Lithium Niobate Transducer Research Articles

A novel miniature swimmer propelled by 36° Y-cut lithium niobate acoustic propulsion system

Self-propelled swimmers using ultrasonic transducers have been proposed and studied. The screw and bionic propulsion systems have dominated underwater robots. However, the complex structures make miniaturization difficult. The swimmers with ultrasonic transducers have no moving parts such as fins or propellers and can be driven by the nanomechanical-vibration in the surface of the transducer. Simple structure and high driving frequency make it easy to miniaturize. A 36° Y-cut lithium niobate (LN) thickness-vibration-mode transducer is used to investigate an underwater acoustic propulsion system. LN transducers are manufactured to 10 × 10 mm, 7 × 7 mm, and 4 × 4 mm square plates. The zero-speed propulsion and no-load speed are investigated to evaluate the swimmer performance. A mm-order swimmer is studied with a 4 × 4 mm LN transducer. At last, the multi-degrees-of-freedom swimmer driven by three 7 × 7 mm LN transducers is demonstrated with the advance and sway locomotion. In the future, a small-scale and agile self-propelled swimmer with an acoustic propulsion system can be expected for narrow and complex environment tasks, such as seagrass-prone areas and narrow pipelines.

Effect of the area of a lithium niobate transducer on the efficiency of ultrasonic atomization driven by resonance vibration

In recent years, individual control of one’s personal environment has been drawing increasing attention due to the growing interest in health care. Wearable devices are especially useful because of their controllability regardless of location. Humidity is one of the inevitable factors in the personal environment as a preventive against infectious diseases. Although atomization devices are commonly used as a method of humidity control, at present, there are no wearable humidity control devices. Vibration of a lithium niobate (LN) device in the thickness mode is a promising piezoelectric method for miniaturization of atomization devices for humidity control. To miniaturize the atomization device, the transducer size needs to be small not so much as to decrease the atomization efficiency. However, the effect of the device area on the atomization efficiency of LN at a size suitable for mounting in wearable devices has not been studied. Here, we conducted an atomization demonstration of LN devices with different sizes to evaluate particle size and atomization efficiency. Furthermore, to reveal the relationship between vibration behavior and atomization efficiency, resonance vibration in the MHz frequency band was evaluated by the finite element method and an impedance analyzer. The results showed that the peak size of water particles atomized by each device was in the range of 3.2 to 4.2 µm, which is smaller than particles produced by typical piezoelectric ceramics. Moreover, the best LN size for efficient atomization was found to be 8 mm × 10 mm among the five LN device sizes used in experiments. From the relationship between vibration behavior and atomization efficiency, the size of the transducer was suggested to affect the vibration mode. The obtained result suggested that the LN device is suitable for small wearable nebulizer devices.

Direct observation of capillary waves due to high frequency ultrasound and their relation to atomized droplets

Ultrasonic atomization has been studied and used in applications for decades, but a mechanistic understanding of droplet production does not exist at a quantitative level. Early work seemed to indicate that droplet size follows from the driving frequency according to Kelvin's equation. The underlying assumptions in this model do not hold at larger frequencies, and the model relies on a fitting parameter that has not been consistent across experimental studies. Additionally, modern experiments often indicate multi-modal droplet size distributions further complicating the physics. It is difficult to experimentally measure relevant quantities like capillary wavelength because of the time and length scales involved and the fact that the phenomenon occurs at a free liquid surface. We use a high speed digital holographic microscope, the only one of its kind in the world, to image the liquid surface—in full 3D and real time—fast enough to resolve capillary waves generated by 5–50 MHz ultrasound. We extract from this data the spectrum of capillary wavelengths and then compare these to droplet size distributions measured with laser diffraction particle sizing. Both thickness mode and surface acoustic wave lithium niobate transducers are included as well as a range of frequencies in each case. It is shown that droplet size does depend directly on capillary wavelength, but that capillary wavelength is not related to the driving frequency in a simple way.

