Abstract This study presents an acoustics-based method for helium leakage detection and validates the method by measuring the acoustic wave transmission time in a mixture of helium and air. As acoustic waves have different speeds in helium and air, the helium/air ratio in a mixture should affect the traveling time of waves transmitting through the mixture. To understand the sensing mechanism, we theoretically investigated the relation between the acoustic wave traveling time and the helium/air ratio using two different models, where helium and air are assumed to be unmixed and well-mixed, respectively. Moreover, experiments are performed to validate the theoretical prediction for the model of the unmixed case. The experimental setup consists of a U-shaped waveguide, an acoustic transmitter with 20 kHz resonant frequency, and an acoustic receiver. The acoustic waveguide was filled with a mixture of helium and air as the carrier medium for acoustic wave propagation. The experimental result reveals a monotonic trend between the wave traveling time and the helium/air ratio. Furthermore, the trend observed from the experimental result is consistent with the theoretical prediction. We expect that this study can inspire future research for developing acoustics-based helium leakage detection methods.
Controllable, precise, and stable rotational manipulation of model organisms is valuable in many biomedical, bioengineering, and biophysics applications. We present an acoustofluidic chip capable of rotating Caenorhabditis elegans (C. elegans) in both static and continuous flow in a controllable manner. Rotational manipulation was achieved by exposing C. elegans to a surface acoustic wave (SAW) field that generated a vortex distribution inside a microchannel. By selectively activating interdigital transducers, we achieved bidirectional rotation of C. elegans, namely counterclockwise and clockwise, with on-demand switching of rotation direction in a single chip. In addition to continuous rotation, we also rotated C. elegans in a step-wise fashion with a step angle as small as 4° by pulsing the signal duration of SAW from a continuous signal to a pulsed signal down to 1.5 ms. Using this device, we have clearly imaged the dopaminergic neurons of C. elegans with pdat-1:GFP expression, as well as the vulval muscles and muscle fibers of the worm with myo-3::GFP fusion protein expression in different orientations and three dimensions. These achievements are difficult to realize through conventional (i.e., non-confocal) microscopy. The SAW manipulations did not detectably affect the health of the model organisms. With its precision, controllability, and simplicity in fabrication and operation, our acoustofluidic devices will be well-suited for model organism studies.
In this paper, a compact reconfigurable diplexer with the wideband tuning operation and high isolation is presented. Two pairs of half-wavelength (λ/2) resonators with loaded stepped-impedance open-stubs (SIOSs) are used to allocate resonances. Meanwhile, the passband selectivity is improved due to the intrinsic transmission zero generated by SIOSs. Two pairs of varactors embedded between the resonator and SIOSs are utilized for the wideband tuning operation. To further improve the tuning configuration of passband, straight- and ring-slots under resonators and I/O ports are introduced. Based on structures mentioned above, a tunable diplexer is fabricated, which exhibits the fractional tuning range of 21.8% and 21% for dual-channel with isolation greater than 35 dB, respectively.
This paper presents a single Lamb mode phased array beamforming by using a hybrid piezoelectric transducer (PZT)-scanning laser Doppler vibrometer (SLDV) system. The array system consists of a surface mounted PZT to generate Lamb waves and a non-contact SLDV to acquire high spatial resolution time-space wavefield remotely. The time-space wavefield contains Lamb waves which can be generated from the PZT excitation, damage scattering, mode conversion, etc. A frequency-wavenumber (f-k) decomposition technique is used to decompose the miscellaneous Lamb waves into individual wave mode components and wave propagations in different directions. The f-k decomposition allows using a single wave component as the phased array input for beamforming. The single mode array beamforming methodology was verified through PZT-SLDV experimental tests on an aluminum plate with a bonded quartz rod as a simulated damage
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