Sienting Lau

High-Frequency Ultrasonic Hydrophone Based on a Cladding-Etched DBR Fiber Laser

Distributed-Bragg-reflector (DBR) fiber-laser-based ultrasonic hydrophone has been found to possess increased detectable frequency range due to the improved sensitivity in the high-frequency region when the fiber cladding thickness was reduced. A wet etching technique is utilized to reduce the fiber diameter of the DBR laser. The peak response frequency moves from 21 to 40 MHz when the fiber diameter was reduced from 125 to 68 m.

PMN-PT single crystal thick films on silicon substrate for high-frequency micromachined ultrasonic transducers

In this work, a novel high-frequency ultrasonic transducer structure is realized by using PMNPT-on-silicon technology and silicon micromachining. To prepare the single crystalline PMNPT-on-silicon wafers, a hybrid processing method involving wafer bonding, mechanical lapping and wet chemical thinning is successfully developed. The active element is fixed within the stainless steel needle housing. The measured center frequency and -6 dB bandwidth of the transducer are 35 MHz and 34%, respectively. Owing to the excellent electromechanical property of PMNPT film, the transducer shows good energy conversion performance with a very low insertion loss down to 8.3 dB at the center frequency.

Characterization of a 40-MHz focused transducer with a fiber grating laser hydrophone

A novel fiber-optic hydrophone based on a dual-polarization, short-cavity fiber grating laser as the sensing element is described. Wet chemical etching was used to fabricate a thinned fiber sensor to extend its frequency response as well as spatial resolution. The lateral beam profile at the focal plane of a 40-MHz lens-focused lithium niobate (LiNbO3) transducer was measured with the fiber sensor, and a tomographic technique was used to compute the transducer profile, which is compared with that obtained by a PVDF hydrophone. The fiber hydrophone has a sensitivity of approximately -259 dB re 1 V/muPa up to 40 MHz, which is higher than that of a commercial PVDF hydrophone. Moreover, it is capable of accurately characterizing the beam generated by high-frequency transducer.

Fiber grating laser hydrophone

We demonstrate a fiber grating laser hydrophone that can measures ultrasound and temperature simultaneously. It can detect ultrasound with frequency up to 40 MHz and has advantage of ease of demodulation.

Characterization of a fibre grating laser-based hydrophone for detection of high frequency medical ultrasound : A comparison with PVDF membrane hydrophone

An ultrasonic hydrophone with a dual polarization distributed Bragg reflector (DBR) fibre laser as the sensing element is described, and its application to the characterization of high frequency ultrasonic field is demonstrated. The principle of the hydrophone is based on the detection of ultrasonically modulated birefringence of the fibre laser output. The generated upper and lower sideband frequency components can be used to determine the frequency and amplitude of the ultrasonic field. It has been found that the performance of the fibre grating laser-based hydrophone, including linearity, sensitivity and frequency response, compares favorably with that of commercial PVDF membrane hydrophone. It suggests that this type of hydrophone can provide a practical alternative to piezoelectric hydrophone technology.

PZT/P(VF/TrFE) nanocomposite hydrophones for ultrasonic measurements

Needle-type hydrophones for the calibration of medical ultrasonic transducers have been fabricated using lead zirconate titanate/vinylidene fluoride-trifluoroethylene [PZT/P(VDF-TrFE)] 0-3 nanocomposite films. The 0-3 nanocomposite film has been prepared by incorporating nanosized PZT powder (derived from a sol-gel process) in a P(VDF-TrFE) matrix. Since the piezoelectric coefficients of PZT and P(VDF-TrFE) have opposite signs, the PZT and P(VDF-TrFE) phases in the nanocomposites have been poled in opposite directions in order to give enhanced piezoelectric activity. A nanocomposite hydrophone with 0.2 volume fraction of PZT has been characterized and found to be more sensitive than a P(VDF-TrFE) hydrophone of similar structure.

High-frequency ultrasound measurement using fiber grating laser hydrophone

A fiber laser hydrophone system for measuring tone-burst ultrasonic signals up to 40 MHz is developed. The hydrophone consists of a cladding-etched dual polarization distributed Bragg reflector (DBR) fiber laser. The sensing mechanism is based on the modulation of the fiber lasers birefringence induced by the ultrasonic pressure. The ultrasonic signal waveform is demodulated using an FM-DEM (frequency modulation-demodulation) circuit and measured with a digital oscilloscope. Incorporating the time delay measurement of ultrasonic signal, this fiber laser hydrophone system achieves a spatial resolution of 37.5 μm at 40 MHz.