HTS-SQUID Gradiometer Research Articles

Eddy Current Testing Based Non-Destructive Inspection for Metal 3D Additive Manufacturing Objects With HTS-SQUID

In this work, we applied eddy-current-testing-based HTS-SQUID non-destructive inspection (ECT-based HTS-SQUID NDI) system for inspection of metal 3D additive manufacturing (AM) objects, which were made of AlSi10Mg powder with powder bed fusion (PBF) method. The inspection system combines an ECT probe with an HTS-SQUID gradiometer as high sensitive readout magnetic sensor in low frequency range to overcome disadvantage of conventional ECT. We prepared 5 samples with different densities by changing parameters in the PBF process. Densities of the samples #1-#5 were estimated to be 2.65, 2.64, 2.62, 2.58, and 2.51 g/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , respectively. The samples were measured by the inspection system with an excitation current of 20 mA at 1.6 kHz, and lift-off of about 1 mm. In inspection results, anomalous magnetic patterns appeared on the sample #3, #4 and #5. The inspection results were verified with X-ray CT scanning. Comparison between the ECT inspection and the X-ray CT results reveals that the positions of the anomalous magnetic patterns show strong correlation with the positions of high porosity existing in the samples.

Development of an HTS-SQUID Based Nondestructive Evaluation System for Boiler Tubes On-Site Inspection in Thermal Power Plant

In ultra-supercritical (USC) thermal power plants, Super304H (KA-SUS304J1HTB, ASME code: 2328) is widely used in the superheater and reheater tubes in boilers because of its excellent creep rupture strength under high-temperature and -pressure conditions. Thus, a degradation diagnosis of these tubes after long-term operation should be conducted using a quick and easy inspection. In this study, in order to discover the degradation of the boiler tubes for early diagnose before they rupture, a high-temperature superconductor (HTS)–superconducting quantum interference device (SQUID) with high sensitivity was used. A SQUID-based nondestructive evaluation system for the on-site inspection of boiler tubes in an USC thermal power plant was developed. Our system comprises a movable eddy current testing (ECT) probe and HTS-SQUID gradiometer. Five LED markers were set on a manually operated ECT probe for position detection using a stereo camera. Customized software was used for data acquisition through a lock-in amplifier and data visualization on a PC with a connected smart glass. Thus, the system can be used for quick inspection by time-sequence signals and detailed scanning through a two-dimensional contour map projected on the smart glass. Therefore, this study successfully introduced an HTS-SQUID-based nondestructive evaluation system for the on-site inspection of boiler tubes.

Creep Life Assessment Method for Super304H Boiler Tubes Based on HTS-SQUID Gradiometer

This paper presents a novel method for the creep life assessment of Super304H (KA-SUS304J1HTB, ASME code: 2328) boiler tubes based on a discrete-type eddy-current-testing (ECT) HTS-SQUID nondestructive evaluation (NDE) system. Six specimens were subjected to internal pressure creep tests at a stress level of 110 MPa and a temperature of 700°C. The specimens were inspected at various creep test times using our NDE system, which included an ECT probe and a HTS-SQUID gradiometer. By studying the physical characteristics and microstructures of the specimens at different test times, we found that the electrical conductivity and permeability of the specimens varied with an increasing test time. The detected signals may have been generated from creep voids and/or surface microcracks. Based on the NDE inspection results, creep life assessment curves that can be used for assessing the remaining creep life of the Super304H boiler tubes were plotted. The results confirmed the possibility of assessing the remaining creep life using our HTS-SQUID-based system in a nondestructive manner.