Piezoelectric creep in LiNbO3, PMN-PT and PZT-5A at low temperatures

Creep and hysteresis were directly measured for shear displacements of three widely used piezoelectric materials: 41° X-cut lithium niobate (LiNbO3), single crystal lead magnesium niobate-lead titanate (PMN-PT), and ceramic lead zirconium titanate (PZT-5A). Measurements were made at temperatures between 0.1 K and 310 K and at voltages up to 150 V. No creep or hysteresis was seen for the single domain lithium niobate transducer. PMN-PT exhibited large creep and hysteresis with a strong temperature dependence even at temperatures as low as 10 K. The temperature dependence was complicated and included an unusual region of negative creep around 250 K. The ceramic PZT-5A had significant creep near room temperature, which disappeared below about 35 K. The widths of the measured hysteresis loops mirrored the magnitudes of the creep that produces the hysteresis. We discuss the behavior of the three materials in terms of intrinsic and extrinsic mechanisms of piezoelectricity. Our results provide guidance in selecting materials for piezoelectric actuators for precise positioning applications like scanning tunneling microscopy. Although it is seldom used in actuator stacks, lithium niobate is the best choice for many cryogenic applications.

1P2-2 Development of laminated lithium niobate transducer available at 500℃

1P2-2 Development of laminated lithium niobate transducer available at 500℃

The acoustofluidic focusing and separation of rare tumor cells using transparent lithium niobate transducers.

Research on circulating tumor cells (CTCs) is of great significance in cancer diagnosis, prognosis and even the development of personalized therapy. Here, we present a simple and transparent acoustofluidic device for CTC separation in a label-free and non-invasive manner, instead of traditional acoustic devices based on silicon substrates, which are not only expensive, but also not conducive to optical visualization. The device is based on cheaper glass fabrication and integrated with a 36°Y-rotated cut lithium niobate single crystal (36° LNO) coated indium tin oxide (ITO) acoustic actuator instead of piezoceramics. It could greatly reduce the generation of heat when the signal is excited by utilizing the thickness vibration mode of the 36° LNO single crystal material because of its super-linear performance. Moreover, pre-aligning the particles in the sample inlet in a two-dimensional (2D) mode served to improve the separation efficiency of the device. It was proved that the separation efficiency of polystyrene particles was 97.1 ± 1.0%. The average separation efficiency of cancer cell lines (MCF7 and HeLa) mixed with white bloods cells was about 91.5 ± 4.5%. Owing to the excellent light transmittance of this acoustofluidic device, it has great potential for application to related optical techniques for cell detection while simultaneously separating cells relying on an acoustic field.

Ultrasound Transducers for Biomedical Imaging and Therapy

Ultrasound Transducers for Biomedical Imaging and Therapy

Electrical Control of the Frequencies of a Fabry–Perot Acoustic Resonator

The effect electronic tuning has on the frequency of the acoustic resonance of an acousto-optic modulator intended for active laser mode locking is studied theoretically and experimentally. The problem of exciting a Fabri–Perot acoustic resonator with a plate-like piezoelectric transducer is solved in the approximation of plane acoustic waves, with allowance for the real parameters of the HF generator and the matching elements of the transducer and the generator. Expressions for the basic electrical and acoustic parameters are obtained. Theoretical analysis confirms the frequency shift effect of acoustic resonances, observed earlier experimentally upon varying the matching electrical elements. The experiment is performed using an acousto-optic quartz cell and a lithium niobate transducer.

A light lithium niobate transducer for the ultrasonic de-icing of wind turbine blades

This paper proposes a non-thermal method for wind turbine blade de-icing. A lead-free lithium niobate compound is based to fabricate a light ultrasonic transducer as such material has a high Curie temperature of 1210 °C, compared with the commonly used piezoelectric ceramics (PZT). The detail of fabricating the transducer is provided, which includes an examination of the critical properties of the material, construction of the transducer and harmonic analysis of the plate-ice layered model. Test results showed that the lithium niobate transducer can remove effectively the ice layer created in a freezer at −15 °C on the outer surface of wind turbine blade sample. In addition, the optimal frequency of ultrasonic de-icing for wind turbine blade is found to be at 442 kHz driven under 50 V, which is agreeable with theoretical analysis.

