Single Transducer Research Articles

Complex analytical transducer model of a permanent magnet synchronous motor for vibroacoustic applications

This paper presents the complex analytical transducer model of a Permanent Magnet Synchronous Motor (PMSM) for vibroacoustic applications, meaning when the motor actually does not rotate but only the rotor oscillates with low amplitude around an equilibrium position relative to the stator. Using only two assumptions – sinusoidal air-gap flux density and evenly distributed winding – the single phase transducer model is introduced, which is then extended to cover motors with any number of phases. The article proposes adequate transducer symbols and transmission equations as well. In order to enhance the practical relevance of the proposed approach, it is shown that using complex amplitudes and appropriate phase shift vectors in the transducer equations, a complex parameter transducer model can be obtained for sinusoidal signals.

A theragnostic HIFU transducer and system for inherently registered imaging and therapy.

One big challenge with high intensity focused ultrasound (HIFU) is the difficulty in accurate prediction of focal location due to the complex wave propagation in heterogeneous medium even with imaging guidance. This study aims to overcome this by combining therapy and imaging guidance with one single HIFU transducer using the vibro-acoustography (VA) strategy. Based on the VA imaging method, a HIFU transducer consisting of 8 transmitting elements was proposed for therapy planning, treatment and evaluation. Inherent registration between the therapy and imaging created unique spatial consistence in HIFU transducer's focal region in the above three procedures. Performance of this imaging modality was first evaluated through in-vitro phantoms. In-vitro and ex-vivo experiments were then designed to demonstrate the proposed dual-mode system's ability in conducting accurate thermal ablation. Point spread function of the HIFU-converted imaging system had a full wave half maximum of about 1.2 mm in both directions at a transmitting frequency of 1.2 MHz, which outperformed the conventional ultrasound imaging (3.15 MHz) in in-vitro situation. Image contrast was also tested on the in-vitro phantom. Various geometric patterns could be accurately 'burned out' on the testing objects by the proposed system both in vitro and ex vivo. Implementation of imaging and therapy with one HIFU transducer in this manner is feasible and it has potential as a novel strategy for addressing the long-standing problem in the HIFU therapy, possibly pushing this non-invasive technique forward towards wider clinical applications.

Sleeved waveguide ultrasonic sensor for monitoring concrete health

This article reports the development of a novel embedded waveguide ultrasonic sensor for detecting the onset of damage in reinforced concrete structures. A sleeved waveguide is proposed to confine guided ultrasonic waves in one-dimension, with leakage to the surrounding media only through specially created openings, thus reducing attenuation losses and enhancing the capability to inspect large structures from a single transducer location. The test frequency and mode are identified through modelling, and the interaction of leaky guided ultrasonic waves with delamination within the concrete volume is studied. Numerical simulations validated by experiments are used to study the changes in wave features such as mode velocity, wavelength and wave reflection in the delamination region, helping to estimate its location. Further simulation studies are carried out to demonstrate the possibility of using multiple waveguide sensors and sleeve openings to provide a full view of the concrete volume. The results are encouraging for practical long-range and large-scale monitoring of concrete volumes using the proposed sleeved waveguide ultrasonic sensors.

Acoustic driven circulation around cylindrical obstructions in microchannels

We introduce an approach to generate direction-controlled circulation around cylindrical obstructions in channels using a piezoelectric transducer embedded porous-channel device fabricated by photolithography. To transmit acoustic signals into the channel, a single piezoelectric transducer was attached, operating at voltage levels of 5, 10, 15, and 20 V. Microscopic particle image velocimetry was employed to analyze the flow patterns in the channels. The analysis revealed two opposing circulation tendencies around the pillars located at two opposite sides of the channel in the longitudinal direction. The strength of circulation was found to be minimal in the middle of the channel and increased gradually toward the two ends of the channels. Furthermore, we observed that the circulation strength was maximum near the axial centerline and minimum at the boundaries along the width of the channels. Comparing the voltage levels, the higher voltage signals produced a higher strength of circulation than the lower voltage signals in all cases. Additionally, we found that the strength of circulation increased almost linearly and then decayed exponentially in the radial direction from the surfaces of the pillars. The observed velocity fields around individual cylinders matched well with the Görtler vortex model. The reported circulation phenomenon around pillars can be applied in non-contact fluid stirring and mixing in bio-chemical systems and lab-on-a-chip systems and may also provide additional degrees of freedom in object tweezing, trapping, and levitation.

