Transducer Size Research Articles

Performance analysis of piezoelectric drum transducers as shoe-based energy harvesters

ABSTRACTPiezoelectric materials have been at the centre of energy harvesting research for a few decades now. This article explores the performance of piezoelectric drum transducers made using piezoelectric buzzer elements as shoe-based energy harvesters. Two sizes of drum transducers were fabricated, viz. 27 and 35 mm. Two different arrangements of these drums in stack as well as individual form were designed, embedded in shoes and tested with walk profile. Peak powers of 3.86 and 3.21 mW were obtained using a standard interface circuit whereas 1.23 and 0.38 mW using a MOSFET bridge with model 1 and 2, respectively. NiMH batteries of different capacities were charged using the shoe-based energy harvesters. An energy harvesting circuit using LTC 3588-1 energy harvesting IC was fabricated to obtain a regulated output voltage of 3.6 V using the shoe harvesters. Results show that these drum harvesters can be easily embedded in shoes and have the potential to act as excellent energy scavengers and generate enough power to drive low power sensors that can be used to design a smart body monitoring system.

An impedance measurement system for piezoelectric array element transducers

Abstract Impedance measurement of piezoelectric element materials is an important factor to estimate the transducer performances. The measurement method involves manually contacting the surface of the piezoelectric material. However, this method is not appropriate to measure the impedance accurately, since the element size of the ultrasound transducers used for the cardiovascular, trans-esophageal, and transrectal areas is small. Therefore, reliability issues are a critical concern of the miss-contact generated by human errors or inaccuracy of the contact positions produced by non-constant pressures. In order to resolve the issue, we developed a novel impedance measurement system (IMS) for piezoelectric array element transducers through precise motion control techniques. The basic structure of the system uses a 3-axis motion stage. The control program is to drive the motion control and data acquisition units with the impedance analyzer. Each axis of the motion control stages has a 10 μm resolution, which can measure fine-pitch of the array elements that has less than 0.5 mm. The control program can provide the functions to define the velocity of the each motion and moving distances per one pulse. The electrical impedances (EIs) were measured using a precise 50 Ω resistor around 10 times in order to prove the reliability of the IMS. The results showed that the value of the minimum and maximum measured EI values were 50.83 Ω and 50.95 Ω, respectively. The maximum standard deviation of the each element was 7.6253 × 10−3 Ω, indicating that the standard deviation was under 8 × 10−3 Ω. Therefore, the IMS provides accurate capability of the repeatable impedance measurement. The EIs of the randomly selected transducer elements were also measured by this system. This system could be useful to repair, manufacture and research of the ultrasound array element transducers.

Contrast Enhanced Superharmonic Imaging for Acoustic Angiography Using Reduced Form-Factor Lateral Mode Transmitters for Intravascular and Intracavity Applications

Techniques to image the microvasculature may play an important role in imaging tumor-related angiogenesis and vasa vasorum associated with vulnerable atherosclerotic plaques. However, the microvasculature associated with these pathologies is difficult to detect using traditional B-mode ultrasound or even harmonic imaging due to small vessel size and poor differentiation from surrounding tissue. Acoustic angiography, a microvascular imaging technique that utilizes superharmonic imaging (detection of higher order harmonics of microbubble response), can yield a much higher contrast-to-tissue ratio than second harmonic imaging methods. In this paper, two dual-frequency transducers using lateral mode transmitters were developed for superharmonic detection and acoustic angiography imaging in intracavity applications. A single element dual-frequency intravascular ultrasound transducer was developed for concept validation, which achieved larger signal amplitude, better contrast-to-noise ratio (CNR), and pulselength compared to the previous work. A dual-frequency [Pb(Mg1/3Nb2/3)O3]-x[PbTiO3] array transducer was then developed for superharmonic imaging with dynamic focusing. The axial and lateral sizes of the microbubbles in a 200- [Formula: see text] tube were measured to be 269 and [Formula: see text], respectively. The maximum CNR was calculated to be 22 dB. These results show that superharmonic imaging with a low frequency lateral mode transmitter is a feasible alternative to thickness mode transmitters when the final transducer size requirements dictate design choices.

