Ultrasonic Nondestructive Testing Techniques Research Articles

Early detection of steel tube welded joint failure using SPC-I nonlinear ultrasonic technique

Welding is a commonly used method for joining two or more parts together in steel construction. Various defects in weld regions such as cracks, pores, and slag inclusion can be present from the beginning, generated during the welding process, or can be developed while in service. Such defects are the weak spots that degrade the structure’s quality and can lead to structural failures. Therefore, early detection of these defects in welded joints, before visible cracks appear, is very important. Using appropriate ultrasonic non-destructive testing and evaluation (NDT&E) techniques, one can detect these defects and take remedial actions to prevent catastrophic structural failures. Guided acoustic wave-based techniques have been proven to be effective for damage detection in steel pipes and rods. Several studies have previously attempted to detect damage in steel tubes using guided ultrasonic waves. Unlike earlier attempts which mostly focused on conventional linear ultrasonic techniques, a relatively new nonlinear ultrasonic technique called sideband peak count-index (SPC-I) is carried out in this research. For this investigation, cast steel components and round hollow structural sections are welded together, and a four-point bending test is conducted under fatigue loading. The welded joints are continuously monitored in real time using strain gages and lead zirconate titanate (PZT) transducers. The PZT transducers are used to generate and receive guided acoustic waves. The signal is propagated through the specimen in a single-sided transmission mode setup. The strain gage readings and the nonlinear ultrasonic parameter, the SPC-I values, are monitored simultaneously. The results obtained from the nonlinear ultrasonic NDT&E measurements are compared with the data obtained from the strain gages to determine the robustness and reliability of the SPC-I technique for monitoring welded joints. This investigation also shows the potential effectiveness of the nonlinear ultrasonic parameter SPC-I for early detection of weld failure.

Quantitative ultrasonic imaging of weave structure in textile composites

Textile composites owe their desirable mechanical properties to the intricate fabric architecture. However, manufacturing deviations can influence these attributes, significantly affecting their mechanical performance. Thus, ensuring the quality and structural integrity of fabric architectures has become pivotal, leading to the advancement of ultrasonic non-destructive testing techniques. However, existing techniques, primarily tailored for unidirectional laminates, often struggle with weave pattern extraction, given the complex features of fabric laminates. To address this gap, a pulse-echo ultrasound coupled to a 2D analytic-signal analysis is proposed. The 2D analytic-signal methodology autonomously discerns the complex ultrasound features from fabric laminates, streamlining weave pattern analysis. The study showcases ply-by-ply reconstruction of local weave patterns of fabric laminates with nominal layups of [#(0/90)]8 and [#(+45/−45)#(0/90)]5s, respectively. The efficacy of the methodology is ascertained through quantitative metrics, highlighting its innovative potential for through-depth extraction of local weave patterns in a swift and automated manner.

Modeling of Ultrasonic Flaw Detection Processes in the Task of Searching and Visualizing Internal Defects in Assemblies and Structures

Introduction. Inverse problems are a specific type of tasks where the consequences of phenomena are studied to identify their causes. They are widely used in scientific studies, specifically, those dealing with large amounts of experimental data. In the presented paper, inverse problems in mechanical engineering and structural diagnostics are considered. These areas require precise methods to identify internal defects in various materials, which can be critical to ensure the safety and efficiency of technical structures. Despite the many flaw detection methods available, there is a need for innovative developments that can provide higher accuracy and efficiency. This study integrates different scientific methods and technologies. It opens up new perspectives in nondestructive testing for the detection of internal defects in various materials and structures. Its objective is to develop and implement nondestructive testing methods based on a neural network device to improve the accuracy of defect identification, as well as to build a neural network model and evaluate its effectiveness for the refinement of ultrasonic visualization of internal defects in solid materials. In this regard, the task to be solved is to create a reliable tool for accurate visualization of sizes, shapes, location and orientation of internal defects in various materials.Materials and Methods. The technique of determining the geometric parameters of defects in materials through nondestructive testing is used. The approach combining modeling of ultrasonic wave propagation in acoustic medium and artificial neural network technologies is applied. This approach identifies nonlinear relationships between the geometry of defects and the amplitude-frequency and amplitude-time data obtained during signal analysis. Artificial neural networks are a model that can be trained on examples, which provides for an effective solution to problems that are difficult to express in traditional forms. The study uses the finite difference method in the time domain. It is applied to identify and visualize internal defects in materials using ultrasonic nondestructive testing and convolutional generative neural networks.Results. A convolutional neural network has been developed to visualize internal defects using ultrasonic nondestructive testing techniques. This neural network successfully determines the size of defects, their location, shape and orientation with high accuracy and reliability.Discussion and Conclusion. The authors highlight the key influence of defect size on the accuracy of ultrasonic imaging in various scenarios. The validation of the model for three different cases of defects with different mechanical parameters has shown that for successful visualization of defects, the wavelength of the ultrasonic pulse must be ten times smaller than the size of the defect. When analyzing the impact of defect size on the accuracy of the neural network, it is found that the visualization error increases for defects of smaller size. It has also been found that the relative speed of sound in materials has a greater effect on the accuracy of the method than the relative density of the material. Based on the results obtained by the authors, it can be argued that the developed methods and technical solutions are of great importance for future research in the field of flaw detection. They have significant potential for scientific and practical applications.