Maximum Likelihood Identification of Backflow Vortex Instability in Rocket Engine Inducers

Abstract Bayesian estimation is applied to the analysis of backflow vortex instabilities in typical three- and four-bladed liquid propellant rocket engine inducers. The flow in the impeller eye is modeled as a set of equally intense and evenly spaced 2D axial vortices, located at the same radial distance from the axis and rotating at a fraction of the impeller speed. The circle theorem is used to predict the flow pressure in terms of the vortex number, intensity, rotational speed, and radial position. The theoretical spectra so obtained are frequency broadened to mimic the dispersion of the experimental results and parametrically fitted to the measured data by maximum likelihood estimation with equal and independent Gaussian errors. The method is applied to three inducers, tested in water at room temperature and different operating conditions. It successfully characterizes backflow instabilities using the signals of a single pressure transducer flush-mounted in the impeller eye, effectively bypassing the aliasing limitations and the data acquisition/reduction complexities of traditional multiple-sensor cross-correlation methods. The identification returns the estimates of the model parameters and their standard deviations, providing the information necessary for assessing the accuracy and statistical significance of the results. The flowrate is found to be the major factor affecting the backflow vortex instability, which, on the other hand, is rather insensitive to the occurrence of cavitation. The results are consistent with the data reported in the literature, as well as with those generated by the auxiliary models specifically developed for initializing the maximum likelihood searches and supporting the identification procedure.

Non-destructive triaxial vibroacoustic modal testing with a single sound transducer: a railway sleeper case study

ABSTRACT Vibrational experimental modal analysis (EMA) is among the most widely used modal parameter estimation techniques. However, it has several drawbacks, such as requiring accelerometer(s) mounting and using local measurements. Therefore, this study investigated whether vibroacoustic modal testing (VMT), a rarely studied method, would be a suitable alternative for EMA. In this context, a comparative case study was conducted on railway sleepers. First, modal parameter determination techniques in the literature were compared (time/frequency-domain, with/without normalisation, structural/acoustic excitation, and acoustic/vibrational response). Then, VMT and EMA test setups were reorganised considering the deficiencies identified in the literature. As a result, the difference between the VMT and EMA resonance frequency and damping ratios in the proposed mode shapes is determined as 0.06% and 3.46%, respectively. Consequently, this novel VMT setup using a single microphone that can take non-destructive, non-contact, and non-local (triaxial) measurements has been proven to provide reliable results and is recommended for future studies.

Dual-frequency piezoelectric micromachined ultrasound transducer based on polarization switching in ferroelectric thin films

Due to its additional frequency response, dual-frequency ultrasound has advantages over conventional ultrasound, which operates at a specific frequency band. Moreover, a tunable frequency from a single transducer enables sonographers to achieve ultrasound images with a large detection area and high resolution. This facilitates the availability of more advanced techniques that simultaneously require low- and high-frequency ultrasounds, such as harmonic imaging and image-guided therapy. In this study, we present a novel method for dual-frequency ultrasound generation from a ferroelectric piezoelectric micromachined ultrasound transducer (PMUT). Uniformly designed transducer arrays can be used for both deep low-resolution imaging and shallow high-resolution imaging. To switch the ultrasound frequency, the only requirement is to tune a DC bias to control the polarization state of the ferroelectric film. Flextensional vibration of the PMUT membrane strongly depends on the polarization state, producing low- and high-frequency ultrasounds from a single excitation frequency. This strategy for dual-frequency ultrasounds meets the requirement for either multielectrode configurations or heterodesigned elements, which are integrated into an array. Consequently, this technique significantly reduces the design complexity of transducer arrays and their associated driving circuits.

