1,720,992 research outputs found
Tracking a Millimetric Dual-Magnet Assembly: Toward Detecting Torsional Eye Motion
Full text linkTracking eye movements with high precision is crucial for various medical and technological applications, yet detecting subtle torsional motion remains a challenge. This paper presents a magnetic sensor system that accurately tracks the full 6-degree-of-freedom motion (6-DoF) of a miniature dual-magnet assembly. This work leverages two (nearly) orthogonal magnetic dipoles, building upon previous results achieved with a single-dipole source. The 6-DoF tracking and the achieved level of precision may enable the detection of complex eye movements, including torsion. Moreover, the system can also track head orientation, expanding its applications in biomedical research, assistive technologies, and human-computer interaction
A Non-Inductive Magnetic Eye-Tracker: From Dipole Tracking to Gaze Retrieval
Full text linkWe analyze the information that can be retrieved from the tracking parameters produced by an innovative wearable eye tracker. The latter is based on a permanent-magnet marked corneal lens and by an array of magnetoresistive detectors that measure the magnetostatic field in several positions in the eye proximity. We demonstrate that, despite missing information due to the axial symmetry of the measured field, physiological constraints or measurement conditions make possible to infer complete eye-pose data. Angular precision and accuracy achieved with the current prototypical device are also assessed and briefly discussed. The results show that the instrumentation considered is suitable as a new, moderately invasive medical diagnostics for the characterization of ocular movements and associated disorders
Multichannel optical atomic magnetometer operating in unshielded environment
No full textA multichannel atomic magnetometer operating in an unshielded environment is described and characterised. The magnetometer is based on D1 optical pumping and D2 polarimetry of Cs vapour contained in gas-buffered cells. Several technical implementations are described and discussed in detail. The demonstrated sensitivity of the setup is 100 fT/√Hz when operating in the difference mode
Tri-axial time-dependent magnetic field calibrated in-situ by harmonic analysis of adiabatically evolving atomic spins
Full text linkWe introduce a methodology to calibrate in situ a set of coils generating bi- or tri-axial magnetic fields, at frequencies where a calibration performed under static conditions would be inaccurate. The methodology uses harmonic analysis of one component of the magnetization of an atomic sample whose spins adiabatically follow an ad hoc applied time-dependent field. The procedure enables the identification of phases and amplitudes of the coil currents required to produce a dynamic magnetic field with the assigned polarization. This determines coil constants that can be subsequently used to produce arbitrary three-dimensional time-dependent fields
Spin dynamic response to a time dependent field
Full text linkThe dynamic response of a parametric system constituted by a spin precessing in a time dependent magnetic field is studied by means of a perturbative approach that unveils unexpected features, and is then experimentally validated. The first-order analysis puts in evidence different regimes: beside a tailorable low-pass-filter behaviour, a band-pass response with interesting potential applications emerges. Extending the analysis to the second perturbation order permits to study the response to generically oriented fields and to characterize several non-linear features in the behaviour of such kind of systems
Larmor frequency dressing by a nonharmonic transverse magnetic field
No full textWe present a theoretical and experimental study of spin precession in the presence of both a static and an orthogonal oscillating magnetic field, which is nonresonant, not harmonically related to the Larmor precession, and of arbitrary strength. Due to the intrinsic nonlinearity of the system, previous models that account only for the simple sinusoidal case cannot be applied. We suggest an alternative approach and develop a model that closely agrees with experimental data produced by an optical-pumping atomic magnetometer. We demonstrate that an appropriately designed nonharmonic field makes it possible to extract a linear response to a weak dc transverse field, despite the scalar nature of the magnetometer, which normally causes a much weaker, second-order response
Self-adaptive loop for external-disturbance reduction in a differential measurement setup
No full textWe present a method developed to actively compensate common-mode magnetic disturbances on a multisensor device devoted to differential measurements. The system uses a field-programmable-gated-array card, and operates in conjunction with a high-sensitivity magnetometer: compensating the common mode of magnetic disturbances results in a relevant reduction of the difference-mode noise. The digital nature of the compensation system allows for the use of a numerical approach aimed at automatically adapting the feedback-loop filter response. A common-mode-disturbance attenuation exceeding 50 dB is achieved, resulting in a final improvement of the differential noise floor by a factor of 10 over the whole spectral interval of interest
All-optical magnetometry for NMR detection in micro-Tesla field and unshielded environment
No full textAn all-optical atomic magnetometer is used to detect a proton free-precession signal from a water sample polarized in a 0.7 T field and remotely analyzed in a 4 lT field. Nuclear spins are manipulated either by p=2 pulses or by non-adiabatic rotation. The magnetometer operates at room temperature, in an unshielded environment and has a dual-channel sensor for differential measurements
All optical sensor for automated magnetometry based on coherent population trapping
No full textAn automated magnetometer suitable for long lasting measurement under stable and controllable experimental
conditions has been implemented. The device is based on coherent population trapping (CPT) produced by
a multifrequency excitation. CPT resonance is observed when a frequency comb, generated by diode laser current
modulation, excites Cs atoms confined in a /42.521 cm3, 2 Torr N2 buffered cell. A fully optical
sensor is connected through an optical fiber to the laser head allowing for truly remote sensing and minimization
of the field perturbation. A detailed analysis of the CPT resonance parameters as a function of the optical
detuning has been made in order to get high sensitivity measurements. The magnetic field monitoring
performances and the best sensitivity obtained in a balanced differential configuration of the sensor are
presented
Restoring narrow linewidth to a gradient-broadened magnetic resonance by inhomogeneous dressing
No full textWe study the possibility of counteracting the line broadening of atomic magnetic resonances due to inhomogeneities of the static magnetic field by means of spatially dependent magnetic dressing, driven by an alternating field that oscillates much faster than the Larmor precession frequency. We demonstrate that an intrinsic resonance linewidth of 25 Hz that has been broadened up to hundreds of hertz by a magnetic field gradient can be recovered by the application of an appropriate inhomogeneous dressing field. The findings of our experiments may have immediate and important implications, because they enable the use of atomic magnetometers as robust, high-sensitivity sensors to detect in situ the signal from ultralow-field NMR-imaging setups
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