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The rapid development of modern science and technology puts forward higher and higher requirements for displacement measurement. As a non-contact measurement technology, laser ranging has played an important role in various fields for the unique advantages and has become a hot topic in the field of measurement research. At present, there are little research on high-precision displacement measurement at medium and long distance, the needs of which are widespread in practical application, so this work has important value. Among various laser ranging technologies, the laser triangulation method has the advantages of high-speed, high precision, simple structure, etc. Therefore, this paper chooses the direct laser triangulation method to carry out the research after analyzed the common types of laser triangulation system. In view of the requirements of high-precision displacement measurement requirements at medium and long distance, this article discussed the design of laser triangulation measuring system and the selection of structural parameters. Then we proposed a direct laser triangulation measurement structure under Scheimpflug conditions. This system selects PSD displacement transducer to collect the position information of the scattered light spot. After that, this paper discusses the principle of laser triangulation distance measurement and simulates the system. Then the influence of different parameters on high-precision displacement measurement and the relationship between them are investigated. Based on the research talked above, we got a set of structural parameters of the displacement measurement system. The measurement accuracy can be ~micron with the working distance of 500mm.

Quartz-enhanced photoacoustic spectroscopy (QEPAS) [1] is one of the most efficient ways to obtain sensitive, selective, robust gas sensors. The main drawback of QEPAS comes from usage of quartz tuning fork (QTF) as a mechanical transducer. QTF is not specifically design for photoacoustic gas sensing and its further integration is limited. As a solution we propose a silicone resonant MEMS based on capacitive transduction mechanism. This sensor, specifically designed for acoustic sensing purposes, can be an efficient transducer for sound wave detection able to advantageously replace a QTF. Capacitive transduction allows reaching high sensitivity of the sensor while choice of silicon is favorable in design flexibility, fabrication maturity, stability and further integration with CMOS electronics. We have developed and fabricated various resonator designs on silicon. Specific designs were created to sensor voltage output using an analytic model developed by our group [2]. Photoacoustic measurement was performed on calibrated mixtures of methane using commercial Eblana distributed feedback laser laser emitting at 1.63 μm. We achieved a reproducible limit of detection on methane: 1000ppmv in 5s for 2f detection and 700ppm in 5s for 1f detection (figure 1) (resonator resonance frequency 22.65 kHz and Q-factor of 250). Then, we compared the experimental results with standard QTF in off-beam configuration for which the limit of detection: 30ppmv in 5s for 2f detection and 25 ppm in 5s for 1f detection. Thus, the difference of detection limit between QTF and MEMS amounts factor 28 for 1f detection and 33 for 2f detection. [1] Kosterev, A. A., Bakhirkin, Y. A., Curl, R. F., & Tittel, F. K. (2002). Quartz-enhanced photoacoustic spectroscopy. Optics letters, 27(21), 1902-1904. [2] Trzpil, Wioletta, et al. "Analytic Optimization of Cantilevers for Photoacoustic Gas Sensor with Capacitive Transduction." Sensors 21.4 (2021): 1489.

We demonstrate efficient and compact electro-optic free-space modulators that employ hybrid high-Q Mie resonators embedded in low-loss, high-performance electro- optic molecules to achieve full amplitude modulation of a telecom carrier. By minimizing losses and maximizing the overlap between all interacting fields, we shift the resonance by 11 nm.

The problem with existing flow meters is a relatively high measurement error, which is associated with a lack of information on the flow profile. In order to create a reference device that makes it possible to study the flow profile due to a larger number of sensors, with bore size 50 mm primary transducer with fourteen channels is developing and manufacturing. This device can provide more accurate results due to the use of multiple channels of ultrasonic signal passage, which makes it possible to calculate large time points along the entire section of the pipe, as well as the ability to visualize the flow profile. In the course of the work, a 3D model of the primary transducer was developed in accordance with the requirements and conditions for the passage of ultrasound through a liquid medium, when it was necessary to take into account the simultaneous operation of several channels at once, taking into account the fact that the paths of ultrasound passage should not intersect. Processing several signals at once becomes possible, since five TDC microcontrollers will be used for all channels.

The properties of laser-accelerated ion bunches are demanding and require development of suitable beam diagnostics. In particular, the short and intense particle bunches with a broad energy spectrum emitted in conjunction with a strong electromagnetic pulse (EMP) are challenging for conventional and well established monitoring systems. An approach based on measuring the acoustic signals of particles depositing their energy in water, referred to as ionoacoustics [https://doi.org/10.1118/1.4905047] was recently developed into Ion-Bunch Energy Acoustic Tracing (I-BEAT)\cite{haffa_i-beat:_2019}. I-BEAT allows online detection of single proton bunches while being cost effective and EMP resistant. A simple water phantom equipped with only one ultrasound transducer positioned on the ion axis allows for reconstructing a rather complex energy spectrum that is typical for (manipulated) laser-accelerated ion bunches. To deduce the lateral bunch properties, additional transducers can be added, for example perpendicular to the ion beam axis. This established setup has been adapted for use closely behind the laser target and tested at the PHELIX laser at GSI. The capability of the system to retrieve information about the broad proton spectrum close to the source despite the harsh conditions has been demonstrated. Future improvements are required, most importantly the increase of dynamic range. Nevertheless, I-BEAT holds promise to evolve into an online diagnostic tool particularly suited for laser-driven source development and optimization at high repetition rates.

