Thermoacoustic Research Articles

Simulation Analysis of Thermoacoustic Effect of CNT Film with Metasurface-Enhanced Acoustic Autofocusing.

This study introduces a novel thermoacoustic (TA) focusing system enhanced by Airy beam-based acoustic metasurfaces, significantly improving acoustic focusing and efficiency. The system integrates a TA emitter, fabricated from carbon nanotube (CNT) films, with a binary acoustic metasurface capable of generating quasi-Airy beams. Through finite element simulations, the system's heat conduction, acoustic focusing, and self-healing properties were thoroughly analyzed. The results demonstrate that the system achieves superior sub-wavelength focusing, tunable focal length via frequency control, and robust self-healing, even in the presence of obstacles. These findings address current limitations in TA emitters and suggest broader applications in medical ultrasound and advanced technology.

Analysis of Transient Thermoacoustic Characteristics and Performance in Carbon Nanotube Sponge Underwater Transducers.

Recent advancements in marine technology have highlighted the urgent need for enhanced underwater acoustic applications, from sonar detection to communication and noise cancellation, driving the pursuit of innovative transducer technologies. In this paper, a new underwater thermoacoustic (TA) transducer made from carbon nanotube (CNT) sponge is designed to achieve wide bandwidth, high energy conversion efficiency, simple structure, good transient response, and stable sound response, utilizing the TA effect through electro-thermal modulation. The transducer has potential application in underwater acoustic communication. An electro-thermal-acoustic coupled simulation for the open model, sandwich model, and encapsulated model is presented to analyze the transient behaviors of CNT sponge TA transducers in liquid environments. The effects of key design parameters on the acoustic performances of both systems are revealed. The results demonstrate that a short pulse excitation with a low duty cycle could greatly improve the heat dissipation of the encapsulated transducer, especially when the thermoacoustic response time becomes comparable to thermal relaxation time.

Fully dense generative adversarial network for removing artifacts caused by microwave dielectric effect in thermoacoustic imaging

Microwave-induced thermoacoustic (TA) imaging (MTAI) combines pulsed microwave excitation and ultrasound detection to provide high contrast and spatial resolution images through dielectric contrast, which holds great promise for clinical applications. However, artifacts caused by microwave dielectric effect will seriously affect the accuracy of MTAI images that will hinder the clinical translation of MTAI. In this work, we propose a deep learning-based method fully dense generative adversarial network (FD-GAN) for removing artifacts caused by microwave dielectric effect in MTAI. FD-GAN adds the fully dense block to the generative adversarial network (GAN) based on the mutual confrontation between generator and discriminator, which enables it to learn both local and global features related to the removal of artifacts and generate high-quality images. The practical feasibility was tested in simulated, experimental data. The results demonstrate that FD-GAN can effectively remove the artifacts caused by the microwave dielectric effect, and shows superiority in denoising, background suppression, and improvement of image distortion. Our approach is expected to significantly improve the accuracy and quality of MTAI images, thereby enhancing the diagnostic accuracy of this innovative imaging technique.

In Vivo Microwave-Induced Thermoacoustic Endoscopy for Colorectal Tumor Detection in Deep Tissue.

Optical endoscopy, as one of the common clinical diagnostic modalities, provides irreplaceable advantages in the diagnosis and treatment of internal organs. However, the approach is limited to the characterization of superficial tissues due to the strong optical scattering properties of tissue. In this work, a microwave-induced thermoacoustic (TA) endoscope (MTAE) was developed and evaluated. The MTAE system integrated a homemade monopole sleeve antenna (diameter = 7 mm) for providing homogenized pulsed microwave irradiation to induce a TA signal in the colorectal cavity and a side-viewing focus ultrasonic transducer (diameter = 3 mm) for detecting the TA signal in the ultrasonic spectrum to construct the image. Our MTAE, system combined microwave excitation and acoustic detection; produced images with dielectric contrast and high spatial resolution at several centimeters deep in soft tissues, overcome the current limitations of the imaging depth of optical endoscopy and mechanical wave-based imaging contrast of ultrasound endoscopy, and had the ability to extract complete features for deep location tumors that could be infiltrating and invading adjacent structures. The practical feasibility of the MTAE system was evaluated i n vivo with rabbits having colorectal tumors. The results demonstrated that colorectal tumor progression could be visualized from the changes in electromagnetic parameters of the tissue via MTAE, showing its potential clinical application.

