Piezoelectric Lead Zirconate Titanate Transducers Research Articles

A Deep Learning Approach for Autonomous Compression Damage Identification in Fiber-Reinforced Concrete Using Piezoelectric Lead Zirconate Titanate Transducers.

Effective damage identification is paramount to evaluating safety conditions and preventing catastrophic failures of concrete structures. Although various methods have been introduced in the literature, developing robust and reliable structural health monitoring (SHM) procedures remains an open research challenge. This study proposes a new approach utilizing a 1-D convolution neural network to identify the formation of cracks from the raw electromechanical impedance (EMI) signature of externally bonded piezoelectric lead zirconate titanate (PZT) transducers. Externally bonded PZT transducers were used to determine the EMI signature of fiber-reinforced concrete specimens subjected to monotonous and repeatable compression loading. A leave-one-specimen-out cross-validation scenario was adopted for the proposed SHM approach for a stricter and more realistic validation procedure. The experimental study and the obtained results clearly demonstrate the capacity of the introduced approach to provide autonomous and reliable damage identification in a PZT-enabled SHM system, with a mean accuracy of 95.24% and a standard deviation of 5.64%.

Flexure-critical stress and damage identification in RC beam structure using embedded piezoelectric transducers: 2D modelling and experimental investigations

This paper proposed a real-time identification approach of flexure-critical stress and damage in reinforced concrete (RC) beam structure using embedded Piezoelectric lead Zirconate Titanate (PZT) transducers. Effect of structural stress and damage were theoretically incorporated into mechanical impedance to derive a novel two-dimensional (2D) embedded PZT-structure interaction model. Analytical analysis was conducted to calculably interpret the identification of tensile/compressive stress and damage based on the electromechanical admittance (inverse of impedance, EMA) signatures. The proposed approach was validated by experiment on an RC beam subjected to four-point bending test, which was continuously monitored by cement-embedded PZT (CEP) transducers. Analytical and experimental results showed that resonance peak and frequency shift of the EMA spectrums of CEPs exhibited converse behaviors when responding to tension and compression stresses, while typical frequency decrease and peak increase accurately indicated the occurrence of initial cracking. Comparative studies also revealed that CEPs were superior to visual inspection and bonded PZT transducer in identification of concrete cracking, and that located in compressive zone was more efficacious in prediction of the forthcoming yield and final failure of the RC beam. Results of this study cogently demonstrated the potentialities of CEP transducer as a means of on-line monitoring of stress/damage in flexure-critical RC infrastructures.

Structural Health Monitoring of Fiber-Reinforced Concrete Prisms with Polyolefin Macro-Fibers Using a Piezoelectric Materials Network under Various Load-Induced Stress

This experimental study investigates the influence of synthetic macro-fibers added in fiber-reinforced concrete (FRC) prismatic specimens on their flexural response and overall cracking performance. Application of a novel structural health monitoring (SHM) system that implements the electromechanical impedance (EMI) technique and the use of piezoelectric lead zirconate titanate (PZT) transducers installed in the FRC prisms are also included. The applied PZT-enabled EMI-based monitoring system was developed to diagnose damage and the overall performance in reinforced concrete (RC) structural members subjected to cyclic repeated loading, simulating seismic excitations in existing RC buildings. The paper also aims to determine the sensitivity of the real-time, wireless, and portable monitoring technique corresponding to the location, the distance, the direction of polarization of the PZT transducers and the location and magnitude of damage due to flexural cracking. Further, the influence of the effect of stresses corresponding at various loading levels and the observed changes in the ΕΜΙ frequency response of the PZT transducers are also examined. Test results indicated that cracking detection is achieved using this SHM system by prompt damage level assessment due to the FRC’s flexural load at early seismic loading stages in existing RC buildings.

An Electromechanical Impedance-Based Application of Realtime Monitoring for the Load-Induced Flexural Stress and Damage in Fiber-Reinforced Concrete

Effective real-time structural health monitoring in concrete structures is paramount to evaluating safety conditions and the timely maintenance of concrete structures. Especially, the presence of discrete fibers in fiber-reinforced concrete restrains crack propagation into small and thin cracks, which increases the difficulty in detecting damage. In this study, an array of piezoelectric lead zirconate titanate (PZT) transducers was applied to study the effects of external load-induced flexural stress and damage in fiber-reinforced concrete beams using the electromechanical impedance (EMI) or electromechanical admittance (EMA) methods. Beams were subjected to a four-point bending test under repeatable loading, while PZTs evaluated corresponding flexural stress and induced damage simultaneously. Due to the influence of the medium’s stress fields in the different types of wave propagation in structural elements, PZT transducers measurements are accordingly affected under variable stress fields, in addition to the effect of the higher level of damage that occurred in the medium. According to the results of the tests, variation in EMA signatures, following flexural stress and gradual damage changes, provided convincing evidence for predicting stress and damage development.

