Micronized Recycle Rubber Particles Modified Multifunctional Polymer Composites: Application to Ultrasonic Materials Engineering

Abstract

There is a growing interest in multifunctional composites and in the identification of novel applications for recycled materials. In this work, the design and fabrication of multiple particle-loaded polymer composites, including micronized rubber from end-of-life tires, is studied. The integration of these composites as part of ultrasonic transducers can further expand the functionality of the piezoelectric material in the transducer in terms of sensitivity, bandwidth, ringing and axial resolution and help to facilitate the fabrication and use of phantoms for echography. The adopted approach is a multiphase and multiscale one, based on a polymeric matrix with a load of recycled rubber and tungsten powders. A fabrication procedure, compatible with transducer manufacturing, is proposed and successfully used. We also proposed a modelling approach to calculate the complex elastic modulus, the ultrasonic damping and to evaluate the relative influence of particle scattering. It is concluded that it is possible to obtain materials with acoustic impedance in the range 2.35–15.6 MRayl, ultrasound velocity in the range 790–2570 m/s, attenuation at 3 MHz, from 0.96 up to 27 dB/mm with a variation of the attenuation with the frequency following a power law with exponent in the range 1.2–3.2. These ranges of values permit us to obtain most of the material properties demanded in ultrasonic engineering.

Acoustic Properties of Stretchable Liquid Metal‐Elastomer Composites for Matching Layers in Wearable Ultrasonic Transducer Arrays

“…[55][56][57] The acoustic impedances for EGaIn and Galinstan are comparable to aluminum (Al) particles (Z = 17.28 Mrayl), but are lower than other metals and metal oxides often used in impedance matching layers, such as cerium dioxide or aluminum oxide with acoustic impedance > 40 Mrayl. [25,27,55,58] Mercury (Z = 19.58 Mrayl) is the only other liquid with an impedance comparable to EGaIn and Galinstan; however, its high toxicity makes it unsuitable for wearable applications.…”

“…[20] Thus far, matching layers have not been implemented in most wearable ultrasound devices due to the rigid nature of conventional matching layers that are often constructed by doping epoxy with rigid particle fillers. [21][22][23] Although rigid particles can be incorporated into silicones, urethanes, and acrylate-based elastomers to increase their acoustic impedance, [24][25][26][27] the loading required to achieve significant acoustic property enhancement can degrade the mechanical properties of these soft and stretchable material systems. [28][29][30] Furthermore, the large mismatch in density and elastic modulus between the rigid filler and matrix can cause high attenuation.…”

Ultrasonic Transducers for In-Service Inspection and Continuous Monitoring in High-Temperature Environments

“…As only part of the crystal is covered by the backing, the resonance of the piezoelectric element is such that the bandwidth is increased but adequate sensitivity is retained. Most backing elements have relatively low acoustic impedance (2.35–15.6 MRayl) [ 22 ], which results in an interface. At the interface between two materials, a wave will reflect according to an energy reflection coefficient R , and transmit according to an energy transmission coefficient T : where is the acoustic impedance of the piezoelectric material, and is the acoustic impedance of the backing layer.…”

“…This mixture also leads to a heterogeneous layer, thus increasing the scattering of the waves thanks to its pores. Epoxy–tungsten mixtures typically have strong attenuation (0.25–5 dB/mm) [ 22 ]. This mixture allows for an effective backing layer, affordable and easy to realize, but unfortunately completely unsuitable for high-temperature applications as epoxy cannot be used above 350 C.…”