Transducer Technology Research Articles

Piezoelectric Micromachined Ultrasound Transducer Technology: Recent Advances and Applications

The objective of this article is to review the recent advancement in piezoelectric micromachined ultrasound transducer (PMUT) technology and the associated piezoelectric materials, device fabrication and characterization, as well as applications. PMUT has been an active research topic since the late 1990s because of the ultrasound application needs of low cost large 2D arrays, and the promising progresses on piezoelectric thin films, semiconductors, and micro/nano-electromechanical system technology. However, the industrial and medical applications of PMUTs have not been very significant until the recent success of PMUT based fingerprint sensing, which inspired growing interests in PMUT research and development. In this paper, recent advances of piezoelectric materials for PMUTs are reviewed first by analyzing the material properties and their suitability for PMUTs. PMUT structures and the associated micromachining processes are next reviewed with a focus on the complementary metal oxide semiconductor compatibility. PMUT prototypes and their applications over the last decade are then summarized to show the development trend of PMUTs. Finally, the prospective future of PMUTs is discussed as well as the challenges on piezoelectric materials, micro/nanofabrication and device integration.

Piezoelectric ceramic materials on transducer technology for energy harvesting: A review

Recently, energy harvesting through the means of piezoelectric transducer technology has increasingly attracted the attention of engineers and scientists in producing/generating electricity for human consumption. However, understanding of piezoelectric materials for application in piezoelectric transducer devices in energy harvesting remains important in today’s energy systems engineering. Thus, the present review study is centered on piezoelectric materials for a better understanding of the properties of different piezoelectric materials (ceramic) when placed under mechanical stress or vibration and electrical field during energy harvesting using transducer devices. With the available literature, lead zirconate titanate materials showed to be the most common piezoelectric material with a high energy-generating performance but possessed more mechanical failure and also compromised in a harsh environment compared to lead-free piezoelectric materials. As such, the authors conclude that lead-free piezoelectric materials, such as zinc oxide and barium titanate, remain the best conducive piezoelectric material over lead zirconate titanate, which basically affects the human environment due to its toxicity. Thus, to widen the use of lead-free piezoelectric materials in energy harvesting, owing to their improved properties and environment-friendly nature, the authors recommend further enhancement of the lead-free piezoelectric material properties via nanodielectric filler incorporations using the spark plasma sintering technique.

Ultrasound-guided Ganglion Impar Block during the COVID-19 Pandemic: Two Case Reports

Blocks of the ganglion impar are used to treat both malignant and benign causes of visceral and sympathetic pelvic and perineal pain. While conventionally done under fluoroscopic guidance, significant improvements in transducer technology in the past decade have piqued the interest and enthusiasm of interventional pain specialists toward ultrasound-guided performance. In the setting of a pandemic, it is important to ensure the efficacy of treatment as well as the safety of both patients and health care workers. This paper presents two patients who underwent two approaches of ultrasound-guided ganglion impar blocks in a tertiary government hospital in the Philippines during the COVID-19 pandemic.

Array Transducer Design: A Vibrant Research Theme in Medical Ultrasonics

Since the 1970s, when portable transducer arrays were first introduced for medical ultrasound imaging, they have undergone substantial technological developments. The development of advanced arrays is often motivated by the need to achieve high diagnostic and therapeutic efficacy and to serve new fields of application. In the past few decades, medical ultrasound array design has been an active research area with challenging technical requirements that continually seek to reduce physical size, improve sensitivity, optimize the number of array elements, realize wide bandwidth, and achieve high output power. The need to devise arrays with increased performance has concurrently stimulated advances in transducer technologies, microelectronics, and array layout design. Nowadays, representative examples can be found for both 2-D and 3-D applications such as high-intensity-focused ultrasound arrays, very-high-frequency or dual-frequency probes, kerf-less arrays, 2-D sparse arrays, and probes with embedded application-specific integrated circuits. The emergence of these advanced arrays has, in turn, stimulated the development of novel, customized transmission and reception approaches, image reconstruction algorithms, and data recovery strategies to exploit or deal with the peculiarities of a specific array.

Design, Implementation, and Medical Applications of 2-D Ultrasound Sparse Arrays.

