Broadband Transducers Research Articles

A new measurement method of separation percentage for human blood plasma based on ultrasound attenuation

In this research, the separation accuracy of blood-plasma-based multi-decay pulse-power technique (MDPPT) was presented. The MDPPT provides adjustable-path measurements according to the amplitude of transmitted pulses and accurate attenuation measurements of propagation echoes through blood and blood plasma; thus, reduction of time and power consumption during the plasma separation process was achieved using the centrifuge technique. A mathematical model of separation accuracy and attenuation was derived and it was used for concluding the blood plasma concentration based on attenuation. Multi levels of concentration yield 20, 35, 50, 80 and 93% of blood plasma separation percentage; whereas attenuation that is more than 80% of the separation percentage may prove useful for purity inspection and contaminant detection. The platform of separation process was built with multi-level pulse power controlled by the fuzzy logic approach and broadband transducers affixed on the outside of a low-reflection coefficient thin vessel. The signal in the receive transducer permits the measurement of the attenuation and the velocity by measuring the time of flight. The fast Fourier transform (FFT) of the appropriate plasma signal for each echo was obtained and was compared with that of blood to yield the attenuation as a function of separation percentage. The data show the feasibility for measuring a plasma separation of 97%. Therefore, such measurements can be proven useful for detecting contaminants in blood plasma and blood serum. The blood plasma separation accuracy measurements prove advantageous for saving time and power consumption of the separation process required. Key words: Attenuation measurements, blood plasma percentage, centrifuge device separation accuracy, contaminant detection.

Morphologic Characterization of Intraneural Flow Associated With Median Nerve Pathology

A prospective cohort of 47 symptomatic patients who reported for nerve conduction studies and 44 asymptomatic controls was examined with sonography to evaluate the median nerve. Doppler studies of the median nerve were collected with handheld sonography equipment and a 12-MHz linear broadband transducer. Strict inclusion criteria were established for assessing 435 waveforms from 166 wrists. Two sonographers agreed that 245 waveforms met the a priori criteria and analyzed the corresponding data. Spectral Doppler waveforms provided direct quantitative and qualitative data for comparison with indirect provocative testing results. These Doppler data were compared between the recruitment groups. No statistical difference existed in waveforms between the groups (P < .05). Trending of the overall data indicated that as the number of positive provocative tests increased, the mean peak systolic velocity within the carpal tunnel (mid) also increased, whereas the proximal mean peak systolic velocity decreased. However, by using multiple provocative tests as an indirect comparative measure, researchers may find mean peak spectral velocity at the carpal tunnel inlet a helpful direct measure in identifying patients with carpal tunnel syndrome.

Ultrasonic characterization of a fluid layer using a broadband transducer

A measurement method is proposed for the ultrasonic characterization of a fluid layer, corresponding to the resin transfer molding (RTM) manufacturing process. The ultrasonic velocity and attenuation of the silicone oil are measured in three samples having different viscosities. The measurement method is established on the basis of the attenuation of ultrasonic waves in fluids. A correction of the beam diffraction is implemented to improve measurement precision. A single element transducer with central frequency of 15 MHz is used. The tested fluids simulate the industrial resin used to manufacture composite materials. When injecting this resin, its viscosity increases until it reaches a critical state of polymerization. In this paper we focus on ultrasonic characterization of three fluids representing three intermediate cases of fluid resin during its injection before reaching the polymerization state.

Optimization of tuning and matching of broadband transducers with power switching amplifiers

Underwater transducers for broadband communication rely on effective tuning and matching to a power amplifier for maximum signal bandwidth and efficiency. This analysis follows a systematic approach to design an efficient and effective broadband acoustic transmit system. Power switching (class D) amplifiers use a variety of modulation schemes to reduce the losses incurred at the high power amplification stage. Lowpass filtering at the output stage of the switching amplifier is often employed to attenuate the high frequency carrier signal from the modulation stage. A matching transformer steps up the voltage delivered to the transducer. The tuning network can be designed to provide optimum cancellation of reactance over a wide band, thus improving the power factor bandwidth.

Comparison of the features of composite and mosaic piezotransducers for the ultrasonic testing of products with a high attenuation level of ultrasonic signals

The problem of the creation of stacked (mosaic and composite) broadband transducers that simultaneously provide a broad band and a high electroacoustic transduction efficiency is analyzed. The mosaic technology is shown to be optimal for the practical implementation of ultrasonic broadband low-frequency electroacoustic transducers. Being functionally flexible, the mosaic technology allows the development of numerous variants of electroacoustic transducers for the solution of different ultrasonic testing problems and, first of all, for the undistorted transduction of signals.