Ultrasonic transducer is a sensor that realizes the mutual conversion of ultrasonic and electrical signals, and it is widely used in quality inspection, biomedical imaging and other fields. Commonly used ultrasonic transducers have a small detection range and low sensitivity due to the diffraction of sound waves. Focused transducers are used to improve detection sensitivity. Unfortunately, focused transducers have narrow depth of field. Here, we developed a Bessel ultrasonic transducer for large depth of field by using conical acoustic lens. An acoustic lens is attached to a unfocused ultrasonic. And the acoustic lens is a cuboid prism with a concave cone on the bottom, made of fused silica. Similar to an axicon that can generate a Bessel beam, the Bessel ultrasonic transducer can produce nondiffracting Bessel ultrasonic beams. Therefore, extended depth of field with uniformly high resolution and high detection sensitivity can be obtained. We used COMSOL to simulate the transmission of ultrasonic field of the designed conical acoustic lens, and compare it with the spherical focused ultrasonic transducer. The results show that the depth of field of the Bessel ultrasonic transducer is about 8 times that of the conventional spherical focused ultrasonic transducer. And the depth of field of the Bessel ultrasonic transducer can be further adjusted by adjusting the cone angle of the conical acoustic lens. The Bessel ultrasonic transducer will help improve the capabilities of the ultrasound probe and expand its application range. For example, an ultrasonic probe with a large depth of field will expand the imaging depth of photoacoustic microscopy and enhance its ability in non-destructive testing.

Transducers based on dielectric elastomers (DEs) consist of a polymer as dielectric between two compliant electrodes and can convert electrical into mechanical energy and vice versa. The geometry significantly determines the performance of DEs, which is mainly reflected by the static and dynamic behavior of pressure and strain. The goal of multilayered dielectric elastomer stack-transducers (DETs) is to maximize the force while maintaining a reasonable deflection. To scale the voltage down to 1 kV the thickness of the elastomeric film must be reduced. For this purpose, a roll-to-sheet lamination process has been adopted by modifying an existing process in order to use elastomeric films with a thickness of 20 µ m, applied with electric field strength up to 50 V/ µ m. In a first step, 10 films are laminated in a semi-automated process resulting in submodules. Fully functional submodules are stacked to form a multilayered stack-transducer up to hundreds of thin films. The production process can be divided into 5 partial processes which are described in detail. The goal of each manufacturing step as well as challenges are presented. With this outline, the outcome of the mentioned manufacturing approach of thin film-based multilayered DE stack-transducers is investigated. The roll-to-sheet lamination approach to produce DETs via submodules provides a good basis for further research in this field.

In this study, we explore the postbuckling instability of piezoelectric-integrated cylinders under axial displacement for energy harvest applications. Experiments are conducted using 3D printed cylinders with piezoelectric transducers bonded on their outer and inner surfaces. The local and global postbuckling responses of the cylinders are triggered based on their design and geometry. Numerical simulations are carried out to study the effect of varying cylinder geometries on the harvested energy. A comparative study is performed between the numerical and experimental results. Furthermore, a corrugated design is proposed to tailor the postbuckling response of the cylinders from local buckling to global buckling. The results shows that the new corrugated designs for the cylinders improves the energy harvesting efficiency.

This paper presents an ultrasonic guided wave tomography for detecting and sizing delaminations in composites using pure shear horizontal (SH) wave. In this method, pure SH0 wave excitation was achieved using the adjustable angle beam transducers (ABT) in quasi-isotropic composite plates. First, a 3-mm quasi-isotropic composite plate with simulated delaminations by Teflon inserts was manufactured. Then, the ABT tuning angle of SH0 mode was calculated from the theoretical phase-velocity dispersion curve based on Snell’s law. Experiments were conducted on the 3-mm quasi-isotropic composite plate for pure SH0 wave excitation and delamination detection. It was found that a significant decrease in the signal amplitude was observed due to the delaminations. Finally, a linear scanning approach in 0° and 90° directions was conducted to cover the whole delamination area. The collected signals were used to visualize the damage through damage imaging methods. SH0 wave tomography based on the reconstruction algorithm for probabilistic inspection of defects (RAPID) was applied for delamination detection and characterization. The experimental results show that the SH0 wave tomography has a good performance for delamination detection, size estimation, and localization in aerospace composites.

Ultrasonic transducer is a sensor that realizes the mutual conversion of ultrasonic and electrical signals, and it is widely used in quality inspection, biomedical imaging and other fields. Commonly used ultrasonic transducers have a small detection range and low sensitivity due to the diffraction of sound waves. Focused transducers are used to improve detection sensitivity. Unfortunately, focused transducers have narrow depth of field. Here, we developed a Bessel ultrasonic transducer for large depth of field by using conical acoustic lens. An acoustic lens is attached to a unfocused ultrasonic. And the acoustic lens is a cuboid prism with a concave cone on the bottom, made of fused silica. Similar to an axicon that can generate a Bessel beam, the Bessel ultrasonic transducer can produce nondiffracting Bessel ultrasonic beams. Therefore, extended depth of field with uniformly high resolution and high detection sensitivity can be obtained. We used COMSOL to simulate the transmission of ultrasonic field of the designed conical acoustic lens, and compare it with the spherical focused ultrasonic transducer. The results show that the depth of field of the Bessel ultrasonic transducer is about 8 times that of the conventional spherical focused ultrasonic transducer. And the depth of field of the Bessel ultrasonic transducer can be further adjusted by adjusting the cone angle of the conical acoustic lens. The Bessel ultrasonic transducer will help improve the capabilities of the ultrasound probe and expand its application range. For example, an ultrasonic probe with a large depth of field will expand the imaging depth of photoacoustic microscopy and enhance its ability in non-destructive testing.

The paper provides a model for multi-hit limited sample POD analysis for simulated raster scanning that is used for flaw detection in nondestructive evaluation. Raster scanning of the transducer is used in ultrasonic testing of parts. In multi-hit POD analysis system, resolution is taken into account. The scan data, known as C-scan, is represented as a 2D pixel grid. Typically, the pixel gray value is equal to signal amplitude. The data is taken at every step or index between the pixels. Each pixel represents an area of the part that is sampled by the transducer. The sampled area or the aperture provides the signal amplitude. The step size may be equal to or smaller than the aperture, creating either a non-overlapping or overlapping aperture scan pattern. Optimal scanning uses least number of steps or pixels that can provide reliable flaw detection, accurate flaw sizing and adequate spatial resolution for the target size and larger flaws. Here, the scan patterns are defined in relation to the target flaw size, transducer aperture, and step size. In this work, flaw field is simulated as symmetrical bivariate standard distribution and transducer as a receiver with square aperture. This arrangement is similar to a raster scan with an unfocused transducer. The optimal scan pattern is determined by simulating a number of scan patterns and comparing their signal amplitude, flaw sizing accuracy, probability of detection and probability of false positive in relation to contrast-to-noise ratio. If results of such simulation are corroborated in empirical data, the model can be used in assessing reliability of flaw detection in NDE as well as for choosing optimal scan pattern.

