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Special Issue "Ultrasonic Sensors and Transducers for Applications in Biology, Medicine and NDT"

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A special issue of Sensors (ISSN 1424-8220).

Deadline for manuscript submissions: closed (15 December 2014)

Special Issue Editor

Guest Editor
Prof. Dr. Xiaoning Jiang (Website)

North Carolina State University, 911 Oval Drive, Raleigh, NC 27695, USA
Fax: +919 515 7968
Interests: micro/nanofabrication of smart materials and structures; ultrasound sensors and transducers; ultrasound imaging, therapy and sensing; sensors and transducers for extreme environments

Special Issue Information

Dear Colleagues,

Ultrasound has profoundly affected today’s world in a broad range of technologies, including underwater sonar, industrial non-destructive testing (NDT), industrial sensing, precision actuation, material processing and manufacturing, medical imaging, medical therapy, biological sensing, drug delivery, etc. Ultrasonic sensors and transducers, as the core of ultrasound technologies, have been unprecedentedly challenged to meet a broad range of applications. This special issue aims to bring together recent research and development concerning novel ultrasonic sensors and transducers, as well as their applications in medicine, biology, and NDT.

Papers addressing a wide range of ultrasonic sensing and transduction innovations are sought, including but not limited to recent research and developments in the following areas:

  • ultrasonic sensing and transduction materials and structures
  • ultrasonic sensor and transducer design, fabrication, and characterization
  • ultrasound imaging
  • ultrasound therapy
  • ultrasonic biosensors
  • ultrasound in cell culturing and sensing
  • ultrasonic micro/nano-sensors
  • ultrasonic drug delivery
  • ultrasonic surgical tools
  • and other associated devices and applications
Both review articles and original research papers associated with acoustic/ultrasonic sensors, transducers and their applications in medicine, biology, and NDT are solicited. There is a particular interest in papers concerning applications of ultrasonic micro/nano-sensors and transducers in cell and tissue engineering; non-destructive, non-contact or minimally invasive interactions are preferred topics.

Prof. Dr. Xiaoning Jiang
Guest Editor

Submission

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. Papers will be published continuously (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are refereed through a peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Sensors is an international peer-reviewed Open Access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs).


Keywords

  • ultrasonic sensors
  • acoustic sensors
  • ultrasound transducers
  • micro/nano-fabrication
  • micro/nano-sensors
  • ultrasound imaging
  • ultrasound therapy
  • ultrasonic cell sensing
  • acoustic/ultrasound cell sorting
  • ultrasound/acoustic NDT

Published Papers (29 papers)

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Open AccessArticle Lower Extremity Joint Angle Tracking with Wireless Ultrasonic Sensors during a Squat Exercise
Sensors 2015, 15(5), 9610-9627; doi:10.3390/s150509610
Received: 12 December 2014 / Revised: 6 April 2015 / Accepted: 16 April 2015 / Published: 23 April 2015
Cited by 1 | PDF Full-text (1161 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents an unrestrained measurement system based on a wearable wireless ultrasonic sensor network to track the lower extremity joint and trunk kinematics during a squat exercise with only one ultrasonic sensor attached to the trunk. The system consists of an [...] Read more.
This paper presents an unrestrained measurement system based on a wearable wireless ultrasonic sensor network to track the lower extremity joint and trunk kinematics during a squat exercise with only one ultrasonic sensor attached to the trunk. The system consists of an ultrasound transmitter (mobile) and multiple receivers (anchors) whose positions are known. The proposed system measures the horizontal and vertical displacement, together with known joint constraints, to estimate joint flexion/extension angles using an inverse kinematic model based on the damped least-squares technique. The performance of the proposed ultrasonic measurement system was validated against a camera-based tracking system on eight healthy subjects performing a planar squat exercise. Joint angles estimated from the ultrasonic system showed a root mean square error (RMSE) of 2.85° ± 0.57° with the reference system. Statistical analysis indicated great agreements between these two systems with a Pearson’s correlation coefficient (PCC) value larger than 0.99 for all joint angles’ estimation. These results show that the proposed ultrasonic measurement system is useful for applications, such as rehabilitation and sports. Full article
Open AccessArticle Feasibility of Multiple Micro-Particle Trapping—A Simulation Study
Sensors 2015, 15(3), 4958-4974; doi:10.3390/s150304958
Received: 16 December 2014 / Revised: 14 January 2015 / Accepted: 10 February 2015 / Published: 27 February 2015
PDF Full-text (2842 KB) | HTML Full-text | XML Full-text
Abstract
Both optical tweezers and acoustic tweezers have been demonstrated for trapping small particles in diverse biomedical applications. Compared to the optical tweezers, acoustic tweezers have deeper penetration, lower intensity, and are more useful in light opaque media. These advantages enable the potential [...] Read more.
Both optical tweezers and acoustic tweezers have been demonstrated for trapping small particles in diverse biomedical applications. Compared to the optical tweezers, acoustic tweezers have deeper penetration, lower intensity, and are more useful in light opaque media. These advantages enable the potential utility of acoustic tweezers in biological science. Since the first demonstration of acoustic tweezers, various applications have required the trapping of not only one, but more particles simultaneously in both the axial and lateral direction. In this research, a method is proposed to create multiple trapping patterns, to prove the feasibility of trapping micro-particles. It has potential ability to electronically control the location and movement of the particles in real-time. A multiple-focus acoustic field can be generated by controlling the excitation of the transducer elements. The pressure and intensity of the field are obtained by modeling phased array transducer. Moreover, scattering force and gradient force at various positions are also evaluated to analyze their relative components to the effect of the acoustic tweezers. Besides, the axial and lateral radiation force and the trapping trajectory are computed based on ray acoustic approach. The results obtained demonstrate that the acoustic tweezers are capable of multiple trapping in both the axial and lateral directions. Full article
Figures

