Three-dimensional photothermoacoustic depth-profilometric imaging by use of a linear frequency sweep lock-in heterodyne method

2004 ◽  
Author(s):  
Ying Fan ◽  
Andreas Mandelis ◽  
Gloria Spirou ◽  
I. Alex Vitkin ◽  
William M. Whelan
Keyword(s):  
Three Dimensional ◽  
Frequency Sweep ◽  
Heterodyne Method ◽  
Linear Frequency ◽  
Lock In

scholarly journals Laser Photothermoacoustic Heterodyned Lock-in Depth Profilometry in Turbid Tissue Phantoms

2021 ◽  
Author(s):  
Ying Fang ◽  
Andreas Mandelis ◽  
Gloria Spirou ◽  
I. Alex Vitkin ◽  
William M. Whelan
Keyword(s):  
Frequency Domain ◽  
Delay Time ◽  
Turbid Media ◽  
Laser Source ◽  
Depth Information ◽  
Chirp Signal ◽  
Sweep Method ◽  
Frequency Sweep ◽  
Linear Frequency ◽  
Lock In

Frequency-domain correlation and spectral analysis photothermoacoustic FD-PTA imaging is a promisingnew technique, which is being developed to detect tumor masses in turbid biological tissue. Unlike conventional biomedical photoacoustics which uses time-of-flight acoustic information induced by a pulsed laser to indicate the tumor size and location, in this research, a new FD-PTA instrument featuring frequency sweep chirp and heterodyne modulation and lock-in detection of a continuous-wave laser source at 1064 nm wavelength is constructed and tested for its depth profilometric capabilities with regard to turbid media imaging. Owing to the linear relationship between the depth of acoustic signal generation and the delay time of signal arrival to the transducer, information specific to a particular depth can be associated with a particular frequency in the chirp signal. Scanning laser-fluence modulation frequencies with a linear frequency sweep method preserves the depth-to-delay time linearity and recovers FD-PTA signals from a range of depths. Combining with the depth information carried by the back-propagated acoustic chirp signal at each scanning position, one could rapidly generate subsurface three-dimensional images of the scanning area at optimal signal-to-noise ratios and low laser fluences, a combination of tasks that is difficult or impossible by use of pulsed photoacoustic detection. In this paper, results of PTA scans performed on tissue mimicking control phantoms with various optical, acoustical, and geometrical properties are presented. A mathematical model is developed to study the laser-induced photothermoacoustic waves in turbid media. The model includes both the scattering and absorption properties of the turbid medium. A good agreement is obtained between the experimental and numerical results. It is concluded that frequency domain photothermoacoustics using a linear frequency sweep method and heterodyne lock-in detection has the potential to be a reliable tool for biomedical depth-profilometric imaging.

scholarly journals Laser Photothermoacoustic Heterodyned Lock-in Depth Profilometry in Turbid Tissue Phantoms

2021 ◽  
Author(s):  
Ying Fang ◽  
Andreas Mandelis ◽  
Gloria Spirou ◽  
I. Alex Vitkin ◽  
William M. Whelan
Keyword(s):  
Frequency Domain ◽  
Delay Time ◽  
Turbid Media ◽  
Laser Source ◽  
Depth Information ◽  
Chirp Signal ◽  
Sweep Method ◽  
Frequency Sweep ◽  
Linear Frequency ◽  
Lock In

Frequency-domain correlation and spectral analysis photothermoacoustic FD-PTA imaging is a promisingnew technique, which is being developed to detect tumor masses in turbid biological tissue. Unlike conventional biomedical photoacoustics which uses time-of-flight acoustic information induced by a pulsed laser to indicate the tumor size and location, in this research, a new FD-PTA instrument featuring frequency sweep chirp and heterodyne modulation and lock-in detection of a continuous-wave laser source at 1064 nm wavelength is constructed and tested for its depth profilometric capabilities with regard to turbid media imaging. Owing to the linear relationship between the depth of acoustic signal generation and the delay time of signal arrival to the transducer, information specific to a particular depth can be associated with a particular frequency in the chirp signal. Scanning laser-fluence modulation frequencies with a linear frequency sweep method preserves the depth-to-delay time linearity and recovers FD-PTA signals from a range of depths. Combining with the depth information carried by the back-propagated acoustic chirp signal at each scanning position, one could rapidly generate subsurface three-dimensional images of the scanning area at optimal signal-to-noise ratios and low laser fluences, a combination of tasks that is difficult or impossible by use of pulsed photoacoustic detection. In this paper, results of PTA scans performed on tissue mimicking control phantoms with various optical, acoustical, and geometrical properties are presented. A mathematical model is developed to study the laser-induced photothermoacoustic waves in turbid media. The model includes both the scattering and absorption properties of the turbid medium. A good agreement is obtained between the experimental and numerical results. It is concluded that frequency domain photothermoacoustics using a linear frequency sweep method and heterodyne lock-in detection has the potential to be a reliable tool for biomedical depth-profilometric imaging.

scholarly journals Experimental observation of frequency lock-in of roughness-induced instabilities in a laminar boundary layer

2019 ◽  
Vol 870 ◽  
pp. 680-697
Author(s):  
Dominik K. Puckert ◽  
Ulrich Rist
Keyword(s):  
Boundary Layer ◽  
Aspect Ratio ◽  
Laminar Boundary Layer ◽  
Roughness Element ◽  
Water Channel ◽  
Three Dimensional ◽  
Boundary Layer Theory ◽  
Linear Stability Theory ◽  
Mode Decomposition ◽  
Lock In

