CN110389307B - Quartz resonance type MEMS magnetic field sensor - Google Patents
Quartz resonance type MEMS magnetic field sensor Download PDFInfo
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- CN110389307B CN110389307B CN201810338947.1A CN201810338947A CN110389307B CN 110389307 B CN110389307 B CN 110389307B CN 201810338947 A CN201810338947 A CN 201810338947A CN 110389307 B CN110389307 B CN 110389307B
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
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- G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
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Abstract
The invention provides a quartz resonance type MEMS magnetic field sensor, which comprises a quartz tuning fork, a current-carrying elastic supporting beam, an oscillating circuit and a frequency meter, wherein the quartz tuning fork is arranged on the current-carrying elastic supporting beam; two ends of the quartz tuning fork are respectively fixed on a current-carrying elastic supporting beam; the oscillating circuit is connected with an electrode on the quartz tuning fork and used for exciting the tuning fork to generate resonance; the frequency meter is used for detecting a frequency signal output by the oscillating circuit; the ampere force generated by the current-carrying elastic support beam under the action of the magnetic field is transferred to the quartz tuning fork to enable the quartz tuning fork to be stressed axially, so that the resonant frequency of the quartz tuning fork is changed, and the frequency change quantity of the quartz tuning fork is detected by using a frequency meter to detect the magnetic field. The invention has high Q value, low loss, high detection sensitivity and resolution, and can be used for detecting static, quasi-static and low-frequency magnetic fields.
Description
Technical Field
The invention relates to a quartz resonance type MEMS magnetic field sensor, in particular to a magnetic field sensor adopting a quartz crystal resonator with a high Q value.
Background
The traditional magnetic field sensor mainly comprises a Hall sensor, a fluxgate sensor, a superconducting quantum interferometer, a giant magneto-impedance sensor, an electromagnetic induction sensor, a magnetic sensing diode magnetic sensor, a magnetic sensing triode magnetic sensor and the like. These conventional magnetic sensors generally output weak analog signals, often require complex signal conditioning circuits to process the analog signals, and have poor signal interference resistance.
A novel magnetoelectric sensor formed by laminating and compounding a magnetostrictive material and a piezoelectric material is currently available. The magnetostrictive/piezoelectric composite material obtains a magnetoelectric effect due to a product effect, converts a magnetic field to be measured into an electric signal, and has the typical advantages that the magnetoelectric conversion coefficient is large, but the output of the magnetostrictive/piezoelectric composite material is an analog signal, and when the magnetostrictive/piezoelectric composite material is used for measuring a static magnetic field and a quasi-static magnetic field, an external excitation magnetic field source is needed, so that the problem of complicated driving and demodulating circuits exists.
A resonant sensor is a sensor that operates by relying on a resonant structure, and is widely used for detecting various parameters. When the resonant magnetic field sensor detects a magnetic field, the magnetic field acts on the current-carrying elastic support beam to generate an ampere force, and then the ampere force is transmitted to the resonator to change the resonant frequency of the resonant structure. The ampere force is measured by measuring the variable quantity of the resonance frequency modulated by the ampere force, and the aim of magnetic field detection can be achieved through a theoretical conversion formula. The resonant magnetic field sensor designed by Joshua E. -Y.Lee et al adopts silicon to manufacture a resonator, the silicon does not have piezoelectricity, the resonator needs to be excited to vibrate in an electrostatic excitation mode during working, the signal detection mode also adopts an electrostatic excitation capacitor to detect, and an excitation and detection circuit is complex.
Disclosure of Invention
Aiming at various defects of the magnetic field sensor, the invention provides the quartz resonance type MEMS magnetic field sensor, which adopts a quartz tuning fork resonator made of a high-Q value quartz material as a core unit for magnetic field detection, has the advantages of high Q value and low loss during magnetic field detection, has high sensitivity and high resolution, can be used for high-sensitivity detection of static, quasi-static and low-frequency magnetic fields, and has small volume and low cost.
In order to solve the above technical problem, the present invention provides a quartz resonant MEMS magnetic field sensor, which includes a quartz tuning fork, a current-carrying elastic support beam, an oscillation circuit, and a frequency meter; two ends of the quartz tuning fork are respectively fixed on a current-carrying elastic supporting beam; the oscillating circuit is connected with an electrode on the quartz tuning fork and used for exciting the tuning fork to generate resonance; the frequency meter is used for detecting a frequency signal output by the oscillating circuit.
