Ultrasonic Applications Research Articles

Concave Array Ultrasonic Transducer From Multilayer Piezoelectric Ceramic for Photoacoustic Imaging.

Implementation of piezoelectric multilayer ceramic (MLC) is an effective way to reduce impedance and improve the performance of linear-array transducer for ultrasonic system applications. However, the ultrasonic image derived from a planar linear-array transducer generally suffers from degradation of lateral resolution and contrast. In this article, we designed and fabricated a focused 5-MHz 128-element linear-array ultrasonic transducer with concave structure using five-layered 0.1Pb (Ni1/3Nb2/3)O3 -0.35Pb(Zn1/3Nb2/3)O3 -0.15Pb(Mg1/3Nb2/3)O3-0.1PbZrO3-0.3PbTiO3 (PNN-PZN-PMN-PZ-PT) piezo- electric ceramic. The transducer showed a bandwidth of 63% at -6 dB and the lateral resolution up to 0.33 mm. An improved transmission signal of 90% higher than a commercial single-layer ceramic transducer was also achieved. We further demonstrated high-resolution photoacoustic imaging with the obtained concave linear-array transducer.

Single-chip mixer-based subarray beamformer for sub-Nyquist sampling in ultrasound imaging

Compressed sensing (CS) has been proposed as a method of breaking the seemingly inherent tradeoff between sampling rate and resolution in a variety of applications, such as ultrasound imaging. Although various studies have demonstrated the effectiveness of using CS for sub-Nyquist sampling in ultrasound imaging, a dedicated integrated circuit (IC) has not yet been presented. This work introduces a single-chip mixer-based subarray beamformer, an important component for sub-Nyquist sampling in a CS ultrasound imaging system. The beamformer chip, which performs mixing, filtering, and summation of delayed signals within a subarray, is implemented using a single operational transconductance amplifier. We evaluated the performance of the proposed mixer-based subarray beamformer circuit fabricated using a 65 nm CMOS process with 0.4 mW ch−1 power consumption from a 1.2 V supply. Measurement results indicate that the prototype chip is suitable for subarray beamforming with a 5 ns resolution digital mixing sequence. The IC presented here is the first known implementation of a mixer-based subarray beamformer for sub-Nyquist sampling in ultrasonic applications and is expected to reduce sampling data requirements by a factor of 32.

Development and Evaluation of an Ultrasonic Humidifier to Control Humidity in a Cold Storage Room for Postharvest Quality Management of Dates

Dates are subjected to postharvest losses in quality and quantity caused by water loss, fermentation, insect infestation, and microbial spoilage during storage. Cold storage is the main element in the postharvest quality management used for fruit preservation. Although cold storage is used for dates, precision control of the relative humidity (RH) using ultrasonic applications is not used thus far, or it is applied to other fruits on a small scale. Therefore, we designed and constructed an ultrasonic humidifier (DUH) for RH control in the cold storage room (CSR) of dates. The optimum air velocity of 3 m s−1 at the outlets of the DUH ducts produced a mist amount of 6.8 kg h−1 with an average droplet diameter of 4.26 ± 1.43 µm at the applied voltage of 48 V and frequency of 2600 kHz of the transducers. The experimental validation was carried out by comparing a CSR controlled with the DUH with two conventional CSRs. The three tested CSRs were similar in dimensions, cooling system, and amount of stored dates. The time required for cooling 800 kg of dates in the controlled CSR from 25 °C to the target temperature of 5 °C was approximately 48 h. The DUH precisely controlled the RH at the maximum RH set point of 80% in the tested CSR at 5 °C. The controlled RH at 80% has a positive impact on the physicochemical characteristics of the stored dates. It significantly reduced the weight loss of the fruits and preserved fruit mass, moisture content, water activity, firmness, and color parameters. However, no significant effect was observed on fruit dimensions, sphericity, and aspect ratio. The microbial loads of mesophilic aerobic bacteria, molds, and yeasts fell within the acceptable limits in all tested CSRs. Both stored date fruits and artificially infested dates showed no signs of insect activity in the controlled CSR at the temperature of 5 °C and RH of 80%. The DUH proved to be a promising technology for postharvest quality management for dates during cold storage.