Guided Wave Transceive Technique Using Magnetostrictive Effect of STPG370 Pipe itself and High-Temperature Superconductor SQUID

We developed a non-contacting ultrasonic guided wave testing technique using magnetostrictive effects and high-temperature superconductor (HTS) SQUID for STPG370 steel pipes. A pair of C-shaped electromagnets was used to magnetize the STPG370 pipe while rotating the pipe, in order to give uniform remnant fields as bias fields. Conditions to give larger remnant field in the pipe were investigated using an electromagnetic field simulation. The simulation results indicated that C-shaped pb permalloy iron cores with an aperture angle of 20 degree and a diameter of 20 mm should be utilized for the magnetization. An excitation coil was wound around one of the magnetized parts, which is used as a transmitter. One cycle sine current of 9 App at 50 kHz was repeatedly supplied to the coil to generate T(0,1) mode guided waves in the pipe. The other magnetized part, which was used as a receiver, was combined with the HTS-SQUID gradiometer, which was located above the pipe with a lift-off of 4 mm. In measurements, the pipe was rotated to perform all-round measurements. A contour map of the time-series signal distribution of T(0, 1) mode guided wave was obtained around the pipe.

Development of Magnetostriction-Based Non-Contacting Ultrasonic Guided Wave Testing For Ferromagnetic Pipes Using HTS-SQUID Gradiometer

In this work, a magnetostriction-based non-contacting ultrasonic guided wave testing (UGWT) technique was developed and demonstrated. Magnetization method to transceive T (0, 1) mode ultrasonic guided wave (UGW) on pure nickel thin pipe was studied with both electromagnetic field simulator and experiments. The latter utilized HTS-SQUID gradiometer as a part of receiver of the UGW. In the both studies, a pair of electromagnets sandwiching the Ni pipe was used to magnetize the pipe, while rotating the pipe between the electromagnets. The simulation results indicate the magnetization method can give roughly uniform remnant magnetic field of about 240 mT in the circumference of the Ni pipe with supplying 15 A DC current to the electromagnets. In the experiments, we successfully transceived T (0, 1) mode UGWs on the Ni pipe using the magnetization method and the HTS-SQUID gradiometer. All-round UGWT around the pipe was conducted with lift-off distance of about 10 mm. The experimental result indicated that the magnetization distribution in the circumference of the pipe was roughly uniform as well as the simulation result. Improvement of the uniformity of the magnetization was realized with stepwise magnetization and resulted in better uniformity in the magnetic signal peak distribution. The reason of the better uniformities by the new magnetization method is discussed.

Multipoint measurements of a Pipe Using HTS-SQUID and Magnetostriction-Based Ultrasonic Guided Wave

This paper describes study on remote inspection technology for pipes by using magnetostriction-based ultrasonic guided wave and high temperature superconductor (HTS) superconducting quantum interference device (SQUID) gradiometer. Magnetized nickel plates were adhered on an aluminium pipe sample, in order to use them as magnetostriction-based guided wave transceivers. A pair of 10mm-wide nickel plate with different angle arrangement were used to transceive uniformly distributed guided waves at all angles. A field coil was wound around one set of the nickel plates as a transmitter, while the other was used as a receiver. T (0, 1) mode guided wave was generated on the pipe by supplying a burst sine wave current of one cycle at several tens kHz to the coil. Multipoint measurements of the T (0, 1) mode guided waves around the pipe’s circumference were carried out by setting the HTS-SQUID gradiometer above the receiver with lift-off of about 9 mm and rotating the pipe for 360 degrees. Signal of reflected wave from an artificial slit on the sample was well detected. We simulated the distribution of the guided wave propagating on the pipe with the slit using an ultrasonic simulator and compared the distribution with the experiment result. The guided wave signal distributions including the defect signal obtained by experiment and simulation agreed well.

All-Round Inspection of a Pipe Based on Ultrasonic Guided Wave Testing Utilizing Magnetostrictive Method and HTS-SQUID Gradiometer

We developed an ultrasonic guided wave testing system for pipes utilizing magnetostrictive method and hightemperature superconductor (HTS) superconducting quantum interference device (SQUID) gradiometer. Two pre-magnetized nickel thin plates were adhered on an aluminium pipe. One of them with a field coil was used as a magnetostriction-based T (0, 1) mode guided wave transmitter, while the other was used as a receiver. Allround inspections of the pipe without and with a circumference slit were conducted by measuring the T (0,1) mode guide waves around circumference of the pipe using the HTS-SQUID-based guided wave testing system. The optimum experimental setup about excitation frequency and input current to the transmitter was investigated using ez-SQUID electronics. By applying a sine burst current of 0.2 A at 50 kHz with single cycle to the transmitter and rotating the pipe stepwise at 30°, “B-scan” images of the guided wave propagating on the pipe without and with slit were measured. An axisymmetric distribution of a reflected wave from the slit was well detected. We analyzed distribution of incident waves and reflected waves from the end of the pipe based on magnetization in the nickel plates using an electromagnetic simulator and proposed a new transducer.

