A magnetic sensor based on surface acoustic wave mode localization

Abstract

The application provides a magnetic sensor based on surface acoustic wave mode localization, and belongs to the technical field of magnetic sensors.The magnetic sensor comprises a piezoelectric substrate, interdigital transducer units arranged on the end surface of the piezoelectric substrate at intervals along a first preset direction, the first preset direction being the length direction of the piezoelectric substrate, a coupling grid arranged on the end surface of the piezoelectric substrate and located on the side adjacent to the interdigital transducer units, and two reflection grids arranged on the end surface of the piezoelectric substrate and respectively located on the sides not adjacent to the interdigital transducer units, wherein the interdigital transducer units are distributed on the two sides of the center surface of the piezoelectric substrate with unequal masses. The interdigital electrodes, the coupling grid and the reflection grid are reasonably arranged, when the magnetic sensitive interdigital transducer units are subjected to the change of the external magnetic field, the original symmetry of the device is changed, the resonance state is disturbed, and then the change of the external magnetic field is sensitively recognized through the output of the interdigital electrodes according to the principle of mode localization.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of magnetic sensor, and in particular to a magnetic sensor based on surface acoustic wave mode localization. BACKGROUND

[0002] With the continuous progress of technology, especially in the field of material science and microfabrication technology, new materials have significantly improved the sensitivity and stability of sensors. The progress of microelectromechanical systems technology has also driven the miniaturization and integration of magnetic sensors, but still faces some challenges, such as the influence of external environment on sensor performance, and the stability and reliability of sensors in long-term use.

[0003] Mode localization refers to a phenomenon that energy is captured in space after introducing disorder in a coupled oscillation system, which means that the vibration amplitude of certain areas increases significantly, while the vibration amplitude of other areas decreases or almost disappears, which is the phenomenon of spatial localization of modal energy.

[0004] Therefore, it is necessary to provide a magnetic sensor based on surface acoustic wave mode localization, which introduces mode localization on the basis of traditional magnetic sensors to detect small changes in magnetic field strength and achieve high-sensitivity sensing detection. SUMMARY

[0005] Therefore, it is necessary to provide a magnetic sensor based on surface acoustic wave mode localization, which introduces mode localization on the basis of traditional magnetic sensors to detect small changes in magnetic field strength and achieve high-sensitivity sensing detection.

[0006] The technical solution of the present application is as follows: The present application provides a magnetic sensor based on surface acoustic wave mode localization, comprising:

[0007] A piezoelectric substrate;

[0008] Interdigital transducer units are arranged at different positions on the end surface of the piezoelectric substrate along a first predetermined direction; the first predetermined direction is the length direction of the piezoelectric substrate;

[0009] A coupling grid is arranged on the end surface of the piezoelectric substrate and located on one side adjacent to the interdigital transducer units;

[0010] Two reflection grids are arranged on the end surface of the piezoelectric substrate and located on the sides not adjacent to the interdigital transducer units, respectively;

[0011] Among them, the interdigital transducer units are distributed on both sides of the center surface of the piezoelectric substrate with unequal mass.

[0012] On the basis of the above technical scheme, preferably, the interdigital transducing unit comprises a first interdigital transducer, a second interdigital transducer, a third interdigital transducer and a fourth interdigital transducer, the first interdigital transducer and the second interdigital transducer are adjacent and located on one side of the end face of the piezoelectric substrate, the third interdigital transducer and the fourth interdigital transducer are adjacent and located on the other side of the end face of the piezoelectric substrate; the resistances of the first interdigital transducer, the second interdigital transducer, the third interdigital transducer and the fourth interdigital transducer are the same, and the material of the fourth interdigital transducer is different from that of the first interdigital transducer, the second interdigital transducer and the third interdigital transducer.

[0013] Preferably, the distances from the second interdigital transducer and the third interdigital transducer to the center plane of the piezoelectric substrate are equal; the distances from the first interdigital transducer and the fourth interdigital transducer to the center plane of the piezoelectric substrate are equal.

