2024-04-10, Vergne, Céline, Pinto Inácio, José Miguel, Quirin, Thomas, Sargent, David, Madec, Morgan, Pascal, Joris

A significant progress has been made in the development of magnetic micromanipulation for minimally invasive surgery. The development of systems to localize millimeter-sized robots during magnetic manipulation without line-of-sight detection remains, however, a challenging task. In this study, we focused on the development of a tracking system aiming to fill this gap. A robot, which consists of a cylindrical magnet of 1-mm diameter, is localized using a 2-D array of 3-D magnetoresistive sensors. The system, also called magnetic-field camera (MFC), provides tracking of the robot with a refresh rate of 2 Hz. The developed tracking algorithm reaches a mean absolute error (MAE) for the position and the orientation of, respectively, 0.56 mm and 5.13° in 2-D. This system can be added to the existing magnetic manipulation systems (MMSs) allowing closed-loop control of the navigation. The performances of the MFC are not affected by an exposure to strong magnetic fields. Exposures up to 3 T have been validated. Increasing the integrability of the MFC into MMSs. The presented tracking system makes it possible to target applications, such as minimally invasive eye surgery or drug delivery. The high spatial and magnetic resolutions allow the tracking of magnetic particles, down to 200- μm diameter, when placed close to the surface. The system could also be suitable for the localization of small objects for 2-D biomanipulation.

2023-09, Nicolas, Hugo, Sousa, Ricardo C., Mora-Hernández, Ariam, Prejbeanu, Ioan-Lucian, Hebrard, Luc, Kammerer, Jean-Baptiste, Pascal, Joris

This paper presents the use of the spin transfer torque effect in perpendicular magnetic tunnel junctions to operate the devices as magnetic sensors. The junctions, specifically designed for sensing applications exhibit close to low-coercivity, allowing the sensitivity to be as high as 25 mV/mT for a large dynamic range of 20 mT. In addition, the junctions have diameters ranging from 20 to 100 nanometers, making them among the smallest magnetic sensing elements ever reported to our knowledge. A single operational amplifier operates the junction and outputs a voltage proportional to the external magnetic field. This paper opens the way to a monolithic integration of both the conditioning electronics and the perpendicular magnetic tunnel junction.

2023, Nicolas, Hugo, Sousa, Ricardo C., Mora-Hernández, Ariam, Prejbeanu, Ioan-Lucian, Hebrard, Luc, Kammerer, Jean-Baptiste, Pascal, Joris

This article demonstrates a new type of magnetic sensor using a perpendicular spin transfer torque magnetic tunnel junction (MTJ). The sensing element has a cylindrical shape of 50 nm in diameter and is to our knowledge among the smallest magnetic sensor ever reported. This article describes the principle of operation of the sensing element and the associated signal processing electronics, which delivers a signal proportional to the external magnetic field. Experimental results are detailed and compared to the state-of-the-art commercially available integrated magnetic sensors as well as published magnetoresistive sensors based on MTJs with comparable size. The measured sensitivity of the developed sensor is 1.28 V/T, and its dynamic range reaches 80 mT. The measured noise level is 21.8μT/√ Hz. Two different operating principles of the proposed sensor are described and compared, one based on a time-to-digital converter and one based on a pulsewidth-modulated (PWM) signal. Both methods require only standard microelectronics components, which are suitable for monolithic integration of the sensing element with its conditioning electronics. Subsequent improvements of the sensing element as well as conditioning electronics are required to further lower the noise level. The sensing element and its conditioning electronics are compatible with fabrication processes already used in magnetic random access memory fabrication. This opens the way to mass production and addresses various markets, such as consumer electronics, automotive, industrial sensing, physics experiments, or medical devices.