Single Transducer Research Articles

Finite Element Method Modeling for Extended Depth of Focus Acoustic Transducer

Abstract Extended depth of focus (DOF) with high lateral resolution is the primary requirement of the transducer in scanning acoustic microscopy to generate high-resolution images of the three-dimensional sample over a large depth. Traditionally, focused ultrasonic spherical transducers are used to tightly focus the acoustic waves generated from a piezoelectric material for a wide range of applications in industrial, medical, and other fields. Such transducers have a problem of narrow DOF which restricts the imaging range in depth. In the present work, we propose three different transducer designs such as single axicon, central flat axicon, and double axicon, which enable the possibilities of high transverse resolution imaging over greater depths due to the significant increase in DOF. Finite element modeling (FEM) in comsol of a spherical, single axicon, central flat axicon, and double axicon transducer is systematically performed and compared in terms of transverse resolution, DOF, and acoustic pressure in the central lobe. In addition, the single axicon and double axicon transducer modeling is done for different apex angles. It is observed that the central flat axicon transducer allows customizable DOF and the double axicon transducer provides high lateral resolution and reduced pressure in the side lobes compared to a single axicon lens.

Combined drug delivery and treatment monitoring using a single high frequency ultrasound system

Ultrasound-mediated drug delivery is typically performed using transducers with center frequencies ≤ 1 MHz to promote acoustic cavitation. Such frequencies are not commonly used for diagnostic ultrasound due to limited spatial resolution. Therefore, delivery and monitoring of therapeutic ultrasound typically requires two transducers to enable both treatment and imaging. This study investigates the feasibility of using a single commercial ultrasound imaging transducer operating at 5 MHz for both drug delivery and real-time imaging. We compared a single-transducer system (STS) at 5 MHz with a conventional dual-transducer system (DTS) using a 1.1 MHz therapeutic transducer and an imaging probe. in vitro experiments demonstrated that the STS could achieve comparable extravasation depth and area as the DTS, with higher drug deposition observed at 5 MHz. Additionally, extravasation patterns were influenced by peak negative pressure (PNP) and duty cycle, with the narrower beam width at 5 MHz offering potential advantages for targeted drug delivery. in vivo experiments in a murine bladder cancer model confirmed the efficacy of the STS for real-time imaging and drug delivery, with cavitation dose correlating with drug deposition. The results suggest that a single-transducer approach may enhance the precision and efficiency of ultrasound-mediated drug delivery, potentially reducing system complexity and cost.

Multi-bolt looseness monitoring using guided waves: a cross-correlation approach of the wavelet energy envelope

Abstract This paper proposes a novel approach for monitoring multi-bolt looseness using guided waves and the cross-correlation of the wavelet energy envelope. By assessing variations in the wave packet, the looseness in multi-bolt assemblies can be estimated. First, the dispersion effects of Lamb waves were theoretically analyzed using the Rayleigh-Lamb equation. Next, the wavelet energy was derived through wavelet transform, and the Lamb wave envelope was obtained as a criterion for accurately separating the wave packet. Cross-correlation analysis was employed to quantitatively evaluate the dispersion of wave packets for varying levels of bolt looseness. A looseness index, termed the normalized decorrelation coefficient of wavelet energy (NDCWE), was defined. Then, validation experiments were conducted using a joint with five M8 bolts, each tightened to a standard torque of 42 N·m. Two piezoelectric transducers were attached to the periphery of the bolt group. Three preload conditions were tested for each bolt: fully tightened, 80% of the standard torque, and 10% of the standard torque, corresponding to no looseness (NL), minor looseness (ML), and significant looseness (SL), respectively. Results showed that when significant looseness occurs, the NDCWE value exceeds 0.4, confirming the effectiveness of NDCWE in detecting substantial reductions in bolt preload. Experiments assessing the effect of temperature revealed that temperature has a negligible effect on the waveforms of the S0 and A0 mode waves. Finally, to quantitatively evaluate the efficiency of the ultrasonic transducers, the bolt-to-sensor ratio (BSR) was introduced. In this study, the BSR reached 2.5, indicating that a single piezoelectric transducer can monitor the preload of 2.5 bolts. The proposed approach shows great potential for multi-bolt looseness monitoring.

