Ultrasound generation from an optical fiber, based on the photoacoustic principle, is a promising approach to many ultrasonic applications, specifically those requiring wide bandwidth and compact size in order to achieve high resolution as well as the capability of being operated in limited space. A fiber-optic ultrasound generator using gold nanopores is reported. The gold nanopores, having high absorption efficiency, were fabricated using a focused ion beam (FIB) on the fiber endface, which was excited by a nanosecond laser in order to generate ultrasound signals via the photoacoustic principle. Experimental results demonstrate that these wide bandwidth ultrasound signals can be generated by this compact fiber-optic ultrasound generator fabricated using a FIB.
This paper presents a nondestructive ultrasound test method for characterizing resonant frequencies of
polydimethylsiloxane (PDMS) thin films by using a miniature fiber optic photoacoustic (PA) probe. The PA probe was
fabricated with an optical fiber and the synthesized gold nanocomposite. During the experiment, a PDMS film with
thickness of 25 μm was cured and immersed into water media within a designed holder to clamp the film. An acoustic pulse was generated from the PA probe, propagated in the water media and excited the clamped film. A fiber optic pressure sensor based on Fabry-Perot (FP) principle was applied to collect excited acoustic signals on the other side of the film. The sensed response of the acoustic pulse was used to compute the resonant frequencies of the PDMS thin film based on de-convolution method.
Ultrasound generation on optical fiber based on photoacoustic principle is a promising approach for many advanced
ultrasonic applications, which require wide bandwidth and compact size in order to achieve high resolution as well as the capability of being operated in limited space. This paper reports a fiber optic photoacoustic ultrasound generator using gold nanopattern. The gold nanopattern with high absorption efficiency was fabricated using focused ion beam (FIB) on the fiber endface, which was excited by a nanosecond laser to generate ultrasound signals via the photoacoustic principle. Experimental results demonstrated that ultrasound signals can be generated by this approach and the fiber optic ultrasound generator can be used in the advanced ultrasonic applications.
Recently, many advanced ultrasound applications require wide bandwidth and compact ultrasound generators to achieve better resolution as well as the capability of being operated in a compact space. Generating ultrasound signals through photoacoustic principle is a promising way to generate wide bandwidth ultrasound signals by the optical approach. Meanwhile, optical fibers are ideal candidates for applications where compact size is required. Therefore, fiber optic photoacoustic generators, which put advantages of the photoacoustic principle and optical fibers together, lead to novel ultrasound generation devices which can meet the most advanced ultrasound applications requirements. This paper firstly reports using the gold nanocomposite to achieve the fiber optic photoacoustic ultrasound generator. The gold nanocomposite was synthesized by directly mixing the gold salt in polydimethylsiloxane. The gold nanocomposite showed high optical energy absorption capability and the high coefficient of thermal expansion. The photoacoustic generation efficiency was increased by applying such material. The synthesis protocol of the gold nanocomposite was presented in this paper. The optical fiber was coated with the gold nanocomposite to generate ultrasound signals. Experimental results have demonstrated that ultrasound signals can be generated by this approach and the fiber optic ultrasound generator can be used in ultrasound applications.
This paper presents a miniature fiber optic temperature sensor and its application in concrete structural health
monitoring. The temperature sensor is based on Fabry-Perot (FP) principle. The endface of the fiber was wet etched. A
piece of borosilicate glass was thermally deposited into the cavity on the etched endface to form an FP cavity.
Temperature calibration experiments were performed. A sensor with 30 μm microcavity length was demonstrated to
have a sensitivity of 0.006 nm/°C and linearity coefficient of 0.99. During the early-age of concreting, the sensor was
embedded in the concrete structure to monitor the temperature change caused by the exothermic chemical reaction
between the cement and water. The dramatically increased temperature inside the structure was directly related to its
future structural health. During the concrete hydration experiment, the measured peak temperature of concrete specimens
was 59.7 °C 12.5 hour after concrete casting.
