Electromagnetic sensor for testing rotation angle of finger and measuring method

Abstract

The invention discloses an electromagnetic sensor for testing the rotation angle of a finger, which comprises a transmission band, a substrate, a metal grounding layer and coaxial connectors, and is characterized in that the transmission band and the metal grounding layer are respectively fixed on two end surfaces of the substrate, and the two coaxial connectors are respectively connected to two sides of the transmission band; and the middle part of the transmission band is cut off, interdigital capacitors which are staggered in pairs are connected to the cut-off part, and a complementary split resonant ring structure is etched on the metal grounding layer. The electromagnetic sensor is novel in structural design, the finger is close to the interdigital capacitor on the upper layer, the position is a local electric field concentration area of the electromagnetic sensor, small changes of electromagnetic characteristics of a transmission line can be accurately sensed when the finger rotates, and then accurate measurement of the rotation angle of the finger is provided.

Description

Technical Field

[0001] The invention relates to an electromagnetic sensor for testing the rotation angle of a finger and a measuring method. Background Art

[0002] Nowadays, with the continuous development of electromagnetic sensing technology, it is widely used in industry, agriculture, biology, medicine and other fields due to its fast response speed, low cost, high sensitivity, non-invasiveness and many other advantages. Among them, electromagnetic sensing technology has become one of the research hotspots in the field of human recognition. As a part of human recognition, the detection of finger rotation angle is widely used in human-computer interaction, virtual reality (VR), gesture recognition, medical rehabilitation and other fields.

[0003] Existing finger angle measurement methods are divided into two types: wearable detection method and non-wearable detection method.

[0004] 1. Wearable detection method. The measurement of finger rotation angle based on wearable sensors mainly relies on biomyoelectric sensors and data gloves and other equipment. Biomyoelectric sensors use surface electromyography sensors to measure the changes in bioelectric signals on the skin surface during muscle movement to achieve hand movement recognition;

[0005] The data gloves are composed of multiple sensors such as gyroscopes, accelerometers and bending sensors. The testers collect gesture data by wearing data gloves to measure the rotation angle of the fingers.

[0006] 2. Non-wearable detection method: The non-wearable method is now generally based on the measurement of finger rotation angle through visual recognition technology. Visual recognition captures the instantaneous snapshot of human hand movements through a camera, and then uses a computer to process it to realize the recognition of gestures.

[0007] Among the above-mentioned measurement methods, although the application of wearable sensors in gesture recognition can provide higher accuracy and detailed motion capture, its defects such as poor wearing comfort, limited usage scenarios and high prices have limited its popularity and application to a certain extent; non-wearable visual recognition detects the finger rotation angle, and its image acquisition relies on visible light, which is easily affected by interference from environmental factors.

[0008] In summary, the existing finger rotation angle measurement methods all have defects. However, there are few electromagnetic sensors for finger angle measurement, especially electromagnetic sensors based on microwave and radio frequency technology. There is no perfect solution for finger angle measurement. Therefore, in order to improve the above problems, the electromagnetic sensor invented in this paper is based on a novel structure of microstrip patch and complementary split resonant ring with co-digital capacitor to measure the angle of finger rotation. Summary of the invention

[0009] The present invention aims to solve the problems existing in the prior art and provides an electromagnetic sensor and a measuring method for testing the rotation angle of a finger.

[0010] The technical solutions adopted in the present invention are:

[0011] An electromagnetic sensor for testing the rotation angle of a finger comprises a transmission belt, a substrate, a metal grounding layer and a coaxial connector. The transmission belt and the metal grounding layer are respectively fixed on the two end surfaces of the substrate, two coaxial connectors are respectively connected to the two sides of the transmission belt, the transmission belt is cut off in the middle and two-phase staggered cross-toe capacitors are connected at the cutoff point, and a complementary split resonant ring structure is etched on the metal grounding layer.

[0012] Furthermore, the resonant ring structure is formed by etching three concentric circles on the metal grounding layer, and the circles coincide with the center of the metal grounding layer, and the center of the metal grounding layer coincides with the center of the substrate.

[0013] Furthermore, the interdigital capacitor is located at the center of the corresponding end surface of the substrate.

[0014] Furthermore, the three concentric circles are etched so that an annular band is formed between adjacent concentric circles, and two annular bands are connected by a connecting line.

