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The schematic representation of the acoustic propagation of a holographic-modulated ultrasound wave from the hologram plane (left) to the target plane (right) to form a star-shaped amplitude pattern. The time waveforms' linear (blue) and nonlinear (red) evolutions are depicted. The linear monochromatic pressure amplitude distribution at the target plane (top right) is also shown, as are the fundamental and higher harmonic amplitudes for the broadband nonlinear field (bottom right). The nonlinear asymmetric distorted waveform and its broadband spectrum are depicted (bottom right).
Source publication
Holographic acoustic lenses (HALs), also known as acoustic holograms, are used for generating unprecedented complex focused ultrasound (FU) fields. HALs store the phase profile of the desired wavefront, which is used to reconstruct the acoustic pressure field when illuminated by a single acoustic source. Nonlinear effects occur as the sound intensi...
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... (50 time periods with respect to the excitation frequency). All simulations in this paper used the same set of parameters. To investigate the nonlinear effects in holographic-modulated ultrasound, the iterative angular spectrum algorithm (IASA) 14 was first used to create a starshaped amplitude pattern 25 mm from the hologram plane, as shown in Fig. 1. The algorithm was initialized with a uniform phase and amplitude input and then used to iteratively calculate the required phase map at the hologram plane (50 iterations). Figure 1 shows the computed phase map at the hologram plane and the simulated linear pressure field at the target plane. The computed phase was then used as a ...
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... algorithm was initialized with a uniform phase and amplitude input and then used to iteratively calculate the required phase map at the hologram plane (50 iterations). Figure 1 shows the computed phase map at the hologram plane and the simulated linear pressure field at the target plane. The computed phase was then used as a Dirichlet boundary condition in the nonlinear simulations. ...
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... in the nonlinear problem, diffraction and focusing effects cause a relative phase shift in the harmonics with respect to the fundamental component, resulting in an asymmetric waveform and a discrepancy between the peak positive pressure (PPP) and the peak negative pressure (PNP). The effects mentioned above are depicted schematically in Fig. 1. The PPP is connected to the thermal effects in therapeutic ultrasound, whereas the PNP MPa (c)-(f) conditions, the PPP (P þ ), PNP (P À ), intensity, and heat deposition are shown. The PPP and PNP are spatially identical in the linear case. Furthermore, the linear spatial structure of the wave intensity and heat deposition are ...
Citations
... While curved singleelement and phased-array transducers are commonly used for concentrating ultrasound energy in current applications, acoustic holographic lenses (AHLs), also known as acoustic holograms, have recently emerged as a promising solution for constructing complex ultrasound fields due to their ability to manipulate ultrasound effectively [18,19,[19][20][21][22]. AHLs, in their most basic form, record the phase profile of the required wavefront, which is then utilized to rebuild the acoustic pressure field when lit by a single acoustic source. Overall, the present popularity of acoustic holograms originates from their ease of use, durability, high resolution, and low cost, giving them an alternate option for a variety of biomedical operations [21,[23][24][25][26][27]. From the thermal field mapping and controlling standpoint, there has been relatively limited research on the use of AHLs to induce specific temperature fields [28,29]. ...
Acoustic holographic lenses (AHLs) show great potential as a straightforward, inexpensive, and reliable method of sound manipulation. These lenses store the phase and amplitude profile of the desired wavefront when illuminated by a single acoustic source to reconstruct ultrasound pressure fields, induce localized heating, and achieve temporal and spatial thermal effects in acousto-thermal materials like polymers. The ultrasonic energy is transmitted and focused by AHL from a transducer into a particular focal volume. It is then converted to heat by internal friction in the polymer chains, causing the temperature of the polymer to rise at the focus locations while having little to no effect elsewhere. This one-of-a-kind capability is made possible by the development of AHLs to make use of the translation of attenuated pressure fields into programmable heat patterns. However, the impact of acousto-thermal dynamics on the generation of AHLs is largely unexplored. We use a machine learning-assisted single inverse problem approach for rapid and efficient AHLs’ design to generate thermal patterns. The process involves the conversion of thermal information into a holographic representation through the utilization of two latent functions: pressure phase and amplitude. Experimental verification is performed for pressure and thermal measurements. The volumetric acousto-thermal analyses of experimental samples are performed to offer a knowledge of the obtained pattern dynamics, as well as the applicability of holographic thermal mapping for precise volumetric temperature control. Finally, the proposed framework aims to provide a solid foundation for volumetric analysis of acousto-thermal patterns within thick samples and for assessing thermal changes with outer surface measurements.
... These offsets could emerge from simple uncertainties in the transducer position, power, and phase, or could emerge from non-linearity, inhomogeneity, or the existence of other scatterers in the field. Recent advances in computational modeling have begun to enable the inclusion of complex nonlinear fields produced by acoustic holograms 24 , or complex fields with scatterers in the field 9,25 . However, it is still computationally expensive and cumbersome to include nonlinearity, and experimental deviations are susceptible to minor changes in the environment. ...
