Showing papers on "Transducer published in 2019"

A Two-DOF Ultrasonic Motor Using a Longitudinal–Bending Hybrid Sandwich Transducer

Abstract: A two-degrees-of-freedom (two-DOF) ultrasonic motor, which could output linear motions with two-DOF by using only one longitudinal–bending hybrid sandwich transducer, is proposed and tested in this paper. The motion in the horizontal ( X ) direction is achieved by the hybrid of the second longitudinal and fifth bending vibrations of the motor, while the motion in the vertical ( Y ) direction is gained by the composition of two orthogonal fifth bending vibrations. The proposed ultrasonic motor is designed and the principles for the two-DOF driving were analyzed. Then, the simulation analyses of the motor are accomplished to verify the described principles. Finally, a prototype is fabricated and its mechanical output characteristics are tested. The results indicate that the maximum no-load velocities of the motor in horizontal and vertical directions are 572 and 543 mm/s under the preload of 100 N and the voltage of 300 Vp-p, respectively. The maximum output forces in horizontal and vertical directions are 24 and 22 N when the preload is 200 N. The simulation and experiment results verify the feasibility of the proposed two-DOF ultrasonic motor.

Development of a Planar Piezoelectric Actuator Using Bending–Bending Hybrid Transducers

Abstract: A planar piezoelectric actuator with large travel range is presented in this paper. The actuator is composed of four uniform piezoelectric transducers, and each transducer can bend along the horizontal direction or vertical direction independently. Trapezoidal-wave signals are used to excite the hybrid bending of the transducers and form rectangular movements on their driving feet. The actuator can move step by step by the static friction forces in nonresonant mode, and a long reliability life is obtained as there is no wear and tear problem. The operating principle is simulated by finite-element method, which reveals the generation of rectangular trajectory on each driving foot and the large structure stiffness of the actuator. A prototype is fabricated and its experiment system is established. A resolution of 16 nm is achieved at the quasi-static mode, a minimum step distance repeatability error rate of 1.06% is obtained at the stepper mode; the maximum output speed and carrying load of 300 μm/s and 35 kg are achieved at voltage of 400 V $_{{\text{p-p}}}$ and frequency of 40 Hz. The experiments also shows that the output speed is linearly related to the exciting voltage; the motion along any direction in the platform is achieved by controlling the voltage signals.

Microwave-to-optical conversion using lithium niobate thin-film acoustic resonators

Abstract: We demonstrate conversion of up to 4.5 GHz-frequency microwaves to 1500 nm-wavelength light using optomechanical interactions on suspended thin-film lithium niobate. Our method utilizes an interdigital transducer that drives a free-standing 100 $\mu$m-long thin-film acoustic resonator to modulate light travelling in a Mach-Zehnder interferometer or racetrack cavity. Owing to the strong microwave-to-acoustic coupling offered by the transducer in conjunction with the strong photoelastic, piezoelectric, and electro-optic effects of lithium niobate, we achieve a half-wave voltage of $V_\pi$ = 4.6 V and $V_\pi$ = 0.77 V for the Mach-Zehnder interferometer and racetrack resonator, respectively. The acousto-optic racetrack cavity exhibits an optomechancial single-photon coupling strength of 1.1 kHz. Our integrated nanophotonic platform coherently leverages the compelling properties of lithium niobate to achieve microwave-to-optical transduction. To highlight the versatility of our system, we also demonstrate a lossless microwave photonic link, which refers to a 0 dB microwave power transmission over an optical channel.

