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Transducer sample and performance test. (a) The fabricated matching layer has a diameter of 20 mm and a thickness of 1000 μ m. A transducer was fabricated to demonstrate the performance and practical use of this new metamaterial matching layer. A low acoustic impedance porous piezoelectric ceramic slab with a centre frequency of 4 MHz was used in this transducer. The acoustic impedance of the backing material is 7.8 MRayls. (b) The pulse echo tests were conducted on a 1 cm thick polystyrene test block. An aluminium plate acted as the acoustic total reflection body. The traditional λ /4 acoustic impedance matching layer transducer was tested using the same equipment for comparison.
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High-quality broadband ultrasound transducers yield superior imaging performance in biomedical ultrasonography. However, proper design to perfectly bridge the energy between the active piezoelectric material and the target medium over the operating spectrum is still lacking. Here, we demonstrate a new anisotropic cone-structured acoustic metamateri...
Citations
... [6][7][8] To overcome the problem of narrowband, composite structures stacking two or more quarterwavelength layers have been extensively studied to achieve broadband sound transmission, [9][10][11][12][13][14][15] in which a challenging work is to obtain suitable matching layers with specific impedance. In comparison, some acoustic metamaterials with deep sub-wavelength structure, 5,16,17 periodic phononic crystal, 18 and gradient refractive index material [19][20][21] have been implemented to break through the limitations in material availability and achieve broadband acoustic impedance matching. ...
In this paper, we propose a broadband tunable acoustic matching layer (BTAML) comprising an array of piezoelectric elements with non-uniform gradient shunt circuits (NGSCs). The effective impedance of the BTAML can be controlled in real time by regulating the parameters of NGSCs. The theoretical results demonstrate that BTAML is capable of adjusting impedance from 1.5 to 20 MRayl and has a broad bandwidth compared with the traditional matching layer. Furthermore, we experimentally verified the acoustic transmission property of the BTAML, and good agreement was achieved with numerical simulations. The approach can significantly promote research on tunable acoustic matching and offer effective impedance matching layers with a broad bandwidth in industrial applications.
... There have been many studies on acoustic metamaterials over the last decade [2][3][4][5][6][7][8][9][10][11]. Acoustic metamaterials are structures in which fine structures are created within the material and behavior as if the acoustic properties of the material are controlled. ...
A micromachined ultrasonic transducer (MUT)‐type acoustic metamaterial that achieved acoustic impedance matching between materials with different acoustic impedances was successfully fabricated. The fabricated device consisted of a thin membrane that vibrated when acoustic waves impinged on the surface of the device, along with tapered trench structures located beneath the membrane. The device fabrication process consisted of seven steps, using four silicon wafers. An acoustic evaluation of the system with the fabricated MUT‐type acoustic metamaterial showed that the water‐to‐silicon transmission property was 30% higher than that of a system without the MUT‐type acoustic metamaterial. This result confirms that MUT‐type acoustic metamaterials are useful for matching the acoustic impedance between materials with different acoustic impedances. © 2024 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.
... Looking at tunable acoustic metamaterials suitable for sound reduction, most of the approaches seem to be combine piezo with acoustic metamaterials [109][110][111][112]. A theoretical examination of an acoustic metamaterials consisting of piezoelectric boundaries was carried out [113]. ...
Despite the emergence of acoustic metamaterials with superior sound absorption and transmission loss, their adoption for building sound insulation has been limited. Sound insulation design in buildings is still informed by the acoustic performance of conventional materials, where the mass law contradicts light weighting when it comes to acoustic design. In any case buildings close to noisy environments such as motorways, railway lines and airports still suffer from significant low frequency noise pollution. Although the limited working bandwidth of acoustic metamaterials is a major issue limiting its application, combining meta-units that interact at various frequencies alongside multi-layer conventional solutions can deliver superior sound insulation in buildings. The review put forwards acoustic metamaterials, specifically emphasising superior sound absorption and transmission/insertion loss as critical properties for effective building sound insulation. The paper reveals a variety of acoustic metamaterials that can be adopted to compliment conventional sound insulation approaches for acoustically efficient building design. The performance of these metamaterials is then explained through their characteristic negative mass density, bulk modulus or repeating or locally resonating microstructure. The review is also extended to air transparent acoustic metamaterials that can be used for sound insulation of building ventilation. Lastly the prospects and challenges regarding the adoption of acoustic metamaterials in building insulation are also discussed. Overall, tuneable, and multifunctional acoustic metamaterials when thoughtfully integrated to building sound insulation can lead to significant acoustic comfort, space-saving and light-weighting.