Feasibility of Reference Material Certification for Speed of Sound and Attenuation Coefficient Based on Standard Tissue-Mimicking Material

Speed of sound and attenuation are essential for characterizing reference materials such as biological tissue-mimicking materials (TMMs) used in ultrasonic applications. There are many publications on the manufacture of TMMs and the measurement of their properties. However, no studies in the literature have applied the metrological approach of International Organization for Standardization (ISO) Guide 35 to certify biological ultrasound TMMs as candidates for reference materials (RMs). The work described here was aimed at studying the process for manufacturing fat, muscle and aorta artery TMMs, including the study of the homogeneity, stability, trend and characterization of TMMs. The properties of interest were the speed of sound (SoS) and attenuation coefficient (AttC) at 7.5 MHz, with target expanded uncertainty of 40 m/s and 0.3 dB/cm, respectively. The short-term stability study was 2 mo at 4°C and 40°C (simulating possible transportation conditions). The long-term stability study lasted an additional 4 mo with the TMM at 22°C (simulating possible storage conditions). Homogeneity was evaluated before the stability study. Uncertainties associated with homogeneity, stability, characterization and trend were duly calculated. No trend was observed in this study, but the AttC spread widely during the stability test, substantially enlarging the final uncertainty. Therefore, this property could not be used to certify TMM candidates as RMs. However, the SoSs for most TMMs lay within the target uncertainty, disclosing viability to certify TMMs as RMs for this property. Assigned values for SoS were 1560 m/s for aorta TMM with an average expanded uncertainty for certificate validity of 12 mo (Ue;12=20 m/s), 1552 m/s for muscle TMM (Ue;12=20 m/s) and 1494 m/s for fat TMM (Ue;12=11 m/s). Thus, TMMs were proved suitable to be certified as RMs for SoS.

Engineering the electromechanical response of piezoelectric transducers: Some challenging applications

Piezoelectric transducers are widely used for ultrasonic applications both as actuators to excite and as sensors to receive vibration/wave response. The electromechanical characteristics of the piezoelectric transducers dictate their choice for specific applications. These can be tuned in several ways ranging from modifying the geometry and material properties of the element to changing the excitation electrode pattern and the boundary conditions of the vibrating piezoelectric element. This talk discusses two different ways to achieve such tuning for single-element piezoelectric transducers and their corresponding applications. The first application is to achieve a low-frequency collimated beam using lateral stiffening of a piezoelectric disc vibrating in its radial resonance. The resonance and vibration characteristics of such a disc are presented and the ultrasonic wave propagation from such a laterally stiffened disc in fluids is discussed. The second application uses tailored polarization profiles for piezoelectric elements to enhance/suppress specific resonant modes in an otherwise homogeneous element. The fundamental theory for such behavior is presented and some applications of such polarization-tuned piezoelectric elements are discussed.

Three-dimensional phononic crystal with ultra-wide bandgap at megahertz frequencies

Phononic crystals have attracted wide attention in diverse scientific communities due to their ability to efficiently reflect, focus, and guide acoustic and elastic waves. Their use in ultrasonic applications such as medical imaging, however, remains elusive since three-dimensional phononic crystals with lattice constants in the range of hundreds of micrometers are required to operate with MHz ultrasound, smaller than what most additive manufacturing solutions can provide. This work presents a three-dimensional phononic crystal with a cubic symmetry having an experimental ultra-wide complete bandgap extending from 0.6 MHz to 7.5 MHz. Crystal specimens are manufactured using two-photon lithography at the microscale, with a lattice constant of 300 μm, and are characterized using heterodyne interferometry.