Stretchable Ultrasonic Transducer Arrays for Three-Dimensional Imaging on Complex Surfaces

Abstract: Ultrasonic imaging technology has been widely implemented in the fields of medical imaging, non-destructive evaluation, and structural health monitoring. Tradition- ally, rigid and semi-flexible ultrasound probes in current bulky packages can detect the sub-surface defects of a component with a flat surface, but neither is suitable for the accurate defect inspection with three-dimensional curvatures, which significantly constrains the universality and practicability of ultrasonic imaging technology. This study reports the development of flexible and stretchable ultrasound two-dimensional (2D) array probe that exploits an ’island-bridge’ structured interconnection and multi-layer electrodes to integrate miniature ultrasound transducer elements with thin, low modulus silicone elastomeric polymer matrix. The achieved soft device, owning dense transducer distribution, excellent piezoelectric performance, bare internal cross-talk, and over 60% stretchability, is capable of long-time seamlessly conforming on almost any curved com- ponents, and reconstructing the object images with high resolution. With the designed probe, mono-view 2D images of internal defects in a specimen with a convex surface are collected. The entire geometries of two internal defects are reconstructed in threedimensional space. The proposed flexible and stretchable ultrasonic device along with the imaging reconstruction algorithm provides an effective, accurate, and straightforward solution for ultrasonic imaging of complex-shaped structure components.

Development of Acoustic Emission Sensor Optimized for Partial Discharge Monitoring in Power Transformers.

Abstract: The acoustic emission (AE) technique is one of the unconventional methods of partial discharges (PD) detection. It plays a particularly important role in oil-filled power transformers diagnostics because it enables the detection and online monitoring of PDs as well as localization of their sources. The performance of this technique highly depends on measurement system configuration but mostly on the type of applied AE sensor. The paper presents, in detail, the design and manufacturing stages of an ultrasensitive AE sensor optimized for partial discharge detection in power transformers. The design assumptions were formulated based on extensive laboratory research, which allowed for the identification of dominant acoustic frequencies emitted by partial discharges in oil–paper insulation. The Krimholtz–Leedom–Matthaei (KLM) model was used to iteratively find optimal material and geometric properties of the main structures of the prototype AE sensor. It has two sensing elements with opposite polarization direction and different heights. The fully differential design allowed to obtain the desired properties of the transducer, i.e., a two-resonant (68 kHz and 90 kHz) and wide (30–100 kHz) frequency response curve, high peak sensitivity (−61.1 dB ref. V/µbar), and low noise. The laboratory tests confirmed that the prototype transducer is characterized by ultrahigh sensitivity of partial discharge detection. Compared to commonly used commercial AE sensors, the average amplitude of PD pulses registered with the prototype sensor was a minimum of 5.2 dB higher, and a maximum of 19.8 dB higher.

Racemic Amino Acid Piezoelectric Transducer.

Abstract: Single crystal $L$-amino acids can exhibit technologically useful piezoelectric and nonlinear optical properties. Here we predict, using density functional theory, the piezoelectric charge and strain and voltage tensors of the racemic amino acid $DL$ alanine, and use the modeling data to guide the first macroscopic and nanoscopic piezoelectric measurements on $DL$-alanine single crystals and polycrystalline aggregates. We demonstrate voltage generation of up to 0.8 V from $DL$-alanine crystal films under simple manual compression, twice as high as other amino acid crystals. Our results suggest that net molecular chirality is not a prerequisite for piezoelectric behavior in organic crystals. The transducer presented herein demonstrates that $DL$-alanine crystals can be used in applications such as temperature and force measurement in biosensors, data storage in flexible electronic devices, and mechanical actuation in energy harvesters.

Investigation of Broadband Characteristics of Multi-Frequency Piezoelectric Micromachined Ultrasonic Transducer (MF-pMUT)

Abstract: Multi-frequency ultrasonic transducers are highly promising devices in biomedical applications for providing both good imaging resolution and large detection depth. However, most conventional multi-frequency ultrasonic transducers are designed through integrating multiple single-frequency transducers, with complicated fabrication process, imperfect beam profiles, and limited bandwidths. In this paper, a single-element multi-frequency piezoelectric micromachined ultrasonic transducer (MF-pMUT) is proposed and investigated in terms of broadband property. Three rectangular-diaphragm MF-pMUTs with different length-to-width aspect ratios are fabricated with the microelectromechanical system (MEMS) technology and characterized both in air and underwater. All MF-pMUT samples exhibit at least two broad bands. After optimization of the aspect ratio, two smooth bands with comparable sound pressure level are achieved, providing −6 dB bandwidths of 112%/38% and corresponding central frequencies of 0.615 MHz/1.63 MHz. Benefited from such broadened multi-frequency property and simple structure design, the proposed MF-pMUT shows a great potential in ultrasonic detection, diagnosis, and imaging applications as well as wireless acoustic energy transmission.