... This mismatch results in reduced transmission efficiency. Li et al. [13] developed an acoustic metamaterial matching layer with an anisotropy conical structure, which has an acoustic impedance gradient from 11.4 to 3.0 MRayls in the direction of its thickness, effectively transiting the acoustic impedance difference between the piezoelectric material and the target medium, allowing the transducer to transmit ultrasonic waves over a wide frequency range. This design has a great improvement compared with the traditional design, and provides a practical solution for the impedance matching of medical ultrasonic transducer. ...
... In addition, during the development and testing of acoustic metamaterials, a frequencyresolved broadband characterisation of materials is necessary. Examples of metamaterials with dispersive longitudinal waves can be found in the literature [10][11][12]. Thus, broadband, frequency-resolved measurements of sound velocity and attenuation open up new possibilities for materials analysis. ...
Optoacoustics is a metrology widely used for material characterisation. In this study, a measurement setup for the selective determination of the frequency-resolved phase velocities and attenuations of longitudinal waves over a wide frequency range (3– 55MHz) is presented. The ultrasonic waves in this setup were excited by a pulsed laser within an absorption layer in the thermoelastic regime and directed through a layer of water onto a sample. The acoustic waves were detected using a self-built adaptive interferometer with a photorefractive crystal. The instrument transmits compression waves only, is low-contact, non-destructive, and has a sample-independent excitation. The limitations of the approach were studied both by simulation and experiments to determine how the frequency range and precision can be improved. It was shown that measurements are possible for all investigated materials (silicon, silicone, aluminium, and water) and that the relative error for the phase velocity is less than 0.2 .
... DLs are generally fabricated using a single material, and their impedance is matched only with the sensor, leading to a potentially large impedance mismatch between the target and DL. If the impedance mismatch is large, it causes a large amount of the acoustic energy to be reflected at the interface, and also creates a strong standing wave in the DL [7]. A single quarter wavelength matching (λ/4) layer is a popular solution to couple the source and target that has different impedance by taking advantage of the constructive and destructive interferences in the matching layer [8,9]. ...
... A single quarter wavelength matching (λ/4) layer is a popular solution to couple the source and target that has different impedance by taking advantage of the constructive and destructive interferences in the matching layer [8,9]. However, this method leads to a narrow operational frequency range [7]. Stacking multiple matching layers would theoretically improve the broadband characteristic of transmission, but it undesirably lengthens the coupling medium, especially for low-frequency (20-100 KHz) applications. ...
... The problem of acoustic impedance mismatch has also started to be addressed by various groups using acoustic metamaterials [17][18][19][20]. Research work by [7,21,22] showed that graded impedance matching metamaterials can improve broadband energy transmission in high frequency (1)(2)(3)(4)(5) applications. ...
Metamaterials exhibit unique ultrasonic properties that are not always achievable with traditional materials. However, the structures and geometries needed to achieve such properties are often complex and difficult to obtain using common fabrication techniques. In the present research work, we report a novel metamaterial acoustic delay line with built-in impedance matching that is fabricated using a common 3D printer. Delay lines are commonly used in ultrasonic inspection when signals need to be separated in time for improved sensitivity. However, if the impedance of the delay line is not perfectly matched with those of both the sensor and the target medium, a strong standing wave develops in the delay line, leading to a lower energy transmission. The presented metamaterial delay line was designed to match the acoustic impedance at both the sensor and target medium interfaces. This was achieved by introducing graded engineered voids with different densities at both ends of the delay line. The measured impedances of the designed metamaterial samples show a good match with the theoretical predictions. The experimental test results with concrete samples show that the acoustic energy transmission is increased by 120% and the standing wave in the delay line is reduced by over a factor of 2 compared to a commercial delay line.
