Linear optoacoustic underwater communication

The linear mechanism for optical-to-acoustic energy conversion is explored for optoacoustic communication from an in-air platform or surface vessel to a submerged vessel such as a submarine or unmanned undersea vehicle. The communication range that can be achieved is addressed. A number of conventional signals used in underwater acoustic telemetry applications are shown to be capable of being generated experimentally through the linear optoacoustic regime conversion process. These results are in agreement with simulation based on current theoretical models. A number of practical issues concerning linear optoacoustic communication are addressed that lead to a formulation of a linear-regime optoacoustic communication scheme. The use of oblique laser beam incidence at the air-water interface to obtain considerable in-air range from the laser source to the in-water receiver is addressed. Also, the effect of oblique incidence on in-water range is examined. Next, the optimum and suboptimum linear optoacoustic sound-generation techniques for selecting the optical wavelength and signaling frequency for optimizing in-water range are addressed and discussed. Optoacoustic communication techniques employing M-ary frequency shift keying and multifrequency shift keying are then compared with regard to communication parameters such as bandwidth, data rate, range coverage, and number of lasers employed.     

Focusing with an optoacoustic transducer

A prototype of an ultrasonic transducer has been developed that uses an optical input to control the ultrasonic output. This transducer is called an optoacoustic transducer (OAT) and provides an ultrasonic pattern that is spatially similar to the optical pattern used to illuminate it. When a focus-inducing optical pattern, such as a zone plate, is used, an acoustic focus is achieved. The success of this procedure depends on the use of amplitude-modulated light at the input and on filtering the received signal to eliminate the primary frequency. This provides an increase, from 30 dB to 70 dB, in the ratio of acoustic pressure in the illuminated regions to that in the dark regions. The prototype operates at 2.8 MHz and has been used to provide a good acoustic focus in water. A 3-dB beamwidth of 3.5 mm was measured at a range of 92 mm. The construction techniques and materials used are discussed.     

Characterization of threshold-induced phenomena in deterministic driven devices

In the field of measurement nonlinear behavior is typical of a large set of sensors (mechanical, electrical, pneumatic, and so on). In several devices, SQUID and piezoelectric sensors being very well-known examples, the nonlinearity is strictly correlated to the hysteresis phenomenon, which can be described by introducing the quartic double well (QDW) potential in the system model. The analysis addresses the influence of potential characteristics on the performance of hysteretic measuring devices. A Brownian system with a QDW potential is used as a general prototype of hysteretic phenomena. This paper applies to the general class of hysteretic devices forced with low-amplitude signals and gives suitable outlines for the design of several measuring devices.     

Characterization of ZnO-degraded varistors used in high-tension devices

The effects of the degradation process on the structural, microstructural and electrical properties of ZnO-based varistors were analyzed. Rietveld refinement showed that the BiO_2−x phase is affected by the degradation process. Besides the changes in the spinel phase, the degradation process also affects the lattice microstrain in the ZnO phase. Scanning electron microscopy analysis showed electrode-melting failure, while wavelength dispersive X-ray spectroscopy qualitative analysis showed deficiency of oxygen species at the grain boundaries in the degraded samples. Atomic force microscopy using electrostatic mode force illustrated a decrease in the charge density at the grain boundaries of the degraded sample. Transmission electron microscopy showed submicrometric spinel grains embedded in a ZnO matrix, but their average grain size is smaller in the degraded sample than in the standard one. Long pulses appeared to be more harmful for the varistors’ properties than short ones, causing higher leakage current values. The electrical characteristics of the degraded sample are partially restored after heat treatment in an oxygen-rich atmosphere.     