Open AccessArticle Enhanced Visualization of Fine Needles Under Sonographic Guidance Using a MEMS Actuator
Sensors 2015, 15(2), 3107-3115; doi:10.3390/s150203107
Received: 16 December 2014 / Accepted: 27 January 2015 / Published: 30 January 2015
Cited by 2 | PDF Full-text (1247 KB) | HTML Full-text | XML Full-text
Abstract
Localization of a needle tip is important for biopsy examinations in clinics. However, the needle tip is sometimes difficult to discern under the guidance of sonography due to its poor visibility. A mini actuator that radiates a low-intensity ultrasound wave was manufactured [...] Read more.
Localization of a needle tip is important for biopsy examinations in clinics. However, the needle tip is sometimes difficult to discern under the guidance of sonography due to its poor visibility. A mini actuator that radiates a low-intensity ultrasound wave was manufactured using micro-electro-mechanical system (MEMS) technology. Interference between the radiated and diagnostic ultrasound pulses was observed as bright lines in the B-mode ultrasound image, from which the mini actuator could be recognized with ease. Because the distance between the mini actuator and the needle tip is fixed, the needle tip can be determined despite its inconsistent appearance in the sonography. Both gel phantom and ex vivo tissue evaluation showed that the needle tip can be determined reliably utilizing the acoustic interference pattern. Full article
Open AccessArticle A Flexible Ultrasound Transducer Array with Micro-Machined Bulk PZT
Sensors 2015, 15(2), 2538-2547; doi:10.3390/s150202538
Received: 30 October 2014 / Accepted: 22 December 2014 / Published: 23 January 2015
Cited by 1 | PDF Full-text (1557 KB) | HTML Full-text | XML Full-text
Abstract
This paper proposes a novel flexible piezoelectric micro-machined ultrasound transducer, which is based on PZT and a polyimide substrate. The transducer is made on the polyimide substrate and packaged with medical polydimethylsiloxane. Instead of etching the PZT ceramic, this paper proposes a [...] Read more.
This paper proposes a novel flexible piezoelectric micro-machined ultrasound transducer, which is based on PZT and a polyimide substrate. The transducer is made on the polyimide substrate and packaged with medical polydimethylsiloxane. Instead of etching the PZT ceramic, this paper proposes a method of putting diced PZT blocks into holes on the polyimide which are pre-etched. The device works in d31 mode and the electromechanical coupling factor is 22.25%. Its flexibility, good conformal contacting with skin surfaces and proper resonant frequency make the device suitable for heart imaging. The flexible packaging ultrasound transducer also has a good waterproof performance after hundreds of ultrasonic electric tests in water. It is a promising ultrasound transducer and will be an effective supplementary ultrasound imaging method in the practical applications. Full article
Open AccessArticle Application of Wavelet Packet Entropy Flow Manifold Learning in Bearing Factory Inspection Using the Ultrasonic Technique
Sensors 2015, 15(1), 341-351; doi:10.3390/s150100341
Received: 29 October 2014 / Accepted: 16 December 2014 / Published: 26 December 2014
Cited by 2 | PDF Full-text (998 KB) | HTML Full-text | XML Full-text
Abstract
For decades, bearing factory quality evaluation has been a key problem and the methods used are always static tests. This paper investigates the use of piezoelectric ultrasonic transducers (PUT) as dynamic diagnostic tools and a relevant signal classification technique, wavelet packet entropy [...] Read more.
For decades, bearing factory quality evaluation has been a key problem and the methods used are always static tests. This paper investigates the use of piezoelectric ultrasonic transducers (PUT) as dynamic diagnostic tools and a relevant signal classification technique, wavelet packet entropy (WPEntropy) flow manifold learning, for the evaluation of bearing factory quality. The data were analyzed using wavelet packet entropy (WPEntropy) flow manifold learning. The results showed that the ultrasonic technique with WPEntropy flow manifold learning was able to detect different types of defects on the bearing components. The test method and the proposed technique are described and the different signals are analyzed and discussed. Full article
Open AccessArticle A Novel Ultrasound Technique for Detection of Osteochondral Defects in the Ankle Joint: A Parametric and Feasibility Study
Sensors 2015, 15(1), 148-165; doi:10.3390/s150100148
Received: 8 October 2014 / Accepted: 13 December 2014 / Published: 24 December 2014
Cited by 2 | PDF Full-text (2131 KB) | HTML Full-text | XML Full-text
Abstract
(Osteo)chondral defects (OCDs) in the ankle are currently diagnosed with modalities that are not convenient to use in long-term follow-ups. Ultrasound (US) imaging, which is a cost-effective and non-invasive alternative, has limited ability to discriminate OCDs. We aim to develop a new [...] Read more.
(Osteo)chondral defects (OCDs) in the ankle are currently diagnosed with modalities that are not convenient to use in long-term follow-ups. Ultrasound (US) imaging, which is a cost-effective and non-invasive alternative, has limited ability to discriminate OCDs. We aim to develop a new diagnostic technique based on US wave propagation through the ankle joint. The presence of OCDs is identified when a US signal deviates from a reference signal associated with the healthy joint. The feasibility of the proposed technique is studied using experimentally-validated 2D finite-difference time-domain models of the ankle joint. The normalized maximum cross correlation of experiments and simulation was 0.97. Effects of variables relevant to the ankle joint, US transducers and OCDs were evaluated. Variations in joint space width and transducer orientation made noticeable alterations to the reference signal: normalized root mean square error ranged from 6.29% to 65.25% and from 19.59% to 8064.2%, respectively. The results suggest that the new technique could be used for detection of OCDs, if the effects of other parameters (i.e., parameters related to the ankle joint and US transducers) can be reduced. Full article
Open AccessArticle Fabrication of a PMN-PT Single Crystal-Based Transcranial Doppler Transducer and the Power Regulation of Its Detection System
Sensors 2014, 14(12), 24462-24471; doi:10.3390/s141224462
Received: 18 June 2014 / Revised: 24 November 2014 / Accepted: 24 November 2014 / Published: 19 December 2014
PDF Full-text (1826 KB) | HTML Full-text | XML Full-text
Abstract
Doppler sonographic measurement of flow velocity in the basal cerebral arteries through the intact skull was developed using a pulsed Doppler technique and 2 MHz emitting frequency. Relaxor-based ferroelectric single crystals Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) were chosen [...] Read more.
Doppler sonographic measurement of flow velocity in the basal cerebral arteries through the intact skull was developed using a pulsed Doppler technique and 2 MHz emitting frequency. Relaxor-based ferroelectric single crystals Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) were chosen to be the piezoelectric transducer material due to their ultrahigh piezoelectric coefficients, high electromechanical coupling coefficients and low dielectric loss. The pulse-echo response of the transducer was measured using the conventional pulse-echo method in a water bath at room temperature. The −6 dB bandwidth of the transducer is 68.4% and the sensitivity is −17.4 dB. In order to get a good match between transducer and detection system, different transmission powers have been regulated by changing the impedance of the transmitting electric circuit. In the middle cerebral artery (MCA) measurement photograph results, as the transmission power is increasing, the detection results become clearer and clearer. A comparison at the same transmission power for different transducers shows that the detection photograph obtained by the crystal transducer was clearer than that obtained with a commercial transducer, which should make it easier for doctors to find the cerebral arteries. Full article
Open AccessArticle Influence of the Lift-Off Effect on the Cut-Off Frequency of the EMAT-Generated Rayleigh Wave Signal
Sensors 2014, 14(10), 19687-19699; doi:10.3390/s141019687
Received: 15 August 2014 / Revised: 14 October 2014 / Accepted: 15 October 2014 / Published: 22 October 2014
Cited by 3 | PDF Full-text (483 KB) | HTML Full-text | XML Full-text
Abstract
The electromagnetic acoustic transducer (EMAT), a non-contact NDT tool with large lift-off, is becoming an attractive method for detecting the cracks in the metal parts. However, the lift-off of the transducer has a direct effect on the feature that is used to [...] Read more.