Absolute backscatter coefficient estimates of tissue-mimicking phantoms in the 5–50 MHz frequency range

Absolute backscatter coefficients in tissue-mimicking phantoms were experimentally determined in the 5-50 MHz frequency range using a broadband technique. A focused broadband transducer from a commercial research system, the VisualSonics Vevo 770, was used with two tissue-mimicking phantoms. The phantoms differed regarding the thin layers covering their surfaces to prevent desiccation and regarding glass bead concentrations and diameter distributions. Ultrasound scanning of these phantoms was performed through the thin layer. To avoid signal saturation, the power spectra obtained from the backscattered radio frequency signals were calibrated by using the signal from a liquid planar reflector, a water-brominated hydrocarbon interface with acoustic impedance close to that of water. Experimental values of absolute backscatter coefficients were compared with those predicted by the Faran scattering model over the frequency range 5-50 MHz. The mean percent difference and standard deviation was 54% ± 45% for the phantom with a mean glass bead diameter of 5.40 μm and was 47% ± 28% for the phantom with 5.16 μm mean diameter beads.

Acoustic emission characterization of the fracture process in fibre reinforced concrete

The present study occupies with the characterization of the fracture process of steel fibre reinforced concrete. Different acoustic emission indices are correlated with the accumulation of damage and the type of source. The amplitude distribution of the acquired signals is very sensitive to micro-cracking, while individual mechanisms like matrix cracking and fibre pull-out can be distinguished by the average frequency of the corresponding signals which exhibits a severe decrease at the moment of main. As a result, acoustic emission can be used as a warning against the failure of this material while the broadband transducers can be used to characterize the different damage mechanisms.

Endoscopic Ultrasonography and Contrast-Enhanced Endoscopic Ultrasonography

Endoscopic ultrasonography (EUS) is superior to all other imaging modalities in detecting small pancreatic cancers. However, its ability to characterize hypoechoic pancreatic masses is limited: most carcinomas, neuroendocrine tumors, and inflammatory pseudotumors are simply depicted as hypoechoic masses. Contrast enhancement helps EUS to characterize such hypoechoic masses. Intravenous ultrasound (US) agents increase the signal from the blood and, thus, act as amplifiers and improve visualization of blood flow in small vessels using Doppler US. Contrast-enhanced Doppler EUS can differentiate small pancreatic carcinomas that cannot be detected by other imaging modalities. The development of second-generation US contrast agents and an EUS system with a broad-band transducer enabled the visualization of microvessels and the parenchymal perfusion in the pancreas. This contrast-enhanced harmonic EUS has shown that most pancreatic cancers exhibit hypovascular heterogeneous enhancement with irregular network-like microvessels. Moreover, it can diagnose pancreatic cancers with a high sensitivity (89–92%).

Backscattering measurement from a single microdroplet

Backscattering measurements for acoustically trapped lipid droplets were undertaken by employing a P[VDF-TrFE] broadband transducer of f-number = 1, with a bandwidth of 112%. The wide bandwidth allowed the transmission of the 45 MHz trapping signal and the 15 MHz sensing signal using the same transducer. Tone bursts at 45 MHz were first transmitted by the transducer to hold a single droplet at the focus (or the center of the trap) and separate it from its neighboring droplets by translating the transducer perpendicularly to the beam axis. Subsequently, 15 MHz probing pulses were sent to the trapped droplet and the backscattered RF echo signal received by the same transducer. The measured beam width at 15 MHz was measured to be 120 μ m. The integrated backscatter (IB) coefficient of an individual droplet was determined within the 6-dB bandwidth of the transmit pulse by normalizing the power spectrum of the RF signal to the reference spectrum obtained from a flat reflector. The mean IB coefficient for droplets with a 64 μ m average diameter (denoted as cluster A) was -107 dB, whereas it was -93 dB for 90-μm droplets (cluster B). The standard deviation was 0.9 dB for each cluster. The experimental values were then compared with those computed with the T-matrix method and a good agreement was found: the difference was as small as 1 dB for both clusters. These results suggest that this approach might be useful as a means for measuring ultrasonic backscattering from a single microparticle, and illustrate the potential of acoustic sensing for cell sorting.

Synthesis of low-frequency broadband ultrasonic mosaic transducers with nondistorting spatiotemporal characteristics

It is shown that the spatial distribution of the acoustic field of a broadband transducer may influence the degree of distortion of ultrasonic signals. The principle for forming a uniform acoustic-field distribution within the directivity characteristic of a low-frequency broadband transducer based on the chosen topology of a mosaic transducer is proposed. The comparative spatiotemporal characteristics of mosaic broadband transducers with optimized and nonoptimized mosaic topologies are obtained as a result of simulation. It is shown that for an optimized topology uniform field distributions can be obtained in both far- and near-field zones of the broadband transducers.

