Rahul Kishor

Coexisting and mixing phenomena of thermoacoustic and magnetoacoustic waves in water

Concurrent generation and mixing phenomenon of thermoacoustic (TA) and magnetoacoustic (MA) waves in water are predicted and observed. A theory unifying TA and MA is further put forward to analyze it. By scaling down the radio frequency in thermoacoustics to the low mega Hertz range and by incorporating appropriately a static magnetic field, TA and MA waves are simultaneously generated in the conductive matter. The two waves propagate concurrently in water and produce dynamic acoustic radiation force due to water absorption. Such dynamic radiation force vibrates the absorbing water and consequently yields acoustic emissions at the inter-modulation frequencies of TA and MA waves, creating mixing effect similar to that of vibro-acoustography. The mixing effect can be potentially utilized to mimic vibro-acoustography imaging without firing external ultrasound towards intrinsic dual-contrast (elasticity and conductivity) imaging.

Photoacoustic induced surface acoustic wave sensor for concurrent opto-mechanical microfluidic sensing of dyes and plasmonic nanoparticles

While there are a large number of reports on acoustic wave based sensors for evaluating mechanical parameters of fluid samples such as density, viscosity etc., devices for the simultaneous optical and mechanical characterization of fluids remain unexplored. In this context, effective utilization of surface acoustic wave (SAW) sensors comprising elliptically polarized evanescent waves for optical characterization of an analyte is intriguing. A combination of SAW and photoacoustic (PA) techniques presents promising capabilities for optical and mechanical characterization of fluids in micro volumes. We present a SAW-PA integrated device combining PA and SAW where the samples are introduced into a microfluidic channel. The PA signal generated from a sample in the microchannel of the SAW-PA device is mode-converted into SAW signals upon reaching the piezoelectric substrate, which is detected using the inter-digital transducer (IDT) deposited on the substrate. We further demonstrate the use of this SAW-PA compact platform for investigating the opto-acoustical properties of standard dye solutions and gold nanoparticles whose absorption is due to plasmonic resonance.

Single laser pulse generates dual photoacoustic signals for differential contrast photoacoustic imaging

Photoacoustic sensing and imaging techniques have been studied widely to explore optical absorption contrast based on nanosecond laser illumination. In this paper, we report a long laser pulse induced dual photoacoustic (LDPA) nonlinear effect, which originates from unsatisfied stress and thermal confinements. Being different from conventional short laser pulse illumination, the proposed method utilizes a long square-profile laser pulse to induce dual photoacoustic signals. Without satisfying the stress confinement, the dual photoacoustic signals are generated following the positive and negative edges of the long laser pulse. More interestingly, the first expansion-induced photoacoustic signal exhibits positive waveform due to the initial sharp rising of temperature. On the contrary, the second contraction-induced photoacoustic signal exhibits exactly negative waveform due to the falling of temperature, as well as pulse-width-dependent signal amplitude. An analytical model is derived to describe the generation of the dual photoacoustic pulses, incorporating Gruneisen saturation and thermal diffusion effect, which is experimentally proved. Lastly, an alternate of LDPA technique using quasi-CW laser excitation is also introduced and demonstrated for both super-contrast in vitro and in vivo imaging. Compared with existing nonlinear PA techniques, the proposed LDPA nonlinear effect could enable a much broader range of potential applications.

An analytical study of photoacoustic and thermoacoustic generation efficiency towards contrast agent and film design optimization

Photoacoustic (PA) and thermoacoustic (TA) effects have been explored in many applications, such as bio-imaging, laser-induced ultrasound generator, and sensitive electromagnetic (EM) wave film sensor. In this paper, we propose a compact analytical PA/TA generation model to incorporate EM, thermal and mechanical parameters, etc. From the derived analytical model, both intuitive predictions and quantitative simulations are performed. It shows that beyond the EM absorption improvement, there are many other physical parameters that deserve careful consideration when designing contrast agents or film composites, followed by simulation study. Lastly, several sets of experimental results are presented to prove the feasibility of the proposed analytical model. Overall, the proposed compact model could work as a clear guidance and predication for improved PA/TA contrast agents and film generator/sensor designs in the domain area.