[0014] Further preferably, the first interdigital transducer, the second interdigital transducer, the third interdigital transducer, the coupling grid and the two reflection grids all adopt non-magnetic sensitive metal materials; the material of the fourth interdigital transducer is a magnetic sensitive metal material.

[0015] More preferably, the non-magnetic sensitive metal material is aluminum, copper, silver or gold, and the magnetic sensitive metal material is nickel, iron or cobalt.

[0016] Preferably, the interdigital transducing unit and the coupling grid are both provided with a plurality of metal electrode pairs, each of the plurality of metal electrode pairs comprises a first electrode and a second electrode arranged alternately, and the length, width and spacing of the adjacent first electrode and second electrode are all equal.

[0017] Further preferably, each of the two reflection grids comprises a plurality of third electrodes, and the plurality of third electrodes are arranged at intervals along the first preset direction; the length and width of the third electrode are equal to the length and width of the second electrode, and the spacing between the adjacent third electrodes is also equal to the spacing between the adjacent first electrode and second electrode.

[0018] More preferably, the widths of the first interdigital transducer, the second interdigital transducer, the third interdigital transducer and the fourth interdigital transducer along the first preset direction are all equal, and the width of each interdigital transducer along the first preset direction is smaller than the width of the coupling grid along the first preset direction.

[0019] More preferably, the ratio of the width of a single reflection grid along the first preset direction to the width of the coupling grid along the first preset direction is 1:2.

[0020] Further preferably, the number of the metal electrode pairs of the first interdigital transducer, the second interdigital transducer, the third interdigital transducer and the fourth interdigital transducer is 10 pairs.

[0021] The application provides a magnetic sensor based on surface acoustic wave mode localization.

[0022] (1) The application is based on the mode localization principle on the basis of a traditional surface acoustic wave magnetic sensor, utilizes the principle of symmetry sensitive characteristics, when the magnetic sensitive metal material of the interdigital transducer unit on one side of the piezoelectric substrate senses the magnetic field change, the original resistance symmetry is broken and the output characteristics are changed, so that the magnetic field can be identified with high sensitivity.

[0023] (2) The width of the single-sided reflection grid and the width of the coupling grid are 1:2, so that the sensor has good magnetic sensitivity characteristics, especially for the magnetic field sensitive performance in the range of 0-50nT, and the width ratio constraint relationship changes will affect the magnetic sensitivity characteristics of the sensor. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description. Obviously, the drawings in the following description are only some embodiments of the application, and for those skilled in the art, other drawings can also be obtained without creative labor.

[0025] Figure 1 The spring model diagram of the mode localization of the application of a kind of magnetic sensor based on surface acoustic wave mode localization;

[0026] Figure 2 The graph of the vector X1 changing with the parameter delta of the application of a kind of magnetic sensor based on surface acoustic wave mode localization under different coupling conditions;

[0027] Figure 3 The structural schematic diagram of the application of a kind of magnetic sensor based on surface acoustic wave mode localization;

[0028] Figure 4 The structure diagram corresponding to embodiment 1 of the application of a kind of magnetic sensor based on surface acoustic wave mode localization;

[0029] Figure 5 The test result diagram corresponding to embodiment 1 of the application of a kind of magnetic sensor based on surface acoustic wave mode localization;

[0030] Figure 6 The graph of the relationship between the applied magnetic field and the peak voltage of embodiment 1 of the application of a kind of magnetic sensor based on surface acoustic wave mode localization;

[0031] Figure 7A structure schematic diagram of a comparative example of a magnetic sensor based on surface acoustic wave mode localization according to the present application;

[0032] Figure 8 A test result diagram of the comparative example of the magnetic sensor based on surface acoustic wave mode localization according to the present application.

[0033] Fig. 1 is a structure schematic diagram of a magnetic sensor based on surface acoustic wave mode localization according to the present application. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present application will be clearly and completely described in combination with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0035] As shown in Figure 1 , Figure 2 and Figure 3 , the present application provides a magnetic sensor based on surface acoustic wave mode localization, comprising:

[0036] a piezoelectric substrate 01;

[0037] an interdigital transducing unit 100, which is arranged at different positions on the end surface of the piezoelectric substrate 01 at intervals along a first preset direction; the first preset direction is the length direction of the piezoelectric substrate 01, i.e. Figure 3 the corresponding screen width direction in the middle.