Methodology of residual strength prediction of composite structures with low-velocity impact damage based on NDT inspections and numerical-experimental CAI testing

One of the most challenging tasks is to evaluate a structural condition and predict a residual strength when damage is present in a composite structure. Such a prediction is usually performed based on experimental destructive testing on specimens, which often does not reflect the geometrical complexity of a component with damage, or based on numerical simulations, which are difficult to parametrize due to the complexity of fracture mechanisms of composite materials. In this paper, we proposed a hybrid methodology based on evaluation of results of the ultrasonic non-destructive testing technique supported with numerical modeling and compression after impact (CAI) tests to evaluate residual strength of glass- and carbon-reinforced polymer composite structures. Based on ultrasonic C-scans processing and incorporation of impact damage shapes in numerical models and further evaluation of the obtained results in the light of CAI tests, the model for the prediction of residual strength in composites was developed.

A Methodology to Automatically Segment 3D Ultrasonic Data Using X-ray Computed Tomography and a Convolutional Neural Network

Ultrasonic non-destructive testing (UT) is a proficient method for detecting damage in composite materials; however, conventional manual testing procedures are time-consuming and labor-intensive. We propose a semi-automated defect segmentation methodology employing a convolutional neural network (CNN) on 3D ultrasonic data, facilitated by the fusion of X-ray computed tomography (XCT) and Phased-Array Ultrasonic Testing (PAUT) data. This approach offers the ability to develop supervised datasets for cases where UT techniques inadequately assess defects and enables the creation of models with genuine defects rather than artificially introduced ones. During the training process, we recommend processing the 3D volumes as a sequence of 2D slices derived from each technique. Our methodology was applied to segment porosity, a common defect in composite materials, for which characteristics such as void size and shape remain immeasurable via UT. Precision, recall, F1 score, and Intersection over Union (IoU) metrics were used in the evaluation. The results of the evaluation show that the following challenges have to be faced for improvement: (i) achieving accurate 3D registration, (ii) discovering suitable similar keypoints for XCT and UT data registration, (iii) differentiating ultrasonic echoes originating from porosity versus those related to noise or microstructural features (interfaces, resin pockets, fibers, etc.), and, (iv) single out defect echoes located near the edges of the component. In fact, an average F1 score of 0.66 and IoU of 0.5 were obtained.

Effect of thermal fatigue on mechanical properties and microstructure of concrete in constant ambient humidity

The daily and annual temperature differences in mid and high latitudes areas vary greatly, which leads to thermal fatigue deterioration of concrete. The deterioration of concrete properties can also be generated by the cyclic change of humidity in concrete. In the experiment, the thermal fatigue tests of concrete with two strength grades were carried out at the temperature difference of 20 °C, 30 °C, and 40 °C (the initial temperature is 20 °C) under the condition of constant ambient humidity. The macroscopic properties change of concrete such as compressive strength and splitting tensile strength were measured. The microstructure changes of concrete were determined by ultrasonic nondestructive testing technique and mercury intrusion test. The results indicated that thermal fatigue has obvious deterioration effect on concrete. With the increase of temperature difference and cycle number, the strength of concrete decreased dramatically and the decrease of C40 concrete was greater than that of C25 concrete. The splitting tensile strength was more sensitive to thermal fatigue than compressive strength. The ultrasonic wave velocity gradually decreased and the damage factor increased, indicating the internal crack defects of concrete increased. At the same temperature difference, the porosity, total pore volume, average pore diameter, medium pore diameter, and the most probable pore diameter of concrete increased gradually with the increase of the cycle number, while the total pore surface area decreased. The pore structure showed the characteristics of coarsening and the trend of deterioration. The porosity of C40 concrete was less than that of C25 concrete, but the relative change value of porosity was larger, which reveals the internal reason for the strength damage of concrete under thermal fatigue at the microscopic level.