Piezoelectric materials are versatile. They were made into various successful engineering products, such as sensors, actuators, and generators. However, almost all of the previous designs were found only capable of one specific function among those three. From a more fundamental physical point of view, a piezoelectric element, as a transducer, provides a bidirectional channel for energy conversion between mechanical and electrical domains. It makes no bias to any of those functions. This paper analyzes the obstacle against developing multi-functional piezoelectric devices, clears that barrier, and further proposes a switched-mode interface circuit towards an unprecedented multi-functional piezoelectric design. It was developed based on a buck-boost switched-mode circuit. By properly controlling the switch actions, this interface circuit can realize all functions of dynamics sensing, energy harvesting (generation), and vibration excitation (actuation) in a time-sharing manner. The dynamics sensing function is realized according to the time ratio between piezoelectric capacitor discharging (through an inductor) and the inductor’s freewheeling. The discharging period is set to be as short as possible to avoid much interference to the stored charge of the piezoelectric capacitor, which is related to the dynamic displacement. The energy harvesting function is carried out by discharging the piezoelectric capacitor through an inductor (more drastically than that in sensing mode). The extracted energy in the inductor then freewheels into a storage capacitor. For the vibration excitation function, the control logic reverses. It first pumps energy from the storage capacitor to the inductor, then freewheels the energy to the piezoelectric capacitor. The actual control scheme is more complicated because the piezoelectric voltage is an ac output. The multi-functional design should comprehensively consider the discharging and freewheeling requirements under positive and negative polarities. Under these working principles, a prototyped multi-functional piezoelectric interface circuit is implemented and tested. The three functions are successfully demonstrated. By making a comprehensive collaboration between piezoelectric transducers and power electronics, this design starts a new chapter for the applications of piezoelectric materials toward multi-functional engineering designs.

The paper provides a model for multi-hit limited sample POD analysis for simulated raster scanning that is used for flaw detection in nondestructive evaluation. Raster scanning is used in ultrasonic testing with unfocused and focused transducers. In multi-hit POD analysis, system resolution is taken into account. The scan data, known as C-scan, is represented as a 2D pixel grid. Typically, the pixel gray value is equal to the ultrasonic signal amplitude. The data is taken at every step or index between the pixels. Each pixel represents an area of part that is sampled by the transducer. The sampled area or the aperture provides the signal amplitude. The step size may be equal to or smaller than the aperture, creating either a non-overlapping or overlapping aperture scan pattern. Optimal scanning uses least number of steps or pixels that can provide reliable flaw detection, accurate flaw sizing and adequate spatial resolution for the target size and larger flaws. Here, the scan patterns are defined in relation to the target flaw size, transducer aperture, and step size. In this work, probe field is simulated as symmetrical bivariate standard distribution and distribution and flaw as a square shaped reflector. This arrangement is similar to a raster scan with focused transducer. The optimal scan pattern is determined by simulating a number of scan patterns and comparing their signal amplitude, flaw sizing accuracy, probability of detection and probability of false positive in relation to contrast-to-noise ratio. If results of such simulation are corroborated in empirical data, the model can be used in assessing reliability of flaw detection in NDE as well as for choosing optimal scan pattern.

Artificially introduced cracks in necked double shear lugs are monitored using piezoelectric transducers attached to the lug shaft and analyzed by the electro-mechanical impedance (EMI) method with a model-based approach. Numerical simulations with coupled-field finite element (FE) models are used to study the frequency response behavior of necked lugs. Through-cracks with lengths up to 3 mm are located at 90° to the lug axis, which is a critical spot for damage initiation. The shift of a selected resonance frequencies found by analytical and numerical calculations are used to estimate the crack length. Results of numerical FE simulations are validated with multiple experimental measurements .

Structural health monitoring (SHM)/nondestructive evaluation (NDE) is an emerging multi-disciplinary field that aims at detecting/characterizing structural damage and providing diagnosis/prognosis of structural health status in a real-time or on-demand manner. It can reduce maintenance costs, shorten the machine service downtime, and improve the safety and reliability of the engineering structures. Acoustic emission (AE) is one of the SHM/NDE methods by means of detecting elastic waves due to dynamic motions at AE sources, such as cracking, delamination, cleavage, and fretting in a material. The acoustic emission inspection technique relies on the AE sensors to collect the AE signals from the structure to monitor the structural health. Conventionally, these AE sensors need to be permanently attached to the structure through the bonding adhesive layer which may introduce contamination to the structure. In this work, the research is focused on investigating non-contact passive sensing of acoustic emission (AE) signals using an air-coupled transducer (ACT). The well-acknowledged pencil-lead-break method has been used to simulate the AE source. A resonant type ACT is used to passively sense the AE signals, which leaves the testing object intact and provides a non-intrusive sensing method. The non-contact AE test on a thin aluminum structure as well as a thick steel structure is first conducted. Next, the investigation is extended to composite structures. Both single-layer composite structure and bonded composite structure are investigated. The results successfully demonstrate the capability of non-contact passive sensing of the AE signals using the ACT method.

