Fabrication and evaluation of a single-element Bi0.5Na0.5TiO3-based ultrasonic transducer

High Frequency Ultrasound Transducer Based on Sm-Doped Pb(Mg1/3Nb2/3)O3-0.28PbTiO3 Ceramic for Intravascular Ultrasound Imaging

Sm-doped Pb(Mg1/3Nb2/3)O3-0.28PbTiO3 (PMN-0.28PT) ceramic has been reported to exhibit very large piezoelectric response (d33~1300 pC/N) that can be comparable with PMN-0.30PT single crystal. Based on the Sm-doped PMN-0.28PT ceramics, a high frequency ultrasound transducer with the center frequency above 30 MHz has been designed and fabricated for intravascular ultrasound imaging, and the performance of the transducer was investigated via ultrasound pulse-echo tests. Further, for a porcine vessel wall, the 2D and 3D ultrasound images were constructed using signal acquisition and processing from the fabricated high-frequency transducer. The obtained details of the vessel wall by the IVUS transducer indicate that Sm-doped PMN-0.28PT ceramic is a promising candidate for high frequency transducers.

High-Frequency Linear Array (20 MHz) Based on Lead-Free BCTZ Crystal

Centimeter-sized BaTiO3-based crystals grown by top-seeded solution growth from the BaTiO3-CaTiO3-BaZrO3 system were used to process a high-frequency (HF) lead-free linear array. Piezoelectric plates with (110)pc cut within 1° accuracy were used to manufacture two 1-3 piezo-composites with thicknesses of 270 and [Formula: see text] for resonant frequencies in air of 10 and 30 MHz, respectively. The electromechanical characterization of the BCTZ crystal plates and the 10-MHz piezocomposite yielded the thickness coupling factors of 40% and 50%, respectively. We quantified the electromechanical performance of the second piezocomposite (30 MHz) according to the reduction in the pillar sizes during the fabrication process. The dimensions of the piezocomposite at 30 MHz were sufficient for a 128-element array with a 70- [Formula: see text] element pitch and a 1.5-mm elevation aperture. The transducer stack (backing, matching layers, lens, and electrical components) was tuned with the characteristics of the lead-free materials to deliver optimal bandwidth and sensitivity. The probe was connected to a real-time HF 128-channel echographic system for acoustic characterization (electroacoustic response and radiation pattern) and to acquire high-resolution in vivo images of human skin. The center frequency of the experimental probe was 20 MHz, and the fractional bandwidth at -6 dB was 41%. Skin images were compared against those obtained with a lead-based 20-MHz commercial imaging probe. Despite significant differences in sensitivity between elements, in vivo images obtained with a BCTZ-based probe convincingly demonstrated the potential of integrating this piezoelectric material in an imaging probe.

Lead-Free Piezoelectric Transducers

Research activities on lead-free piezoelectric materials have been ongoing for over 20 years. Generally, the applicability of the main material families is less universal than that of lead-based compositions such as lead zirconate titanate, but in some cases, the corresponding applications have already been identified. Due to the extensive research, it is now possible to manufacture demonstrators and prototypes for different applications and the authors propose in this article to take stock of these advances. For this, we have chosen to first recall briefly the main new material systems using a simplistic "soft" and "hard" classification for approaching the various resonant transducer applications. Medical imaging applications that represent one of the most important fields are presented in a second step together with other low-power transducers. Then, a variety of applications are merged under the heading of high-power transducers. In addition, we mention two points that are important to consider when manufacturing at a larger scale. For the design of transducers, complete datasets must be available, especially if modeling tools are used. Finally, the commercialization of these lead-free materials imposes essential secondary requirements in terms of availability, reproducibility, sample size, and so on.

