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

Magnetic fields from neuronal action potentials (APs) pass largely unperturbed through biological tissue, allowing magnetic measurements of AP dynamics to be performed extracellularly or even outside intact organisms. To date, however, magnetic techniques for sensing neuronal activity have either operated at the macroscale with coarse spatial and/or temporal resolution-e.g., magnetic resonance imaging methods and magnetoencephalography-or been restricted to biophysics studies of excised neurons probed with cryogenic or bulky detectors that do not provide single-neuron spatial resolution and are not scalable to functional networks or intact organisms. Here, we show that AP magnetic sensing can be realized with both single-neuron sensitivity and intact organism applicability using optically probed nitrogen-vacancy (NV) quantum defects in diamond, operated under ambient conditions and with the NV diamond sensor in close proximity (∼10 µm) to the biological sample. We demonstrate this method for excised single neurons from marine worm and squid, and then exterior to intact, optically opaque marine worms for extended periods and with no observed adverse effect on the animal. NV diamond magnetometry is noninvasive and label-free and does not cause photodamage. The method provides precise measurement of AP waveforms from individual neurons, as well as magnetic field correlates of the AP conduction velocity, and directly determines the AP propagation direction through the inherent sensitivity of NVs to the associated AP magnetic field vector.

https://www.pnas.org/content/pnas/113/49/14133.full.pdf

Optical magnetic detection of single-neuron action potentials using quantum defects in diamond.

Superconducting quantum interference devices (SQUIDs) have been a key factor in the development and commercialization of ultrasensitive electric and magnetic measurement systems. In many cases, SQUID instrumentation offers the ability to make measurements where no other methodology is possible. We review the main aspects of designing, fabricating, and operating a number of SQUID measurement systems. While this article is not intended to be an exhaustive review on the principles of SQUID sensors and the underlying concepts behind the Josephson effect, a qualitative description of the operating principles of SQUID sensors and the properties of materials used to fabricate SQUID sensors is presented. The difference between low and high temperature SQUIDs and their suitability for specific applications is discussed. Although SQUID electronics have the capability to operate well above 1MHz, most applications tend to be at lower frequencies. Specific examples of input circuits and detection coil configuration for different applications and environments, along with expected performance, are described. In particular, anticipated signal strength, magnetic field environment (applied field and external noise), and cryogenic requirements are discussed. Finally, a variety of applications with specific examples in the areas of electromagnetic, material property, nondestructive test and evaluation, and geophysical and biomedical measurements are reviewed.

Superconducting quantum interference device instruments and applications

This critical review is devoted to semiconducting and high spin polymers which are of great scientific interest in view of further development of the organic electronics and the emerging organic spintronic fields. Diversified synthetic strategies are discussed in detail leading to high molecular mass compounds showing appropriate redox (ionization potential (IP), electron affinity (EA)), electronic (charge carrier mobility, conductivity), optoelectronic (electroluminescence, photoconductivity) and magnetic (magnetization, ferromagnetic spin interactions) properties and used as active components of devices such as n- and p-channel field effect transistors, ambipolar light emitting transistors, light emitting diodes, photovoltaic cells, photodiodes, magnetic photoswitches, etc. Solution processing procedures developed with the goal of depositing highly ordered and oriented films of these polymers are also described. This is completed by the description of principal methods that are used for characterizing these macromolecular compounds both in solution and in the solid state. These involve various spectroscopic methods (UV-vis-NIR, UPS, pulse EPR), electrochemistry and spectroelectrochemistry, magnetic measurements (SQUID), and structural and morphological investigations (X-ray diffraction, STM, AFM). Finally, four classes of polymers are discussed in detail with special emphasis on the results obtained in the past three years: (i) high IP, (ii) high |EA|, (iii) low band gap and (iv) high spin ones.

