The Use of Phononic Crystals to Design Piezoelectric Power Transducers

It was recently proposed that the lateral resonances around the working resonance band of ultrasonic piezoelectric sandwich transducers can be stopped by a periodic array of circular holes drilled along the main propagation direction (a phononic crystal). In this work, the performance of different transducer designs made with this procedure is tested using laser vibrometry, electric impedance tests and finite element models (FEM). It is shown that in terms of mechanical vibration amplitude and acoustic efficiency, the best design for physiotherapy applications is when both, the piezoceramic and an aluminum capsule are phononic structures. The procedure described here can be applied to the design of power ultrasonic devices, physiotherapy transducers and other external medical power ultrasound applications where piston-like vibration in a narrow band is required.We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI).J.L.A. wishes to thank DGAPA-UNAM-PAPIIT for financial support through grant IN110817. F.M. wishes to thank to CICYT DPI2013-46915-C2-1-R and DPI2016-80254-R support. Finally, F.M. and J.L.A. thank the “Programa de Movilidad Académica de la Coordinación de la Investigación Científica-UNAM

Contactless acoustic micro/nano manipulation:a paradigm for next generation applications in life sciences

Acoustic actuation techniques offer a promising tool for contactless manipulation of both synthetic and biological micro/nano agents that encompass different length scales. The traditional usage of sound waves has steadily progressed from mid-air manipulation of salt grains to sophisticated techniques that employ nanoparticle flow in microfluidic networks. State-of-the-art in microfabrication and instrumentation have further expanded the outreach of these actuation techniques to autonomous propulsion of micro-agents. In this review article, we provide a universal perspective of the known acoustic micromanipulation technologies in terms of their applications and governing physics. Hereby, we survey these technologies and classify them with regards to passive and active manipulation of agents. These manipulation methods account for both intelligent devices adept at dexterous non-contact handling of micro-agents, and acoustically induced mechanisms for self-propulsion of micro-robots. Moreover, owing to the clinical compliance of ultrasound, we provide future considerations of acoustic manipulation techniques to be fruitfully employed in biological applications that range from label-free drug testing to minimally invasive clinical interventions

Photoacoustic imaging in biomedicine

Photoacoustic imaging (also called optoacoustic or thermoacoustic imaging) has the potential to image animal or human organs, such as the breast and the brain, with simultaneous high contrast and high spatial resolution. This article provides an overview of the rapidly expanding field of photoacoustic imaging for biomedical applications. Imaging techniques, including depth profiling in layered media, scanning tomography with focused ultrasonic transducers, image forming with an acoustic lens, and computed tomography with unfocused transducers, are introduced. Special emphasis is placed on computed tomography, including reconstruction algorithms, spatial resolution, and related recent experiments. Promising biomedical applications are discussed throughout the text, including (1) tomographic imaging of the skin and other superficial organs by laser-induced photoacoustic microscopy, which offers the critical advantages, over current high-resolution optical imaging modalities, of deeper imaging depth and higher absorptioncontrasts, (2) breast cancerdetection by near-infrared light or radio-frequency–wave-induced photoacoustic imaging, which has important potential for early detection, and (3) small animal imaging by laser-induced photoacoustic imaging, which measures unique optical absorptioncontrasts related to important biochemical information and provides better resolution in deep tissues than optical imaging

Laser-interferometric analysis of surface acoustic wave resonators

The research work described in this Thesis concentrates on studying surface acoustic wave (SAW) resonators, in particular resonators which utilize the leaky surface acoustic wave (LSAW) mode. Such resonators constitute building blocks for radio-frequency SAW bandpass filters, which are widely employed in modern cordless and cellular telecommunication systems. The number of radio frequency SAW filters produced presently exceeds 3 billion per year. The work is carried out with an optical Michelson laser interferometer developed at the Materials Physics Laboratory specifically for the purpose of studying SAW components. In the course of this work the interferometer was equipped with a high-speed photodetector and state-of-the-art detection electronics, enabling the measurement of surface vibrations at frequencies as high as 2 GHz with amplitudes on the order of a few picometers. Furthermore, the setup was equipped with high-precision motorized scanning stages and computer control in order to facilitate automatically performed two-dimensional scans with a large number of scanning points and measuring speeds up to 50 000 points per hour. The optical setup features a spatial resolution better than one micrometer, enabling measurement of surface waves with wavelengths down to 2 micrometers. The interferometer can be used for analysis of surface acoustic wave devices as well as for thin-film bulk acoustic wave resonators and radio-frequency microelectromechanical systems (RF-MEMS). Laser-interferometric measurements were performed on LSAW resonators and filters on rotated Y-cut lithium tantalate (LiTaO3). As a result, an unexpected acoustic field distribution was observed. Further measurements and simulations showed that the observed field distributions resulted from LSAWs escaping outside the resonator into the busbars. This acoustic loss mechanism can significantly degrade the performance of an LSAW filter. The obtained results have been acknowledged by SAW filter manufacturers in Japan and in Europe. In addition, measurements of bulk acoustic wave (BAW) radiation from LSAW resonators were carried out. Such radiation is inherent for LSAW resonators. Theoretical models and numerical simulations characterizing the phenomenon exist but very few direct measurements have been reported. Here, direct measurement results of BAW radiation fields generated by an LSAW resonator on LiTaO3 are reported revealing both fast shear and slow shear bulk waves. Furthermore, two coupling mechanisms, backscattering and direct excitation, were identified. Such information can be used in the development of more accurate simulation models.reviewe