[0015] Furthermore, the cross-digital capacitor includes an input end and an output end, which are connected at the middle cutoff of the transmission belt. Rectangular grooves are provided on the input end and the output end, and capacitor electrodes are formed between adjacent rectangular grooves on the input end and the output end. The rectangular grooves at the input end and the rectangular grooves at the output end are plugged into each other, and the spacing between adjacent capacitor electrodes is 0.2 mm.

[0016] The present invention also discloses a measuring method, comprising the following steps:

[0017] Connect the two coaxial connectors in the electromagnetic sensor to the corresponding interface feeder in the vector network analyzer to transmit the microwave signal in the transmission belt. In this process, debug the vector network analyzer, measure and record the reflection coefficient, S11 curve resonant frequency point and corresponding amplitude of the electromagnetic sensor under no-load condition;

[0018] The electromagnetic sensor is equivalent to a parallel or series resonant circuit consisting of an inductor L and a capacitor C. The resonant frequency of the equivalent resonant circuit is expressed as:

[0019]

[0020] Place the tip of the index finger at the interdigital capacitor in the electromagnetic sensor, measure at different angles, and select three samples, corresponding to: the index finger is placed at 0° angle, 60° angle, and 120° angle at the interdigital capacitor, so as to measure and record the different offsets of the return loss resonance point at different angles;

[0021] When the electromagnetic sensor of the present invention measures the rotation angle of a finger, after the finger is placed at the upper end of the cross-digital capacitor, the dielectric constant of the finger is larger than that of air, which will cause the capacitance of the sensor to change. When the electric field distribution and the capacitance value change, this affects the transmission characteristics of the electromagnetic wave, thereby changing the resonant frequency of the return loss S11.

[0022] When the index finger rotates at a certain angle, the capacitance of the cross-digital capacitor will change as the index finger approaches, and the size of the changed capacitance is expressed as ΔC:

[0023]

[0024] Where: ε0 is the dielectric constant of vacuum, ε r is the relative dielectric constant of the index finger, A is the effective area of ​​the index finger in contact with the cross-digital capacitor electrode, and d is the distance between adjacent capacitor electrodes after the rectangular slot at the input end and the rectangular slot at the output end are plugged into each other;

[0025] At this time, the new resonant frequency f′0 is calculated by the following formula:

[0026]

[0027] The present invention has the following beneficial effects:

[0028] The present invention has a novel structural design. The finger is placed close to the interdigital capacitor of the upper layer, which is the local electric field concentration area of ​​the electromagnetic sensor. It can accurately sense the slight changes in the electromagnetic characteristics of the transmission line when the finger rotates, thereby providing accurate measurement of the finger rotation angle. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a structural diagram of the transmission belt on the substrate.

[0030] Figure 2 The structural diagram of the complementary split resonant ring structure on the metal ground layer.

[0031] Figure 3 This is the structural diagram of the cross-finger capacitor.

[0032] Figure 4 Physical diagram of the present invention.

[0033] Figure 5 Physical diagram of the present invention.

[0034] Figure 6 It is a graphical representation of the no-load return loss S11 curve of the electromagnetic sensor of the present invention.

[0035] Figure 7 This is a graph showing the return loss S11 curve when the electromagnetic sensor of the present invention detects the finger rotation angle being positioned at 0°.

[0036] Figure 8 This is a graph showing the return loss S11 curve when the electromagnetic sensor of the present invention detects the finger rotation angle being positioned at 60°.

[0037] Fig. 9 This is a graph showing the return loss S11 curve when the electromagnetic sensor of the present invention detects the finger rotation angle being positioned at 120°. DETAILED DESCRIPTION

[0038] The present invention will be further described below in conjunction with the accompanying drawings.

[0039] like Figures 1 to 3 The present invention discloses an electromagnetic sensor for testing the rotation angle of a finger. The present invention adds a cross-toe capacitor 11 to a transmission belt 1 and etches a complementary split resonant ring structure 12 to a metal ground layer. The sensor structure is novel in design. The finger is placed close to the cross-toe capacitor of the upper layer, which is the local electric field concentration area of ​​the electromagnetic sensor. When the finger rotates, the sensor can accurately sense the slight changes in the electromagnetic characteristics of the transmission line, thereby providing accurate measurement of the finger rotation angle.