Cracking and Fiber Debonding Identification of Concrete Deep Beams Reinforced with C-FRP Ropes against Shear Using a Real-Time Monitoring System.

Traditional methods for estimating structural deterioration are generally costly and inefficient. Recent studies have demonstrated that implementing a network of piezoelectric transducers mounted to critical regions of concrete structural members substantially increases the efficacy of the structural health monitoring (SHM) method. This study uses a recently developed electro-mechanical-admittance (EMA)-based SHM system for real-time damage diagnosis of carbon FRP (C-FRP) ropes installed as shear composite reinforcement in RC deep beams. The applied SHM technique uses the frequency response measurements of a network of piezoelectric lead zirconate titanate (PZT) patches. The proposed strengthening methods using C-FRP ropes as ETS and NSM shear reinforcement and the applied anchorage techniques significantly enhanced the strength and the overall performance of the examined beams. The retrofitted beams exhibited increased shear capacity and improved post-peak response with substantial ductility compared with the brittle failure of the non-strengthened specimens. The health condition and the potential debonding failure of the applied composite fiber material were also examined and quantified using the proposed SHM technique. Damage quantification of C-FRP ropes is achieved by comparing and assessing the values of several statistical damage indices. The experimental results demonstrated that the proposed monitoring system successfully diagnosed the region where the damage occurred by providing early warning of the forthcoming critical shear cracking of concrete and C-FRP rope debonding failures. Furthermore, the internal PZT transducers showed sound indications of the C-FRP rope's health condition, demonstrating a direct correlation with the mechanical performance of the fibers.

Efficacy and Damage Diagnosis of Reinforced Concrete Columns and Joints Strengthened with FRP Ropes Using Piezoelectric Transducers.

Recent research has indicated that the implantation of a network of piezoelectric transducer patches in element regions of potential damage development, such as the beam-column joint (BCJ) area, substantially increases the efficacy and accuracy of the structural health monitoring (SHM) methods to identify damage level, providing a reliable diagnosis. The use of piezoelectric lead zirconate titanate (PZT) transducers for the examination of the efficiency of an innovative strengthening technique of reinforced concrete (RC) columns and BCJs is presented and commented on. Two real-scale RC BCJ subassemblages were constructed for this investigation. The columns and the joint panel of the second subassemblage were externally strengthened with carbon fiber-reinforced polymer (C-FRP) ropes. To examine the efficiency of this strengthening technique we used the following transducers: (a) PZT sensors on the ropes and the concrete; (b) tSring linear variable displacement transducers (SLVDTs), diagonally installed on the BCJ, to measure the shear deformations of the BCJ panel; (c) Strain gauges on the internal steel bars. From the experimental results, it became apparent that the PZT transducers successfully diagnosed the loading step at which the primary damage occurred in the first BCJ subassemblage and the damage state of the strengthened BCJ during the loading procedure. Further, data acquired from the diagonal SLVDTs and the strain gauges provided insight into the damage state of the two tested specimens at each step of the loading procedure and confirmed the diagnosis provided by the PZT transducers. Furthermore, data acquired by the PZT transducers, SLVDTs and strain gauges proved the effectiveness of the applied strengthening technique with C-FRP ropes externally mounted on the column and the conjunction area of the examined BCJ subassemblages.

Adhesively bonding a reusable PZT transducer for structural health monitoring (SHM) with an ethylene-acrylic acid copolymer adhesive

A novel approach to bonding a piezoelectric lead zirconate titanate (PZT) transducer on a structure for health monitoring was developed to replace the traditional method of bonding PZT permanently. Several experiments demonstrated the feasibility of a reusable PZT transducer based on the adhesive film made using ethylene-acrylic acid copolymer (EAA). Additionally, the adhesion performance of using EAA for bonding PZT at different temperatures and the effect of heating temperature on reusable PZT transducer removal from the test structure was investigated. The effect of adhesive thickness on the mechanical property and the performance of PZT has also been explained. Experimental results showed that the optimized heating temperature of the adhesive film was around 140 °C due to the stability of PZT being sensitive to high temperature and the ease of removing PZT from the test structure without damage. An analysis of the varying thickness of the adhesive layer on PZT performance indicated that the amplitude of Lamb wave signals changed with adhesive thickness, increasing with greater adhesive thickness. Therefore, the adhesive layer made using EAA provides a new approach to conducting Lamb wave-based structural health monitoring.

