Fiber-optic multipoint laser-ultrasonic excitation transducer using coreless fibers

Multipoint Energy-Balanced Laser-Ultrasonic Transducer Based on a Thin-Cladding Fiber

This study proposes a novel multipoint transducer system by utilizing the single-mode-multimode-thin-cladding fiber (SMTC) structure. This structure leverages the disparity in mode field diameter between the multimode fiber (MMF) and thin-cladding fiber (TCF) to generate high-amplitude ultrasonic signals safely and efficiently. The fabricated transducer exhibits signal amplitudes 2-3-fold higher compared to conventional laser-ultrasonic transducers. Simulation analysis investigates the impact of the length of the MMF and the diameter of the TCF on coupling efficiency. The coupling efficiency of individual transducer units can be accurately controlled by adjusting the length of the MMF. A three-point energy-balanced laser-ultrasonic transducer system was achieved, with improved energy conversion efficiencies, and the optimal thickness of candle soot nanoparticles (CSNPs) is experimentally determined. Additionally, we carried out experiments to compare the performance of the proposed SMTC-based transducer system under different material conditions using two different photoacoustic materials: graphite-epoxy resin and candle soot nanoparticle-polydimethylsiloxane (CSNP-PDMS) composite. CSNPs, as a cost-effective and easy-to-prepare composite material, exhibit higher photoacoustic conversion efficiency compared to graphite-epoxy resin. The proposed system demonstrates the potential for applications in non-destructive testing techniques.

Single optical fiber based forward-viewing all-optical ultrasound self-transceiving probe

All-optical ultrasound probes with fully integrated ultrasound generation and detection functions demonstrate some unique advantages over traditional electroacoustic counterparts. However, due to the lack of an effective solution, the most commonly used method is to assemble two separate functional optical fibers together for ultrasound generation and detection, respectively. In this Letter, an innovative strategy, to the best of our knowledge, is developed to integrate the photoacoustic effect based ultrasound generation and the Fabry-Pérot (FP) interference based ultrasound detection structures together at the end of a single double clad optical fiber (DCF), so as to make a compact forward-viewing ultrasound self-transceiving probe (1-mm diameter). From the experiment results, the as-fabricated probe can generate an ultrasound signal with an amplitude of 2.36 MPa at 2.25 mm in the transmitting mode, and its peak frequency and -6-dB bandwidth are measured to be 10.64 MHz and 22.93 MHz, respectively. When being operated under the receiving mode, the probe has a detection sensitivity of 208.4 mV/MPa for ultrasound signals with the peak frequency of 8.24 MHz, and the noise equivalent pressure (NEP) is 76.8 kPa. In addition, the forward-viewing format ultrasound self-transceiving experiment is also performed and the pulse-echo signal varying with the transmission distance is successfully captured for the first time.

The effect of copper grain size on laser ultrasonic backscattered signal

Grain size has an essential influence on the serviceability of metallic materials. In this paper, a noncontact laser ultrasonic testing platform is built to study the effect of copper grain size on the laser ultrasonic backscattered signal. According to the correlation between grain size and ultrasonic wavelength, the ultrasonic scattering by copper grains in the experiment contains not only Rayleigh scattering but also the transition region from Rayleigh scattering to stochastic scattering. Using time-frequency analysis, the influence of copper grain size on the characteristic parameters of backscattering was explored, and a prediction model of grain size was established, which was compared with the prediction model based on the attenuation method to verify the accuracy of the backscattering model. The results show that the backscattered signal can adequately characterize the grain size information and laser ultrasonics is a method that can realize on-line detection of grain size.

Optical Fiber Sensors for Ultrasonic Structural Health Monitoring: A Review

Guided waves (GW) and acoustic emission (AE) -based structural health monitoring (SHM) have widespread applications in structures, as the monitoring of an entire structure is possible with a limited number of sensors. Optical fiber-based sensors offer several advantages, such as their low weight, small size, ability to be embedded, and immunity to electro-magnetic interference. Therefore, they have long been regarded as an ideal sensing solution for SHM. In this review, the different optical fiber technologies used for ultrasonic sensing are discussed in detail. Special attention has been given to the new developments in the use of FBG sensors for ultrasonic measurements, as they are the most promising and widely used of the sensors. The paper highlights the physics of the wave coupling to the optical fiber and explains the different phenomena such as directional sensitivity and directional coupling of the wave. Applications of the different sensors in real SHM applications have also been discussed. Finally, the review identifies the encouraging trends and future areas where the field is expected to develop.

Photoacoustic imaging with fiber optic technology: A review

Photoacoustic imaging (PAI) has achieved remarkable growth in the past few decades since it takes advantage of both optical and ultrasound (US) imaging. In order to better promote the wide clinical applications of PAI, many miniaturized and portable PAI systems have recently been proposed. Most of these systems utilize fiber optic technologies. Here, we overview the fiber optic technologies used in PAI. This paper discusses three different fiber optic technologies: fiber optic light transmission, fiber optic US transmission, and fiber optic US detection. These fiber optic technologies are analyzed in different PAI modalities including photoacoustic microscopy (PAM), photoacoustic computed tomography (PACT), and minimally invasive photoacoustic imaging (MIPAI).

Ultrasound beam steering using a fiber optic ultrasound phased array

In this Letter, a novel fiber optic ultrasound phased-array technology is proposed to solve the ultrasound beam steering problems for fiber optic ultrasound biomedical imaging. The ultrasound beam steering feasibility is explored and verified by our unique time-delay approach. A theoretical analysis is performed to predict the beam steering angle. Experiments have been performed to verify that the ultrasound beam is steered by using our approach. Four fiber optic ultrasound generators were fabricated and used to build the phased-array emitter. The successful accomplishment of this project established a foundation of the prototype of the fiber optic ultrasound imaging transducer.