In this study, an omnidirectional shear horizontal (SH) wave acoustic transducer (OSH-WAT) is proposed, composed of a circular aluminum structure driven by twelve thickness-mode (d33) piezoelectric wafer active sensors (PWAS). The OSH-WAT contains six units to form an axisymmetric structure, and each unit consists of a cylinder with a cantilever beam and two cubic stubs. Two d33 PWASs acting like a couple, as the actuation sources, are bonded on the opposite sides of the cantilever beam to drive the excitation. The thickness-mode PWASs can produce a forcing pair, which can be converted to a circumferential shear deformation by two adjacent cubic stubs, contributing to the omnidirectional SH0 wave generation. Multiphysics finite element model (FEM) is constructed based on such a design. Harmonic analysis is conducted to obtain the spectral response of a circular aluminum plate to investigate the omni-directivity of the SH0 wave excited by the OSH-WAT, so as to identify the “sweet” frequency bands. Thereafter, the coupled field transient dynamic FEM simulations are carried out to acquire the dynamic response of a pitch-catch active sensing procedure. A voltage signal in the form of a 5-count tone burst is applied on each d33-type PWAS to generate SH0 mode waves into the aluminum host plate. The received signals demonstrate the outstanding performance of the successful generation and reception of SH0 waves. The proposed OSH-WAT may possess great potential in future Structural Health Monitoring (SHM) and Nondestructive Evaluation (NDE) applications. The paper finishes with summary, concluding remarks, and suggestions for future work.

Evaluation of optimal slope angle of an air-coupled transducer (ACT) is important, to allow for effective generation of Lamb waves in solid structures. This effectiveness relies on both generation of desired wave modes, amplitude of measured signals and large coverage area for damage detection. Phenomenon of non-contact elastic waves generation in plate based on ACT is considered assuming few approaches. Numerical modeling in COMSOL is related to the analysis of different plate thicknesses and ACT excitation frequencies. Experimental research is based on wave excitation using piezoceramic ACT with a base excitation frequency of 40 kHz and SLDV measurements for a 1 mm-thick plate. A comprehensive investigation of optimal ACT slope angle for the generation of A0 mode is included. Propagation of S0 mode was not observed in numerical as well as experimental results. Optimal slope angle values were estimated in different ways numerically and experimentally with the use of dispersion curves and based on the amplitude of generated waves. Finally, the optimal angle value was determined and utilized for damage detection and localization problem in an aluminum plate.

Piezoelectric wafer active transducers (PWaTs) play an important role for smart structures. Typically, they are bonded on the surface of structures to excite and sense mechanical vibrations or waves. The resonant characteristics of the surface bonded PWaT is very different from those of the free-standing PWaT. Since the resonances of the PWaTs strongly influence the transducer efficiency, it is important to understand their resonant behaviors. In this paper, an analytical model of the surface bonded PWaT is implemented to study the resonant characteristics of surface bonded PWaT in details. The study reveals that the PWaT supports two modes that have very different propagation constants below and above a cut-off frequency, leading to different resonance behaviors. These resonance behaviors can be explained with respect to the propagation of these two modes in the PWaT and the mode conversion at the edges of the PWaT. These fundamental understanding will benefit the design and optimization of the PWaTs.

In this paper, the non-linear dynamic response of circular air-backed panel subjected to underwater impulsive loading has been studied in the fluid-structure interaction (FSI) experiments. This is helpful for the design and improvement of thin plate structures in practical engineering field. Three typical copper plates, (a) clamped, and (b) bolted were selected, fixed on the end of the anvil tube by the flange ring cover. A high-speed photography system recorded the full-field shape and displacement profiles of the specimens in real time. The pressure history of the underwater impulsive wave was measured by a pair of dynamic pressure transducers. The 3D transient deformation fields’ measurements were obtained using a 3D digital image correlation (DIC) technique. Strain results from DIC and the strain gauges technique were in good agreement. The results also show a high level of correlation with that results simulated by AUTODYN. The 3D-DIC is proven to be an effective method to measure 3D full-field dynamic response of structures under underwater impact loading. Moreover, this work will be helpful on understanding the failure process and predicting the modes.

X-ray induced acoustic (XA) imaging is a promising imaging technique that can identify X-ray absorption contrast with much reduced ionizing radiation. In this study, we developed the X-ray induced acoustic imaging system that uses a synchrotron and a single-element focused ultrasound transducer. The synchrotron has an energy of 4-20 keV, a pulse width of 30 ps, a pulse-repetition period of 2 ns, and a bunch-repetition period of 940 ns. Due to the short pulse repetition, we obtained the XA amplitude in the frequency domain. Then, we successfully obtained 2D phantom imaging with a lead rectangular target.

We characterized the stiffness and anisotropy of the equatorial sclera and its dependence on intraocular pressure (IOP). Porcine eyes were tested using ultrasound elastography under IOP control. Shear waves were induced using a mechanical shaker, and an off-axis 17.8 MHz transducer used to track the wave propagation in the equatorial and anterior-posterior directions. Wave speed was measured and used to estimate directional Young’s moduli. Anisotropy was defined as the ratio of the equatorial moduli to the anterior-posterior moduli. Sclera was stiffer in the equatorial direction, with anisotropy decreasing with IOP, from, 5.1 at 10 mmHg to 3.7 at 30 mmHg.

We introduce transparent TOBE CMUT arrays for multimodal optical camera imaging, ultrasound imaging and photoacoustic imaging. We used an adhesive wafer bonding process technique to fabricate the 128-element lambda-pitch transducers and achieve high transparency ranging from visible to near-infrared with ultrasound center frequencies of 7.5-9 MHz. The arrays are anticipated to have utility for endoscopic, intravascular, and intra-operative probes for multimodal interventional guidance.

