Ultrasound Transmission Research Articles

Dental Ultrasonography for Visualizing Osteoimmune Conditions and Assessing Jaw Bone Density: A Narrative Review.

Despite the widespread use of ultrasonography (US) in medical diagnostics, there is no similar US device available for visualizing jawbone density. This study is a narrative review of the possible applications of US in dentistry. This review is divided as follows: (a) Pulse-echo ultrasonography: the applications offer new perspectives for periodontal and peri-implant assessment. (b) Through-transmission alveolar US (TTAU): this technique was a novel imaging modality until 2004, when TTAU devices were last available. Quantitative US scaling made the device useful for diagnosing chronic inflammatory conditions in the jaw. (c) Ultrasound transmission velocity (UTV): in 2008, this technique was introduced in German university dental clinics to analyze the mechanical properties of the jawbone without translating the scientific findings into a practical device. (d) Trans-alveolar US device (TAU): the growing importance of "osteoimmune focal bone marrow defects" has led practitioners to develop a new TAU device. The attenuation of US was used for imaging of jawbone density. (e) Patients who benefit from TAU-guided jawbone surgery: research has shown remarkable results in specific disease cases. This review concludes that US has been undervalued as a diagnostic tool in dentistry. The new TAU-n unit offers the opportunity to change this in the future.

Preparation and methodological analysis of chitosan-based ultrasound-coupled hydrogel pads

This study aims to optimize the process for preparing chitosan-based ultrasound-coupled hydrogel pads and investigate their application potential in ultrasonography. Chitosan, 2-acrylamido-2-methylpropanesulfonic acid, and N-isopropylacrylamide were used as the main materials to prepare chitosan-based ultrasound-coupled hydrogel pads. The free-radical polymerization conditions were optimized by a three-factor, three-level orthogonal test with the tensile strength and ultrasound image quality of the hydrogel pads as evaluation indicators. The optimal prescription was selected by optimizing three factors of raw material ratio, polymerization temperature, and freeze-drying time. The structure and performance of the hydrogel pads were characterized by a scanning electron microscope, a universal testing machine, and an ultrasonic diagnostic instrument. The results showed that the optimal prescription was as follows: the chitosan: 2-acrylamide-2-methylpropanesulfonic acid: N-isopropylacrylamide ratio of 2:0.55:17.27, the polymerization temperature of 25 ℃, and the freeze-drying time of 48 h. The ultrasonically-coupled hydrogel pads prepared under these conditions were transparent, with a porous structure, good adhesion, and high tensile strength. The hydrogel pads had good swelling properties and the swelling degree decreased slowly on day 10. The quality of the ultrasound images obtained via chitosan-based hydrogel pads was not significantly different from that obtained via medical ultrasound coupling agent. In this study, we analyzed the effects of different preparation processes on the gel formation of chitosan-based ultrasound-coupled hydrogel pads. The hydrogel pads were transparent and mild and non-irritating to the human body, serving as an ultrasound transmission material for ultrasonography.

Mild Focused Ultrasound-Induced Microscopic Heating of Nanoparticles Observed by Lanthanide Luminescence for Precise Sonothermal Cancer Therapy.

Focused ultrasound (FUS) is a recognized tool that can be used clinically for the thermal ablation of tumors. However, excessive heat can cause side effects on the ultrasound transmission path and normal tissues around the tumor. To address the issue, this work detected for the first time the effect of microscopic heating of nanoparticles under the action of FUS through the luminescence intensity ratio (LIR) and luminescence lifetime of temperature-responsive lanthanide-doped nanoparticles. When FUS is applied to the tissue embedded with nanoparticles, the increase in the microscopic temperature of the nanoparticles synchronously monitored by LIR is more obvious than the increase in the macroscopic temperature. Based on this phenomenon, the intensity of focused ultrasound can be finely regulated to avoid overheating while ensuring a therapeutic effect. This work achieves the measurement of the microscopic heating of nanoparticles under FUS, which is of great significance for the development of sonothermal cancer therapy.