[0038] a coupling gate 05, which is arranged on the end surface of the piezoelectric substrate 01 and located on one side adjacent to the interdigital transducing unit 100;

[0039] two reflection gates, which are arranged on the end surface of the piezoelectric substrate 01 and respectively located on the sides not adjacent to the interdigital transducing unit 100;

[0040] wherein the interdigital transducing unit 100 is distributed on both sides of the center plane of the piezoelectric substrate 01 in the horizontal direction, and the masses on both sides are not equal.

[0041] Now, the present application will be described in combination with the accompanying drawings, Figure 1 , Figure 1With the simplest modal localization spring model, only the basic force situation is considered, and the force analysis of each part of the basic spring model is listed and the equation is listed.

[0042] With the right as the positive direction, only one-dimensional motion is considered, and k1, k2 and k C The coupling amount of the three springs, the masses M1 and M2; for the left mass, the force is: F1=k C (x2-x1)-k1x1;

[0043] For the right mass, the force is: F2=-k C (x2-x1)-k2x2; x1 and x2 are the displacements of masses M1 and M2;

[0044] According to Newton's second law, it satisfies: k C (x2-x1)-k1x1=M1x″3(t); -k C (x2-x1)-k2x2=M2x″2(t); x″1(t) and x″2(t) are the second derivatives of displacement; the form of the equation directly solved is too complex, and under the stable mode, the solution of x1 and x2 is in the form of wave function, so it is set as: After taking the second derivative, we get: Where when the two masses are in a stable mode, the angular frequency of their motion must be equal, so set ω1=ω2=ω. The characteristic equation can be obtained:

[0045]

[0046] In order to further simplify, normalize each parameter, and at this time the two masses are equal, let k1=k2=k, k C / k=κ, M1=M2=M; the characteristic equation is rewritten as:

[0047] λ1=1, λ2=1+2κ, It can be seen that when the masses are equal, the system has two modes of same phase and opposite phase. In the same phase state, the amplitudes and directions of the two are the same, and in the opposite phase state, the amplitudes are the same and the directions are opposite.

[0048] When the two masses are not equal, assume that the mass deviation ΔM of the two masses is small, ΔM / M=δ<<1; then the characteristic equation becomes:

[0049] At this time, the characteristic values of λ and X solved are more complex, and the calculation is as follows:

[0050] In order to more clearly see the influence of the change of the parameters κ and δ on the formula, Figure 2 The curve of the first value in the vector X1 is described. It can be seen that when the parameter δ = 0, the value of the vector X1 is 1 no matter the value of the parameter κ, that is, when the two mass blocks are completely equal, the motion amplitudes of the two are also completely equal, regardless of the coupling amount k C

[0051] When the parameter δ takes a very small value, the value of the formula will change in the direction less than 1, and the smaller the parameter κ, the more obvious the change, that is, as long as there is a slight difference between the two mass blocks, the kinetic energy of the system will be concentrated on the mass block with larger mass.

[0052] As shown in Figure 3 , the interdigital transducing unit 100 comprises a first interdigital transducer 03, a second interdigital transducer 04, a third interdigital transducer 06 and a fourth interdigital transducer 07, the first interdigital transducer 03 and the second interdigital transducer 04 are adjacent and located on one side of the end face of the piezoelectric substrate 01, and the third interdigital transducer 06 and the fourth interdigital transducer 07 are adjacent and located on the other side of the end face of the piezoelectric substrate 01; the resistances of the first interdigital transducer 03, the second interdigital transducer 04, the third interdigital transducer 06 and the fourth interdigital transducer 07 are the same, and the material of the fourth interdigital transducer 07 is different from that of the first interdigital transducer 03, the second interdigital transducer 04 and the third interdigital transducer 06. It should be noted that the position of the fourth interdigital transducer 07 and the positions of the other three interdigital transducers can be interchanged, and the effect of the scheme is not affected, such as exchanging the position of the fourth interdigital transducer 07 with the position of any one of the first interdigital transducer, the second interdigital transducer and the third interdigital transducer, and the described position of the fourth interdigital transducer 07 is only used to illustrate the structure of the interdigital transducing unit 100, and is not regarded as a limitation on the scheme.