Hardening effect in lead-free piezoelectric ceramics

Ecologically sustainable development of piezoelectric ceramics has been the primary target of the community over the past 20 years. While the development of “soft” lead-free piezoelectric ceramics has been of high maturity, the understanding of “hard” lead-free piezoelectric ceramics is still far from satisfactory, leading to a limited chance for high-power applications. The review starts with an introduction of loss mechanisms and the hardening effect in piezoelectric ceramics, including three different models mainly developed based on the lead zirconate titanate system. Then, studies on the hardening behavior of BaTiO3-based, (Bi0.5Na0.5)TiO3-based, and (K0.5Na0.5)NbO3-based lead-free piezoelectric ceramics are summarized with emphasis on the approaches to enhance mechanical quality factor. Meanwhile, three different characterization methods of high-power performances are introduced: the constant-voltage method, constant-current method, and transient (or burst) method. Finally, the state-of-the-art lead-free ultrasonic transducer applications are highlighted. This paper concludes with the remaining challenges for the development of “hard” lead-free piezoelectric ceramics for high-power piezoelectric applications.

Enhanced mechanically induced red-light emitting novel mechanoluminescence materials for ultrasonic visualization and monitoring applications

When Ca2+ is substituted with Sr2+, the optical band gap of (Ca, Sr)ZnOS:Mn2+ becomes narrower and the trap depths becomes deeper, which leads to ML enhanced. The monitoring of ultrasonic intensity was achieved by using this ML material.

A proposal for 1×4 phononic switch/demultiplexer using composite lattices

This study introduces the complete investigation and design procedure of a two-dimensional fluid/fluid phononic crystal structure that operates as an acoustic wave demultiplexer and switch. The designed phononic crystal is made of a periodic array – consisting ethyl nonafluorobutyl ether cylindrical rods - embedded in a mercury background. Also, presented demultiplexer-switch structure includes four different cavities, which have improved dual separating and switching performances. The finite element method has been used to calculate the designed phononic crystal band diagrams and corresponding transmission spectrums. The acoustic demultiplexer can also operate as ultrasonic wave switch, as a result of the proposed structure material dependence to temperature. To the best of our knowledge, this is the first two-dimensional fluid/fluid phononic crystal structure proposed for ultrasonic switch-demultiplexer dual applications with temperature control.

Modeling and optimization of directive acoustical particle velocity sensors for ultrasonic applications

Acoustical particle velocity sensors for applications in the ultrasonic frequency range are investigated by means of finite element simulations. The operating principle of these devices is modulation of the heat transfer between pairs of parallel microwires, caused by the propagation of the acoustic wave. The sensing structure has been designed to be compatible with a commercial CMOS process followed by a simple post-processing procedure. An efficient enhanced-2D model has been used for the simulation of three different sensing structures. The dependence of the frequency response on geometrical parameters is investigated, demonstrating that one of the three analyzed structures can be actually optimized to obtain usable performances up to ultrasound frequencies.

Lead-Free KNN-Based Textured Ceramics for High-Frequency Ultrasonic Transducer Application.

Environment-friendly lead-free piezoelectric materials with excellent piezoelectric properties are needed for high-frequency ultrasonic transducer applications. Recently, lead-free 0.915(K0.45Na0.5Li0.05)NbO3-0.075BaZrO 3-0.01(Bi0.5Na0.5)TiO3 (KNLN-BZ-BNT) textured piezo- electric ceramics have high piezoelectric response, superior thermal stability, and excellent fatigue resistance, which are promising for devices applications. In this work, the KNLN-BZ-BNT textured ceramics were prepared by the tape-casting method. Microstructural morphology, phase transition, and electrical properties of KNLN-BZ-BNT textured ceramics were investigated. High-frequency needle-type ultrasonic transducers were designed and fabricated with these textured ceramics. The tightly focused transducers have a center frequency higher than 80 MHz and a -6-dB fractional bandwidth of 52%. Such transducers were built for an f -number close to 1, and the desired focal depth was achieved by press-focusing technology associated with a set of customer design fixture. Its lateral resolution was better than [Formula: see text] by scanning a 15- [Formula: see text] tungsten wire target. These promising results demonstrate that the lead-free KNLN-BZ-BNT textured ceramic is a good candidate for high-frequency ultrasonic transducer applications.