Capacitive micromachined ultrasound transducers for intravascular ultrasound imaging

Intravascular ultrasound (IVUS) is a burgeoning imaging technology that provides vital information for the diagnosis of coronary arterial diseases. A significant constituent that enables the IVUS system to attain high-resolution images is the ultrasound transducer, which acts as both a transmitter that sends acoustic waves and a detector that receives the returning signals. Being the most mature form of ultrasound transducer available in the market, piezoelectric transducers have dominated the field of biomedical imaging. However, there are some drawbacks associated with using the traditional piezoelectric ultrasound transducers such as difficulties in the fabrication of high-density arrays, which would aid in the acceleration of the imaging speed and alleviate motion artifact. The advent of microelectromechanical system (MEMS) technology has brought about the development of micromachined ultrasound transducers that would help to address this issue. Apart from the advantage of being able to be fabricated into arrays with lesser complications, the image quality of IVUS can be further enhanced with the easy integration of micromachined ultrasound transducers with complementary metal-oxide-semiconductor (CMOS). This would aid in the mitigation of parasitic capacitance, thereby improving the signal-to-noise. Currently, there are two commonly investigated micromachined ultrasound transducers, piezoelectric micromachined ultrasound transducers (PMUTs) and capacitive micromachined ultrasound transducers (CMUTs). Currently, PMUTs face a significant challenge where the fabricated PMUTs do not function as per their design. Thus, CMUTs with different array configurations have been developed for IVUS. In this paper, the different ultrasound transducers, including conventional-piezoelectric transducers, PMUTs and CMUTs, are reviewed, and a summary of the recent progress of CMUTs for IVUS is presented.

Fabrication and Characterization of Single-Aperture 3.5-MHz BNT-Based Ultrasonic Transducer for Therapeutic Application

This paper discusses the fabrication and characterization of 3.5-MHz single-element transducers for therapeutic applications in which the active elements are made of hard lead-free BNT-based and hard commercial PZT (PZT-841) piezoceramics. Composition of (BiNa_0.88K_0.08Li_0.04)_0.5(Ti_0.985Mn_0.015)O₃ (BNKLT88-1.5Mn) was used to develop lead-free piezoelectric ceramic. Mn-doped samples exhibited high mechanical quality factor ( ) of 970, thickness coupling coefficient ( ) of 0.48, a dielectric constant ( ) of 310 (at 1 kHz), depolarization temperature ( ) of 200 °C, and coercive field ( ) of 52.5 kV/cm. Two different unfocused single-element transducers using BNKLT88-1.5Mn and PZT-841 with the same center frequency of 3.5 MHz and similar aperture size of 10.7 and 10.5 mm were fabricated. Pulse-echo response, acoustic frequency spectrum, acoustic pressure field, and acoustic intensity field of transducers were characterized. The BNT-based transducer shows linear response up to the peak-to-peak voltage of 105 V in which the maximum rarefactional acoustic pressure of 1.1 MPa, and acoustic intensity of 43 W/cm² were achieved. Natural focal point of this transducer was at 60 mm from the surface of the transducer.

Finite element static displacement optimization of 20-100 kHz flexural transducers for fully portable ultrasound applicator

This paper focuses on the development of a finite-element model and subsequent stationary analysis performed to optimize individual flexural piezoelectric elements for operation in the frequency range of 20-100kHz. These elements form the basic building blocks of a viable, un-tethered, and portable ultrasound applicator that can produce intensities on the order of 100mW/cm(2) spatial-peak temporal-peak (I(SPTP)) with minimum (on the order of 15V) excitation voltage. The ultrasound applicator can be constructed with different numbers of individual transducer elements and different geometries such that its footprint or active area is adjustable. The primary motivation behind this research was to develop a tether-free, battery operated, fully portable ultrasound applicator for therapeutic applications such as wound healing and non-invasive transdermal delivery of both naked and encapsulated drugs. It is shown that careful selection of the components determining applicator architecture allows the displacement amplitude to be maximized for a specific frequency of operation. The work described here used the finite-element analysis software COMSOL to identify the geometry and material properties that permit the applicator's design to be optimized. By minimizing the excitation voltage required to achieve the desired output (100mW/cm(2)I(SPTP)) the power source (rechargeable Li-Polymer batteries) size may be reduced permitting both the electronics and ultrasound applicator to fit in a wearable housing.