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The Resolution Enhancement Compression (REC) technique is a coded excitation method developed for improving the axial resolution of ultrasound images. It consists on emitting an amplitude modulated chirp signal that transmits more energy at the frequencies where the ultrasound transducer is less efficient. The focus of this study is to elaborate a new beamforming strategy, which consists of implementing...
Measuring broadband signals demands complex calibration of a detector over a sufficient bandwidth. For inertial cavitation emissions, the shock waves will be convolved with the transfer function of the hydrophone, and introduce artefacts to the measurement. Use of appropriately calibrated detectors would thus facilitate meaningful comparison of the cavitation emission data reported from groups using...
Air-coupled transducers are used to conduct fast non-contact inspections in NDT. Normally, the bandwidth of a conventional transducer can be enhanced, but with a cost to its sensitivity. However, low sensitivity is very disadvantageous in air-coupled NDT. This paper presents a methodology for improving the bandwidth of an air-coupled diaphragm transducer without sensitivity loss by connecting a number...
The study of beampatterns and their use in imaging systems has a long history in optics and acoustics. In addition, the topic of limited diffraction fields has received increasing attention since the characterization of Bessel beams in optics. The class of “localized waves” include X-beams, Airy beams, and related monochromatic and broadband solutions.
The concept of contrast imaging using microbubble superharmonic signals was introduced in 2002[1]. A number of implementations with detection above 10 MHz have been reported, in particular by our group using a 25–30 MHz single element receive transducer concentric with a low 2–4 MHz transmit ring[2]. In the present work, the implementation of dual frequency (DF) imaging on a Vevo 2100 (VisualSonics,...
Synthetic aperture (SA) ultrasound imaging is a well-known technique in which RF signals for every transmit and receive element combinations is first obtained and a 2-way-focused image is synthetically formed afterwards. Despite its benefits, one of its main shortcomings is reduced penetration depth caused by low acoustic power from single element firing. To address this challenge, we propose a spatial...
Ultrasonic sensor has been widely used, ranging from underwater communication to many aspects, such as medical imaging and therapy. Compared with the traditional piezoelectric sensors, Capacitive micro-machined ultrasonic transducer(CMUT) have advantages of wide band, easy to integration, good consistency and low cost, which make it a research hotspot in the field of ultrasound. As the core of the...
There are two generally used ultrasonic approaches to extract sets of quantitative parameters: the Lizzi-Feleppa (LF) and quantitative ultrasound (QUS) approaches. The LF approach estimates LF parameters from the linear fit of the backscatter coefficient (BSC), and yields slope, intercept and midband. The QUS approach relies on the attenuation coefficient (AC) and BSC versus frequency, and yields...
Finite element method (FEM) has been extensively used for analyzing both static and dynamic behaviour of CMUTs. Typical parameters being evaluated include the pull-in voltage, pressure, sensitivity, bandwidth, and crosstalk. PZFlex is a commercial FEA software and has been optimized for the ultrasound industry and is commonly used to design piezo-electric ultrasound transducers. However, PZFlex is...
Ultrafast ultrasound has contributed to a renewed interested in vector Doppler. Sampling RF signals at a rate 4 times the carrier frequency is the standard procedure since this rule complies with the Nyquist sampling theorem, regardless of the transducer bandwidth. RF acquisition with a high-performance multi-channel system generates massive datasets, especially in 3-D ultrafast ultrasound. The objective...
Combined endoscopic imaging and therapeutic tools for minimally invasive procedures may lead to increased efficacy of the procedure and reduced patient risk. Currently, our lab is investigating the use of histotripsy tissue ablation during ultrasound guided neurosurgery. In this work, we will present our progress toward the miniaturization of the histotripsy transducer for simultaneous, real-time...
Assessment of medium nonlinearity parameter in pulse-echo mode usually demands information on the second harmonic. However, the acquisition of quantitative data on backscattered amplitude at the fundamental and second harmonic components is difficult using the same probe due to its limited bandwidth. In this paper we propose how to assess medium nonlinearity using only the fundamental harmonic and...
Capacitive Micromachined Ultrasound Transducers (CMUTs) have become a better alternative to traditional piezoelectric transducers because of their better impedance matching characteristic and wider bandwidth. These advantages make CMUTs ideal for medical ultrasound imaging, ultrasonic flow metering, gesture sensing and other airborne applications. However conventional vacuum CMUTs have narrow bandwidth...
In ultrafast imaging using pulse compression, the image quality is limited by the bandwidth of the ultrasonic (US) transducer. Thus extending the effective bandwidth of the US transducers could improve the performance of the current US imaging methods. Resolution Enhancement Compression (REC) allows bandwidth enhancement by exciting the ultrasound transducer with frequency and amplitude modulated...
The energy transduction of a Capacitive Micromachined Ultrasonic Transducer (CMUT) depends on the movement of a flexible plate, which has a low mechanical impedance compared to its bulky piezoelectric counterpart. Consequently, the output pressure of a CMUT is generally lower. This limits the penetration depth, and thus the visualization of deeper structures in the body, as well as non-linear imaging...
Physiologically important pressures in the heart and aorta are currently assessed with invasive pressure catheters. The subharmonic signal from ultrasound contrast agents, however, may be exploited to estimate pressures non-invasively. The objective of this work was (i) to develop a static phantom from commercially-available components for easy replication across different laboratories, and (ii) to...
Ultrasonic transducers for industrial applications often require front protection layer which have to be chemically inert material such as stainless steel (SS). This is particularly important for process control of semiconductor device production so as not to contaminate processing agent. It is known when metallic layer is added at front of ultrasonic transducers, boundary reflections reduce wave...
Though a fairly new technology, CMUTs present many advantages over traditional piezoelectric transducers, including wider frequency bandwidths, easier integration with circuitry, and cheaper and easier production. The wide frequency bandwidth of CMUTs makes them ideal for multi-frequency ultrasound (US) applications in particular. In this work, we present a CMUT-specific version of the dual-frequency...
The resonance frequency of an active element in a piezoelectric ultrasonic transducer is dependent on its length scale. Inspired by natural occurring auditory systems, incorporation of elements with varying length scales in the piezoelectric transducer design can result in a wider operational bandwidth. A mathematical algorithm has been developed to define the feature of a fractal geometry called...
New ultrasound imaging and therapeutic modalities may require complex transducer designs that are not easily facilitated by conventional design guidelines. This motivates the investigation of numerical optimization methods that can include the effect of structural layers (e.g. bonding and electrodes), electrical loading, and more than one piezoceramic layer in the design and optimization procedure...
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