... While these optimizers are effective in achieving their targets, they require prior calibration, or experimental finite differences that do not scale well with the number of variables. These experimental deviations are known to cause performance degradation in the practical applications of acoustic holograms 8,22,24 , and there is an increasing need for better and more efficient approaches to optimize acoustic holograms in experiments. This will ultimately help to improve the haptic quality in ultrasonic tactile displays, improve the graphic generation capabilities of acoustophoretic volumetric displays, and improve the positioning accuracy in the potential application of acoustic levitation. ...
... The generation of higher harmonics has been discussed as a potential issue by Andrade et al. 21 and it has also been reported to cause issues in underwater acoustics 24 . Figure 3 shows the measured nonlinearity from the non-optimized field, and Fig. 3a shows that the second harmonics generation (F2) grows as the target amplitude increases. ...
The need for the accurate generation of acoustic holograms has increased with the prevalence of the use of acoustophoresis methods such as ultrasonic haptic sensation, acoustic levitation, and displays. However, experimental results have shown that the actual acoustic field may differ from the simulated field owing to uncertainties in the transducer position, power and phase, or from nonlinearity and inhomogeneity in the field. Traditional methods for experimentally optimizing acoustic holograms require prior calibration and do not scale with the number of variables. Here, we propose a digital twin approach that combines feedback from experimental measurements (such as a microphone and an optical camera) in the physical setup with numerically obtained derivatives of the loss function, using automatic differentiation, to optimize the loss function. This approach is number of transducers times faster and more efficient than the classical finite difference approach, making it beneficial for various applications such as acoustophoretic volumetric displays, ultrasonic haptic sensations, and focused ultrasound therapy.
... Ultrasound power transfer (UPT) systems are a new prospective technology for wireless power delivery to difficult-to-reach components in essential engineering applications, 1,2 including medical ultrasound, where acoustic wave manipulation and focusing to confine acoustic intensity is of great importance. [3][4][5] The underlying mechanism of UPT systems involves the transmission of acoustic waves by a piezoelectric transmitter, propagating acoustic waves through a medium, and piezoelectric transduction of acoustic waves at a piezoelectric receiver. The received acoustic waves at the receiver end are usually used to power external attached circuits. ...
We use a high pattern-fidelity technique on piezoelectric electrodes to selectively excite high-order vibration modes, while isolating other modes, in multi-layered through-wall ultrasound power transfer (TWUPT) systems. Physical mechanisms, such as direct and inverse piezoelectric effects at transmitting and receiving piezoelectric elements, as well as wave propagation across an elastic barrier and coupling layers, all contribute to TWUPT. High-order radial modes in a TWUPT system feature strain nodes, where the dynamic strain distribution changes sign in the direction of disks' radii. This study explains theoretically and empirically how covering the strain nodes of vibration modes with continuous electrodes results in substantial cancelations of the electrical outputs. A detailed analysis is given for predicting the locations of the strain nodes. The electrode patterning for creating the transmitter and receiver shapes is determined by the regions where local force and charge cancelation do not occur, i.e., the two modal principal stress components have the same sign. Patterning for creating the electrode shapes is performed by high-fidelity numerical modeling supported by experiments. Using differential excitation on the transmitter side while monitoring transmitted power and efficiency on the reception side at various vibration modes is made possible by the unique nature of TWUPT systems. Due to an improvement in system quality and power factors, it is determined that employing the proposed electrode pattern designs enhances overall device efficiency and active power. The suppression of other modes makes up a filter feature that is paired with the enhancement at the mode under consideration.
Accurate and efficient numerical simulation of highly nonlinear ultrasound propagation is essential for a wide range of therapeutic and physical ultrasound applications. However, due to large domain sizes and the generation of higher harmonics, such simulations are computationally challenging, particularly in three-dimensional problems with shock waves. Current numerical methods are based on computationally inefficient uniform meshes that require the highest harmonic to be resolved across the entire domain. To address this challenge, we present an adaptive numerical algorithm for computationally efficient nonlinear acoustic holography. At each propagation step, the algorithm monitors the harmonic content of the acoustic signal and adjusts its discretization parameters accordingly. This enables efficient local resolution of higher harmonics in areas of high nonlinearity while avoiding unnecessary resolution elsewhere. Furthermore, the algorithm actively adapts to the signal’s nonlinearity level, eliminating the need for prior reference simulations or information about the spatial distribution of the harmonic content of the acoustic field. The proposed algorithm incorporates an upsampling process in the frequency domain to accommodate the generation of higher harmonics in forward propagation and a downsampling process when higher harmonics are decimated in backward propagation. The efficiency of the algorithm was evaluated for highly nonlinear three-dimensional problems, demonstrating a significant reduction in computational cost with a nearly 50-fold speedup over a uniform mesh implementation. Our findings enable a more rapid and efficient approach to modeling nonlinear high-intensity focused ultrasound wave propagation.