... The superior acoustic performance of phonon crystals provides a new solution idea for the optimized design of the ultrasonic transducer. 23,24 In 2017, Li et al. 25 proposed acoustic metamaterial matching layers for broadband gradient impedance matching of ultrasonic transducers. In 2019, Han et al. 26 designed a singlecell UHF acoustic signal acquisition model for rotating bodies based on acoustic metamaterials, realizing the local field enhancement effect of the model at different frequencies. ...
In the photoacoustic detection of breast cancer, the weak intensity and severe energy attenuation of photoacoustic signals excited by the breast tissue become an important factor limiting the efficient acquisition of the ultrasound transducer. To overcome this problem, we proposed a linear defect channel and bifurcated acoustic transmission channel models at the front of the ultrasonic transducers based on the phononic crystal bandgap characteristics and defect state structure. The results of numerical analyses and simulations carried out using COMSOL demonstrated that the photoacoustic signal transmission channel proposed could confine the acoustic energy within the defects, while achieving the directional transmission and local enhancement of the acoustic field of high-frequency breast photoacoustic signals. This design effectively reduces the signal transmission loss and amplifies the mammographic signal intensity, which is conducive to efficient acquisition. In addition, the directional transmission effect is found to be strongly dependent on frequency, which makes the channel have great frequency selectivity. Through the flexible modulation of the transmission path of the artificial acoustic structure, breast photoacoustic signals of specific frequencies can be exported in separate paths to reduce the interference of noise signals. This study combines biomedical tumor detection with phononic crystals to present a novel method for efficient acquisition and deep detection of acoustic signals in tissue photoacoustic detection from the signal perspective, which is conducive to improving the sensitivity of breast cancer detection.
... However, there is still a lack of proper design to bridge the energy generated by a piezoelectric actuator and the target elastic medium over the wide operating spectrum [15]. The design of such devices needs to be optimized in order to maximize the energy transfer efficiency [16]. Thus, Li et al. [16] developed an anisotropic cone-structured EMM layer for matching piezoelectric actuator and substrate for improvement of broadband ultrasound transducers. ...
Optimization of the structure of piezoelectric transducers such as the proper design of matching layers can increase maximum wave energy transmission to the host structure and transducer sensitivity. A novel configuration of an ultrasonic transducer, where elastic metamaterial insertion is introduced to provide bulk wave mode conversion and to increase wave energy transfer into a substrate, is proposed. Configurations of layered elastic metamaterials with crack-like voids are examined theoretically since they can provide wide band gaps and strong wave localization and trapping. The analysis shows that the proposed metamaterial-based matching layers can sufficiently change wave energy transmission from a piezoelectric active element for various frequency ranges (relatively low frequencies as well as higher ones). The proposed configuration can also be useful for advanced sensing with higher sensitivity in certain frequency ranges or for demultiplexing different kinds of elastic waves.
... On the other hand, acoustic impedance gradient matching techniques have gained attention. Compared to traditional quarter-wavelength single/multi-layer matching techniques, acoustic impedance gradient matching effectively broadens the transducer's operating bandwidth and improves sensitivity, enhancing overall performance [11][12][13]. Phononic crystal, with its characteristics such as bandgaps and defective state, offers control over the propagation of sound and elastic waves [14][15][16]. Ji et al. [17,18] designed a phononic crystal air-coupled ultrasonic transducer. ...