Characterization of piezoelectric polymer composites for MEMS devices

Composite piezoelectric ceramics are important materials for transducer applications in medical diagnostic devices and MEMS devices. In micrometer scale the material properties of piezopolymers or piezoceramics do not coincide with that of bulk materials. The present work is aimed at simulating the material properties of piezoceramics and piezo-polymer composite thin films in the micrometer scale and then to determine the piezo-composite material properties. Piezoceramics have very high electromechanical coupling coefficient (k). But they have very high acoustic impedance and they are very brittle especially when thin films are fabricated. Piezopolymer like PVDF has low acoustic impedance and can be fabricated into thin films but it has very low k value and high dielectric losses. The combination of piezoceramics and piezopolymers form the piezocomposites, which have suitable material properties for transducer applications. The composites can have different connectivities. For 2?C2 composite, we can select two layers or a stack of PZT and PVDF layers. It is intended to determine the material properties both analytically and by simulation using computer simulation ANSYS software which implements finite element method (FEM). Although the simulation process presents approximate results, it can be verified from the large available experimental data from the literature with the simulated data.     

Optimal statistical approach to optoacoustic image reconstruction

An optimal statistical approach is applied to the task of image reconstruction in photoacoustics. The physical essence of the task is as follows: Pulse laser irradiation induces an ultrasound wave on the inhomogeneities inside the investigated volume. This acoustic wave is received by the set of receivers outside this volume. It is necessary to reconstruct a spatial image of these inhomogeneities. Developed mathematical techniques of the radio location theory are used for solving the task. An algorithm of maximum likelihood is synthesized for the image reconstruction. The obtained algorithm is investigated by digital modeling. The number of receivers and their disposition in space are arbitrary. Results of the synthesis are applied to noninvasive medical diagnostics (breast cancer). The capability of the algorithm is tested on real signals. The image is built with use of signals obtained in vitro. The essence of the algorithm includes (i) summing of all signals in the image plane with the transform from the time coordinates of signals to the spatial coordinates of the image and (ii) optimal spatial filtration of this sum. The results are shown in the figures.     

Clinical translation of optical and optoacoustic imaging

Macroscopic optical imaging has rather humble technical origins; it has been mostly implemented by photographic means using appropriate filters, a light source and a camera yielding images of tissues. This approach relates to human vision and perception, and is simple to implement and use. Therefore, it has found wide acceptance, especially in recording fluorescence and bioluminescence signals. Yet, the difficulty in resolving depth and the dependence of the light intensity recorded on tissue optical properties may compromise the accuracy of the approach. Recently, optical technology has seen significant advances that bring a new performance level in optical investigations. Quantitative real-time multi-spectral optical and optoacoustic (photoacoustic) methods enable high-resolution quantitative imaging of tissue and disease biomarkers and can significantly enhance medical vision in diagnostic or interventional procedures such as dermatology, endoscopy, surgery, and various vascular and intravascular imaging applications. This performance is showcased herein and examples are given to illustrate how it is possible to shift the paradigm of optical clinical translation.     

High frequency optoacoustic arrays using etalon detection

Two-dimensional phased arrays for high frequency (>30 MHz) ultrasonic imaging are difficult to construct using conventional piezoelectric technology. A promising alternative involves optical detection of ultrasound, where the array element size is defined by the focal spot of a laser beam. Element size and spacing on the order of a few microns are easily achieved, suitable for imaging at frequencies exceeding 100 MHz. We have previously shown images made from a receive-only, two-dimensional optoacoustic array operating at 10 to 50 MHz. The main drawback of optical detection has been poor sensitivity when compared with piezoelectric detection. In this paper, we explore a different form of optical detection demonstrating improved sensitivity and offering a potentially simple method for constructing two-dimensional arrays. Results from a simple experiment using an etalon sensor confirm that the sensitivity of etalon detection is comparable with piezoelectric detection. This paper concludes with a proposal for a high frequency optoacoustic array system using an etalon.     

Characterization of glass ionomers for surgical applications

The clinical use of glass ionomers is well established in the odontological field. In particular; (i) high biocompatibility (unincreased macrophages activity), and consquently no inflammation in post-operative course; (ii) total non-toxicity of components; (iii) absence of mutagenic consequence on osteoblasts; (iv) dimensional stability and absence of macroscopic changes after very long implantation times; (v) stability to water and biological compounds, make these materials attractive for further clinical applications. The high adhesion both to metallic or ceramic surfaces and bone tissue makes this materials excellently usable for the adjustment of bone defects. This goal necessitates suitable knowledge of the mechanical, chemical, physical and biological properties of commercial materials so that the most suitable product can be identified. The characterization of representative products of each of the principal classes of glass ionomers material is reported.     