The Feasibility Study of Quantitative Flaw Detection of Grouted Sleeve Connection by Ultrasonics

Grouted sleeve connection has been widely used to connect rebars in prefabricated concrete (PC) structures. Due to the complexities of materials and internal configurations, the flaws or defects are inevitable, which may cause the negative impact on the mechanical properties of reinforcement sleeve connection, ultimately leading to the hidden risk in the PC structures. It is challenging to explore a reliable and efficient flaw detection method for the grouting sleeve. In this paper, an active grout defects detection approach for grouted sleeve connectors using UT wave measurement is proposed, where piezoelectric-lead-zirconate-titanate (PZT) transducer are mounted on surface of the sleeve as transmitter and receivers; and experimental study is carried out to validate the feasibility of the proposed method. In order to investigate the effect of grout defects on UT wave measurement, five grouted sleeve specimens with different degrees of the artificial grout defects are designed and analysis on the PZT transducer was used for measurement. By comparing the PZT transducers measurement of different specimens with different grout defects under an identical impulse excitation signal, the grout defect is detected. Experimental results indicate grout defect leads to decrease in PZT transducers measurement UT energy, the relationship between the UT energy ratio and the internal grouting flaws is established: the UT energy decreases with the increment of flaw size. Therefore, the UT method provides a feasible option to evaluate the internal flaws of grouted sleeve connection.

Structural Integrity Assessment of Composites Plates with Embedded PZT Transducers for Structural Health Monitoring.

Active sensing using ultrasonic guided waves (UGW) is widely investigated for monitoring possible damages in composite structures. Recently, a novel diagnosed film based on a circuit-printed technique with piezoelectric lead zirconate titanate (PZT) transducers has been developed. The diagnostic film is a replacement for the traditional cable connection to PZT sensors and has been shown to significantly reduce the weight of the host structure. In this work, the diagnosed films were embedded into composite structures during manufacturing using a novel edge cut-out method during lay-up, which allowed for edge trimming after curing. In this paper, the effect of fatigue loading on the integrity of PZT transducers is initially investigated. The electro-mechanical impedance (EMI) properties at different fatigue loading cycles were used as the diagnostic measure for the performance of the sensors. At the same time, the behaviours of UGW were investigated at different fatigue loading cycles. It was found that the EMI properties and active sensing behaviours remained stable up to 1 million cycles for the force ranges of 0.5~5 kN and 1~10 kN. Next, the effect of embedding the diagnosed film on the mechanical properties of the host composite structure was investigated. Tensile and compressive tests were conducted and the elastic modulus of composite coupons with and without embedded PZT diagnosed films were compared. The elastic modulus of composite coupons with PZT diagnosed films embedded across the entire coupon reduced by as much as 20% for tensile tests and just over 10% for compressive tests compared to the coupons without embedded sensors. These reductions are considered the worst-case scenario, as in real structures the film would only be embedded in a relatively small area of the structure.

Reusable piezoelectric transducer for structural health monitoring using both Lamb wave and electromechanical impedance modes

A variety of structural health monitoring techniques have been developed to support the efficient online monitoring of structural integrity. Moreover, Lamb wave and electromechanical impedance methods are increasingly used for structural health monitoring applications due to their high sensitivity and effectiveness in detecting damage. However, these techniques require transducers to be permanently attached to structures because of the usage of baselines recorded under the condition without damage. In this study, a reusable piezoelectric lead zirconate titanate transducer for monitoring corrosion damage on the aluminum plate is introduced, which can be removed from the test specimen and reused with the repeatability of signals. The reusable piezoelectric lead zirconate titanate transducer is bonded on the aluminum plate using the ethylene-acrylic acid copolymer with an aluminum enclosure. A series of experiments are conducted on an aluminum plate, including the investigation for repeatability of signals and the capability of corrosion detection of the designed piezoelectric lead zirconate titanate transducer through the Lamb wave and electromechanical impedance methods. The simulated corrosion defect with the area of 15 × 15 mm2 is detected during experiments. The experimental results confirm that the reusable piezoelectric lead zirconate titanate transducer can effectively evaluate the corrosion damage to plate structure and can be reused many times.