Phase holograms for the three-dimensional patterning of microparticles in a traveling wave field

Acoustic fields can generate radiation forces that can align particles in patterns. Forces from standing waves pattern particles in three dimensions (3-D) at either nodal or anti-nodal regions. These patterns can be utilized to form 3-D microstructures for applications in tissue engineering or fabrication of layered materials. However, standing waves require more than one transducer or a reflector, which can complicate implementation. Here, we developed a method to suspend and align microspheres using a traveling wave from a single transducer. Acoustic fields were shaped to align polyethylene microspheres mimicking tissue cells in parallel planes along the axis of the transducer. A Bessel-like beam was developed using diffraction theory and an iterative angular spectrum approach were used to design phase holograms to shape pressure fields. Gor’kov potential was used to calculate radiation forces while minimizing the axial forces to create a stable trap. The resulting pressure fields and particle patterns matched predictions with a similarity index >0.92, where 1 is a perfect match. The transverse radiation force was ten times each microsphere’s weight and comparable to the standing wave radiation forces. Next steps are in vivo implementation of cell patterning for tissue engineering. [Work supported by NIH K25-DK132416 and P01-DK043881.]

An improved lumped parameter model of the single free-flooded ring transducer using Helmholtz–Kirchhoff integral solution

The Helmholtz-Kirchhoff integral (HKI) may be considered as the boundary element method (BEM) used to calculate the acoustic pressure at any position in the 3D-radiation problem from a vibrating surface. This method provides valuable insights into the radiation characteristics of vibrating structures, which may offer significant information and tools to underwater transducer design engineers during the early stages of development. It may save considerable computational costs in the design processes for the underwater transducer such as Hull Mount Sonar. This study illustrates usefulness of the HKI-based approach by developing a simple model of the Free Flooded Ring (FFR) transducer using a piezoelectric ring model and the HKI solution on the surface acoustic pressure of the ring through their physical conditions on their connected interfaces. The FFR transducer is widely utilized as a low-frequency acoustic source in underwater environments due to its broad operating frequency bandwidth and relatively small size. The developed approach aims to construct a precise model that considers the sound-structure interactions between the piezoelectric ring and the acoustic medium around it. To validate the accuracy of the proposed method, the acoustic pressure and electrical admittance are compared with those obtained through finite element method (FEM) simulations.

High-Performance Electrode-Post CMUTs: Fabrication Details and Best Practices.

Capacitive micromachined ultrasound transducers (CMUTs) have been investigated for over 25 years due to their promise for mass manufacturing and electronic co-integration. Previously, CMUTs were fabricated with many small membranes comprising a single transducer element. This, however, resulted in suboptimal electromechanical efficiency and transmit performance, such that resulting devices were not necessarily competitive with piezoelectric transducers. Moreover, many previous CMUT devices were subject to dielectric charging and operational hysteresis that limited long-term reliability. Recently, we demonstrated a CMUT architecture using a single long rectangular membrane per transducer element and novel electrode-post (EP) structures. This architecture not only offers long-term reliability, but also provides performance advantages over previously published CMUT and piezoelectric arrays. The purpose of this article is to highlight these performance advantages and provide details of the fabrication process, including the best practices to avoid common pitfalls. The objective is to provide sufficient detail to inspire a new generation of microfabricated transducers, which could lead to performance gains of future ultrasound systems.

Verification of relationship between transmission/reception conditions of high-frequency plane wave compounding and evaluation accuracy of extended amplitude envelope statistics

Amplitude envelopment statistics is one of the effective analysis method for quantitative ultrasound. In the studies using a single transducer of around 15–25 MHz and the Double-Nakagami (DN) model, it was possible to evaluate fat mass in rat livers. In order to realize clinical applications, it is essential to study with array probes, especially to understand the influence of the sound field characteristics on the amplitude envelope statistics. In this study, fatty liver simulated phantoms which were containing two types of scatterers was observed with five types of high-frequency(15–40 MHz) linear array probes, and the amplitude enveloping characteristics were analyzed using the DN model to evaluate the fat constitution. As a result, it was possible to evaluate fatty components with high accuracy under conditions in which fat is distributed in low density, such as in mild fatty liver. No significant differences in evaluation systems were observed among the probes, probably due to the effect of parallel plane wave transmission and reception.