Wideband audio systems for hearing aid devices

Multi-loudspeaker design has been one of the most widely used methods for improving the sound quality of audio systems. Some of the electroacoustic design concepts defined for typical earphones can be used for other wideband miniature audio systems as well. However, wideband audio for hearing aid devices and smart earphones introduce new design factors. Efficiency and transducer size are among the factors that become important in the electroacoustic design. In this paper, the electroacoustic design factors for woofer-tweeter audio systems are revisited and discussed for hearing aid devices. Simulation and measurement results are presented and analyzed.

Excitation of Surface Acoustic Wave on a Glass Substrate Using a LiNbO3 Piece

Surface acoustic waves (SAWs) are used in many applications. Here, we consider application of SAWs to actuators, which require relatively large vibration amplitudes. In conventional applications, a SAW propagates on a LiNbO3 substrate that serves as an elastic medium. This implies that the maximal size of a SAW transducer is limited by the LiNbO3 wafer size. Better actuators require larger-size SAW transducers. Here, we propose a transducer in which an excited SAW propagates on an inexpensive elastic medium (indirect excitation method). The method combines a piezoelectric material and a non-piezoelectric material substrate. These two materials are coupled. Electric energy is provided by an interdigital transducer (IDT). We designed and studied three different transducer configurations. To determine the optimal configuration, various materials and their combinations were considered with the proposed method. Electrical and mechanical characteristics were quantified in terms of the frequency response of admittance and vibration response, respectively. A suitable combination of materials was determined after measuring and analyzing the properties of different transducers. For this combination, the vibration velocity of the novel transducer was as large as that obtained using the conventional direct excitation method.

MEMS Based Broadband Piezoelectric Ultrasonic Energy Harvester (PUEH) for Enabling Self-Powered Implantable Biomedical Devices.

Acoustic energy transfer is a promising energy harvesting technology candidate for implantable biomedical devices. However, it does not show competitive strength for enabling self-powered implantable biomedical devices due to two issues – large size of bulk piezoelectric ultrasound transducers and output power fluctuation with transferred distance due to standing wave. Here we report a microelectromechanical systems (MEMS) based broadband piezoelectric ultrasonic energy harvester (PUEH) to enable self-powered implantable biomedical devices. The PUEH is a microfabricated lead zirconate titanate (PZT) diaphragm array and has wide operation bandwidth. By adjusting frequency of the input ultrasound wave within the operation bandwidth, standing wave effect can be minimized for any given distances. For example, at 1 cm distance, power density can be increased from 0.59 μW/cm2 to 3.75 μW/cm2 at input ultrasound intensity of 1 mW/cm2 when frequency changes from 250 to 240 kHz. Due to the difference of human body and manual surgical process, distance fluctuation for implantable biomedical devices is unavoidable and it strongly affects the coupling efficiency. This issue can be overcome by performing frequency adjustment of the PUEH. The proposed PUEH shows great potential to be integrated on an implanted biomedical device chip as power source for various applications.

Evaluating the intensity of the acoustic radiation force impulse (ARFI) in intravascular ultrasound (IVUS) imaging: Preliminary in vitro results

The ability to measure the elastic properties of plaques and vessels is significant in clinical diagnosis, particularly for detecting a vulnerable plaque. A novel concept of combining intravascular ultrasound (IVUS) imaging and acoustic radiation force impulse (ARFI) imaging has recently been proposed. This method has potential in elastography for distinguishing between the stiffness of plaques and arterial vessel walls. However, the intensity of the acoustic radiation force requires calibration as a standard for the further development of an ARFI–IVUS imaging device that could be used in clinical applications. In this study, a dual-frequency transducer with 11MHz and 48MHz was used to measure the association between the biological tissue displacement and the applied acoustic radiation force. The output intensity of the acoustic radiation force generated by the pushing element ranged from 1.8 to 57.9mW/cm2, as measured using a calibrated hydrophone. The results reveal that all of the acoustic intensities produced by the transducer in the experiments were within the limits specified by FDA regulations and could still displace the biological tissues. Furthermore, blood clots with different hematocrits, which have elastic properties similar to the lipid pool of plaques, with stiffness ranging from 0.5 to 1.9kPa could be displaced from 1 to 4μm, whereas the porcine arteries with stiffness ranging from 120 to 291kPa were displaced from 0.4 to 1.3μm when an acoustic intensity of 57.9mW/cm2 was used. The in vitro ARFI images of the artery with a blood clot and artificial arteriosclerosis showed a clear distinction of the stiffness distributions of the vessel wall. All the results reveal that ARFI–IVUS imaging has the potential to distinguish the elastic properties of plaques and vessels. Moreover, the acoustic intensity used in ARFI imaging has been experimentally quantified. Although the size of this two-element transducer is unsuitable for IVUS imaging, the experimental results reported herein can be applied in ARFI–IVUS imaging applications.