Axial stress monitoring strategy in arbitrary cross-section based on acoustoelastic guided waves using PZT sensors

Axial stress monitoring in arbitrary cross sections is a challenging task. Stringers are the main axial load carrying components of aircraft skin structures and have typical complex cross sections. This paper investigates the strategy of axial stress monitoring in an arbitrary cross section based on acoustoelastic guided waves using piezoelectric lead zirconate titanate (PZT) sensors. To select appropriate guided wave frequencies and modes sensitive for axial stress monitoring in an arbitrary cross section, the feature guided waves are investigated using acoustoelastic theory combined with the semianalytical finite element method. The mode shapes are derived, which show that these longitudinal-like modes are more sensitive to axial stress. A PZT transducer array is also considered to maximize desired modes. Piezoelectric sensors are used to excite and detect the guided waves in the experiments. Results from acoustoelastic measurements on a T-type stringer are presented, showing the feasibility of this method for axial stress monitoring.

Nonlinear ultrasonic inspection of smart carbon fibre reinforced plastic composites with embedded piezoelectric lead zirconate titanate transducers for space applications

Carbon fibre reinforced plastic composites used in spacecraft structures are susceptible to delamination, debonds and fibre cracking that may arise during manufacturing, assembly or in-service operations (e.g. caused by debris impacts in near-Earth orbital spaceflights). Therefore, in situ and real-time health monitoring is necessary to avoid time-consuming and unsafe visual inspections performed either on-ground or during extra vehicular activities. In this article, a recently created ‘smart’ carbon fibre reinforced plastic composite structure with embedded piezoelectric lead zirconate titanate transducers was used to detect multiple areas of artificial delamination and real impact damage of different size using nonlinear ultrasound. The electrical insulation of embedded piezoelectric lead zirconate titanate transducers was achieved by interlacing a dry layer of woven glass fibre fabric between the sensor and the carbon fibre reinforced plastic plies before curing. Damage detection was successfully demonstrated using both second harmonic generation and nonlinear modulation (sidebands) of the measured ultrasonic spectrum. The material nonlinear response at the second harmonic and sidebands frequencies was also measured with a laser Doppler vibrometer to validate the nonlinear ultrasonic tests and provide damage localisation. Experimental results revealed that the proposed configuration of embedded piezoelectric lead zirconate titanate transducers can be utilised for on-board ultrasonic inspection of spacecraft composite parts.

Control of the Surface Profile of a Thixotropic Fluid With Ultrasound

The viscosity and the surface profile of a thixotropic gel were controlled via ultrasound vibrations. The ultrasound device consisted of two piezoelectric lead zirconate titanate transducers glued to each end of a 60-mm-long rectangular glass substrate. It generated a 71-kHz flexural standing wave along the length. A 0.9-mm-thick thixotropic gel film made from silicone oil and hydrophobic fumed silica was formed on the glass substrate. The ultrasound vibration decreased the film viscosity, and its surface profile could be changed by the acoustic radiation force acting from the gel to the surrounding air, generated by the flexural vibration of the substrate. The transient response of the surface profile was observed by switching the ultrasound excitation ON and OFF. When the excitation was switched OFF, the gel displacement gradually decreased, but the surface profile did not return to that of the initial steady state, indicating that the viscosity recovered in time to preserve the surface profile. When a pulsed megahertz (MHz) signal was used to control the gel deformation, the surface profile rapidly approached the initial steady-state profile after the excitation.

Temperature effect on electromechanical admittance–based concrete structural health monitoring

Concrete structures in service are often subjected to environmental/operational temperature effects, which change their inherent properties and also inflict a challenge to their extrinsic monitoring systems. Recently, piezoelectric lead zirconate titanate (PZT)-based electromechanical admittance technique has been increasingly growing into an effective tool for concrete structural health monitoring; however, uncertainty in the changes of monitoring signals induced by temperature impact on concrete/PZT sensor would inevitably cause interference to structural damage detection, which adversely hinder its application from laboratory to engineering practice. This article, aiming at exploring the temperature effect on the electromechanical admittance–based concrete damage evaluation, primarily covered a series of theoretical/numerical analysis with rigorously experimental verifications. Three aspects of comparative studies were performed in theoretical/numerical analysis: (1) thermal-dependent parameters were inclusively evaluated in contribution to the electromechanical admittance characteristics via PZT-structure interaction models; (2) three-dimensional finite element analysis in multi-physics coupled field was employed to qualitatively assess the singular temperature effect on the electromechanical admittance behaviors of free-vibrated PZT, surface-bonded PZT/inside-embedded PZT coupled healthy concrete cubes; and (3) depending on the modeling of surface-bonded PZT-/inside-embedded PZT-cracked concrete cube, thermal effect on damage evaluation was addressed via quantification on the electromechanical admittance variations. In the experimental study, rigorous validation tests were carried out on a group of lab-scale concrete cubes, where surface-bonded PZT/inside-embedded PZT transducers were simultaneously employed for electromechanical admittance monitoring in view of thermal difference between concrete surface and its inner part. Correlation coefficient deviation value-based effective frequency shifts algorithm was also employed to compensate the temperature effect. Moreover, temperature effect was further testified on the monitoring of a full-scale shield-tunnel segment structure. Experimental results indicated that temperature triggered different behaviors of electromechanical admittance signatures for surface-bonded PZT/inside-embedded PZT transducers and contaminated the electromechanical admittance responses for damage detection. Structural damage severity level can be disadvantageously amplified by temperature increment even if under the same damage scenarios.

