Transparent Transducer Research Articles

Acoustofluidic trapping device for high-NA multi-angle imaging

In the life sciences, there has been growing awareness that the traditional 2D cell culture model has its limitations in advancing our understanding of the mechanisms that underlie cell behavior, as the behavior and response of cells depend on the 3D microenvironment. Studying models such as suspended cell clusters and organoids is a step toward closing the gap between in vitro and in vivo studies. The fact that sample confinement and contact with surfaces have an impact on cells creates a need for contact-less tools for the inspection of live biological samples. Recently, we developed an acoustofluidic chip to trap and manipulate sub-millimeter-sized biological samples, and here, we demonstrate that this device can be adapted to support high-resolution imaging and illumination scanning for multi-view image acquisition. After coupling acoustic bulk waves into a microfluidic chip, the sample is levitated by an optically transparent transducer in the vertical direction. Two orthogonal side-transducers give additional control over the sample. By tuning the relative strengths of the three transducers and thus inducing an acoustic torque, we can transiently rotate the sample into various orientations for image acquisition. Under different operating conditions, exciting other modes, we can also induce sustained rotation of samples by means of other torque contributions and around axes perpendicular to the imaging axis, which is important to avoid “missing cone” artifacts in the tomographic reconstruction of the sample. We will discuss the modifications to our previously established device that were necessary to comply with the requirements for high-NA imaging and high-NA illumination. We provide a characterization of the performance and show examples of rotation and reorientation of biological samples, such as large pollen grains and cancer spheroids.

Bi-modal near-infrared fluorescence and ultrasound imaging via a transparent ultrasound transducer for sentinel lymph node localization: publisher's note.

This publisher's note contains a correction to Opt. Lett.47, 393 (2022)10.1364/OL.446041.

Design of Photoacoustic Microscope Based on Transparent Ultrasonic Transducer

Design of Photoacoustic Microscope Based on Transparent Ultrasonic Transducer

Bias-sensitive transparent single-element ultrasound transducers using hot-pressed PMN-PT

Here we introduce electrostrictive hot-pressed lead magnesium niobate (PMN) with low lead titanate (PT) doping as a candidate transparent transducer material. We fabricate transparent high-frequency single-element transducers and characterize their optical, electrical, and acoustic properties. PMN-PT may offer sensitivity advantages over other transducer materials such as lithium niobate owing to its high electromechanical efficiency and bias-voltage sensitivity. The transparency of the fabricated transducer was measured ∼67% at 532 nm wavelength with a maximum electromechanical coefficient of ∼0.68 with a DC bias level of 100 V. The photoacoustic impulse response showed a center frequency of ∼27.6 MHz with a −6 dB bandwidth of ∼61% at a DC bias level of 40 V. Results demonstrate that the new transparent transducers hold promise for future optical-ultrasonic and photoacoustic imaging applications.

Acoustic force mapping in a hybrid acoustic-optical micromanipulation device supporting high resolution optical imaging.

Many applications in the life-sciences demand non-contact manipulation tools for forceful but nevertheless delicate handling of various types of sample. Moreover, the system should support high-resolution optical imaging. Here we present a hybrid acoustic/optical manipulation system which utilizes a transparent transducer, making it compatible with high-NA imaging in a microfluidic environment. The powerful acoustic trapping within a layered resonator, which is suitable for highly parallel particle handling, is complemented by the flexibility and selectivity of holographic optical tweezers, with the specimens being under high quality optical monitoring at all times. The dual acoustic/optical nature of the system lends itself to optically measure the exact acoustic force map, by means of direct force measurements on an optically trapped particle. For applications with (ultra-)high demand on the precision of the force measurements, the position of the objective used for the high-NA imaging may have significant influence on the acoustic force map in the probe chamber. We have characterized this influence experimentally and the findings were confirmed by model simulations. We show that it is possible to design the chamber and to choose the operating point in such a way as to avoid perturbations due to the objective lens. Moreover, we found that measuring the electrical impedance of the transducer provides an easy indicator for the acoustic resonances.

Quantification of water content in water–ethanol solutions using photothermal transparent transducer method

In this letter we exhibit a series of results obtained using the technique of photothermal spectroscopy to determine the concentration of water in water–ethanol solutions. At low concentrations water is completely miscible with ethanol and particularly difficult to separate into parts in order to determine the complementary amount of each component, especially when considering measurements for such quantification in large scale. Ethanol has been promoted to a special class of product in the last decade due to its use as a renewable fuel for cars. However, it is of extreme importance to control the amount of water mixed in ethanol in order to avoid all sorts of erroneous possibilities regarding the indications for best performance of the engines. The results presented in this paper indicate the possibility of a new systematic setup to determine accurately the water content on water–ethanol solutions using photo-thermal techniques.