Mechanical properties of lightweight photocatalytic marbelite

This study investigated the mechanical performance of lightweight photocatalytic marbelite (LPM). In the production of LPM, titanium dioxide (TiO2) and various fiber additives were used to impart self-cleaning properties to the LPM with photocatalytic effect. In the study, fibers were added to the LPM mix at different ratios (0%, 0.5%, 1%) and unit weight, ultrasound transmission rate, bending, splitting tensile and compressive strength tests were carried out on these specimens. The mixture was prepared with perlite and polyester resin and enriched with TiO2 and fiber additives. Perlite was used as an aggregate in the LPM and lightweighting properties were added to the specimens. The experimental results show that increasing the fiber content significantly improves the mechanical strength of the LPM. The improvement in bending strength reached 60%, while in compressive strength it reached 25% and in splitting tensile strength it reached 35%. With the addition of TiO2, the bending strength of LPM increased by 15%, while the compressive strength increased by 12% and the splitting tensile strength increased by 7%. These ratios were higher with increasing fiber content. These results suggest that LPM, which provide environmental benefits with their photocatalytic properties and improved mechanical performance, can be more effectively used in industrial applications.

Capacitive Micromachined Transducers With Out-of-Plane Repulsive Actuation for Enhancing Ultrasound Transmission in Air

Capacitive Micromachined Transducers With Out-of-Plane Repulsive Actuation for Enhancing Ultrasound Transmission in Air

The Mechanical Dynamics of Lithium-Metal Battery Formation Protocols

Formation, the first charge of an SEI forming battery system, is well understood to affect the cycling behavior of the system. This is particularly crucial for anode-free lithium metal batteries due to the significant effect of initial Li plating morphology and SEI on subsequent plating and, therefore, long-term cyclability. Low-cost, operando tools that spatially map heterogeneities are important for the study and validation of formation protocols. Here, we use spatially-resolved ultrasound transmission during formation to study variations in gas formation and morphology of Li metal anode-free cells as a function of temperature, pressure, and current density. These non-invasive results are validated with ex situ optical and SEM imaging, and XPS is used to determine the SEI speciation. We then cycled these formed cells at increased rates while measuring the systems with one-dimensional acoustics to correlate formation with mechanical and electrochemical cycling performance.

Design of α–alumina integrated ultrasound transducer for wireless power transmission system

Traditional ultrasound wireless power transmission (UWPT) technology often faces challenges such as low power transmission efficiency and safety concerns. This paper proposes a highly reliable α–alumina integrated ultrasound transducer–based ultrasound wireless power transmission (IUT–UWPT) system designed for metallic medium. The proposed system is capable of powering and communicating with embedded sensors inside metal–sealed tanks. An acoustic wave transmission model for the IUT–UWPT system is developed based on acoustic theory to optimize the thickness of the matching layer and bonding layers between piezoelectric ceramics and metallic medium. The effect of the α–alumina integrated ultrasound transducer on the input–output characteristics of the system is analyzed using the mason equivalent circuit method considering acoustic attenuation and finite element simulation. Experimental results show that, compared to traditional UWPT systems without α–alumina integrated ultrasound transducer, the IUT–UWPT system exhibits a broader frequency response range from 0.8 MHz to 1.2 MHz and achieves a 13.19 % increase in maximum output power. Notably, the insulating properties of the α–alumina integrated ultrasound transducer prevent electrical generation on the surface of the metal–sealed tank. This system is well–suited for health monitoring in storage facilities such as gas pipelines, liquid nitrogen tanks and nuclear waste containers.