[0053] Further improvement, in the present application, the distances from the second interdigital transducer 04 and the third interdigital transducer 06 to the center plane in the horizontal direction of the piezoelectric substrate 01 are equal; the distances from the first interdigital transducer 03 and the fourth interdigital transducer 07 to the center plane in the horizontal direction of the piezoelectric substrate 01 are equal. Such a structure is to limit the relative symmetry relationship of the positions of the four interdigital transducers.

[0054] ​The first interdigital transducer 03, the second interdigital transducer 04, the third interdigital transducer 06, the coupling grid 05, and the two reflection grids, i.e., the first reflection grid 02 and the second reflection grid 08, are made of non-magnetic sensitive metal materials; and the fourth interdigital transducer 07 is made of magnetic sensitive metal materials. Specifically, the non-magnetic sensitive metal materials are aluminum, copper, silver or gold, and in this embodiment, aluminum is selected as an example; and the magnetic sensitive metal materials are nickel, iron or cobalt, and in this embodiment, nickel is selected as an example. In this way, when the external magnetic field changes, only the fourth interdigital transducer 07 made of the magnetic sensitive metal materials is affected, and other parts are not directly affected by the magnetic field.

[0055] The interdigital transducing unit 100 and the coupling grid 05 are both provided with a plurality of metal electrode pairs, each of which includes the first electrode 200 and the second electrode 300 arranged alternately, and the length, width and spacing of the adjacent first electrode 200 and second electrode 300 are all equal. The two reflection grids each include a plurality of third electrodes 400, and the third electrodes 400 are arranged at intervals along the first preset direction; the length and width of the third electrode 400 are equal to the length and width of the second electrode 300, and the spacing between the adjacent third electrodes 400 is also equal to the spacing between the adjacent first electrode 200 and second electrode 300. The first electrode 200 and the second electrode 300 of the metal electrode pair extend relative to each other and do not contact each other, and there is a gap between them, which is defined as being equivalent to the width of the first electrode or the second electrode.

[0056] The widths of the first interdigital transducer 03, the second interdigital transducer 04, the third interdigital transducer 06 and the fourth interdigital transducer 07 along the first preset direction are all equal, and the width of each interdigital transducer along the first preset direction is less than the width of the coupling grid 05 along the first preset direction.

[0057] In order to ensure the magnetic sensitivity of the sensor, the present application further limits the ratio of the width of a single reflection grid along the first preset direction to the width of the coupling grid 05 along the first preset direction to be 1:2.

[0058] The number of metal electrode pairs of the first interdigital transducer 03, the second interdigital transducer 04, the third interdigital transducer 06 and the fourth interdigital transducer 07 is 10 pairs. The number can be increased or decreased according to actual needs.

[0059] The technical effects of the present application will be described below through Example 1 and Comparative Example.

[0060] Embodiment 1: A grounding terminal 09 is prepared on the surface of a piezoelectric substrate 01 made of 128° YX-LiNbO3 material along a crystal direction; then a first interdigital transducer 03, a second interdigital transducer 04, a third interdigital transducer 06 and a fourth interdigital transducer 07 are prepared along a first preset direction of the piezoelectric substrate 01 and an extension direction of the grounding terminal 09; a coupling gate 05 is prepared on the surface of the piezoelectric substrate 01 between the second interdigital transducer 04 and the third interdigital transducer 06, and a first reflecting gate 02 and a second reflecting gate 08 are respectively prepared outside the first interdigital transducer 03 and the fourth interdigital transducer 07. As shown in Figure 4 , the width of the first electrode, the second electrode and the third electrode and the spacing p between adjacent electrodes are all 5 μm; the first interdigital transducer 03, the second interdigital transducer 04, the third interdigital transducer 06, the coupling gate 05, the first reflecting gate 02 and the second reflecting gate 08 are all made of aluminum material with a thickness of 100 nm; the fourth interdigital transducer 07 is made of nickel material with a metallization rate of 50% and a thickness of 250 nm. The width of the first reflecting gate 02 and the second reflecting gate 08 along the first preset direction is d1=d7=400p=2 mm. The width of the first interdigital transducer 03, the second interdigital transducer 04, the third interdigital transducer 06 and the fourth interdigital transducer 07 along the first preset direction is d2=d3=d5=d6=40p=200 μm; the width of the coupling gate 05 along the first preset direction is d4=800p=4 mm. The width of a single reflecting gate is ensured to be 1:2 of the width of the coupling gate.