Application of Ultrasonography and Radiography in Detection of Hemothorax; a Systematic Review and Meta-Analysis.

Hemothorax is one of the most prevalent injuries caused by thoracic traumas. Early detection and treatment of this injury is of utmost importance in prognosis of the patient, but there are still controversial debates on the diagnostic value of imaging techniques in detection of hemothorax. Therefore, the present study aimed to evaluate the diagnostic value of chest ultrasonography and radiography in detection of hemothorax through a systematic review and meta-analysis. Two independent reviewers performed an extended systematic search in databases of Medline, EMBASE, ISI Web of Knowledge, Scopus, Cochrane Library, and ProQuest. Data were extract and quality of the relevant studies were assessed. The number of true positive, false positive, true negative and false negative cases were extracted and screening performance characteristics of two imaging techniques were calculated using a mixed-effects binary regression model. Data from 12 studies were extracted and included in the meta-analysis (7361 patients, 77.1% male). Pooled sensitivity and specificity of ultrasonography in detection of hemothorax were 0.67 (95% CI: 0.41-0.86; I2= 68.38, p<0.001) and 0.99 (95% CI: 0.95-1.0; I2= 88.16, p<0.001), respectively. These measures for radiography were 0.54 (95% CI: 0.33-0.75; I2= 92.85, p<0.001) and 0.99 (95% CI: 0.94-1.0; I2= 99.22, p<0.001), respectively. Subgroup analysis found operator of the ultrasonography device, frequency of the transducer and sample size to be important sources of heterogeneity of included studies. The results of this study showed that although the sensitivity of ultrasonography in detection of hemothorax is relatively higher than radiography, but it is still at a moderate level (0.67%). The specificity of both imaging modalities were found to be at an excellent level in this regard. The screening characteristics of ultrasonography was found to be influenced of the operator and frequency of transducer.

Synthetic tracked aperture ultrasound imaging: design, simulation, and experimental evaluation.

Ultrasonography is a widely used imaging modality to visualize anatomical structures due to its low cost and ease of use; however, it is challenging to acquire acceptable image quality in deep tissue. Synthetic aperture (SA) is a technique used to increase image resolution by synthesizing information from multiple subapertures, but the resolution improvement is limited by the physical size of the array transducer. With a large F-number, it is difficult to achieve high resolution in deep regions without extending the effective aperture size. We propose a method to extend the available aperture size for SA-called synthetic tracked aperture ultrasound (STRATUS) imaging-by sweeping an ultrasound transducer while tracking its orientation and location. Tracking information of the ultrasound probe is used to synthesize the signals received at different positions. Considering the practical implementation, we estimated the effect of tracking and ultrasound calibration error to the quality of the final beamformed image through simulation. In addition, to experimentally validate this approach, a 6degree-of-freedom robot arm was used as a mechanical tracker to hold an ultrasound transducer and to apply in-plane lateral translational motion. Results indicate that STRATUS imaging with robotic tracking has the potential to improve ultrasound image quality.