Machine learning based segmentation of delamination patterns from sparse ultrasound data of barely visible impact damage in composites

Composite laminates, known for their strength and flexibility, are widely used but can delaminate under certain barely visible impact. Ultrasound Transmission (UT) scans can detect such failures, but the noise in the scans makes automation of delamination morphology challenging. Machine learning could solve this, but it requires substantial training data. Furthermore, given the considerable time and cost of conducting impact tests on composite laminates, such data remains sparse. This study overcomes data sparsity by enlarging UT scan dataset using image augmentation techniques and synthetic data generation methods. A combination of rotation and elastic deformation of real UT images produced augmented data. Synthetic data was generated by mimicking the statistical variations in real data, including delamination length and rotation per ply, and adding gradients to match the original image noise. A U-Net based machine learning segmentation approach was utilized to capture local and global information through a series of convolutions to apply per-pixel classification. Systematic experimentation was conducted to study the influence of adding augmented and synthetic data on segmentation accuracy. The results show that the use of augmented data increases accuracy significantly. With the addition of synthetic data to the augmented data, there is a marginal improvement in accuracy. However, feature edge accuracy is significantly improved. The preliminary results presented here show the promising use of machine learning techniques for complex, non-destructive inspection methods.

All-optical platform for ultrasound transmission matrix measurements

Piezoelectric ultrasound transducers are constrained by size, bandwidth, and angular response, limiting their ability to fully characterize the acoustic properties of objects. In this study, we introduce a novel modular all-optical platform for ultrasound generation and detection to overcome these limitations, demonstrating wideband operation (>50 MHz), omnidirectional response, and high signal fidelity. Ultrasound generation is performed via the optoacoustic effect by illuminating an optically absorbing coating with spatially modulated pulsed light, and ultrasound detection is carried out using a silicon-photonic acoustic detector. By illuminating patterns that span a basis and scanning the detector, the full transmission matrix is measured, consisting of the acoustic waveforms for all the transmitter–receiver pairs in the measurement geometry. Our method is experimentally demonstrated in transmission mode for beam steering, beam focusing, and imaging, achieving excellent agreement with the theory.

Revisiting oxidation and reduction reactions for synthesizing a three-dimensional hydrogel of reduced graphene oxide.

An improvement to Hummers' method involving a cascade-design graphite oxidation reaction is reported to optimize safety and efficiency in the production of graphite oxide (GrO) and graphene oxide (GO). Chemical reduction using highly alkaline ammonia solution is a novel approach to synthesizing reduced graphene oxide (RGO). In this original research, we revisit the oxidation and reduction reactions, providing significant findings regarding the synthetic pathway to obtain a bioinspired water-intercalated hydrogel of RGO nanosheets. Influential factors in the graphite oxidation reaction, typically the exothermic reaction temperature and hydrogen peroxide effect, are described. Furthermore, the chemical reaction of GO reduction using highly alkaline ammonia solution (pH 14) was investigated to produce hydrated RGO nanosheets assembled in a hydrogel structure (97% water). Three-dimensional assembly and water intercalation are key to preserve the non-stacking state of RGO nanosheets. Therefore, ultrasound transmission to aqueous channels in the macroscopic RGO hydrogel vibrated and dispersed the RGO nanosheets in water. Analytical results revealed the single-layer nanostructures, functional groups, optical band gaps, optimized C/O ratios, particle sizes and zeta potentials of GO and RGO nanosheets. The reversible self-assembly of RGO hydrogels is essential for many applications, such as RGO coatings and polymer/RGO nanocomposites. In a water purification application, the RGO hydrogel was dispersed in aqueous solution by simple agitation and showed a high capacity for organic dye adsorption. After the adsorption, the RGO/dye particles were easily removed by filtration through ordinary cellulose paper. The process of adsorption and filtration is effective and inexpensive for practical environmental remediation. In summary, a bioinspired structure of RGO hydrogel is conceptualized for prospective nanotechnology.