[0061] According to the above parameters, a radio frequency voltage is applied to the first interdigital transducer 03 and the fourth interdigital transducer 07 on both sides to excite a Rayleigh wave of about 196 MHz in the piezoelectric substrate 01, and the direction of sound wave propagation is perpendicular to the length extension direction of each electrode. When the fourth interdigital transducer 07 senses a change in the external magnetic field, its resistance will change, which will change the original symmetry of the device, so that the change can be sensitively recognized through the electrical signal output by the third interdigital transducer 06 according to the principle of modal localization.

[0062] When there is no external magnetic field, a sharp peak appears near the resonance frequency of the test voltage. As the external magnetic field increases, the original symmetry of the device is destroyed, the resonance state is disturbed, and the peak value frequency of the originally sharp peak decreases. The sensitivity of the sensor can reach the order of nT. The test results are shown in Figure 5

[0063] After multiple measurements, the relationship between the applied magnetic field and the induced voltage is obtained, as shown in Figure 6 It can be seen that the modal localization sensor is relatively sensitive to the change of the magnetic field within 50 nT, especially in the range of 0 to 20 nT.

[0064] ​Comparative Example: A first interdigital transducer 03, a second interdigital transducer 04, a third interdigital transducer 06 and a fourth interdigital transducer 07 are prepared on the surface of a piezoelectric substrate 01 made of 128°YX-LiNbO3; a coupling grating 05 is prepared on the surface of the piezoelectric substrate 01 between the second interdigital transducer 04 and the third interdigital transducer 06; and a first reflecting grating 02 and a second reflecting grating 08 are prepared outside the first interdigital transducer 03 and the fourth interdigital transducer 07, respectively, all in the same manner as in Example 1. Figure 7 As shown in FIG. 1, the width of the first electrode, the second electrode and the third electrode and the spacing p between adjacent electrodes are all 5 μm; the first interdigital transducer 03, the second interdigital transducer 04, the third interdigital transducer 06, the coupling grating 05, the first reflecting grating 02 and the second reflecting grating 08 are all made of aluminum and have a thickness of 100 nm; and the fourth interdigital transducer 07 is made of nickel and has a metallization rate of 50% and a thickness of 250 nm.

[0065] The difference is that the width of the first reflecting grating 02 and the second reflecting grating 08 along the first preset direction is d1=d7=400p=2 mm. The width of the first interdigital transducer 03, the second interdigital transducer 04, the third interdigital transducer 06 and the fourth interdigital transducer 07 along the first preset direction is d2=d3=d5=d6=40p=200 μm; and the width of the coupling grating 05 along the first preset direction is d4=400p=2 mm. The width of a single reflecting grating is ensured to be 1:1 of the width of the coupling grating.

[0066] According to the above parameters, a radio frequency voltage is applied to the first interdigital transducer 03 and the fourth interdigital transducer 07 on both sides to excite a Rayleigh wave of about 196 MHz in the piezoelectric substrate 01, and the direction of the sound wave propagation is perpendicular to the length extension direction of each electrode. At this time, the inductive magnetic field intensity capability of the device is significantly reduced, as shown in FIG. 2. Figure 8 As shown in FIG. 2, it can be seen that the magnetic sensor based on the surface acoustic wave mode localization of the present embodiment has better sensitivity only when the width of a single reflecting grating is 1:2 of the width of the coupling grating.