Defect Detection of Pipes using Guided Wave and HTS-SQUID

In this paper, we investigated ultrasonic guided wave measurements on aluminium pipes with defects using high temperature superconducting (HTS) SQUID gradiometer and magnetostrictive sensors (MsS), which utilized pre-magnetized nickel thin plates. One of the pipes was provided with an axial defect, and the other was provided with a circumferential defect. The MsSs were used by adhering them on circumferences of the pipes to generate ultrasonic guided waves and to receive the waves by converting them into the magnetic signals, which were measured by the HTS-SQUID gradiometer. Guided wave measurements using the MsSs and the gradiometer demonstrated that magnetic signals of about 3.3 mΦ0 due to reflected waves from both the defects were successfully detected. Reflected wave signals of about 1.4 mΦ0 from thin nickel plates of the MsS on the pipes were also detected.

HTS-SQUID NDE Technique for Pipes based on Ultrasonic Guided Wave

This article describes research on the novel high-temperature superconductor (HTS) superconducting quantum interference device (SQUID) non-destructive evaluation (NDE) technique for metallic pipes based on ultrasonic guided waves. We constructed HTS-SQUID NDE system for pipes based on ultrasonic guided waves, which were generated and received by means of the magnetostrictive effects. Using the system, we measured magnetic signals due to T (0, 1) mode ultrasonic guided waves that transmitted on aluminium pipe, and investigated influences of measurement parameters to the magnetic signals, such as direction of a HTS-SQUID gradiometer, lift-off distance, and intensity and frequency of input current fed to a magnetostrictive transmitter. With the gradiometer oriented parallel to the pipe axis, more than 10 times larger signals were measured compared with that oriented perpendicular to the pipe axis. Magnetic signals measured by the gradiometer were inverse proportional to the power of the list- off distance, and proportional to the intensity of the input current up to 1 App. Relation between the frequency of the input current and the measured signal was shown and discussed.

Mobile NDE System Utilizing Robust HTS-SQUID Magnetometer for Use in Unshielded Environments

In this paper, we demonstrated detection of deep-lying defects in aluminum alloy samples utilizing an eddy current technique while moving a robust HTS-SQUID magnetometer integrated on a robot-based NDE system in an unshielded environment. A bicrystal-Josephson-junction-based HTS-SQUID magnetometer, which was covered by an alternative HTS film as a superconducting shield, both having a mesh structure with a 5-μm line width, was used in the system. An active magnetic shield scheme was also utilized in order to cancel magnetic flux coupling to the magnetometer during motion. For comparison, detection of the same defects using a ramp-edge-Josephson-junction-based HTS-SQUID gradiometer, which has the roughly equivalent area with the magnetometer, was also carried out. Experimental results showed that the magnetometer had better capability to detect deeper defects in conductive materials than the gradiometer.

Development of Non-destructive Evaluation System Using an HTS-SQUID Gradiometer with an External Pickup Coil

We are developing a new eddy-current non-destructive evaluation (NDE) system using a high-temperature superconducting quantum interference device (HTS-SQUID) gradiometer with the aim of applying it to power plants. Electric power facilities such as ducts and vessels are generally untransportable because of their size, and thus it is difficult to apply a conventional SQUID NDE system. The new NDE system employs an external Cu pickup coil which is supposed to be driven flexibly by a robot arm at room temperature and an HTS-SQUID chip which is placed in a magnetically shielded vessel. In the present research, we investigated the performance of an HTS-SQUID sensor connected with external pickup coils before mounting them to a robot arm. By varying the Cu coil conditions such as their sizes, the number of turns, and the diameter of wire, we qualitatively evaluated the frequency dependence of the effective area and the cutoff frequency.