Developing a diagnostic system: combining ultrasound and electrical impedance tomography for enhanced urinary tract analysis

The study aims to develop a reconstruction and measurement system for data analysis using ultrasound transmission tomography (UST) and electrical impedance tomography (EIT), which can be implemented in wearable solutions for non-invasive monitoring and diagnosis of functional urinary tract disorders. Functional disorders can be associated with many urinary system defects, constipation, and central nervous system defects (spina bifida, cerebral palsy). The lack of non-invasive diagnostic methods for a functional and comprehensive analysis of the state of the urinary tract reduces the likelihood of a correct diagnosis and effective treatment. Furthermore, constructing a physical model of a tomograph is problematic due to the complexity of acoustic phenomena necessary for modeling in the case of a heterogeneous environment of propagation of waves in small, limited spaces. Nevertheless, the radial propagation model used in UST is sufficient for effectively detecting disturbances in the interior of objects and is used in medical solutions. The innovation of the solution lies in the simultaneous assessment of urinary tract function based on the analysis of images obtained using EIT and UST. As a non-invasive diagnostic, UST allows for visualization of the body's internal structures (including muscles, blood vessels, and internal organs). However, UST-based diagnostic systems of the urinary tract are not present in world markets. Moreover, building such a system requires solving many problems: limited research fields, dependence on the body structure, difficulties in imaging bone structures, and areas filled with gases.

Predicting ultrasound wave stimulated bone growth in bioinspired scaffolds using machine learning

For conditions like osteoporosis, changes in bone pore geometry even when porosity is constant have been shown to correlate to increased fracture risk using techniques such as dual-energy x-ray absorptiometry (DXA) and computed tomography (CT). Additionally, studies have found that bone pore geometry can be characterized by ultrasound to determine fracture risk, since certain pore geometries can cause stress concentration which in turn will be a source for fracture. However, it is not yet fully understood if changes in pore geometry can be detected by ultrasound when the porosity is constant. Therefore, this study develops an unsupervised machine learning model classifying pore geometry between bioinspired and quadrilateral pore scaffolds with constant porosity using experimental ultrasound wave transmission data. Our results demonstrate that differences in pore geometry can be detected by ultrasound, even at constant porosity, and that these differences can be distinguished in an unsupervised manner with machine learning. For traumatic bone injuries and late-stage osteoporosis where fracture occurs, tissue scaffolds are used to aid the healing of fractures or bone loss. The scaffold design is optimized to match material properties closely with bone, and healing can be enhanced with ultrasound stimulation. In this study we predict the combined effects of ultrasound parameters, such as wave frequency and mode of displacement, and scaffold material properties on bone tissue growth. We therefore develop an unsupervised machine learning clustering model of bone tissue growth in the scaffolds using finite element analysis and bone growth algorithms evaluating effects of pore geometry, scaffold materials, ultrasound wave type and frequency, and mesenchymal stem cell distribution on bone tissue growth. The computational predictions of tissue growth agreed within 10% of comparable experimental studies. The data corresponding to pore geometry, mesenchymal stem cell distribution, and scaffold material demonstrate distinct clusters of total bone formation, while ultrasound frequency and mesenchymal stem cell distribution show distinct clusters in bone growth rate. These variables can be tuned to tailor the scaffold design and optimize the required amount and rate of bone growth to meet a patient's specific needs.

Ultrasound‐Driven Highly Stable Implantable Triboelectric Nanogenerator with Human‐Tissue Acoustic Impedance‐Matched Polyether Ether Ketone

