JPH09113590A - Magnetic sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain high precision and high resolution in a magnetic sensor for a magnetic encoder moved relatively to magnetized media magnetized so as to have reverse polarity alternately at specified magnetizing pitches for detecting the magnetic fields of the magnetized media by a magnetic impedance effect. SOLUTION: This sensor is constructed in such a manner that a highly magnetically permeable magnetic film 12 is formed on a non-magnetic substrate 10. The magnetic film 12 is formed in a zigzag pattern composed of a plurality of linear magnetic flux flowing-in parts 12a arranged in parallel at the intervals of odd multiple of a magnetizing pitch P and a plurality of linear magnetic detecting part 12b for interconnecting these parts in a sequentially folding manner. The magnetic film 12 is placed to face a magnetized medium 14 in parallel by causing the extended direction of the magnetic flux flowing-in part 12a to be in parallel with a direction for connecting the same phase of the magnetization of the medium 14, a high frequency current is applied from both ends to the magnetic film 12 and the change of impedance generated between both end parts of the magnetic film 12 by a magnetic flux from the medium is converted into an electric signal and thereby an output is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic encoder used for position detection or the like, wherein the magnetizing medium is moved relative to a magnetizing medium which is alternately magnetized to have a reverse polarity at a predetermined magnetizing pitch. The present invention relates to a magnetic sensor that detects a magnetic field of a medium, and particularly to a magnetic sensor for a high-precision magnetic encoder that detects a magnetic field by utilizing a magnetic impedance effect.

[0002]

2. Description of the Related Art Recent video camera autofocus, high-resolution printer, position detection in measuring equipment, etc.
The positioning mechanism is becoming smaller and more accurate, and it is expected that the magnetic encoder used there will also have higher accuracy and higher resolution.

A magnetic sensor for a conventional magnetic encoder mainly uses a magnetoresistive effect element (hereinafter, abbreviated as MR element). However, due to high accuracy and high resolution, the magnetizing pitch of a magnetizing medium is shortened. The magnetic flux leaking from the magnetizing medium to the outside becomes extremely small, and there is concern that sensitivity may be insufficient in the future.

Therefore, a magnetic detection element (hereinafter referred to as an MI element) utilizing the magneto-impedance effect by an amorphous wire, which is disclosed in Japanese Patent Laid-Open No. 7-181239, has recently been attracting attention. What is the magneto-impedance effect? When a high frequency current in the MHz band is passed through a magnetic material, the impedance of the magnetic material changes due to an external magnetic field,
This is a phenomenon in which the amplitude of the voltage across the magnetic body changes by several tens of percent with a minute magnetic field of several Gauss.

The resolution of the magnetic flux detection of the MI element is as high as about 10 ^-5 Oe as compared with the low sensitivity of 0.1 Oe of the MR element, so that the MI element can be applied to a magnetic sensor for a magnetic encoder. Is expected.

[0006]

The function of the MI element is found in the amorphous wire, and the amorphous wire is excellent in productivity as a material. However, since the amorphous wire has a circular cross section and has a small diameter and is easily bent, it is difficult to secure the linearity required for the detection element body of the magnetic sensor for the magnetic encoder and to form a complicated pattern.

Further, in the magnetic sensor for the magnetic encoder, it is usually necessary to detect and average the magnetic fluxes of a plurality of magnetizations in order to reduce the influence of the magnetization unevenness of the magnetization medium.
For this reason, in the conventional magnetic sensor using the MR element, as shown in FIG. 8, the magnetic film 101 as the MR element body is generally folded back at the same pitch as the magnetization pitch P of the magnetizing medium 102. A structure formed in a zigzag folded pattern is used. In this case, each of the straight line portions in the vertical direction in the drawing arranged in parallel at the pitch P is the magnetic detection unit 101a on which the magnetoresistance effect acts. Since the MR element detects the magnetic flux in the width direction with respect to the magnetic body of the element body, the width direction of the magnetic detection portion 101a is made parallel to the magnetization direction of each magnetization shown by the arrow of the magnetizing medium 102. That is, the longitudinal direction in which the magnetic detection unit 101a extends is made parallel to the direction connecting the same phase of each magnetization shown as the direction of each magnetization boundary (boundary of magnetization reversal) 102a indicated by the broken line, and magnetic field detection is performed. . The magnetic film 101 has magnetic anisotropy so that the easy axis of magnetization is parallel to the longitudinal direction (longitudinal direction in the drawing) in which the magnetic detection unit 101a extends in the film plane.

On the other hand, since the MI element detects the magnetic flux in the longitudinal direction in which the magnetic body of the element body extends, it is necessary to devise a different averaging method from that of the MR element.

Therefore, an object of the present invention is a magnetic sensor utilizing the magnetic impedance effect, which is capable of detecting magnetic fields of a plurality of magnetizations of a magnetized medium and averaging them, and is a high-precision and high-resolution magnetic encoder. An object of the present invention is to provide a magnetic sensor suitable for use as a magnetic field.

