In this work, we built ultrasonic disc-shaped transducer for targeted neuromodulation with the addition of a solid axicon lens based on a polydimethylsiloxane (PDMS) interface. We made a numerical and experimental characterization of its acoustic field. The motor cortex of CF-1 mice was stimulated, through the skin and skull into the intact brain, with low-intensity pulsed ultrasound. Evoked muscle responses in different body segments were clearly observed, including hindlimb, forelimb, and tail. Axicon lens affixed on the face of the transducer makes possible a targeted modulation of the motor cortex by pulsed ultrasound, inducing muscle contraction in a specific body segment. In this approach, the lateral and axial spatial resolution is comparable to spherical segment ultrasound transducers, but with a shorter focal length. Thus, ultrasound axicon looks attractive to investigate the functional contributions of fine-grained spatial structures in the brain.

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Acoustic measurements or ultrasonic testing can be strongly affected by reflections or echoes from test tank walls. In order to create a non-reflecting environment equivalent to infinite medium, a pyramidal structured absorber (PSA) can be used to coat the walls of an ultrasonic tank. In this work, we model an array of tetragonal pyramid ultrasonic wave absorbers. This model is based on two coupled first-order equations describing the stress and particle velocity within an isotropic medium. For absorbing media, the Kelvin-Voigt model of viscoelasticity is used. The equations are discretized in 2D using an efficient time-stepping pseudo-spectral scheme that takes in consideration both, the acoustic properties and attenuation characteristics of the composite materials. We then built a 3D printed PSA using a Stratasys Objet500 Connex 3D printer, which allows to combine photopolymers in specific concentrations and microstructures. We designed PSA covering the frequency ranges from 0.5 MHz to 5 MHz and from 1 MHz to 10 MHz, with double homogeneous layer: a core of rubber material with a skin of a variety of elastomers by combining rigid and flexible materials. Each single pyramid contains two major parts: the ground of the pyramid (9.4 mm base × 4.7 mm height, for 0.5 MHz and 4.7 mm base × 2.35 mm height, for 1 MHz) and the body of the pyramid (23.5 mm height, for 0.5 MHZ and 11.75 mm height, for 1 MHz). The measured echo-reduction was greater than 35 dB at the covering frequency range and the transmission loss was estimated by 20 dB. Echoes increase rapidly for frequencies below the minimum frequency of the covering range. The modeling and 3D printing of PSA with different sizes, in a wide range of frequencies, is a cost-effective custom solution for a wide range of applications including for example, radiation force balances, hydrophone mounts and medical ultrasound equipment.

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