Reflective acoustic holograms for arbitrary pressure patterning and focusing

Monolithic passive holographic lenses (MPHLs) are being proposed as an alternative technology to phased array transducers (PATs) and subwavelength structured metamaterials due to their unprecedented spatial control over the sound field. These new capabilities enable precise focusing of acoustic energy or high resolution elaborate pressure patterning without the limitations associated with the aforementioned techniques. In particular, PATs and metamaterials require either an impractical high number of active elements or face fabrication limitations when operated at ultrasonic frequencies, especially underwater or inside the human body. MPHLs do not have such limitations and are being utilized in a wide range of crucial ultrasonic applications such as medical imaging and therapy, ultrasonic contactless energy transfer and nondestructive testing. In this work, we introduce a 3-D-printed metal reflective acoustic hologram. We will present the modeling and design process of such holograms as well as their capabilities for constructing single and multifocal spatial distributions of acoustic energy in a target plane. The effects of operating frequency, hologram material and propagation distance will also be highlighted. The results are verified using finite element multiphysics simulations in COMSOL as well as experimental investigations. [This work was supported by NSF Grant Nos. ECCS—1711139 and IIP-1738689, which are gratefully acknowledged.]

Effects of liquid compressibility on the dynamics of ultrasound contrast agent microbubbles

Ultrasound contrast agents (UCA) have been widely used in ultrasonic medical applications. The dynamics of UCA should be simulated accurately to maximize the application effects. The acoustic radiation of UCA oscillations is affected by the liquid compressibility which has to be considered. This paper deduces a simple equation based on Keller-Miksis equation to describe the dynamics of UCA with a polymer shell, taking consideration of compressibility of the liquid. The volume of UCA shell is constant. The shell is described by the Kelvin-Voigt viscoelasticity model.The extended compressible model is verified by comparing with experimental data and Hoff model in predicting the variations of bubble radius with time, resonance frequency, damping constants and acoustical scattering cross section of the UCA microbubbles. The physical explanations of the differences between the extended compressible model and Hoff model in predicting resonance frequency and acoustical scattering cross section are listed. The liquid compressibility correction in UCA model can be better used to predict the bubble dynamics at large radius with high excitation frequency, and it will give us some valuable references in ultrasonic medical applications.

Ultrasonically enhanced electrohydraulic discharge for removal of organic compounds

We investigate the decomposition of phenol using a hybrid reactor that combines a pulsed electrohydraulic discharge plasma with ultrasound application to increase the efficiency of wastewater treatments. The discharge and grounded electrodes are a needle-type electrode and a perforated plate, respectively. Ultrasound is directly applied to the plasma reactor through water by using ultrasonic oscillators. Hybridization of the pulsed high-voltage discharge with ultrasound generates a continuous streamer discharge by cavitation-induced bubbles. The phenol removal efficiency (energy yield) becomes higher than that corresponding to the sum of the efficiencies of the pulsed high-voltage discharge and ultrasonic applications.

Guest Editorial: Non‐Destructive Testing

Guest Editorial: Non‐Destructive Testing

Elastic metamaterial rod for mode filtering in ultrasonic applications

The proposed 1D elastic metamaterial rod finds application in non-destructive evaluation, as a filter in the transduction side, where only the torsional and flexural modes need to be generated by isolating longitudinal modes. In this Letter, this is achieved by obtaining a wide bandgap in low-frequency ultrasound regime. The novelty of the proposed design arises from the use of a high impedance mismatch between the materials selected for the rod. The proposed concept is demonstrated and verified with numerical simulations. The effectiveness of the proposed technique is confirmed by comparing the results obtained from the rod made of a single material.