Further, the ampere force generated by the current-carrying elastic support beam under the action of the magnetic field is transferred to the quartz tuning fork to enable the quartz tuning fork to be stressed axially, so that the resonant frequency of the quartz tuning fork is changed, and the frequency change quantity of the quartz tuning fork is detected by using a frequency meter to detect the magnetic field.
Furthermore, the two current-carrying elastic supporting beams are parallel to each other, two ends of each current-carrying elastic supporting beam are mounted on the frame, and the length direction of the quartz tuning fork is perpendicular to that of the current-carrying elastic supporting beams.
Further, the quartz tuning fork is manufactured by using a Z-cut quartz substrate.
Further, the quartz tuning fork comprises two vibrating beams, the tuning fork vibrating beams are provided with four surfaces and four electrodes, two of the four electrodes are positive electrodes, the other two electrodes are negative electrodes, and the positive electrodes and the negative electrodes are arranged at intervals; dividing the tuning fork vibrating beam into three parts by taking two positions with stress close to zero as demarcation points, wherein each electrode also comprises three parts which are sequentially connected along the length direction of the vibrating beam, and the three parts of the tuning fork vibrating beam correspond to the three parts of the electrode; meanwhile, three parts of each electrode are respectively positioned on three adjacent surfaces on the vibrating beam.
Further, assuming that the length of the tuning fork vibrating beam is L, two positions where the stress is close to zero are 0.22L and 0.76L, respectively.
Furthermore, welding pads are led out from two ends of each electrode and are used for being connected with the oscillating circuit.
Furthermore, the surface of the current-carrying elastic support beam is plated with a metal current conductor along the length direction, and under the working state, currents with equal magnitude and opposite directions flow along the length direction of the two current-carrying elastic support beams.
Further, the current is provided by a current generating module.
Furthermore, a current input pad is led out of the metal current conductor and used for being connected with the current generation module, and the current input pad is installed on the frame.
Compared with the prior art, the invention has the remarkable advantages that:
(1) the output of the resonant MEMS magnetic field sensor is a digital frequency signal, and compared with a magnetic field sensor for outputting an analog signal, the resonant MEMS magnetic field sensor does not need a complex detection circuit and does not need A/D conversion;
(2) the invention adopts the piezoelectric quartz with high Q value to manufacture the resonator, can make the tuning fork vibrate only by extremely small driving power consumption, and has simple driving circuit and detection circuit;
(3) the resonance frequency of the quartz tuning fork resonator is dozens of kilohertz and far higher than the environmental noise, and the broadband and quick response can be still kept even if a filter is adopted for noise reduction, so that the method for realizing magnetic field measurement through frequency measurement has the advantages of inherent insensitivity to noise, strong anti-interference capability and suitability for use in severe electromagnetic environments.
Drawings
FIG. 1 is a schematic diagram of a quartz resonant magnetic field sensor in accordance with the present invention;
FIG. 2 is a schematic structural diagram of a magnetic sensing unit in the quartz resonant magnetic field sensor according to the present invention;
FIG. 3 is a partial enlarged view of a current-carrying resilient support beam in the resonant magnetically susceptible unit;
FIG. 4 is a schematic diagram of the application of tuning fork vibration beam electrodes in the quartz resonant magnetic field sensor according to the present invention.
Detailed Description
It is easily understood that according to the technical solution of the present invention, those skilled in the art can imagine various embodiments of the quartz resonant MEMS magnetic field sensor of the present invention without changing the essential spirit of the present invention. Therefore, the following detailed description and the accompanying drawings are merely illustrative of the technical aspects of the present invention, and should not be construed as all of the present invention or as limitations or limitations on the technical aspects of the present invention.
In the quartz resonant MEMS magnetic field sensor, the resonant magnetic sensitive unit adopts an integrated structure design, and a quartz tuning fork with two fixed ends, a current-carrying elastic support beam and an electrode are integrated on a quartz substrate. When the quartz tuning fork works in a magnetic field, the current-carrying elastic support beam generates an ampere force under the action of the magnetic field, the ampere force is transmitted to the quartz tuning fork to enable the quartz tuning fork to be axially stressed, the quartz tuning fork which transversely vibrates is very sensitive to the axial force, therefore, the resonant frequency of the tuning fork is changed, and the purpose of magnetic field detection can be achieved by detecting the frequency variation of the quartz tuning fork.