An ultrasound sparse array consists of a sparse distribution of elements over a 2-D aperture. Such an array is typically characterized by a limited number of elements, which in most cases is compatible with the channel number of the available scanners. Sparse arrays represent an attractive alternative to full 2-D arrays that may require the control of thousands of elements through expensive application-specific integrated circuits (ASICs). However, their massive use is hindered by two main drawbacks: the possible beam profile deterioration, which may worsen the image contrast, and the limited signal-to-noise ratio (SNR), which may result too low for some applications. This article reviews the work done for three decades on 2-D ultrasound sparse arrays for medical applications. First, random, optimized, and deterministic design methods are reviewed together with their main influencing factors. Then, experimental 2-D sparse array implementations based on piezoelectric and capacitive micromachined ultrasonic transducer (CMUT) technologies are presented. Sample applications to 3-D (Doppler) imaging, super-resolution imaging, photo-acoustic imaging, and therapy are reported. The final sections discuss the main shortcomings associated with the use of sparse arrays, the related countermeasures, and the next steps envisaged in the development of innovative arrays.

From sonar to medical ultrasound—The impact of Paul Langevin

The technical developments and discoveries of Paul Langevin figuratively and literally powered an incredible spectrum of scientific achievement. The quartz transducer technology of his 1918 patent (Procédé et appareils d'émission et de réception des ondes élastiques sous-marines à l'aide des propriétés piézo-électriques du quartz. – French Patent No. 505,703) enabled a level of acoustic output power generally unavailable at ultrasonic frequencies along with an increase in detection sensitivity. While there were disputes as to who should have been included on this patent, its effect on the field of ultrasonics is clear. The impetus for this work was largely high-power sonar for military application but his reported observations of effects on fish and even humans ushered in a new era of ultrasound bioeffects investigations including those of the famous Loomis Laboratory and numerous others. This is arguably the genesis of the rich tradition of research in ultrasound bioeffects and helped drive the pursuit of diagnostic and therapeutic applications of ultrasound including work by such famous researchers as the Fry Brothers. This presentation will review the evolution of bioeffects from the Langevin’s work and its impact on the field of medical ultrasound.

Research and Development of Digital Assembly Process System for Ultrasonic Transducers

In order to solve the problem of design efficiency of the digital assembly process, the author proposes a research using ultrasonic transducer technology. The main content of this research is to study the ultrasonic transducer elements according to the basic structure of the ultrasonic transducer.Through the study of equivalent circuit of ultrasonic transducer, the model of impedance matching design is constructed. Finally, the feasibility of ultrasonic transducer technology is obtained through experiments. Experimental results show that the transducer multichip structure of the ultrasonic transducer system and the LC matching network circuit can make the AOTF system achieve better results, and the diffraction efficiency is up to more than 70%, which is of great significance to the research and development of the current digital assembly process system. Conclusion. It is proven that the research of ultrasonic transducer technology can meet the needs of digital assembly process design efficiency.

A Novel Matching Layer Design for Improving the Performance of Transparent Ultrasound Transducers.

Transparent ultrasound transducer (TUT) technology allows easy co-alignment of optical and acoustic beams in the development of compact photoacoustic imaging (PAI) devices with minimum acoustic coupling. However, TUTs suffer from narrow bandwidth and low pulse-echo sensitivity due to the lack of suitable transparent acoustic matching and backing layers. Here, we studied translucent glass beads (GB) in transparent epoxy as an acoustic matching layer for the transparent lithium niobate piezoelectric material-based TUTs (LN-TUTs). The acoustic and optical properties of various volume fractions of GB matching layers were studied using theoretical calculations, simulations, and experiments. These results demonstrated that the GB matching layer has significantly enhanced the pulse-echo sensitivity and bandwidth of the TUTs. Moreover, the GB matching layer served as a light diffuser to help achieve uniform optical fluence on the tissue surface and also improved the photoacoustic (PA) signal bandwidth. The proposed GB matching layer fabrication is low cost, easy to manufacture using conventional ultrasound transducer fabrication tools, acoustically compatible with soft tissue, and minimizes the use of the acoustic coupling medium.

Recent Progress on Triboelectric Nanogenerators for Vibration Energy Harvesting and Vibration Sensing.

The triboelectric nanogenerator (TENG) is a recent technology that reforms kinetic energy generation and motion sensing. A TENG comes with variety of structures and mechanisms that make it suitable for wide range of applications and working conditions. Since mechanical vibrations are abundant source of energy in the surrounding environment, the development of a TENG for vibration energy harvesting and vibration measurements has attracted a huge attention and great research interest through the past two decades. Due to the high output voltage and high-power density of a TENG, it can be used as a sustainable power supply for small electronics, smart devices, and wireless sensors. In addition, it can work as a vibration sensor with high sensitivity. This article reviews the recent progress in the development of a TENG for vibration energy harvesting and vibration measurements. Systems of only a TENG or a hybrid TENG with other transduction technologies, such as piezoelectric and electromagnetic, can be utilized for vibrations scavenging. Vibration measurement can be done by measuring either vibration displacement or vibration acceleration. Each can provide full information about the vibration amplitude and frequency. Some TENG vibration-sensing architectures may also be used for energy harvesting due to their large output power. Numerous applications can rely on TENG vibration sensors such as machine condition monitoring, structure health monitoring, and the Internet of things (IoT).