[0040] The electromagnetic sensor of the present invention comprises a transmission belt 1, a substrate 2, a metal grounding layer 3 and a coaxial connector 4. The transmission belt 1 is a 50-ohm metal microstrip transmission line, which is connected from the input side to the output side. The transmission line is evenly disconnected in the middle section, and two-phase staggered interdigital capacitors 11 are added to the disconnection point.

[0041] The interdigital capacitor 11 structure of the present invention can enhance the sensitivity of the electric field sensing of the sensor, and when the finger approaches the interdigital capacitor and the finger rotates the angle, the sensor capacitance value changes to complete the measurement, and this structure can also improve the sensitivity and accuracy of the sensor.

[0042] The bottom of the substrate is a complementary split resonant ring structure, that is, three rings are etched at the center of a complete metal ground layer. The three rings are divided into large, medium and small rings, forming a large ring containing the medium ring, the medium ring containing the small ring, and the centers of the three rings are at the same point. Figure 2 The smallest ring contains the interdigital capacitance of the transmission belt, and the center of the small ring is at the center point of the interdigital capacitance structure.

[0043] The complementary split resonant ring structure etched in the lower layer can enhance the local resonance characteristics of the electromagnetic field of this sensor, and can effectively control the propagation characteristics of the electromagnetic wave. In addition, this lower layer complementary split resonant ring structure cooperates with the upper layer cross-digital capacitor structure and plays a very critical role in the entire electromagnetic sensor. The two complement each other and enhance the performance of the sensor, which not only optimizes the electric field distribution, but also improves the high sensitivity and accuracy of detecting the finger rotation angle.

[0044] The input and output sides of the transmission belt are respectively welded to the female connector of the radio frequency coaxial connector through connector pins, wherein the grounding pin of the radio frequency coaxial connector is welded to the metal grounding layer.

[0045] The substrate 2 of the present invention has a total length of 36.6 mm, a total width of 27 mm, a thickness of 0.813 mm, and is made of a Rogers Ro4003c plate, with a relative dielectric constant of 3.38 and a dielectric loss tangent of 0.0027.

[0046] The geometric structure and electric field distribution of the cross-digital capacitor in the transmission belt 1 affect the propagation characteristics of the electromagnetic wave. The complementary split resonant ring structure of the metal ground layer 3 can enhance the electromagnetic wave in a specific area. The two structures cooperate to improve the sensitivity and accuracy of the sensor in measuring the rotation angle of the finger.

[0047] The total length of the transmission belt 1 is 36.6mm, the total width is 1.86mm, and the total height is 18um. The middle section is a co-digital capacitor structure. The co-digital capacitor 11 includes an input end and an output end. The input end and the output end are connected at the middle cutoff of the transmission belt 1. Rectangular grooves are provided on the input end and the output end. Capacitor electrodes 10 are formed between adjacent rectangular grooves on the input end and the output end. After the rectangular grooves of the input end and the rectangular grooves of the output end are plugged into each other, the spacing between adjacent capacitor electrodes 10 is 0.2mm. The length, width and height of the capacitor electrodes on the input end and the output end are the same, which are 7.3mm long, 0.212mm wide and 18um high respectively.

[0048] The lower metal grounding layer 3 has a total length of 36.6mm, a total width of 27mm, and a thickness of 18um. Three circular rings are etched at the center point. The centers of the three circular rings are at the same position, namely the large circular ring, the middle circular ring, and the small circular ring. The outer diameters are 8.5mm, 7.49mm, and 6.48mm respectively. The circle widths of the three etched rings are the same, all 0.4mm. Thus, two circular cylinders and a circular cylindrical structure 10 appear in the lower metal grounding layer. The two circular cylinders are respectively a large circular cylinder and a small circular cylinder. Their outer diameters are 8.0mm and 7.09mm respectively. The ring widths of the two circular cylinders are the same, all 0.61mm. The radius of the circular cylindrical structure is 6.08mm.

[0049] A ring band 13 is formed between the two annular cylinders. In order to adjust the electromagnetic and resonance characteristics of the sensor, a connecting line 14 is set on the output end side of the large annular cylinder, the small annular cylinder and a circular cylinder structure formed by etching the lower metal ground layer to connect them to each other. The width of this connection point is 0.42mm.