Examples
As shown in fig. 1, the quartz resonant MEMS magnetic field sensor of the present embodiment includes a resonant magnetic sensitive unit, a current generating module, and an oscillating circuit. The resonant type magnetic sensitive unit is an integrated structure made of a high-Q quartz material, and as shown in FIG. 2, the resonant type magnetic sensitive unit comprises a quartz tuning fork 1 with two fixed ends, a current-carrying elastic support beam 2, a current input pad 3 and a tuning fork excitation pad 4.
The quartz tuning fork comprises a quartz tuning fork 1 with two fixed ends, wherein the quartz tuning fork 1 comprises two vibrating beams which are the same in size and are parallel to each other. The two ends of the quartz tuning fork 1 are respectively fixed in the middle of the two current-carrying elastic support beams 2, the length direction of the quartz tuning fork 1 is perpendicular to the length direction of the current-carrying elastic support beams 2, and the two ends of the current-carrying elastic support beams 1 are respectively fixed on a frame integrated with the current-carrying elastic support beams.
Preferably, the quartz tuning fork 1 is made of a Z-cut quartz substrate insensitive to temperature response. The electrodes with special shapes are prepared on the upper, lower, left and right surfaces of the vibration beam of the tuning fork through the processes of photoetching, corrosion, electrode sputtering and the like. Assuming that the length of the vibrating beam is L, the invention reverses the coating positive and negative electrodes near the positions of 0.224 and 0.776 times (0.224L, 0.776L) the length of the vibrating beam, as shown in FIG. 4. In fig. 4, the electrode (Vd) on the plane perpendicular to the Z axis, represented by the section a-a (left part of the vibration beam in the horizontal view), and the electrode (Vd) on the plane perpendicular to the X axis, represented by the section C-C (right part of the vibration beam in the horizontal view), are positive electrodes, the electrode (Vd) on the plane perpendicular to the X axis, represented by the section B-B, are positive electrodes, and the electrode (G) on the plane perpendicular to the Z axis, are negative electrodes. That is, when the positive and negative electrodes are connected to the oscillation circuit, the electric polarization direction inside the oscillation beam is reversed with the (0.224L, 0.776L) position as a boundary point, and the stress distribution direction generated inside the oscillation beam due to the inverse piezoelectric effect is also reversed, so that the oscillation modes with opposite oscillation directions and symmetrical oscillation shapes are induced. The advantage of this mode of vibration is that the bending moments of the two vibrating beams at the two ends cancel each other out, which greatly reduces the energy loss. In order to facilitate exciting the vibration of the quartz tuning fork vibration beam and detecting the electric signals in the surface electrode of the vibration beam, the positive electrode and the negative electrode are respectively led out to the bonding pad 4, as shown in fig. 4. In addition, the two ends of the electrode pad are respectively provided with an extraction electrode, namely two pads G and a pad Vd are respectively arranged, and the manufacturing quality of the surface electrode can be judged by detecting whether the two pads G are conducted or not and the resistance value between the two pads Vd
Specifically, when the tuning forks generate vibration modes with opposite vibration directions and symmetric vibration shapes, the stress is close to 0 in the vicinity of the positions 0.22 times and 0.76 times the tuning fork length L. By taking the position where the stress is close to 0 as a demarcation point, the vibration beam of the tuning fork can be divided into three sections, and then the stress distribution direction inside the three sections of vibration beams is reversed, so that the electric polarization inside the electromagnetic super (piezoelectric) material is reversed, and therefore the positive electrode and the negative electrode on the surface of the vibration beam for extracting the electric charges generated by the electric polarization are sequentially reversed in the three sections. As shown in fig. 4, for the right vibration beam, the upper section a-a of the right vibration beam and the lower section C-C of the vibration beam, the electrode perpendicular to the Z-axis is the positive electrode G, the surface perpendicular to the X-axis is the negative electrode Vd, the middle section B-B of the vibration beam, the electrode perpendicular to the Z-axis is the negative electrode Vd, and the surface perpendicular to the X-axis is the positive electrode G; wherein, the lower positive electrode G of the upper section A-A section, the right positive electrode G of the middle section B-B section and the bottom positive electrode G of the lower section C-C section are the same positive electrode which is inverted on the bottom surface, the right side surface and the upper surface of the right side vibration beam in turn; the upper positive electrode G of the upper section A-A section, the left positive electrode G of the middle section B-B section and the upper positive electrode G of the lower section C-C section are the inversions of the same positive electrode on the upper surface, the left surface and the lower surface of the right vibrating beam in sequence. In the same way, the other two negative electrodes are reversely arranged on the vibrating beam in three sections in sequence. The left vibrating beam has the same structure as the right vibrating beam, the upper section A-A, the lower section of the vibrating beam and the C-C section of the vibrating beam, the electrode vertical to the Z-axis surface is a negative electrode Vd, the surface vertical to the X-axis surface is an positive electrode G, the middle section B-B of the vibrating beam, the electrode vertical to the Z-axis surface is a positive electrode G, and the surface vertical to the X-axis surface is a negative electrode Vd. On the four faces of the left vibrating beam, two pairs of electrodes are also inverted in three sections. However, on two opposite surfaces of the left vibration beam and the right vibration beam, the three corresponding electrodes are opposite.
