Resonant Magnetic Field Sensor With Frequency Output

Abstract

This paper presents a novel type of resonant magnetic field sensor exploiting the Lorentz force and providing a frequency output. The mechanical resonator, a cantilever structure, is embedded as the frequency-determining element in an electrical oscillator. By generating an electrical current proportional to the position of the cantilever, a Lorentz force acting like an additional equivalent spring is exerted on the cantilever in the presence of a magnetic field. Thus, the oscillation frequency of the system, which is a function of the resonator's equivalent spring constant, is modulated by the magnetic field to be measured. The resonant magnetic field sensor is fabricated using an industrial CMOS process, followed by a two-mask micromachining sequence to release the cantilever structure. The characterized devices show a sensitivity of 60 kHz/Tesla at their resonance frequency f 0 = 175 kHz and a short-term frequency stability of 0.025 Hz, which corresponds to a resolution below 1 T. The devices can thus be used for Earth magnetic field applications, such as an electronic compass. The novel resonant magnetic field sensor benefits from an efficient continuous offset cancellation technique, which consist in evaluating the frequency difference measured with and without excitation current as output signal.[1676]

Magnetic Field Sensors Based on Microelectromechanical Systems (MEMS) Technology

“…Other examples of piezoresistive magnetic sensors on the microscale have been reported in the literature (Beroulle et al (2003), Sunier et al (2006)). …”

Development of Resonant Magnetic Field Microsensors: Challenges and Future Applications

“…It has a sensitivity of 0.53 VT -1 , a theoretical resolution of 2 T, a thermal noise of 5.3 nVHz -1/2 , a resonant frequency of 8.97 kHz, a quality factor of 59, and a mass of 750 ng. Sunier et al (2006) developed a magnetic field microsensor using a resonant silicon structure, a planar aluminium coil, two heating resistors, and P-channel Metal Oxide Semiconductor (PMOS) transistors (see Fig. 11).…”

Effects of the pulse-driven magnetic field detuning on the calibration of coil constants while using noble gases

“…[7][8][9][10] In order to provide a precise magnetic field, an accurate calibration of its coil constant is of great importance. There are many different ways for achieving this purpose.…”