[0067] The above description is only the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A magnetic sensor based on localization of surface acoustic wave modes, characterized in that, The application relates to a piezoelectric substrate (01) and an interdigital transducing unit (100) arranged at different positions on the end surface of the piezoelectric substrate (01) along a first preset direction; the first preset direction is the length direction of the piezoelectric substrate (01); the interdigital transducing unit (100) comprises a first interdigital transducer (03), a second interdigital transducer (04), a third interdigital transducer (06) and a fourth interdigital transducer (07); the first interdigital transducer (03) and the second interdigital transducer (04) are adjacent and located on one side of the end surface of the piezoelectric substrate (01); the third interdigital transducer (06) and the fourth interdigital transducer (07) are adjacent and located on the other side of the end surface of the piezoelectric substrate (01); the resistances of the first interdigital transducer (03), the second interdigital transducer (04), the third interdigital transducer (06) and the fourth interdigital transducer (07) are the same; the material of the fourth interdigital transducer (07) is different from that of the first interdigital transducer (03), the second interdigital transducer (04) and the third interdigital transducer (06); a coupling grid (05) is arranged on the end surface of the piezoelectric substrate (01) and located between the adjacent sides of the second interdigital transducer (04) and the third interdigital transducer (06); two reflection grids are arranged on the end surface of the piezoelectric substrate (01) and located on the sides not adjacent to the first interdigital transducer (03) and the fourth interdigital transducer (07) respectively; the interdigital transducing unit (100) is distributed on the two sides of the central surface of the coupling grid (05) and the masses on the two sides are not equal; the width of a single reflection grid along the first preset direction is 1 / 2 of the width of the coupling grid (05) along the first preset direction; the distances from the second interdigital transducer (04) and the third interdigital transducer (06) to the central surface of the piezoelectric substrate (01) are equal; the distances from the first interdigital transducer (03) and the fourth interdigital transducer (07) to the central surface of the piezoelectric substrate (01) are equal; the first interdigital transducer (03), the second interdigital transducer (04), the third interdigital transducer (06), the coupling grid (05) and the two reflection grids are all made of non-magnetic sensitive metal materials; the material of the fourth interdigital transducer (07) is a magnetic sensitive metal material; the non-magnetic sensitive metal material is aluminum, copper, silver or gold; the magnetic sensitive metal material is nickel, iron or cobalt; the interdigital transducing unit (100) and the coupling grid (05) are both provided with a plurality of metal electrode pairs; each metal electrode pair comprises first electrodes (200) and second electrodes (300) arranged alternately; the length, width and spacing of the adjacent first electrodes (200) and second electrodes (300) are equal; each reflection grid comprises a plurality of third electrodes (400) arranged alternately along the first preset direction; the length and width of the third electrodes (400) are equal to those of the second electrodes (300); the spacing between the adjacent third electrodes (400) is equal to that between the adjacent first electrodes (200) and second electrodes (300). ​ ​ ​ ​ ​ ​ ​ 2. The magnetic sensor based on surface acoustic wave mode localization according to claim 1, characterized in that, ​ 3. The magnetic sensor based on surface acoustic wave mode localization according to claim 2, characterized in that, ​ 4. The magnetic sensor based on surface acoustic wave mode localization according to claim 3, characterized in that, ​ 5. The magnetic sensor based on surface acoustic wave mode localization according to claim 1, characterized in that, ​ 6. The magnetic sensor based on surface acoustic wave mode localization according to claim 5, characterized in that, ​ 7. The magnetic sensor based on surface acoustic wave mode localization according to claim 6, characterized in that, The first interdigital transducer (03), the second interdigital transducer (04), the third interdigital transducer (06) and the fourth interdigital transducer (07) have equal widths along the first preset direction, and the width of each interdigital transducer along the first preset direction is less than the width of the coupling gate (05) along the first preset direction.

8. The magnetic sensor based on surface acoustic wave mode localization according to claim 5, characterized in that, The number of metal electrode pairs of the first interdigital transducer (03), the second interdigital transducer (04), the third interdigital transducer (06) and the fourth interdigital transducer (07) is 10 pairs.

Images