Piezosähköisesti tuotetun äänen eteneminen nesteellä täytetyssä putkessa

This thesis studies the transmission of piezoelectrically induced sound in a liquid-filled elastic tube. This type of sound transmission would be useful in functional Magnetic Resonance Imaging (fMRI), in which the strong magnetic fields prevent the use of typical electromagnetic sound sources. The liquid would act as hearing protection against powerful fMRI noise, while sound would be transmitted through the liquid to the test subject’s eardrum. In order to test this idea, a proof-of-concept measurement system was built including a waveguide, a tube and a sensor. The purpose of the experiment was to measure sound transmission through the tube. PVC tubes filled with viscous emulsion and water were measured. The results indicate that the pressure release-walled PVC tube and the liquid form a coupled system with complex vibrational behaviour including longitudinal and transverse propagation modes. More research on the topic is required to determine whether or not the quality of sound transmission is sufficient for fMRI use.Tässä diplomityössä tutkitaan pietsosähköisesti tuotetun äänen etenemistä nesteellä täytetyssä elastisessa putkessa. Tämän kaltainen äänen välittyminen olisi hyödyllistä toiminnallisessa magneettikuvauksessa (fMRI), jossa voimakkaat magneettikentät estävät tyypillisten sähkömagneettisten äänilähteiden käytön. Neste voisi toimia kuulonsuojauksena fMRI-laitteen melua vastaan samalla, kun ääni kulkisi koehenkilön tärykalvolle nesteen kautta. Idean kokeilemiseksi rakennettiin testilaitteisto aaltojohdosta, putkesta ja sensorista. Kokeen tarkoituksena oli mitata äänen etenemistä putkessa. Vedellä ja viskoosilla emulsiolla täytettyjä PVC-putkia mitattiin. Tulokset viittaavat siihen, että äänenpaineen vaikutuksesta muotoaan muuttava putki ja neste muodostavat monimutkaisen yhteen kytkeytyneen järjestelmän, jossa ääni etenee sekä pitkittäisenä, että poikittaisena aaltona. Lisätutkimusta tarvitaan, jotta saadaan selville äänenlaadun riittävyys fMRI-käytössä

Application of laser methods for identification of authenticity of documents fabricated from thermoplastic composite material

Processes of globalization and integration are pervasive all over the world, and rapid innovation of advanced transportation systems resulted in enormous increase in number of persons travelling cross-border. Normally, persons crossing the border are checked at the first control line. Therefore, application of innovative methods that allow identification of partial alterations in a document or a fully counterfeit document, for initial checking of documents remains a relevant issue. The holographic interferometry represents one of the non-destructive control methods applicable for document check that enables assessment of defects in the entire area of a document being checked. This paper presents validation of the real-time method of holographic interferometry used for document check as well as parameters of a holographic setup, description of document investigation and analysis of the obtained finding

Modeling of ultrasonic scattering experiments with applications to system and transducer characterization

The voltage signal output by the receiver electronics, which represents the observable quantity in an ultrasonic scattering experiment, is written as a product, in the frequency domain, of two factors: the system efficiency and the scattering coefficient. The system efficiency represents the combined electrical properties of both the generator and receiver electronics and is a function of frequency only. The scattering coefficient represents the acoustic nature of the experiment (the radiation, propagation, scattering and reception of ultrasonic waves) and depends on the distributed field properties of the transducers involved and their locations and orientations, on the number and type of scattering obstacles and their locations and orientations, on the acoustic properties of the media through which the waves travel, and on the nature and shape of any interfaces through which the waves pass. Based on a generalized principle of electroacoustic reciprocity, formulae are developed for the evaluation of the scattering coefficient. The most general of these involve an integration over either the volume or the surface of the scattering obstacle. More specific formulae are also developed which express the scattering coefficient in terms of either the spherical wave transition matrix or the plane wave scattering amplitude of the obstacle;In order to demonstrate the use of the formulae developed, the calculation of the scattering coefficient is considered for two common ultrasonic scattering experiments. The first experiment involves the pulse-echo scattering from an infinite, flat elastic plate immersed in water. This arrangement is often used for the measurement of the velocity and attenuation of elastic waves, and also as a reference experiment for the determination of the system efficiency. The second experiment involves the pulse-echo scattering from an elastic sphere immersed in water. Particular attention is given to the specular reflection component of the scattering, which is demonstrated to be approximately equivalent to a point measurement of the pressure field radiated by the transducer. This approximation is subsequently used as the basis for obtaining experimental data for transducer characterization. The characterization itself is based on expanding in a set of basis functions, each weighted by an unknown coefficient, the normal velocity profile across the plane flush with the face of the probe. Values for the coefficients are obtained by determining the best fit between the experimental pressure data and the pressure calculated from the assumed velocity profile. Results are presented for two commercially manufactured immersion transducers, one planar (unfocused) and the other focused