This paper presents the design, fabrication and testing of a diaphragm-based, all-silica fiber tip pressure sensor. A piece of 1.2-μm thick silica diaphragm was thermally bonded to the end face of an etched fiber with an outer diameter (OD) of 125 μm to form a Fabry-Perot (FP) interferometer. The diameter of the etched FP cavity is 105 μm, enabling the sensing area to be large, and thus a static pressure sensitivity of 12.4 nm/kPa (85.3 nm/psi) is accomplished with no need of any post polishing or etching. The sensor also shows a low temperature cross sensitivity during tests, owing to its all-silica structure. It is suitable for extensive production and it has a great potential to work in applications where miniature size and high sensitivity are essential, such as medical applications.

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.

This paper presents the design, fabrication, and characterization of a novel fiber optic ultrasonic sensing system based on the photoacoustic (PA) ultrasound generation principle and Fabry-Perot interferometer principle for high temperature monitoring applications. The velocity of a sound wave traveling in a medium is proportional to the medium’s temperature. The fiber optic ultrasonic sensing system was applied to measure the change of the velocity of sound. 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. Two tests were performed. The system verification test proves the ultrasound sensing capability. The high temperature test validates the high temperature measurement capability. The sensing system survived 700 °C. It successfully detects the ultrasonic signal and got the temperature measurements. The test results agreed with the reference sensor data. Two potential industry applications of fiber optic ultrasonic sensing system are, it could serve as an acoustic pyrometer for temperature field monitoring in an industrial combustion facility, and it could be used for exhaust gas temperature monitoring for a turbine engine.

Radiofrequency ablation (RFA) is a clinical technique which inactivates targeted biological tissues by heating to remove tumors or to cure diseases like atrial fibrillation. Temperature is a fundamental parameter for ablation dose control and treatment effect evaluation. This paper presents the design, fabrication and characterization of an all-optical fiber ultrasound temperature measurement probe. The novelty of this probe is to both generate and receive ultrasound optically through fibers. The ultrasound generation was achieved with a 425 μm multi-mode fiber based on photoacoustic (PA) principle and the receiving part applied a 125 μm single mode fiber with a Fabry–Pérot (FP) interferometer on its tip. The temperature was measured through detecting the time-of-flight (TOF) of the reflected ultrasound pulses. The probe’s feasibility of measuring temperature during ablation had been verified in vitro while excised bovine liver tissue was used as the ultrasound reflector.

A fiber optic pressure sensor that can survive 2200 psi and 140 °C was developed. The sensor’s pressure sensitivity was measured to be 14 times higher than bare FBG when tested inside stacks of ultra-high-molecular-weight polyethylene (UHMWPE) composite fabric. The sensitivity can be further improved 6-fold through the Vernier effect. Its tiny sensing length (hundreds of microns) and uniform outer diameter (125 µm) make it a suitable candidate for real-time point pressure monitoring under harsh environments with limited space, such as in composite-forming procedures.

This letter presents a fiber optic acoustic pyrometer for temperature monitoring in an exhaust pipe of an industrial scale combustion test facility. The acoustic pyrometer consists of a fiber optic acoustic generator and a Fabry-Pérot (FP) fiber sensor receiver. The proposed acoustic pyrometer was tested and verified at an exhaust pipe over the Industry Scale Burner Facility (ISBF) at GE's Clean Energy Center, at a temperature of 320 °C. Further research on such fiber optic acoustic pyrometers will advance the study of 2D/3D temperature distribution reconstruction in industrial combustion facilities.