[0050] Figure 4 and Figure 5For this purpose, the actual display diagrams produced and processed according to the size are respectively the top view and the bottom view of this electromagnetic sensor. These diagrams respectively show the microstrip transmission line structure containing the cross-digital capacitors on the upper layer of the microwave sensor introduced above, and the ground layer of the complementary split resonant ring structure etched on the lower layer.

[0051] When the finger approaches or touches the upper end of the cross-digital capacitor of the sensor, the dielectric constant of the finger is larger than that of the air, which will cause the capacitance of the sensor to change. When the electric field distribution and the capacitance value change, this will affect the transmission characteristics of the electromagnetic wave. However, when the rotation angle of the finger changes, this will cause the geometric shape, size and electric field distribution of the cross-digital capacitor to change with the change of the rotation angle, thereby changing the propagation path and propagation characteristics of the electromagnetic wave in the sensor, resulting in a change in the resonant frequency of the return loss S11.

[0052] The S11 return loss reflects the reflection characteristics of electromagnetic waves in the sensor, specifically the amplitude ratio between the input signal and the reflected signal. When the propagation characteristics of the electromagnetic wave change, the shape and position of the S11 return loss curve will shift. As the electric field distribution of the cross-digital capacitance changes due to the rotation of the finger, the propagation characteristics of the electromagnetic wave will change accordingly, resulting in a change in the frequency response of the S11 return loss.

[0053] By analyzing the change in the S11 return loss curve, the change in the resonant frequency of the electromagnetic wave can be extracted. Since there is a certain relationship between the capacitance value and the resonant frequency, the degree of deviation of the S11 return loss curve can reflect the rotation angle of the finger.

[0054] Figure 6 , Figure 7 , Figure 8 and Fig. 9 They are the actual test finger tip placed on the upper end of the interdigital capacitor of the sensor, and the resonant frequency points and corresponding amplitudes of the reflection coefficient S11 curve under four different conditions: no load, and the finger tip placed at 0°, 60° and 120°.

[0055] Figure 6 As shown, at this time, the finger tip is not placed above the cross-toe capacitor of the upper transmission line 1, that is, it is in an unloaded state. At this time, the resonance point of S11 is 4.95 GHz, and the amplitude is -21 dB.

[0056] Figure 7 As shown, at this time, the finger tip is placed on the cross-toe capacitor of the upper transmission line 1, and the position is 0° as specified in this experiment. At this time, the S11 resonance point is 4.64 GHz, and the amplitude is -22.1 dB.

[0057] Figure 8As shown, at this time, the finger tip is placed on the cross-toe capacitor of the upper transmission line 1, and the position is 60° as specified in this experiment. At this time, the S11 resonance point is 4.641 GHz and the amplitude is -33.024 dB.

[0058] Fig. 9 As shown, at this time, the finger tip is placed on the cross-toe capacitor of the upper transmission line 1, and the position is 120° as specified in this experiment. At this time, the S11 resonance point is 4.646 GHz, and the amplitude is -26 dB.

[0059] The above test results show that through the design of the co-digital capacitor and the complementary split resonant ring, when the fingertip is on the co-digital capacitor of the electromagnetic sensor of this invention, it is rotated according to the angle specified in this experiment, and different resonant frequency points and corresponding amplitudes of the reflection coefficient S11 curve will be generated. The rotation angle can be calculated by the change of the curve. This invention not only has high sensitivity and high precision, but also can realize non-contact measurement. It is expected to be widely used in smart devices, virtual reality, gesture control and other fields in the future.

[0060] The electromagnetic sensor for testing the finger rotation angle invented in this invention has the following advantages:

[0061] 1. Structural novelty: The opening connection of the complementary split resonant ring at the ground layer of the electromagnetic sensor invented in this invention is a same-direction opening structure. Different from the traditional complementary split ring model, the complementary split resonant ring introduces a same-direction opening design to make the electric field distribution more uniform, and increase the sensor's response sensitivity to electric field changes when an external object (such as a finger) approaches. This design ensures that the sensor can respond to tiny electric field changes and improves the measurement accuracy and sensitivity.