Acoustic Radiation Patterns of Different Polygon Piston Surfaces

Transducers are used in acoustic remote sensing and several other modern applications. The radiating surface geometry of a single acoustic transducer affects its beam pattern and has a cumulative effect on the overall performance of an array configuration. In addition, the transducers with polygon radiating surfaces provide more compact structure in an array than the circular pistons due to their flat surface edges. However, until now, the radiation patterns of acoustic polygonal pistons have not been exclusively studied and documented. In this study, the directional factors of acoustic pistons with polygonal surfaces of three to ten sides were derived analytically from the first principle using the Rayleigh integral. These directional factors were used to synthesise and characterise the radiation patterns of the piston sources in comparison with the baffled circular piston of an equivalent surface area. The rectangular, the triangular, and the rest of the polygons have the same performance with the circular piston when the surface diameter is not higher than 0.5λ, 0.28λ and 0.43λ, respectively. The main lobe of the acoustic emissions from the square is very close to that of the circular piston whose diameter is greater than a wavelength while that of the rectangle is wider. The results show that the radiating surface perimeter and symmetry are the two most critical factors affecting the beam characteristics of a piston source rather than the surface area or the number of sides. The theoretical results were validated using the finite element method with an excellent compliance.

A wearable echomyography system based on a single transducer

A wearable echomyography system based on a single transducer

High-Intensity focused ultrasound linear array and system for dermatology treatment

Dermatological lesions are typically located just a few millimeters below the surface of the skin, which constrains the efficacy of optical-based therapeutic methods such as photothermal and photodynamic therapy due to limited therapeutic depth caused by optical scattering. As an alternative, high-intensity focused ultrasound (HIFU) has been explored for its potential to treat a variety of dermatological conditions because it offers greater flexibility in terms of treatment depth. Since dermatological lesions have a small thickness ranging from 1.5 to 2.0 mm, high-frequency ultrasound (3–10 MHz or higher) is preferred as the focal area is proportional to the operating frequency. However, due to the difficulty in fabricating HIFU array transducers at this frequency range, the majority of HIFU treatments for dermatology rely on single element transducers. Despite the advantages of HIFU, single-element-based HIFU systems are limited in prevalent use for dermatology treatment due to their fixed focal length and mechanical movement for treatment, which can be time-consuming and unsuitable for treating multiple lesions. To address this, we present a newly developed HIFU linear array and 128-channel driving electronics specifically designed for dermatology treatment. This array consists of 128 elements, has a center frequency of 3.7 MHz, an elevation focal length of 28 mm, and an F-number of 1.27 in the elevation direction. The array has a footprint of 71.6 mm by 22 mm. Experiments using a tissue-mimicking phantom have demonstrated that the HIFU linear array and system are capable of transmitting sufficient ultrasound energy to create coagulation inside the phantom.

Assessment of aging degradation in rubber using quasi-static components of ultrasonic longitudinal waves

Abstract Aging degradation is the main form of failure of rubber in service, leading to a decline in its physical and mechanical properties. This paper presents an efficient method for assessing the aging degradation of rubber using the quasi-static component (QSC) of ultrasonic longitudinal waves induced by acoustic radiation. The experiments quantitatively observe the response of the QSC pulse to different levels of ageing degradation. A pulse-echo ultrasonic transducer is employed to simultaneously capture the primary longitudinal wave (PLW) and QSC echoes, enabling the determination of the acoustic nonlinearity parameter of QSC with a single transducer excitation. The results suggest that, in comparison to traditional linear ultrasonic techniques based on attenuation coefficient and wave velocity measurements, the relative acoustic nonlinear parameter of QSC proves to be more sensitive to aging degradation in rubber. Particularly, the amplitude of the QSC pulse undergoes a significant change with increasing aging degradation, even when the PLW tone burst is completely attenuated. These findings confirm the effectiveness of QSC as a method for evaluating aging degradation in highly attenuative materials.