Characterisation of smart CFRP composites with embedded PZT transducers for nonlinear ultrasonic applications

Embedded piezoelectric lead zirconate titanate (PZT) transducers in carbon fibre reinforced plastic (CFRP) composites are typically electrically insulated by interlaying materials such as polyimide Kapton films between the PZT and the laminate ply. However, the presence of polymeric films may cause debonding at the layer interface, thus reducing the structural performance. This paper proposes an alternative insulation technique in which PZTs are covered by a thin patch of woven E-glass fibre fabric for enhanced adhesion with the surrounding epoxy matrix. An analysis of variance on experimental test results showed that the compressive, flexural and interlaminar shear strengths of plain CFRP specimens were equal to the means of the smart CFRP composite (0.41 < p-value < 0.58), but significantly higher than those of Kapton specimens (0.0001< p-value < 0.05). Moreover, a post-test fractographic analysis indicated that damage opening in Kapton specimens was significantly larger (p-value = 0.03) than that in plain specimens. Brooming failure compression was also the same for the smart CFRP composite and plain samples, whereas Kapton specimens failed by through-thickness shear. Finally, nonlinear ultrasonic experiments were conducted on CFRP laminates with artificial in-plane delamination using glass fibre insulated PZTs. Remarkably, the effect of second harmonic generation was found to be nearly two times higher than conventionally surface-bonded PZTs.

Monitoring of the load-induced RC beam structural tension/compression stress and damage using piezoelectric transducers

Efficacious monitoring the mechanical stress of engineering structures or components holds the key to understanding the occurrence of structural damage in Structural Health Monitoring (SHM) domains. This paper investigated the monitoring of the load-induced structural tension/compression stress and damage using smart Piezoelectric lead Zirconate Titanate (PZT) transducers mounted to specific locus on structures. Structural tension/compression stress was theoretically incorporated into mechanical impedance to formulate a novel one-dimensional PZT-structure dynamic interaction model. Proof-of-concept experimentation was conducted using a reinforced concrete (RC) beam subjected to a four-point bending test till failure, in which tension and compression stress were simultaneously produced at the bottom/top edge of the beam and captured by two mounted PZT transducers. Load-induced structural tension/compression stress and stress-induced damage were qualitatively evaluated through analyzing the characters of electromechanical admittance (EMA) signatures and comparing to that of the non-stressed PZT transducer. Quantification assessment of stress and damage using statistical root mean square deviation index were also presented. Test results indicated that the peak variation and frequency shift of EMA signatures responding to tension and compression stress were converse in nature, and their gradual changes provided cogent evidences for predicting the development of stress and damage. Results of this paper can be potentially to help monitor structural stress and discriminate from damages in real-life SHM applications.

Experimental damage evaluation of reinforced concrete steel bars using piezoelectric sensors

This study presents an experimental effort for the damage assessment of concrete reinforcing bars using bonded piezoelectric transducers and the implementation of an integration analytical approach based on the electromechanical admittance method. Tests are performed in (i) single steel reinforcing bars with predefined and artificially induced damages corresponding to two different damage states and (ii) steel reinforcing bars embedded in typical large scale reinforced concrete beams subjected to flexural load at two different loading levels (before and after yielding) that inevitably cause two different damage levels. The damage of the embedded steel bars in the concrete beams after yielding is the result of excessive elongation of the bars due to yielding caused by flexural deformation of the beams. Test measurements of healthy and damaged steel bars and reinforced concrete beams have been conducted using the developed monitoring system. The experimental program comprises data acquisition of current intensity curves for healthy and damaged bars as detected by the test instrumentation and implementation of the adopted admittance-based procedure to evaluate damages at different levels. It can be concluded that the sensitivity of the piezoelectric transducers greatly depends on the selection of the excitation frequencies. Admittance signatures showed a clear gradation of the examined damage levels. The experimental results provide cogent evidence that piezoelectric lead zirconate titanate transducers are sensitive to damage detection in concrete and in steel reinforcing bars from an early stage of the performed tests. Thus, the use of these sensors for monitoring and detecting concrete cracking and steel yielding by employing the electromechanical admittance approach can be considered as a highly promising non-destructive structural health monitoring method.