[0062] 2. Synergy of complementary split ring co-directional opening, interdigital capacitor and left-right hand structure: The combination of interdigital capacitor structure and complementary split ring co-directional opening achieves effective adjustment in electromagnetic wave propagation characteristics, which can better improve the sensor's sensitivity to changes in finger rotation angle. By precisely designing the interaction between the complementary split resonant ring and the transmission line, the resonant frequency of the sensor can be adjusted and the accuracy of finger rotation angle measurement can be further improved.

[0063] 3. Highly integrated and easy to implement: The present invention integrates the transmission line, the cross-digital capacitor, the dielectric substrate, the complementary split resonant ring and the ground layer in a compact three-layer structure, making the device miniaturized, easy to integrate and low-cost to manufacture. This design is not only suitable for devices with limited volume, but also maintains high performance.

[0064] The above description is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements without departing from the principle of the present invention, and these improvements should also be regarded as within the protection scope of the present invention.

Claims

1. An electromagnetic sensor for testing the rotation angle of a finger, characterized in that: The invention comprises a transmission belt (1), a substrate (2), a metal grounding layer (3) and a coaxial connector (4); the transmission belt (1) and the metal grounding layer (3) are respectively fixed on the two end surfaces of the substrate (2); two coaxial connectors (4) are respectively connected to the two sides of the transmission belt (1); the transmission belt (1) is cut off in the middle and two-phase interdigitated capacitors (11) are connected at the cutoff point; and a complementary split resonant ring structure (12) is etched on the metal grounding layer (3).

2. The electromagnetic sensor for testing finger rotation angle as claimed in claim 1, characterized in that: The resonant ring structure (12) is formed by etching three concentric circles on the metal grounding layer (3), and the circles coincide with the center of the metal grounding layer (3), and the center of the metal grounding layer (3) coincides with the center of the substrate (2).

3. The electromagnetic sensor for testing the rotation angle of a finger as claimed in claim 2, characterized in that: The interdigital capacitor (11) is located at the center of the corresponding end surface of the substrate (2).

4. The electromagnetic sensor for testing finger rotation angle as claimed in claim 2, characterized in that: The three concentric circles are etched so that an annular band (13) is formed between adjacent concentric circles, and two annular bands (13) are connected via a connecting line (14).

5. The electromagnetic sensor for testing the rotation angle of a finger as claimed in claim 2, characterized in that: The cross-digital capacitor (11) comprises an input end and an output end, the input end and the output end are connected at the middle cutoff of the transmission belt (1), rectangular grooves are provided on the input end and the output end, capacitor electrodes (10) are formed between adjacent rectangular grooves on the input end and the output end, the rectangular grooves at the input end and the rectangular grooves at the output end are plugged into each other, and the spacing between adjacent capacitor electrodes (10) is 0.2 mm.

6. A method for measuring an electromagnetic sensor as claimed in any one of claims 1 to 5, characterized in that: The steps include: Connecting two coaxial connectors (4) in the electromagnetic sensor to corresponding interface feeders in the vector network analyzer to transmit the microwave signal in the transmission belt (1); debugging the vector network analyzer during this process to measure and record the reflection coefficient, the resonant frequency point of the S11 curve and the corresponding amplitude of the electromagnetic sensor under no-load conditions; The electromagnetic sensor is equivalent to a parallel or series resonant circuit consisting of an inductor L and a capacitor C. The resonant frequency of the equivalent resonant circuit is expressed as: The tip of the index finger is placed at the interdigital capacitor (11) in the electromagnetic sensor, and measurements are performed at different angles. Three samples are selected, corresponding to the angles of 0°, 60°, and 120° when the tip of the index finger is placed at the interdigital capacitor, so as to measure and record different offsets of the resonance point of the return loss at different angles. When the index finger rotates at a certain angle, the capacitance of the cross-digital capacitor will change as the index finger approaches, and the size of the changed capacitance is expressed as ΔC: Where: ε0 is the dielectric constant of vacuum, ε r is the relative dielectric constant of the index finger, A is the effective area of ​​the index finger in contact with the cross-digital capacitor electrode, and d is the distance between adjacent capacitor electrodes (10) after the rectangular groove at the input end and the rectangular groove at the output end are plugged into each other; At this time, the new resonant frequency f′0 is calculated by the following formula:

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