AbstractImplantable electrical neurostimulators offer a promising avenue for treating neurological disorders. However, their dependency on a finite battery life limits their long‐term utility. Emerging transcutaneous ultrasound‐driven triboelectric nanogenerator (TENG) techniques provide solutions for converting external ultrasound waves into internal electricity. This study proposes an implantable ultrasound‐driven TENG (IU‐TENG) using polyether ether ketone (PEEK) for its exceptional stability inside a human body and acoustic impedance compatibility with human tissues. This IU‐TENG remarkably surpasses traditional titanium‐based encapsulation, resulting in a 99.94% efficiency in ultrasound transmission. In addition, PEEK contains numerous electron‐donating functional groups, making it suitable for TENG applications, particularly as a positive triboelectric layer. The device exhibits robust voltage outputs, reaching up to 11.50 and 8.75 V in water and in vivo, respectively, under body‐safe ultrasound intensities. Moreover, its ability to sustain a stable electrical output for over 300 min emphasizes the durability and mechanical resilience of PEEK. In vivo mouse models and ex vivo porcine tissue trials demonstrate the effectiveness of the IU‐TENG in nerve stimulation, showing its potential in medical treatments, enhancing the functionality and longevity of implantable medical devices.

Acoustically transparent alumina-based cranial implants enhance ultrasound transmission through a combined mechano-acoustic resonant effect

Therapeutic ultrasound for brain stimulation has increased in the last years. This energy has shown promising results for treating Alzheimer’s disease, Parkinson’s disease and traumatic brain injury, among other conditions. However, the application of ultrasound in the brain should trespass a natural but highly attenuating and distorting barrier, the cranium. Implantable ceramic materials can be used to replace part of the cranium as an alternate method to enhance ultrasound transmission. In this work, it is presented the acoustic characterization of alumina ceramic disks that can be employed as cranial implants for acoustic windows-to-the-brain. Alumina samples were prepared using current-activated pressure-assisted densification and were acoustically characterized. Acoustic impedance and attenuation of the samples were determined for different porosities. Additionally, measured and modeled acoustic fields are presented and analyzed in terms of the total ultrasound transmitted through the ceramics. Results indicate a resonant behavior in the alumina disks when the thickness corresponds to a half-wavelength of ultrasound; this resonance permits a total of 95.4% of ultrasound transmission; for thicknesses out of the resonant zone, transmission is 53.0%. Alumina proves to be an excellent medium for ultrasound transmission that, in conjunction with its mechanical and optical properties, can be useful for cranium replacement in mixed opto-acoustic applications.

Ultrasound propagation characteristics within the bone tissue of miniature ultrasound probes: implications for the spinal navigation of pedicle screw placement.

The accuracy of pedicle screw fixation is crucial for patient safety. Traditional navigation methods based on computed tomography (CT) imaging have several limitations. Therefore, this study aimed to investigate the ultrasonic propagation characteristics of bone tissue and their relationship with CT imaging results, as well as the potential application of ultrasound navigation in pedicle screw fixation. The study used three bovine spine specimens (BSSs) and five human vertebral allograft bones (HABs) to progressively decrease the thickness of the cancellous bone layer, simulating the process of pedicle screw perforation. Five unfocused miniature ultrasound probes with frequencies of 2.2, 2.5, 3, 12, and 30 MHz were employed for investigating the ultrasonic propagation characteristics of cancellous and cortical bone through ultrasound transmission and backscatter experiments. The CT features of the bone tissue was obtained with the Skyscan 1174 micro-CT scanner (Bruker, Billerica, MA, USA). The experimental results demonstrated that low-frequency (2-3 MHz) ultrasound effectively penetrated the cancellous bone layer up to a depth of approximately 5 mm, with an attenuation coefficient below 10 dB/cm. Conversely, high-frequency (12 MHz) ultrasound exhibited significant signal attenuation in cancellous bone, reaching up to 55.8 dB/cm. The amplitude of the backscattered signal at the cancellous bone interface exhibited a negative correlation with the bone sample thickness (average r=-0.84), meaning that as the thickness of the cancellous bone layer on the cortical bone decreases, the backscattered signal amplitude gradually increases (P<0.05). Upon reaching the cortical bone interface, there was a rapid surge in echo signal amplitude, up to 8 times higher. Meanwhile, the statistical results indicated a significant correlation between the amplitude of the echo signal and the micro-CT scanning results of bone trabecular structure. Theoretically, using multiple ultrasonic probes (≥3) and regions of interest (ROIs) (≥5) has the potential to provide surgeons with early warning signals for pedicle perforation based on three or more successive increases in echo signal amplitude or a sudden substantial increase. The statistical results indicate a significant correlation between the amplitude of the echo signal and the micro-CT scanning results of bone trabeculae, suggesting the potential use of ultrasound as opposed to CT for real-time intraoperative bone navigation.