The influence of mass configurations on velocity amplified vibrational energy harvesters

Vibrational energy harvesters scavenge ambient vibrational energy, offering an alternative to batteries for the autonomous operation of low power electronics. Velocity amplified electromagnetic generators (VAEGs) utilize the velocity amplification effect to increase power output and operational bandwidth, compared to linear resonators. A detailed experimental analysis of the influence of mass ratio and number of degrees-of-freedom (dofs) on the dynamic behaviour and power output of a macro-scale VAEG is presented. Various mass configurations are tested under drop-test and sinusoidal forced excitation, and the system performances are compared. For the drop-test, increasing mass ratio and number of dofs increases velocity amplification. Under forced excitation, the impacts between the masses are more complex, inducing greater energy losses. This results in the 2-dof systems achieving the highest velocities and, hence, highest output voltages. With fixed transducer size, higher mass ratios achieve higher voltage output due to the superior velocity amplification. Changing the magnet size to a fixed percentage of the final mass showed the increase in velocity of the systems with higher mass ratios is not significant enough to overcome the reduction in transducer size. Consequently, the 3:1 mass ratio systems achieved the highest output voltage. These findings are significant for the design of future reduced-scale VAEGs.

Kinetics and Signal Activation Properties of Circulating Factor(s) From Healthy Volunteers Undergoing Remote Ischemic Pre-Conditioning

SummaryAlthough remote ischemic pre-conditioning (RIPC) reduced infarct size in animal experiments and proof-of-concept clinical trials, recent phase III trials failed to confirm cardioprotection during cardiac surgery. Here, we characterized the kinetic properties of humoral factors that are released after RIPC, as well as the signal transduction pathways that were responsible for cardioprotection in an ex vivo model of global ischemia reperfusion injury. Venous blood from 20 healthy volunteers was collected at baseline and 5 min, 30 min, 1 h, 6 h, and daily from 1 to 7 days after RIPC (3 × 5/5 min upper-limb ischemia/reperfusion). Plasma-dialysates (cut-off: 12 to 14 kDa; dilution: 1:20) were infused into Langendorff-perfused mouse hearts subjected to 20/120 min global ischemia/reperfusion. Infarct size and phosphorylation of signal transducer and activator of transcription (STAT)3, STAT5, extracellular-regulated kinase 1/2 and protein kinase B were determined. In a subgroup of plasma-dialysates, an inhibitor of STAT3 (Stattic) was used in mouse hearts. Perfusion with baseline-dialysate resulted in an infarct size of 39% of ventricular mass (interquartile range: 36% to 42%). Perfusion with dialysates obtained 5 min to 6 days after RIPC significantly reduced infarct size by ∼50% and increased STAT3 phosphorylation beyond that with baseline-dialysate. Inhibition of STAT3 abrogated these effects. These results suggest that RIPC induces the release of cardioprotective, dialyzable factor(s) within 5 min, and that circulate for up to 6 days. STAT3 is activated in murine myocardium by RIPC-induced human humoral factors and is causally involved in cardioprotection.

Ultrasound Transducers

Diagnostic medical ultrasound transducers have evolved through the years and have contributed significantly to improved patient care. This article discusses the history and types of transducers and the elements that have changed over time. There has been a sharp transition from natural to human-made elements and from one to many in a single transducer. Ergonomics also now plays a role in transducer design and will continue to do so; the grip, weight, and size of transducers are in the forefront of design considerations. The evolution of transducers has changed not only how well we visualize anatomy and what anatomy we see but also how the patient’s care is managed. Different, new, and emerging technologies certainly will continue to be identified within the sonography community.

Эффективный метод учета потерь в контактном слое при ультразвуковой дефектоскопии

At ultrasonic flaw detection it is necessary to take into account an acoustic loss in a contact layer, especially for products with a statistically rough surface (roughness, waviness). Using samples with the surface identical to the product’s one is the most desirable variant, it is regulated in many techniques, but in practice in vast majority of cases this is not so. Measurements with profilographs or profilometers are taken on a very small area (less than the piezoelectric transducer size) and cannot give an estimation of a real contact layer condition under the whole transducer area. For integral roughness estimation in “CNIITMASH” the capacitance-type sensor DShV has been developed. The sensor is compatible with flaw detectors of any type; it forms a service signal with amplitude that is inversely proportional to a roughness height.&#x0D; Within a frequency rate of 1.8–5 MHz and an incident angle rate of 35–70° the correlation between sensor readings and acoustic losses in a contact layer has been ascertained; a general dependence for them has been obtained, a heuristic equation has been derived and nomograms for piezoelectric transducers of different manufacturers on the sample basis of 123 measurements have been plotted.&#x0D; As a result the new technique of ultrasonic flaw detection has been developed that includes: estimation of tested object real surface roughness with the DShV sensor, flaw detector sensitivity adjustment using a sample with a smooth surface, a gain factor correction by the value taken from a nomogram or calculated on the formula basis. Equivalent defect area should also be measured according to the algorithm described. This technique on principle increases repeatability and reliability of flaw detection results.