Electronic tuning of acoustic resonances in acousto-optic mode lockers

Abstract The effect of electronic tuning of acoustic resonances in an acousto-optic mode locker is studied theoretically and experimentally. The tuning is implemented by means of changing a matching inductance connected to the transducer in parallel. Experimental investigations are carried out with a mode locker made of a fused quartz with a lithium niobate transducer. Varying magnitude of the inductor from 0.025 to 0.25 mH has made it possible to retune the acoustic resonance frequency by 0.19 MHz, i.e. wider than the acoustic resonance half-width.

A light lithium niobate transducer design and ultrasonic de-icing research for aircraft wing

Due to the strong piezoelectric effect possessed by lithium niobate and the fact that the adhesive bond of ice–substrate interface is relatively weak in shear, an ultrasonic de-icing technique that uses lithium niobate to design a light transducer for aircraft wing de-icing is proposed in this paper. The main contents of this paper are as follows: Firstly, a light de-icing lithium niobate transducer is designed to affix on the inner surface of the leading edge at the locations, where highest amount of ice accretion on the outer surface occurs. Secondly, the outdoor wing de-icing experiments are conducted to determine the optimal ultrasonic de-icing frequency. Finally, the design scheme of light-weight supersonic generator installed in the aircraft is presented. Research results show that this de-icing technique for aircraft wing de-icing is feasible, promising for further investigation.

Near-field acoustic microbead trapping as remote anchor for single particle manipulation

We recently proposed an analytical model of a two-dimensional acoustic trapping of polystyrene beads in the ray acoustics regime, where a bead diameter is larger than the wavelength used. As its experimental validation, this paper demonstrates the transverse (or lateral) trapping of individual polystyrene beads in the near field of focused ultrasound. A 100 μm bead is immobilized on the central beam axis by a focused sound beam from a 30 MHz single element lithium niobate transducer, after being laterally displaced through hundreds of micrometers. Maximum displacement, a longest lateral distance at which a trapped bead can be directed towards the central axis, is thus measured over a discrete frequency range from 24 MHz to 36 MHz. The displacement data are found to be between 323.7 μm and 470.2 μm, depending on the transducer's driving frequency and input voltage amplitude. The experimental results are compared with their corresponding model values, and their relative errors lie between 0.9% and 3.9%. The results suggest that this remote maneuvering technique may be employed to manipulate individual cells through solid microbeads, provoking certain cellular reactions to localized mechanical disturbance without direct contact.

Custom Lithium Niobate Transducer Arrays for Detecting Material Distribution of Hybrid Workpieces

Abstract Ultrasonic non-destructive testing is presented as a method to determine differences in material distribution at elevated temperatures in hybrid workpieces made of different metals. Varying material distribution causes differences in transit time and can be detected by ultrasonic transit time measurements. Therefore, custom transducers are manufactured to perform transit time measurements on hybrid workpieces. Results of these measurements are shown.

Mass-spring matching layers for high-frequency ultrasound transducers: a new technique using vacuum deposition.

We have developed a technique of applying multiple matching layers to high-frequency (>30 MHz) imaging transducers, by using carefully controlled vacuum deposition alone. This technique uses a thin mass-spring matching layer approach that was previously described in a low-frequency (1 to 10 MHz) transducer design with epoxied layers. This mass- spring approach is more suitable to vacuum deposition in highfrequency transducers over the conventional quarter-wavelength resonant cavity approach, because thinner layers and more versatile material selection can be used, the difficulty in precisely lapping quarter-wavelength matching layers is avoided, the layers are less attenuating, and the layers can be applied to a curved surface. Two different 3-mm-diameter 45-MHz planar lithium niobate transducers and one geometrically curved 3-mm lithium niobate transducer were designed and fabricated using this matching layer approach with copper as the mass layer and parylene as the spring layer. The first planar lithium niobate transducer used a single mass-spring matching network, and the second planar lithium niobate transducer used a single mass-spring network to approximate the first layer in a dual quarter-wavelength matching layer system in addition to a conventional quarter-wavelength layer as the second matching layer. The curved lithium niobate transducer was press focused and used a similar mass-spring plus quarter-wavelength matching layer network. These transducers were then compared with identical transducers with no matching layers and the performance improvement was quantified. The bandwidth of the lithium niobate transducer with the single mass-spring layer was measured to be 46% and the insertion loss was measured to be -21.9 dB. The bandwidth and insertion loss of the lithium niobate transducer with the mass-spring network plus quarter-wavelength matching were measured to be 59% and -18.2 dB, respectively. These values were compared with the unmatched transducer, which had a bandwidth of 28% and insertion loss of -34.1 dB. The bandwidth and insertion loss of the curved lithium niobate transducer with the mass-spring plus quarter-wavelength matching layer combination were measured to be 68% and -26 dB, respectively; this compared with the measured unmatched bandwidth and insertion loss of 35% and -37 dB. All experimentally measured values were in excellent agreement with theoretical Krimholtz-Leedom-Matthaei (KLM) model predictions.