Luminescent Aptamer-Based Bioassays for Sensitive Detection of Food Allergens.

The presence of hidden allergens in food products, often due to unintended contamination along the food supply chain (production, transformation, processing, and transport), has raised the urgent need for rapid and reliable analytical methods for detecting trace levels of such species in food products. Indeed, food allergens represent a high-risk factor for allergic subjects due to potentially life-threatening adverse reactions. Portable biosensors based on immunoassays have already been developed as rapid, sensitive, selective, and low-cost analytical platforms that can replace analyses with traditional bench-top instrumentation. Recently, aptamers have attracted great interest as alternative biorecognition molecules for bioassays, since they can bind a variety of targets with high specificity and selectivity, and they enable the development of assays exploiting a variety of transduction and detection technologies. In particular, aptasensors based on luminescence detection have been proposed, taking advantage of the development of ultrasensitive tracers and enhancers. This review aims to summarize and discuss recent efforts in the field of food allergen analysis using aptamer-based bioassays with luminescence detection.

Comparison of a laser precipitation monitor, piezoelectric transducer and particle imaging transient visual measurement technology under simulated rainfall in laboratory conditions

• Three instruments were compared in the lab under simulated rainfall conditions. • The raindrop size was most accurately described using the geometric mean diameter. • The raindrop visual measurement method could provide accurate raindrop shapes. • The laser precipitation monitor was more sensitive to measuring raindrops of < 1 mm. • Based on rainfall tests, the applicability of the three instruments was discussed. Precipitation microphysics, which describes the basic characteristics of rainfall, is important for agricultural praxis, weather prediction, aviation safety, and soil erosion prediction. In this study, three types of instruments (a laser precipitation monitor, LPM; piezoelectric transducer, PT; and particle imaging transient visual measurement technology, PIV) were employed to measure and compare the raindrop size distribution (DSD) and rainfall kinetic energy rate ( KE t ) under simulated rainfall conditions. Comparisons of the results indicated that under the same simulated rainfall conditions, the number of raindrops per unit area measured by LPM was larger than that measured by PIV. The DSD measured by PIV was more uniform than that of the PT and LPM under the same rainfall conditions. The raindrop size range measured by the LPM was smaller than that measured by the PT and PIV. In addition, the geometric mean diameter was a more accurate representation of raindrop size because PIV can capture the true irregular shape of raindrops. Compared to the PIV sensor, the LPM underestimates the raindrop diameter. The median raindrop diameter measured and calculated by PIV using the geometric mean diameter was approximately 1.61 times that of LPM. The KE t values measured by PIV and PT were approximately similar, while the KE t calculated by LPM was 0.51 and 0.57 times that of PIV and PT for the same rainfall conditions, respectively. A correction factor of 1.75 provided an approximate reference for the calibration of the kinetic energy calculation of the LPM instrument. The above results can provide basic insights for calibration and application of the three instruments.

Transducer Technologies for Biosensors and Their Wearable Applications.

The development of new biosensor technologies and their active use as wearable devices have offered mobility and flexibility to conventional western medicine and personal fitness tracking. In the development of biosensors, transducers stand out as the main elements converting the signals sourced from a biological event into a detectable output. Combined with the suitable bio-receptors and the miniaturization of readout electronics, the functionality and design of the transducers play a key role in the construction of wearable devices for personal health control. Ever-growing research and industrial interest in new transducer technologies for point-of-care (POC) and wearable bio-detection have gained tremendous acceleration by the pandemic-induced digital health transformation. In this article, we provide a comprehensive review of transducers for biosensors and their wearable applications that empower users for the active tracking of biomarkers and personal health parameters.

A Review of High-Frequency Ultrasonic Transducers for Photoacoustic Imaging Applications.

Photoacoustic imaging (PAI) is a new and rapidly growing hybrid biomedical imaging modality that combines the virtues of both optical and ultrasonic (US) imaging. The nature of the interaction between light and ultrasound waves allows PAI to make good use of the rich contrast produced by optics while retaining the imaging depths in US imaging. High-frequency US transducers are an important part of the PAI systems, used to detect the high-frequency and broad-bandwidth photoacoustic signals excited by the target tissues irradiated by short laser pulses. Advancement in high-frequency US transducer technology has influenced the boost of PAI to broad applications. Here, we present a review on high-frequency US transducer technologies for PAI applications, including advanced piezoelectric materials and representative transducers. In addition, we discuss the new challenges and directions facing the development of high-frequency US transducers for PAI applications.