Phase-domain photoacoustic sensing

As one of the fastest-growing imaging modalities in recent years, photoacoustic imaging has attracted tremendous research interest for various applications including anatomical, functional, and molecular imaging. The majority of the photoacoustic imaging systems are based on the time-domain pulsed photoacoustic method, which utilizes a pulsed laser source to induce a wideband photoacoustic signal, revealing optical absorption contrast. An alternative way is the frequency-domain photoacoustic method utilizing the chirping modulation of laser intensity to achieve lower system cost. In this paper, we report another way of the photoacoustic method, called phase-domain photoacoustic sensing, which explores the phase difference between two consequent intensity-modulated laser pulse induced photoacoustic measurements to reveal the optical properties. The basic principle is introduced, modeled, and experimentally validated in this paper, which opens another potential pathway to perform photoacoustic sensing and i...

FEM modelling of a SAW microfluidic sensor based on the photoacoustic effect

Surface acoustic wave (SAW) integrated with microfluidics has been used for various acoustofluidic applications including sensing mechanical properties of fluids such as viscosity and density of fluids. We have recently demonstrated the excitation of a surface acoustic wave using the photoacoustic (PA) effect in a microfluidic channel. The opto-mechanical properties of the liquids in the microchannel can be detected using the mode-converted SAW. In this work, we investigated the response mechanism of the sensor using detailed numerical FEM simulation. The simulation study has shown that the microfluidic channel on the substrate acts as an acoustic resonator with multiple eigen modes. PA signals generated inside the microfluidic channel resonates at these modes. The displacement profile on the piezoelectric surface confirmed that the pressure mode propagating parallel to the piezoelectric substrate has the highest mode conversion efficiency (longitudinal wave to SAW). This mode is sensitive to the microchannel dimensions. The study has shown that a SAW device matched to this mode-frequency could be used for improving the sensitivity of the sensor. Experimental observation confirmed the theory.

High-performance hybrid organic-inorganic perovskite nanoparticles based piezoelectric energy harvester

The present study provides a new facile route for hybrid piezoelectric nanogenerator based on a composite of piezoelectric formamidinium lead halide perovskite (FAPbBr3) nanoparticles and polydimethylsiloxane (PDMS) polymer. The piezoelectric device exhibits high performance with a maximum recordable output voltage of 8.5 V and current density of 3.8 & #x00B5;Acm-2 under periodical vertical compression and release operation. The alternating energy generated from nanogenerator is used to charge a capacitor through a bridge rectifier. This result innovatively expands the feasibility of organic-inorganic lead halide perovskite materials in the application of both piezoelectric and photovoltaic hybrid devices for energy harvesting.

Surface acoustic wave RF sensing and actuation for lab-on-a-chip platforms

This paper presents different surface acoustic wave (SAW) active components including actuators and sensors to realize the whole chain necessary to establish a lab-on-chip system. The SAW actuation is based on the acoustic streaming effect caused by the leakage of SAW into fluids in the microfluidic channel. A novel SAW sensor to determine the optical and mechanical absorption properties of liquid samples in a microfluidic channel is also discussed.

Nonlinear electromagnetic-acoustic sensing and imaging

In this paper, we will introduce some recent research progress on nonlinear electromagnetic (EM) acoustic sensing and imaging techniques. Being different from the conventional linear EM-acoustic technique based on pulsed EM illumination and impulse response of the object, the nonlinear EM-acoustic technique utilizes various ways of nonlinear enhancement ways, including resonance, mixing, thermal modulation, as well as close-loop feedback. By presenting some most recent research results, this paper will be interesting to wide range of general readers to inspire further developments of this technique towards real biomedical applications and beyond.