Nikolay Smagin

Generation of broadband surface acoustic waves using a dual temporal-spatial chirp method

Wideband surface acoustic wave (SAW) generation with a spatial chirp-based interdigital transducer was optimized for non-destructive characterization and testing of coatings and thin layers. The use of impulse temporal excitation (Dirac-type negative pulse) leads to a wide band emitter excitation but with significantly limited SAW output amplitudes due to the piezoelectric crystal breakdown voltage. This limitation can be circumvented by applying a temporal chirp excitation corresponding in terms of frequency band and duration to the spatial chirp transducer configuration. This dual temporal-spatial chirp method was studied in the 20 to 125 MHz frequency range and allowed to obtain higher SAW displacement amplitudes with an excitation voltage lower than that of the impulse excitation.

Compact selective tweezers based on focalized acoustical vortices and spiraling interdigitated transducers

With the emergence of regenerative medicine, cell printers, and labs on chips, the contactless selective manipulation of microscopic objects such as particles, cells, or drops has become a key feature. To complete this task, acoustic tweezers appear as a tremendous alternative to their magnetic and optical counterpart. Indeed, they do not require pre-tagging of the manipulated object and they enable particles trapping with forces several orders of magnitude larger than optical tweezers at same input power. Recently, Baresh et al. [Phys. Rev. Lett., 116, 024301 (2016)] demonstrated the selective 3D manipulation of particles with a specific class of waves called acoustical vortices. Nevertheless, such manipulation was achieved with a complex transducer array coupled with a high end programmable electronics. This system is cumbersome, not compatible with microscopes and hardly miniaturizable. To overcome these difficulties, our team developed new tweezers [Riaud et al., Phys. Rev. Appl. 7, 024007 (2017)] based on spiraling interdigitated transducers (IDTs), some electrodes sputtered at the surface of piezoelectric substrates patterned by photolithography. The shape of the electrodes encodes the phase of the field like a hologram. For applications, these tweezers have many attractive features: they are selective, flat, easily integrable, and compatible with disposable substrates.

Doppler ultrasonography using wave phase conjugation

Ultrasound wave phase conjugation (WPC) is an efficient tool for velocimetry of flows due to its sensibility to the break of time reversal invariance of acoustic fields in moving media. The presence of flow leads to the non compensated Doppler phase shift of the backward phase conjugate wave relatively to the primary probing wave. This phase shift provides detection, diagnostics and velocimetry of flows and does not require the presence of any scatterers in a flow. Furthermore the phase shift of phase conjugate wave can be used in liquid flowmeters. As it was shown in previous works the sensitivity of liquid flowmeters using phase conjugate ultrasonic waves essentially increases by using nonlinear effects appearing during propagation of phase conjugate waves in a moving liquid. In the present paper we report the theoretical and experimental results on imaging of flow velocity distributions in tubes and phantoms of blood vessel. The scanning auto‐confocal system based on parametric ultrasonic wave phase co...

Nonlinear phase conjugate ultrasonic waves in moving media

The basic principle of acoustic wave phase conjugation provides compensation of phase incursions during back propagation of the phase conjugate waves (PCW) towards the source of the primary emission. This feature of PCW results from time reversal invariance of acoustic field in a stationary medium. In moving media or in the presence of flows the time reversal invariance is broken resulting in essential modification of PCW properties. The incident wave spatial distribution is not reproduced completely by the phase conjugate wave and the phase incursions are not compensated any more. In the present paper the general theory of PCW propagation in moving nonlinear media is developed. The theory is applied for description of PCW acoustic rays and calculation of noncompensated phase shift of PCW on the source of the primary probing wave. The treatment of the phase shift of the PCW is developed as a new method of diagnostics and imaging of flow velocity distributions in liquid. The method is approved experimental...