Progress on nonlinear ultrasonic evaluation of damages within the adhesively bonded composites

<p indent="0mm">Adhesively bonded composite structures are widely used in aerospace, shipbuilding and automotive industries because of such advantages as lower structural weight and more uniformly distributed stresses. As an important component of the adhesive joints, properties of the adhesive interface determine the integrity of the whole adhesive structure, making the research on damage detection and evaluation of the adhesive interface an extensively concerned topic in the related fields. The ultrasonic nondestructive testing technique, which has a long history of development since its appearance, is an effective technology for testing, evaluating and characterizing material properties and damages. Because of the advantage of realizing the detection without causing additional destruction to the structure and materials, the ultrasonic nondestructive testing has been widely used in engineering practice. However, the existing traditional ultrasonic nondestructive testing technology mainly concerns the initiation and accumulation of material damages, final failure of the structure on service. It is difficult in characterizing the bonding strength, bonding force, early degradation and micro-damage of the bonding surface directly and quantitatively, which is not capable of realizing the structural health monitoring and life prediction of the adhesive joints. It is promising that the nonlinear ultrasonic technology developed in recent years can effectively solve the problems mentioned above. When nonlinear waves are employed, this technique has higher sensitivity in characterizing the change of micro-structure of materials and micro-damages, whose spatial dimension is much smaller than the wavelength of ultrasonic waves. Considering these advantages, nondestructive testing and evaluation employing nonlinear waves have been widely investigated in recent years; a series of new methods have appeared and many important achievements have been obtained. Detection and evaluation of damages within bonded composite structures and adhesively jointed interfaces are more complicated. There are two types of adhesive failure: Adhesion failure in the interface layer between the adhesive and the adhered, and cohesion failure in the adhesive layer. Due to the existence of adhesive interfaces, complex refraction, reflection and scattering will occur when ultrasonic waves propagate in the adhesive composite structure and interfaces, particularly the existence of the adhesive layer will increase the attenuation of the wave energy. These problems make the investigation of wave propagation in the adhesively bonded structure even more complicated. Based on the nonlinear ultrasonic technique, many investigations have been carried out and many fruitful achievements have been obtained in examining and evaluating the early degradation of the bonded interface. Generally, bulk waves, guided waves and mixing waves are employed in theoretical and experimental research. Bulk waves can be excited and received without much difficulty, and guided waves are effective in examining plate and shell structures. In both cases, the magnitude of high-order harmonic waves and related nonlinear parameters are used in the process of evaluation and characterization. As to the mixing wave method, the amplitude of the mixing resonance waves and the nonlinear parameter based on the mixing resonance waves are employed in evaluating and locating the early damage within the composite structure and the adhesively bonded interface. In this paper, we review the progress of applying the nonlinear ultrasonic waves in evaluating early degradation and micro-damage of the adhesively bonded composite structures and interface damage, including the theoretical and experimental investigations of employing transmitted bulk waves, guided waves and mixed waves. Furthermore, future research related to the characterization of composite structures and adhesive joints is suggested.

A review of two types of non-destructive testing technique for pressure pipelines

Pulsed eddy current testing (PECT) and electromagnetic ultrasonic non-destructive testing (NDT) techniques are important methods for detecting defects in pressure pipelines. Although these methods have the advantages of no contact requirement, fast detection and simple signal processing, there is a near-surface blind area in electromagnetic ultrasonic detection and pulsed eddy current detection cannot accurately detect deep locations due to the skin depth. However, these two techniques can be combined to potentially overcome their individual limitations. This paper presents an in-depth study of the use of pulsed eddy current testing and electromagnetic ultrasonic non-destructive testing techniques to detect defects in pipelines. Moreover, the basic principles, numerical simulation methods, testing systems and application characteristics of the individual methods and their combined use are discussed.