Detection of ultrawide-band ultrasound pulses in optoacoustic tomography

A laser optoacoustic imaging system (LOIS) uses time-resolved detection of laser-induced pressure profiles in tissue in order to reconstruct images of the tissue based on distribution of acoustic sources. Laser illumination with short pulses generates distribution of acoustic sources that accurately replicates the distribution of absorbed optical energy. The complex spatial profile of heterogeneous distribution of acoustic sources can be represented in the frequency domain by a wide spectrum of ultrasound ranging from tens of kilohertz to tens of megahertz. Therefore, LOIS requires a unique acoustic detector operating simultaneously within a wide range of ultrasonic frequencies. Physical principles of an array of ultrawide-band ultrasonic transducers used in LOIS designed for imaging tumors in the depth of tissue are described. The performance characteristics of the transducer array were modeled and compared with experiments performed in gel phantoms resembling optical and acoustic properties of human tissue with small tumors. The amplitude and the spectrum of laser-induced ultrasound pulses were measured in order to determine the transducer sensitivity and the level of thermal noises within the entire ultrasonic band of detection. Spatial resolution of optoacoustic images obtained with an array of piezoelectric transducers and its transient directivity pattern within the field of view are described. The detector design considerations essential for obtaining high-quality optoacoustic images are presented.     

Characterization of flux-grown PZN-PT single crystals for high-performance piezo devices

Relaxor ferroelectric Pb(Zn(1/3)Nb(2/3))O(3-x)PbTiO(3) (PZN-PT) and Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3)(PMN-PT) single crystals are the potential candidates for future high-performance piezoelectric devices due to their exceptionally high dielectric and piezoelectric properties. Characterization on flux-grown PZN-PT single crystals of different orientations revealed that PZN-(6-7)%PT single crystals show good homogeneity in dielectric and electromechanical properties and composition. When poled in [001] direction, these crystals exhibit high longitudinal-mode properties with dielectric constant (K(T)) approximately equal to 7000, piezoelectric coefficients (d(33)) approximately equal to 2800 pC/N, and electromechanical coupling factors (k(33)) > or = 0.92. For [011]-cut crystals, optimally poled PZN-7%PT single crystal exhibits very high transverse-mode dielectric and piezoelectric properties with K(T) > or = 5000, d(32) approximately equal to -3800 pC/N and k(32) > or = 0.90. [011]- poled PZN 6%PT has d(32) approximately equal to -3000 pC/N and comparable k(32) and K(T) values. In comparison with melt-grown PMNPT single crystals, flux-grown PZN-PT single crystals show good compositional homogeneity, superior and consistent dielectric and electromechanical properties, and higher depolarization temperatures (TDP).     

Time-resolved optoacoustic measurement of absorption of light by inhomogeneous media

A method for measuring the absorption of light with optically turbid media is considered. The method is based on the registration of the temporal shape (leading-edge slope) of the developing optoacoustic signal in a medium that is absorbing a short laser pulse. Results of experiments with a Nd:YAG laser (10 ns) demonstrate the effectiveness of the method for both homogeneous and inhomogeneous optical media.     

基于无监督学习的高分辨光声重建

光声断层成像(Optoacoustic Tomography,OAT)是一种新兴的生物医学成像技术,在基础医学研究与临床实践中具有重要作用。针对现有光声断层成像空间分辨率较低的问题,提出了一种结合物理点扩散函数(Point Spread Function,PSF)模型和卷积神经网络(Convolutional Neural Network,CNN)的新型高分辨光声重建网络方法(Physical Attention U-Net,Phys-AU-Net)。该方法采用无监督学习策略,结合物理PSF模型和基于注意力机制的U-Net网络。其中,物理PSF模型用于完成对衍射受限机制的模拟,基于注意力机制的U-Net网络用于实现对高密度重叠吸收体图像的特征提取。在二者共同作用下,Phys-AU-Net突破了声衍射极限对于OAT成像空间分辨率的限制。实验结果表明,Phys-AU-Net能够有效实现对声衍射受限光声断层图像的高分辨重建,其性能相较于U-Net网络具有较大程度提升,在结构相似性指标(Structural Similarity,SSIM)方面提升了43.5%,在峰值信噪比(Peak Sign...     