Water content in hydrated ethanol fuel measured by a photothermal chamber with a transparent transducer

Abstract A photothermal chamber with a transparent transducer and a 1450 nm laser were used to measure the water content of hydrated ethanol biofuel. The values of water content in the fuel samples assessed using the photothermal chamber were compared with reference values certified by Karl-Fischer titration. The results indicate good agreement between these two methodologies. Detection thresholds of 0.73 and 0.89 (% w/w) and sensitivity of 0.039 and 0.014 mV/(% w/w) were assessed at the laser powers of 340 and 125 mW, respectively. This study proves that the analytical approach based on the photothermal chamber with a transparent transducer is convenient to determine the water content in ethanol fuel because it is capable of providing reliable results in a quick and accurate way.

ITO/poly(aniline)/sol-gel glass: An optically transparent, pH-responsive substrate for supported lipid bilayers.

Described here is fabrication of a pH-sensitive, optically transparent transducer composed of a planar indium-tin oxide (ITO) electrode overcoated with a a poly(aniline) (PANI) thin film and a porous sol-gel layer. Adsorption of the PANI film renders the ITO electrode sensitive to pH, whereas the sol-gel spin-coated layer makes the upper surface compatible with fusion of phospholipid vesicles to form a planar supported lipid bilayer (PSLB). The response to changes in the pH of the buffer contacting the sol-gel/PANI/ITO electrode is pseudo-Nernstian with a slope of 52 mV/pH over a pH range of 4-9. Vesicle fusion forms a laterally continuous PSLB on the upper sol-gel surface that is fluid with a lateral lipid diffusion coefficient of 2.2 μm2/s measured by fluorescence recovery after photobleaching. Due to its lateral continuity and lack of defects, the PSLB blocks the pH response of the underlying electrode to changes in the pH of the overlying buffer. This architecture is simpler to fabricate than previously reported ITO electrodes derivatized for PSLB formation, and should be useful for optical monitoring of proton transport across supported membranes derivatized with ionophores and ion channels.

Quantification of water in ethanol using a photothermal transparent transducer

Ethanol with added water may be found during the process of assessing its physical and chemical properties. This addition can damage automotive vehicle engines and also may contribute to tax evasion. The present contribution describes a method based on a photothermal transparent transducer to determine the water content in ethanol. A chamber with a window of lithium tantalate coated with a thin layer of indium tin oxide was used, and a 1450-nm laser diode was employed as the excitation source. The results indicated a nearly linear response of the apparatus, as a function of the water content in water/ethanol solutions ranging from 0 to 100 (vol.%). The results for the dependency of the photothermal signal on the laser power and chopping frequency suggested that reliable results can be obtained using laser power and chopping rates above 100mW and 10Hz, respectively. The results reported here may be useful in the development of an alternative method that can provide real-time data on the water concentration in ethanol in a rapid, portable and unambiguous way, and that can be easily used in laboratory analyses or in gas stations.

Real-time calibration acoustic array

A method and apparatus for acoustic array calibration. A housing with an opening on one side contains the acoustic transducer element. An acoustically transparent window covers the opening in the housing. A separate piece of substantially acoustically transparent planar transducer film is positioned in front of each transducer element. This film monitors the acoustic energy transmitted by the transducer elements, or alternatively transmits energy to the transducer elements. The transducer film can also operate as an independent hydrophone. A method for calibrating acoustic arrays is also disclosed. The transducer film monitors the acoustic energy transmitted by each acoustic transducer. The level of transmitted acoustic energy is independently measured by external calibration equipment. The acoustic energy received by each transducer film is compared with that measured by the external equipment to determine a calibration factor for each transducer element. Further, the transducer film can be energized to send acoustic energy to the transducer elements. Again, the acoustic energy transmitted by the film and received by the transducer elements is compared to the energy transmitted by the external calibration equipment and received by the transducer elements to determine a calibration factor for each transducer element.

Multiple frequency steerable acoustic transducer

A multiple frequency acoustic transducer is constructed as a stacked confration of N groups of multi-layer transducer elements separated from one another by an electrical insulating material. Each multi-layer transducer element in an n-th one of the N groups has a layer of acoustically transparent electroacoustic transducer material whose thickness is determined by the n-th frequency of operation. Each multi-layer transducer element has opposing planar surfaces with electrically conductive material deposited thereon. For each multi-layer transducer element, the electrically conductive material is formed into parallel strips electrically isolated from one another on at least one of each element's opposing planar surfaces. The parallel strips associated with each multi-layer transducer element in any one of the n-th groups have a unique angular orientation in the n-th group.

Determination of Material Thermal Properties Using Photoacoustic Signals Detected by a Transparent Transducer

We demonstrated a new simultaneous determination technique for the thermal diffusivity and the thermal conductivity of a material using photoacoustic (PA) signals detected by a transparent transducer. The samples were illuminated by a pump beam directly or through the transducer, and these two kinds of PA signals were analyzed. It was shown theoretically that we cannot ignore the two effects of small optical absorption of the transducer and the thermal resistance between the sample and the transducer upon detection of PA signals from the viewpoint of quantitative evaluation. The thermal resistance was provided by a small air gap layer. The thermal properties of Si, InP and Ta were determined by this technique and these measured values were in good agreement with those in the literature.