The interaction of disturbance modes behind an isolated cylindrical roughness element in a laminar boundary layer is investigated by means of hot-film anemometry and particle image velocimetry in a low-turbulence laminar water channel. Both sinuous and varicose disturbance modes are found in the wake of a roughness with unit aspect ratio (diameter/height $=$ 1). Interestingly, the frequency of the varicose mode synchronizes with the first harmonic of the sinuous mode when the critical Reynolds number from three-dimensional global linear stability theory is exceeded. The coupled motion of sinuous and varicose modes is explained by frequency lock-in. This mechanism is of great importance in many aspects of nature, but has not yet received sufficient attention in the field of boundary-layer theory. A Fourier mode decomposition provides detailed analyses of sinuous and varicose modes. The observation is confirmed by a second experiment with the same aspect ratio at a different position in the laminar boundary layer. When the aspect ratio is increased, the flow is fully governed by the varicose mode. Thus, no frequency lock-in can be observed in this case. The significance of this work is to explain how sinuous and varicose modes can co-exist behind a roughness and to propose a mechanism which is well established in physics but not encountered often in boundary-layer theory.

Vortex Shedding From Two Surface-Mounted Prismatic Obstacles in Lock-in Regime

2003 ◽  
Author(s):  
Robert J. Martinuzzi ◽  
Brian Havel
Keyword(s):  
Boundary Layer ◽  
Vortex Shedding ◽  
Three Dimensional ◽  
Front Face ◽  
Thin Boundary Layer ◽  
Tandem Arrangement ◽  
Freestream Velocity ◽  
Square Cylinders ◽  
Shedding Frequency ◽  
Lock In

Periodic vortex shedding from two surface-mounted cubes, of height H, in tandem arrangement placed in a thin boundary layer is investigated for a spacing 2H using phase-averaged laser Doppler velocimetry measurements. Tests were conducted for a Reynolds number of 22000, based on H and the freestream velocity, and an approximately 0.07H thick laminar boundary layer. For this obstacle spacing, the shedding frequency scales linearly with the obstacle spacing. It is shown that in this lock-in regime, periodic shedding is triggered by the displacement of the vertical flow along the front face of the downstream obstacle and is thus different from that observed for two-dimensional cylinders in uniform streams. The existence of this three-dimensional effect is then used to explain why lock-in cannot be observed for square cylinders in tandem arrangement.

Lock-in amplifier error prediction and correction in frequency sweep measurements

2007 ◽  
Vol 78 (1) ◽  
pp. 014701 ◽  
Author(s):  
Maximiliano Osvaldo Sonnaillon ◽  
Fabian Jose Bonetto
Keyword(s):  
Error Prediction ◽  
Frequency Sweep ◽  
Lock In

Circular Cylinder Wake Configurations: A Flow Visualization Survey

1991 ◽  
Vol 44 (6) ◽  
pp. 255-305 ◽  
Author(s):  
Madeleine Coutanceau ◽  
Jean-Rene´ Defaye
Keyword(s):  
Circular Cylinder ◽  
High Speed ◽  
Three Dimensional ◽  
Cylinder Wake ◽  
Periodic Motions ◽  
Extended Range ◽  
Different Types ◽  
Speed Regime ◽  
Lock In ◽  
Evolution With Time

The survey starts with the presentation of the general principles underlying the different types of techniques which are most often used in wake visualization with their advantages, but also their respective limits. Then information deduced from flow pictures collected from the literature from the beginning of the century up to the present has been used to characterize the wake structure of a circular cylinder (at rest or submitted to various motions) and its evolution with the Reynolds number for an extended range (0 < Re < 107). Incompressible flow has been more particularly considered, both in the quasi-established phase (ten regimes are differentiated and extensively described) and in the transient phase (specific features are pointed out). Special attention has been paid to three-dimensional and memory effects by a combined presentation of crosswise and spanwise observations of the wake phenomena as well as their evolution with time. The influence of compressibility in the high-speed regime and of superimposed periodic motions, either on the cylinder or on the stream, have been also investigated and the main characteristics of the lock-in regime have been described. The survey is illustrated by 40 figures and completed by a table in which are reported the successive studies related to the flow around a circular cylinder based upon visualization, including a brief account of the experimental setups and methods, as well as a description of the main phenomena observed in the corresponding pictures.

A Nonlinear Dynamics Analysis of Vortex-Structure Interaction Models

2001 ◽  
Vol 123 (4) ◽  
pp. 475-479 ◽  
Author(s):  
N. W. Mureithi ◽  
S. Goda ◽  
H. Kanki ◽  
T. Nakamura
Keyword(s):  
Nonlinear Dynamics ◽  
Parameter Space ◽  
Vortex Structure ◽  
Three Dimensional ◽  
Order Model ◽  
Third Order ◽  
Interaction Models ◽  
Structure Interaction ◽  
Lock In ◽  
Fifth Order

Vortex-structure interaction models are studied in the work presented here. The third- order model by Hartlen and Currie (HC model) can reproduce the correct response amplitude, while a fifth-order model by Landl predicts the observed hysterisis effect. Using concepts from nonlinear dynamics and bifurcation theory, the range of possible dynamics of the models is investigated in parameter space; essentially, a class of nonlinear oscillators deriving “naturally” from the HC model is studied. It is found that perturbations of the HC model in parameter space lead to qualitatively physically meaningful dynamics. Forced excitation of the HC model is the highlight of the work. In this case, it is shown that a subharmonic lock-in predicted by the model may be related to a three-dimensional secondary subharmonic instability of a periodic flow. Experimental results are presented for comparison.

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