Underwater Thermoacoustic Generation by a Hierarchical Tetrapodal Carbon Nanotube Network.

Solid-state fabricated carbon nanotube (CNT) sheets have shown promise as thermoacoustic (TA) sound generators, emitting tunable sound waves across a broad frequency spectrum (1-105 Hz) due to their ultralow specific heat capacity. However, their applications as underwater TA sound generators are limited by the reduced mechanical strength of CNT sheets in aqueous environments. In this study, we present a mechanically robust underwater TA device constructed from a three-dimensional (3D) tetrapodal assembly of carbon nanotubes (t-CNTs). These structures feature a high porosity (>99.9%) and a double-hollowed network of well-interconnected CNTs. We systematically explore the impact of different dimensions of t-CNTs and various annealing procedures on sound generation performance. Furnace-annealed t-CNTs, in contrast to directly resistive Joule heating annealing, provide superior, continuous, and homogeneous hydrophobicity across the surface of bulk t-CNTs. As a result, the t-CNTs-based underwater TA device demonstrates stable, smooth, and broad-spectrum sound generation within the frequency range of 1 × 102 to 1 × 104 Hz, along with a weak resonance response. Furthermore, these devices exhibit enhanced and more stable sound generation performance at nonresonance frequencies compared to regular CNT-based devices. This study contributes to advancing the development of underwater TA devices with characteristics such as being nonresonant, high-performing, flexible, elastically compressible, and reliable, enabling operation across a broad frequency range.

Thermoacoustic performance of 100 kHz wide-band packaged projector in water tank with three-dimensional graphene

This paper presents the demonstration of underwater thermoacoustic (TA) sound generation using three-dimensional graphene (3D-C). 3D-C is able to interface with water as the immediate acoustic medium, resulting in reduced attenuation across solid packaging encapsulation due to favorable acoustic impedance matching. This is shown using array configurations of 2*2 and 4*4 individual 3D-C elements prepared onto printed circuit boards and secured within a watertight cuboid Delrin container with deionized water. Comparisons of underwater acoustic performance between internal medium of water and air shows significant improvement in measured sound pressure level (SPL) with internal water medium, in contrast with internal air medium where SPL were below noise floor. This demonstration opens up new possibilities of 3D-C for underwater acoustic applications. Simulations are conducted using 3D finite element model generated with COMSOL Multiphysics and validated with experimental results. A revised formulation of transmission voltage response (TVR) specific to TA sound generation is proposed due to the difference in power scaling of TA sound generation and subsequently validated using simulation.

Novel Coil Transducer Induced Thermoacoustic Detection of Rail Internal Defects Towards Intelligent Processing

A novel resonant tri-coil transducer is proposed to induce thermoacoustic (TA) signals for detecting rail internal defects. It consists of a ferrite plate-backed tri-coil and its associated circuits, a shielding layer, and a three-dimensional printed enclosure for supporting and securing. General TA detection theory is illustrated to understand how to detect rail internal defects. For achieving electromagnetic (EM) field shaping and focusing, the physical structure of the proposed transducer is optimized. It reduces backward EM fields and interference. Then, an equivalent circuit model between the proposed transducer and the rail is constructed to analyze optimal power transfer efficiency as a function of distance and frequency. To validate the design concept, the proposed transducer is fabricated for inducing TA signals, and experiments are performed. Several engineered rail specimens (UIC-60E) with different types of defects are prepared. The induced TA waves are found to be compressional. With selected features, a support vector machine algorithm-based multinomial classifier model is trained and employed for intelligent processing. Then, the proposed transducer is integrated into the self-designed automatic rail monitoring system. Experimental results show that the self-designed system can achieve an accuracy rate of 96.4%, successfully identifying defects in defect classification. The proposed transducer has low cost in fabrication and maintenance, focused magnetic fields with a large lift-off distance and enhanced acoustic wave intensity. Compared to earlier version of the system, the spacing between the transmitter and the rail has been further increased.

