CN102052989A - Capacitance pressure sensor with high Q value and large relative variable quantity - Google Patents

Abstract

The invention discloses a capacitance pressure sensor which is used for wireless and passive measurement. A capacitor is composed of an elastic vibrating diaphragm of which the periphery is fixedly supported; by means of adjusting the ratio of the radium of a circular electrode to the radius of the vibrating diagram and arranging insulated salient points and the like, the vibrating diagram is in a large strain state; and the ratio of the maximum capacitance to the initial capacitance is as big as possible so as to obtain the capacitance with high Q value and large relative variable quantity. After being connected with a surface acoustic wave transmitter, the capacitance pressure sensor with high Q value and large relative variable quantity can realize wireless and passive high-precise measurement on pressure and can be used for the monitoring field of automobile tyre pressure.

Description

The big relative variation capacitive pressure transducer of high Q value

Technical field:

The invention belongs to the pressure monitoring technical field, particularly a kind of pressure transducer that is adapted to the passive and wireless sensing, especially pole-changing is apart from capacitance pressure transducer.

Technical background:

Sensor with the work of passive and wireless mode is adapted to bad working environment, as high temperature, heavily contaminated, strong jamming etc., and the measurement that is not suitable for line and battery on rotation and the mobile object and provides various physics, chemistry or biomass under the situation of energy.Sensor with the work of passive and wireless mode in the prior art mainly contains two kinds: LC resonant mode and SAW (surface acoustic wave) formula.The former generally adopts capacitance type sensor, is measuring amount with the resonance frequency, realizes energy and information transmission in the inductive coupling mode, adapts to short operating distance.

Features such as volume is little, in light weight, frequency of operation is high for The latter SAW element (comprising resonator and lag line), the insertion loss is little, both can the SAW element this as sensing unit, can the SAW element be that transmission channel and traditional impedance transducer are realized the passive and wireless sensing together also.The SAW element can make traditional impedance transducer realize longer-distance data transmission with the work of passive and wireless mode with combining of traditional impedance transducer, can expand the application of SAW sensor again.

Based on the passive and wireless sensor of SAW element the requirement of impedance load sensor is comprised two: the one, the quality factor height, the 2nd, its value as electric capacity, has bigger relative variation.

Chinese patent literature CN1127354A discloses a kind of capacitive pressure or differential pressure pick-up, comprises the substrate of being made by stupalith, simultaneously is provided with an electrode and a glassy layer of being made by the pristine glass material at it; Diaphragm, the pristine glass raw material that is played the separation layer effect by stupalith system be connected to pressure seal to substrate, separation layer is fixed into diaphragm and substrate and forms a chamber from a distance.This patent of invention is used to solve the short circuit problem of capacitive pressure transducer.

Chinese patent literature CN1334451A discloses a kind of ceramic pressure sensor and differential pressure pick-up, its pedestal and diaphragm ceramic material of the same race, pore is set on the pedestal, the corresponding surface of pedestal and diaphragm is established the electrode of surface coverage inorganic material insulation course respectively, the periphery of pedestal and diaphragm all is provided with a circle boss with inorganic material, seals with the seal glass layer in the middle of the corresponding surface of boss.Wherein the insulation course of coated electrode plays anti-short circuit and overload.

Above-mentioned patent documentation is the problem of covering insulating material layer solution electric pole short circuit on electrode all, but also produced under the externally pressure effect, the problem that the deformation that vibrating membrane takes place reduces, i.e. the existence of insulation course has increased the thickness of vibrating membrane, makes that deformation reduces under the identical external force effect.

In addition, all do not pay close attention to the relative variation of electric capacity and the problem of Q value in the above-mentioned patent documentation.

Summary of the invention:

Purpose of the present invention not only is to provide the ceramic capacitive pressure sensors that a kind of creep is little, reaction is fast, temperature stability is good, corrosion-resistant, anti-interference, overload-resistant, precision is high, and is to provide a kind of ceramic capacitive pressure sensors that higher Q value and bigger relative capacitance change are arranged.