Low-Loss and Wideband Acoustic Delay Lines

Abstract: This paper demonstrates low-loss acoustic delay lines (ADLs) based on shear-horizontal waves in thin-film LiNbO3 for the first time. Due to its high electromechanical coupling, the shear-horizontal mode is suited for producing devices with large bandwidths. Here, we show that shear-horizontal waves in LiNbO3 thin films are also excellent for implementing low-loss ADLs based on unidirectional transducers. The high acoustic reflections and large transducer unidirectionality induced by the mechanical loading of the electrodes on a LiNbO3 thin film provide a great tradeoff between delay line insertion loss and bandwidth. The directionality for two different types of unidirectional transducers has been characterized. Delay lines with variations in the key design parameters have been designed, fabricated, and measured. One of our fabricated devices has shown a group delay of 75 ns with an IL below 2 dB over a 3-dB bandwidth of 16 MHz centered at 160 MHz (fractional bandwidth = 10%). The measured insertion loss for other devices with longer delays and different numbers of transducer cells are analyzed, and the loss contributing factors and their possible mitigation are discussed.

Eco-Friendly Highly Sensitive Transducers Based on a New KNN–NTK–FM Lead-Free Piezoelectric Ceramic for High-Frequency Biomedical Ultrasonic Imaging Applications

Abstract: High-frequency ultrasonic imaging with improved spatial resolution has gained increasing attention in the field of biomedical imaging. Sensitivity of transducers plays a pivotal role in determining ultrasonic image quality. Conventional ultrasonic transducers are mostly made from lead-based piezoelectric materials that may be harmful to the human body and the environment. In this study, a new (K,Na)NbO 3 -KTiNbO 5 -BaZrO 3 -Fe 2 O 3 -MgO (KNN-NTK-FM) lead-free piezoelectric ceramic was utilized in developing eco-friendly transducers for high-frequency biomedical ultrasonic imaging applications. A needle transducer with a small active aperture size of 0.45 × 0.55 mm 2 was designed and evaluated. The fabricated transducer exhibits great performance with a high center frequency (52.6 MHz), a good electromechanical coupling (k eff ~ 0.45), a large bandwidth (64.4% at -6 dB), and a very low two-way insertion loss (10.1 dB). Such high sensitivity is superior to those transducers based on other lead-free piezoelectric materials and can even be comparable to the lead-based ones. Imaging performance of the KNN-NTK-FM needle transducer was analyzed by imaging a wire phantom and an agar tissue-mimicking phantom. Imaging capabilities of the transducer were further demonstrated by ex vivo imaging studies on a porcine eyeball and a rabbit aorta. The results suggest that the KNN-NTK-FM piezoceramic has many attractive properties over other lead-free piezoelectric materials in developing eco-friendly highly sensitive transducers for high-frequency biomedical ultrasonic imaging applications.

Design of a New Stress Wave-Based Pulse Position Modulation (PPM) Communication System with Piezoceramic Transducers.