The characteristic analysis of phase-controlled array thermo-acoustic emission with multiple emitting surfaces

Thermo-acoustic (TA) ultrasound, particularly when combined with phased-controlled array technology, has garnered significant interest in the past decade due to its numerous advantages. This paper establishes a theoretical expression for thermo-acoustic phased array (TAPA) emission to investigate different acoustic fields based on input heat flow frequencies, quantities and distances of TA emission surfaces, area of emission surfaces, and phase changes between emission surfaces. The study finds that a TAPA with two emitting surfaces in a line pattern produces a consistent acoustic field compared to a single emitting surface arranged in a semicircle. Additionally, applying different phases on the surfaces narrows the scanning range with an increase in frequency, area of the TA emission surface, and the amount of emission surfaces, while enhancing the directivity of the TA wave. Moreover, increasing the distance between emitting surfaces in a square-shaped TAPA does not affect the ultrasound pressure of the main TA ultrasound but increases the quantity and size of side lobes. Furthermore, enlarging the area of emitting surfaces enhances the directivity of the TA ultrasound, necessitating a reduction in the distance between emitting surfaces or an increase in the area of the emitting surfaces in a square-shaped TAPA to enhance directivity. This paper provides a comprehensive study of TAPA to aid further research in this field.

Exergy-based methodology to develop design guidelines for performance optimization of a coupled co-axial thermoacoustic refrigerator

Performance of thermoacoustic (TA) systems are very complex, and their performance optimization is a difficult task, and most TA systems have relatively very low efficiencies. The main objective of this study was to develop an exergy analysis to introduce a guide for a designer, how to optimize the performance of a TA system. We have applied this methodology to a coupled thermoacoustic engine and refrigerator with a standing wave in the engine and a traveling wave in the refrigerator. In an optimization procedure, a lumped systems numerical analysis was performed to predict the main parameters of the thermoacoustic system. The numerical method was validated by comparison with numerical and experimental results in the literature. The cost function was the total system coefficient of performance, and design parameters include the refrigerator regenerator length, location, and hydraulic radius. The performance index was decomposed into three main subsystem indices, i.e., the efficiency of the engine, the efficiency of the resonator, and the coefficient of performance of the refrigerator. The optimum point for each component was found, and the total system optimal point which is a result of thermoacoustic interaction of all segments were analyzed. It was illustrated how a change in design parameters could affect the pressure and velocity amplitude and phase distribution in different subsystems, which help the designer deal with the challenge of the optimal parameter selection to enhance the system performance. Finally, an exergy analysis was introduced to assess loss mechanism's contribution to each refrigerator's component. This result in a roadmap for optimization of the system. A new parameter called non-dimensional exergy loss portion (NELP) was introduced, which may significantly show the improvement potential in each system component.

Experimental investigation of two- and three-dimensional graphene-based thermo-acoustic sound generating devices: Analysis of gap separation effect

Advances in nanomaterials over the last decade have enabled the practical exploration of the “thermophone” concept based on a thermoacoustic (TA) mechanism. By applying an alternating current to thin-film conductive materials that are strong, stiff and of high emissivity, it is possible to rapidly heat and cool the surrounding fluid (air or gas) through resistive heating and convection cooling. The resulting temperature oscillation of the fluid causes it to expand and shrink, which in turn generates acoustic waves with a sound pressure level (SPL) over a wide frequency band. Motivated by two-dimensional (2D) and three-dimensional (3D) graphene thin films possessing the essential characteristics needed for high performance TA, we present herein a comprehensive investigation on the performance of TA sound-generating devices made by mounting 2D and 3D graphene materials on a substrate with a 50-μm gap separation. The effect of the gap, the types of graphene films, and the substrate materials are investigated. Compared with 2D graphene thin films, 3D graphene foams were found to exhibit higher sound generation capability and TA efficiency. In addition, the mechanical properties of the substrate have a small effect on the SPL response of 3D-graphene foam TA devices but strongly affect the SPL response of 2D-graphene thin-film TA devices.