Wave propagation in glass fibre-reinforced polymer (GFRP) bars subjected to progressive damage—Experimental and numerical results

Glass fibre reinforced polymer (GFRP) is a material of increasing interest in civil engineering applications. It is used as internal reinforcement for concrete structures (especially in extremely corrosive environments), as well as structural profiles, plates, and gratings. However, estimating the life of GFRP structures represents a challenge for the construction industry. To address this challenge, a numerical model of elastic wave propagation in GFRP bars is presented in this paper so that it can be used to reduce the number of physical testing required to estimate the degradation of GFRP bars in the field.The proposed numerical model is designed to assist the application of ultrasonic non-destructive testing (NDT) techniques and develop a framework for the evaluation of progressive damage of GFRP bars due to a highly alkaline environment. The proposed methodology consists of: (i) development and calibration of a numerical model of elastic wave propagation in GFRP bars in Abaqus, (ii) simulation of deterioration of the bars, and (iii) comparison of experimental, large and low strain tests (shear test and ultrasonic evaluation) with results of numerical simulations.The results show that the model (low strain properties) correctly captures the deterioration rates seen in the shear strength test (large strains). The model is used to study ultrasonic features and demonstrates that low strain measurements (e.g. wave dispersion, wave amplitude) can be used to estimate the effect of progressive damage on large strain properties in GFRP bars, which can result in a decreased number of required destructive tests.

Preliminary exploration of processability and self-lubricating properties of polythioetherimides/PEEK blends and their composites

Polythioetherimides (STPI) were first synthesized from 3- and 4-chlorophthalic anhydrides, and 4,4’-oxydianline and 1,3-bis(4-aminophenoxy) benzene by a two-step poly- condensation procedure via their soluble poly (amic acid) precursors. Then a series of isomeric polythioetherimides/polyetheretherketone (STPI/PEEK) blends samples with compositions (wt%) of 30/70, 40/60 and 50/50 were prepared and characterized. The structure characterization of STPI demonstrated by FTIR, Raman and elemental analysis show that there are little S-S bonds of the copolythioetherimides chains. Thermal, rheological, ultrasonic nondestructive testing technique, mechanical measurements and dynamic thermomechanical analysis were conducted to process and assess the morphology and mechanical properties of the STPI/PEEK blends, and 30/70 weight composition of STPI/PEEK was preferred. There are few voids or air gaps in the molding samples. The samples of STPI/PEEK-30/70 show two relaxations at 164.2 °C and 243.5 °C, an average tensile modulus of 1.264 GPa, an average bending elastic modulus of 2.061 GPa and a bending strength of 78.3 MPa. Finally, the friction-wear characteristics of STPI/PEEK composites with solid lubricants such as graphite, MoS2 and PTFE were investigated, indicating a promising way to develop a STPI-based thermoplastic for tribological applications.

УЛЬТРАЗВУКОВОЙ КОНТРОЛЬ РАДИУСНЫХ ЗОН КОНСТРУКЦИЙ ИЗ ПКМ (обзор)

The review of FRP structures radius zones ultrasonic non-destructive testing techniques is given in the paper. It is shown that both single-element piezoelectric transducers and phased arrays can currently be used to solve this problem. It is necessary to use special tools for positioning and creating an acoustic contact with both types of transducers. Ultrasonic testing using the described tools allows detecting defects in radius zones up to 6 mm in size.

Air-Coupled, Contact, and Immersion Ultrasonic Non-Destructive Testing: Comparison for Bonding Quality Evaluation

The objective of this study is to compare the performance of different ultrasonic non-destructive testing (NDT) techniques for bonding quality evaluation. Aluminium-epoxy-aluminium single lap joints containing debonding in the form of release film inclusions have been investigated using three types of ultrasonic NDT methods: contact testing, immersion testing, and air-coupled testing. Apart from the traditional bulk wave ultrasound, guided wave testing was also performed using air coupled and contact transducers for the excitation of guided waves. Guided wave propagation within adhesive bond was numerically simulated. A wide range of inspection frequencies causing different ultrasonic wavelengths has been investigated. Average errors in defect sizing per ultrasonic wavelength have been used as a feature to determine the performance of each ultrasonic NDT technique. The best performance is observed with bulk wave investigations. Particularly, the higher frequencies (10–50 MHz) in the immersion testing performed significantly better than air-coupled testing (300 kHz); however, air coupled investigations have other advantages as contactless inspection. Whereas guided wave inspections show relatively lower accuracy in defect sizing, they are good enough to detect the presence of the debonding and enable to inspect long range. Even though each technique has its advantages and limitations, guided wave techniques can be practical for the preliminary in-situ inspection of adhesively bonded specimens.

Air-Coupled Reception of a Slow Ultrasonic A0 Mode Wave Propagating in Thin Plastic Film.