Ceramic capacitive pressure sensors provided by the invention comprises metal film extension line and outer metal film electrode in round and elastic vibrating diaphragm, sealing-in annulus, insulating material salient point, circular metal membrane electrode, the electrode.

The present invention forms capacitor by the elastic vibration diaphragm of periphery fixed, ratio by adjusting circular electrode and vibrating diaphragm radius, means such as insulation salient point are set, make vibrating diaphragm be in big strain regime (minimum spacing and initial separation ratio are less than 0.99), maximum capacitor is big as far as possible with the ratio of initial capacitance, thereby makes electric capacity reach the purpose of big relative variation.

For realizing that the concrete technical scheme that purpose of the present invention adopts is:

A kind of capacitive pressure transducer; comprise two round and elastic vibrating diaphragms; the annulus that seal, sealing materials is made; two circular metal membrane electrodes; metal film extension line and outer metal film electrode in the electrode; the annulus that described two round and elastic vibrating diaphragm outer rims are made by described seal, sealing materials bonds together; form inside cavity is arranged; the elastic membrane of periphery fixed; described two circular metal membrane electrodes are arranged at respectively on two round and elastic vibrating diaphragm medial surfaces; the metal film extension line is embedded in the middle of the annulus of seal, sealing materials making in the described electrode; be used to connect circular metal membrane electrode and outer metal film electrode; described outer metal film electrode one end is arranged on the annulus of described seal, sealing materials making; link to each other with metal film extension line in the electrode; the other end exposes the extension line as whole sensor; it is characterized in that; the radius of described metal film circular electrode is less than the radius of round and elastic vibrating diaphragm; described sensor can be operated under the big strain regime; in addition; described capacitive pressure transducer also comprises a plurality of insulating material salient points; it is evenly arranged on one of two round and elastic vibrating diaphragms and/or the circular metal membrane electrode, is used for anti-electric pole short circuit and plays overload protection.

As a further improvement on the present invention, the material of described round and elastic vibrating diaphragm is an aluminium oxide ceramics.

As a further improvement on the present invention, described seal, sealing materials is a low temperature glass.

The salient point that described insulating material is made plays anti-electric pole short circuit and overload protection.Owing to be the some spots of Discrete Distribution, its influence to the vibrating membrane strain can be ignored than insulation course, has overcome the insulation course influence that deformation brings to vibrating membrane of adopting coated electrode in the aforementioned patent.

The capacitance electrode of ceramic capacitive pressure sensors and interior outer lead are all made by thick-film technique, as screen printing technique and metal film calendering technology (as the rolled copper foil of 12 micron thickness) etc.; Weld in the open mode between internal lead and outer lead, as ultrasonic metal solder.Generous film and firm fluxless had both guaranteed in conjunction with the plane that electric capacity can have higher quality factor q, also provided convenience for postorder operations such as serigraphy sealing layers.

Technique scheme can obtain little short circuit and the overload protection measure of vibrating membrane strain influence obtained higher quality factor and bigger relative capacitance change simultaneously, adapts to the demand based on the passive and wireless sensor-based system of SAW element.

Description of drawings

Fig. 1 is two vibrating membrane structure stress synoptic diagram;

Fig. 2 is the maximum capacitor of capacitive pressure transducer and the relation between initial capacitance;

Fig. 3 is a side view of the present invention; Fig. 4 is the vertical view of Fig. 3;

Same numeral among Fig. 3,4 is represented the same position of sensor.Label corresponding position title is respectively:

1 round and elastic vibrating diaphragm

2 round and elastic vibrating diaphragm or substrates

The annulus that 3,4 seal, sealing materials are made

5,6 circular metal membrane electrodes

Metal film extension line in 7,8 electrodes

9,10 outer metal film electrodes

11 insulating material salient points

Embodiment

The invention will be further described below in conjunction with the drawings and specific embodiments.