An Inertial Noncontact Piezoelectric Rotary Energy Harvester with Linear Reciprocating Motion

Herein, an inertial noncontact piezoelectric rotary energy harvester with linear reciprocating motion (L‐PREH) is presented. The existing piezoelectric rotary harvester employing gravity excitation has limited performance when the rotation speed is high due to the negative influence of centrifugal force. L‐PREH translates rotational motion into linear motion via the transmission chain and employs inertial force excitation to overcome high‐speed performance limitations. Using the Euler–Bernoulli beam theory, the motion governing equations of piezoelectric transducers have been derived, and an electromechanical coupling model has been constructed. Moreover, the piezoelectric transducer is simulated and analyzed. The control variable approach is used to explore the key parameters impacting output performance. When the mass is positioned in symmetrical method, the guide rod is fixed in noncentral place, the limiter is fixed in longest distance, the distance between the mass's center and the main frame is the maximum, and the rotating speed is 450 RPM, the maximum peak‐to‐peak output voltage of an L‐PREH single transducer is 24 V. The highest power of two piezoelectric transducers linked in parallel with a load resistance of 400 kΩ is 0.27 mW, which can light up more than 70 light‐emitting diodes. The L‐PREH can drive low‐power devices.

Estimating Young’s moduli based on ultrasound and full-waveform inversion

Ultrasound is commonly utilized to determine the dynamic Young’s moduli for estimating material deterioration or quantifying material parameters. This is either done with a resonance frequency analysis or ultrasound for rock or concrete specimens in geophysics or civil engineering. For ultrasound, these are typically cylindrical specimens measured in a through-transmission arrangement. However, this method presents some challenges, such as the need to accurately determine the onset of each wave mode and to calibrate system latency. To overcome these challenges, this study introduces a novel method that utilizes wavefield simulation and full-waveform inversion to estimate p- and s-wave, also called compression and shear wave, velocities. Where the traditional method requires two measurements, this innovative approach requires only one measurement with a single p-wave transducer. The s-wave velocity is estimated considering mode conversions within the specimen. High-fidelity ultrasound simulations are necessary for this approach. For that reason, the spatially distributed excitation of the ultrasound transducer is characterized by a laser Doppler vibrometer measurement. This led to a good estimate of the directivity pattern of the ultrasound transducer. The inverse problem for determining p- and s-wave velocity was solved successfully using a suitable misfit or cost function, the so-called graph-optimal-transport misfit. The specimens for the proof of concept study include six different metals. The precision of the estimated velocities using full-waveform inversion was compared with manual picking. As the simulated and measured waveforms matched well, this study can be seen as a starting point for material parameter determination for more complex geometries and heterogeneous materials using full-waveform inversion.

Blade Strain Peak Localization Method With Single Transducer During Multimode Vibration

Abstract The dynamic strain/stress measurement of blades provides an effective method to anticipate fatigue life and investigate of failure causes. Unlike the blade strain peak is fixed during singlemode, which can be measured by a single transducer, the strain peak distribution changes over time and space during multimode vibration situations. The existing method reconstructs the full-field strain to find the peak point with multiple transducers. In this work, a single transducer-based full-field dynamic strain reconstruction technique is presented to find the strain peak position on rotor blades. First, the mode response is obtained by separating the measured response from a single strain gauge based on Ensemble Empirical Mode Decomposition. Second, based on the strain mode shape from the finite element model, the reconstructed strain transmissibility matrix is created between a single measured location and the full field. Third, the dynamic strain of the blade can be reconstructed at any location and time by combining the separated mode response with the RST matrix. Finally, the strain peak localization is identified according to the distribution of full-field dynamic strain during multimode vibration. The above process is verified by experimental data from rotor blades with the maximum error of reconstructed strain below 12% and three explicitly recognized strain peak positions.

