skip to main content


Title: Imaging acoustic standing waves in the presence of flowing gas

A method for imaging an acoustic standing wave in the presence of flowing gas is described. The optical power at the acoustic frequency in each pixel of a series of high-speed transmission electronic speckle pattern interferograms is used to map the steady-state pressure variations of an acoustic standing wave. The utility of the process is demonstrated by imaging the standing wave inside a transparent organ pipe.

 
more » « less
Award ID(s):
2109932
NSF-PAR ID:
10385766
Author(s) / Creator(s):
; ; ;
Publisher / Repository:
Optical Society of America
Date Published:
Journal Name:
Applied Optics
Volume:
62
Issue:
1
ISSN:
1559-128X; APOPAI
Format(s):
Medium: X Size: Article No. 46
Size(s):
["Article No. 46"]
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Intensity modulators are an essential component in optics for controlling free-space beams. Many applications require the intensity of a free-space beam to be modulated at a single frequency, including wide-field lock-in detection for sensitive measurements, mode-locking in lasers, and phase-shift time-of-flight imaging (LiDAR). Here, we report a new type of single frequency intensity modulator that we refer to as a longitudinal piezoelectric resonant photoelastic modulator. The modulator consists of a thin lithium niobate wafer coated with transparent surface electrodes. One of the fundamental acoustic modes of the modulator is excited through the surface electrodes, confining an acoustic standing wave to the electrode region. The modulator is placed between optical polarizers; light propagating through the modulator and polarizers is intensity modulated with a wide acceptance angle and record breaking modulation efficiency in the megahertz frequency regime. As an illustration of the potential of our approach, we show that the proposed modulator can be integrated with a standard image sensor to effectively convert it into a time-of-flight imaging system.

     
    more » « less
  2. The capability to modulate the intensity of an optical beam has scientific and practical significance. In this work, we demonstrate Y-Z cut lithium niobate acousto-optic modulators with record-high modulation efficiency, requiring only 1.5 W/cm2for 100% modulation at 7 MHz. These modulators use a simple fabrication process; coating the top and bottom surfaces of a thin lithium niobate wafer with transparent electrodes. The fundamental shear acoustic mode of the wafer is excited through the transparent electrodes by applying voltage with frequency corresponding to the resonant frequency of this mode, confining an acoustic standing wave to the electrode region. Polarization of light propagating through this region is modulated at the applied frequency. Polarization modulation is converted to intensity modulation by placing the modulator between polarizers. To showcase an important application space for this modulator, we integrate it with a standard image sensor and demonstrate 4 megapixel time-of-flight imaging.

     
    more » « less
  3. The acoustic standing wave near the end of an open pipe is investigated using spectrally analyzed high-speed transmission electronic speckle pattern interferometry. It is shown that the standing wave extends beyond the open end of the pipe and the amplitude decays exponentially with distance from the end. Additionally, a pressure node is observed near the end of the pipe in a position that is not spatially periodic with the other nodes in the standing wave. A sinusoidal fit to the amplitude of the standing wave inside the pipe indicates that the end correction is well predicted by current theory.

     
    more » « less
  4. Abstract

    Acoustic waves are increasingly used to concentrate, separate, and pattern nanoparticles in liquids, but the extent to which nanoparticles of different size and composition can be focused is not well‐defined. This article describes a simple analytical model for predicting the distribution of nanoparticles around the node of a 1D bulk acoustic standing wave over time as a function of pressure amplitude, acoustic contrast factor (i.e., nanoparticle and fluid composition), and size of the nanoparticles. Predictions from this model are systematically compared to results from experiments on gold nanoparticles of different sizes to determine the model's accuracy in estimating both the rate and the degree of nanoparticle focusing across a range of pressure amplitudes. The model is further used to predict the minimum particle size that can be focused for different nanoparticle and fluid compositions, and those predictions are tested with gold, silica, and polystyrene nanoparticles in water. A procedure combining UV‐light and photoacid is used to induce the aggregation of nanoparticles to illustrate the effect of nanoparticle aggregation on the observed degree of acoustic focusing. Overall, these findings clarify the extent to which acoustic resonating devices can be used to manipulate, pattern, and enrich nanoparticles suspended in liquids.

     
    more » « less
  5. Ultrasound directed self-assembly (DSA) allows organizing particles dispersed in a fluid medium into user-specified patterns, driven by the acoustic radiation force associated with a standing ultrasound wave. Accurate control of the spatial organization of the particles in the fluid medium requires accounting for medium viscosity and particle volume fraction. However, existing theories consider an inviscid medium or only determine the effect of viscosity on the magnitude of the acoustic radiation force rather than the locations where particles assemble, which is crucial information to use ultrasound DSA as a fabrication method. We experimentally measure the deviation between locations where spherical microparticles assemble during ultrasound DSA as a function of medium viscosity and particle volume fraction. Additionally, we simulate the experiments using coupled-phase theory and the time-averaged acoustic radiation potential, and we derive best-fit equations that predict the deviation between locations where particles assemble during ultrasound DSA when using viscous and inviscid theory. We show that the deviation between locations where particles assemble in viscous and inviscid media first increases and then decreases with increasing particle volume fraction and medium viscosity, which we explain by means of the sound propagation velocity of the mixture. This work has implications for using ultrasound DSA to fabricate, e.g., engineered polymer composite materials that derive their function from accurately organizing a pattern of particles embedded in the polymer matrix.

     
    more » « less