Nonlinear sensitivity enhancement of resonant microsensors and its application to low power magnetic sensing

Abstract

Nonlinearities in resonating structures can be used to increase the sensitivity of sensors based on these structures. An example system, a torsional resonant magnetic sensor, is analyzed to illustrate the effect. The system is composed of a disk-type silicon resonator combined with a permanent magnet supported by multiple micromachined silicon beams, excitation and sensing coils, and a magnetic feedback loop. The effects of nonlinearity on sensitivity have been characterized as a function of beam width and the number of beams using analytical models as well as numerical analysis. By increasing the number of beams while reducing the beam width (and thereby maintaining constant nominal linear resonant frequency), large nonlinearity has been obtained, resulting in an increased change in operating resonant frequency per unit applied magnetic field. The interaction between an external magnetic field surrounding the sensor and the permanent magnet generates a rotating torque on the silicon resonator disk, changing the effective stiffness of the beams and therefore the resonant frequency of the sensor. By monitoring shifts in the resonant frequency while changing the orientation of the sensor with respect to the external magnetic field, the direction of the external magnetic field can be determined. Self-resonance-based electromagnetic excitation of the mechanical resonator enables it to operate with very low power consumption and low excitation voltage. A total system power consumption of less than 140 μW and a resonator actuation voltage of 1.4 mVrms from a ±1.2 V power supply have been demonstrated with a sensitivity of 0.28 Hz/rotational degree to the Earth's magnetic field.

Fabrication and Characterization of CMOS-MEMS Magnetic Microsensors

“…In comparison to Beroulle et al [30], Herrera-May et al [31] and Domínguez-Nicolás et al [33], the sensitivity of this work exceeds that of Beroulle et al [30] and Herrera-May et al [31]. The power consumption of the magnetic sensor proposed by Choi et al [7] was 140 μW, and the magnetic sensor presented by Li et al [8] had a power consumption of 0.58 mW. Comparing to Choi et al [7] and Li et al [8], the power consumption of this work is higher than that of both Choi et al [7] and Li et al [8].…”

A 3-D Micromechanical Multi-Loop Magnetometer Driven Off-Resonance by an On-Chip Resonator

“…the performance in [1]- [4]) are rapidly becoming competitive with commonly adopted technologies like Hall-effect, magnetic tunnel junction (MTJ) and anisotropic magneto-resistance (AMR) devices [5], [6]. This achievement is due to the conception and refinement of new operating principles, like parametric amplification [7], internal thermal-piezoresistive amplification [8], nonlinear sensitivity enhancement [9], off-resonance operation [1] or frequency modulation (FM) [2]. From a technological standpoint, it is advantageous to rely on MEMS magnetometers compatible with processes used for accelerometers and gyroscopes, so to form single-chip, single-process multi-parameter, multi-axis inertial measurement units (IMUs).…”

A MEMS-based magnetic field sensor with simple resonant structure and linear electrical response

“…Choi et al [11,12] developed a magnetic field sensing system to detect the direction of the Earth's magnetic field. This system consists of a disktype silicon resonator, a permanent magnet, excitation and sensing coils, and a magnetic feedback loop.…”