A human ear-inspired ultrasonic transducer (HEUT) for 3D localization of sub-wavelength scatterers

The proposed technology aims to enable 3D localization of scatterers using single element ultrasonic transducers, which are traditionally limited to 1D measurements. This is achieved by designing a bespoke acoustic lens with a spiral-shaped pattern similar to the human outer ear, a shape that has evolved for sound source localization. This lens breaks the surface symmetry of the transducer, allowing ultrasonic waves arriving from different directions to be encoded in a certain way that can later be decoded to extract directional information. By employing the mechanism of spatial-encoding of the received signals and decoding via signal processing, the location of sub-wavelength scatterers can be detected in 3D with a single measurement for sparsely distributed scatterers. The proposed technology is first verified through a simulation study, and then 3D printed acoustic lenses are used to demonstrate the 3D encoding functionality of the Human Ear-inspired Ultrasonic Transducer (HEUT) experimentally. A framework is created to localize scatterers in 3D by processing received signals acquired by a HEUT prototype. With this technology, a single transducer can obtain multi-dimensional information with a single pulse-echo measurement, reducing the number of elements required for performing 3D ultrasound localization. The proposed spatial-encoding and -decoding technology can be applied to other wave-based imaging methods to develop affordable, practical, and compact sensing devices.

An electrical impedance matching method of dual-frequency transducers for ultrasound internal imaging

A micro single transducer with two resonant frequencies can solve the inherent contradiction between detection depth and resolution by simultaneously emitting two frequency bands of ultrasonic waves. But the difference of impedance values in the two resonant frequency bands seriously affects dual-frequency echo signal efficiency. In order to improve the quality of transducer sensitivity, a dual-frequency electrical impedance matching method is proposed in the study. By selecting a specific matching structure to match one frequency without messing up the impedance of another frequency, the two frequencies can be designed independently to achieve preliminary impedance matching. The matching networks for single frequency are combined to form a complete dual-frequency matching circuit, and adjust the initial matching value to obtain a suitable matching state. The performances of the matching network have been tested and verified by experiments. After matching, the low-frequency and high-frequency sensitivities of the transducer increased 1.86 times and 2.26 times, respectively. In addition, system noise was also reduced by 29.6% after adding the matching network. The results demonstrate that this dual-frequency matching network can simultaneously increase the amplitude of high-frequency and low-frequency echoes to obtain better quality images.

Feasibility of Ultrasonic Heating through Skull Phantom Using Single-element Transducer.

Noninvasive neurosurgery has become possible through the use of transcranial focused ultrasound (FUS). This study assessed the heating ability of single element spherically focused transducers operating at 0.4 and 1.1 MHz through three-dimensional (3D) printed thermoplastic skull phantoms. Phantoms with precise skull bone geometry of a male patient were 3D printed using common thermoplastic materials following segmentation on a computed tomography head scan image. The brain tissue was mimicked by an agar-based gel phantom developed in-house. The selection of phantom materials was mainly based on transmission-through attenuation measurements. Phantom sonications were performed through water, and then, with the skull phantoms intervening the beam path. In each case, thermometry was performed at the focal spot using thermocouples. The focal temperature change in the presence of the skull phantoms was reduced to less than 20 % of that recorded in free field when using the 0.4 MHz transducer, whereas the 1.1 MHz trans-skull sonication produced minimal or no change in focal temperature. The 0.4 MHz transducer showed better performance in trans-skull transmission but still not efficient. The inability of both tested single element transducers to steer the beam through the high attenuating skull phantoms and raise the temperature at the focus was confirmed, underlying the necessity to use a correction technique to compensate for energy losses, such those provided by phased arrays. The proposed phantom could be used as a cost-effective and ergonomic tool for trans-skull FUS preclinical studies.

A phased array ultrasound system with a robotic arm for neuromodulation.

