Electromagnetic gradiometers

Abstract

An electromagnetic gradiometer that includes multiple torsionally operated MEMS-based magnetic and/or electric field sensors with control electronics configured to provide magnetic and/or electric field gradient measurements. In one example a magnetic gradiometer includes a first torsionally operated MEMS magnetic sensor having a capacitive read-out configured to provide a first measurement of a received magnetic field, a second torsionally operated MEMS magnetic sensor coupled to the first torsionally operated MEMS magnetic sensor and having the capacitive read-out configured to provide a second measurement of the received magnetic field, and control electronics coupled to the first and second torsionally operated MEMS magnetic sensors and configured to determine a magnetic field gradient of the received magnetic field based the first and second measurements from the first and second torsionally operated MEMS electromagnetic sensors.

What is claimed is: 
     
         1 - 20 . (canceled) 
     
     
         21 . A magnetic gradiometer, comprising:
 a first torsionally operated microelectromechanical systems (MEMS) magnetic sensor having a capacitive read-out configured to provide a first measurement of a received magnetic field;   a second torsionally operated MEMS magnetic sensor coupled to the first torsionally operated MEMS magnetic sensor and having the capacitive read-out configured to provide a second measurement of the received magnetic field; and   control electronics coupled to the first and second torsionally operated MEMS magnetic sensors and configured to determine a magnetic field gradient of the received magnetic field based the first and second measurements from the first and second torsionally operated MEMS electromagnetic sensors.   
     
     
         22 . The magnetic gradiometer of  claim 21 , wherein in each of the first and second torsionally operated MEMS magnetic sensors includes:
 a proof-mass;   a magnetic dipole source coupled to the proof mass;   a substrate having a substrate offset space defined therein, wherein the proof-mass is suspended above the substrate offset space; and   a first sense electrode disposed on the substrate within the substrate offset space and positioned proximate the proof-mass, the first sense electrode being configured to measure a change in capacitance relative to the proof mass from torsional movement of the proof-mass in response to the received magnetic field at the magnetic dipole source.   
     
     
         23 . The magnetic gradiometer of  claim 22 , wherein each of the first and second torsionally operated MEMS magnetic sensors further includes a counterbalance coupled to the proof-mass, wherein the magnetic dipole source is coupled to a first surface of the proof-mass and the counterbalance is coupled to a second surface of the proof-mass distal the magnetic dipole source. 
     
     
         24 . The magnetic gradiometer of  claim 22 , wherein each of the first and second torsionally operated MEMS magnetic sensors further includes a second sense electrode disposed on the substrate, and wherein the first sense electrode and the second sense electrode are configured to provide a differential capacitance measurement based on the change in capacitance from the torsional movement of the proof-mass. 
     
     
         25 . The magnetic gradiometer of  claim 22 , wherein each of the first and second torsionally operated MEMS magnetic sensors further includes at least one drive electrode positioned proximate the proof-mass and configured to produce a feedback torque on the proof-mass. 
     
     
         26 . The magnetic gradiometer of  claim 22 , wherein the magnetic dipole source is a permanent magnet. 
     
     
         27 . The magnetic gradiometer of  claim 26 , wherein the permanent magnet is a Neodymium Iron Boron (NdFeB) rare Earth permanent magnet. 
     
     
         28 . The magnetic gradiometer of  claim 22 , wherein each of the first and second torsionally operated MEMS magnetic sensors further includes at least one support coupled to the proof-mass and configured to suspend the proof-mass above the substrate offset space. 
     
     
         29 . The magnetic gradiometer of  claim 28 , further comprising an electronic feedback loop configured to stabilize a scale factor of the magnetic gradiometer by monitoring and adjusting a resonant frequency of the at least one support. 
     
     
         30 . The magnetic gradiometer of  claim 23 , further comprising a circuit board that electrically couples the first torsionally operated MEMS magnetic sensor to the second torsionally operated MEMS magnetic sensor, wherein the control electronics is formed on the circuitboard. 
     
     
         31 . The magnetic gradiometer of  claim 30 , further comprising a reference structure that magnetically couples the first torsionally operated MEMS magnetic sensor to the second torsionally operated MEMS magnetic sensor. 
     
     
         32 . The magnetic gradiometer of  claim 31 , further comprising at least one reference magnet that produces a reference magnetic field configured to mutually align the first and second torsionally operated MEMS magnetic sensors to a common vector such that their magnetic moments are aligned. 
     
     
         33 . The magnetic gradiometer of  claim 32 , further comprising a high permeability shunt that couples together the first and second torsionally operated MEMS magnetic sensors and the at least one reference magnet. 
     
     
         34 . The magnetic gradiometer of  claim 33 , wherein the high permeability shunt includes a soft ferrite cage configured to provide shielding for the control electronics. 
     
     
         35 . An electric field gradiometer, comprising:
 a first torsionally operated microelectromechanical systems (MEMS) electric field sensor having a capacitive read-out configured to provide a first measurement of a received electric field;   a second torsionally operated MEMS electric field sensor coupled to the first torsionally operated MEMS electric field sensor and having the capacitive read-out configured to provide a second measurement of the received electric field; and   control electronics coupled to the first and second torsionally operated MEMS electric field sensors and configured to determine an electric field gradient of the received electric field based the first and second measurements from the first and second torsionally operated MEMS electric field sensors.   
     
     
         36 . The electric field gradiometer of  claim 35 , further comprising at least one electric field generator that produces a reference field configured to mutually align the first and second torsionally operated MEMS electric field sensors to a common vector such that their electric dipole moments are aligned. 
     
     
         37 . A gradiometer system comprising:
 at least two magnetic gradiometers, each magnetic gradiometer including:
 a first torsionally operated microelectromechanical systems (MEMS) magnetic sensor having a first magnetic field capacitive read-out configured to provide a first measurement of received magnetic field, 
 a second torsionally operated MEMS magnetic sensor coupled to the first torsionally operated MEMS magnetic sensor and having a second magnetic field capacity read-out configured to provide a second measurement of the received magnetic field, and 
 magnetic sensor control electronics coupled to the first and second torsionally operated MEMS magnetic sensors and configured to determine a magnetic field gradient of the received magnetic field based on the first and second measurements from the first and second torsionally operated MEMS electromagnetic sensors. 
   
     
     
         38 . The gradiometer system of  claim 37 , further comprising at least one electric field generator that produces a reference field configured to mutually align the first and second torsionally operated MEMS electric field sensors to a common vector such that their electric dipole moments are aligned. 
     
     
         39 . The gradiometer system of  claim 38 , wherein each of the first and second torsionally operated MEMS magnetic sensor includes:
 a proof-mass;   a magnetic dipole source coupled to the proof mass;   a substrate having a substrate offset space defined therein, wherein the proof-mass is suspended above the substrate offset space; and   a first sense electrode disposed on the substrate within the substrate offset space and positioned proximate the proof-mass, the first sense electrode being configured to measure a change in capacitance relative to the proof mass from torsional movement of the proof-mass in response to the received magnetic field at the magnetic dipole source.   
     
     
         40 . The magnetic gradiometer of claim  19 , wherein each of the first and second torsionally operated MEMS magnetic sensors further includes a counterbalance coupled to the proof-mass, wherein the magnetic dipole source is coupled to a first surface of the proof-mass and the counterbalance is coupled to a second surface of the proof-mass distal the magnetic dipole source.