Abstract: Stress wave-based communication has great potential for succeeding in subsea environments where many conventional methods would otherwise face excessive difficulty, and it can benefit logging well by using the drill string as a conduit for stress wave propagation. To achieve stress wave communication, a new stress wave-based pulse position modulation (PPM) communication system is designed and implemented to transmit data through pipeline structures with the help of piezoceramic transducers. This system consists of both hardware and software components. The hardware is composed of a piezoceramic transducer that can generate powerful stress waves travelling along a pipeline, upon touching, and a PPM signal generator that drives the piezoceramic transducer. Once the transducer is in contact with a pipeline surface, the generator integrated with an amplifier is utilized to excite the piezoceramic transducer with a voltage signal that is modulated to encode the information. The resulting vibrations of the transducer generates stress waves that propagate throughout the pipeline. Meanwhile, piezoceramic sensors mounted on the pipeline convert the stress waves to electric signals and the signal can be demodulated. In order to enable the encoding and decoding of information in the stress wave, a PPM-based communication protocol was integrated into the software system. A verification experiment demonstrates the functionality of the developed system for stress wave communication using piezoceramic transducers and the result shows that the data transmission speed of this new communication system can reach 67 bits per second (bps).

Coherent Multi-Transducer Ultrasound Imaging

Abstract: This work extends the effective aperture size by coherently compounding the received radio frequency data from multiple transducers. As a result, it is possible to obtain an improved image, with enhanced resolution, an extended field of view (FoV), and high-acquisition frame rates. A framework is developed in which an ultrasound imaging system consisting of $N$ synchronized matrix arrays, each with partly shared FoV, take turns to transmit plane waves (PWs). Only one individual transducer transmits at each time while all $N$ transducers simultaneously receive. The subwavelength localization accuracy required to combine information from multiple transducers is achieved without the use of any external tracking device. The method developed in this study is based on the study of the backscattered echoes received by the same transducer and resulting from a targeted scatterer point in the medium insonated by the multiple ultrasound probes of the system. The current transducer locations along with the speed of sound in the medium are deduced by optimizing the cross correlation between these echoes. The method is demonstrated experimentally in 2-D for two linear arrays using point targets and anechoic lesion phantoms. The first demonstration of a free-hand experiment is also shown. Results demonstrate that the coherent multi-transducer ultrasound imaging method has the potential to improve ultrasound image quality, improving resolution, and target detectability. Compared with coherent PW compounding using a single probe, lateral resolution improved from 1.56 to 0.71 mm in the coherent multi-transducer imaging method without acquisition frame rate sacrifice (acquisition frame rate 5350 Hz).

Multiwalled Carbon Nanotubes–Poly(3-octylthiophene-2,5-diyl) Nanocomposite Transducer for Ion-Selective Electrodes: Raman Spectroscopy Insight into the Transducer/Membrane Interface

Abstract: An approach to overcome drawbacks of well-established transducer materials for all-solid-state ion-selective electrodes is proposed; it is based on the formulation of the nanocomposite of multiwalled carbon nanotubes (MWCNTs) and poly(3-octylthiophene-2,5-diyl) (POT), in which the polymer is used as a dispersing agent for carbon nanotubes. Thus, the obtained material is characterized with unique properties that are important for its application as solid contact in ion-selective electrodes, including high: electronic conductivity, capacitance, and lipophilicity. Performance of the obtained all-solid-state electrodes was studied using a standard approach as well as Raman spectroscopy to allow insight into distribution of the transducer material within the sensor phases: the membrane and the transducer. Application of the composite prevents unwanted partition of POT to the membrane phase, thus eliminating the risk of alteration of the sensor performance due to uncontrolled change in the membrane composition.

Energy harvesting and evaluation of a novel piezoelectric bridge transducer

Abstract: A novel bridge transducer based on the cymbal design has been developed for energy harvesting from impact loading by vehicle-induced deformations on pavement. The bridge transducer consists of a 2 mm thick 32 × 32 mm square soft PZT ceramic and hardened steel end caps. A unique electrode design enables the PZT to be poled along its length, effectively utilizing d33 mode for enhanced energy generation. The effective d33, of d33eff of a bridge transducer is 19,000 pC/N and the effective piezoelectric voltage coefficient, g33eff, is 2150 × 10−3 Vm/N. When compared to the conventional cymbal transducer design, horizontal poling increases energy and voltage considerably. Each loading at 600 lbs generates 0.83 mJ of energy from the prototype transducer module with 64 transducers in parallel. Loading under simulated traffic conditions at 500 lb and 5 Hz generates 2.1 mW at a resistive load of 330 kOhm. The reliability and cycles to failure of the transducer design is studied and the transducers are evaluated after 50,000 loading cycles. Inconsistency in the epoxy layer thickness has been identified as the cause of premature failure.

