CN111983255A - Flexible acceleration sensor based on heat convection principle - Google Patents
Flexible acceleration sensor based on heat convection principle Download PDFInfo
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- CN111983255A CN111983255A CN202010894299.5A CN202010894299A CN111983255A CN 111983255 A CN111983255 A CN 111983255A CN 202010894299 A CN202010894299 A CN 202010894299A CN 111983255 A CN111983255 A CN 111983255A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
- G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
- G01P15/006—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of fluid seismic masses
- G01P15/008—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of fluid seismic masses by using thermal pick-up
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Abstract
The invention discloses a flexible acceleration sensor based on a thermal convection principle, which comprises a top cover with a cavity, wherein the top cover is prepared from a polydimethylsiloxane material; a chamber containing gas including air, inert gas, etc., or liquid including water and oil filling; the heating element is arranged in the middle of the sealed cavity; a plurality of temperature sensing elements arranged in the sealed cavity and symmetrical around the heating element; a flexible substrate made of polyimide, flexible PVC polymer material. A Wheatstone bridge is formed by the measuring circuit and the temperature sensing element, and the acceleration is obtained by measuring the voltage value change at two ends of the Wheatstone bridge and combining the proportional relation. The invention adopts the working principle of the micro-mechanical heat convection type acceleration sensor, has no flexible acceleration sensor with a suspended and movable structure, and greatly improves the reliability and the impact resistance of the flexible acceleration sensor compared with the prior flexible acceleration sensor; the manufacturing cost and the process complexity are reduced.
Description
Technical Field
The invention relates to a flexible acceleration sensor.
Background
An acceleration sensor is a device that measures the magnitude and direction of acceleration acting on a system. Is widely applied to various fields. An airbag system of an automobile and a suspension for attitude control are typical examples of applications of the device. Currently, its application range and frequency are increasing. Therefore, portable small-sized electronic devices such as smart phones and tablet computers are equipped with acceleration sensors. With the application of acceleration sensors to advanced small electronic devices, the demand for small acceleration sensors is increasing. Some common sensor types include capacitive, piezoelectric, piezoresistive and tunnel acceleration sensors, most of which have a solid, movable suspended mass that changes its position due to an applied acceleration. Such devices have low impact survival rates and other problems such as sticking, mechanical ringing and hysteresis due to the mechanical motion involved.
The heat convection type acceleration sensor senses acceleration by measuring temperature distribution change of gas in the sealed cavity. The structure of a uniaxial thermal acceleration sensor typically consists of microcavities created by bulk micromachining of the front side of a silicon wafer. A resistive heating element is suspended centrally in the chamber and a pair of temperature sensing elements (e.g. thermistors; or thermopiles made of thermocouples connected in series) are symmetrically placed around the heating element. The fluid (e.g. air) present in the cavity is still enclosed by the housing (package). The working principle is as follows: due to the heat dissipation of the heating element, a thermal field of fluid is formed around it. In a steady state (i.e. without any acceleration) the temperature profile within the cavity remains symmetrical with respect to the heating element and the symmetrically placed temperature sensing elements sense the same temperature. However, in the case of an applied acceleration, the temperature distribution may tilt due to physical displacement of the thermal field, with the temperature increasing on one side of the heating element and decreasing on the other. The resulting temperature difference is proportional to the applied acceleration and is measured by the temperature sensing element. The adoption of the hot fluid simplifies the structure of the sensor, simplifies the manufacturing process and reduces the cost. Furthermore, it is more important that no movable suspended structure is more advantageous for impact resistance.
Meanwhile, the traditional heat convection type acceleration sensor based on the silicon micro-mechanical process needs to use complex semiconductor processes including photoetching, ion etching, deposition and the like, and the cost is high. And the acceleration sensor prepared based on the rigid substrate can not be tightly attached when facing some objects to be tested with flexible surfaces, and the test performance is influenced to a certain extent.
Disclosure of Invention
The purpose of the invention is as follows: aiming at the prior art, a flexible acceleration sensor structure based on a thermal convection principle and a preparation method are provided, the problem that a movable mass block or a suspended structural part is required in the conventional acceleration sensor structure is solved, and the preparation method with simple manufacturing process and low cost is provided.