Ultrasonic method development of fluid flow velocity measurement

In this article short analysis was done on main ultrasonic methods and means of fluid and gaseous flow control. New mathematical model of ultrasound wave distribution in fluid was proposed and ultrasonic method of fluid flow measurement on its basis. After research of various scientific works regarding near size of ultrasonic transducers a mathematical equation was derived that shows ultrasound frequency dependency on fluid flow velocity. Consequently, stated mathematical model was simulated in Matlab environment shoving some efficient results. Research on physics process of forming a sound wave in piezoelectric elements helped to discover frequency dependency on flow speed, which in turn made it possible, due to the new approach, to develop a mean of flow rate measurement and furthermore to propose perspective fluid and gas flow meters.

An optimisation of IDTs for surface acoustic wave sensor

Acoustic wave devices have been applied for detecting chemical and physical phenomena in gas and liquid applications. For the surface acoustic wave sensors (SAW sensors), the mechanical waves propagating through a piezoelectric crystal include Rayleigh and shear modes. They are influenced by the shape and size of the metal electrodes interdigital transducers (IDTs). Traditionally, IDTs were fabricated in the form of long straight parallel fingers on the piezoelectric substrate. This paper presents a piezoelectric device with focused IDTs (FIDTs) placed on a Y–Z lithium niobate (LiNbO3) substrate to achieve Rayleigh wave energy convergence. The energy conservation principle, called the Rayleigh principle, is used to prove the effective performance of IDTs with concentric shape. Amplitude fields of the conventional and concentric structures are shown. In addition, the energy loss and the output signal changes are compared between the two cases.

DC-Biased Piezoelectret Film Transducers for Airborne Ultrasound

Ultrasonic senders with DC-biased piezoelectret films were built and characterized. The generated sound pressure of the transducers is inversely proportional to the distance from the transducer and proportional to transducer size, AC-voltage, square of the frequency, and effective d33-coefficient of the films. With polypropylene films and DC-voltages of 1000 V, effective d33-coefficients of more than 750 pC/N are obtained. For an applied signal AC-voltage of 46 Vrms, a transducer area of 1.8 cm2, and a distance of 60 mm, sound pressures exceeding 10 Pa were measured in the frequency range above 100 kHz. With stacks of 2 and 3 piezoelectret film layers, effective d33-coefficients up to 1500 pC/N and sound pressures of about 20 and 40 Pa, respectively, could be obtained at frequencies between 60 and 120 kHz. This represents, for otherwise equal parameters, an increase by about a factor of four compared to previous piezoelectret transducers.

Acoustic characterization of contrast-to-tissue ratio and axial resolution for dual-frequency contrast-specific acoustic angiography imaging.