Influence of stiffeners on acoustic emission monitoring of ship structures

Naval vessels are valuable assets that are expensive to build and maintain. Predictive maintenance is crucial to enhance efficiency and operability and to extend the service life of these structures. Fatigue is regarded as one of the main damage modes affecting the structural integrity of ship structures. Fatigue cracks can develop at the intersections of stiffeners and other structural elements, without being detected until they substantially grow, introducing a degree of uncertainty in the estimation of the fatigue damage. Acoustic emission (AE) is a passive ultrasound method for the detection and localization of different types of damage. AE is sensitive to crack propagation and can cover large areas, making it suitable for structural health monitoring of ship hulls. However, for accurate fatigue crack detection via AE it is crucial to understand how ultrasound waves interact with structural members i.e. stiffeners and longitudinal frames. Dispersion, scattering, reflection, and multimodality have so far hindered the application of AE in this context. This study aims to assess ultrasound wave behavior in ship structures in the presence of structural elements such as stiffeners and longitudinal/transversal frames. It investigates the ultrasound wave transmission dependence on source frequency and angle of incidence using spectral finite element (SEM) simulations and experimental measurements. The experimental setup includes a 10mm thick steel plate with a stiffener and a longitudinal beam (Figure 1). Pairs of sensors are placed on each side of the stiffener to record the incoming and transmitted waves, and to determine the transmission coefficient. By combining the results of both simulation and experiments, an expression for the transmission coefficient as a function of different frequencies and angles is presented. The results of this study can be used to maximize the coverage of AE monitoring systems and enhance their sensitivity for detection of fatigue cracks on ship structures.

Exploring the Use of Cold Atmospheric Plasma for Sound and Vibration Generation.

In this study, we investigate the potential of cold atmospheric plasma (CAP) as a non-contact excitation device, comparing its performance with an ultrasound transmitter. Utilizing a scanning Laser Doppler Vibrometer (LDV), we visualize the acoustic wavefront generated by a CAP probe and an ultrasound sensor within a designated 50 mm × 50 mm area in front of each probe. Our focus lies in assessing the applicability of a CAP probe for exciting a small polymethyl methacrylate (PMMA) sample. By adjusting the dimensions of the sample to resonate at the excitation frequency of the probe, we can achieve high vibrational velocities, enabling further mechanical analysis. In contrast with traditional vibration excitation techniques such as electrodynamical shakers and hammer impact excitation, a plasma probe can offer distinct advantages without altering the structure's dynamics since it is contactless. Furthermore, in comparison with laser excitation, plasma excitation provides a higher power level. Additionally, while pressurized air systems are applicable for limited low frequencies, plasma probes can perform at higher frequencies. Our findings in this study suggest that CAP is comparable with acoustic excitation, indicating its potential as an effective mechanical excitation method.

Oblong-shaped piezoelectric ultrasound energy harvester for high-performance wireless power charging