Capacitive pressure transducer of the present invention comprises the interior metal film extension line 7 and 8 of annulus 3 and 4, circular metal membrane electrode 5 and 6, electrode, the outer metal film electrode 9 and 10 that round and elastic vibrating diaphragm 1, round and elastic vibrating diaphragm or substrate 2, seal, sealing materials are made, and a plurality of insulating material salient point 11

Described round and elastic vibrating diaphragm 1, round and elastic vibrating diaphragm or substrate 2 adopt bonding technology that its edge is bonded on the sealing-in annulus 3,4, form the elastic membrane of periphery fixed, as the deformable member of detected pressures.The vibrating diaphragm material includes but not limited to aluminium oxide ceramics.

The annulus 3 and 4 that described seal, sealing materials is made is between the round and elastic vibrating diaphragm 1,2, is used for fixing the edge of vibrating diaphragm 1,2.Seal, sealing materials includes but not limited to low temperature glass.

Described circular metal membrane electrode 5 is arranged on round and elastic vibrating diaphragm 1 inboard, circular metal membrane electrode 6 is arranged on round and elastic vibrating diaphragm or substrate 2 inboards, the electrode that is used for capacitor, the radius of wherein said metal film circular electrode is less than round and elastic vibrating diaphragm radius.

Be embedded in the middle of the annulus 3,4 of seal, sealing materials making before the sintering when metal film extension line 7 and 8 is made in the described electrode, be used to connect circular metal membrane electrode 5,6 and outer metal film electrode 9,10.Metal film extension line 7,8 adopts thick metal film to make in the electrode.

Described outer metal film electrode 9 links to each other with metal film extension line 7,8 in the electrode with annulus 3,4 centres that 10 1 ends are arranged on the seal, sealing materials making, and the other end exposes the extension line as whole sensor.

Described a plurality of insulating material salient point 11 is arranged on one of two round and elastic vibrating diaphragms or the passive circular metal membrane electrode.The salient point that described insulating material is made (Fig. 3,4) plays anti-electric pole short circuit and overload protection.Owing to be the some spots of Discrete Distribution, its influence to the vibrating membrane strain can be ignored than insulation course, has overcome the insulation course influence that deformation brings to vibrating membrane of adopting coated electrode.

When external pressure changes, deformation takes place in round and elastic vibrating diaphragm 1 and round and elastic vibrating diaphragm or substrate 2, because its two ends all are fixed on the annulus 3 and 4 of seal, sealing materials making, so center section generation deformation maximum, deformation is decreased to zero with reducing away from the vibrating diaphragm center to fixing edge.Round and elastic vibrating diaphragm 1 and round and elastic vibrating diaphragm or substrate 2 are in large deformation amount duty, can obtain bigger electric capacity relative variation like this, thereby the measurement range of sensor is enlarged.The insulating material salient point 11 that is provided with can play and prevent that vibrating diaphragm 1,2 excessive deformations or contact from making the effect of electric pole short circuit.Change has also taken place attached to circular metal membrane electrode 5 and 6 spacings on 1,2 in the deformation along with 1,2, so the electric capacity between them is also corresponding that variation taken place.Be drawn out to outer metal film electrode 9,10 by metal film extension line in the electrode 7,8, be connected to outside surface acoustic wave sensor, can measure.

Wherein, described circular electrode radius need be less than the foundation of vibrating membrane radius: the sheet-type elastic vibration film of periphery fixed under external force, its central point amount of deflection d ₀Maximum, distance center are far away more, and amount of deflection is more little, as shown in Equation (1).

$d=d_0{(1-\frac{r^2}{a^2})}^2---\left(1\right)$

Wherein a is the vibrating membrane radius, and r is for investigating the distance of point apart from the vibrating membrane center.