Magneto-thermal-acoustic imaging of magnetic nanoparticles with tissue structure imaging function

Magneto-thermal-acoustic imaging with magnetic nanoparticles (MNPs) is a novel medical imaging modality based on the thermoacoustic (TA) effect of MNPs. We proposed a new dual-modality imaging strategy that combines the TA and echo signals. Based on the synthetic aperture method, we used TA signals to image cancer tissues labeled with MNPs and applied echo signals to achieve tissue structure imaging. In the simulation, we constructed a breast cancer model and assumed that cancer tissue was labeled with MNPs. Under a limited field of view, the TA and echo signals were collected using a multi-element transducer array. By fusing the imaging results of the TA and echo signals, we obtained a boundary distribution map of the breast cancer model, and accurately located the tumor tissue. In this experiment, we built a multi-channel acquisition system. Pork tissue labeled with MNPs was used as the breast cancer phantom. We collected a total of 120 TA and echo signals at 1 mm intervals using a multi-element transducer array and faithfully imaged the boundary distribution map of the phantom. Compared with the traditional linear back projection method based on focused transducers, we demonstrated that the proposed method not only improves the lateral resolution of the image, but also makes accurate cancer identification easier. This provides a promising medical imaging technology for clinical applications.

Portable Microwave-Acoustic Coaxial Thermoacoustic Probe With Miniaturized Vivaldi Antennas for Breast Tumor Screening.

Microwave-induced thermoacoustic (TA) imaging (MTAI), which exploits dielectric contrasts to provide images with high contrast and spatial resolution, holds the potential to serve as an additional means of clinical diagnosis and treatment. However, conventional MTAI usually uses large and heavy metal antennas to radiate pulsed microwaves, making it challenging to image different target areas flexibly. In this work, we presented the design and evaluation of a portable microwave-acoustic coaxial TA probe (51 mm × 63 mm × 138 mm) that can flexibly image the region of interest. The TA probe contains two miniaturized symmetrically distributed Vivaldi antennas (7.5 g) and a 128-element linear ultrasonic transducer. By adjusting the geometry of the antennas and the ultrasonic transducer, the TA probe's acoustic field and microwave field can be designed to be coaxial, which helps achieve homogeneous microwave illumination and high-sensitivity ultrasonic detection. The practical feasibility of the proposed probe was tested on an in vitro ewe breast and a healthy volunteer. The results demonstrate that the MTAI system with the proposed TA probe can visualize the anatomical structure of the breast tumor in ewe breast and a healthy volunteer breast with resolutions in hundreds of microns (transverse: 910 μm, axial: 780 μm) and an excellent signal-to-noise ratio can be obtained in deep adipose tissue (10 dB in 6 cm fat). The miniaturized portable TA probe takes a solid step forward in translating MTAI technology to clinical breast tumor diagnosis.

A high-efficient excitation-detection thermoacoustic imaging probe for breast tumor detection.

Microwave-induced thermoacoustic (TA) imaging (MTAI) is a promising alternative to biomedical imaging due to its high resolution, deep imaging depth, and minimal biohazard. To provide images of different anatomical regions and apply them to different clinical scenarios, the development of miniaturized portable TA probes is imperative. This study is aimed to propose a highly efficient handheld non-reflective microwave-acoustic coaxial TA probe to advance the translation of MTAI for the clinical use. The TA probe integrates a hollowed microwave antenna with a forward radiating uniform microwave field and a linear ultrasonic transducer array which is placed in the hole in the middle of the antenna that has almost no effect on the microwave distribution. The integrated probe was evaluated for properties, including the excitation efficiency of the microwave and the reception efficiency of the acoustic signal. Finally, an isolated EMT6 cell tumor was embedded in a sheep mammary gland to simulate the natural breast tumor environment, and the tumor was detected with the proposed MTAI probe to evaluate its practical feasibility. Compared with the previous TA imaging probe, it has improved the detection efficiency of TA signals by up to 41%, contributing to an improved signal-to-noise ratio (SNR) of the image. The proposed TA probe successfully detected tumors embedded in the breast with a contrast ratio 3.27 times higher than the surrounding tissue in phantom experiments. The proposed TA probe with the features of microwave illumination and ultrasonic detection of coaxial, avoiding TA signal attenuation due to reflection, enables high-efficient TA signal excitation and detection. The proposed TA probe is essential for improving the excitation and detection efficiency of TA signals, and increasing the flexibility of the probe, providing a bright future for the clinical application of MTAI technology.

