backscattering spectral magnitude as a function of the tilt angle (measured from broadside incidence) of the cylinder. Results are plotted as a function of frequency and angle. These plots reveal large backscattering enhancements associated with elastic excitations at high tilt angles, which extend to end-on incidence in the coincidence frequency region. Similar features are present in approximate calculations for finite cylindrical shells based on full elasticity theory and t...

Enhancement of the backscattering of high‐frequency tone bursts by thin spherical shells associated with a backwards wave: Observations and ray approximation

A prominent feature predicted for the backscattering of tone bursts by thin spherical shells is an enhancement of a guided wave contribution near the first longitudinal resonance. This has been explained with a backward ray model of a leaky Lamb wave where energy is leaked off without having circumnavigated the far side of the shell [P. L. Marston et al., J. Acoust. Soc. Am. 90, 2341 (1991); D. H. Hughes, Ph.D. thesis, Washington State University (1992)]. The relevant s2b Lamb wave has opposing group and phase velocities giving rise to prompt radiation following the direct specular echo. The present research gives a comparison between a ray theory approximation and experiments in which tone bursts having carrier frequencies in the range 585<ka<630 were incident on an empty stainless‐steel spherical shell of radius a=12.7 cm in water. The sphere’s thickness to radius ratio is approximately 0.02. Measurements of the superposition of the specular reflection and s2b Lamb wave contribution agree with the predi...

Measurement and interpretation of the impulse response for backscattering by a thin spherical shell using a broad‐bandwidth source that is nearly acoustically transparent

A novel source was developed to produce a plane‐wave unipolar pressure impulse with a wide range of frequency components. The source consisted of a PVDF sheet with water in contact with both sides. The PVDF was driven by a step voltage. This source is nearly acoustically transparent and was used for backscattering from an empty stainless‐steel spherical shell. The shell was placed in the near field of the source where it experienced a plane‐wave pressure impulse followed much later by edge contributions resulting from the finite source size. A hydrophone was placed in the far field of the scatterer on the opposite side of the source. Prominent features in the shell’s calculated impulse response are observed over a wide frequency interval. Time records reveal an approximately Gaussian wave packet from the excitation of the subsonic a0− wave associated with the backscattering enhancement near the coincidence frequency (≊309 kHz). Superposed on the same records are large contributions from the low‐frequency ...

Novel cylindrical, air-coupled acoustic levitation/concentration devices

A new class of devices for levitation and/or concentration of aerosols and small liquid/solid samples (up to several millimeters in diameter) in air has been developed. The novelty of these devices is their simplicity in design. These are inexpensive, low-power, and, in their simplest embodiment, do not require accurate alignment of a resonant cavity. Best of all, these can be off-the-shelf items. The devices are constructed from a hollow, cylindrical piezoelectric tube. The main design criteria requires a resonant mode of the tube to match a resonant mode of the interior air-filled cavity. Once matched, it is shown that drops of water in excess of 1 mm in diameter may be levitated inside the cylinder cavity against the force of gravity for less than 1 Watt of input electrical power. Efficient concentration/agglomeration of aerosol particles in air is also demonstrated.

Fundamentals of Acoustic Cytometry

Acoustic cytometry is a new technology that replaces or partly replaces hydrodynamic focusing of cells or particles with focusing derived from acoustic radiation pressure forces. It offers new possibilities for improving current flow cytometry assays and creating new ones. To take full advantage of these possibilities, it is necessary to understand the fundamental benefits and limitations of acoustic focusing as employed in flow cytometry analysis, either as a substitute for hydrodynamic focusing or in combination with it. Curr. Protoc. Cytom. 49:1.22.1‐1.22.12.

Acoustic concentration of particles in piezoelectric tubes: Theoretical modeling of the effect of cavity shape and symmetry breaking

A new class of simple, highly efficient, cylindrical acoustic concentration devices has been developed based upon cylindrical (or near cylindrical) geometries [Kaduchak et al., Rev. Sci. Instrum. 73, 1332–1336 (2002)] for aerosol concentration applications. The concentrators are constructed from single PZT tubes driven at or near the breathing mode resonance. Acoustic concentration of aerosols is performed within the tube cavity. It has been found that slight modifications to the cylindrical cavity geometry can significantly increase the collection efficiency and assist in precise particle positioning. This paper analyzes the theoretical framework for the acoustic concentration of particles in these devices for various geometrical perturbations. The cavity geometries studied are (1) hollow cylindrical piezoelectric tube, (2) hollow piezoelectric tube with an inner concentric solid cylinder insert, (3) a hollow piezoelectric tube with a concentric elliptic insert which breaks the circular-cylindrical symme...

Elastic wave contributions in high‐resolution acoustic images of fluid‐filled, finite cylindrical shells in water

Recent studies of plane wave scattering by finite, evacuated cylindrical shells at oblique incidence describe monostatic echo contributions from surface elastic waves. These waves follow helical paths along the shell’s surface and are guided back in the source direction after reflection from the cylinder truncation. The present research examines similar effects viewed in the time signature of a high‐resolution acoustic imaging system. The experimental technique utilizes a narrow beam consisting of a short tone burst to probe a cylindrical shell along its axis of symmetry. The echo returns contain information which yields insight into local scattering processes at the impedance discontinuities of the finite scatterer. The cylindrical shell has a thickness‐to‐radius ratio h/a=5.5%. It is immersed in water and is subject to both exterior and interior fluid loading. Prominent artifacts are shown to coincide with near axial coincidence of the s0 and a0 Lamb waves. The echo contributions are extremely sensitive...

Observation of the midfrequency enhancement of tone bursts backscattered by a thin spherical shell in water near the coincidence frequency

A prominent feature predicted for the backscattering of tone bursts by thin spherical shells is an enhancement of a guided wave contribution in the midfrequency range [L. G. Zhang et al., J. Acoust. Soc. Am. 91, 1862–1874 (1992)]. This feature may be useful for certain inverse problems and is associated with a strongly coupled slightly subsonic wave denoted by some authors as the a0− wave. The present research gives a comparison between a ray approximation and experiments in which tone bursts having carrier frequencies in the range 35<ka<70 were incident on an empty stainless steel shell in water of radius a. The sphere’s radius to thickness ratio is a/h=43.8. Time records of echoes provided a means for measuring the guided wave contribution distinct from that of the specular reflection. As predicted, the guided wave echo can be over three times the amplitude of the specular echo and the ka dependence generally follows the predicted hump. Echoes manifest structures similar to those calculated by a time do...