Cell membrane deformation induced by a fibronectin-coated polystyrene microbead in a 200-MHz acoustic trap

The measurement of cell mechanics is crucial for a better understanding of cellular responses during the progression of certain diseases and for the identification of the cell's nature. Many techniques using optical tweezers, atomic force microscopy, and micro-pipettes have been developed to probe and manipulate cells in the spatial domain. In particular, we recently proposed a two-dimensional acoustic trapping method as an alternative technique for small particle manipulation. Although the proposed method may have advantages over optical tweezers, its applications to cellular mechanics have not yet been vigorously investigated. This study represents an initial attempt to use acoustic tweezers as a tool in the field of cellular mechanics in which cancer cell membrane deformability is studied. A press-focused 193-MHz single-element lithium niobate (LiNbO3) transducer was designed and fabricated to trap a 5-μm polystyrene microbead near the ultrasound beam focus. The microbeads were coated with fibronectin, and trapped before being attached to the surface of a human breast cancer cell (MCF-7). The cell membrane was then stretched by remotely pulling a cell-attached microbead with the acoustic trap. The maximum cell membrane stretched lengths were measured to be 0.15, 0.54, and 1.41 μm at input voltages to the transducer of 6.3, 9.5, and 12.6 Vpp, respectively. The stretched length was found to increase nonlinearly as a function of the voltage input. No significant cytotoxicity was observed to result from the bead or the trapping force on the cell during or after the deformation procedure. Hence, the results convincingly demonstrated the possible application of the acoustic trapping technique as a tool for cell manipulation.

Acoustic Radiation Force Impulse (ARFI) Imaging of Zebrafish Embryo by High-Frequency Coded Excitation Sequence

Acoustic radiation force impulse (ARFI) imaging has been developed as a non-invasive method for quantitative illustration of tissue stiffness or displacement. Conventional ARFI imaging (2-10 MHz) has been implemented in commercial scanners for illustrating elastic properties of several organs. The image resolution, however, is too coarse to study mechanical properties of micro-sized objects such as cells. This article thus presents a high-frequency coded excitation ARFI technique, with the ultimate goal of displaying elastic characteristics of cellular structures. Tissue mimicking phantoms and zebrafish embryos are imaged with a 100-MHz lithium niobate (LiNbO₃) transducer, by cross-correlating tracked RF echoes with the reference. The phantom results show that the contrast of ARFI image (14 dB) with coded excitation is better than that of the conventional ARFI image (9 dB). The depths of penetration are 2.6 and 2.2 mm, respectively. The stiffness data of the zebrafish demonstrate that the envelope is harder than the embryo region. The temporal displacement change at the embryo and the chorion is as large as 36 and 3.6 μm. Consequently, this high-frequency ARFI approach may serve as a remote palpation imaging tool that reveals viscoelastic properties of small biological samples.

