Conventional Piezoelectric Sensors Research Articles

Loosening Monitoring of Bolted Joints Using Optical Fiber Bending Sensor for Aircraft Lug Assembly

Bolted joints of aircraft lug assembly play an important role in connecting the wing and fuselage of an aircraft structure. Generally, the bolted joints get loosened because they are frequently exposed to the dynamic loads induced when an aircraft is in service. For this reason, it is important to monitor the condition of the bolted joints to avoid any critical defect that will lead to any risk in human life. However, it is difficult to conduct the bolted joints’ loosening inspection by an operator. In past few decades, optical fiber based sensor has been widely used due to its advancement over a conventional piezoelectric (PZT) sensor, especially due to its small size and light weight. With regard to this, a loosening monitoring of bolted joints using optical fiber bending sensor for aircraft lug assembly is proposed in this paper. The lug assembly specimen, which consists of a stainless steel lug, CFRP/Nomex honeycomb sandwich panel, carbon-steel bolt, nut and washer, and the monitoring system, which consists of a single mode fiber with ten optical fiber bending sensor nodes and an Optical Time-domain Reflectometer (OTDR) were used to determine the bolt loosening at every 1 degree interval.

Strain measurement on stiff structures: experimental evaluation of three integrated measurement principles

This paper presents an experimental evaluation of three different strain measuring principles. Mounted on a steel beam resembling a car engine mount, metal foil strain gauges, piezoresistive silicon strain gauges and piezoelectric patches are investigated to measure structure-borne forces to control an active mounting structure. FEA simulation determines strains to be measured in the range of 10−8 up to 10−5 m × m−1. These low strains cannot be measured with conventional metal foil strain gauges, as shown in the experiment conducted. Both piezoresistive and piezoelectric gauges show good results compared to a conventional piezoelectric force sensor. Depending on bandwidth, overload capacity and primary electronic costs, these principles seem to be worth considering in an adaptronic system design. These parameters are described in detail for the principles investigated.

Acoustic emission measurement using a strain-insensitive fiber Bragg grating sensor under varying load conditions

Acoustic emission (AE) during a pressure test of a carbon fiber-reinforced plastic tank was measured using a fiber Bragg grating (FBG) sensor and, for comparison, using a conventional piezoelectric sensor. The FBG-inscribed optical fiber was used not only as an optical transmission line but also as an ultrasonic transmission line. The FBG sensor showed resonant characteristics and could detect AE continuously during the test. AE detected with the FBG sensor exhibited a cumulative behavior similar to that detected with the piezoelectric sensor. The FBG sensor was demonstrated to have comparable AE detection capability to piezoelectric sensors.

Acoustic-wave-mode separation using a distributed Bragg grating sensor

This paper reports on the measurement and modal decomposition of structural plate wavesusing a single optical fibre sensor comprising an array of uniformly distributedBragg gratings. Following a brief description of the design and fabrication of thesensor, numerical and experimental work is shown to demonstrate the fidelity ofdynamic strain measurements furnished by the sensor at frequencies in excess of200 kHz. The capacity of the sensor to provide a spatially resolved acoustic measurementrepresents an important advancement over conventional piezoelectric sensors as it allows forthe decomposition of an elastic wave field into its constituent modes. This provides apotentially powerful diagnostic framework for structural health monitoring using guidedwaves. Experimental work on a metallic plate is presented to demonstrate the use ofwave-mode conversion as a basis for the detection of structural damage, and itsinsensitivity to environmental effects.

Investigation of fatigue crack in stainless steel using a mobile fiber Bragg grating ultrasonic sensor

A mobile fiber Bragg grating (FBG) sensor was applied to detect a closed fatigue crack in 18Cr–8Ni stainless steel by ultrasonic pitch–catch method. Response to ultrasound that crossed fatigue crack showed a time delay compared with the reference response in intact area. Conventional piezoelectric sensors were applied to the similar experiment and the response signal was compared with that detected with the FBG sensor. Experimental results showed that FBG sensors could determine the location of crack tip more precisely than piezoelectric sensors.

連続計測されたレーザAE波形の時間周波数解析によるノイズ低減

A laser AE method is non-contact measurement of AE by using laser interferometer sensor. However, the sensitivity of laser interferometer is lower than conventional piezoelectric sensor. In this study, a method to improve signal-to-noise ratio of the output waveform of interferometer is investigated. A new system was developed to record and analyze the waveform continuously. Continuous waveform was transformed into time-frequency-magnitude data by short time Fourier transform (STFT) or wavelet transform. After noise component in this time-frequency-magnitude data is cut, inverse STFT or WT is applied to obtain clear AE signals in time domain. Simulated AE signal generated by thermal stress of YAG laser pulse was analyzed and detection capability of AE event was improved compared to the conventional signal processing method.

Ultrasound and damage detection in CFRP using fiber Bragg grating sensors

Ultrasound detection using fiber Bragg gratings (FBGs) and its application to damage detection were investigated. Two types of FBG ultrasonic sensing system were constructed using different light source: a broadband light source and a tunable laser source. Ultrasonic waves generated with a piezoelectric transducer were propagated through a cross-ply CFRP and were detected by the FBG sensing systems at several ultrasonic source-sensor intervals. Furthermore, the FBG sensing systems were applied to ultrasonic inspection of an impact damaged cross-ply CFRP in order to examine their capability for damage detection. Both FBG sensing systems produced better detection of the damage in the composite than piezoelectric sensors. The FBG ultrasonic sensing system including a tunable laser possessed high sensitivity to ultrasonic wave and proved to be an alternative to conventional piezoelectric sensors in ultrasonic inspection of structural composite materials.