Recently, dual-frequency transducers have enabled high-spatial-resolution and high-contrast imaging of vasculature with minimal tissue artifacts by transmitting at a low frequency and receiving broadband superharmonic echoes scattered by microbubble contrast agents. In this work, we examine the imaging parameters for optimizing contrast-to-tissue ratio (CTR) for dual-frequency imaging and the relationship with spatial resolution. Confocal piston transducers are used in a water bath setup to measure the SNR, CTR, and axial resolution for ultrasound imaging of nonlinear scattering of microbubble contrast agents when transmitting at a lower frequency (1.5 to 8 MHz) and receiving at a higher frequency (7.5 to 25 MHz). Parameters varied include the frequency and peak negative pressure of transmitted waves, center frequency of the receiving transducer, microbubble concentration, and microbubble size. CTR is maximized at the lowest transmission frequencies but would be acceptable for imaging in the 1.5 to 3.5 MHz range. At these frequencies, CTR is optimized when a receiving transducer with a center frequency of 10 MHz is used, with the maximum CTR of 25.5 dB occurring when transmitting at 1.5 MHz with a peak negative pressure of 1600 kPa and receiving with a center frequency of 10 MHz. Axial resolution is influenced more heavily by the receiving center frequency, with a weak decrease in measured pulse lengths associated with increasing transmit frequency. A microbubble population containing predominately 4-μm-diameter bubbles yielded the greatest CTR, followed by 1- and then 2-μm bubbles. Varying concentration showed little effect over the tested parameters. CTR dependence on transmit frequency and peak pressure were confirmed through in vivo imaging in two rodents. These findings may lead to improved imaging of vascular remodeling in superficial or luminal cancers such as those of the breast, prostate, and colon.

Formulation of 36-noded piezoelectric spectral finite element scheme with active/passive layers coupled by Lagrange multipliers

A novel spectral finite element formulation scheme is presented for modeling a plate structure with surface-mounted piezoelectric transducers. Surface-mounted piezoelectric transducers may asymmetrically distribute the mass in the thickness direction of the plate/panel structure, resulting in a coupled mass matrix in spectral element formulation. A new procedure is developed by equating the layer-wise kinematics of the element using undetermined Lagrange multipliers to achieve the diagonal mass matrix. To demonstrate the effectiveness of the element formulation scheme, a two-dimensional piezoelectric spectral element is constructed with 36 nodes and five active/passive layers (layers: transducer/bond/plate/bond/transducer). The performance of the developed element is illustrated by (a) simulation of Lamb wave propagation and estimation of its velocity, and (b) simulation of the effect of transducer size, its dynamics and shear lag on sensor’s response. The results presented highlight the importance of modeling the dynamics of transducers and understanding the effects on sensor response. The presented technique has relevance in the field of structural health monitoring, wherein it can be used to model and simulate aircraft panels with surface-mounted piezoelectric transducers.

An improved ultrasonic method for lubricant-film thickness measurement in cylindrical roller bearings under light radial load

Focusing on measuring the oil-film thickness with ultrasonic approaches in roller bearings, a new feasible method is proposed to improve the measuring accuracy. The spatial resolution, which has great influence on the measuring accuracy, is mainly determined by the focus size of the ultrasound transducer. Under the light load conditions, the width of the Hertz contact area is smaller than the focus size, which results in overlapping measurement regions by the high pulse-repetition frequency and then brings about large measurement errors. By introducing reflection coefficients of sound pressure in the non-overlapping areas, the new method improves the measuring accuracy successfully. The experimental results are achieved from the real-time lubricant-film thickness monitoring system for cylindrical roller bearings, which show good agreement with the theoretical solutions.

Low-Echo Sphere Phantoms and Methods for Assessing Imaging Performance of Medical Ultrasound Scanners

Tissue-mimicking phantoms and software for quantifying the ability of human observers to detect small low-echo spheres as a function of depth have been developed. Detectability is related to the imager's ability to delineate the boundary of a 3-D object such as a spiculated tumor. The phantoms accommodate a broad range of transducer shapes and sizes. Three phantoms are described: one with 2-mm-diameter spheres (for higher frequencies), one with 3.2-mm-diameter spheres (for lower frequencies) and one with 4-mm-diameter spheres (for lower frequencies). The spheres are randomly distributed in each phantom. The attenuation coefficients of spheres and surroundings are nearly identical; thus, compromising shadowing or enhancement distal to spheres does not occur. Reproducibility results are given for pairs of independent data sets involving eight different combinations of scanner, transducer and console settings. The following comparison results are also reported: (i) only the selected frequency differs; (ii) transducers and scan parameters are nearly the same but manufacturers differ; (iii) ordinary B-scanning, spatial compounding and tissue harmonic imaging are addressed. The phantoms and software promise to be valuable tools for scanning system and setup comparisons and for acceptance testing.