Characterization of antiresonant reflecting optical waveguide devices by scanning near-field optical microscopy

Silicon-based antiresonant reflecting optical waveguide (ARROW) devices were studied by means of a scanning near-field optical microscope. Various structures such as a Y junction of a Mach-Zehnder interferometer and a directional optical coupler were characterized, showing the propagation of the light inside the devices simultaneously with the topography. Scattering on the splitting point of the Y junction was shown, as well as a partial coupling of the light between the two branches of the coupler. Measurements on the decay length of the evanescent field were also performed to study the use of the ARROW waveguide for sensor purposes.     

多光谱光声层析技术在肿瘤学中的应用进展

多光谱光声层析技术是一种新兴的光声成像技术,兼具光声断层扫描和多光谱成像的优点。该成像技术需要利用内源性和外源性光声成像对比剂进行成像。成像时,激光发射器发射多个波长的激光束照射组织,组织发生热弹性膨胀并产生超声波,将超声换能器接收的光声信号进行后处理,分解光谱信息并重建图像。目前,多光谱光声层析技术已广泛用于多种肿瘤的研究。文章着重介绍光声成像对比剂和多光谱光声层析技术的发展近况以及在临床转化中取得的研究进展。     

Experimental demonstration of multiple pulse nonlinear optoacoustic signal generation and control

Generating underwater acoustic signals from a remote, aerial location by use of a high-energy pulsed infrared laser has been demonstrated. The laser beam is directed from the air and focused onto the water surface, where the optical energy was converted into a propagating acoustic wave. Sound pressure levels of 185 dB re microPa (decibel re microPa) were consistently recorded under freshwater laboratory conditions at laser-pulse repetition rates of up to 1000 pulses/s. The nonlinear optoacoustic transmission concept is outlined, and the experimental results from investigation of the time-domain and frequency-domain characteristics of the generated underwater sound are provided. A high repetition rate, high-energy per pulse laser was used in this test under freshwater laboratory conditions. A means of deterministically controlling the spectrum of the underwater acoustic signal was investigated and demonstrated by varying the laser-pulse repetition rate.     

Characterization of phosphorus oxinitride (PON) gate insulators for InP metal-insulator-semiconductor devices

A new gate-insulating film consisting of phosphorus oxinitride (PON) was formed on an (n)InP surface by vapour transport technique. The substrate temperature was in the range of 280–350°C. The deposited films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS). The interfacial properties of phosphorus oxinitride/(n)InP metal-insulator-semiconductor were investigated. The minimum value of the interface states density distribution (D_it), evaluated from high-frequency capacitance-voltage (C-V) measurement was 1.2 × 10¹¹ eV⁻¹ cm⁻² at about 0.48 eV below the conduction band edge of Inp.     

Monte Carlo modeling of optoacoustic signals from human internal jugular veins

Monitoring of blood oxygenation, in particular, cerebral venous oxygenation, is necessary for management of a variety of life-threatening conditions. An optoacoustic technique can be used for noninvasive monitoring of blood oxygenation in blood vessels, including large veins. We calculated optoacoustic signals from a cylinder mimicking a blood vessel using a modified Monte Carlo code and analyzed their temporal profiles. The rate of decrease of the integrated optoacoustic signal at different wavelengths of incident near-infrared radiation was related to the effective attenuation coefficient of normally oxygenated venous blood. We obtained good correlation of this parameter with the blood effective attenuation coefficient in a wide spectral range that may be useful in providing an accurate and robust optoacoustic monitoring of blood oxygenation. We also estimated the accuracy of effective attenuation coefficient calculations.