Simultaneous Measurements of Harmonic Waves at Fatigue-Cracked Interfaces

Nonlinear harmonic waves generated at cracked interfaces are investigated theoretically and experimentally. A compact tension specimen is fabricated and the amplitude of the transmitted wave is analyzed as a function of position along the fatigued crack surface. In order to measure as many nonlinear harmonic components as possible, broadband lithium niobate (LiNbO3) transducers are employed together with a calibration technique for making absolute amplitude measurements with fluid-coupled receiving transducers. Cracked interfaces are shown to generate high acoustic nonlinearities, which are manifested as harmonics in the power spectrum of the received signal. The first subharmonic f/2 and the second harmonic 2f waves are found to be dominant nonlinear components for an incident toneburst signal of frequency f. To explain the observed nonlinear behavior, a partially closed crack is modeled by planar half interfaces that can account for crack parameters, such as crack opening displacement and crack surface conditions. The simulation results show reasonable agreement with the experimental results.

Lithium niobate transducers for MRI-guided ultrasonic microsurgery

Focused ultrasound surgery (FUS) is usually based on frequencies below 5 MHz-typically around 1 MHz. Although this allows good penetration into tissue, it limits the minimum lesion dimensions that can be achieved. In this study, we investigate devices to allow FUS at much higher frequencies, in principle, reducing the minimum lesion dimensions. Furthermore, FUS can produce deep-sub-millimeter demarcation between viable and necrosed tissue; high-frequency devices may allow this to be exploited in superficial applications which may include dermatology, ophthalmology, treatment of the vascular system, and treatment of early dysplasia in epithelial tissue. In this paper, we explain the methodology we have used to build high-frequency high-intensity transducers using Y-36°-cut lithium niobate. This material was chosen because its low losses give it the potential to allow very-high-frequency operation at harmonics of the fundamental operating frequency. A range of single-element transducers with center frequencies between 6.6 and 20.0 MHz were built and the transducers' efficiency and acoustic power output were measured. A focused 6.6-MHz transducer was built with multiple elements operating together and tested using an ultrasound phantom and MRI scans. It was shown to increase phantom temperature by 32°C in a localized area of 2.5 x 3.4 mm in the plane of the MRI scan. Ex vivo tests on poultry tissue were also performed and shown to create lesions of similar dimensions. This study, therefore, demonstrates that it is feasible to produce high-frequency transducers capable of high-resolution FUS using lithium niobate.

Characterization of a 40-MHz focused transducer with a fiber grating laser hydrophone

A novel fiber-optic hydrophone based on a dual-polarization, short-cavity fiber grating laser as the sensing element is described. Wet chemical etching was used to fabricate a thinned fiber sensor to extend its frequency response as well as spatial resolution. The lateral beam profile at the focal plane of a 40-MHz lens-focused lithium niobate (LiNbO3) transducer was measured with the fiber sensor, and a tomographic technique was used to compute the transducer profile, which is compared with that obtained by a PVDF hydrophone. The fiber hydrophone has a sensitivity of approximately -259 dB re 1 V/muPa up to 40 MHz, which is higher than that of a commercial PVDF hydrophone. Moreover, it is capable of accurately characterizing the beam generated by high-frequency transducer.

HYPERSPECTRAL AND POLARIZATION IMAGING WITH DOUBLE-TRANSDUCER AOTFS FOR WIDER SPECTRAL COVERAGE

We have developed a number of programmable hyperspectral imagers operating from the ultraviolet to the longwave infrared using an acousto-optic tunable filter (AOTF) in conjunction with a suitable camera. Each of these AOTFs is fabricated with a single transducer to operate over only one octave in wavelength. Recently, we have developed two separate tellurium dioxide ( TeO 2) noncollinear AOTF cells that operate over two octave range. Each cell has an aperture of 1.5 × 1.5 cm 2 with a field-of-view of 4.2°, and two thin-plate lithium niobate transducers are bonded on it. The tuning range of the first cell is 0.43–2.1 μm , and 0.69–4.0 μm for the second cell. We have used each of these cells to carry out spectral imaging experiments with CCD, InGaAs , and InSb cameras to cover the spectral region from the visible to the midwave infrared. We image the two orthogonally polarized diffracted beams to get spectropolarimetric information from the scene, as well as a broadband image by using one of the undiffracted beams. In this paper, we discuss the two AOTF cells, the imaging experiments, and present the results obtained.