CN115290223A - Flexible force-sensitive sensing test method based on RC oscillation frequency detection - Google Patents

Abstract

The invention discloses a flexible force-sensitive sensing test method based on RC oscillation frequency detection, which is characterized in that a CNT/PDMS force-sensitive structure is tested in an alternating current state, the stress applied to the nanocomposite force-sensitive structure is considered, the positions, shapes and the like of carbon nano tubes in a polymer are changed, the distances among a plurality of nano tubes are also changed, a conductive network is changed, the resistance is changed, the capacitance is also considered to be changed, and finally the whole circuit is analyzed and considered. Therefore, the flexible force-sensitive sensing method for high-precision and high-sensitivity RC oscillation frequency detection is realized.

Description

A testing method for flexible force-sensitive sensing based on RC oscillation frequency detection

technical field

The invention relates to the technical field of flexible force-sensitive sensing methods, in particular to a flexible force-sensitive sensing testing method based on RC oscillation frequency detection.

Background technique

Flexible pressure sensors can be attached to irregular surfaces due to their soft properties and can be used to monitor external mechanical signals, so they have been widely used in wearable electronics, robotics, medical monitoring, human-machine interface and other fields. According to different signal transmission methods, flexible pressure sensors can be divided into three categories: piezoresistive, capacitive, and piezoelectric. and high sensitivity have been extensively studied.

At present, the test of the sensitivity of the flexible pressure sensor is mainly carried out through the change of resistance under the action of stress, and the sensitivity of the sensor is obtained by testing the change of resistance under different pressure. However, testing the sensitivity of the force-sensitive structure through the change of resistance has the problem of low test accuracy, which further affects the improvement of sensitivity.

With the development of various composite force-sensitive structures, in order to obtain higher sensitivity and precision. After the stress is applied under the AC condition, the change of the impedance of the composite force-sensitive structure is divided into two parts: the change of the resistance and the capacitive reactance, which is more accurate than the change of the single resistance under the DC condition. Therefore, a flexible force-sensitive sensing method based on RC oscillation frequency detection can be designed.

Contents of the invention

The present invention is aimed at the CNT/PDMS composite force-sensing structure with good flexibility. Under AC conditions, when stress is applied to the force-sensing structure of the nanocomposite material, the position and shape of the carbon nanotubes inside the polymer change, and multiple nanometer The distance between the tubes will also change, so that the conductive network will change, resulting in a change in resistance, and the resistance change rate will also change accordingly. In addition to the change in resistance, there will also be a change in capacitance between conductive grids. Based on this, the proposed A flexible force-sensitive sensing test method based on RC oscillation frequency detection.

The present invention is realized by adopting the following technical solutions:

A kind of flexible force sensitive sensor testing method based on RC oscillation frequency detection, comprises the following steps:

(1) Preparation of CNT/PDMS force-sensitive structure

Weigh carbon nanotubes as a conductive filler, add alcohol to it, and then ultrasonically vibrate for one hour in an ultrasonic cell pulverizer to disperse the carbon nanotubes evenly in the alcohol; then add PDMS to it for mechanical stirring, mix well, and put Add the curing agent, stir evenly, and then pour it into the mold; then put the mixed solution into a vacuum oven, vacuumize it for 1 hour, and finally place it on a heating table, set the temperature at 80°C, and cure it for 2 hours; obtain CNT/PDMS Force-sensitive structure, finally cut into a size of 2cm×1cm for performance measurement;

(2) Connect the two ends of the prepared CNT/PDMS force-sensitive structure to external wires, and then connect it to a high-precision multimeter;

(3) Fix the two ends of the connected force-sensitive structure between two fixtures, and realize the precise control of the tension of the force-sensitive structure by controlling the displacement of the fixture;

(4) Stretch the force-sensitive structure to different degrees, the stretching range is 10%~100%, and increase by 10% each time, calculate the sensitivity of the force-sensitive structure, and repeat;

(5) Through calculation and analysis, the relationship diagram between the resistance change rate and the tension of the force-sensing structure and the relationship diagram between the frequency and the tension of the force-sensing structure are obtained.

The invention uses an AC circuit to conduct experiments on the CNT/PDMS force-sensing structure, and compared with a DC circuit, it solves the problem of low accuracy caused by the traditional DC circuit ignoring capacitance changes. Under AC conditions, when stress is applied to the CNT/PDMS force-sensitive structure, in addition to the change of resistance between the conductive grids, there will also be a change of capacitance, which can be replaced by equivalent impedance.

The invention has reasonable design and good practical application value.

Description of drawings

Figure 1 shows a flexible force-sensitive sensing system based on RC oscillation frequency detection.

Figure 2 shows the relative resistance change rate of the sensor under different stretching conditions.

Figure 3 shows the equivalent circuit of the composite force-sensitive structure in the case of a DC/AC circuit.

Figure 4 shows a graph of the relationship between frequency and stretching of the force-sensitive structure.

In the figure: 1-AC power supply, 2-wire, 3-CNT/PDMS force-sensitive structure, 4-high-precision multimeter.

Detailed ways

Specific embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings.

