Low‐frequency detection of acoustic signals using fiber as an ultrasonic guide with a distant in‐fiber Bragg grating

Abstract

This article shows the development of a photonic detector of low-frequency ultrasonic signals. These signals latter reach a sensitive single-mode optical fiber as an acoustic guide conveying the signals (around 43 kHz) over 70 cm to a distant and protected in-fiber Bragg grating. The grating reflects a spectrum centered around 1550 and 2.6 nm bandwidth and is interrogated by a tunable laser in their linear and most sensitive region. As a result, real-time passive demodulation of communication or monitoring of ultrasonic signals propagating through solid materials is possible. The detector may also be applied to other physical media. In this study, a new passive technique to thermally desensitize the fiber-Bragg gratings (FBG) is also proposed, though the proposed technique is not experimentally tested. K E Y W O R D S acoustic communications, acoustic guide, acoustic monitoring, fiber Bragg grating, optical fiber, ultrasound AbstractThis article presents a novel multi-band rectifier utilizing modified hybrid structure for radio frequency (RF) energy harvesting. The proposed multi-band rectifier consists of a modified hybrid junction and three rectifying branches. The rectifying branches are placed inside the modified hybrid to reduce the layout size. The proposed multi-band rectifier is designed for GSM-1800, UMTS-2100, and Wi-Fi bands. Measured peak efficiency of the proposed rectifier reaches 61.7% at 9 dBm input power level. The results show a good overall performance on operation bands, LI ET AL. | 817

The effects of scaling and bends in a fiber‐optic modalmetric acoustic detector

“…The modalmetric detector is easy to fabricate, straightforward to operate, and does not require any spectral alignment, as generally FBG sensors do this. 24 It is likely that the thermal fluctuations of a long length 12,14 s-MMF limit the sensitivity of the modalmetric detector, that is, "the noise level due to the thermally induced length fluctuations may overcame any sensitivity increases". 12 We could not find in the literature any report of the limitation on the sensitivity of a modalmetric detector due to thermal noise generated by the sensitive fiber.…”

High linear sensitivity humidity and temperature sensing based on chiral long-period fiber grating

“…(2) Attach a weight to one end of the fiber and fix the other end to the stepper motor so that it is always vertical and rotates at a constant speed. (3) The voltage between the needle and the collector was set to 18.5 kV and the injector was driven to advance at 0.0015 mm∕s, and the speed time of the drive affected the thickness of the film.…”

Partial Discharge Ultrasound Detection Using the Sagnac Interferometer System

“…With the increase of discharge, the ultrasonic spectrum moves to a low frequency. In the needle plate PD model, the relationship between the three characteristic quantities and the discharge volume q is as follows [ 44 ] where A represents the magnitude of the ultrasonic amplitude, q represents the discharge quantity, F represents the ultrasonic frequency, and T represents the signal duration time [ 35 ].…”

“…The influence of various sensing probes on the characteristics of PD detection were innovatively studied. Compared with other point-like ultrasonic sensors such as FBG [ 34 , 35 ], the first advantage of this proposed optical fiber sensing probe consisting of a fiber coil is the ability of long distance detection while the FBG sensor is limited by the optical power attenuation existing in the transmission gratings, whose function is similar to a bandpass filter [ 36 , 37 ]. Secondly, the fiber coil is easy to implement and can be modified according to different field environments, which makes it suitable for field tests and applications.…”