Photoacoustic microscopy (PAM), an emerging biomedical imaging technology, has provided the label-free imaging of biomolecules with the aid of superior optical contrast in them. A pulsed laser with wavelength of 532 nm is widely used to visualize the microvascular structures of small animal or human in vivo. Employing a customized 1-axis high-speed scanning device and ring-shaped ultrasound transducer (RUT), we developed a high-speed PAM system which enables wide field-of-view (FOV) imaging with high sensitivity. The optical and ultrasonic beam can be automatically aligned without opto-ultrasound beam combiner (OUC) by transmitting the laser through the hole in the transducer. Especially the transducer used in our system was designed to have a long focal length and a large sensing area to achieve wide-field imaging with high sensitivity. To verify the high sensitivity of the developed system, we performed ultrasonic pulse-echo experiments on quartz and PA in vitro imaging on leaf skeletons. Compared to the conventional beam alignment method which adopts OUC, the enhancement of signal-to-noise ratio (SNR) was 15 dB and 12 dB in those experiments, respectively. In addition, the high-speed scanner was designed to scan up to 12 mm long at resonant frequency of 80 Hz and to cover the wide sensing area of the transducer. By utilizing these specifications, the microvascular structures in a whole mouse ear could be imaged within 30 seconds without any additional image registration. The developed system could be a practical imaging platform for future studies in microvasculatures such as hemodynamic changes, oxygen saturation, and metabolism.

Deep tissue applications (>1 cm) for photoacoustic imaging are currently limited for traditional Fabry-Perot ultrasound transducers interrogated by tightly focused Gaussian beams due to beam walk-off. We investigate the optical confinement of the beam using plano-concave microresonators with a model based on the ABCD formalism and the use of high-sensitive and high-density multi-element arrays. The results show an improvement in the sensitivity enabling an increase of the penetration depth in tomographic photoacoustic imaging.

In this paper, a novel Delay and Glow (DAG), back projection-based photoacoustic reconstruction, for point source recovery is presented. The projections of the absorber coefficients are delayed and weighed based on the transducer directivity sensitivity and matched with the other projections from other transducer elements leading to glow the point source at the exact location. The DAG was tested with 2-D experimental and simulation studies and compared with conventional delay and sum (DAS) reconstruction method. The proposed algorithm outperforms the DAS in terms of contrast to noise ratio (CNR) and RMS errors.

Photoacoustic imaging (PAI) is a hybrid imaging modality that uses ultrasound waves generated from light absorbing tissue chromophores to provide high spatial resolution and depth-resolved molecular information. However, conventional PAI setups involve complicated arrangement of optical components surrounding opaque ultrasound transducers to achieve a co-aligned optical illumination and ultrasound receiving field. This opacity of traditional ultrasound transducers impedes the miniaturization of the imaging head, besides precluding integration with other imaging modalities. To overcome these limitations, we recently fabricated a single element transparent ultrasound transducer (TUT) window using indium tin oxide (ITO) coated lithium niobate (LiNbO3) piezoelectric material and demonstrated its application for endoscopy and microscopy PAI applications. Extending on this work, we report new developments of TUTs to improve their detection bandwidth, sensitivity, and signal to noise ratio (SNR) while maintaining sufficient transparency. This includes investigating LiNbO3 and PMN-PT as transparent piezoelectric materials with different matching layer designs. Fabricated TUTs were characterized using pulse echo and electrical impedance analysis. The PAI performance of the fabricated TUTs were characterized using photoacoustic A-line signals from light absorbing targets. The proposed TUTs are low cost, easy to fabricate, and can be scaled and easily integrated into different PAI geometries such as: endoscopy, microscopy, and computed tomography systems for high-throughput imaging applications.

We present a fast, multispectral acoustic resolution optoacoustic microscope using a new burst-mode triggering scheme. Three pulsed laser sources are combined to retrieve spectral images across large field-of-views extending over 25mm by 25mm at 28μm lateral and 14μm axial resolution with an overfly scan of a few minutes. Highly sensitive PVDF transducer allows detection of structures 3.8mm below the human skin surface with per pulse energies of only 25μJ. The newly developed system overcomes limitations of previously reported scanning optoacoustic microscopy and mesoscopy implementations, offering a major leap forward in terms of clinical usability, laser safety, effective penetration depth and spectral unmixing capabilities.

Visualizing whole-body dynamics across entire living organisms is crucial for understanding complex biology, disease progression as well as evaluating efficacy of new drugs and therapies. Existing small animal functional and molecular imaging modalities either suffer from low spatial and temporal resolution, limited penetration depth or poor contrast. In this work, we present flash scanning volumetric optoacoustic tomography (fSVOT) imaging system that enables the acquisition speeds required for visualizing fast kinetics and biodistribution of optical contrast agents across whole mice. fSVOT can render images of intricate vascular and organ anatomy with rich contrast by capitalizing on the large angular coverage of a spherical matrix array transducer rapidly scanned around the mouse. Volumetric (three-dimensional) images with 200 µm resolution can be acquired within 45 seconds, which corresponds to an imaging speed gain of an order of magnitude with respect to existing state-of-the-art modalities offering comparable resolution performance. We demonstrate volumetric tracking and quantification of gold nanorod kinetics and their differential uptake across the spleen, liver and kidneys. Overall, fSVOT offers unprecedented capabilities for multi-scale imaging of pharmacokinetics and bio-distribution of agents with high contrast, resolution and image acquisition speed.

Capacitive micromachined ultrasound transducers (CMUTs) are gaining more interest for photoacoustic imaging due to its low-cost, high bandwidth and flexibility in size and shape. However, the beampattern of CMUTs usually exhibits wide mainlobes and high sidelobes, degrading the imaging resolution and contrast. We propose to improve the beampattern with optimization of apodization by imposing conditions on the angular distribution of the signal energy received from a PA point source to minimize the sidelobes magnitude and maintain the mainlobe energy. Both simulations and experiments results demonstrate that the proposed apodization suppress the sidelobes up to 30dB when compared with Uniform weights.

We have designed and developed an air-coupled ultrasonic radiation force probe co-focused with a phase-sensitive optical coherence tomography system (ACUS-OCT). Our custom-made 1 MHz spherically focused piezo-electric transducer with a concentric circular opening of 10 mm diameter allows for the confocal micro-excitation of waves and the spatial (2D, 3D) motion measurement of tissues. Phantom studies demonstrated the capabilities of this probe to produce quasi-harmonic excitation up to 4 kHz for the generation of highly localized elastic waves. Experimental results in ocular tissues showed the highly localized 2D/3D elasticity mapping capabilities of this approach with great potential for clinical translation.

