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This paper provides a comprehensive review of quantum spin sensing with a focus on the nitrogen vacancy (NV) center in diamond. Beginning with the discovery of optically detected magnetic resonance in NV centers, we trace the evolution of this technology and its integration with complementary metal-oxide-semiconductor technology, marking a significant advancement in measurement science. The unique optical and spin properties of NV centers, operational at room temperature and under ambient conditions, have broadened their application spectrum, notably in magnetometry for nanoscale magnetic field detection. This work describes the transition from isolated NV centers to dense ensembles, highlighting the challenges and advancements in microfabrication and nanofabrication that have facilitated the integration of these centers with photonic structures and electronic devices. The efficient readout of NV spin states and the challenges in miniaturization are addressed, showcasing the development of compact, portable quantum sensors. We also discuss the potential impact of these sensors in various domains, including vehicle sensor systems and biomedical applications, underscoring the significance of environmental influences on magnetometric readings. [ABSTRACT FROM AUTHOR]

ABSTRACT Loading a capacitor into a metallic loop allows one to tune the resonance frequency of the induced current on the loop and enhance the current amplitude for the normally incident magnetic field. We show that in an array of variable-capacitor-loaded loops, a null spot of the magnetic field generated some distance away can be moved laterally and crossed the array by manipulating current amplitude of each loop via the variable capacitor. We develop an analytic model for expressing the curl of the current source on the loop by using the delta function so that the magnetic field behavior in the vicinity of the array is characterized together with physical insight. Moreover, the control of a null spot is explained by the decomposition of the curl of current sources. The concept of a null-spot control is crucial for manipulating the kilohertz/megahertz magnetic field. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:2891-2895, 2015 [ABSTRACT FROM AUTHOR]

Here, we show, analytically and numerically, that in a pair of metallic periodic-ladder structures placed with a central gap, the normally incident magnetic field is focused on a spot of 3 mm (0.6 × 10-5 free space wavelength) full width at half maximum at a 1 mm distance away at 600 kHz. The ladder structures are designed by exploiting the curl of the induced current at each unit cell in the periodic structure. This investigation paves the way for kilohertz magnetic field manipulations. [ABSTRACT FROM AUTHOR]

We present a device capable of focusing a kilohertz magnetic field and enhancing the associated magnetic force. The device comprises a two-by-two array of electrically conductive metallic loops embedded in a base substrate. Analytical calculations and numerical simulations verify that the induced electrical current in the loop structure influences the magnetic field distribution thus leading to magnetic force enhancement. Experimental measurements of the magnetic force generated by the device operating at one kilohertz are compared with measurements of a control sample without loops. Such devices have logical applications in electromechanical actuators and transducers. [ABSTRACT FROM AUTHOR]

Abstract: The focus of this paper is to show that the magnetic force generated by a linear actuator may be enhanced through the optimization and design of the devices air-gap magnetic field distribution. Specifically, the use of a periodic ladder structure is proposed for magnetic field manipulation, and a simplified finite element analysis is adopted in lieu of a higher cost computational model. The optimal magnetic field distribution that maximizes the actuator force is then found via structural topology optimization. This force enhancement is explained using a Maxwell stress tensor analysis and validated through experimental studies. Finally, a periodic-ladder structure is designed for an equivalent optimal magnetic field distribution, and the linear actuator force enhancement is confirmed. [Copyright &y& Elsevier]