Paul Bartlett
University College London, Physics and Astronomy, Faculty Member
- Physics, Engineering, Mechanical Engineering, Materials Science, Electronics, Control Systems Engineering, and 18 moreMaterials Engineering, Dynamical Systems, Applied Physics, Electromagnetism, Engineering Management, Engineering Physics, Vibrations, Metallurgical Engineering, Mechanical Behaviour, Microstructural Evolution, Magnetics, Magnetostriction, Energy Harvesting, Physics and Astronomy, Materials Science and Engineering, Materials, Materials Characterisation, Magnetic Materials, Magnetism, and Non Destructive Testingedit
Research Interests:
Magnetostrictive materials have been utilized for the production of ultrasonic frequency vibrations for a number of years. This has particularly been the case in laminated nickel-based ultrasonic dental-scaler cleaning systems. In this... more
Magnetostrictive materials have been utilized for the production of ultrasonic frequency vibrations for a number of years. This has particularly been the case in laminated nickel-based ultrasonic dental-scaler cleaning systems. In this study, a comparison has been ...
Research Interests:
Research Interests:
Magnetic induction tomography (MIT) is a non-contact electromagnetic imaging technique that has potential applications in security, industry and medicine. In this study the resolution of a simple MIT system was investigated, as well as... more
Magnetic induction tomography (MIT) is a non-contact electromagnetic imaging technique that has potential applications in security, industry and medicine. In this study the resolution of a simple MIT system was investigated, as well as the system’s ability to image metallic objects through metal shields. The technique employs a driver coil and single sensor-coil. The sample object is imaged via phase variance measurements between the driver and sensor coils, due to inductive coupling between the coils and the sample object. The sensor coil is a commercially available 680 μH inductor. The resolution of the MIT system was investigated by producing images of different arrangements of steel ball bearings, as two dimensional (2D) and one dimensional (1D) plots. From our measurements, we estimated the resolution of the system to be of the order of 20 mm. The penetrating power of the system was also demonstrated by successfully imaging a mild-steel bar through a ferromagnetic shield.
Magnetic Induction Tomography (MIT) is a non-contact electromagnetic imaging technique that has potential applications in security, industry and medicine. This paper describes an automated set-up developed to image metallic objects. The... more
Magnetic Induction Tomography (MIT) is a non-contact electromagnetic imaging technique that has potential applications in security, industry and medicine. This paper describes an automated set-up developed to image metallic objects. The instrument employs a pair of coils in the Helmholtz configuration for the driving field and a planar array of 400 sensor coils. The sample object is imaged via phase variation measurements between the driver and sensor coils potential difference, due to inductive coupling between the coils and the sample object. The imaging system is automated via LabVIEW. A multiplexer with 400 channels automatically connects each sensor coil to a dual-phase lock-in amplifier, so that measurements of voltage phase-difference between the sensor and driver coils could be taken. These measurements were used to generate an image of the sample object. The planar geometry of the sensor coil array makes the system scalable to a full 3D imaging system, by simply adding two more driver and sensor assemblies orthogonally to the existing one. However, this requires the ability to image objects at a finite distance from the array plane. An experiment was conducted to explore the imaging capability for various heights of sample-lift-off above the array. This proved that the system is scalable to a full 3D imaging system.
Reluctance accelerators are used to apply linear forces to ferromagnetic projectiles via solenoids. Efficiency increases for a single-stage reluctance accelerator were produced by manipulating the input current pulse supplied by a... more
Reluctance accelerators are used to apply linear forces to ferromagnetic projectiles via solenoids. Efficiency increases for a single-stage reluctance accelerator were produced by manipulating the input current pulse supplied by a discharging capacitor. The development of a theoretical model allowed for the calculation of optimized pulse-shapes. A digital pulse-width modulated switching method was used to control the current pulse-shape using an Arduino Uno microcontroller which supplied signals to the gate of a MOSFET transistor that controlled the current to the system solenoid. An efficiency increase of 5.7% was obtained for a reluctance accelerator with an optimized current pulse-shape in comparison to a capacitor discharge with no pulse-shaping.
A novel hybrid force sensor system has been produced and successfully shown to be able to measure dynamic kN-level forces. It uses an innovative frequency modulation (FM) based system using an amorphous wire sensor wound around a... more
A novel hybrid force sensor system has been produced and successfully shown to be able to measure dynamic kN-level forces. It uses an innovative frequency modulation (FM) based system using an amorphous wire sensor wound around a magnetically biased Terfenol-D rod to detect dynamic, stress-induced changes in magnetisation. The hybrid sensor is able to successfully detect low-frequency sinusoidal forces up to 2kN. It is considered that the sensor system will be able to detect compressive cyclic stresses, applied forced waveforms and forces.
Two large actuators employing magnetostrictive Terfenol-D active elements have been manufactured for low frequency anti-vibration applications. Each driver element comprised two Terfenol-D rods of 254 mm length by 30 mm diameter utilised... more
Two large actuators employing magnetostrictive Terfenol-D active elements have been manufactured for low frequency anti-vibration applications. Each driver element comprised two Terfenol-D rods of 254 mm length by 30 mm diameter utilised in series. These devices were designed to counter vibrations in a civil engineering structure that were between 1 and 10 Hz. Through the use of a simple strain amplification lever mechanism, displacements between 0.5 and 4 mm were achieved with associated forces of between ∼6 and 0.5 kN, respectively. Transducer performance has met predicted specifications through careful consideration of important design criteria such as mechanical losses and effective magnetic circuit design.
Gd5(SixGe1−x)4, known for its giant magnetocaloric effect, also exhibits a colossal strain of the order of 10,000 ppm for a single crystal near its coupled first-order magnetic–structural phase transition, which occurs near room... more
Gd5(SixGe1−x)4, known for its giant magnetocaloric effect, also exhibits a colossal strain of the order of 10,000 ppm for a single crystal near its coupled first-order magnetic–structural phase transition, which occurs near room temperature for the compositions 0.41≤x≤0.575. Such colossal strain can be utilised for both magnetic sensor and actuator applications. In this study, various measurements have been carried out on strain as a function of magnetic field strength and as a function of temperature on single crystal Gd5Si2Ge2 (x=0.5), and polycrystalline Gd5Si1.95Ge2.05 (x=0.487) and Gd5Si2.09Ge1.91 (x=0.52). Additionally a giant magnetostriction/thermally induced strain of the order of 1800 ppm in polycrystalline Gd5Si2.09Ge1.91 was observed at its first order phase transition on varying temperature using a Peltier cell without the use of bulky equipment such as cryostat or superconducting magnet.