A flexible force-sensitive sensing working system based on RC oscillation frequency detection, including carbon nanotube (CNT), polydimethylsiloxane (PDMS), fixture, AC voltage source, wire, and high-precision multimeter. The specific connection relationship is shown in Figure 1.

The AC circuit is used to fully consider the capacitance change in the CNT/PDMS force-sensing structure, so that the calculation results are more accurate and higher sensitivity and precision are obtained.

The specific test method includes the following steps:

(1) Preparation of CNT/PDMS force-sensitive structure

Weigh 0.25 g of carbon nanotubes as a conductive filler, add 1 ml of alcohol to it, and then ultrasonically vibrate for one hour in an ultrasonic cell pulverizer to uniformly disperse the carbon nanotubes in the alcohol; then add PDMS to it for mechanical stirring, and mix After uniformity, put in the curing agent, stir evenly, and then pour it into the mold; in order to remove the air bubbles in the sample, put the uniformly mixed solution into a vacuum oven, vacuumize for 1 hour, and finally place it on a heating table, set the temperature to Cured at 80°C for 2 hours; the CNT/PDMS force-sensitive structure was obtained, and finally cut into a size of 2cm×1cm for performance measurement.

(2) Connect the two ends of the prepared CNT/PDMS force-sensitive structure to external wires, and then connect it to a high-precision multimeter.

(3) Fix the two ends of the connected force-sensitive structure between two clamps, and realize the precise control of the stretching of the force-sensitive structure by controlling the displacement of the clamps.

(4) Stretch the force-sensitive structure to different degrees, the stretching range is 10%~100%, and each time increases by 10%, calculate the sensitivity of the force-sensitive structure, and repeat.

(5) Through calculation and analysis, the relationship diagram between the resistance change rate and the stretching of the force-sensitive structure and the relationship diagram between the frequency and the stretching of the force-sensitive structure are obtained.

As shown in Figure 2, the relative resistance change rate of the sensor under different stretching conditions, where ΔR is the change value of the resistance of the sensor under different stretching states. It can be found that the greater the stretch, the greater the relative resistance change rate.

As shown in Figure 3, the equivalent circuit of the CNT/PDMS force-sensing test under DC conditions ((a) (b)) and AC conditions ((c) (d)). Under DC conditions, the composite force-sensing structure ignores capacitance changes, while under AC conditions, fully considers capacitance changes, thus making the measurement more accurate.

As shown in Figure 4, the force-sensitive characteristic test of the force-sensitive structure under different tensile stresses. The abscissa of this figure represents the frequency. By observing different stretching conditions, it can be found that the maximum value of the frequency has changed.

The test method for flexible force-sensitive sensing based on RC oscillation frequency detection provided in this example is to conduct experiments on the CNT/PDMS force-sensitive structure in the AC state. In addition to considering the stress applied to the force-sensitive structure of the nanocomposite material, the When the internal position and shape of the polymer change, the distance between multiple nanotubes will also change, causing the conductive network to change, resulting in a change in resistance. The change in capacitance is also considered, and finally the overall circuit is analyzed and considered, so that A flexible force-sensitive sensing method for high-precision and high-sensitivity RC oscillation frequency detection is realized.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than limit them. Although detailed descriptions have been made with reference to the embodiments of the present invention, those of ordinary skill in the art should understand that the technical solutions of the present invention are modified Or equivalent replacements do not deviate from the spirit and scope of the technical solutions of the present invention, and all of them should be included in the protection scope of the claims of the present invention.

Claims (1)

1. A flexible force-sensitive sensing test method based on RC oscillation frequency detection is characterized in that: the method comprises the following steps:

(1) Preparing CNT/PDMS force sensitive structure

Weighing carbon nano tubes as a conductive filler, adding alcohol into the conductive filler, and then carrying out ultrasonic oscillation for one hour in an ultrasonic cell crusher to uniformly disperse the carbon nano tubes in the alcohol; then adding PDMS into the mixture to be mechanically stirred, adding a curing agent after uniformly mixing, uniformly stirring, and then pouring into a mould; then putting the uniformly mixed solution into a vacuum oven, vacuumizing for 1h, and finally putting the solution on a heating table, setting the temperature to be 80 ℃, and curing for 2 hours; obtaining a CNT/PDMS force-sensitive structure, and finally cutting the CNT/PDMS force-sensitive structure into 2cm multiplied by 1cm for performance measurement;

(2) Respectively connecting two ends of the prepared CNT/PDMS force-sensitive structure with external leads, and then connecting the CNT/PDMS force-sensitive structure with a high-precision multimeter;

(3) Fixing two ends of the connected force-sensitive structure between two clamps, and realizing accurate control of the tension of the force-sensitive structure by controlling the displacement of the clamps;

(4) Stretching the force-sensitive structure to different degrees, wherein the stretching range is 10% -100%, the stretching is increased by 10% each time, calculating the sensitivity of the force-sensitive structure, and repeating the steps;

(5) And obtaining a relation graph of the resistance change rate and the stretching of the force-sensitive structure and a relation graph of the frequency and the stretching of the force-sensitive structure through operation and analysis.

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