In-plane nonlinear vibration of circular dielectric elastomer membranes with extreme stretchability

This work investigates large in-plane stretches in thin circular membranes pre-stretched mechanically and dynamically excited by fluctuating voltages applied through their thicknesses. The nonlinear equation of motion is derived using Hamilton’s principle. Nonlinearity arises from the elastomer’s material behavior and electromechanical coupling from applied voltages. Primary and secondary resonances exhibit typical softening nonlinearity characterized by a range of frequencies where two coexisting vibrations, referred to as the upper branch and lower branch response, are possible. Our focus is the upper branch response, where extremely large dynamic stretches in the hundreds of percent are possible. These large stretches have not been fully investigated by prior research. The membrane’s upper branch vibrations can be found by decreasing frequency sweeps through resonance, and may not be captured if only increasing frequency sweeps are analyzed. Large-amplitude upper branch stretches occur when the membrane vibrates about both small-stretch and large-stretch equilibria. In addition to larger amplitudes, the upper branch dynamic stretches near secondary resonances have dominant frequencies different from the excitation frequency. Whether the dielectric elastomer membrane vibrates on the lower or upper branch depends on its initial conditions, and the initial conditions that result in each case are quantified. A technique is demonstrated to switch the membrane’s vibration from the lower to upper branch using impulse-like voltages superposed on the nominal sinusoidal component. The large-amplitude nonlinear dynamic stretches highlighted in this work, and the strategies we propose for accessing and controlling them, could be leveraged for improved performance in existing soft transducer technologies.

Circuits on miniaturized ultrasound imaging system-on-a-chip: a review.

Trends of medical system move from a traditional in-person visit to virtual healthcare increases demands on point-of-care devices. Because ultrasound (US) is non-invasive, the demands highlight US imaging among other imaging modalities. Thanks to the development of US transducer technology, miniaturized US with application-specific integrated circuits (ASIC) have been researched. For example, applications that require small aperture sizes such as intravascular US (IVUS) and intra-cardiac echocardiography (ICE) require integration of system-on-a-chip (SoC) on the transducer. This paper reviews circuit techniques on the transmitter (TX) and receiver (RX) of the US imaging system. As TX circuits, pulser, T/RX switch, TX beamformer, and power management circuits are discussed. State-of-the-art transducer modeling, pre-amplifier, time-gain compensation, RX beamformer, quadrature sampler, and output driver are introduced as RX circuits.

New 3-Dimensional Volumetric Ultrasound Method for Accurate Quantification of Atherosclerotic Plaque Volume

BackgroundCarotid and femoral plaque burden is a recognized biomarker of cardiovascular disease risk. A new electronic-sweep 3-dimensional (3D)–matrix transducer method can improve the functionality and image quality of vascular ultrasound atherosclerosis imaging. ObjectivesThis study aimed to validate this method for plaque volume measurement in early and intermediate–advanced plaques in the carotid and femoral territories. MethodsPlaque volumes were measured ex vivo in pig carotid and femoral artery specimens by 3-dimensional vascular ultrasound (3DVUS) using a 3D-matrix (electronic-sweep) transducer and its associated 3D plaque quantification software, and were compared with gold-standard histology. To test the clinical feasibility and accuracy of the 3D-matrix transducer, an experiment was conducted in intermediate–high risk individuals with carotid and femoral atherosclerosis. The results were compared with those obtained using the previously validated mechanical-sweep 3D transducer and established 2-dimensional (2D)–based plaque quantification software. ResultsIn the ex vivo study, the authors assessed 19 atherosclerotic plaques (plaque volume, 0.76 µL-56.30 μL), finding strong agreement between measurements with the 3D-matrix transducer and the histological gold-standard (intraclass correlation coefficient [ICC]: 0.992; [95% CI: 0.978-0.997]). In the clinical analysis of 20 patients (mean age 74.6 ± 4.45 years; 40% men), the authors found 64 (36 carotid and 28 femoral) of 80 scanned territories with atherosclerosis (measured atherosclerotic volume, 10 μL-859 μL). There was strong agreement between measurements made from electronic-sweep and mechanical-sweep 3DVUS transducers (ICC: 0.997 [95% CI: 0.995-0.998]). Agreement was also high between plaque volumes estimated by the 2D and 3D plaque quantification software applications (ICC: 0.999 [95% CI: 0.998-0.999]). Analysis time was significantly shorter with the 3D plaque quantification software than with the 2D multislice approach with a mean time reduction of 46%. Conclusions3DVUS using new matrix transducer technology, together with improved 3D plaque quantification software, simplifies the accurate volume measurement of early (small) and intermediate–advanced plaques located in carotid and femoral arteries.