The technical scheme is as follows: a flexible acceleration sensor based on a thermal convection principle comprises a flexible top cover, a heating element, a plurality of temperature sensing elements, a flexible substrate and a measuring circuit; the flexible top cover and the flexible substrate are respectively prepared from flexible heat insulation materials, the flexible top cover is connected with the flexible substrate, and a sealed cavity is formed between the flexible top cover and the flexible substrate; the heating element is fixed in the center of the flexible substrate in the sealed cavity; the temperature sensing elements are fixed on the flexible substrate in the sealed cavity and are symmetrically distributed around the heating element, and the temperature sensing elements are connected with the measuring circuit; and gas or liquid is filled in the sealed cavity.
Furthermore, the flexible top cover is made of polydimethylsiloxane or silicon rubber and is prepared through pouring, nano-imprinting and 3D printing.
Further, the temperature sensing element is a conductive film prepared from graphene, carbon nanotubes, platinum or gold, and the conductive film is prepared on the flexible substrate by spin coating, screen printing, sputtering or inkjet printing.
Further, the heating element is a conductive film prepared from nichrome, and the conductive film is prepared on the flexible substrate in a spin coating, screen printing, sputtering or ink jet printing mode.
Further, the sealed cavity is filled with air or inert gas, or oil or water.
Furthermore, the flexible substrate is made of polyimide or polyvinyl chloride, and the heating element and the temperature sensing element are both attached to the flexible substrate.
Furthermore, the ends of the heating element and the temperature sensing element penetrate out of the sealed cavity and are connected to the electrodes.
Furthermore, the measuring circuit is a Wheatstone bridge, and the acceleration is obtained by measuring the change of the output voltage value of the Wheatstone bridge and combining the proportional relation.
Has the advantages that: compared with a capacitive acceleration sensor, a resistive acceleration sensor and the like, the flexible acceleration sensor based on the thermal convection principle does not need to manufacture a movable mass block or a suspension part, greatly simplifies the structure and the preparation process of a device, and improves the impact resistance of the acceleration sensor. Preparing a flexible upper top cover with a cavity by using flexible materials such as polydimethylsiloxane, silicon rubber and the like in a pouring, nano-imprinting or 3D printing mode, and closely attaching the flexible upper top cover with the substrate prepared from materials such as polyimide, polyvinyl chloride and the like to form a sealed cavity; preparing a flexible conductive film as a temperature sensing element by using metal materials such as platinum, gold and the like or nano materials such as graphene, carbon nano tubes and the like, and preparing a heating element by using materials such as nickel-cadmium alloy and the like; the cavity is filled with gas such as air and inert gas or liquid such as water and oil to serve as hot fluid. Compared with the existing acceleration sensor, the manufacturing cost and the process complexity are greatly reduced.
Drawings
FIG. 1 is a schematic diagram of a sensor according to an embodiment of the present invention;
FIG. 2 is a cross-sectional view of FIG. 1;
FIG. 3 is a schematic view of a sensor according to an embodiment of the present invention under bending;
FIG. 4 is a cross-sectional view of a sensor of an embodiment of the present invention in operation without acceleration;
FIG. 5 is a cross-sectional view of a sensor according to an embodiment of the present invention during acceleration;
fig. 6 is a schematic diagram of a measurement circuit according to an embodiment of the invention.
Detailed Description
The invention is further explained below with reference to the drawings.
As shown in fig. 1 to 5, a flexible acceleration sensor based on the thermal convection principle comprises a flexible top cover 1, a heating element 3, a plurality of temperature sensing elements 4, a flexible substrate 5 and a measuring circuit 6.
The flexible top cover 1 is made of flexible heat insulation materials such as polydimethylsiloxane or silicon rubber and is made in the modes of pouring, nano-imprinting and 3D printing, and the flexible top cover 1 is provided with a cavity.
The flexible substrate 5 is made of flexible heat insulating material, such as polyimide or polyvinyl chloride, and the heating element 3 and the temperature sensing element 4 are tightly attached to the flexible substrate 5, and a sealed cavity 2 is formed between the two. The sealed cavity 2 is filled with gas such as air and inert gas or liquid such as water and oil as hot fluid.