In order to facilitate the detection of electric signals on the quartz vibrating beam surface electrode, a positive electrode bonding pad G and a negative electrode bonding pad Vd are respectively led out from the two ends of the positive electrode and the negative electrode. The manufacturing quality of the surface electrode can be judged by detecting whether the positive electrode bonding pads G at the two ends of the vibration beam are conducted or not and the resistance value between the negative electrode bonding pads Vd at the two ends of the vibration beam
The tuning fork excitation pad 4 is connected to an oscillator circuit, preferably a gate circuit as shown in the dashed box of fig. 1. When the power supply in the oscillating circuit is switched on, a tiny disturbing signal which is a non-sinusoidal signal and contains a series of sinusoidal components with different frequencies is excited in the oscillating circuit and is amplified and fed back to the quartz resonator, the quartz resonator is a frequency selection network and can select a sinusoidal component with a single frequency to be output, and the output frequency signal can be detected by a frequency meter.
Preferably, the oscillation circuit may be a pierce oscillation circuit, a butler oscillation circuit, or the like.
The surface of the current-carrying elastic supporting beam 2 is plated with metal electrodes in the axial direction for current transmission, current input pads 3 are led out from two ends of the elastic supporting beam 2 to a fixed frame of the elastic supporting beam, and when a current output end of the current generation module is connected with the current input pads 3 of the current-carrying elastic supporting beam 2, current passes through the surface electrodes of the current-carrying elastic supporting beam 2. Through designing the connection relation between the current positive and negative output ends and the current input bonding pad 3, the two current-carrying elastic supporting beams 2 flow the currents with equal magnitude but opposite directions.
The current generation module can generate alternating current or direct current with the amplitude of 0.5 mA-200 mA, and can be typically realized by a programmable current source of a shelf product, such as LT3092 and the like.
When the sensor works, when the current direction in the current-carrying elastic support beam 2 on the left is a vertical direction from bottom to top, and the current direction in the current-carrying elastic support beam 2 on the right is a vertical direction from top to bottom opposite to the left, the direction of the magnetic field B is perpendicular to the paper surface and faces inwards, the current-carrying elastic support beam on the left generates an ampere force F horizontally towards the left, and the current-carrying elastic support beam on the right receives the ampere force F with equal magnitude and opposite direction (namely horizontally towards the right), as shown in fig. 1, the ampere force F is transmitted to the quartz tuning fork in the middle to enable the quartz tuning fork 1 to be axially stressed (pulled or pressed), so that the resonance frequency of the quartz crystal tuning fork resonator changes due to the force frequency effect. The magnetic field measurement can be realized by detecting the variation of the resonant frequency through the frequency meter.
The frequency meter can be realized by taking reference to the existing frequency measurement circuit and method, and can typically realize high-precision frequency measurement by adopting a non-periodic synchronization method based on an FPGA chip.
It is known from the knowledge about the lorentz force that the moving charges in the magnetic field are acted by the magnetic field to generate the lorentz force, and the moving charges in the current are negative charges, so that the current-carrying conductors in the magnetic field are acted by the same magnitude of the lorentz force and opposite direction of the lorentz force. In the quartz resonant MEMS magnetic field sensor, two ends of a quartz tuning fork resonator are connected with a current-carrying elastic supporting beam, the current-carrying elastic supporting beam generates Lorentz force under the action of a magnetic field in the magnetic field, the Lorentz force is transmitted to a quartz tuning fork to enable the quartz tuning fork to be stressed axially, and the tuning fork vibrating transversely is sensitive to the axial force, so that the change of the resonant frequency of the quartz tuning fork, namely frequency drift, can be caused. The magnetic field detection can be achieved by measuring the change of the resonant frequency of the quartz tuning fork and converting the change into the change of the magnetic field. The output signal of the quartz resonance type MEMES magnetic field sensor is a digital frequency signal which has strong anti-interference capability and does not need a complex signal processing circuit, thereby greatly reducing the noise influence caused by adopting the complex signal processing circuit and having important significance for improving various performance indexes of the magnetic field sensor.