Improvement of unidirectional focusing periodic permanent magnet shear-horizontal wave electromagnetic acoustic transducer by oblique bias magnetic field

Abstract: We propose a new unidirectional point focusing shear horizontal (SH) guided wave electromagnetic ultrasonic transducer (EMAT) with an angled periodic permanent magnet (PPM) in this work. The angled PPM developed here provides an angled bias magnetic field to achieve the EMAT’s unidirectional focusing capability. The characteristics of the magnetic field distribution are analyzed by numerical and theoretical calculations. The simulation and experimental results are proven to be in good agreement when studying the bidirectional normalized amplitudes of the displacement of the single-coil SH-guided EMAT with oblique permanent magnets. Both the proposed angled transducer structure and the traditional paralleled transducer structure are performed and simulated using the three-dimensional Finite Element Method (FEM) to compare their unidirectional focusing capabilities. The results show that the SH guided wave EMAT of the focusing coils with an oblique permanent magnet enhances the signal on the focusing side and weakens the signal on the other side effectively. This performance can suppress the influence of the reflected signal from the unfocused side and further improve the ultrasonic signal’s resolution. Moreover, it is shown in the study that increasing the oblique angle of the PPM makes it difficult to increase the signal strength at the focal point when the angle reaches a certain value, but it is still effective at weakening the signal on the unfocused side.

A PZT-Based Electromechanical Impedance Method for Monitoring the Soil Freeze⁻Thaw Process.

Abstract: It is important to conduct research on the soil freeze–thaw process because concurrent adverse effects always occur during this process and can cause serious damage to engineering structures. In this paper, the variation of the impedance signature and the stress wave signal at different temperatures was monitored by using Lead Zirconate Titanate (PZT) transducers through the electromechanical impedance (EMI) method and the active sensing method. Three piezoceramic-based smart aggregates were used in this research. Among them, two smart aggregates were used for the active sensing method, through which one works as an actuator to emit the stress wave signal and the other one works as a sensor to receive the signal. In addition, another smart aggregate was employed for the EMI testing, in which it serves as both an actuator and a receiver to monitor the impedance signature. The trend of the impedance signature with variation of the temperature during the soil freeze–thaw process was obtained. Moreover, the relationship between the energy index of the stress wave signal and the soil temperature was established based on wavelet packet energy analysis. The results demonstrate that the piezoceramic-based electromechanical impedance method is reliable for monitoring the soil freezing and thawing process.

Compact and sensitive mid-infrared all-fiber quartz-enhanced photoacoustic spectroscopy sensor for carbon monoxide detection.

Abstract: A compact and sensitive quartz-enhanced photoacoustic spectroscopy (QEPAS) based sensor for carbon monoxide (CO) detection was demonstrated by using a mid-infrared all-fiber structure as well as a 3D-printed acoustic detection module. An all-fiber configuration has advantages of easier optical alignment, lower insertion loss, improvement in system stability, reduction in sensor size and lower cost. The 3D-printed acoustic detection module was introduced to match the mid-infrared all-fiber structure and further decrease the sensor volume, which resulted in a small size of 3.5 cm3 and a weight of 5 grams. A 2.33 μm distributed feedback fiber-coupled diode laser was used as the laser excitation source. A custom quartz tuning fork (QTF) with a small-gap of 200 μm was used as the acoustic wave transducer in order to improve the signal level of the QEPAS sensor. An acoustic micro resonator was utilized as the acoustic wave enhancer. The gas pressure and laser wavelength modulation depth were optimized, respectively. Water vapor was used to accelerate the vibrational-translational relaxation rate of the targeted CO molecule. Finally, a minimum detection limit (MDL) of 4.2 part per million (ppm) was achieved, corresponding to a normalized noise equivalent absorption (NNEA) coefficient of 7.4 × 10−9 cm−1W/√Hz. An Allan deviation analysis was used to evaluate the long-term stability of the reported CO-QEPAS sensor system. With an integration time of 150 s, the MDL was improved to be 1.3 ppm.