Study on Non-destructive Evaluation of Flaws in Multilayer Duct Using an HTS-SQUID Gradiometer

We have investigated the performance of an eddy-current non-destructive evaluation (NDE) system using an HTS Superconducting quantum interference device (SQUID) gradiometer with the aim of applying it to the equipment in power plants. Use of the SQUID-NDE technique has an advantage, because SQUID has a high sensitivity or low noise characteristics at low frequencies for detecting magnetic signals. In the present research, we have tried to detect flaws in test samples simulating a multilayer duct in a plant, which consists of multilayer aluminum and resin plates. In the test samples, resin plates were sandwiched by aluminum plates. The top aluminum plate and the bottom multilayer aluminum plates were assumed as outer and inner duct layers, and the resin plates were assumed as an insulation layer in a multilayer duct of the plant. A slit-shaped through hole was opened in the bottom layer, and was assumed as a flaw in the duct layer. By using a SQUID-ECT system, we could detect signals from flaws located at more than 10mm deep positions in the test samples.

Development of HTS-SQUID Gradiometer with an External HTS Multiturn Thin Film Pickup Coil

Highly-sensitive HTS-SQUIDs are applied to various systems such as eddy-current non-destructive evaluation (NDE) and compact magnetometer systems. To avoid unstable operation of the SQUID due to an excitation field, a flux transformer made of normal Cu wire is used to separate the pickup coil and SQUID. However, the resistance of the flux transformer generates thermal noise and reduces the signal bandwidth at low frequencies. In this study, we investigate use of a superconducting flux transformer with resistive connections (SFTR). The SFTR consists of pickup and input coils made of HTS thin films. The two coils are connected by using an HTS coated conductor. The input coil is stacked on an HTS thin film gradiometer. From the measured results of resistances of the connections between each coil and the coated conductor, it was found that the resistance of bonding wire was a dominant component. The estimated resistance of the SFTR was 7.2 mΩ, corresponding to a lower cut-off frequency of 11.7Hz.

Fabrication of SQUID chip for large planer gradiometer using HTS coated conductor

We have fabricated a large high-Tc superconducting (HTS) SQUID gradiometer with a baseline length of 130mm for geophysical application. It consists of an HTS-SQUID gradiometer chip with an integrated input coil and a large pickup coil made of an HTS coated conductor (CC). In this work, fabrication of the chip containing ramp-edge Josephson junctions and multilayer structures is reported. An MgO(100) substrate with a size of 15×15mm2 was used. The half area of the substrate was occupied by gold pads for connection with an HTS-CC. A directly-coupled thin-film gradiometer with a baseline length of 7mm was prepared in the remained half area. SmBCO and La-doped ErBCO having Tc’s around 90K were used for base- and counter-electrodes, respectively. A 5.5-turn input coil made of La-doped ErBCO was formed on the thin-film pickup coil made of SmBCO. The fabricated gradiometer chip was operated by supplying electrical current through the input coil, but modulation corresponding to only three flux quanta was observed in the V–Φ curve. We found that the critical current density of the thin-film pickup coil was insufficient. We speculated that the rather wide pickup coil was not fully oxygenated. After longer annealing treatment, the number of modulation peaks in the V–Φ curve was significantly increased.

Nondestructive evaluation of ±45° flat-braided carbon-fiber-reinforced polymers with carbon nanofibers using HTS-SQUID gradiometer

Step-by-step tensile tests were applied to flat-braided carbon-fiber-reinforced polymers with and without added dispersions of carbon nanofibers (CNFs) and with and without sample sides cut off to study their mechanical properties and destructive mechanisms by means of in situ observation and stress–strain measurements. An ex situ nondestructive evaluation technique, using a high-temperature superconductor superconducting quantum interference device gradiometer, was also applied to the samples to study their electrical properties; the relationships between the mechanical and electrical properties by visualizing current maps in the samples during ac current injection was also studied. Clear differences were observed in the mechanical and electrical properties and the destructive mechanisms between the samples with and without CNFs and with and without cut off sides. These differences were mainly attributed to the addition of CNFs, which enhanced the mechanical and electrical connections between the carbon fiber bundles.