To further improve the operational performance of a phononic crystal air-coupled ultrasonic transducer while reducing the number of simulations, an intelligent optimization design strategy is proposed by combining finite element simulation analysis and artificial intelligence (AI) methods. In the proposed strategy, the structural design parameters of 1–3 piezoelectric composites and acoustic impedance gradient matching layer are sampled using the optimal Latin hypercube sampling (OLHS) method. Moreover, the COMSOL software is utilized to calculate the performance parameters of the transducer. Based on the simulation data, a radial basis function neural network (RBFNN) model is trained to establish the relationship between the design parameters and the performance parameters. The accuracy of the approximation model is verified through linear regression plots and statistical methods. Finally, the NSGA-II algorithm is used to determine the design parameters of the transducer. After optimization, the band gap widths of the piezoelectric composites and acoustic impedance gradient matching layer are increased by 16 kHz and 13.5 kHz, respectively. Additionally, the −6 dB bandwidth of the transducer is expanded by 11.5%. The simulation results and experimental results are consistent with the design objectives, which confirms the effectiveness of the design strategy. This work provides a feasible strategy for the design of high-performance air-coupled ultrasonic transducers, which is of great significance for the development of non-destructive testing technology.
... The acoustic impedance gradient material has been proved to exhibit the characteristics of high-frequency conduction, and the quasi-continuous acoustic impedance change can be realized in the range of material by selecting the type of filler and adjusting the filling proportion [26,27]. Therefore, using an artificial acoustic impedance gradient composite is a promising way to solve the above problem [27,28]. In recent years, many researchers have tried to apply impedance gradient composites to ultrasonic transducers with traditional piezoelectric ceramics. ...
... In 2016, Lu prepared a new anisotropic conical ultrasonic matching layer material by etching the stripped silica fiber bundle in a hydrofluoric acid solution. The corresponding −6 dB bandwidth of the ultrasonic transducer equipped with this matching layer can reach 107%, which strongly proves that the acoustic impedance gradient matching material is suitable for the broadband sound transmission ability of a single crystal 28 . However, the acoustic impedance of this structure can only change linearly along the thickness direction, and because the acoustic impedance gradient is realized by using the change in the geometric size of the high impedance filler in the matching layer, this structure is only suitable for the frequency band where the wavelength is much larger than the chassis size of high impedance filler of each unit [28]. ...
... The corresponding −6 dB bandwidth of the ultrasonic transducer equipped with this matching layer can reach 107%, which strongly proves that the acoustic impedance gradient matching material is suitable for the broadband sound transmission ability of a single crystal 28 . However, the acoustic impedance of this structure can only change linearly along the thickness direction, and because the acoustic impedance gradient is realized by using the change in the geometric size of the high impedance filler in the matching layer, this structure is only suitable for the frequency band where the wavelength is much larger than the chassis size of high impedance filler of each unit [28]. ...
High-performance broadband ultrasound transducers provide superior imaging quality in biomedical ultrasound imaging. However, a matching design that perfectly transmits the acoustic energy between the active piezoelectric element and the target medium over the operating spectrum is still lacking. In this work, an anisotropic gradient acoustic impedance composite material as the matching layer of an ultrasonic transducer was designed and fabricated; it is a non-uniform material with the continuous decline of acoustic impedance along the direction of ultrasonic propagation in a sub-wavelength range. This material provides a broadband window for ultrasonic propagation in a wide frequency range and achieves almost perfect sound energy transfer efficiency from the piezoelectric material to the target medium. Nano tungsten particles and epoxy resin were selected as filling and basic materials, respectively. Along the direction of ultrasonic propagation, the proportion of tungsten powder was carefully controlled to decrease gradually, following the natural exponential form in a very narrow thickness range. Using this new material as a matching layer with high-performance single crystals, the −6 dB bandwidth of the PMN-PT ultrasonic transducer could reach over 170%, and the insertion loss was only −20.3 dB. The transducer achieved a temporal signal close to a single wavelength, thus there is the potential to dramatically improve the resolution and imaging quality of the biomedical ultrasound imaging system.