High-Frequency Output Characteristics of Giant Magnetostrictive Transducer

Abstract: This paper presents a theoretical and experimental study on high-frequency (>5000 Hz) output characteristics of the giant magnetostrictive transducer (GMT) at varied operating conditions. Based on the Jiles–Atherton model, Maxwell’s equations, Newton’s law, and Fourier’s heat transfer equation, a nonlinear electromagnetic–mechanical–thermal multi-field coupled finite element model for GMT is established. The output displacement amplitude of the magnetostrictive rod and the acceleration of vibrating horn at the GMT device are measured and analyzed at varied exciting amplitude of ac magnetic field and frequencies (from 5600 to 7000 Hz). The frequency dependences of permeability and magnetoelastic coupling coefficient obtained from the experimental results are used in revising the model parameters. These output characteristics analysis results can provide theoretical and experimental guidance in the optimization of structural design and precise controlling for high-frequency GMT system.

An ultrathin integrated nanoelectromechanical transducer based on hafnium zirconium oxide

Abstract: Nanomechanical resonators that can operate in the super high frequency (3–30 GHz) or the extremely high frequency (30–300 GHz) regime could be of use in the development of stable frequency references, wideband spectral processors and high-resolution resonant sensors. However, such operation requires the dimensions of the mechanical resonators to be reduced to tens of nanometres, and current devices typically rely on transducers, for which miniaturization and chip-scale integration are challenging. Here, we show that integrated nanoelectromechanical transducers can be created using 10-nm-thick ferroelectric hafnium zirconium oxide (Hf0.5Zr0.5O2) films. The transducers are integrated on silicon and aluminium nitride membranes, and can yield resonators with frequencies from 340 kHz to 13 GHz and frequency–quality-factor products of up to 3.97 × 1012. Using electrical and optical probes, we show that the electromechanical transduction behaviour of the Hf0.5Zr0.5O2 film is based on the electrostrictive effect, and highlight the role of nonlinear electromechanical scattering in the operation of the resonator. Nanomechanical resonators with frequencies from 340 kHz to 13 GHz can be created using an integrated 10-nm-thick transducer layer of hafnium zirconium oxide.

Bio-Inspired Rectangular Shaped Piezoelectric MEMS Directional Microphone

Abstract: The noise floor of a piezoelectric MEMS directional microphone largely depends on piezoelectric materials and transducer modes. A careful choice of these parameters (piezoelectric materials and transducer modes) can help to significantly improve the difficulties of noise floor. Here, we present a unique diaphragm-based biomimetic MEMS directional microphone having multiple-port sensing schemes. The diaphragm is separated into two wings and supported by two torsional beams, which are hinged to a fixed support as to imitate the unique inter-tympanal feature of the fly Ormia ochracea . In this microphone, the thermal-mechanical noise (Johnson noise) is minimized by adopting aluminium nitride-based piezoelectric sensing. The d33 mode is incorporated with a prime focus on sensitivity enhancement which leads to signal-to-noise ratio improvement. Measured directivity patterns of both wings show a strong agreement with the direction of applied acoustic pressure as expected for an ideal bi-directional microphone. The measured noise floor at 1-kHz frequency and overall A-weighted noise floor across the audio frequency are 31.35 dB SPL and 32.5 dBA, respectively, which are quite less than some notable works on directional microphones. The experimental results verify the uniqueness of this work.