Development of non-destructive evaluation system using an HTS-SQUID gradiometer for magnetized materials

We have developed a new eddy-current non-destructive evaluation (NDE) system using an HTS SQUID gradiometer with the aim of applying it to practical materials with magnetization. The new NDE system employs a LN2-cooled external Cu pickup coil and an HTS SQUID chip placed in a magnetic shield made of HTS material. The HTS SQUID chip consists of an HTS planar gradiometer manufactured by using a ramp-edge junction technology and a multi-turn HTS thin film input coil coupled with the flip-chip configuration. The first-order coaxial gradiometric Cu pickup coil with a diameter of 16 mm and the baseline of 5.6 mm was used in the present NDE experiments. By using this NDE system, we could observe defect-induced magnetic signals without an appreciable influence of magnetization up to 10 mT. We also examined the ability of detecting deep-lying defects and compared with the results obtained using our previous NDE system.

Prediction of Initiation Site of Destruction of Flat Braided Carbon Fiber Composites Using HTS-SQUID Gradiometer

Abstract Carbon fiber reinforced polymers (CFRPs) are composite materials with lightweight and high specific strength. As the braided CFRPs have continuous carbon-fiber bundles in their longitudinal direction, they are stronger than conventional CFRPs. In this study, we applied a current-injection-based NDE method using a HTS-SQUID gradiometer to the flat braided CFRPs with and without carbon nanotubes (CNTs), and estimated conditions of the carbon fibers while applying a step-by-step tensile load to the CFRPs. From the results, a possibility to predict an initiation site of the destruction in the braided CFRPs was demonstrated.

Noise properties of HTS-SQUID gradiometer in an elevated magnetic field

Abstract Stability of a high-temperature superconducting quantum interference device (HTS-SQUID) gradiometer with ramp-edge Josephson junctions against application of magnetic fields was investigated. The gradiometer with a SQUID inductor having a 5-μm-wide line and pickup coils of 0.5x1.5 mm for one side was used. Noise spectra were measured for the gradiometer in zero field after cooled in dc magnetic fields up to 300 μT. no increase in noise level was observed until 95 T, being higher than the earth field. Noise spectra in elevated magnetic fields up to 320 μT were also measured for the gradiometer cooled in zero field. No appreciable increase in noise was observed until 150 μT. By decreasing the applied field from 320 μT to zero, the gradiometer recovered the original low noise level. These results indicated that the examined gradiometer had a good durability against magnetic fields and could be used without a magnetic shield for various applications.

Non-Destructive Evaluation of Deep-Lying Defects in Multilayer Conductors Using HTS SQUID Gradiometer

We examined the ability to detect deep-lying defects in multilayer stacks of aluminum plates using an eddy-current testing technique with HTS planar-type SQUID gradiometers. In addition to a previous gradiometer with a baseline of 1 mm, a new gradiometer with a baseline of 8.5 mm and a larger effective area fabricated by HTS multilayer and ramp-edge junction technologies was used. The frequency and depth dependences of the SQUID signal were compared between the two gradiometers. By employing the longer-baseline gradiometer and an excitation frequency of 35 Hz, a slit-like defect located at about 38 mm in depth could be clearly observed with a signal-to-noise ratio larger than 10.

Two-Channel HTS SQUID Gradiometer System for Detection of Metallic Contaminants in Lithium-Ion Battery

A two-channel high-Tc SQUID gradiometer system for the detection of magnetic foreign matter in a lithium-ion battery was developed. Finding ultra-small metallic foreign particles can be a big issue for a manufacturer that produces commercial products such as lithium-ion batteries. If the presence of such particles is detected in its products, the manufacturer has to recall the products and thereby suffers a significant loss. Previously, we developed a detection system based on a single-channel SQUID gradiometer and horizontal magnetization. For practical use, we need to increase the detection width of the system by employing multiple sensors. In this paper, we present a two-channel high-Tc SQUID gradiometer system for the inspection of a lithium-ion battery. In order to increase the inspection width, two SQUID gradiometers were employed along with a specially designed cryostat. As a result, small iron particles with a diameter of less than 100 μm were detected by the system with a width of 22 mm. This is the first multi-channel high-Tc SQUID gradiometer system for detection of the contaminants in a lithium-ion battery.