Piezoelectric Transducer Elements Research Articles

Design and Fabrication of 15-MHz Ultrasonic Transducers Based on a Textured Pb(Mg1/3Nb2/3)O3-Pb(Zr, Ti)O3 Ceramic.

Ultrasound medical imaging is an entrenched and powerful tool for medical diagnosis. Image quality in ultrasound is mainly dependent on performance of piezoelectric transducer elements, which is further related to the electromechanical performance of the constituent piezoelectric materials. With rising need for piezoelectric materials with better performance and low cost, a highly 〈001〉 textured piezo ceramic, Pb(Mg1/3Nb2/3)O3-Pb(Zr, Ti)O3, has been developed. Recently, textured ceramic materials can be produced at low cost and exhibit high piezoelectric strain constants and large electromechanical coupling coefficients. In this work, 15-MHz ultrasonic transducers with an effective aperture of 2.5 mm in diameter based on these highly 〈001〉 textured ceramics have been successfully fabricated. The fabricated transducers achieved a central frequency of 15 MHz, a fractional bandwidth of 67% (at -6 dB), a high effective electromechanical coupling coefficient [Formula: see text] of 0.55, and a low insertion loss (IL) of 21 dB. Ex vivo ultrasonic imaging of a porcine eyeball was used to assess the tomography quality of the transducer. The results show that utilized textured ceramic has a great potential in developing ultrasonic devices for biomedical imaging purposes.

Outperforming piezoelectric ultrasonics with high-reliability single-membrane CMUT array elements

It has long been hypothesized that capacitive micromachined ultrasound transducers (CMUTs) could potentially outperform piezoelectric technologies. However, challenges with dielectric charging, operational hysteresis, and transmit sensitivity have stood as obstacles to these performance outcomes. In this paper, we introduce key architectural features to enable high-reliability CMUTs with enhanced performance. Typically, a CMUT element in an array is designed with an ensemble of smaller membranes oscillating together to transmit or detect ultrasound waves. However, this approach can lead to unreliable behavior and suboptimal transmit performance if these smaller membranes oscillate out of phase or collapse at different voltages. In this work, we designed CMUT array elements composed of a single long rectangular membrane, with the aim of improving the output pressure and electromechanical efficiency. We compare the performance of three different modifications of this architecture: traditional contiguous dielectric, isolated isolation post (IIP), and insulated electrode-post (EP) CMUTs. EPs were designed to improve performance while also imparting robustness to charging and minimization of hysteresis. To fabricate these devices, a wafer-bonding process was developed with near-100% bonding yield. EP CMUT elements achieved electromechanical efficiency values as high as 0.95, higher than values reported with either piezoelectric transducers or previous CMUT architectures. Moreover, all investigated CMUT architectures exhibited transmit efficiency 2–3 times greater than published CMUT or piezoelectric transducer elements in the 1.5–2.0 MHz range. The EP and IIP CMUTs demonstrated considerable charging robustness, demonstrating minimal charging over 500,000 collapse-snap-back actuation cycles while also mitigating hysteresis. Our proposed approach offers significant promise for future ultrasonic applications.

A Transceiver ASIC for a Single-Cable 64-Element Intra-Vascular Ultrasound Probe

This article presents an application-specific integrated circuit (ASIC) designed for intra-vascular ultrasound imaging that interfaces 64 piezoelectric transducer elements to an imaging system using a single micro-coaxial cable. Thus, it allows a single-element transducer to be replaced by a transducer array to enable 3-D imaging. The 1.5-mm-diameter ASIC is intended to be mounted at the tip of a catheter, directly integrated with a 2-D array of piezoelectric transducer elements. For each of these elements, the ASIC contains a high-voltage (HV) switch, allowing the elements to transmit an acoustic wave in response to an HV pulse generated by the imaging system. A low-noise amplifier then amplifies the resulting echo signals and relays them as a signal current to the imaging system, while the same cable provides a 3-V supply. Element selection and other settings can be programmed by modulating configuration data on the supply, thus enabling full synthetic aperture imaging. An integrated element test mode measures the element capacitance to detect bad connections to the transducer elements. The ASIC has been fabricated in a 0.18- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> HV CMOS technology and consumes only 6 mW in receive. Electrical measurements show correct switching of 30-V transmit pulses and a receive amplification with a 71-dB dynamic range, including 12 dB of programmable gain over a 3-dB bandwidth of 21 MHz. The functionality of the ASIC has been successfully demonstrated in a 3-D imaging experiment.