Optical-Resolution Photoacoustic Microscopy Using Transparent Ultrasound Transducer.

Abstract: The opacity of conventional ultrasound transducers can impede the miniaturization and workflow of current photoacoustic systems. In particular, optical-resolution photoacoustic microscopy (OR-PAM) requires the coaxial alignment of optical illumination and acoustic-detection paths through complex beam combiners and a thick coupling medium. To overcome these hurdles, we developed a novel OR-PAM method on the basis of our recently reported transparent lithium niobate (LiNbO3) ultrasound transducer (Dangi et al., Optics Letters, 2019), which was centered at 13 MHz ultrasound frequency with 60% photoacoustic bandwidth. To test the feasibility of wearable OR-PAM, optical-only raster scanning of focused light through a transducer was performed while the transducer was fixed above the imaging subject. Imaging experiments on resolution targets and carbon fibers demonstrated a lateral resolution of 8.5 µm. Further, we demonstrated vasculature mapping using chicken embryos and melanoma depth profiling using tissue phantoms. In conclusion, the proposed OR-PAM system using a low-cost transparent LiNbO3 window transducer has a promising future in wearable and high-throughput imaging applications, e.g., integration with conventional optical microscopy to enable a multimodal microscopy platform capable of ultrasound stimulation.

Highly Sensitive FBG Pressure Sensor Based on a 3D-Printed Transducer

Abstract: In this work, we describe a fiber Bragg grating (FBG) pressure sensor with high sensitivity. The sensor exploits a three-dimensional printed mechanical transducer capable of converting the external pressure very efficiently into strain, measured by a first FBG, whereas a second one is used for temperature compensation. The pressure sensitivity of this sensor is found as high as 240 pm/kPa with an accuracy of 112 Pa over 10 kPa, which makes this sensor up to 80,000 times more sensitive than a bare fiber Bragg grating. Moreover, it is experimentally shown that it is capable of detecting fast dynamic pressure change up to 100 Hz. Thanks to these performances, this device can be used in many static and dynamic low-pressure measurement applications, and it is here demonstrated as a sub-millimetric surface water waves detector.

An enhanced Lamb wave virtual time reversal technique for damage detection with transducer transfer function compensation

Abstract: The Lamb wave time reversal method has widely been investigated as a baseline-free damage detection technique for structural health monitoring. Due to the mode tuning effects from the transducer-wave interactions, even for a pristine wave path, the reconstructed signal waveform may differ much from the original excitation waveform. Consequently, it becomes difficult to distinguish the differences between undamaged and damaged wave paths. This article presents an enhanced Lamb wave virtual time reversal (VTR) algorithm with transducer transfer function compensation to eliminate the transducer influence for dispersive, multimodal Lamb waves. This VTR procedure builds upon a complete 2D analytical model for Lamb wave generation, propagation, and reception. The analytical solution shows that, with the transducer transfer function compensation, a perfect reconstruction of the original excitation waveform can be achieved for both symmetric and antisymmetric Lamb modes. In addition, finite element modeling and experimental validations are further performed to verify the enhanced time reversal procedure. Finally, a time reversal tomography experiment is conducted with a piezoelectric transducer array for structural damage imaging. The enhanced VTR method can achieve more accurate and robust damage imaging results. The paper finishes with discussion, concluding remarks, and suggestions for future work.

High-resolution MEMS inertial sensor combining large-displacement buckling behaviour with integrated capacitive readout.

