There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Core/Shell Nanoparticles: Classes, Properties, Synthesis Mechanisms, Characterization, and Applications

Magnetic sensors can be classified according to whether they measure the total magnetic field or the vector components of the magnetic field. The techniques used to produce both types of magnetic sensors encompass many aspects of physics and electronics. Here, we describe and compare most of the common technologies used for magnetic field sensing. These include search coil, fluxgate, optically pumped, nuclear precession, SQUID, Hall-effect, anisotropic magnetoresistance, giant magnetoresistance, magnetic tunnel junctions, giant magnetoimpedance, magnetostrictive/piezoelectric composites, magnetodiode, magnetotransistor, fiber optic, magnetooptic, and microelectromechanical systems-based magnetic sensors. The usage of these sensors in relation to working with or around Earth's magnetic field is also presented

Magnetic sensors and their applications

https://shell.cas.usf.edu/~phanm//PMS.pdf

Giant magnetoimpedance materials: Fundamentals and applications

Micromachining and micro-electromechanical system (MEMS) technologies can be used to produce complex structures, devices and systems on the scale of micrometers. Initially micromachining techniques were borrowed directly from the integrated circuit (IC) industry, but now many unique MEMS-specific micromachining processes are being developed. In MEMS, a wide variety of transduction mechanisms can be used to convert real-world signals from one form of energy to another, thereby enabling many different microsensors, microactuators and microsystems. Despite only partial standardization and a maturing MEMS CAD technology foundation, complex and sophisticated MEMS are being produced. The integration of ICs with MEMS can improve performance, but at the price of higher development costs, greater complexity and a longer development time. A growing appreciation for the potential impact of MEMS has prompted many efforts to commercialize a wide variety of novel MEMS products. In addition, MEMS are well suited for the needs of space exploration and thus will play an increasingly large role in future missions to the space station, Mars and beyond. (Some figures in this article are in colour only in the electronic version)

https://iopscience.iop.org/article/10.1088/0964-1726/10/6/301/pdf

Microelectromechanical systems (MEMS):fabrication, design and applications

The object of this book is to present the principles, instrument designs and applications of available magnetic transducers. In order to accomplish this task, the author begins with a fundamental chapter that focuses on the phenomenological magnetism, units and sensor specifications. The book continues by dedicating a full chapter to each magnetic sensor family: Induction, Fluxgate, Magnetoresistor, Hall effect, Magneto-optical, Resonance, SQUIDS and other principles. It ends with three chapters on applications, testing, calibration and magnetic sensors for non-magnetic variables. Various authors have contributed to some of the chapters. In spite of this, the content, presentation, opinion and notation are consistent throughout the book and uniform. Furthermore, each chapter can be read individually without losing its scope. The author(s) have focused on devices that are developed or under prototyping by commercial or public institutions. The book's objectives are also to get an insight into sensor design properties for a specific application and to understand the limitations and/or suitability of a specific sensor. Each chapter is therefore accompanied by an extensive list of scientific and technical material that provides a good reference for those interested in further reading. There are a number of books treating magnetic materials and their applications. However, often only a fundamental point of view is given. Magnetic Sensors and Magnetometers is a comprehensive book on the practice of magnetic transducers and their bases with many contributions from different experts in this field. Indeed, many professionals and researchers have (or will have) the need at some point for a magnetic sensor or transducer, and therefore a book of this nature is a very good reference for building and designing the most suitable solution for a specific application. It also provides design hints for connecting magnetic sensors to electronic devices, such as amplifier noise matching, etc. The book may also be of interest to teachers, students and researchers at universities, to instrumentation and application designers and users and the like. It is appropriate to list and comment on the various chapters for the reader to know what can be found in them: Basics (by Hauser and Ripka with 25 references): magnetic material types and properties and sensor specification. Induction Sensors (by Ripka with 29 refs) describes the air coils and their limitations, coils with ferromagnetic cores, amplifier noise matching, and other induction-based techniques such as rotating, moving, extracting and vibrating coils. Fluxgate Sensors (by Ripka with 159 refs) presents the principle of the transducer with different sensor geometries. Several aspects of this widely used type of sensor are discussed in more detail: demagnetization, core materials, second-harmonic analogue magnetometer, nonselective detection, short-circuited or current-output, noise and offset stability. Also, different design applications are described. Magnetoresistors (by Hauser and Tondra with 32 refs) illustrates the sensors and applications of the anisotropic magnetoresistance effect utilized in thin films and the giant magnetoresistance phenomenon. Hall-effect Magnetic Sensors (by Popovic et al with 51 refs) describes the basic sensor and thin-film Hall elements. Furthermore, integrated and multi-axes Hall sensors are presented. Magneto-optical Sensors (by Didosyan and Hauser with 33 refs) with the Faraday and Kerr effects and a description of the magneto-optical current transformer. Resonance Magnetometers (by Primdahl with 52 refs) describes the proton precession and the Overhauser variant effects and the optically pumped magnetometers. SQUIDs (by Fagaly with 38 refs) illustrates the sensors and operations with regard to noise and cancellation, input circuits, refrigeration and gradiometry. Other Principles (by Ripka and Kraus with 39 refs) describes, among others, magnetoimpedance, magnetoelastic and magnetostrictive sensors and biological applications. Application Magnetic Sensors (by Ripka and Acu na with 72 refs) in navigation, automotive, military, testing and planetary magnetic fields. Testing and Calibration Instruments (by Sasada et al with 38 refs) describes the application of magnetic coils and shieldings. Magnetic Sensors for Nonmagnetic Variables (by Ripka et al with 40 refs) is an interesting chapter on how to use magnetic properties to measure other physical effects like position, proximity, force, pressure, torque, current, etc. Appendix. Magnetic Sensors, Magnetometers and Calibration Equipment Manufacturers. It gives a fairly comprehensive list of manufacturers in the field. Overall, I recommend this book to professionals working in magnetism, magnetic instrumentation and related areas. It is highly relevant and contains an extensive and valuable amount of reference material. Jose M G Merayo