Development of a Class-C Power Amplifier with Diode Expander Architecture for Point-of-Care Ultrasound Systems.

Point-of-care ultrasound systems are widely used in ambulances and emergency rooms. However, the excessive heat generated from ultrasound transmitters has an impact on the implementation of piezoelectric transducer elements and on battery consumption, thereby affecting the system’s sensitivity and resolution. Non-linear power amplifiers, such as class-C amplifiers, could substitute linear power amplifiers, such as class-A amplifiers, which are currently used in point-of-care ultrasound systems. However, class-C power amplifiers generate less output power, resulting in a reduction of system sensitivity. To overcome this issue, we propose a new diode expander architecture dedicated to power amplifiers to reduce the effects of sinusoidal pulses toward the power supply. Thus, the proposed architecture could increase the input pulse amplitudes applied to the main transistors in the power amplifiers, hence increasing the output voltage of such amplifiers. To verify the proposed concept, pulse-echo responses from an ultrasonic transducer were tested with the developed class-C power amplifier using a resistor divider and the designed diode expander architecture. The peak-to-peak amplitude of the echo signals of the ultrasonic transducers when using a class-C power amplifier with a diode expander architecture (2.98 Vp–p) was higher than that for the class-C power amplifier with a resistor divider architecture (2.51 Vp–p). Therefore, the proposed class-C power amplifier with diode expander architecture is a potential candidate for improving the sensitivity performance of piezoelectric transducers for point-of-care ultrasound systems.

Prelinearized Class-B Power Amplifier for Piezoelectric Transducers and Portable Ultrasound Systems.

Portable ultrasound systems typically suffer from unwanted heat and limited battery life, resulting in reduced system performance or the applicable number of piezoelectric transducer elements. This can be a bottleneck in widely used portable ultrasound systems. Class-A power amplifiers are typically used in portable ultrasound systems. However, unwanted heat dissipation needs to be reduced by using large cooling fans and heat pipe structures. To reduce unwanted heat, class-B power amplifiers may be a possible solution. However, the non-linearity of class-B power amplifiers could limit their integration with piezoelectric transducers because non-linearity in the high-voltage output of the power amplifiers deteriorates the sensitivity of portable ultrasound systems. To improve the linearity of the power amplifier, we developed prelinearized class-B power amplifiers for piezoelectric transducers and portable ultrasound systems. To verify our proposed method, we compared the performances of class-B and prelinearized class-B power amplifiers in their pulse-echo responses. Therefore, prelinearized class-B power amplifiers are a possible solution to produce better echo signal performance in piezoelectric transducers and portable ultrasound systems.

An Element-Matched Electromechanical &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$\Delta\Sigma$ &lt;/tex-math&gt; &lt;/inline-formula&gt; ADC for Ultrasound Imaging

This paper presents a power- and area-efficient approach to digitizing the echo signals received by piezoelectric transducer elements, commonly used for ultrasound imaging. This technique utilizes such elements not only as sensors but also as the loop filter of an element-level $\Delta \Sigma $ analog to digital converter (ADC). The receiver chain is thus greatly simplified, yielding savings in area and power. Every ADC becomes small enough to fit underneath a $150\,\,\mu \mathrm {m} \times 150\,\,\mu \mathrm {m}$ transducer element, enabling simultaneous acquisition and digitization from all the elements in a 2-D array. This is especially valuable for miniature 3-D probes. Experimental results are reported for a prototype receiver chip with an array of $5 \times 4$ element-matched ADCs and a transducer array fabricated on top of the chip. Each ADC consumes 800 $\mu \mathrm {W}$ from a 1.8 V supply and achieves a SNR of 47 dB in a 75% bandwidth around a center frequency of 5 MHz.

A Front-End ASIC With High-Voltage Transmit Switching and Receive Digitization for 3-D Forward-Looking Intravascular Ultrasound Imaging

This paper presents an area- and power-efficient application-specified integrated circuit (ASIC) for 3-D forward-looking intravascular ultrasound imaging. The ASIC is intended to be mounted at the tip of a catheter, and has a circular active area with a diameter of 1.5 mm on the top of which a 2-D array of piezoelectric transducer elements is integrated. It requires only four micro-coaxial cables to interface 64 receive (RX) elements and 16 transmit (TX) elements with an imaging system. To do so, it routes high-voltage (HV) pulses generated by the system to selected TX elements using compact HV switch circuits, digitizes the resulting echo signal received by a selected RX element locally, and employs an energy-efficient load-modulation datalink to return the digitized echo signal to the system in a robust manner. A multi-functional command line provides the required sampling clock, configuration data, and supply voltage for the HV switches. The ASIC has been realized in a 0.18- $\mu \text{m}$ HV CMOS technology and consumes only 9.1 mW. Electrical measurements show 28-V HV switching and RX digitization with a 16-MHz bandwidth and 53-dB dynamic range. Acoustical measurements demonstrate successful pulse transmission and reception. Finally, a 3-D ultrasound image of a three-needle phantom is generated to demonstrate the imaging capability.