The electromagnetic acoustic transducer (EMAT), a non-contact NDT tool with large lift-off, is becoming an attractive method for detecting the cracks in the metal parts. However, the lift-off of the transducer has a direct effect on the feature that is used to characterize the defects. A detailed investigation on the relationship between the feature and the lift-off of the EMAT is crucial in the detection process. This paper investigates the lift-off effect on the feature, cut-off frequency of EMAT in the Rayleigh wave. The study can be divided into two parts. Firstly, with a multi-field coupling environment, 2-D electromagnetic and wave generation EMAT models are built to simulate the interaction of the Rayleigh wave with the surface crack. Then, the lift-off effect on the cut-off frequency is investigated through simulation and experiment. Compared to the previous studies, it is found that lift-off would cause a negative result when the lift-off varies in the testing process. Besides, the calibration obtained from the tests at a random lift-off value can be used in other tests with any different lift off value provided that the lift-off is kept as a constant during the detection process. Full article
Open AccessArticle Implementation of a Rotational Ultrasound Biomicroscopy System Equipped with a High-Frequency Angled Needle Transducer — Ex Vivo Ultrasound Imaging of Porcine Ocular Posterior Tissues
Sensors 2014, 14(9), 17807-17816; doi:10.3390/s140917807
Received: 16 June 2014 / Revised: 10 September 2014 / Accepted: 15 September 2014 / Published: 24 September 2014
PDF Full-text (3782 KB) | HTML Full-text | XML Full-text
Abstract
The mechanical scanning of a single element transducer has been mostly utilized for high-frequency ultrasound imaging. However, it requires space for the mechanical motion of the transducer. In this paper, a rotational scanning ultrasound biomicroscopy (UBM) system equipped with a high-frequency angled [...] Read more.
The mechanical scanning of a single element transducer has been mostly utilized for high-frequency ultrasound imaging. However, it requires space for the mechanical motion of the transducer. In this paper, a rotational scanning ultrasound biomicroscopy (UBM) system equipped with a high-frequency angled needle transducer is designed and implemented in order to minimize the space required. It was applied to ex vivo ultrasound imaging of porcine posterior ocular tissues through a minimal incision hole of 1 mm in diameter. The retina and sclera for the one eye were visualized in the relative rotating angle range of 270° ~ 330° and at a distance range of 6 ~ 7 mm, whereas the tissues of the other eye were observed in relative angle range of 160° ~ 220° and at a distance range of 7.5 ~ 9 mm. The layer between retina and sclera seemed to be bent because the distance between the transducer tip and the layer was varied while the transducer was rotated. Certin features of the rotation system such as the optimal scanning angle, step angle and data length need to be improved for ensure higher accuracy and precision. Moreover, the focal length should be considered for the image quality. This implementation represents the first report of a rotational scanning UBM system. Full article
Open AccessArticle Non-Destructive Evaluation of Depth of Surface Cracks Using Ultrasonic Frequency Analysis
Sensors 2014, 14(9), 17146-17158; doi:10.3390/s140917146
Received: 12 June 2014 / Revised: 2 September 2014 / Accepted: 9 September 2014 / Published: 15 September 2014
Cited by 3 | PDF Full-text (1156 KB) | HTML Full-text | XML Full-text
Abstract
Ultrasonic is one of the most common uses of a non-destructive evaluation method for crack detection and characterization. The effectiveness of the acoustic-ultrasound Structural Health Monitoring (SHM) technique for the determination of the depth of the surface crack was presented. A method [...] Read more.
Ultrasonic is one of the most common uses of a non-destructive evaluation method for crack detection and characterization. The effectiveness of the acoustic-ultrasound Structural Health Monitoring (SHM) technique for the determination of the depth of the surface crack was presented. A method for ultrasonic sizing of surface cracks combined with the time domain and frequency spectrum was adopted. The ultrasonic frequency spectrum was obtained by Fourier transform technique. A series of test specimens with various depths of surface crack ranging from 1 mm to 8 mm was fabricated. The depth of the surface crack was evaluated using the pulse-echo technique. In this work, three different longitudinal waves with frequencies of 2.25 MHz, 5 MHz and 10 MHz were employed to investigate the effect of frequency on the sizing detection of surface cracks. Reasonable accuracies were achieved with measurement errors less than 7%. Full article
Open AccessArticle An Ultrasonic Contactless Sensor for Breathing Monitoring
Sensors 2014, 14(8), 15371-15386; doi:10.3390/s140815371
Received: 10 June 2014 / Revised: 2 August 2014 / Accepted: 5 August 2014 / Published: 20 August 2014
Cited by 7 | PDF Full-text (1587 KB) | HTML Full-text | XML Full-text
Abstract
The monitoring of human breathing activity during a long period has multiple fundamental applications in medicine. In breathing sleep disorders such as apnea, the diagnosis is based on events during which the person stops breathing for several periods during sleep. In polysomnography, [...] Read more.
The monitoring of human breathing activity during a long period has multiple fundamental applications in medicine. In breathing sleep disorders such as apnea, the diagnosis is based on events during which the person stops breathing for several periods during sleep. In polysomnography, the standard for sleep disordered breathing analysis, chest movement and airflow are used to monitor the respiratory activity. However, this method has serious drawbacks. Indeed, as the subject should sleep overnight in a laboratory and because of sensors being in direct contact with him, artifacts modifying sleep quality are often observed. This work investigates an analysis of the viability of an ultrasonic device to quantify the breathing activity, without contact and without any perception by the subject. Based on a low power ultrasonic active source and transducer, the device measures the frequency shift produced by the velocity difference between the exhaled air flow and the ambient environment, i.e., the Doppler effect. After acquisition and digitization, a specific signal processing is applied to separate the effects of breath from those due to subject movements from the Doppler signal. The distance between the source and the sensor, about 50 cm, and the use of ultrasound frequency well above audible frequencies, 40 kHz, allow monitoring the breathing activity without any perception by the subject, and therefore without any modification of the sleep quality which is very important for sleep disorders diagnostic applications. This work is patented (patent pending 2013-7-31 number FR.13/57569). Full article
Open AccessArticle Wave Dispersion and Attenuation on Human Femur Tissue
Sensors 2014, 14(8), 15067-15083; doi:10.3390/s140815067
Received: 30 May 2014 / Revised: 27 July 2014 / Accepted: 6 August 2014 / Published: 15 August 2014
Cited by 4 | PDF Full-text (1529 KB) | HTML Full-text | XML Full-text
Abstract
Cortical bone is a highly heterogeneous material at the microscale and has one of the most complex structures among materials. Application of elastic wave techniques to this material is thus very challenging. In such media the initial excitation energy goes into the [...] Read more.
Cortical bone is a highly heterogeneous material at the microscale and has one of the most complex structures among materials. Application of elastic wave techniques to this material is thus very challenging. In such media the initial excitation energy goes into the formation of elastic waves of different modes. Due to “dispersion”, these modes tend to separate according to the velocities of the frequency components. This work demonstrates elastic wave measurements on human femur specimens. The aim of the study is to measure parameters like wave velocity, dispersion and attenuation by using broadband acoustic emission sensors. First, four sensors were placed at small intervals on the surface of the bone to record the response after pencil lead break excitations. Next, the results were compared to measurements on a bulk steel block which does not exhibit heterogeneity at the same wave lengths. It can be concluded that the microstructure of the tissue imposes a dispersive behavior for frequencies below 1 MHz and care should be taken for interpretation of the signals. Of particular interest are waveform parameters like the duration, rise time and average frequency, since in the next stage of research the bone specimens will be fractured with concurrent monitoring of acoustic emission. Full article