Acoustic-resolution optoacoustic microscopy (AR-OAM) visualizes internal tissue structures at millimeter to centimeter scale depths with high spatial resolution. The imaging performance mainly depends on the geometry and detection characteristics of the ultrasound transducer. Reconstruction methods incorporating transducer effects are essential to optimize achievable resolution, contrast and overall image quality. Model-based (MB) reconstruction has been shown to provide excellent imaging performance in several optoacoustic embodiments, due to its capacity to accurately model the transducer. However, the applicability of MB reconstruction methods in AR-OAM has been hampered by the high computational cost. Here, we propose an efficient MB reconstruction framework for largescale AR-OAM by considering scanning symmetries, which enabled capitalizing the computational power of a graphics processing unit. The suggested MB reconstruction method is shown to significantly improve the imaging performance of AR-OAM compared to synthetic aperture focusing technique, as validated in in vivo mouse skin experiment.

Photoacoustic Tomography (PAT) is a novel biomedical imaging modality, whose reconstructed image is based on the target responds of the instantaneous pulse laser excitation. The target emits photoacoustic (PA) signal upon the laser impulse excitation, which contains the information of light absorption of the target. To reconstruct a high quality image of PAT, recovering the full bandwidth of the PA signal is necessary. While practical transducers cannot cover the full bandwidth of the PA signal, and has low sensitivity for ultralow frequency PA signal that induce the PA image distortion. In this study, a broadband PA signal enhancement method with morphological frequency convolution is proposed to recover PA signal. From the original reconstructed PA image frequency analyses, we get the convolution kernels and process the PA signal. The recovered full-bandwidth signal reconstructed the PA image more realistic and with less distortion.

Photoacoustic tomography (PAT) reconstruction with linear transducer arrays suffers from limited view artifacts, which impairs the reconstruction accuracy. Here, we introduce a modified Tikhonov regularization method to include vascular map obtained by Ultrasound localized microscopy (ULM) as a spatial prior in PAT reconstruction. We suggest an approach based on L-curve and Pearson correlation map to guide the selection of optimal regularization parameters. Simulation results suggest that spatial prior-based Tikhonov regularization can effectively address the limited view artifacts of PAT reconstruction with linear transducer arrays, paving the way of integrating PAT with ULM to enhance reconstruction accuracy in limited-view PAT.

The monitoring of cardiopulmonary functions is essential to diagnose various heart diseases. Moreover, with the spread of the novel coronavirus which is particularly fatal to human life due to ‘silent hypoxia’, the monitoring of cardiopulmonary is being more and more important. We here demonstrate a multimodal necklace capable of monitoring blood oxygenation but also blood flow rate, velocity, and possibly blood pressure. The necklace consists of pulse oximeter sensors and single-element ultrasound transducers. The estimation of a pulse wave velocity (PWV), which is highly correlated with blood pressure, is investigated by exploiting the pulse oximeter sensor and ultrasound transducer in this study. The developed multimodal necklace was evaluated through in vivo study. The results showed that both the chemical and mechanical information of cardiopulmonary function can be monitored with low hardware complexity and resource using the multimodal necklace.

In photoacoustic microscopy (PAM), the ultrasound transducer plays a critical role in detecting the PA signals. However, conventional ultrasound transducers are optically opaque, which could hinder the effective delivery of the excitation laser onto the target. Recently, optically-transparent ultrasound transducers have been investigated to address this issue. Nevertheless, the transparent transducers demonstrated so far have either a small numerical aperture (NA) or narrow bandwidth, which limits their acoustic focal spot sizes and therefore achievable spatial resolutions. In this paper, we report a new focused transparent polyvinylidene fluoride (PVDF) transducer with a high NA of 0.64 and a wide acoustic pulseecho bandwidth of 120%. Experiment characterization shows that it has an acoustic center frequency and bandwidth of 36 MHz and 44 MHz, respectively. The acoustic focal diameter and zone are 37.8 μm and 210 μm, respectively. With the new transparent transducer, dual-modal acoustic-resolution PAM (AR-PAM) and pulse-echo ultrasound microscopy (PEUSM) have been demonstrated with a target consisting of black-ink-filled polyimide tubing buried in chicken breast at different depths. The imaging results show that both the (acoustic) lateral and axial resolutions can be maintained even at a penetration depth of larger than 3 mm.

Tissue mechanics have been widely studied for the past two decades because they are significantly associated with disease states. The variations of mechanical properties in soft tissues are considerable indicators used for clinical diagnosis and disease monitoring. Optical coherence elastography (OCE) has been extensively developed to characterize the mechanical properties of various tissues. However, these methods are generally based on time-domain data and measure the time-offlight of the localized shear wave propagations. Here, we propose a method to evaluate phase velocity in four-dimensional (4D) space (x, y, z, f), called 4D-OCE phase velocity, and applied it to a heterogeneous phantom with a 4 mm diameter inclusion. A 7.5 MHz highly focused transducer transmitting a toneburst of 500 μs was used to provide an acoustic radiation force (ARF) for transient elastography. A customized 4D acquisition pattern was developed under Microsoft Visual C++ 2019 development environment. The 3D-OCE group velocity was reconstructed to compare with 4D-OCE phase velocity as cross-verification. The experimental result from the heterogeneous phantom showed that 4D-OCE phase velocity is capable of accurately reconstructing a 4D-OCE phase velocity map and provides good contrast between two gelatin materials with different concentrations, 7% versus 14%. The proposed 4D-OCE phase velocity can provide further information to better understand the delicate change of mechanical properties of various biological tissues in each voxel over a range of temporal frequencies.