At low frequencies, in thin plates the phase velocity of the guided A0 mode can become slower than that of the ultrasound velocity in air. Such waves do not excite leaky waves in the surrounding air, and therefore, it is impossible to excite and receive them by conventional air-coupled methods. The objective of this research was the development of an air-coupled technique for the reception of slow A0 mode in thin plastic films. This study demonstrates the feasibility of picking up a subsonic A0 mode in plastic films by air-coupled ultrasonic arrays. The air-coupled reception was based on an evanescent wave in air accompanying the propagating A0 mode in a film. The efficiency of the reception was enhanced by using a virtual array which was arranged from the data collected by a single air-coupled receiver. The signals measured at the points corresponding to the positions of the phase-matched array were recorded and processed. The transmitting array excited not only the A0 mode in the film, but also a direct wave in air. This wave propagated at ultrasound velocity in air and was faster than the evanescent wave. For efficient reception of the A0 mode, the additional signal-processing procedure based on the application of the 2D Fourier transform in a spatial–temporal domain. The obtained results can be useful for the development of novel air-coupled ultrasonic non-destructive testing techniques.

Interface Waves for Detecting Defects in Bonded Hybrid Joints

Damage nucleation and growth can be complex in hybrid bonded structures composed of metals and laminated composites. There are limited reliable analytical and empirical methods to evaluate the bond integrity of such structures and to quantify the state of bonding in hybrid joints. Depending on the geometry and accessibility to hybrid joint sections, ultrasonic Nondestructive Testing (NDT) techniques are available for inspection of these structures. The interfacial damages at the bondline of structural joints represent challenging detection tasks for traditional ultrasonic nondestructive inspection (NDI) methods such as the pulse–echo method. This work investigates a method for bonded joint inspection that uses interface guided ultrasonic waves propagating along the bondline of these hybrid joints. An analysis, based on the use of finite element models for hybrid structures, is conducted to examine the use of interface waves to detect common defects found at or in the vicinity of interfaces of hybrid isotropic-anisotropic structures. Both cohesive and adhesive damage in a bonded joint are examined. Several damage scenarios are numerically studied and the guided wave time of flight (TOF) is shown to be sensitive to the size and location of interfacial damages. The results of this study suggest that interface guided waves can be used for integrity assessment and damage detection in hybrid structures.

Air-Coupled and Resonant Pulse-Echo Ultrasonic Technique.

An ultrasonic, resonant, pulse-echo, and air-coupled nondestructive testing (NDT) technique is presented. It is intended for components, with regular geometries where it is possible to excite resonant modes, made of materials that have a high acoustic impedance (Z) and low attenuation coefficient (α). Under these conditions, these resonances will present a very large quality factor (Q) and decay time (τ). This feature is used to avoid the dead zone, produced by the echo coming from the first wall, by receiving the resonant echo from the whole specimen over a longer period of time. This echo is analyzed in the frequency domain to determine specimen resonant frequency, which can be further used to determine either velocity or thickness. Using wideband air-coupled transducers, we tested the technique on plates (steel, aluminum, and silicone rubber) by exciting the mode of the first thickness. As expected, the higher the Z and the lower the α, the better the technique performed. Sensitivity to deviations of the angle of incidence away from normal (±2°) and the possibility to generate shear waves were also studied. Then, it was tested on steel cylindrical pipes that had different wall thicknesses and diameters. Finally, the use of this technique to generate C-Scan images of steel plates with different thicknesses was demonstrated.

Comparison of X-ray computed tomography and immersion ultrasonic non-destructive testing techniques in the case of qualitative and quantitative assessment of brazing quality level

The main aim of this work is to juxtapose directly two non-destructive testing techniques used to evaluate quality of brazed joints between metallic parts, namely X-ray Computed Microtomography (μCT) and immersion ultrasonic inspection (UT). From a general point of view, the application of ultrasound is a more efficient way to assess information about brazing filling imperfections (shorter time needed to obtain results, lower cost of measurements). However, in cases when connected parts have specific shape or geometry that is unfavourable for the application of ultrasound, an alternative approach has to be used such as porosity analysis of 3D data obtained from μCT technique. Hence, both techniques were employed in order to analyse brazed interfaces between copper and stainless steel pipe fitting in eleven cylindrical samples. The proposed methodology as well as developed data processing algorithm and results obtained are presented in this study.

Air-Coupled Excitation of a Slow A₀ Mode Wave in Thin Plastic Films by an Ultrasonic PMN-32%PT Array.