Because the additive property of electric capacity, the total capacitance after then exerting pressure is the integration of each deflection infinitesimal electric capacity:

$C_p={\&Integral;}_0^{\mathrm{<figure-callout\; id="2"\; label="ma"\; filenames="101117144244.png,DEST\_PATH\_110118150705.png"\; state="\{\{state\}\}">ma</figure-callout>}}\frac{{2\mathrm{\&pi;\&epsiv;}}_0}{t_g-2d}r\&CenterDot;\mathrm{dr}=\frac{{\mathrm{\&pi;\&epsiv;}}_0}{t_g}{\&Integral;}_0^{\mathrm{ma}}\frac{1}{1-\frac{2d}{{\mathrm{<figure-callout\; id="2"\; label="t\; g\; dr"\; filenames="101117144244.png,DEST\_PATH\_110118150705.png"\; state="\{\{state\}\}">t</figure-callout>}}_g}}{\mathrm{dr}}^{}{}^2$

$=\frac{{\mathrm{\&pi;\&epsiv;}}_0}{t_g}{\&Integral;}_0^{\mathrm{ma}}\frac{1}{1-\frac{2}{t_g}{d}_0{(1-\frac{r^2}{a^2})}^2}{\mathrm{dr}}^2---\left(2\right)$

$=-\frac{{\mathrm{\&pi;\&epsiv;}}_0}{t_g}\frac{a^2}{\sqrt{k}}(a\tanh \left(\sqrt{k}\frac{1-{\mathrm{<figure-callout\; id="2"\; label="m"\; filenames="101117144244.png,DEST\_PATH\_110118150705.png"\; state="\{\{state\}\}">m</figure-callout>}}^2}{1}\right)-a\tanh \left(\sqrt{k}\right)),k=\frac{{2d}_0}{t_g}$

Wherein, t _gBe dielectric cavity thickness, m is the ratio of capacitance electrode radius and vibrating membrane radius.

In addition, the calculating formula of initial capacitance is:

${\mathrm{<figure-callout\; id="0"\; label="C"\; filenames="101117144241.png"\; state="\{\{state\}\}">C</figure-callout>}}_0=\frac{{\mathrm{\&epsiv;}}_0\mathrm{\&pi;}{\left(\mathrm{ma}\right)}^2}{t_g}---\left(3\right)$

Can obtain the relation of initial capacitance and the corresponding electric capacity of maximum range from above-mentioned two formulas, as when minimum spacing and initial separation ratio k=0.98, then m gets different value to the influence of the ratio of two electric capacity as shown in Figure 2.As can be seen from the figure, m is more little, and two ratios are big more.Work as m=0.37, maximum capacitor is about 10 times of initial capacitance.Its reason is that r is less when electrode radius, and then each on electrode point all has bigger amount of deflection, and corresponding electric capacity on the whole has bigger pole span to change, thereby capacitance has bigger relative variation (about 10).

Claims (3)

1. capacitive pressure transducer, comprise two round and elastic vibrating diaphragms (1,2), the annulus (3 that seal, sealing materials is made, 4), two circular metal membrane electrodes (5,6), metal film extension line (7,8) and outer metal film electrode (9 in the electrode, 10), the annulus (3,4) that described two round and elastic vibrating diaphragm (1,2) outer rims are made by described seal, sealing materials bonds together, form inside cavity is arranged, the elastic membrane of periphery fixed, described two circular metal membrane electrodes (5,6) are affixed on respectively on the opposed medial surface of two round and elastic vibrating diaphragms (1,2), metal film extension line (7 in the described electrode, 8) end is embedded in the annulus (3,4) of seal, sealing materials making, the other end and circular metal membrane electrode (5,6) contact connects, described outer metal film electrode (9, a 10) end is arranged on the annulus (3,4) of described seal, sealing materials making, with metal film extension line (7 in the electrode, 8) link to each other, the other end exposes the extension line as whole sensor, it is characterized in that:

The radius of described metal film circular electrode (5,6) can be operated under the big strain regime described sensor less than the radius of round and elastic vibrating diaphragm (1,2); Described capacitive pressure transducer also has a plurality of insulating material salient points (11), and it is evenly arranged on one of two round and elastic vibrating diaphragms (1,2) and/or the circular metal membrane electrode (5,6), is used for anti-electric pole short circuit and plays overload protection.

2. a kind of capacitive pressure transducer according to claim 1 is characterized in that, the material of described round and elastic vibrating diaphragm (1,2) is an aluminium oxide ceramics.

3. according to claim 1 and 2 described a kind of capacitive pressure transducers, it is characterized in that described seal, sealing materials is a low temperature glass.

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