Pulse-echo Performance Research Articles

3D printing of CaBi4Ti3.925(Nb2/3Mn1/3)0.075O15 ceramics for high temperature ultrasound transducer

Bismuth layer-structured CaBi4Ti3.925(Nb2/3Mn1/3)0.075O15 (CBTNM) piezoelectric ceramics have been prepared using stereolithography (SL) technology. The effects of various solid contents (76–82 wt%) of CBTNM ceramics on the slurry viscosity, phase structure, microstructure, and electric performance were studied in detail. At a solid content of 82 wt%, the ceramic exhibits good piezoelectric properties. The piezoelectric constant d 33, thickness-mode electromechanical coupling coefficient k t, and Curie temperature Tc were 21 pC/N, 47%, and 790 °C, respectively. The piezoelectric constant of the ceramic has a good stability up to 500 °C. Furthermore, a high-temperature ultrasound transducer was designed and fabricated based on the CBTNM ceramic, and its pulse-echo performance was characterized from room temperature to 250 °C. The pulse-echo performance indicates that the −6 dB bandwidth and echo amplitude of the transducer decrease slightly, but still work normally up to 250 °C. These results indicate that the transducer fabricated based on CBTNM ceramics has potential in high-temperature testing applications.

Integrating a Fundus Camera with High-Frequency Ultrasound for Precise Ocular Lesion Assessment.

Ultrasound A-scan is an important tool for quantitative assessment of ocular lesions. However, its usability is limited by the difficulty of accurately localizing the ultrasound probe to a lesion of interest. In this study, a transparent LiNbO3 single crystal ultrasound transducer was fabricated, and integrated with a widefield fundus camera to guide the ultrasound local position. The electrical impedance, phase spectrum, pulse-echo performance, and optical transmission spectrum of the ultrasound transducer were validated. The novel fundus camera-guided ultrasound probe was tested for in vivo measurement of rat eyes. Anterior and posterior segments of the rat eye could be unambiguously differentiated with the fundus photography-guided ultrasound measurement. A model eye was also used to verify the imaging performance of the prototype device in the human eye. The prototype shows the potential of being used in the clinic to accurately measure the thickness and echogenicity of ocular lesions in vivo.

Effect of temperature on the pulse‐echo performance of ultrasonic transducers fabricated with PVDF film

Empirical data is presented on the pulse-echo performance of poly-vinylidenefluoride (PVDF) ultrasound transducers monitored in-situ at temperatures in the range 50–130°C. Measurements were performed over a 5 h period beginning at the sensors’ initial exposure to temperature. A reduction in pulse-echo amplitude was observed at all temperatures in the range and was found to be proportional to temperature increase. Four different thicknesses of PVDF film were used for the trials and small differences in behaviour were observed between sensors constructed using each thickness. On average, the overall loss was found to increase linearly with temperature from a 16% drop in pk–pk pulse-echo voltage observed at 60°C to a 95% drop in performance at 120°C after 5 h. Rates of signal loss were found to follow a logarithmic decay, particularly at temperatures above 70°C where significant reductions were observed in the initial seconds/minutes following exposure to temperature.

Flexible piezoelectric transducer for ultrasonic inspection of non-planar components

This paper presents the fabrication and characterisation of a flexible ultrasonic transducer using commercially available PZT-5A piezoelectric fibers which are lapped to form rectangular piezoelectric elements. The key feature in the device construction is the inclusion of gaps between the piezoelectric fibers to ensure good flexibility in the plane normal to the fiber direction. The spatial response of the transducer ultrasonic output was assessed using acoustographic imaging. The flexibility of the transducer and its applicability in pulse-echo mode on curved sections was demonstrated by testing on a 38 mm diameter steel rod. The transducer response was found to be broad band and highly non uniform but good pulse-echo performance was achieved at 5 MHz.

Comparison of the performance of pmn-pt single-crystal and ceramic composite arrays for NDE applications

Ultrasonic array technology is used in many imaging applications across a wide range of industrial sectors. Perovskite single-crystal materials such as pzn-pt and pmn-pt can be used to manufacture arrays with much increased sensitivity and bandwidth, compared to conventional piezoelectric ceramic designs. One way to take advantage of these new active materials is to incorporate the single-crystal material as the active piezoelectric elements, embedded within a passive polymeric material, in a piezoelectric composite structure. This paper describes a theoretical and experimental investigation into the performance of wideband 1-3 composite arrays utilising pzt5h ceramic and pmn-pt single-crystal as the active materials. Six-element prototype arrays were manufactured with a centre frequency of approximately 2.25 MHz. The comparison of the single-crystal and pzt5h devices is based on laser vibrometer surface displacement cross-talk measurements and electrical impedance measurements as well as transmit and receive measurements in water. The measured electrical impedance and mechanical cross-talk from the manufactured arrays correlates well with that predicted using the FE software package PZFlex. Moreover, the design techniques obtained from PZFlex, are shown to produce arrays with low cross-talk. Overall, the single-crystal device shows considerably improved performance over the pzt5h device as demonstrated by its higher bandwidth and superior pulse-echo performance.

Ferroelectric nylon materials and their feasibility for ultrasound transducers

Measurements of the high frequency electrical and acoustic properties of oriented ferroelectric nylon-7 and nylon-11 are reported for the frequency range of 10 to 50 MHz and temperature range of 20 to 160/spl deg/C. The dielectric properties of nylon films were measured over a broadband frequency range including the fundamental halfwave resonance frequency for each sample, and a curve-fitting resonance technique was used to determine the properties of interest for ultrasound transducer design. Despite the high remanent polarization measured in the nylon films (1.25 mC/cm/sup 2/), the measured electromechanical coupling constant (k/sub t/=0.11), and mechanical quality factor (Q/sub m/=8) were lower than typically seen for PVDF and P(VDF-TrFE) copolymer. Poor thickness uniformity of the nylon film samples is suspected of dampening the features of the dielectric spectra near resonance, resulting in lower measured values for k/sub t/ and Q/sub m/. Comparisons of both simulated and actual measured pulse-echo performance showed the nylon materials to be competitive with PVDF for ultrasonic transducer performance. Actual pulse-echo tests with nylon-7 yielded a -6 dB fractional bandwidth of 144%. Since the ferroelectric nylons are known to be hydrophilic, tests were conducted to quantitatively determine the effects of water absorption on the ultrasonic performance of nylon-7 transducers. The results showed the water exposure slightly reduces the pulse-echo amplitude response and resonant frequency of a nylon-7 transducer. The water absorption effects were shown to be fully reversible upon drying the nylon film.

Ultrasound transducer models for piezoelectric polymer films

A method is presented for determining the piezoelectric constants and the frequency-dependent dielectric properties of the polymers from a five-step algorithm based on analysis of air-loaded broadband impedance measurements. It is shown how to account for the frequency-dependent lossy properties of these films in an equivalent impedance circuit model and a modified Mason's model. Comparisons between the models and actual film transducers show excellent broadband simulation of both electrical input impedance and ultrasonic pulse-echo performance.