Variability in Liver Size Measurements Using Different View Angles in Ultrasound Imaging.

The aim of this study was to compare liver size measurements in different conventional B-mode ultrasound image (US) field views using magnetic resonance imaging (MRI) measurement as a reference. After receiving Institutional Review Board approval and informed consent, three operators measured the largest sagittal and transverse dimensions of adult livers on three US image field views (90°, 120°, and 140°) with a single curvilinear transducer. We analyzed the differences in liver size across three image field views using one-way analysis of variance (ANOVA) and examined the correlations between MRI and ultrasound measurements using Spearman regression. We used 95% Bland-Altman limits of agreement (95% LOA) to analyze the confidence interval for liver size measurements between MRI and US. Intra-observer and inter-observer reliability in measuring liver size were assessed using intraclass correlation coefficient (ICC). Based on sagittal liver length, 28 adult participants (7 men and 21 women, mean age 43 years) were divided into Group 1 (<17 cm, n = 10) or Group 2 (≥17 cm, n = 18). There was a significant difference in the liver size measurements across the three image field views (P < .001) in both groups. The highest correlation in liver size measurements between MRI and US was with ultra-wide-view (R2 = .87 in sagittal; R2 = .79 in transverse). Bland-Altman LOA also indicated good agreement between MRI and ultra-wide-view measurements. Intra-observer and inter-observer reliability in measuring liver size were good (ICC = 0.82-0.98). The study suggests that ultrasound ultra-wide-view provides the most accurate liver size measurement and good intra- and inter-operator reliability.

Ultrasound 3D beam-forming with distributed electrodes and frequency sub-band compounding

Abstract Array probes are commonly used in ultrasound equipment. These are transducers arranged in an array. This system requires multiple transmitter and receiver circuits, making it an expensive system; three-dimensional ultrasound imaging requires a two-dimensional array, which is even more expensive and difficult to popularize. We propose an imaging system with a single transducer and a single transmitter/receiver circuit for low-cost implementation of ultrasound imaging. The system uses a distributed electrode, which consists of multiple electrodes on a single transducer. Each electrode is connected to a single transmit/receive circuit. In this paper, we evaluate the performance of the proposed and existing array probe systems and systems by simulation.

Enhancing Image Contrast in Breast USCT Reflection Imaging Using Coherence Factor Beamforming

Abstract Breast cancer is the most common cancer worldwide, and early screening is essential. Existing breast ultrasound is affordable and convenient, but its 2D image quality is poor, and it heavily relies on the doctor’s skills. The novel breast ultrasound computed tomography (USCT) can use a ring array probe to implement hundreds of single transducer emission for full-view focusing synthetic aperture reflection imaging, thereby obtaining high-resolution 3D images. However, single transducer emission results in low acoustic intensity, which further leads to low signal-to-noise ratio and low contrast of reflection images. To improve image contrast, this study incorporated beamforming with coherence factor (CF) into reflection imaging using ring transducers, promising to produce high-contrast USCT reflection images. For evaluation, we developed a USCT prototype with 2048 elements and conducted phantom experiments. We conducted phantom experiments. Results showed that the contrast achieved by the coherence factor method of the breast phantom image is improved from 24.54 dB to 63.18 dB, and the artifacts are significantly suppressed. It can be seen that the CF method could significantly improve the contrast of the breast USCT reflection image.

Low-cost instrumentation for high frequency ultrasonic guided wave laboratory research in free rock bolts

Guided wave ultrasound offers the ability to inspect slender structures from a single transducer location. However, the propagation of guided waves is more complex than the propagation of bulk waves used in conventional ultrasonic testing, and the experimental equipment required is more sophisticated. Typical equipment is expensive and may limit research and industrial application. This paper investigates what can be achieved by using low-cost instrumentation for laboratory measurements. The application is the measurement of guided waves in rock bolts (cylindrical rods) at relatively high frequencies (5 MHz). The dispersive wave propagation requires the use of narrowband excitation signals. The use of a bench-top waveform generator and oscilloscope is compared to the use of a compact and low-cost USB oscilloscope, which includes an arbitrary waveform generator. The introduction of a pre-amplifier mitigated the poorer noise performance of the USB oscilloscope, and comparable results were obtained from the two setups. It is demonstrated that waves propagated 9 m in a free rock bolt, with 10 dB/m attenuation, could be detected and analyzed with a measurement setup costing approximately USD 1110.