The heating element 3 is a conductive film made of nichrome and is prepared on the flexible substrate 5 by spin coating, screen printing, sputtering or ink jet printing. The heating element 3 has a large electrical resistance and a high thermal conductivity, converts electrical energy into thermal energy, and is fixed in the center of the flexible substrate 5 inside the sealed cavity 2, so that the heat flow distribution inside the cavity is in a symmetrical state without acceleration. The temperature sensing element 4 is a conductive film made of materials with high thermal sensitivity coefficients such as graphene, carbon nanotubes, platinum or gold, and is prepared on the flexible substrate 5 by spin coating, screen printing, sputtering or ink jet printing. The temperature sensing elements 4 are fixed on the flexible substrate 5 in the sealed cavity 2 and are symmetrically distributed around the heating element 3, and the temperature sensing elements 4 are connected with the measuring circuit 6.
The flexible substrate 5 with the heating element 3 and the temperature sensing element 4 is closely attached to an upper top cover made of materials with low thermal conductivity such as polydimethylsiloxane and the like through colloids such as silicon rubber and the like to form a closed cavity. The heating element 3 and the temperature sensing element 4 are generally designed as slender strip-shaped films, the conductive films penetrate through the whole sealed cavity 2, and two ends of the conductive films are connected to electrodes and led out through the electrodes.
In the working state, the current passes through the heating element 3 positioned in the middle of the sealed cavity 2, and heat is released outwards due to the large internal resistance. The gas/liquid in the cavity above the heating element 3 expands when heated, rises and gradually gets away from the heating element, and the gas/liquid with lower temperature fills the vacancy reserved by the rising heat flow and continues to be heated. Finally, stable heat convection conduction is formed, and a more symmetrical temperature distribution is formed in the cavity space. The temperature change is read by different resistance values by temperature sensing elements symmetrically distributed about the heating element.
In this embodiment, the sensor is provided with two temperature sensing elements 4 symmetrically distributed on two sides of the heating element 3, and the working principle is as follows: when the sensor is standing perpendicular to the gravity direction, the whole device is not influenced by additional acceleration except the gravity acceleration. The temperature distribution throughout the sealed housing 2 is symmetrical with respect to the heating element 3 based on the thermal convection movement. At this time, the two temperature sensing elements 4 symmetrically distributed about the heating element 3 detect the same temperature, and thus have the same resistance value, i.e., RT1＝RT2＝R0。
When a horizontal leftward lateral acceleration is applied by the sensor, the gas/liquid in the sealed cavity 2 changes the heat convection form under the action of the acceleration, so that the temperature distribution in the whole sealed cavity 2 changes, the gas/liquid is not symmetrically distributed about the heating element 3 in the middle, the temperature distribution on the left side is obviously lower than that on the right side, the temperature difference on the left side and the right side ensures that the resistances read by the two temperature sensing elements 4 symmetrical about the heating element 3 are not equal any more, the temperature on the left side is reduced by delta T relative to the acceleration-free state, and the temperature on the right side is increased by delta T relative to the acceleration-free state; correspondingly, the following steps are as follows: the left resistance is decreased by Δ R relative to the no acceleration state and the right resistance is increased by Δ R relative to the no acceleration state. Where Δ R ═ α Δ T, α is the temperature coefficient of resistance of the material, determined by the material of the temperature-sensitive element, i.e. when R is presentT1＝R0-ΔR，RT2＝R0+ΔR。
As shown in FIG. 6, the measuring circuit of the present invention and two temperature sensing elements form a Wheatstone bridge, and the measuring circuit includes a power supply VccFirst resistance R1And a second resistor R2The first resistor R1And a second resistor R2Connected with the other end of the temperature sensing resistor RT1Is connected with Vcc, a temperature sensing resistor RT1Another end of (1) and RT2Connected temperature sensing resistor RT2And a second resistor R2Connected and grounded. By measuring V on a Wheatstone bridge01And V02The change of the voltage value between two points can be combined with the proportional relation to obtain the accelerationThe value of (c).