Open AccessArticle Acoustic Devices for Particle and Cell Manipulation and Sensing
Sensors 2014, 14(8), 14806-14838; doi:10.3390/s140814806
Received: 15 June 2014 / Revised: 2 August 2014 / Accepted: 7 August 2014 / Published: 13 August 2014
Cited by 11 | PDF Full-text (32761 KB) | HTML Full-text | XML Full-text
Abstract
An emerging demand for the precise manipulation of cells and particles for applications in cell biology and analytical chemistry has driven rapid development of ultrasonic manipulation technology. Compared to the other manipulation technologies, such as magnetic tweezing, dielectrophoresis and optical tweezing, ultrasonic [...] Read more.
An emerging demand for the precise manipulation of cells and particles for applications in cell biology and analytical chemistry has driven rapid development of ultrasonic manipulation technology. Compared to the other manipulation technologies, such as magnetic tweezing, dielectrophoresis and optical tweezing, ultrasonic manipulation has shown potential in a variety of applications, with its advantages of versatile, inexpensive and easy integration into microfluidic systems, maintenance of cell viability, and generation of sufficient forces to handle particles, cells and their agglomerates. This article briefly reviews current practice and reports our development of various ultrasonic standing wave manipulation devices, including simple devices integrated with high frequency (>20 MHz) ultrasonic transducers for the investigation of biological cells and complex ultrasonic transducer array systems to explore the feasibility of electronically controlled 2-D and 3-D manipulation. Piezoelectric and passive materials, fabrication techniques, characterization methods and possible applications are discussed. The behavior and performance of the devices have been investigated and predicted with computer simulations, and verified experimentally. Issues met during development are highlighted and discussed. To assist long term practical adoption, approaches to low-cost, wafer level batch-production and commercialization potential are also addressed. Full article
Open AccessArticle A Catheter-Based Acoustic Interrogation Device for Monitoring Motility Dynamics of the Lower Esophageal Sphincter
Sensors 2014, 14(8), 14700-14711; doi:10.3390/s140814700
Received: 13 June 2014 / Revised: 2 August 2014 / Accepted: 5 August 2014 / Published: 12 August 2014
Cited by 1 | PDF Full-text (607 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents novel minimally-invasive, catheter-based acoustic interrogation device for monitoring motility dynamics of the lower esophageal sphincter (LES). A micro-oscillator actively emitting sound wave at 16 kHz is located at one side of the LES, and a miniature microphone is located [...] Read more.
This paper presents novel minimally-invasive, catheter-based acoustic interrogation device for monitoring motility dynamics of the lower esophageal sphincter (LES). A micro-oscillator actively emitting sound wave at 16 kHz is located at one side of the LES, and a miniature microphone is located at the other side of the sphincter to capture the sound generated from the oscillator. Thus, the dynamics of the opening and closing of the LES can be quantitatively assessed. In this paper, experiments are conducted utilizing an LES motility dynamics simulator. The sound strength is captured by the microphone and is correlated to the level of LES opening and closing controlled by the simulator. Measurements from the simulator model show statistically significant (p < 0.05) Pearson correlation coefficients (0.905 on the average in quiet environment and 0.736 on the average in noisy environment, D.O.F. = 9). Measuring the level of LES opening and closing has the potential to become a valuable diagnostic technique for understanding LES dysfunction and the disorders associated with it. Full article
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Open AccessArticle Dual-Element Transducer with Phase-Inversion for Wide Depth of Field in High-Frequency Ultrasound Imaging
Sensors 2014, 14(8), 14278-14288; doi:10.3390/s140814278
Received: 4 June 2014 / Revised: 14 July 2014 / Accepted: 28 July 2014 / Published: 5 August 2014
PDF Full-text (3938 KB) | HTML Full-text | XML Full-text
Abstract
In high frequency ultrasound imaging (HFUI), the quality of focusing is deeply related to the length of the depth of field (DOF). In this paper, a phase-inversion technique implemented by a dual-element transducer is proposed to enlarge the DOF. The performance of [...] Read more.
In high frequency ultrasound imaging (HFUI), the quality of focusing is deeply related to the length of the depth of field (DOF). In this paper, a phase-inversion technique implemented by a dual-element transducer is proposed to enlarge the DOF. The performance of the proposed method was numerically demonstrated by using the ultrasound simulation program called Field-II. A simulated dual-element transducer was composed of a disc- and an annular-type elements, and its aperture was concavely shaped to have a confocal point at 6 mm. The area of each element was identical in order to provide same intensity at the focal point. The outer diameters of the inner and the outer elements were 2.1 mm and 3 mm, respectively. The center frequency of each element was 40 MHz and the f-number (focal depth/aperture size) was two. When two input signals with 0° and 180° phases were applied to inner and outer elements simultaneously, a multi-focal zone was generated in the axial direction. The total −6 dB DOF, i.e., sum of two −6 dB DOFs in the near and far field lobes, was 40% longer than that of the conventional single element transducer. The signal to noise ratio (SNR) was increased by about two times, especially in the far field. The point and cyst phantom simulation were conducted and their results were identical to that of the beam pattern simulation. Thus, the proposed scheme may be a potential method to improve the DOF and SNR in HFUI. Full article
Open AccessArticle A Digital Multigate Doppler Method for High Frequency Ultrasound
Sensors 2014, 14(8), 13348-13360; doi:10.3390/s140813348
Received: 15 June 2014 / Revised: 7 July 2014 / Accepted: 7 July 2014 / Published: 24 July 2014
PDF Full-text (1000 KB) | HTML Full-text | XML Full-text
Abstract
Noninvasive visualization of blood flow with high frequency Doppler ultrasound has been extensively used to assess the morphology and hemodynamics of the microcirculation. A completely digital implementation of multigate pulsed-wave (PW) Doppler method was proposed in this paper for high frequency ultrasound [...] Read more.
Noninvasive visualization of blood flow with high frequency Doppler ultrasound has been extensively used to assess the morphology and hemodynamics of the microcirculation. A completely digital implementation of multigate pulsed-wave (PW) Doppler method was proposed in this paper for high frequency ultrasound applications. Analog mixer was eliminated by a digital demodulator and the same data acquisition path was shared with traditional B-mode imaging which made the design compact and flexible. Hilbert transform based quadrature demodulation scheme was employed to achieve the multigate Doppler acquisition. A programmable high frequency ultrasound platform was also proposed to facilitate the multigate flow visualization. Experimental results showed good performance of the proposed method. Parabolic velocity gradient inside the vessel and velocity profile with different time slots were acquired to demonstrate the functionality of the multigate Doppler. Slow wall motion was also recorded by the proposed method. Full article
Open AccessArticle Lamb Wave Line Sensing for Crack Detection in a Welded Stiffener
Sensors 2014, 14(7), 12871-12884; doi:10.3390/s140712871
Received: 10 June 2014 / Revised: 5 July 2014 / Accepted: 14 July 2014 / Published: 18 July 2014
Cited by 5 | PDF Full-text (1927 KB) | HTML Full-text | XML Full-text
Abstract
This paper proposes a novel Lamb wave line sensing technique for crack detection in a welded stiffener. The proposed technique overcomes one of the biggest technical challenges of Lamb wave crack detection for real structure applications: crack-induced Lamb waves are often mixed [...] Read more.