Analysis of Pyroelectric Signal in Photoacoustic Spectroscopy Using a Transparent Transducer

It is shown that a pyroelectric signal from a transparent transducer, Z-cut LiNbO3, depends on the surface state of the measured sample, a Si wafer. The signal of the Si wafer with the native oxide deviates markedly from the normal pyroelectric signal. Also, we develop a three-dimensional theory of 1he transparent pyroelectric transducer method in photoacoustic spectroscopy (PAS). We discuss the cases in which the pump beam illuminates the sample not only directly, but also through the transducer. It is shown that the theoretical calculation results are in good agreement with the experimental data of both PA amplitude and phase signals of Si. This result indicates that the validity of our theoretical model is verified experimentally.

Influence of Piezoelectric and Pyroelectric Effects on Signal of PAS Using a Transparent Transducer

Photoacoustic spectroscopy (PAS) using a transparent transducer LiNbO3 detects not only thermoelastic waves but also thermal waves because LiNbO3 has pyroelectricity as well as piezoelectricity. Then, we investigated the influence of the piezoelectric and pyroelectric effects on PA signal theoretically and experimentally, using three kinds of transparent transducers, Y-, 128° rotated Y- and Z-cut LiNbO3's. It was found that the pyroelectric effect predominates over the signal of the transducer more than the piezoelectric effect when the incident direction of an excitation light was toward to the transducer.

Novel photoacoustic spectroscopy of semiconductor thin films by a transparent transducer: Pyroelectric and piezoelectric effects

We have studied the generation mechanism of photoacoustic (PA) signals in semiconductor thin films by means of a transparent LiNbO3 transducer both experimentally and theoretically. In the transparent transducer method, the PA signal was detected at the light-irradiated surface of the samples. The PA signal of the thin film directly attached to the transducer is mainly due to the pyroelectric effect, and the PA signal of the underlain substrate is the piezoelectric signal caused by sample bending. These results show that this method becomes a powerful tool for measuring optical and thermal properties of thin films on the substrate nondestructively.

Theoretical Analysis of Photoacoustic Signal on PAS Using a Transparent Transducer

We proposed a new theoretical model for photoacoustic spectroscopy (PAS) using a transparent transducer. Based on the Jackson and Amer model, this takes into account not only a very small air gap as thermal resistance between the sample and the transducer but also the transducer displacement due to its own temperature distribution. It is shown that the theoretical calculations based on our model are more consistent with the experimental data for both PA amplitude and phase signals of GaAs than the conventional model. From these results, the validity of our theoretical model is verified experimentally.

Evaluation of Amorphous Semiconductors by Photoacoustic Spectroscopy Using a Transparent Transducer

Optical properties of amorphous semiconductors were studied by photoacoustic (PA) spectroscopy using a transparent LiNbO3 transducer. The PA signal detected at the light-irradiated front surface of the sample has a large value and a good signal-to-noise ratio compared with that at the back surface. It is demonstrated that a light-induced change in the PA signal at the surface in thick samples and PA spectra of multilayered semiconductor films can be obtained using the transparent transducer.

Consideration on PA Signals of Multilayer Structure Measured by PAS Using Transparent Transducer

We measured the spectral dependence of photoacoustic(PA) signal for GaxIn1-xP/GaAs heterostructure by PA spectroscopy (PAS) using a transparent transducer, LiNbO3. Between two layers a sharp dip of PA signal was observed which corresponded to the absorption edge. We discussed the generation mechanism of this PA dip qualitatively and speculated that it was caused by the difference of thermal expansion coefficient between the two layers, that is, a bimetal effect. This indicates that the thermal expansion coefficient is important in the analysis of the PA signal of a multilayer structure.

透明トランスジューサを用いた光音響分光法（ＰＡＳ）による半導体の評価

This is a review of Photoacoustic (PAS) measurement using transparent transducer of semiconductor materials. This technique is very sensitive to detect a PA signal because the light is illuminated to the sample surface through a transparent piezoelectric transducer (LiNbO3) and the PA signal is detected directly from the transducer. In this review the generation mechanisms of PA amplitude and phase signals for layered semiconductor materials (GaInP/GaAs) are experimentally clarified. Then, a theoretical analysis of generation mechanism of PA signal is presented and the validity of the theory is clarified by the experimental results. Finally, the thermal conductivity of InP is estimated by using both the theory and the experiment.

Evaluation of Multilayer Structure and Depth Profile by PAS Using a Transparent Transducer

This paper concerns the experimental evaluation of optical properties of a multilayer semiconductor structure by PAS using a transparent transducer method. The sample is a GaxIn1-xP(1.8 µm)/GaAs (380 µm)/Si(530 µm). Optical absorption edges of this sample are evaluated from PA amplitude and phase signals. Between two layers a sharp dip of the PA signal is observed which corresponds to the absorption edge. Generation mechanism of the PA dip is discussed in comparison with the phase delay of two signals.