Claims (8)
1. The quartz resonance type MEMS magnetic field sensor is characterized by comprising a quartz tuning fork, a current-carrying elastic supporting beam, an oscillating circuit and a frequency meter; two ends of the quartz tuning fork are respectively fixed on a current-carrying elastic supporting beam; the oscillating circuit is connected with an electrode on the quartz tuning fork and used for exciting the quartz tuning fork to generate resonance; the frequency meter is used for detecting a frequency signal output by the oscillating circuit; the ampere force generated by the current-carrying elastic support beam under the action of the magnetic field is transferred to the quartz tuning fork to enable the quartz tuning fork to be stressed axially, so that the resonance frequency of the quartz tuning fork is changed, and the frequency change quantity of the quartz tuning fork is detected by using a frequency meter to detect the magnetic field;
the quartz tuning fork comprises two vibrating beams; the tuning fork vibration beam is provided with four surfaces and four electrodes, wherein two electrodes are positive electrodes, the other two electrodes are negative electrodes, and the positive electrodes and the negative electrodes are arranged at intervals; dividing the tuning fork vibrating beam into three parts by taking two positions with stress close to zero as demarcation points, wherein each electrode also comprises three parts which are sequentially connected along the length direction of the vibrating beam, and the three parts of the tuning fork vibrating beam correspond to the three parts of the electrode; meanwhile, three parts of each electrode are respectively positioned on three adjacent surfaces on the vibrating beam.
2. A quartz resonant MEMS magnetic field sensor according to claim 1 wherein the two current carrying resilient support beams are parallel to each other, both ends of the current carrying resilient support beams are mounted on the frame, and the length of the quartz tuning fork is perpendicular to the length of the current carrying resilient support beams.
3. The quartz resonant MEMS magnetic field sensor of claim 1, wherein the quartz tuning fork is fabricated using a Z-cut quartz substrate.
4. A quartz resonant MEMS magnetic field sensor as claimed in claim 1 wherein assuming a tuning fork beam length L, the two locations where the stress is near zero are 0.22L and 0.76L respectively.
5. A quartz resonator MEMS magnetic field sensor according to claim 1 wherein pads are extended from both ends of each electrode for connection to the oscillator circuit.
6. A quartz resonant MEMS magnetic field sensor according to claim 1 wherein the surfaces of the current carrying resilient support beams are plated with metal current conductors along their lengths, and wherein equal but opposite currents flow along the lengths of the two current carrying resilient support beams during operation.
7. A quartz resonant MEMS magnetic field sensor according to claim 6, wherein the current generating module provides the current.
8. A quartz resonator MEMS magnetic field sensor according to claim 7, wherein the metal current conductor has a current input pad extending therefrom for connection to the current generating module, the current input pad being mounted on the frame.
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| CN103471760A (en) * | 2013-09-18 | 2013-12-25 | 中国电子科技集团公司第二十六研究所 | Force sensing resonant element and manufacturing method thereof |
| CN103713157A (en) * | 2014-01-09 | 2014-04-09 | 中国电子科技集团公司第二十六研究所 | Resonant type acceleration sensor |
| CN105301344A (en) * | 2015-09-24 | 2016-02-03 | 西安电子科技大学 | Quartz resonant DC voltage sensor chip based on driving beam arrays |
| CN205562088U (en) * | 2016-05-03 | 2016-09-07 | 成都皆为科技有限公司 | Quartzy resonance power of integral type is sensing element and dynamometry module frequently |
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- 2018-04-16 CN CN201810338947.1A patent/CN110389307B/en active Active
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101515026A (en) * | 2009-03-20 | 2009-08-26 | 东南大学 | Resonance micro electromechanical system magnetic field sensor and measuring method thereof |
| CN101604007A (en) * | 2009-07-14 | 2009-12-16 | 重庆大学 | The Magnetic Sensor that high-permeability material and quartz tuning-fork are compound |
| CN103471760A (en) * | 2013-09-18 | 2013-12-25 | 中国电子科技集团公司第二十六研究所 | Force sensing resonant element and manufacturing method thereof |
| CN103713157A (en) * | 2014-01-09 | 2014-04-09 | 中国电子科技集团公司第二十六研究所 | Resonant type acceleration sensor |
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