/pdf/magnetic-sensors-and-magnetometers-1bgq5rm29q.pdf

Magnetic Sensors and Magnetometers

The most important milestone in the field of magnetic sensors was when AMR sensors started to replace Hall sensors in many applications where the greater sensitivity of AMRs was an advantage. GMR and SDT sensors finally found applications. We also review the development of miniaturization of fluxgate sensors and refer briefly to SQUIDs, resonant sensors, GMIs, and magnetomechanical sensors.

Advances in Magnetic Field Sensors

Since the 1930s, fluxgate sensors have been used for measuring d.c. magnetic fields up to 1 mT with a maximum resolution of 10 pT. In the sensor core the flux is gated by the excitation field. The preferable sensor geometry is a ring-core; both crystalline and amorphous ferromagnetic materials can be used for the core. Although a lot of fluxgate magnetometer types have appeared, the classical type with detection of the second harmonics by a phase-sensitive detector is the most popular. Fluxgate sensors are reliable and rugged and their applications range from space research to submarine detection.

Review of fluxgate sensors

This paper reviews recent achievements in the technology and design of fluxgate sensors and magnetometers. The major recent trends were decreasing of the sensor size, power consumption and price, and, on the other hand, increasing of the precision in the large range of the measured fields. The potential frequency range was increased up to units of kHz. Present fluxgate sensors have a resolution comparable with high-temperature superconducting quantum interference devices (SQUIDs), while their precision is the best of vectorial field sensors.

Advances in fluxgate sensors

The review makes a brief overview of traditional methods of measurement of electric current and shows in more detail relatively new types of current sensors. These include Hall sensors with field concentrators, AMR current sensors, magneto-optical and superconducting current sensors. The influence of the magnetic core properties on the error of the current transformer shows why nanocrystalline materials are so advantageous for this application. Built-in CMOS current sensors are important tools for monitoring the health of integrated circuits. Of special industrial value are current clamps which can be installed without breaking the measured conductor. Parameters of current sensors are also discussed, including geometrical selectivity. This parameter specific for current sensors means the ability to suppress the influence of currents external to the sensor (including the position of the return conductor) and also suppress the influence on the position of the measured conductor with respect to the current.

/pdf/electric-current-sensors-a-review-4b35763ekq.pdf

Pavel Ripka

Papers

Magnetic Sensors and Magnetometers

Advances in Magnetic Field Sensors

Review of fluxgate sensors

Advances in fluxgate sensors

Electric current sensors: a review