3D finite element analysis of corrugated silicon carbide membrane for ultrasonic MEMS microphone applications

We investigated theoretically the feasibility of the SiC membrane to be applied to a MEMS capacitive microphone system in the ultrasonic frequency range. The fascinating electromechanical properties of SiC materials as membranes were examined to operate beyond 20 kHz to detect sound waves. The finite element method of real behavior microphone was conducted to analyze comprehensively the mechanical, electrical, and thermoviscous-acoustical interaction of the SiC-based microphone. A static analysis study speculated that the SiC membrane has high pull-in voltage that would overcome membrane touch backplate problems in narrow air gap dimension. A complete 3D model of the microphone with acoustic holes and backchamber was proposed in dynamic analysis to evaluate SiC membrane performance as ultrasonic sound detection. The dimension of acoustic holes was varied to optimize low air damping characteristics for the improvement of the microphone resonance frequency. The sensitivity of the proposed model was measured at − 65 dB and can be further improved by designing a corrugated membrane structure with a corrugation width of 40 µm to achieve − 60 dB. The corrugated Si membrane observed the shift in the resonance frequency to 51 kHz as compared to the plane SiC-based microphone that was located at 70 kHz.

Feasibility study on carbonated water for Doppler imaging in medical ultrasonic applications

A medium other than the blood-mimicking fluid generally used for a Doppler ultrasound that allows the appearance of blood-like responses in ultrasound images is investigated in this study. To create the media used in this study, sugar, salt, and starch (1 g each) were diluted in 50 cc of water, and along with distilled water, cooking oil, and carbonated water (50 cc each) without dilution, were then individually added into six latex balloons. A water tank of 18 (W) × 30 (L) × 10 (H) cm3 was filled with water, and all six balloons containing a prepared fluid were fixed three each on opposite walls of the tank 3 cm below the water surface. To obtain a proper Doppler ultrasound, the gain was set to 54, 60, and 66, and the color Doppler was measured. A qualitative evaluation was conducted through blind tests by 15 radiologists, and the coefficient of variation (COV), natural image quality evaluator (NIQE), and blind/referenceless image spatial quality evaluator (BRISQUE) were used for a quantitative evaluation. In the evaluations, carbonated water was evaluated as achieving a clear flow (p < 0.05) and a high value in all cases with a change in gain. This study investigated the Doppler sensitivity using sugar water, salt water, starch, cooking oil, distilled water, and carbonated water, and confirmed that carbonated water achieves the highest Doppler sensitivity. The results of this study can be utilized as basic data in various future studies on Doppler sensitivity using carbonated water.

Low Temperature Adhesive Bonding-Based Fabrication of an Air-Borne Flexible Piezoelectric Micromachined Ultrasonic Transducer.

This paper presents the development of a flexible piezoelectric micromachined ultrasonic transducer (PMUT) that can conform to flat, concave, and convex surfaces and work in air. The PMUT consists of an Ag-coated polyvinylidene fluoride (PVDF) film mounted onto a laser-manipulated polymer substrate. A low temperature (<100 °C) adhesive bonding technique is adopted in the fabrication process. Finite element analysis (FEA) is implemented to confirm the capability of predicting the resonant frequency of composite diaphragms and optimizing the device. The manufactured PMUT exhibits a center frequency of 198 kHz with a wide operational bandwidth. Its acoustic performance is demonstrated by transmitting and receiving ultrasound in air on curved surface. The conclusions from this study indicate the proposed PMUT has great potential in ultrasonic and wearable devices applications.

A frequency generator of 40-60 kHz based on arduino for ultrasonic cleaner applications

In this study, the design and implementation of a frequency generator of 40 to 60 kHz based on Arduino were carried out by using the pulse width modulation (PWM) technique for ultrasonic cleaner applications. The components used in the study are Arduino Uno, Stainless Tank, four digits seven segment, 4×4 keypad module, TM 1637 module, dimmer module, frequency generator module, and switching mode power supply (SMPS). Calibration of the voltage, frequency, and vibration strength using are multimeters, Equivalent Series Resistance (ESR) meters, and vibration meters. This study aims to design and analyze ultrasonic generator drivers used an Arduino for controlling frequency and time. The regulated input frequency of 50-200 Hz produces an output voltage of 0.3-4.0 volt and an output frequency of 40-60 kHz from an ultrasonic generator. The output voltage is more stable and precision than the frequency output. The ultrasonic cleaner produced has a very high level of precision and accuracy. The relationship of vibration to frequency is directly proportional, the greater the frequency, the greater the vibration produced. The voltage and frequency are inversely proportional; the greater the frequency, the voltage will be smaller.