Thermoacoustic concentration imaging of magnetic nanoparticles under single-pulse magnetic fields

Under a single-pulse magnetic field (SMF), we proposed a thermoacoustic (TA) concentration imaging method of magnetic nanoparticles (MNPs). This method derived the relationship between the concentration of MNPs and TA signals based on the mechanism of the TA effect. In the simulation, we ideally reconstructed the concentration map of the MNPs from the simulated TA signals. It proves the feasibility of the proposed method. In the experiment, a multi-channel acquisition system was built, and the MNP suspension with the iron concentration of 1 mg/ml was injected into two gaps of the phantom. Then, 128 TA signals were obtained by a multi-channel acquisition system. Finally, the imaging results faithfully reconstructed the cross-sectional image of the MNP area in the phantom. It is demonstrated that the TA concentration imaging of the MNPs under the SMF has the potential to achieve low-concentration MNP imaging in vivo, which provides a promising molecular imaging method for imaging MNP-labeled cancer tissues.

Characterization of a Thermoacoustic-based Pulsed High Power Microwave Detector Chain.

Detection of microwave-induced thermoacoustic (TA) wave generation was evaluated as a potential technique for detection of high power microwave (HPM) directed energy exposure. Even when HPM is employed for counter-materiel effects, incidental but still potentially harmful personnel exposure is possible. Real-time detection of ongoing exposure with potentially unknown time and frequency domain characteristics is a critical first step in preventing acute health effects by alerting and then enabling the timely use of electromagnetic frequency energy shielding, such as structures and vehicles. Leveraging the TA effect as a field interaction mechanism, a lossy dielectric polymer subjected to pulsed HPM was tested using a planar sample geometry with thin film piezoelectric sensors used to capture the resulting TA output. The piezoelectric signal was analyzed in both the time and frequency domain to determine empirical relationships between incident microwave beam properties and signal components. This analysis was coupled with an empirically-based single term Cole-Cole model approximation fit for the complex permittivity. The results were used to identify appropriate signal conditioning and processing techniques needed to convert the TA response into a useful form for personnel exposure applications. These results also served as a comparison point for multi-physics finite element method computational modeling of the electromagnetic response of a simplified three-layer tissue model.

Controlling dielectric loss of biodegradable black phosphorus nanosheets by iron-ion-modification for imaging-guided microwave thermoacoustic therapy

Microwave-induced thermoacoustic (TA) technology transforms microwave into acoustic waves useable for imaging or therapy, based on the power density of the pulsed microwaves. Exploiting nanoparticles with high biocompatibility, safe metabolism, and high microwave-acoustic conversion is the key to the clinical translational application of TA therapy. In this paper, we proposed a biodegradable and high microwave absorption nanoparticle for TA therapy. The proposed nanoparticle uses iron ions to regulate the atomic defects of biodegradable black phosphorus (BP) nanosheets to augment the dielectric loss. The iron ions adsorb with the lone pair electrons indicated of BP through the conjugated π bond to increase the permanent electric dipoles. With pulsed microwave irradiation, a large number of electric dipoles are repeatedly polarized, causing instantaneous temperature rise and then generating significant TA shockwave via TA cavitation effect. TA shockwave can disrupt cell membranes in situ to trigger programmed apoptosis and produce precise anti-tumor effects. Additionally, the nanoparticle-mediated TA process generates images that deliver valuable data, such as the size, shape, and location of the tumor for treatment planning and monitoring. This hypothesis has been tested in vitro and in vivo with animal models of glioblastoma tumors. The experimental results demonstrate the high theragnostic efficiency for tumor inhibition and TA imaging, exhibiting low systemic cytotoxicity and good biocompatibility after systemic administration. The established BP-based nanoparticle with both safe metabolism and high microwave-acoustic conversion is a promising candidate for precision theranostics without obvious side effects.