Ultrasonic non-destructive testing techniques (NDT) based on the application of guided waves are already used for inspection of plate-type structures made of various materials, including composite materials. Air-coupled ultrasonic techniques are used to test such structures by means of guided waves. The objective of this research was development and investigation of air-coupled excitation of a slow A0 Lamb wave mode in thin plastic films by a PMN-32%PT ultrasonic array. It is known that when the velocity of the A0 mode in the film is less than the ultrasound velocity in air no leaky wave is observed in a surrounding air. It opens new possibilities for NDT of composite structures. The influence of the airborne wave may be eliminated by 3D filtering in a wavenumbers-frequency domain. A special filter and corresponding signals processing technique were developed in order to obtain directivity patterns and velocity maps of the waves propagating in all directions. The measured ultrasound velocity values prove that, with the proposed method, it is possible to excite a slow A0 Lamb wave mode and to separate it from other parasitic waves propagating in air. Measurements of the parameters of the slow A0 mode, such as the propagation velocity in the plastic film, may be applied for the material characterization.

Modeling of Ultrasonic Waves in Fractured Rails with an Explicit Approach

Ultrasonic wave propagation in steel rails with explicit identification of flaws is numerically simulated. The problem is to detect a vertical crack in a railhead by applying ultrasonic nondestructive testing techniques. The propagation of elastic waves in the rail profile is simulated for various sizes and positions of the crack. It is shown that the finite-difference grid-characteristic method in the time domain and full-wave simulation can be used to analyze the effectiveness of rail flaw detection by applying ultrasonic nondestructive testing techniques. Full-wave simulation is also used to demonstrate the failure of the widely used echo-mirror method to detect flaws of certain types. It is shown that techniques for practical application of the ultrasonic delta method can be developed using full-wave supercomputer simulation. The study demonstrates a promising potential of geophysical methods as adapted to the analysis of ultrasonic nondestructive testing results.

A new method for ultrasonic detection of peel ply at the bondline of out-of-autoclave composite assemblies

Out-of-autoclave materials have long been an established material system for secondary structural applications; however, recent advancements in material properties allow for more advanced structural applications. Even though certain out-of-autoclave properties have achieved parity with autoclaved cured materials, out-of-autoclave materials are cured at reduced temperatures and pressures resulting in less compaction and homogeneity. The consequence is extraneous ultrasonic signals, due to internal reflections and refractions that cause attenuation, potentially masking defects leading to unidentifiable indications. Advanced algorithms were developed to improve the signal to noise ratio between constituents of similar acoustic impedance in bonded out-of-autoclave carbon fiber reinforced polymer assemblies. Conventional ultrasonic nondestructive testing techniques and analysis software cannot consistently achieve signal to noise ratios that meet quantifiable rejection thresholds of accurately sized peel ply inserts at the bonded interface of composite assemblies. Ultrasonic pulse echo with full waveform capture was used to inspect a reference standard with peel ply inserts placed between the adhesive and three-dimensional-woven fabric preform. The ultrasonic signal was produced by a 64 element array transducer with a central frequency of 2.8 MHz. Waveform post-acquisition analysis with post processing software was used to analyze and enhance the signal response between the peel ply and the bondline resulting in the final algorithm. To verify the results, the signal to noise ratio of each insert was calculated for both the raw and processed data. As the measure of detectability, the method relies on principles of statistical measurement to provide an industry standard signal to noise response of 3:1.

Ultrasensitive plano-concave optical microresonators for ultrasound sensing

Highly sensitive broadband ultrasound detectors are needed to expand the capabilities of biomedical ultrasound, photoacoustic imaging and industrial ultrasonic non-destructive testing techniques. Here, a generic optical ultrasound sensing concept based on a novel plano-concave polymer microresonator is described. This achieves strong optical confinement (Q-factors > 105) resulting in very high sensitivity with excellent broadband acoustic frequency response and wide directivity. The concept is highly scalable in terms of bandwidth and sensitivity. To illustrate this, a family of microresonator sensors with broadband acoustic responses up to 40 MHz and noise-equivalent pressures as low as 1.6 mPa per √Hz have been fabricated and comprehensively characterized in terms of their acoustic performance. In addition, their practical application to high-resolution photoacoustic and ultrasound imaging is demonstrated. The favourable acoustic performance and design flexibility of the technology offers new opportunities to advance biomedical and industrial ultrasound-based techniques.