Abstract: Commercially available gravimeters and seismometers can be used for measuring Earth’s acceleration at resolution levels in the order of $${\mathrm{ng}}/\sqrt {\mathrm{Hz}}$$ (where g represents earth’s gravity) but they are typically high-cost and bulky. In this work the design of a bulk micromachined MEMS device exploiting non-linear buckling behaviour is described, aiming for $${\mathrm{ng}}/\sqrt {\mathrm{Hz}}$$ resolution by maximising mechanical and capacitive sensitivity. High mechanical sensitivity is obtained through low structural stiffness. Near-zero stiffness is achieved through geometric design and large deformation into a region where the mechanism is statically balanced or neutrally stable. Moreover, the device has an integrated capacitive comb transducer and makes use of a high-resolution impedance readout ASIC. The sensitivity from displacement to a change in capacitance was maximised within the design and process boundaries given, by making use of a trench isolation technique and exploiting the large-displacement behaviour of the device. The measurement results demonstrate that the resonance frequency can be tuned from 8.7 Hz–18.7 Hz, depending on the process parameters and the tilt of the device. In this system, which combines an integrated capacitive transducer with a sensitivity of 2.55 aF/nm and an impedance readout chip, the theoretically achievable system resolution equals 17.02 $${\mathrm{ng}}/\sqrt {\mathrm{Hz}}$$ . The small size of the device and the use of integrated readout electronics allow for a wide range of practical applications for data collection aimed at the internet of things. A micromechanical system (MEMS) has been developed that allows accurate measurement of acceleration at high-resolution levels. Commercially available gravimeters and seismometers can be used for high-resolution measurement of the earth’s acceleration, but they are typically very expensive and bulky. However, a team headed by Guo Qi Zhang at Delft University of Technology, Netherlands was able to design, simulate, fabricate and test a low-cost MEMS device with an integrated miniaturized high-sensitivity transducer for high-resolution acceleration measurements. The team was able to process and package its device by wirebonding it to a printed circuit board containing an application-specific integrated circuit. The authors believe that their extremely compact, low-power inertial sensor has considerable potential for a wide range of practical applications for data collection with the Internet of things.

Transparent capacitive micromachined ultrasonic transducers (CMUTs) for photoacoustic applications.

Abstract: Integration of acoustic and optical techniques prompted the need for transparent ultrasonic transducers to guide the light through the transducer and improve the signal to noise ratio. In the presented paper, capacitive micromachined ultrasound transducers (CMUTs) using glass substrate and indium-tin-oxide electrodes were fabricated by adhesive wafer bonding technique presenting a transparency of up to 82% in the visible range. A receive sensitivity of 65.5 μV/Pa was measured with noise equivalent sensitivity of 95 Pa. Capacity of the produced CMUTs for photoacoustic imaging was also demonstrated by successfully detecting the photoacoustic signal from an aluminum foil target, which was irradiated by a 532-nm pulse laser transmitted through the CMUT. The centre frequency of the detected photoacoustic signal was at 2 MHz with 52.3% -6-dB fractional bandwidth.

A FBG based displacement transducer for small soil deformation measurement

Abstract: A small soil deformation measurement system based on fiber Bragg grating (FBG) has been developed for underground displacement monitoring. This new displacement transducer consists of two anchorage plates for the fixation of displacement sensor in soil, a single FBG sensor for sensing the occurred deformation, and a PolyVinyl Chloride (PVC) tube for the protection of inner FBG sensor. The two anchorage plates were fabricated and fixed on the PVC tube surface by FDM process. Gauge length, maximum measurement displacement, and displacement resolution of the proposed FBG displacement transducer were 90 mm, 0.9 mm, and 0.0747 mm, respectively. Raw material of the anchorage plates was Polylactic Acid (PLA) material. An embankment model was established and installed with multiplexed four FBG displacement transducers for the measurement of internal horizontal displacement in laboratory. Both static load and movable load were applied on the top surface of the embankment model. It is found that maximum error of the four sensors under different static load was less than 6%. The monitored strains of four different FBG displacement transducers under movable load were highly consistent, indicating that the smart FBG based small deformation monitoring system can be used to monitor vehicle flow in future. All monitored displacement values were less than 0.03 mm. Therefore the FBG displacement transducer characterized by high resolution can be used to monitor small displacement occurred underground.