Quality evaluation of rib-to-deck weld of orthotropic steel deck system by ultrasonic test with broad band transducer

Quality evaluation of rib-to-deck weld of orthotropic steel deck system by ultrasonic test with broad band transducer

Electronics for resonant ultrasound.

An essential advantage of resonant ultrasound spectroscopy (RUS) is that there is no need to bond the transducers to the specimen. Needed to preserve the free‐surface boundary conditions so important to RUS, the lack of bonding also makes signals weak. Exacerbating the signal‐level problem is a requirement of RUS to measure over a broad frequency range, precluding the use of gain‐enhancing resonant transducers. So with broadband transducers and weak contact, the demands on RUS electronics, from preamps to computers, are substantial. The evolution of electronics for RUS has paralleled the availability of high‐performance analog‐to‐digital converters, FET‐based electronic components, and digital signal processing. We describe here all the essential features for state‐of‐the‐art RUS signal acquisition. [Work at Los Alamos National Laboratory (LANL) was supported by NSF‐DMR‐0654118, DOE, the State of Florida. NSF‐DMR 0602859 (FSU), and LANL LDRD‐DR20070013. LANL is operated by LANS LLC.]

Spatiotemporal characteristics of broadband ultrasonic transducers

It is shown that the quality of transformation of ultrasonic signals in a broadband transducer is affected by not only the amplitude-frequency but also the spatial characteristics of broadband probes. To evaluate the quality of transformation of ultrasonic broadband signals, integral spatiotemporal characteristics of a broadband probe are introduced, viz., the correlation field distribution and the correlation directivity characteristic. The experimental correlation spatiotemporal characteristics of a mosaic low-frequency broadband transducer are presented.

Preliminary Study of Broadband Transducer for Measurement of Bone Characteristics

The purpose of the study is to diagnose bone diseases using the ultrasonic image. We investigate the broadband transducer with a 0.5–5 MHz frequency range. We fabricated two types of transducers with a thin piezoelectric plate bonded with a thick plate resonator. One is an acoustic lens transducer made of flat lead zirconate titanate (PZT) material, and another is a concave transducer made of PZT rod-polymer 1–3 composite material. The application of the transducers to clinical diagnosis involves the measurement of frequency-dependent characteristics of bone by the penetration method. We measured ultrasonic waves radiated from the transducer at the focal point, and performed frequency analysis. As a result, a flat frequency characteristic of the concave transducer was obtained.

Broadband coupling transducers for magneto-inductive cables

A broadband resonant transducer capable of low-loss coupling between magneto-inductive (MI) waveguides and a real impedance is introduced. The transducer is an L–C circuit resonating at the resonant frequency of the elements forming the guide. However, the values of the components in the transducer are different, and chosen to obtain two separate nulls in reflection so that low reflection is obtained over a wide spectral range. The transducer can be incorporated into the MI waveguide itself, allowing a connection between a MI cable and a conventional system to be made as a simple splice. The design is confirmed using 2 m length of low-loss thin-film MI cables formed using copper-clad polyimide and operating near 100 MHz frequency.

Computational method to determine reflected ultrasonic signals from arbitrary-geometry targets

A computational method based on the impulse response and on the discrete representation computational concept is proposed for the determination of the echo responses from arbitrary-geometry targets. It is supposed that each point of the transducer aperture can be considered as a source radiating hemispherical waves to the reflector. The local interaction with each of the hemispherical waves at the reflector surface can be modeled as a plane wave impinging on a planar surface, using the respective reflection coefficient. The method is valid for all field regions and can be performed for any excitation waveform radiated from an arbitrary acoustic aperture. The effects of target geometry, position, and material on both the amplitude and the shape of the echo response are studied. The model is compared with experimental results obtained using broadband transducers together with plane and cylindrical concave rectangular reflectors (aluminum, brass, and acrylic), as well as a circular cavity placed on a plane surface, in a water medium. The method can predict the measured echoes accurately. This paper shows an improved approach of the method, considering the reflection coefficient for all incident hemispherical waves arriving at each point of the target surface.

Modified single crystals for high‐power, broadband underwater projectors.