Wireless power charging for implantable biomedical electronics (IBEs) can potentially eliminate the need for frequent battery-replacement surgeries, ultimately improving patients’ quality of life. Ultrasound wireless power transfer (US-WPT) based on piezoelectric receivers has demonstrated significant potential, particularly for deep-seated IBEs. However, most studies on US-WPT have overlooked the optimization of piezoelectric receiver dimensions relative to transmitted ultrasound beam profiles for maximizing battery-charging efficiency for IBEs. This study revealed that a piezoelectric receiver should have dimensions corresponding to the main lobe width of the transmit beam profile within a focal area. Moreover, its output power should be proportional to the cube of the receiver area. Considering these findings, an oblong-shaped ultrasound transmitter and receiver (OsUTR) was developed for efficient WPT, capable of fully charging commercial batteries. In water, the OsUTR produced an output power per unit area of 246.93 mW/cm2, which is 6.588 times higher than that achieved by previously reported methods. This resulted in an average charging rate of 1.64 mC/s, enabling the fully charging of a 30 mAh commercial battery in 1.33 h. Experiments with a 50 mm thick porcine tissue demonstrated that the OsUTR provided an output voltage and current of 38.4 Vp-p and 103.4 mAp-p, respectively. Consequently, full charging of the battery was successfully achieved in 1.80 h. This high-performance OsUTR can enable long-term use of IBEs. This innovation reduces the burden of battery replacement and expands the applicability of implantable devices, driving significant advancements in the IBEs industry.

Numerical Investigation of Layered Homogeneous Skull Model for Simulations of Transcranial Focused Ultrasound

Background and ObjectivesThe influence of the intracranial pressure field must be discussed with the development of a single-element transducer for low-intensity transcranial focused ultrasound because the skull plays a significant role in blocking and dispersing ultrasound wave propagation. Ultrasound propagation is mainly affected by the structure and acoustic properties of the skull; thus, we aimed to investigate the impact of simplifying the acoustic properties of the skull on the simulation of the transcranial pressure field to present guidance for efficient skull modeling in full-wave simulations. Materials and MethodsWe constructed a three-dimensional computational model for ultrasound transmission with the same structure but varying acoustic properties of the skull. The structural information and heterogeneous acoustic properties of the skull were acquired from computed tomography images, and we segmented the skull into three layers (3 L), including spongy and compact bones. We then assigned homogeneous acoustic properties to a single layer (1 L) or 3 L of the skull. In addition, we investigated the influence of different types of transducers and different ultrasound frequencies (1.1 MHz, 0.5 MHz, and 0.25 MHz) on the intracranial pressure field to provide a comparison of the heterogenous and homogeneous models. ResultsWe indicated the importance of numerical simulations in estimating the intracranial pressure field of the skull owing to beam distortions. When we simplified the skull model, both the 1 L and 3 L models showed contours of the acoustic focus comparable to those of the heterogeneous model. When we evaluated the peak pressure and volume of the acoustic focus, the 1 L model produced a better estimation of peak pressure with a difference <10%, and the 3 L model is suitable to obtain smaller errors in the volume of the acoustic focus. ConclusionsIn conclusion, we examined the possibility of simplification of skull models using 1 L and 3 L homogeneous properties in the numerical simulation for focused ultrasound. The results show that the layered homogeneous model can provide characteristics comparable to those of the acoustic focus in heterogeneous models.

Multipoint laser ultrasound transmitter using single-multi-single mode fiber structures

Laser ultrasound technology is a promising alternative to piezoelectric ceramics in the field of structural health monitoring, especially the distributed applications. A novel multipoint laser ultrasound transmitter using single-multi-single mode fiber structure was proposed in this study. Both theoretical simulations and experimental results indicate transmitters with controllable coupling ratio can be fabricated by directly changing the length of multimode fiber. To validate the capability of distributed application, a four-point energy-balanced laser ultrasound transmitter system has been achieved by connecting transmitters with different coupling ratio in increasing order. The four transmitters exhibited similar characteristics both in time domain and frequency domain, with a peak-to-peak amplitude of 1018 mV and a center frequency closed to 4 MHz. The transmitters exhibited a relatively high signal-to-noise ratio and an elevated energy conversion efficiency with over 5 times that of previous researches. The proposed transmitter has a potential for distributed applications. However, further analysis of the mode of the ultrasonic waves or packaging of the transmitter is needed before it can be used in structural health monitoring.