Recently, many studies have been exerted on developing ultrasonic transducers that can feature high frequencies for
better resolutions and compact sizes for the limit space nondestructive testing applications. Conventional ultrasonic
transducers, which are made by piezoelectric materials, suffer from issues such as low frequencies and bulky sizes due to
the difficulty of dicing piezoelectric materials into smaller pieces. On the other hand, generating ultrasonic signals by
photoacoustic principle is a promising way to generate a high frequency ultrasonic pulse. Optical fiber is a very compact
material that can carry the light energy. By combining the photoacoustic principle and the optical fiber together, a novel
ultrasonic transducer that features a high frequency and a compact size could be achieved. In this paper, an ultrasonic
transducer using gold nanoparticles as the photoacoustic generation material is described. Gold nanoparticles are
deposited on the end surface of an optical fiber acting as the ultrasonic generator. A cavity and a diaphragm are
fabricated in the center of the fiber using as the ultrasonic receiver. A phase array technique is applied to the transducer
to steer the direction of the acoustic beam. Simulation results demonstrated that the photoacoustic ultrasonic transducer
Traumatic brain injury (TBI, also called intracranial injury) is a high potential threat to our soldiers. A helmet structural
health monitoring system can be effectively used to study the effects of ballistic/blast events on the helmet and human
skull to prevent soldiers from TBI. However, one of the biggest challenges lies in that the pressure sensor installed inside
the helmet system must be fast enough to capture the blast wave during the transient period. In this paper, an ultrafast
optical fiber sensor is presented to measure the blast signal. The sensor is based on a Fabry-Pérot (FP) interferometeric
principle. An FP cavity is built between the endface of an etched optical fiber tip and the silica thin diaphragm attached
on the end of a multimode optical fiber. The sensor is small enough to be installed in different locations of a helmet to
measure blast pressure simultaneously. Several groups of tests regarding multi-layer blast events were conducted to
evaluate the sensors' performance. The sensors were mounted in different segments of a shock tube side by side with the
reference sensors, to measure a rapidly increasing pressure. The segments of the shock tube were filled with different
media. The results demonstrated that our sensors' responses agreed well with those from the electrical reference sensors.
In addition, the home-made shock tube could provide a good resource to study the propagation of blast event in different
Fractional flow reserve (FFR) has proven to be very useful in diagnosis of narrowed coronary arteries. It is a technique
that is used in coronary catheterization to measure blood pressure difference across a coronary artery stenosis in maximal
flow. In-vivo blood pressure measurement is critical in FFR diagnosis. This paper presents a novel miniature all-optical
fiber blood pressure sensor. It is based on Fabry-Perot (FP) interferometry principle. The FP cavity was fabricated by
directly wet etching the fiber tip. Then, a diaphragm with well-controlled thickness was bonded to the end face of the
fiber using the thermal bonding technique. Finally, the sensor was packaged with a bio-compatible and flexible coil for
animal tests. A 25-50 kg Yorkshire swine model was introduced as the animal test target. The left anterior descending
coronary artery (LAD) was exposed, and beyond the takeoff of the largest diagonal branch, a 3.0 mm vascular occluder
was secured. Firstly, standard invasive manometry was used to obtain the blood pressure as baseline. Next, a guiding
catheter was introduced into the ostium of the left main coronary artery, and the miniature blood pressure sensor was
advanced into the LAD at a point beyond the vascular occlude. The blood pressure beyond the vascular occlude was
recorded. The sensor successfully recorded the blood pressure at both near-end and far-end of the vascular occluder.
An optical fiber biosensor featuring miniaturization, electromagnetic interference (EMI)-immunity, and flexibility is
presented. The sensor was fabricated by aligning two gold-deposited optical single-mode fiber facets inside V-grooves
on a silicon chip to form a Fabry-Perot (FP) cavity. The mirrors on the fiber facets were made of deposited gold (Au)
films, which provided a high finesse to produce a highly sensitivity. Microelectromechanical systems (MEMS)
fabrication techniques were used to precisely control the profile and angle of the V-grooves on the silicon. The biotin-terminated
thiol molecule was firstly immobilized on the gold surface. Subsequently, the molecules of Neutravidin were
specifically bound to the biotin-terminated self-assembled monolayers (SAMs). The induced changes of cavity length
and refractive index (RI) upon the gold surface lead to an optical path difference (OPD) of the FP cavity, which was
detected by demodulating the transmission spectrum phase shift. By taking advantage of MEMS techniques, multiple
biosensors can be integrated into one small silicon chip for detecting various biomolecule targets simultaneously.
The adaptive neural network is a standard technique used in nonlinear system estimation and learning applications for
dynamic models. In this paper, we introduced an adaptive sensor fusion algorithm for a helmet structure health
monitoring system. The helmet structure health monitoring system is used to study the effects of ballistic/blast events on
the helmet and human skull. Installed inside the helmet system, there is an optical fiber pressure sensors array. After
implementing the adaptive estimation algorithm into helmet system, a dynamic model for the sensor array has been
developed. The dynamic response characteristics of the sensor network are estimated from the pressure data by applying
an adaptive control algorithm using artificial neural network. With the estimated parameters and position data from the
dynamic model, the pressure distribution of the whole helmet can be calculated following the Bazier Surface
interpolation method. The distribution pattern inside the helmet will be very helpful for improving helmet design to
provide better protection to soldiers from head injuries.