In the development of label-free and real-time optical biosensors, a straightforward and low-cost fabrication of the transducer is important, because it reduces costs and the complexity of the process. One possibility for such easy fabrication is electrospinning. It is a versatile and well-developed technique that allows the manufacturing of layers of nanofibers at a low cost with a Fabry-Perot cavity-based optical response when illuminated with visible light. In this research, the suitability of such layers for the development of label-free and real-time optical biosensors is studied. For such aim, the nanofibers were biofunctionalized in flow with antibodies against bovine serum albumin through an intermediate layer of protein A/G. Then, BSA was flowed at a concentration of 10 µg/ml as the target analyte. As a result, biofunctionalization and biodetection processes were optically monitored in real-time successfully, demonstrating the suitability of such a simple-to-fabricate transducer for the development of label-free and real-time optical biosensors. Furthermore, in comparison with other optical transducers that require complex nanofabrication techniques, electrospun nanofibers can be deposited over vast areas to create several transducers in a single batch and at a low cost.

We investigate the possibilities of improving performance of an acousto-optic imaging system operating in reflection mode geometry with linear ultrasound array and optodes in direct contact with a sample by using plane ultrasound waves instead of focused pulses. Differences in acoustic pressure field distributions for various transducer excitation patterns were determined numerically. Acousto-optic images of phantoms with optically absorbing inclusions were obtained experimentally by measuring laser speckle contrast decrease due to the light modulation by plane wave and focused ultrasound pulses. The light fluence rate maps reconstructed using plane wave imaging proved to be clearer and more distinct.

Photoacoustic (PA) computed tomography (PACT) combines the superiorities of both optical imaging and ultrasound imaging, which is based on the generation of acoustic signal (PA wave) by short pulsed laser light. However, in many applications, the sensor array can only partially enclose the target, resulting in limited-view setup and image reconstruction with severe artifacts. Standard reconstruction always induces artifacts using limited-view signals, which are influenced by limited angle coverage of transducers, finite bandwidth, and uncertain heterogeneous biological tissue. To address these issues, in this paper, a deep learning based approach is proposed to compensate the missing data due to limited view (e.g. only 90 degrees coverage). To acquire the missing data from the other 270 degrees’ view, we trained an end-to-end network to recover the limited-view PA data, which have been delayed to form a pressure map in region of interest.

Patient simulations can be a powerful tool to plan placement of photoacoustic imaging components for surgical guidance. We previously used compressional-wave-only simulations to identify optimal acoustic windows for transcranial photoacoustic imaging. Elastic simulations, which include both compressional and shear waves, are expected to more accurately represent the physical transcranial acoustic process. However, elastic simulations are timing-consuming and memory intensive. This paper contains a comparison of compressional and elastic wave simulations to determine which option is more suitable for preoperative surgical planning. Compressional and elastic photoacoustic k-Wave simulations were performed based on a CT volume of a human cadaver head. Photoacoustic sources were placed in the locations of the internal carotid arteries and likely positions of neurosurgical instrument tips. Transducers received signals from three acoustic windows (i.e., the ocular, nasal, and temporal regions). Target visibility, image-based target size estimates, and target-to-instrument distances were measured using the generalized contrast-to-noise ratio, resolution, and relative source distances, respectively, for each simulation method. The generalized contrast-to-noise ratio and resolution measurements were equivalent between compressional and elastic simulations. Relative source distance measurements were within 0.1 mm of the true distances. These results indicate that it is sufficient to utilize the less time-consuming, less memory-intensive compressional wave simulations for presurgical planning.

Photoacoustic imaging offers “x-ray vision” to see beyond tool tips and underneath tissue during surgical procedures, yet no ionizing x-rays are required. Instead, optical fibers and acoustic receivers enable photoacoustic sensing of major structures – like blood vessels and nerves – that are otherwise hidden from view. The process is initiated by delivering laser pulses through optical fibers to illuminate regions of interest, causing an acoustic response that is detectable with ultrasound transducers. Beamforming is then implemented to create a photoacoustic image. In this talk, I will highlight novel light delivery systems, new spatial coherence beamforming theory, deep learning alternatives to beamforming, and robotic integration methods, each pioneered by the Photoacoustic and Ultrasonic Systems Engineering (PULSE) Lab to enable an exciting new frontier of photoacoustic-guided surgery. This new paradigm has the potential to eliminate the occurrence of major complications (e.g., excessive bleeding, paralysis, accidental patient death) during a wide range of delicate surgeries and procedures, including neurosurgery, cardiac catheter-based interventions, liver surgery, spinal fusion surgery, hysterectomies, biopsies, and teleoperative robotic surgeries.

Ultrasound transducers used in photoacoustic imaging are bandlimited and have a limited detection angle, which degrades the reconstructed image quality. One way to address this problem is to have transducers with multiple frequency bands with acquisition around the sample. This approach is expensive and it is not feasible for systems with a handheld probe using a linear transducer array. In this work, we aim to develop a deep learning method for photoacoustic reconstruction from bandlimited and limited-view data. We have developed a Generative Adversarial Networks (GANs)-based framework conditioned with a photoacoustic measurement for image reconstruction. In this way, the transducer used in the measurement can be incorporated and the generator trying to compensate for the limited data problem. We have developed the model for a handheld photoacoustic system using a linear transducer array with 128 elements having a center frequency of 7MHz and -6dB bandwidth from 4-10 MHz. We trained the network using simulated blood vessel images and tested it on in vivo measurements from the human forearm. We have compared the reconstructed images using the proposed method with the time-reversal on simulated data for detection using a bandlimited and directional transducer and compared it using the ground truth. Further, we compare our results to the in vivo images from the system which uses a delay and sum algorithm. The results from both simulations and experiments show that the proposed approach can remove bandlimited and limited view artifacts and can achieve a better image quality.