Phased array-based nonlinear wave mixing technique: Application to lack-of-fusion porosity characterization in additively manufactured metals.

The objective of this research is to demonstrate the effectiveness of a phased array-based nonlinear wave mixing technique to characterize internal, localized microscale damage in an additively manufactured (AM) component. By using phased arrays for the generation of the incident waves, it is possible to produce a nonlinear wave mixing scanning technique without the need for immersion or changing coupling conditions. The phased arrays can be configured to generate incident waves in multiple directions that meet the resonance conditions required for nonlinear wave mixing at a variety of internal locations. This allows for the scanning of a specimen without the removal and re-coupling of the source transducers, leading to greater scanning speed and repeatability. To demonstrate the accuracy of this phased array wave mixing approach, measurements of acoustic nonlinearity in an AM component are first made with a bulk wave second harmonic generation through thickness measurement. Next, nonlinear wave mixing measurements are made with single element transducers to confirm the sensitivity of the proposed nonlinear wave mixing approach to lack-of-fusion porosity in AM metals. Finally, phased arrays are used to highlight the effectiveness of the proposed nonlinear wave mixing technique in these same AM components.

Electrical de-poling and re-poling of relaxor-PbTiO3 piezoelectric single crystals without heat treatment

Re-poling of unexpected partially depoled piezoelectric materials conventionally needs to be first fully depoled through annealing above their Curie temperature to revive piezoelectric performances. Here, we investigated de-poling and re-poling of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals under electric fields at room temperature. We found that alternating current electric fields with amplitudes near the coercive field at low frequencies (<10 Hz) can be employed to successfully depolarize poled crystals at room temperature. We also demonstrated a reversible polarization switching process with a relaxor-PbTiO3 single crystal ultrasound transducer without device performance degradations. This experimental observation is supported by phase-field simulation, showing that alternating current electric fields can readily induce de-poling at room temperature, while direct current electric fields induce a transient depoled state only within an uncontrollable short period of time. The findings suggest new strategies for unprecedented in-device tailoring of the polarization states of ferroelectric materials.

A practical solution to improve the field of view in circular scanning-based photoacoustic tomography.

One of the primary challenges in ring single-element photoacoustic tomography systems is the low image quality in areas away from the center of the ring. This is mainly due to the limited field of view (FOV) of each transducer, which in turn reduces the imaging FOV. To address this shortcoming, we have put forward a practical and straightforward solution to enhance the FOV of circular scanning-based photoacoustic tomography (CS-PAT). This is accomplished by placing transducers at different angles instead of using a single transducer placed at a normal angle to the imaging target. We also modified the ring scanner inner wall surface to significantly reduce photoacoustic reverberation. By imaging several phantoms, we show a significant improvement in the images generated by our system imaging from 4.1 to over 7 for the signal-to-noise ratio and structural similarity index increased from 41% to 70%.

Feasibility Study for a High-Frequency Flexible Ultrasonic Cuff for High-Precision Vagus Nerve Ultrasound Neuromodulation.