This paper proposes a novel Lamb wave line sensing technique for crack detection in a welded stiffener. The proposed technique overcomes one of the biggest technical challenges of Lamb wave crack detection for real structure applications: crack-induced Lamb waves are often mixed with multiple reflections from complex waveguides. In particular, crack detection in a welded joint, one of the structural hot spots due to stress concentration, is accompanied by reflections from the welded joint as well as a crack. Extracting and highlighting crack-induced Lamb wave modes from Lamb wave responses measured at multi-spatial points along a single line can be accomplished through a frequency-wavenumber domain analysis. The advantages of the proposed technique enable us not only to enhance the crack detectability in the welded joint but also to minimize false alarms caused by environmental and operational variations by avoiding the direct comparison with the baseline data previously accumulated from the pristine condition of a target structure. The proposed technique is experimentally and numerically validated in vertically stiffened metallic structures, revealing that it successfully identifies and localizes subsurface cracks, regardless of the coexistence with the vertical stiffener. Full article
Open AccessArticle High Precision UTDR Measurements by Sonic Velocity Compensation with Reference Transducer
Sensors 2014, 14(7), 11682-11690; doi:10.3390/s140711682
Received: 5 May 2014 / Revised: 13 June 2014 / Accepted: 27 June 2014 / Published: 2 July 2014
Cited by 2 | PDF Full-text (1350 KB) | HTML Full-text | XML Full-text
Abstract
An ultrasonic sensor design with sonic velocity compensation is developed to improve the accuracy of distance measurement in membrane modules. High accuracy real-time distance measurements are needed in membrane fouling and compaction studies. The benefits of the sonic velocity compensation with a [...] Read more.
An ultrasonic sensor design with sonic velocity compensation is developed to improve the accuracy of distance measurement in membrane modules. High accuracy real-time distance measurements are needed in membrane fouling and compaction studies. The benefits of the sonic velocity compensation with a reference transducer are compared to the sonic velocity calculated with the measured temperature and pressure using the model by Belogol’skii, Sekoyan et al. In the experiments the temperature was changed from 25 to 60 °C at pressures of 0.1, 0.3 and 0.5 MPa. The set measurement distance was 17.8 mm. Distance measurements with sonic velocity compensation were over ten times more accurate than the ones calculated based on the model. Using the reference transducer measured sonic velocity, the standard deviations for the distance measurements varied from 0.6 to 2.0 µm, while using the calculated sonic velocity the standard deviations were 21–39 µm. In industrial liquors, not only the temperature and the pressure, which were studied in this paper, but also the properties of the filtered solution, such as solute concentration, density, viscosity, etc., may vary greatly, leading to inaccuracy in the use of the Belogol’skii, Sekoyan et al. model. Therefore, calibration of the sonic velocity with reference transducers is needed for accurate distance measurements. Full article
Open AccessArticle Arterial Mechanical Motion Estimation Based on a Semi-Rigid Body Deformation Approach
Sensors 2014, 14(6), 9429-9450; doi:10.3390/s140609429
Received: 31 January 2014 / Revised: 18 April 2014 / Accepted: 21 May 2014 / Published: 27 May 2014
PDF Full-text (1392 KB) | HTML Full-text | XML Full-text
Abstract
Arterial motion estimation in ultrasound (US) sequences is a hard task due to noise and discontinuities in the signal derived from US artifacts. Characterizing the mechanical properties of the artery is a promising novel imaging technique to diagnose various cardiovascular pathologies and [...] Read more.
Arterial motion estimation in ultrasound (US) sequences is a hard task due to noise and discontinuities in the signal derived from US artifacts. Characterizing the mechanical properties of the artery is a promising novel imaging technique to diagnose various cardiovascular pathologies and a new way of obtaining relevant clinical information, such as determining the absence of dicrotic peak, estimating the Augmentation Index (AIx), the arterial pressure or the arterial stiffness. One of the advantages of using US imaging is the non-invasive nature of the technique unlike Intra Vascular Ultra Sound (IVUS) or angiography invasive techniques, plus the relative low cost of the US units. In this paper, we propose a semi rigid deformable method based on Soft Bodies dynamics realized by a hybrid motion approach based on cross-correlation and optical flow methods to quantify the elasticity of the artery. We evaluate and compare different techniques (for instance optical flow methods) on which our approach is based. The goal of this comparative study is to identify the best model to be used and the impact of the accuracy of these different stages in the proposed method. To this end, an exhaustive assessment has been conducted in order to decide which model is the most appropriate for registering the variation of the arterial diameter over time. Our experiments involved a total of 1620 evaluations within nine simulated sequences of 84 frames each and the estimation of four error metrics. We conclude that our proposed approach obtains approximately 2.5 times higher accuracy than conventional state-of-the-art techniques. Full article
Open AccessArticle A New Method for Ultrasound Detection of Interfacial Position in Gas-Liquid Two-Phase Flow
Sensors 2014, 14(5), 9093-9116; doi:10.3390/s140509093
Received: 3 December 2013 / Revised: 14 May 2014 / Accepted: 19 May 2014 / Published: 22 May 2014
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Abstract
Ultrasonic measurement techniques for velocity estimation are currently widely used in fluid flow studies and applications. An accurate determination of interfacial position in gas-liquid two-phase flows is still an open problem. The quality of this information directly reflects on the accuracy of [...] Read more.
Ultrasonic measurement techniques for velocity estimation are currently widely used in fluid flow studies and applications. An accurate determination of interfacial position in gas-liquid two-phase flows is still an open problem. The quality of this information directly reflects on the accuracy of void fraction measurement, and it provides a means of discriminating velocity information of both phases. The algorithm known as Velocity Matched Spectrum (VM Spectrum) is a velocity estimator that stands out from other methods by returning a spectrum of velocities for each interrogated volume sample. Interface detection of free-rising bubbles in quiescent liquid presents some difficulties for interface detection due to abrupt changes in interface inclination. In this work a method based on velocity spectrum curve shape is used to generate a spatial-temporal mapping, which, after spatial filtering, yields an accurate contour of the air-water interface. It is shown that the proposed technique yields a RMS error between 1.71 and 3.39 and a probability of detection failure and false detection between 0.89% and 11.9% in determining the spatial-temporal gas-liquid interface position in the flow of free rising bubbles in stagnant liquid. This result is valid for both free path and with transducer emitting through a metallic plate or a Plexiglas pipe. Full article
Open AccessArticle Numerical Simulation of Nonlinear Lamb Waves Used in a Thin Plate for Detecting Buried Micro-Cracks
Sensors 2014, 14(5), 8528-8546; doi:10.3390/s140508528
Received: 3 December 2013 / Revised: 14 April 2014 / Accepted: 17 April 2014 / Published: 15 May 2014
Cited by 5 | PDF Full-text (1008 KB) | HTML Full-text | XML Full-text
Abstract
Compared with conventional linear ultrasonic inspection methods, which are sensitive only to severe defects, nonlinear ultrasonic inspection methods are better for revealing micro-cracks in thin plates. However, most nonlinear ultrasonic inspection methods have only been experimentally investigated using bulk or Rayleigh waves. [...] Read more.
Compared with conventional linear ultrasonic inspection methods, which are sensitive only to severe defects, nonlinear ultrasonic inspection methods are better for revealing micro-cracks in thin plates. However, most nonlinear ultrasonic inspection methods have only been experimentally investigated using bulk or Rayleigh waves. Numerical studies, especially numerical simulations of Lamb ultrasonic waves, have seldom been reported. In this paper, the interaction between nonlinear S0 mode Lamb waves and micro-cracks of various lengths and widths buried in a thin metallic plate was simulated using the finite element method (FEM). The numerical results indicate that after interacting with a micro-crack, a new wave-packet was generated in addition to the S0 mode wave-packet. The second harmonics of the S0 mode Lamb waves and the new wave-packet were caused by nonlinear acoustic effects at the micro-crack. An amplitude ratio indicator is thus proposed for the early detection of buried micro-cracks. Full article
Figures