Binary amplitude switch for photoacoustic transducer toward dynamic spatial acoustic field modulation.

Photoacoustic (PA) transducers are an attractive method of producing high-amplitude, high-frequency, broad-bandwidth ultrasound signals with excellent immunity to electromagnetic interference, when compared with their traditional electroacoustic counterparts. However, the lack of effective control over the spatial sound field prohibits PA transducer technology from further widespread application. This paper presents the first, to the best of our knowledge, experimental study on the dynamic spatial ultrasound modulation strategy for the use of PA transducers, in which a novel PA transducer element is designed. This consists of a suspended compound PA conversion film, whose backing condition can be switched between air and glass through pneumatic actuation to create destructive and constructive acoustic wave interference, respectively. As a result, nearly an order of magnitude contrast in the output acoustic amplitude can be obtained by switching the device's backing condition given the same laser excitation, thus achieving a binary amplitude tuning. Furthermore, a linear PA transducer array consisting of three independently controllable elements is used for a proof-of-concept demonstration of the dynamic spatial sound field manipulation. To the best of the authors' knowledge, this is the first time that such a unique capability has been successfully applied to PA transducer technology.

Planar ultrasonic transducer based on a metasurface piezoelectric ring array for subwavelength acoustic focusing in water

The development of a new ultrasonic transducer capable of improved focusing performance has become a necessity to overcome the limitations of conventional ultrasonic transducer technology. In this study, we designed and optimized a metasurface piezoelectric ring device, and using multiphysics finite element analysis, we examined the performance of a planar ultrasonic transducer consisting of this device, a matching layer, a backing layer, and housing in producing a needle-like subwavelength focusing beam in water. For practical experiments, a metasurface piezoelectric ring device was fabricated using a laser ablation process. Subsequently, using a pulse-echo test, we found that the − 6 dB bandwidth of a planar ultrasonic transducer with a center frequency of 1.0 MHz was 37.5%. In addition, the results of an ultrasonic-focusing performance test showed that the full width at half-maximum of the axial subwavelength focusing beam was 0.78λ, and the full lateral width at half-maximum of the subwavelength lateral focusing beam was 7.03λ at a distance of 10.89λ. The needle-like focused ultrasonic beam technology implemented with a piezoelectric ring array based new planar ultrasound transducer is expected to be used in high-resolution imaging devices or medical ultrasound focusing devices in the future.

Ten Good Reasons to Practice Neuroultrasound in Critical Care Setting.

In the beginning, cerebral ultrasound (US) was not considered feasible because the intact skull was a seemingly impenetrable obstacle. For this reason, obtaining a clear image resolution had been a challenge since the first use of neuroultrasound (NUS) for the assessment of small deep brain structures. However, the improvements in transducer technologies and advances in signal processing have refined the image resolution, and the role of NUS has evolved as an imaging modality for the brain parenchyma within multiple pathologies. This article summarizes ten crucial applications of cerebral ultrasonography for the evaluation and management of neurocritical patients, whose transfer from and to intensive care units poses a real problem to medical care staff. This also encompasses ease of use, low cost, wide acceptance by patients, no radiation risk, and relative independence from movement artifacts. Bedsides, availability and reliability raised the interest of critical care intensivists in using it with increasing frequency. In this mini-review, the usefulness and the advantages of US in the neurocritical care setting are discussed regarding ten aspects to encourage the intensivist physician to practice this important tool.

Recent Advancements in Ultrasound Transducer: From Material Strategies to Biomedical Applications.

Ultrasound is extensively studied for biomedical engineering applications. As the core part of the ultrasonic system, the ultrasound transducer plays a significant role. For the purpose of meeting the requirement of precision medicine, the main challenge for the development of ultrasound transducer is to further enhance its performance. In this article, an overview of recent developments in ultrasound transducer technologies that use a variety of material strategies and device designs based on both the piezoelectric and photoacoustic mechanisms is provided. Practical applications are also presented, including ultrasound imaging, ultrasound therapy, particle/cell manipulation, drug delivery, and nerve stimulation. Finally, perspectives and opportunities are also highlighted.