Multiple Back Projection With Impact Factor Algorithm Based on Circular Scanning for Microwave-Induced Thermoacoustic Tomography

Back-projection (BP) algorithm is a common image reconstruction method for microwave-induced thermoacoustic tomography (MITAT). According to the thermoacoustic (TA) signals obtained, which are superimposed with the corresponding time inversion of each pixel in the region of interest (ROI), the BP algorithm can function in a quick response and is suitable for fast real-time MITAT applications. However, high artifacts and background noises caused by incomplete sampling of TA signals seriously affect the image quality. In this paper, a multiple back-projection with impact factor (MBP-IF) algorithm based on circular scanning geometry is proposed to address this problem. Compared with the BP algorithm, the MBP-IF approach calculates not only the initial acoustic pressure of the TA signal of each pixel (i.e., the image obtained by BP), but also the complete acoustic pressure distributions at different time points during the thermoacoustic wave propagation. Then impact factors can be obtained and used to effectively suppress artifacts and eliminate noises. Numerical simulation and phantom experiments prove that the MBP-IF algorithm is advantageous in suppressing image artifacts and noises. Some figures of merit are also obtained to quantify the results. In addition, due to the independence of acoustic pressure distributions at different time points, the MBP-IF can be computed in parallel by GPU, which can be widely used in real-time clinical MITAT system construction.

Multi-Watt-Level 4.9-GHz Silicon Power Amplifier for Portable Thermoacoustic Imaging

Microwave-induced thermoacoustic (TA) imaging, combining high microwave contrast with high ultrasonic resolution has the potential to revolutionize applications such as continuous healthcare monitoring, point-of-care imaging, and biometric authentication. However, the size, cost, and integration of a high-power microwave transmitter is a key bottleneck in making TA imaging truly portable, affordable, and ubiquitous. Toward that end, this work presents a compact 4.9-GHz pulsed power amplifier (PA) with a 4.87-mm² active area implemented in a 55-nm BiCMOS technology, operating in a duty-cycled mode and achieving 37.3-dBm peak output power—the highest demonstrated peak power in PAs fabricated on a silicon substrate with deep submicron CMOS integration. We also reconstruct the first known high-fidelity TA images of tissue phantoms using an integrated silicon PA.

Application of Thermo Acoustical Parameters for the Evaluation of the Available Volume of Ionic Liquid, 1-Butyl-3-Methylimidazolium Chloride in Mixed Solvents at Different Temperatures

The available volume of 1-Butyl-3-methyl imidazolium chloride, [bmim][Cl] in pure water and aqueous solutions of potassium citrate and sodium citrate at different concentrations of solute and T = (298.15 to 318.15) K have been evaluated by making use of ultrasonic velocity and thermo acoustic parameters followed by a comparative study. The thermo acoustic parameters have been used to determine available volume, V a for the solutions under analysis. For well understanding, the values of found from the thermo acoustic methods were tallied with the values found from the well-defined ultrasonic method (Schaaff’s method). The decrease of the available volume with an increase of the mass fraction of ionic liquid and temperature shows the existence of ion-solvent interactions of IL in the studied solutions. To the best of our knowledge, this study is a pioneering effort in the evaluation of available volume present in the investigated solutions by making use of the ultrasonic approach.

Modeling a Lossy Dieletric Polymer-based Thermoacoustic High Power Microwave Directed Energy Exposure Detection System.

Presented are design considerations for a potential detection and measurement technique that could provide operational awareness of high power microwave (HPM) directed energy weapon exposure for force health protection applications, leveraging thermoacoustic (TA) wave generation as the field interaction mechanism. The HPM electromagnetic frequency (EMF) regime, used in applications in both the counter-materiel and non-lethal counter-personnel design space, presents real-time personnel exposure warning challenges due to the potentially wide variation in time and frequency domain characteristics of the incident beam. As with other EM-thermal interactions, the thermoacoustic wave effect provides the potential to determine EM energy and power deposition without the need to measure ambient field intensity values or overload-sensitive EMF survey equipment. Following measurement of relevant EM, thermal, and elastic material property values, a carbon-filled polytetrafluoroethylene (CF-PTFE) lossy dielectric medium subject to pulsed HPM was computationally modeled using the commercial finite element method multi-physics simulation software package COMSOL. The simulation was used to explore the impacts of various material properties on TA signal output as a function of simulated incident field power density, EM frequency, and pulse length, thereby informing the selection of system components for the further development of a full TA-based HPM detection chain.