Open AccessArticle Assessment of the Kinetic Trajectory of the Median Nerve in the Wrist by High-Frequency Ultrasound
Sensors 2014, 14(5), 7738-7752; doi:10.3390/s140507738
Received: 23 February 2014 / Revised: 4 April 2014 / Accepted: 14 April 2014 / Published: 28 April 2014
Cited by 1 | PDF Full-text (812 KB) | HTML Full-text | XML Full-text
Abstract
Carpal tunnel syndrome (CTS) is typically diagnosed by physical examination or nerve conduction measurements. With these diagnostics however it is difficult to obtain anatomical information in the carpal tunnel. To further improve the diagnosis of CTS, an attempt using 30 MHz high-frequency [...] Read more.
Carpal tunnel syndrome (CTS) is typically diagnosed by physical examination or nerve conduction measurements. With these diagnostics however it is difficult to obtain anatomical information in the carpal tunnel. To further improve the diagnosis of CTS, an attempt using 30 MHz high-frequency ultrasound to noninvasively detect the local anatomical structures and the kinetic trajectory of the median nerve (MN) in the wrist was explored. Measurements were performed on the right wrist of 14 asymptomatic volunteers. The kinetic trajectory of the MN corresponding to flexion (from 0° to 90°) and extension (from 90° to 0°) movements of the fingers were detected by a cross correlation-based motion tracking technique. The average displacements of the MN according to finger movements were measured to be 3.74 and 2.04 mm for male and female subjects, respectively. Moreover, the kinetic trajectory of the MN in both the ulnar-palmar and total directions generally follows a sigmoidal curve tendency. This study has verified that the use of high-frequency ultrasound imaging and a motion tracking technique to sensitively detect the displacement and kinetic trajectory of the MN for the assessment of CTS patients is feasible. Full article