Polymers for electronics and spintronics

Nano Superconducting Quantum Interference device: A powerful tool for nanoscale investigations

We attempt a comprehensive review of all published research in nondestructive evaluation (NDE) performed with the superconducting quantum interference device (SQUID) magnetometer since the first work was reported in the mid-1980s The SQUID is the most sensitive detector of magnetic flux known The energy sensitivity of the SQUID may make it the most sensitive detector of any kind The research on SQUIDs for NDE is based on the promise of that sensitivity and on the various other desirable properties developed for SQUID instrumentation in biomagnetism and other fields The sensitivity of SQUID instruments down to very low frequencies allows them to function as eddy-current sensors with unparalleled depth resolution, and to image the static magnetization of paramagnetic materials and the flow of near-dc corrosion currents The wide dynamic range of the SQUID makes it possible to image defects in steel structures and to measure the magnetomechanical behaviour of ferromagnetic materials with high sensitivity In the last decade SQUID instrumentation designed specifically for NDE has appeared and improved the spatial resolution of most work to roughly 1 mm, with promise of another order of magnitude improvement within the next five years Algorithms for flaw detection and image deconvolution have begun to flourish With many talented, industrious people in the field, the future of SQUID NDE looks bright, provided the crucial first niche can be found

http://iopscience.iop.org/article/10.1088/0022-3727/30/3/002/pdf

SQUIDs for nondestructive evaluation

We attempt a comprehensive review of all published research in nondestructive evaluation (NDE) performed with the superconducting quantum interference device (SQUID) magnetometer since the first work was reported in the mid-1980s. The SQUID is the most sensitive detector of magnetic flux known. The energy sensitivity of the SQUID may make it the most sensitive detector of any kind. The research on SQUIDs for NDE is based on the promise of that sensitivity and on the various other desirable properties developed for SQUID instrumentation in biomagnetism and other fields. The sensitivity of SQUID instruments down to very low frequencies allows them to function as eddy-current sensors with unparalleled depth resolution, and to image the static magnetization of paramagnetic materials and the flow of near-dc corrosion currents. The wide dynamic range of the SQUID makes it possible to image defects in steel structures and to measure the magnetomechanical behaviour of ferromagnetic materials with high sensitivity. In the last decade SQUID instrumentation designed specifically for NDE has appeared and improved the spatial resolution of most work to roughly 1 mm, with promise of another order of magnitude improvement within the next five years. Algorithms for flaw detection and image deconvolution have begun to flourish. With many talented, industrious people in the field, the future of SQUID NDE looks bright, provided the crucial first niche can be found.

SQUIDs for Nondestructive Evaluation

Candling, the traditional means of detecting parasites during fish fillet processing, is time consuming and labor intensive. This method is a major factor in reducing the quality and increasing the cost of fish brought to market. The difference in electrical conductivity between fish and an embedded parasite was hypothesized to be a practical basis for an instrument which would have potential for automated parasite detection. A small electrical current was passed through a parasite-containing fillet and the magnetic field above the fillet was recorded by a Superconducting Quantum Interference Device magnetometer. Results indicate potentially successful detection of parasites by the device.

Detection of Parasites in Fish by Superconducting Quantum Interference Device Magnetometry

We examined the potential of an electromagnetic parasite detection technique to become the basis of an automated commercial system. The effects of parasite orientation and position, presence offish bone, and applied signal strength and frequency on resultant magnetic field strength were determined by scanning a conducting cell containing fish fillet and parasite below a SQUID magnetometer. The parasite orientation affected peak-to-peak voltage of the magnetic dipole. The parasite position with respect to myotome structure seemed to affect the orientation of the dipolar signal. A fish bone was readily detected. The magnetic field strength was independent of the frequency of the injected current and scaled with amplitude=.

W.G. Jenks

Papers

SQUIDs for nondestructive evaluation

SQUIDs for Nondestructive Evaluation

Detection of Parasites in Fish by Superconducting Quantum Interference Device Magnetometry

Effects of Parasite Attributes and Injected Current Parameters on Electromagnetic Detection of Parasites in Fish Muscle