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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...
The matching layer inserted between the front protection metal and piezoelectric layer has been designed when the protection metal is half-wavelength thick. This matching layer plays the role of a bonding layer. The optimum thickness ranges from λ/4 to 3λ/8 in the Mason model simulation, which has been confirmed by experiments. In the optimum range, the sensitivity was much higher and the bandwidth...
New ultrasound imaging and therapeutic modalities may require transducer designs that are not easily facilitated by conventional design guidelines and analytical expressions. 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 active piezoceramic layer in the design...
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,...
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. In this paper, a mathematical algorithm was developed first to define the feature of a fractal...
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...
Acoustoelectric imaging (AEI) is a new technique for mapping current densities at high resolution depending on the size of the ultrasound (US) focus. The design and performance of the recording system is crucial for efficient AEI because the amplitude of the AE signal in biological tissue is on the order of a microvolt or less. In this direction, an AE signal processing circuit (AE-SPC), containing...
One of the objectives in ultrasonic imaging is to improve the spatial resolution of the acquired images. The axial resolution is determined by the transducer bandwidth and the beamforming process. The resolution enhancement compression (REC) technique allows extending the bandwidth by combining the concepts of frequency and amplitude modulated excitation with modified Wiener filter compression. More...
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...
This paper presents an experimental study of the acoustic performance of Capacitive Micromachined Ultrasonic Transducers (CMUTs) as function of plate dimensions. The objective is to increase the output pressure without decreasing the pulse-echo signal. The CMUTs are fabricated with a LOCOS process, followed by direct wafer fusion bonding to a Silicon-On-Insulator (SOI) wafer. In this way, the plate...
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...
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