Review

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Open AccessReview Piezoelectric Micromachined Ultrasound Transducer (PMUT) Arrays for Integrated Sensing, Actuation and Imaging
Sensors 2015, 15(4), 8020-8041; doi:10.3390/s150408020
Received: 13 February 2015 / Accepted: 26 March 2015 / Published: 3 April 2015
Cited by 8 | PDF Full-text (3919 KB) | HTML Full-text | XML Full-text
Abstract
Many applications of ultrasound for sensing, actuation and imaging require miniaturized and low power transducers and transducer arrays integrated with electronic systems. Piezoelectric micromachined ultrasound transducers (PMUTs), diaphragm-like thin film flexural transducers typically formed on silicon substrates, are a potential solution for [...] Read more.
Many applications of ultrasound for sensing, actuation and imaging require miniaturized and low power transducers and transducer arrays integrated with electronic systems. Piezoelectric micromachined ultrasound transducers (PMUTs), diaphragm-like thin film flexural transducers typically formed on silicon substrates, are a potential solution for integrated transducer arrays. This paper presents an overview of the current development status of PMUTs and a discussion of their suitability for miniaturized and integrated devices. The thin film piezoelectric materials required to functionalize these devices are discussed, followed by the microfabrication techniques used to create PMUT elements and the constraints the fabrication imposes on device design. Approaches for electrical interconnection and integration with on-chip electronics are discussed. Electrical and acoustic measurements from fabricated PMUT arrays with up to 320 diaphragm elements are presented. The PMUTs are shown to be broadband devices with an operating frequency which is tunable by tailoring the lateral dimensions of the flexural membrane or the thicknesses of the constituent layers. Finally, the outlook for future development of PMUT technology and the potential applications made feasible by integrated PMUT devices are discussed. Full article
Open AccessReview The Utility and Limitations of Contrast-Enhanced Ultrasound for the Diagnosis and Treatment of Prostate Cancer
Sensors 2015, 15(3), 4947-4957; doi:10.3390/s150304947
Received: 17 December 2014 / Revised: 8 February 2015 / Accepted: 10 February 2015 / Published: 27 February 2015
Cited by 1 | PDF Full-text (3337 KB) | HTML Full-text | XML Full-text
Abstract
In association with the widespread use of prostate specific antigen (PSA) screening, the numbers of men identified with early-stage prostate cancer (PCa) are increasing in the developed countries, including Japan. However, the accurate localization of PCa lesions in diagnostic imaging is still [...] Read more.
In association with the widespread use of prostate specific antigen (PSA) screening, the numbers of men identified with early-stage prostate cancer (PCa) are increasing in the developed countries, including Japan. However, the accurate localization of PCa lesions in diagnostic imaging is still difficult because PCa has a tendency to be multifocal in the prostate gland. Contrast-enhanced ultrasound (CEUS) improves the detection of PCa by visualizing cancerous lesions in order to target a needle biopsy. CEUS has the potential to enable not only accurate diagnoses but also novel treatments such as focal therapy. The combination of CEUS and other modalities is expected to improve the diagnosis of PCa and its treatment. Full article
Open AccessReview An Integrated Backscatter Ultrasound Technique for the Detection of Coronary and Carotid Atherosclerotic Lesions
Sensors 2015, 15(1), 979-994; doi:10.3390/s150100979
Received: 4 June 2014 / Accepted: 15 December 2014 / Published: 7 January 2015
Cited by 1 | PDF Full-text (1551 KB) | HTML Full-text | XML Full-text
Abstract
The instability of carotid and coronary plaques has been reported to be associated with acute coronary syndrome, strokes and other cerebrovascular events. Therefore, recognition of the tissue characteristics of carotid and coronary plaques is important to understand and prevent coronary and cerebral [...] Read more.
The instability of carotid and coronary plaques has been reported to be associated with acute coronary syndrome, strokes and other cerebrovascular events. Therefore, recognition of the tissue characteristics of carotid and coronary plaques is important to understand and prevent coronary and cerebral artery disease. Recently, an ultrasound integrated backscatter (IB) technique has been developed. The ultrasound IB power ratio is a function of the difference in acoustic characteristic impedance between the medium and target tissue, and the acoustic characteristic impedance is determined by the density of tissue multiplied by the speed of sound. This concept allows for tissue characterization of carotid and coronary plaques for risk stratification of patients with coronary and cerebral artery disease. Two- and three-dimensional IB color-coded maps for the evaluation of tissue components consist of four major components: fibrous, dense fibrosis, lipid pool and calcification. Although several ultrasound techniques using special mathematical algorithms have been reported, a growing body of literature has shown the reliability and usefulness of the IB technique for the tissue characterization of carotid and coronary plaques. This review summarizes concepts, experimental procedures, image reliability and the application of the IB technique. Furthermore, the IB technique is compared with other techniques. Full article
Open AccessReview Dual-Frequency Piezoelectric Transducers for Contrast Enhanced Ultrasound Imaging
Sensors 2014, 14(11), 20825-20842; doi:10.3390/s141120825
Received: 6 August 2014 / Revised: 3 October 2014 / Accepted: 16 October 2014 / Published: 4 November 2014
Cited by 14 | PDF Full-text (2437 KB) | HTML Full-text | XML Full-text
Abstract
For many years, ultrasound has provided clinicians with an affordable and effective imaging tool for applications ranging from cardiology to obstetrics. Development of microbubble contrast agents over the past several decades has enabled ultrasound to distinguish between blood flow and surrounding tissue. [...] Read more.
For many years, ultrasound has provided clinicians with an affordable and effective imaging tool for applications ranging from cardiology to obstetrics. Development of microbubble contrast agents over the past several decades has enabled ultrasound to distinguish between blood flow and surrounding tissue. Current clinical practices using microbubble contrast agents rely heavily on user training to evaluate degree of localized perfusion. Advances in separating the signals produced from contrast agents versus surrounding tissue backscatter provide unique opportunities for specialized sensors designed to image microbubbles with higher signal to noise and resolution than previously possible. In this review article, we describe the background principles and recent developments of ultrasound transducer technology for receiving signals produced by contrast agents while rejecting signals arising from soft tissue. This approach relies on transmitting at a low-frequency and receiving microbubble harmonic signals at frequencies many times higher than the transmitted frequency. Design and fabrication of dual-frequency transducers and the extension of recent developments in transducer technology for dual-frequency harmonic imaging are discussed. Full article
Figures