Combined embedded and surface-bonded piezoelectric transducers for monitoring of concrete structures

Piezoelectric lead zirconate titanate (PZT) transducers are increasingly used for monitoring various engineering structures. PZT transducers are used for monitoring structures based on the electro-mechanical impedance (EMI) for a single PZT and the wave propagation technique for multiple PZTs. In concrete structures, the EMI sensing region is small due to high damping of the concrete. Using the wave propagation technique with high actuation voltage, a larger area can be monitored. The smart aggregates (embedded PZT transducers) can be employed using the wave transmission technique to monitor very large areas with a reasonably low actuation signal. The combination of smart aggregates (using the wave transmission technique) with surface bonded PZTs (using the wave propagation technique) can provide an effective method to study both the local and overall conditions of the structure. In this work, a concrete beam with the dimensions of 220×40×20cm was cast and nine PZT transducers were embedded or attached on the beam. The PZT readings were correlated with the damage on the structure. Combination of smart aggregates (using the wave transmission technique) with surface bonded PZTs (using the wave propagation technique) for SHM was studied. The results show that this combination provides an effective way to assess both the local and overall conditions of the structure.

Durability of Embedded PZTs in Structural Health Monitoring Systems under Cyclic Loading

Structural Health Monitoring (SHM) systems are developed to decrease the maintenance cost and increase the life of engineering structures by fundamentally changing the way structural inspections are performed. However, this important objective can only be achieved through the consistent and predictable performance of a SHM system under different service conditions. The capability of a Piezoelectric lead Zirconate Titanate (PZT)-based SHM system in detecting structural flaws strongly depends on the sensor signals as well as actuator performance. But service conditions can change the behaviour of transducers, raising questions about long term SHM system capability. Although having a clear understanding of the reliable sensor life is important for surface mounted systems, however, this is particularly critical for embedded sensors. This is due to the fact that opportunity for replacement of sensors exists for surface bonded transducers while for the embedded systems, sensor replacement is not straightforward. Therefore, knowledge of the long term behaviour of embedded-SHM systems is critical for their implementation. This paper reports a study on the degradation of embedded PZT transducers under cyclic loadings. Carbon/epoxy laminates with an embedded PZT were subjected to fatigue loading and their performance was monitored using Scanning Laser Vibrometery (SLV). The functionality of PZT transducers under sensing and actuating modes were studied. High and low cycle fatigue tests were performed to establish strain-voltage relationships which can be used to identify critical cyclic loading parameters (number of cycles and R value) under sensing and actuating modes.

Three-dimensional variable-focus liquid lens using acoustic radiation force

A liquid lens was fabricated with a focal point that can be varied in the axial and radial directions. We have been developing a variable-focus liquid lens that employs acoustic radiation force and does not contain any mechanical moving parts. Our liquid lens is more compact and has a faster response than conventional mechanical lenses. Rapid scanning of its focus at 1 kHz has been realized by excitation with an amplitude-modulation (AM) signal. The liquid lens consists of a cylindrical acrylic cell (inner diameter: 10 mm; thickness: 3 mm), two immiscible liquids with different refractive indices (water and silicone oil), and an annular piezoelectric lead zirconate titanate transducer with four electrodes. The oil-water interface functions as a lens surface and it can be deformed by the acoustic radiation force generated by the transducer; this enables the lens to act as a variable-focus lens. The variation of the oil-water interface was observed by optical coherence tomography. The laser beam path through the lens was calculated by ray-tracing simulations. The oil-water interface could be deformed and its focal point could be varied in three dimensions by controlling the input voltages of the PZT electrodes. The displacement angle in the radial direction was approximately 3° when two of the electrodes were excited by an input voltage of 45 V at a frequency of 1.9 MHz. The dynamic performance of the lens was investigated using a high-speed cam- era. Excitation by AM signals with a phase difference caused the hemispherical water droplet to oscillate, enabling the focus to be scanned in the axial and radial directions.