In the emerging research field of bioelectronic medicine, it has been indicated that neuromodulation of the vagus nerve (VN) has the potential to treat various conditions such as epilepsy, depression, and autoimmune diseases. In order to reduce side effects, as well as to increase the effectiveness of the delivered therapy, sub-fascicle stimulation specificity is required. In the electrical domain, increasing spatial selectivity can only be achieved using invasive and potentially damaging approaches like compressive forces or nerve penetration. To avoid these invasive methods while obtaining a high spatial selectivity, a 2-mm diameter extraneural cuff-shaped proof-of-concept design with integrated lead zirconate titanate (PZT) based ultrasound (US) transducers is proposed in this article. For the development of the proposed concept, wafer-level microfabrication techniques are employed. Moreover, acoustic measurements are performed on the device, in order to characterize the ultrasonic beam profiles of the integrated PZT-based US transducers. A focal spot size of around [Formula: see text] is measured for the proposed cuff. Moreover, the curvature of the device leads to constructive interference of the US waves originating from multiple PZT-based US transducers, which in turn leads to an increase of 45% in focal pressure compared to the focal pressure of a single PZT-based US transducer. Integrating PZT-based US transducers in an extraneural cuff-shaped design has the potential to achieve high-precision US neuromodulation of the VN without requiring intraneural implantation.

Autonomous and heteronomous control of selectivity to pyrocatechol derivatives for near-infrared light-responsive cup-stacked carbon nanofiber/FTO electrodes modified with thermo-responsive polymers

Autonomous and heteronomous switchable selectivity for electrochemical reactions was examined in an electrolyte solution containing pyrocatechol (PC) and dopamine (DA) using a fabricated thermo- and photo-responsive poly(N-isopropylacrylamide) (PNIPA)-modified cup-stacked carbon nanofiber (CSCNF) electrode. PNIPA can be autonomously and reversibly switched by environmental temperature changes between hydrophilic expanded coil structure and hydrophobic collapsed globule structure. CSCNFs as the electrode materials can effectively convert absorbed external near-infrared (NIR) light into heat. Although the molecular size of DA is larger and the octanol-water partition coefficient of DA is smaller than those of PC, both PC and DA could permeate to the CSCNF electrode surface through the expanded coil structure of the PNIPA layer at 25 ˚C, which temperature is below the lower critical solution temperature (LCST), causing their electrochemical signal readout. In contrast, transport of DA to the electrode surface was selectively suppressed by exposing the polymer to temperature at 45 ˚C, which value is above the LCST, or NIR light irradiation (> 940 nm, ca. 77 mW cm–2) to the CSCNF electrode surface even at 25 ˚C due to the steric hindrance and hydrophobicity of collapsed globule structure of the polymer layer. This resulted in the preferential electrochemical signal of PC. The switchable sensitivity of the electrode also allowed it to be successfully demonstrated for the simultaneous determination of PC and DA even at a single transducer, though electrode arrays with different sensitivity and selectivity are widely used for the determination of multiple chemicals simultaneously.

Gestational buprenorphine-naloxone exposure and fetal neurobehavior

BackgroundBuprenorphine-naloxone treatment may confer substantial benefits for the treatment of opioid use disorder (OUD) during pregnancy including lower risk for overdose/death, less diversion potential and reduced use of other substances. Treatment may also result in less severe Neonatal Abstinence Syndrome (NAS), but little is known about the effects of this medication on fetal neurodevelopment. MethodsThe purpose of the current study is to evaluate neurobehaviors among fetuses exposed to buprenorphine-naloxone at four time points over the second and third trimesters of gestation in pregnant women with OUD on buprenorphine-naloxone therapy. Sixty minutes of continuous fetal monitoring via fetal actocardiograph with a single wide array abdominal transducer took place at times of peak and trough buprenorphine-naloxone levels in 24 pregnant women. Data collection, which included measures of fetal heart rate and motor activity, was conducted between 24 and 36 weeks gestation, with the majority (84.6%) monitored at two or more gestational ages. Medication dose and other substance use was monitored throughout the study and infant NAS severity was assessed. ResultsFetal heart rate (FHR), FHR variability, accelerations in FHR, and motor activity were suppressed when buprenorphine-naloxone levels were at pharmacologic peak as compared to trough concentrations at 36 weeks, but not earlier in gestation. Maternal medication dose was unrelated to infant NAS severity. ConclusionsConclusions: There were evident subclinical fetal neurophysiological responses at times of peak maternal buprenorphine/naloxone levels in later gestation, similar to those previously described for buprenorphine only. Further studies evaluating the effects of these changes in fetal neurobehaviors on the longer-term infant development are needed.