Multiview Hilbert transformation in full-ring transducer array-based photoacoustic computed tomography.

Based on the photoacoustic (PA) effect, PA tomography directly measures specific optical absorption, i.e., absorbed optical energy per unit volume. We recently developed a full-ring ultrasonic transducer array-based photoacoustic computed tomography (PACT) system for small-animal whole-body imaging. The system has a full-view detection angle and high in-plane resolution (∼100 μm). However, due to the bandpass frequency response of the piezoelectric transducer elements and the limited elevational detection coverage of the full-ring transducer array, the reconstructed images present bipolar (i.e., both positive and negative) pixel values, which cause ambiguities in image interpretation for physicians and biologists. We propose a multiview Hilbert transformation method to recover the unipolar initial pressure for full-ring PACT. The effectiveness of the proposed algorithm was first validated by numerical simulations and then demonstrated with ex vivo mouse brain structural imaging and in vivo mouse whole-body imaging.

A Front-End ASIC With Receive Sub-array Beamforming Integrated With a $32 \times 32$ PZT Matrix Transducer for 3-D Transesophageal Echocardiography

This paper presents a power- and area-efficient front-end application-specific integrated circuit (ASIC) that is directly integrated with an array of $32 \times 32$ piezoelectric transducer elements to enable next-generation miniature ultrasound probes for real-time 3-D transesophageal echocardiography. The $6.1 \times 6.1$ mm2 ASIC, implemented in a low-voltage 0.18- $\mu \text{m}$ CMOS process, effectively reduces the number of receive (RX) cables required in the probe’s narrow shaft by ninefold with the aid of 96 delay-and-sum beamformers, each of which locally combines the signals received by a sub-array of $3 \times 3$ elements. These beamformers are based on pipeline-operated analog sample-and-hold stages and employ a mismatch-scrambling technique to prevent the ripple signal associated with the mismatch between these stages from limiting the dynamic range. In addition, an ultralow-power low-noise amplifier architecture is proposed to increase the power efficiency of the RX circuitry. The ASIC has a compact element matched layout and consumes only 0.27 mW/channel while receiving, which is lower than the state-of-the-art circuit. Its functionality has been successfully demonstrated in 3-D imaging experiments.

A controllable circular ring acoustic focused field

Based on Huygens principle about the aspect of phased array, this paper presents a structure of cylindrical acoustic transducer consisting of circular ring piezoelectric transducer elements in radial vibration mode, which can be used to achieve the ultrasonic nondestructive test for the cylindrical scanning acoustic field in three-dimensional space. By analyzing the acoustic field of a single ring line source and a single element, the sound field distribution of the phased array is obtained for constructing circular ring acoustic focused field. By means of the phased array incentive mode, the phase difference of driving signals is generated and forms a regular time delay; with the accomplishment of sound field scanning in cylindrical three-dimensional space, the circular ring acoustic focused field can be controlled in real time.Theoretical analysis and finite element simulation results demonstrate that the size of the circular ring acoustic focused field can be controlled by the numbers of the excited array elements, which are 4, 8, 16 and 32 respectively in our work. We find that with more array element numbers, the circular ring acoustic field has better focused features. The radius size of the circular ring acoustic focused field can be controlled by the different locations of the focus positions which are 30 and 50 mm respectively in our work. And we find that as the distance between the focus positions and the center of piezoelectric wafer becomes longer, the radius of the circular ring acoustic focused field becomes bigger, and the position of the focus is equivalent to the radius of the circular ring acoustic focused field. The movement along the axial direction of circular ring acoustic focused field can be controlled by the angle of deflection, which are set as 0, 10 respectively in our work. And we find that the circular ring acoustic focused field is deflected in a corresponding deflection angle along the Z-axis, and the moving distance is FZ = F/sin . With the theoretical analysis and the experimental simulation, it can be shown that the structure of cylindrical acoustic transducer array presented in this paper could create an adjustable circular ring acoustic focused field and can potentially provide an acoustic field scan method in detection ultrasound, medical ultrasound and other areas of a cylindrical space.