Open AccessReview High Temperature, High Power Piezoelectric Composite Transducers
Sensors 2014, 14(8), 14526-14552; doi:10.3390/s140814526
Received: 18 June 2014 / Revised: 30 July 2014 / Accepted: 30 July 2014 / Published: 8 August 2014
Cited by 7 | PDF Full-text (5848 KB) | HTML Full-text | XML Full-text
Abstract
Piezoelectric composites are a class of functional materials consisting of piezoelectric active materials and non-piezoelectric passive polymers, mechanically attached together to form different connectivities. These composites have several advantages compared to conventional piezoelectric ceramics and polymers, including improved electromechanical properties, mechanical flexibility [...] Read more.
Piezoelectric composites are a class of functional materials consisting of piezoelectric active materials and non-piezoelectric passive polymers, mechanically attached together to form different connectivities. These composites have several advantages compared to conventional piezoelectric ceramics and polymers, including improved electromechanical properties, mechanical flexibility and the ability to tailor properties by using several different connectivity patterns. These advantages have led to the improvement of overall transducer performance, such as transducer sensitivity and bandwidth, resulting in rapid implementation of piezoelectric composites in medical imaging ultrasounds and other acoustic transducers. Recently, new piezoelectric composite transducers have been developed with optimized composite components that have improved thermal stability and mechanical quality factors, making them promising candidates for high temperature, high power transducer applications, such as therapeutic ultrasound, high power ultrasonic wirebonding, high temperature non-destructive testing, and downhole energy harvesting. This paper will present recent developments of piezoelectric composite technology for high temperature and high power applications. The concerns and limitations of using piezoelectric composites will also be discussed, and the expected future research directions will be outlined. Full article
Open AccessReview High Performance Relaxor-Based Ferroelectric Single Crystals for Ultrasonic Transducer Applications
Sensors 2014, 14(8), 13730-13758; doi:10.3390/s140813730
Received: 11 June 2014 / Revised: 18 July 2014 / Accepted: 18 July 2014 / Published: 29 July 2014
Cited by 7 | PDF Full-text (1351 KB) | HTML Full-text | XML Full-text
Abstract
Relaxor-based ferroelectric single crystals Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) have drawn much attention in the ferroelectric field because of their excellent piezoelectric properties and high electromechanical coupling coefficients (d33~2000 pC/N, kt~60%) near the morphotropic [...] Read more.
Relaxor-based ferroelectric single crystals Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) have drawn much attention in the ferroelectric field because of their excellent piezoelectric properties and high electromechanical coupling coefficients (d33~2000 pC/N, kt~60%) near the morphotropic phase boundary (MPB). Ternary Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) single crystals also possess outstanding performance comparable with PMN-PT single crystals, but have higher phase transition temperatures (rhombohedral to tetragonal Trt, and tetragonal to cubic Tc) and larger coercive field Ec. Therefore, these relaxor-based single crystals have been extensively employed for ultrasonic transducer applications. In this paper, an overview of our work and perspectives on using PMN-PT and PIN-PMN-PT single crystals for ultrasonic transducer applications is presented. Various types of single-element ultrasonic transducers, including endoscopic transducers, intravascular transducers, high-frequency and high-temperature transducers fabricated using the PMN-PT and PIN-PMN-PT crystals and their 2-2 and 1-3 composites are reported. Besides, the fabrication and characterization of the array transducers, such as phased array, cylindrical shaped linear array, high-temperature linear array, radial endoscopic array, and annular array, are also addressed. Full article

Other

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Open AccessLetter Ultrasonic Lens Based on a Subwavelength Slit Surrounded by Grooves
Sensors 2014, 14(5), 8821-8828; doi:10.3390/s140508821
Received: 10 April 2014 / Revised: 7 May 2014 / Accepted: 15 May 2014 / Published: 19 May 2014
Cited by 1 | PDF Full-text (405 KB) | HTML Full-text | XML Full-text
Abstract
The lensing capabilities of a single subwavelength slit surrounded by a finite array of grooves milled into a brass plate is presented. The modulation of the beam intensity of this ultrasonic lens can be adjusted by varying the groove depth. Numerical simulations [...] Read more.
The lensing capabilities of a single subwavelength slit surrounded by a finite array of grooves milled into a brass plate is presented. The modulation of the beam intensity of this ultrasonic lens can be adjusted by varying the groove depth. Numerical simulations as well as experimental validations at 290 kHz are shown. The experimental results are in good agreement with the numerical simulations. This system is believed to have potential applications for medical ultrasound fields such as tomography and therapy. Full article

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