Investigations of high-Performance Ultrasonic Transducers based on PMN-PT Single Crystals

Ultrasonic transducers for NDE applications are commonly based on Lead Zirconate Titanate or PZT, an inorganic compound and ceramic perovskite material. Until now the advantages of PMN-PT are used in medical applications, but are not implemented in NDE. Lead Magnesium Niobate-Lead Titanate (PMN-PT) is well known for its high sensitivity and broad frequency spectrum. While conventional PZT materials have an electromechanical coupling factor K33 (a measure of the conversion between electrical and acoustic energy) of about 0.72, PMN-PT materials reach peak values of more than 0.93. For applications with low signal amplitudes, high electronic noise and small transducer elements, the performance of ultrasonic probes can be significantly enhanced by using Lead Magnesium Niobate-Lead Titanate (PMN-PT) instead of PZT. This single-crystal material offers significantly better piezo parameters and leads to a higher sensitivity and larger bandwidth. There is a better depth resolution possible with this transducers as practical tests have shown. Similar to PZT it can also be fabricated in 1-3 piezo- composite technology. In a cooperation between Fraunhofer IKTS, iBULe Photonics, and IFU Diagnostic Systems, PMN-PT ultrasonic transducers are developed and optimized. The performance of phased array probes and single element transducers was measured by a so called PCUS® pro electronic front end from Fraunhofer and compared with equivalent PZT-based probes. As a result various single element and phased array transducers with im-proved performances are available for NDT of typical aerospace materials and applications. These test setups were used to weigh up the advantages and disadvantages, such as achievable precision or costs, for the implementation of a PMN-PT-based UT matrix probe. Based on this, a wiring variant adapted to the PMN-PT was developed and optimised for the matrix setups by pre- assembling the matching layers. The most favourable setup turned out to be bonding the PMN- PT composites to the prefabricated matching layers together with a rigid-flexible PCB frame. This enabled direct wire bonding of 64 matrix elements to the matching PCB pads on the rigid frame.

Hadamard acoustic correlated imaging based on photoacoustic modulation with a single transducer

Conventional ultrasound technology based on spot scanning or phased array encounters significant challenge in real-time imaging with a single detector. In this paper, we present a Hadamard acoustic correlated imaging based on photoacoustic modulation with one transducer. The process of accurately generating the Hadamard acoustic field is to apply the carbon-nanotubes–polydimethylsiloxane composite to absorb the optimized Hadamard basis pattern. Taking advantage of correlated imaging, our system without scanning can reduce imaging artifacts and its resolution could be about four times higher than that of traditional ultrasound imaging. The use of a single transducer rather than an array of transducers can reduce the cost of the imaging system. Therefore, the proposed scheme can find applications in biomedical imaging and nondestructive evaluation.

Development of an Infrared Marker based Encoder System as a Non-Contact Positioning System for Ultrasonic Probes

The digitalization of testing procedures is one of the challenges in the development of modern non-destructive testing systems. In order to guarantee a high level of inspection reliability, the assignment of measurement data to the measurement position plays an important role as well as the optimal inspection hardware. In a cooperative research and development project, an optical tracking system has been developed with which it is possible to determine the positions of different ultrasonic probes in space without contact. Thus, the position of the measurement is linked to the measurement results directly. Infrared LED markers attached to the ultrasonic probes are used for this purpose. The position of the markers are tracked in space with a camera. By linking several cameras and trackers, a positional accuracy of a few millimeters can be achieved for a camera specimen distance of 2 m. The more cameras are used the bigger the investigated part can be. For the tracking system, an existing optical camera system is coupled with a conventional of the shelve ultrasonic phased array device by means of a newly developed universal encoder. Different single transducer probes or phased array probes can be used. The costly and time consuming use of mechanical encoders is thus eliminated. This combination enables the further digitalization of hand-guided ultrasonic testing precisely in those areas where robot-based testing is not feasible. Additionally, a much easier way of documentation is possible. Due to the exact position determination a better evaluation of the measurement data can be carried out via a subsequent 3D display of the ultrasound data.