Jingcheng Zhou

All-Optical Photoacoustic Sensors for Steel Rebar Corrosion Monitoring

This article presents an application of an active all-optical photoacoustic sensing system with four elements for steel rebar corrosion monitoring. The sensor utilized a photoacoustic mechanism of gold nanocomposites to generate 8 MHz broadband ultrasound pulses in 0.4 mm compact space. A nanosecond 532 nm pulsed laser and 400 μm multimode fiber were employed to incite an ultrasound reaction. The fiber Bragg gratings were used as distributed ultrasound detectors. Accelerated corrosion testing was applied to four sections of a single steel rebar with four different corrosion degrees. Our results demonstrated that the mass loss of steel rebar displayed an exponential growth with ultrasound frequency shifts. The sensitivity of the sensing system was such that 0.175 MHz central frequency reduction corresponded to 0.02 g mass loss of steel rebar corrosion. It was proved that the all-optical photoacoustic sensing system can actively evaluate the corrosion of steel rebar via ultrasound spectrum. This multipoint all-optical photoacoustic method is promising for embedment into a concrete structure for distributed corrosion monitoring.

Ultrasound generation from an optical fiber sidewall

Ultrasound generation from an optical fiber, based on the photoacoustic principle, could have broad applications, such as ultrasound nondestructive test (NDT) and biomedical ultrasound imaging. There are many advantages of these fiber-optic ultrasonic transducers, such as small size, light weight, ease of use, and immunity to electromagnetic interference. This paper will demonstrate a novel structure which the ultrasound signal is generated on the sidewall of the fiber. Two experimental configurations of the fiber-optic sidewall ultrasonic transducer are discussed. One is that a photoacoustic material is directly coated on the sidewall of the optical fiber. The other one is that the photoacoustic material is directly coated on an aluminum plate and the sidewall fiber is buried in the material. By using this novel sidewall ultrasound generator, we can effectively generate ultrasound signal at multiple, particular locations along one fiber.

High temperature monitoring using a novel fiber optic ultrasonic sensing system

This paper presents a novel fiber optic ultrasonic sensing system to measure high temperature in the air. Traveling velocity of sound in a medium is proportional to medium’s temperature. The fiber optic ultrasonic sensing system was applied to measure the change of sound velocity. A fiber optic ultrasonic generator and a Fabry-Perot fiber sensor were used as the signal generator and receiver, respectively. A carbon black- Polydimethylsiloxane (PDMS) material was utilized as the photoacoustic material for the fiber optic ultrasonic generator. A water cooling system was applied to cool down the photoacoustic material. A test was performed at lab furnace environment (up to 700 ℃). The sensing system survived 700℃. It successfully detect the ultrasonic signal and got the temperature measurements. The test results agreed with the reference sensor data. The paper validated the high temperature measurement capability of the novel fiber optic ultrasonic sensing system. The fiber optic ultrasonic sensing system could have broad applications. One example is that it could serve as acoustic pyrometers for 3D temperature distribution reconstruction in an industrial combustion facility

Characterization of ultrasonic generation from a fiber-optic sidewall

This paper presents a characterization of ultrasonic generation from the sidewall of an optical fiber. Ultrasonic generation from an optical fiber could have broad applications, such as ultrasonic imaging, ultrasonic nondestructive test (NDT), and acoustic pyrometers and so on. There are many advantages of these fiber-optic ultrasonic transducers, such as small size, light weight, ease of use, and immunity to electromagnetic interference. This paper discusses two main factors that will influence the signal strength generated by the sidewall of the ultrasonic generator. The two factors are the thickness of the photoabsorption material and the optical energy emitted from the sidewall fiber. A 20 mm length fiber-optic sidewall ultrasonic generator was used for the characterization. Gold-nanocomposite materials were used as the photoabsorption material. A hydrophone was used to detect the ultrasonic signal. The ultrasonic time and frequency profile and the ultrasonic field distribution at the longitudinal section of this fiber-optic sidewall ultrasonic generator have been characterized in this paper.

All-optically driven system in ultrasonic wave-based structural health monitoring

Ultrasonic wave based structural health monitoring (SHM) is an innovative method for nondestructive detection and an area of growing interest. This is due to high demands for wireless detection in the field of structural engineering. Through optically exciting and detecting ultrasonic waves, electrical wire connections can be avoided, and non-contact SHM can be achieved. With the combination of piezoelectric transducer (PZT) (which possesses high heat resistance) and the noncontact detection, this system has a broad range of applications, even in extreme conditions. This paper reports an all-optically driven SHM system. The resonant frequencies of the PZT transducers are sensitive to a variety of structural damages. Experimental results have verified the feasibility of the all-optically driven SHM system.

Ultrasonic temperature measurements with fiber optic system

Ultrasonic temperature measurements have been developed and widely applied in non-contact temperature tests in many industries. However, using optical fibers to build ultrasound generators are novel. This paper reports this new fiber optic ultrasonic system based on the generator of gold nanoparticles/polydimethylsiloxane (PDMS) composites. The optical acoustic system was designed to test the change of temperature on the aluminum plate and the temperature of the torch in the air. This paper explores the relationship between the ultrasonic transmission and the change of temperature. From the experimental results, the trend of ultrasonic speed was different in the aluminum plate and air with the change of temperature. Since the system can measure the average temperature of the transmission path, it will have significant influence on simulating the temperature distribution.

Ultrasonic transmission from fiber optic generators on steel plate

Fiber optic acoustic generators have generated a lot of interest due to its great potential in many applications including nondestructive tests. This paper reports four acoustic generation configurations. All the configurations are based on gold nanoparticles/polydimethylsiloxane (PDMS) composites. Since gold nanoparticles have high absorption efficiency to optical energy and PDMS has a high coefficient of thermal expansion, the composites can transfer optical energy to ultrasonic waves with high conversion efficiency. The strength and bandwidth of ultrasonic waves generated by the composites can be changed by different designs and structures of the composites. This paper explores the relation between the structure of fiber optic acoustic generators and the profile of generated ultrasonic waves. Experimental results also demonstrated that four ultrasonic generation configurations have similar features of ultrasonic transmission on a steel plate, which is important for future choices of ultrasonic receivers.