For a Wheatstone bridge formed by the test circuit, the voltage at two ends of each resistor can be calculated through ohm's law, and further the voltage difference can be calculated. Let the supply voltage be VccThen flows through the first resistor R1A second resistance R2The current of the bridge arm is: i is1＝Vcc/(R1+R2) Flows through the temperature sensing resistor RT1And a temperature sensing resistor RT2The current of the bridge arm is: i is2＝Vcc/(RT1+RT2) And then the second resistance R can be calculated2And a temperature sensing resistor RT2The voltages at the two ends are respectively: vo1＝I1*R2＝Vcc*R2/(R1+R2)；Vo2＝I2*RT2＝Vcc*RT2/(RT1+RT2)。
So that Δ V is equal to Vo1-Vo2＝Vcc((R2/(R1+R2)-RT2/(RT1+RT2) ); because R isT1＝R0-ΔR，RT2＝R0+ΔR，R0The value of delta R can be calculated by measuring the value of delta V as the initial resistance of the temperature sensing element, and then the temperature of the two temperature sensing resistors is obtained.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (8)
1. A flexible acceleration sensor based on the heat convection principle is characterized by comprising a flexible top cover (1), a heating element (3), a plurality of temperature sensing elements (4), a flexible substrate (5) and a measuring circuit (6); the flexible top cover (1) and the flexible substrate (5) are respectively prepared from flexible heat insulation materials, the flexible top cover (1) is connected with the flexible substrate (5), and a sealed cavity (2) is formed between the flexible top cover and the flexible substrate; the heating element (3) is fixed in the center of the flexible substrate (5) in the sealed cavity (2); a plurality of temperature sensing elements (4) are fixed on a flexible substrate (5) in the sealed cavity (2) and are symmetrically distributed around the heating element (3), and the temperature sensing elements (4) are connected with a measuring circuit (6); and gas or liquid is filled in the sealed cavity (2).
2. The flexible acceleration sensor based on thermal convection principle of claim 1, characterized in that, the flexible top cover (1) is made of polydimethylsiloxane or silicon rubber and is prepared by casting, nano-imprinting and 3D printing.
3. The thermal convection principle based flexible acceleration sensor of claim 1, characterized in that, the temperature sensing element (4) is a conductive film made of graphene, carbon nanotube, platinum or gold, and the conductive film is made on the flexible substrate (5) by spin coating, screen printing, sputtering or inkjet printing.
4. The thermal convection principle based flexible acceleration sensor of claim 1, characterized in that, the heating element (3) is a conductive film made of nichrome alloy, which is prepared on the flexible substrate (5) by spin coating, screen printing, sputtering or ink jet printing.
5. Flexible acceleration sensor based on thermal convection principle according to claim 1 characterized in, that the sealed cavity (2) is filled with air or inert gas or filled with oil, water.
6. The flexible acceleration sensor based on thermal convection principle of claim 1, characterized in that the flexible substrate (5) is made of polyimide or polyvinyl chloride, and the heating element (3) and the temperature sensing element (4) are both attached to the flexible substrate (5).
7. Flexible acceleration sensor based on thermal convection principle according to claim 1 characterized in, that the ends of the heating element (3) and the temperature sensing element (4) are passed out of the sealed cavity (2) and connected to the electrodes.
8. Flexible acceleration sensor based on the heat convection principle according to claim 1 characterized in, that the measuring circuit (6) is a wheatstone bridge, and the magnitude of acceleration is obtained by measuring the change of output voltage value of wheatstone bridge, in combination with the proportional relation.
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| CN202010894299.5A CN111983255A (en) | 2020-08-31 | 2020-08-31 | Flexible acceleration sensor based on heat convection principle |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113325198A (en) * | 2021-06-09 | 2021-08-31 | 东南大学 | Flexible heat convection type acceleration sensor and preparation method thereof |
| CN113325199A (en) * | 2021-06-09 | 2021-08-31 | 东南大学 | Thermopile type high-sensitivity flexible acceleration sensor and preparation method thereof |
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| CN107167630A (en) * | 2017-06-11 | 2017-09-15 | 杭州电子科技大学 | A kind of design of MEMS acceleration transducers based on flexible material and preparation method thereof |
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| CN106441646A (en) * | 2016-10-27 | 2017-02-22 | 江苏科技大学 | Flexible pressure sensor and preparation method thereof |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN113325198A (en) * | 2021-06-09 | 2021-08-31 | 东南大学 | Flexible heat convection type acceleration sensor and preparation method thereof |
| CN113325199A (en) * | 2021-06-09 | 2021-08-31 | 东南大学 | Thermopile type high-sensitivity flexible acceleration sensor and preparation method thereof |
| CN113325198B (en) * | 2021-06-09 | 2022-04-29 | 东南大学 | Flexible heat convection type acceleration sensor and preparation method thereof |
| CN113325199B (en) * | 2021-06-09 | 2022-04-29 | 东南大学 | Thermopile type high-sensitivity flexible acceleration sensor and preparation method thereof |
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