Piezoelectric transduction of flexural modes in pre-stressed microbeam resonators

This paper reports on the optimization of the design of piezoelectric transducer elements integrated on doubly-clamped microbeam resonators utilized as (bio)chemical sensors. We report and emphasize the often forgotten influence of membrane stresses on defining the dimensions and optimal position of the piezoelectric transducer elements. The study takes into account stress induced structural changes and provides models for the equivalent motional parameters of resonators with particular shapes of the transducers matching the flexural modes of vibration. The above is analyzed theoretically using numerical models and is confirmed by impedance measurements and optical measurements of fabricated doubly-clamped beam resonators. We propose various transducer designs and highlight the advantages of using higher order vibration modes by implementing specially designed mode matching transducer elements. It is concluded that the paper describes and highlights the importance of accounting for the membrane stresses to optimize the resonator performance and the low power in electronic feedback of resonating sensing systems.

A simple and novel method to monitor breathing and heart rate in awake and urethane-anesthetized newborn rodents.

Rodents are most useful models to study physiological and pathophysiological processes in early development, because they are born in a relatively immature state. However, only few techniques are available to monitor non-invasively heart frequency and respiratory rate in neonatal rodents without restraining or hindering access to the animal. Here we describe experimental procedures that allow monitoring of heart frequency by electrocardiography (ECG) and breathing rate with a piezoelectric transducer (PZT) element without hindering access to the animal. These techniques can be easily installed and are used in the present study in unrestrained awake and anesthetized neonatal C57/Bl6 mice and Wistar rats between postnatal day 0 and 7. In line with previous reports from awake rodents we demonstrate that heart rate in rats and mice increases during the first postnatal week. Respiratory frequency did not differ between both species, but heart rate was significantly higher in mice than in rats. Further our data indicate that urethane, an agent that is widely used for anesthesia, induces a hypoventilation in neonates whilst heart rate remains unaffected at a dose of 1 g per kg body weight. Of note, hypoventilation induced by urethane was not detected in rats at postnatal 0/1. To verify the detected hypoventilation we performed blood gas analyses. We detected a respiratory acidosis reflected by a lower pH and elevated level in CO2 tension (pCO2) in both species upon urethane treatment. Furthermore we found that metabolism of urethane is different in P0/1 mice and rats and between P0/1 and P6/7 in both species. Our findings underline the usefulness of monitoring basic cardio-respiratory parameters in neonates during anesthesia. In addition our study gives information on developmental changes in heart and breathing frequency in newborn mice and rats and the effects of urethane in both species during the first postnatal week.

The effect of acoustic and solar energy on drying process of pistachios

A new approach of ultrasound-assisted sun drying was tested in this study using a flat bed as product support and two extensional piezoelectric Bolt-clamped 20kHz transducer elements. The mono layer of moist unshelled pistachios was dried under open sun by applying 500 and 1000W power ultrasound. The results showed that the Page model was found to be the most suitable for describing drying curve of pistachios. But, the Logarithmic model was described to satisfactorily drying curve of pistachios for open sun method when the ultrasound power was turned off. By applying the ultrasound about 17W/kg moist pistachios in thin layer, the drying period could be reduced to 4h.

An analytical model for guided wave inspection optimization for prismatic structures of any cross section

This paper presents an analytical modeling technique for the simulation of long-range ultrasonic guided waves in structures. The model may be used to predict the displacement field in a prismatic structure arising from any excitation arrangement and may therefore be used as a tool to design new inspection systems. It is computationally efficient and relatively simple to implement, yet gives accuracy similar to finite element analysis and semi-analytical finite element analysis methods. The model has many potential applications; one example is the optimization of part-circumferential arrays where access to the full circumference of the pipe is restricted. The model has been successfully validated by comparison with finite element solutions. Experimental validation has also been carried out using an array of piezoelectric transducer elements to measure the displacement field arising from a single transducer element in an 88.9-mm-diameter pipe. Good agreement has been obtained between the two models and the experimental data.

Experimental Investigation of Mode Conversions of the T(0,1) Mode Guided Wave Propagating in an Elbow Pipe

Mode conversions from the fundamental torsional guided wave mode, T(0,1), to the higher-order torsional modes, T(1,1), T(2,1), T(3,1), and T(4,1), at a welded elbow pipe were experimentally investigated in a wide frequency range from 30 to 80 kHz. One ring-shaped transducer system was used as the transmitter and another as the receiver. Both systems consist of eight circumferentially located piezoelectric transducer elements. A novel method for a preferential detection of the torsional modes was proposed on the basis of the circumferential wave structures of the modes, which was utilized for investigations of mode conversions. Dispersion relations of the converted modes in frequency ranges from 30 to 80 kHz were also experimentally investigated, which agreed very well with those of the theoretical calculations.