Ultrasonic neuromodulation (UNMOD) provides a non-invasive brain stimulation. However, the high-resolution region-specificity of UNMOD with a single element transducer combined with a mechanical positioning system could have limits due to the intrinsic positioning error from mechanical systems. A phased array system could lead to highly selective neuromodulation with electronic control. A specialized phased-array system with a robotic arm is implemented for a rhesus monkey model. Various primary motor cortex areas related to tail, hand, and mouth were stimulated with a 200μm step size. The ultrasonic parameters were ISPTA of 840mW/cm2, pulse repetition frequency of 100Hz, and a 5% duty factor at 600kHz. The induced movement were recorded and analyzed. Separate digits, mouth, and tongue motions were successfully induced by electronically controlling the focus. The identical body part movement could be induced when the focus was moved back to the identical primary motor cortex with electronic control. Accordingly, the reproducibility of UNMOD could be partially validated with rhesus monkey model. A phased-array system appears to have a potential for the non-invasive and region-selective neuromodulation method.

Performances of Multi-Configuration Piezoelectric Connection with AC-DC Converter in Low Frequency Energy Harvesting System

Harvesting energy by capturing vibration from low frequency energy have been explored extensively. In essence, a single piezoelectric transducer or an array of piezoelectric connections are used to convert kinetic energy into electrical energy in order to produce low frequency energy. In this paper, multi-configuration array piezoelectric connections are used to investigate the performances of different converter circuit types in low energy harvesting applications. This research utilized three pieces of circular piezoelectric sensor to test the combinations of array connection. There are four options for the piezoelectric sensor configuration: parallel (P), series (S), parallel-series (PS), and series-parallel (SP) while the full wave bridge rectifier (FWBR), parallel voltage multiplier (PVM), and parallel Synchronized Switch Harvesting on Inductor (P-SSHI) converter circuit are chosen AC-DC converter circuits. The system is assessed using a variety of load configurations, including 10 kΩ and 1 MΩ with a 3 Hz input frequency. In order to produce the highest possible output of collected power, the observation focuses on identifying the ideal combination of array piezoelectric connections with AC-DC converter. The result shows that 3-Parallel (3P) piezoelectric connection obtained a higher power output among the other types of array piezoelectric which was 5.97μW. The FWBR circuit generated the highest output power with 2.42μW for a combination of piezoelectric sensors array of 3P connection with the AC-DC converter.

An Implantable Wireless System for Remote Hemodynamic Monitoring of Heart Failure Patients.

This article presents an implantable wireless system for remote hemodynamic monitoring, which enables direct, continuous (24/7), and simultaneous measurement of pulmonary arterial pressure (PAP) and cross-sectional area (CSA) of the artery. The implantable device, which measures 3.2 mm × 2 mm × 10 mm, comprises a piezoresistive pressure sensor, an ASIC implemented in 180-nm CMOS, a piezoelectric ultrasound (US) transducer, and a nitinol anchoring loop. An energy-efficient pressure monitoring system, which employs duty-cycling and spinning excitation technique, achieves 0.44 mmHg resolution in a pressure range from -135 mmHg to +135 mmHg and consumes 1.1 nJ conversion energy. The artery diameter monitoring system utilizes the inductive characteristic of the implant's anchoring loop and achieves 0.24 mm resolution within a diameter range of 20 mm to 30 mm, four times higher than echocardiography lateral resolution. The wireless US power and data platform enables simultaneous power and data transfer employing a single piezoelectric transducer in the implant. The system is characterized with an 8.5 cm tissue phantom and achieves a US link efficiency of 1.8%. The uplink data is transmitted by using an ASK modulation scheme parallel to the power transfer and achieves a modulation index of 26%. The implantable system is tested in an in-vitro experimental setup, which emulates the arterial blood flow, and accurately detects fast pressure peaks for systolic and diastolic pressure changes at both 1.28 MHz and 1.6 MHz US powering frequencies, with corresponding uplink data rates of 40 kbps and 50 kbps.