When operating high‐power electromechanical devices, the performance is often limited by self‐heating within the active material. This is especially true in high‐power, broadband underwater projectors using the piezoelectric single crystal Pb(Mg1/3Nb2/3O3–PbTiO3 (PMN‐PT). Although PMN‐PT crystals show an excellent piezoelectric response (d33 > 1500 pC/N) and high‐coupling coefficient (k33 > 0.90), device performance is limited by the high‐mechanical losses (QM < 100) and low‐temperature phase transformation (TRT = 95 °C). This work describes the material property enhancements of two compositional modifications and compares the performance of these crystals in high‐power, broadband transducers. One such modification is the addition of Pb(In1/2Nb1/2O3 (PIN) or PbZrO3 (PZ) to the binary PMN‐PT composition. The greater thermal stability of ternary PIN‐PMN‐PT and PZ‐PMN‐PT crystals is shown by comparing the dielectric permittivity, piezoelectric coefficient, and coupling coefficient to unmodified PMN‐PT as a f...

Diagnosis of pancreatic tumors by endoscopic ultrasonography

Pancreatic tumors are highly diverse, as they can be solid or cystic, and benign or malignant. Since their imaging features overlap considerably, it is often difficult to characterize these tumors. In addition, small pancreatic tumors, especially those less than 2 cm in diameter, are difficult to detect and diagnose. For characterizing pancreatic tumors and detecting small pancreatic tumors, endoscopic ultrasonography (EUS) is the most sensitive of the imaging procedures currently available. This technique also provides good results in terms of the preoperative staging of pancreatic tumors. EUS-guided fine needle aspiration (EUS-FNA) has also proved to be a safe and useful method for tissue sampling of pancreatic tumors. Despite these advantages, however, it is still difficult to differentiate between benign and malignant, solid or cystic pancreatic tumors, malignant neoplasms, and chronic pancreatitis using EUS, even when EUS-FNA is performed. Recently, contrast-enhanced EUS with Doppler mode (CE-EUS) employing ultrasound contrast agents, which indicate vascularization in pancreatic lesions, has been found to be useful in the differential diagnosis of pancreatic tumors, especially small pancreatic tumors. However, Doppler ultrasonography with contrast-enhancement has several limitations, including blooming artifacts, poor spatial resolution, and low sensitivity to slow flow. Consequently, an echoendoscope was developed recently that has a broad-band transducer and an imaging mode that was designed specifically for contrast-enhanced harmonic EUS (CEH-EUS) with a second-generation ultrasound contrast agent. The CEH-EUS technique is expected to improve the differential diagnosis of pancreatic disease in the future. This review describes the EUS appearances of common solid and cystic pancreatic masses, the diagnostic accuracy of EUS-FNA, and the relative efficacies and advantages of CE-EUS and CEH-EUS along with their relative advantages and their complementary roles in clinical practice.

Two-Step Sintering of the Pure K0.5Na0.5NbO3 Lead-Free Piezoceramics and Its Piezoelectric Properties

The two-step sintering method was successfully applied to fabricate the lead-free alkaline niobate (K0.5Na0.5NbO3) piezoelectric ceramics, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were carried out to characterize the samples. The properties of density, piezoelectric and ferroelectric were also investigated. Under the optimal sintering process, the specimens with the relative density 95.2%, which exhibit good electrical properties (d 33 = 121pC/N, k p = 35.2%, Q m = 5, ϵ r = 815). These results show that K0.5Na0.5NbO3 ceramic is a promising lead-free piezoelectric material for the ultrasonic delay-line applications, broadband transducers and sensors. The easy-controlling sintering process can be used in the other piezoelectric ceramics system.

Biologically inspired ultrasonic measurements of porous media, with applications in geophysics.

Biologically inspired ultrasound has been investigated for measuring properties of materials in an underwater environment. Broadband transducers have been deployed which operate in the 40–200-kHz frequency range, with similar frequencies to those used by some echolocating mammals. Signals have been designed, which optimize the available bandwidth of the transducer, and analysis procedures have been developed to extract the desired information from acquired data. Measurements on single-layer targets, comprising plastic, metal, and glass, in solid and porous forms have established the performance of the system on well-controlled synthetic samples. The target thicknesses ranged from 0.5 to 40 mm, thus spanning the wavelength range of the signals used. Adequate penetration of the ultrasound into the samples, at the frequencies used, was demonstrated. Material and thickness discrimination was possible using frequency domain results, and modeling of the traces was performed in order to extract velocity and attenuation information. Scanning electron microscopy measurements on the porous targets revealed structural information that informs the interpretation of the ultrasonic results. The work on synthetic targets forms a basis to inform experimentation on natural geological materials exhibiting a wide range of structural characteristics. Initial results for sandstone samples are presented.