A low-frequency micromechanical resonant vibration sensor for wear monitoring

A micromechanical resonant vibration sensor (MRVS) is presented with a geometrical structure that is designed for the detection of vibrations in the low-frequency range. The MRVS is distinguished from conventional piezoelectric and micromechanical acceleration sensors by the utilization of the resonance effect. The signal-to-noise ratio increases significantly when the sensor is excited with the designed frequencies. The vibrational properties of the MRVS have been investigated in the laboratory. Examples of the sensor response to different vibrational sources are analysed under industrial conditions. The capability of the sensor principle for wear monitoring is discussed.

Smart Vibration Sensor Using Giant Magnetostrictive Materials.

A magnetostrictive vibration sensor has several advantages over conventional piezoelectric sensors. First, due to the high impedance output signal, piezoelectric sensors require a charge to voltage converter and a power supply to process the signal. In the case of the magnetostrictive sensors, the output signal is already a low impedance voltage which can be analyzed directly. A second advantage is its structural simplicity. The sensor can be easily assembled or disassembled. A third advantage of the magnetostrictive vibration sensor can be attributed to the high Curie temperature of magnetostrictive materials, which stands at 380°C as compared to 180°C for a typical piezoelectric material. This study presents a novel application of giant magnetostrictive material to a three-dimensional vibration sensor. The sensor is called three-dimensional because it is intended to measure a vibration exerted along an arbitrary direction. Sensor signals are measured for various directions of vibration based on which the identification of unknown vibration is attempted. A neural network is employed to learn the observed data. The generalization of the trained network is tested on unknown vibrations.

Noninvasive detection of cardiovascular pulsations by optical Doppler techniques

A system has been developed based on the measurement of skin surface vibration that can be used to detect the underlying vascular wall motion of superficial arteries and the chest wall. Data obtained from tissue phantoms suggested that the detected signals were related to intravascular pressure, an important clinical and physiological parameter. Unlike the conventional optical Doppler techniques that have been used to measure blood perfusion in skin layers and blood flow within superficial arteries, the present system was optimized to pick up skin vibrations. An optical interferometer with a 633-nm He:Ne laser was utilized to detect micrometer displacements of the skin surface. Motion velocity profiles of the skin surface near each superficial artery and auscultation points on a chest for the two heart valve sounds exhibited distinctive profiles. The theoretical and experimental results demonstrated that the system detected the velocity of skin movement, which is related to the time derivative of the pressure. The system also reduces the loading effect on the pulsation signals and heart sounds produced by the conventional piezoelectric vibration sensors. The system's sensitivity, which could be optimized further, was 366.2 mm/s for the present research. Overall, optical cardiovascular vibrometry has the potential to become a simple noninvasive approach to cardiovascular screening.

Noninvasive detection of cardiovascular pulsations by optical Doppler techniques

A system has been developed based on the measurement of skin surface vibration that can be used to detect the underlying vascular wall motion of superficial arteries and the chest wall. Data obtained from tissue phantoms suggested that the detected signals were related to intravascular pressure, an important clinical and physiological parameter. Unlike the conventional optical Doppler techniques that have been used to measure blood perfusion in skin layers and blood flow within superficial arteries, the present system was optimized to pick up skin vibrations. An optical interferometer with a 633-nm He:Ne laser was utilized to detect micrometer displacements of the skin surface. Motion velocity profiles of the skin surface near each superficial artery and auscultation points on a chest for the two heart valve sounds exhibited distinctive profiles. The theoretical and experimental results demonstrated that the system detected the velocity of skin movement, which is related to the time derivative of the pressure. The system also reduces the loading effect on the pulsation signals and heart sounds produced by the conventional piezoelectric vibration sensors. The system’s sensitivity, which could be optimized further, was 366.2 mm/s for the present research. Overall, optical cardiovascular vibrometry has the potential to become a simple noninvasive approach to cardiovascular screening. © 1997 Society of Photo-Optical Instrumentation Engineers. [S1083-3668(97)00604-7]

Assessment of Tool Wear in Milling Using Acoustic Emission Detected by a Fiber-Optic Interferometer

Acoustic emission (AE) has previously been shown to be a useful technique in monitoring the state of wear of cutting tools. The piezo-electric transducers conventionally used for AE detection are contacting devices with a limited bandwidth. This paper describes the use of a robust fiber optic interferometer for the in-process measurement of AE during the face milling of annealed En24 steel to provide tool wear information via analysis of the rms AE signal. The interferometer displayed an improved diagnostic capability over a conventional piezoelectric sensor due to its advantages of being non-contacting, broadband with a flat frequency response to displacement, and providing absolute calibration.

アコースティック エミッション (AE) 法による腐食損傷評価

This review describes the utility of acoustic emission (AE) for the detection and monitoring of corrosion, stress corrosion cracking (SCC) and corrosion fatigue (CF). It surveys laboratory studies and field applications, which have been made to date. Various microprocesses that can produce detectable AE are shown and their relative energy levels, emanated as AE, are discussed in terms of peak amplitudes measured on laboratory specimens by conventional piezoelectric sensor. Practical manners to apply AE as a nondestructive test in engineering structures are presented. All the available information clearly demonstrates the potential usefulness of AE technique.