Experimental Investigation of Mode Conversions of the T(0,1) Mode Guided Wave Propagating in an Elbow Pipe

Mode conversions from the fundamental torsional guided wave mode, T(0,1), to the higher-order torsional modes, T(1,1), T(2,1), T(3,1), and T(4,1), at a welded elbow pipe were experimentally investigated in a wide frequency range from 30 to 80 kHz. One ring-shaped transducer system was used as the transmitter and another as the receiver. Both systems consist of eight circumferentially located piezoelectric transducer elements. A novel method for a preferential detection of the torsional modes was proposed on the basis of the circumferential wave structures of the modes, which was utilized for investigations of mode conversions. Dispersion relations of the converted modes in frequency ranges from 30 to 80 kHz were also experimentally investigated, which agreed very well with those of the theoretical calculations.

The application of synthetic focusing for imaging crack-like defects in pipelines using guided waves

This paper deals with quantifying the performance of a technique for detection, location, and sizing of circumferential crack-like defects in pipelines using synthetically focused guided waves. The system employs a circumferential array of piezoelectric transducer elements. A torsional probing guided wave is excited using the array, which subsequently interacts with the reflecting features of the pipe, such as defects or weld caps. The recorded backscattered signals are synthetically focused to every point of interest in the pipe wall, to form an image of the reflecting features of the pipe. The defect image amplitude is used to estimate the defect depth, and the full width at half maximum of the defect image circumferential profile is used to estimate the circumferential extent of the defect. The imaging system is tested with data from finite element simulations and from laboratory experiments. It is found that reliable sizing of circumferential cracks in finite element simulations and experiments can be achieved if the circumferential extent of the defect is greater than 1.5 lambda(S), where lambda(S) is the shear wavelength at the frequency of inspection. This result is theoretically valid for any pipe size, any axial defect location, and any inspection frequency. Amplitude gains of around 18 dB over an unfocused system have been observed experimentally in an 8-inch pipe with a 9 dB SNR improvement.

Trimodal imaging system capable of quantitative phase imaging without 2π ambiguities: erratum

In an earlier paper [Opt. Lett. 33, 216 (2008)], the piezoelectric transducer element in Fig. 1 was incorrectly placed in the input arm of the bidirectional coupler. This element should be in the output arm.

A new technique for measuring the acoustic nonlinearity of materials using Rayleigh waves

This note presents a procedure to generate nonlinear Rayleigh surface waves without having to drive the transmitting piezoelectric transducer at high voltages; driving at low voltages limits the excitation of the intrinsic nonlinearity of the piezoelectric transducer element, and enables an efficient measurement procedure to isolate inherent material nonlinearity. The capabilities of this proposed technique are demonstrated by measuring the material nonlinearity of aluminum alloy 2024 and 6061 plates with Rayleigh surface waves.

Resonance sensor measurements of stiffness variations in prostate tissue in vitro—a weighted tissue proportion model

Prostate cancer is the most common type of cancer in men in Europe and the US. The methods to detect prostate cancer are still precarious and new techniques are needed. A piezoelectric transducer element in a feedback system is set to vibrate with its resonance frequency. When the sensor element contacts an object a change in the resonance frequency is observed, and this feature has been utilized in sensor systems to describe physical properties of different objects. For medical applications it has been used to measure stiffness variations due to various patho-physiological conditions. In this study the sensor's ability to measure the stiffness of prostate tissue, from two excised prostatectomy specimens in vitro, was analysed. The specimens were also subjected to morphometric measurements, and the sensor parameter was compared with the morphology of the tissue with linear regression. In the probe impression interval 0.5–1.7 mm, the maximum R2 ⩾ 0.60 (p < 0.05, n = 75). An increase in the proportion of prostate stones (corpora amylacea), stroma, or cancer in relation to healthy glandular tissue increased the measured stiffness. Cancer and stroma had the greatest effect on the measured stiffness. The deeper the sensor was pressed, the greater, i.e., deeper, volume it sensed. Tissue sections deeper in the tissue were assigned a lower mathematical weighting than sections closer to the sensor probe. It is concluded that cancer increases the measured stiffness as compared with healthy glandular tissue, but areas with predominantly stroma or many stones could be more difficult to differ from cancer.