The advancement in bio-engineering technology has enabled tissues to be artificially cultivated from human cells, providing the opportunity to model disease and discover potential treatments 1 . Blood vessel is an important category of human tissues that can be artificially engineered to facilitate the development of treatment plans for vascular diseases. The growth of tissue engineered blood vessels (TEBVs) is a costly procedure, and effective quality control during the growing process could help reduce waste and optimize the cultivation process. Imaging technologies, such as optical coherence tomography5,6 (OCT), have been applied to obtain cross-sectional images of TEBVs, which could be used as a nondestructive method to assess blood vessel during cultivation. Ultrasound (US) imaging has been widely accepted in clinical practice due to its real-time imaging capacity and zero radiation emission; and compared to optics-based imaging modality it is more accessible financially. We implemented an US computer tomography (USCT) based monitoring system on assisting quality control in TEBV growth. In this prototype, a single element transducer is placed in a circular stand that rotates around the TEBV bioreactor to collect A-lines from different angles. Mechatronics systems are used to actuate the transducer for circular motion. A circular back-projection method is used in image reconstruction. Experiments were carried out with point phantom and the bioreactor to validate the imaging functionality of the prototype. Reconstructed images provide validation to the feasibility of using USCT to monitor the growth of TEBV growth.

Electroporation is a technique that uses short-duration (nanosecond to microsecond) high-voltage electric pulses to create temporary pores in cell membranes or irreversibly destroys target cells for cancer treatment. The versatility of electroporation makes the technique ideal for direct drug delivery and cancer treatment. Electroacoustic tomography (EAT) is a novel imaging modality for electroporation treatment monitoring, that utilizes the existing energy deposited by highvoltage electrical fields created in the electroporation process. In EAT, ultrasound waves are generated by the deposited electric potential energy and captured by different configurations of ultrasound transducers. After being captured, the ultrasound information is used to reconstruct the geometric information of the electric field distribution in the target medium. In this work, we demonstrate the feasibility of electroacoustic tomography (EAT) by creating a 2D reconstruction of an electric field in the water. A custom high-voltage electric pulse generating device was made for delivering nanosecond duration pulses in water through two electrodes. A 500Khz ultrasound transducer was placed near the electrodes and rotated to capture the acoustic information from 180 positions. The corresponding 2D reconstruction of the electric field in water was completed by using filtered back-projection algorithm. The successful reconstruction of the electrical field in water marks the important step of EAT development for in-situ electroporation monitoring.

Cerebrovascular and cardiovascular diseases such as stroke and coronary artery disease show a significant number of cases with a high mortality rate. Early detection of risk factors is important to prevent cerebrovascular and cardiovascular diseases. Measurements of carotid artery stenosis, blood flow rate, and the wall thickness of vessels by 2D and Doppler mode ultrasound are preferred choices due to advantages of their easy access, non-invasiveness, and safety. However, the current ultrasound imaging system with handheld type probes is not suitable for continuous monitoring and imaging, and the manual measurement is required by qualified personnel at a given time interval. Therefore, it is not an ideal solution for collecting continuous time-series data. We developed a 32-element, patch-type linear array transducer with a small footprint of 11.73 mm x 8 mm, which is an acceptable size to be attached over the carotid artery in the neck area. We evaluated the performance of the developed array transducer using the pulse-echo system and obtained its representative center frequency of 4.5 MHz, bandwidth (-6 dB) 64%, and sensitivity -47 dB. We also implemented a compact tabletop ultrasound system capable of 2D-mode real-time imaging of carotid artery and Doppler measurement of blood flow. In addition, with the tissue-mimicking phantom, we evaluated the performance of the developed system by collecting 2D images and Doppler spectrogram. The -6 dB lateral resolutions of the ultrasound system were 0.76, 0.61, and 1.33 mm at 15, 25, and 35 mm, respectively, and the peak velocity of the Doppler signal was close to 100 cm/s.

The backscatter coefficient (BSC) quantifies the frequency-dependent reflectivity of tissues. Accurate estimation of the BSC requires knowledge of the attenuation coefficient slope (ACS) of tissues in the beam path between the transducer and the insonified region of interest, namely, the total attenuation. In this study, the total attenuation is calculated as the cumulative sum of values of a local attenuation map devised using full angular spatial compounding (FASC). The BSC was parameterized through the integrated backscatter coefficient (iBSC) obtaining iBSC maps. Experimental validation of the proposed approach consisted of scanning two cylindrical physical phantoms with off-centered inclusions having different ACS and BSC values than the background. Additional iBSC maps were computed assuming an uniform ACS map of 0.5 dB/cm/MHz (which is a value assumed for soft tissues) instead of the FASC-ACS map. Finally a iBSC map was obtained using an ideal ACS map formed with ground truth ACS values and knowledge of inclusion true position. The results were comparable when using the FASC-ACS map or the ideal ACS map in term of inclusion detectability and estimation accuracy. The use of the uniform ACS map resulted in some cases with very high fractional error (>;9 dB), which highlights the relevance of accurate compensation for total attenuation. These results suggest that BSCs can be reliably estimated using total attenuation compensation from FASC-ACS maps.

Ultrasonic transducer is a sensor that realizes the mutual conversion of ultrasonic and electrical signals, and it is widely used in quality inspection, biomedical imaging and other fields. Commonly used ultrasonic transducers have a small detection range and low sensitivity due to the diffraction of sound waves. Focused transducers are used to improve detection sensitivity. Unfortunately, focused transducers have narrow depth of field. Here, we developed a Bessel ultrasonic transducer for large depth of field by using conical acoustic lens. An acoustic lens is attached to a unfocused ultrasonic. And the acoustic lens is a cuboid prism with a concave cone on the bottom, made of fused silica. Similar to an axicon that can generate a Bessel beam, the Bessel ultrasonic transducer can produce nondiffracting Bessel ultrasonic beams. Therefore, extended depth of field with uniformly high resolution and high detection sensitivity can be obtained. We used COMSOL to simulate the transmission of ultrasonic field of the designed conical acoustic lens, and compare it with the spherical focused ultrasonic transducer. The results show that the depth of field of the Bessel ultrasonic transducer is about 8 times that of the conventional spherical focused ultrasonic transducer. And the depth of field of the Bessel ultrasonic transducer can be further adjusted by adjusting the cone angle of the conical acoustic lens. The Bessel ultrasonic transducer will help improve the capabilities of the ultrasound probe and expand its application range. For example, an ultrasonic probe with a large depth of field will expand the imaging depth of photoacoustic microscopy and enhance its ability in non-destructive testing.