[0010]

In order to solve the above-mentioned problems, according to the present invention, the magnetic recording medium is moved relative to a magnetized medium alternately magnetized with a predetermined magnetizing pitch and having opposite polarities. A magnetic sensor for a magnetic encoder that detects a magnetic field of a magnetized medium by a magnetic impedance effect, the magnetic sensor being formed by forming a high-permeability magnetic film on a non-magnetic substrate, wherein the magnetic film has an odd number of magnetizing pitches. It is formed in a zigzag fold pattern consisting of a plurality of linear magnetic flux inflow portions arranged in parallel at a double interval and a plurality of linear magnetic detection portions that are connected so as to sequentially fold the magnetic flux inflow portions, and is easy to magnetize. Magnetic anisotropy is provided so that the axial direction is perpendicular to the extending direction of the magnetic detecting portion in the film surface, and the extending direction of the magnetic flux inflow portion of the magnetic film is the same as that of the magnetization of the magnetizing medium. Parallel to the direction of connecting the phases Magnetic film parallel to face the Chaku磁媒 body, a high-frequency current is applied from both ends to the magnetic film,
A structure is adopted in which a change in impedance generated between both ends of the magnetic film by a magnetic flux from a magnetized medium is converted into an electric signal to obtain an output.

According to this structure, the magnetic fluxes from the plurality of magnetizations of the magnetized medium are drawn into the respective magnetic detection portions of the magnetic film as the reflux magnetic fluxes by the adjacent magnetic flux inflow portions of the magnetic film. You can By setting the above magnetic anisotropy, the magnetic detection part of the magnetic film can generate a magnetic impedance effect by the magnetic flux drawn. Since the impedance of the entire magnetic film appears as the sum of the impedances of the magnetic flux return portions, it is possible to detect and average the magnetic fluxes of a plurality of magnetizations.

Further, since a magnetic film as an element body is formed on a non-magnetic substrate, it can be formed in a plane and a complicated pattern can be easily formed as an element body. It is suitable for encoders.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

[First Embodiment] FIG. 1 shows a first embodiment of the present invention.
2 shows a basic structure of a magnetic sensor for a magnetic encoder according to the embodiment of FIG.

In FIG. 1, reference numeral 14 denotes a magnetizing medium, which is a tape-shaped medium here and is magnetized in the longitudinal direction at a predetermined pitch P alternately in opposite polarities. The boundaries of the magnetizations of the magnetized medium 14, that is, the boundaries of the magnetization reversal are indicated by broken lines 14a. The magnetic sensor described below moves relative to the magnetized medium 14. That is, the magnetic sensor or the magnetizing medium 14 moves. The moving direction is the direction along the longitudinal direction, which is the direction in which the magnetization of the magnetizing medium 14 continues, as indicated by the arrow.

On the other hand, in FIG. 1, reference numeral 10 denotes a non-magnetic substrate (hereinafter abbreviated as substrate) of the magnetic sensor, which includes calcium titanate (Ti-Ca type ceramic), oxide glass, titania (TiO ₂ ), alumina (Al). It is formed as a rectangular flat plate from a non-magnetic material such as ₂ O ₃ ). The substrate 10 is arranged such that its longitudinal direction is along the longitudinal direction of the magnetized medium 14, and its upper surface is close to and parallel to the surface of the magnetized medium 14.

A high-permeability magnetic film (hereinafter abbreviated as a magnetic film) 12 is formed on the upper surface of the substrate 10 as a magnetic detection element body of a magnetic sensor. The magnetic film 12 is Fe-Co.
-B type amorphous film, Fe-Ta-N type, Fe-
It is composed of a high-permeability metal magnetic film such as a Ta-C-based microcrystalline film, and is a single-layer film here.

The magnetic film 12 is composed of a plurality of (9 in this case) linear magnetic flux inflow portions 12a arranged in parallel at an interval equal to the magnetizing pitch P of the magnetizing medium 14, and a direction in which the magnetic flux inflow portions 12a extend. Along the direction perpendicular to the magnetic flux inflow portion 12a
Multiples that are connected so that they are folded back in sequence (here, 8)
Is formed in a zigzag fold pattern composed of the linear magnetic detection part 12b. Terminals 16A and 16B are continuously provided at both ends of the magnetic film 12 serving as the magnetic flux inflow portion 12a. The terminals 16A and 16B are formed as conductive films of Cu, Au, or the like, or are formed by extending both ends of the magnetic film 12.

In the magnetic film 12, the longitudinal direction thereof, that is, the direction in which the magnetic detection portion 12b extends is parallel to the longitudinal direction of the substrate 10, that is, the longitudinal direction of the magnetizing medium 14, and the magnetic flux inflow portion 12a extends. The direction is made parallel to the direction connecting the same phase of magnetization shown as the direction of each magnetization boundary (boundary of magnetization reversal) 14a of the magnetized medium 14 so as to face the magnetized medium 14 closely in parallel. Will be placed. Although the direction connecting the same phases of the magnetization is the width direction perpendicular to the longitudinal direction of the magnetized medium 14 here, it may be a direction inclined with respect to the longitudinal direction, in which case the magnetic flux inflow portion 12a extends. In order to make the direction parallel to the direction connecting the same phase, the longitudinal direction of the magnetic film 12 (the magnetic detecting portion 12b
The direction in which the direction extends) is inclined.

With such a structure, the magnetic flux inflow portion 12a
Thus, the magnetic flux generated by the magnetization of the magnetized medium 14 can be drawn into the magnetic detection unit 12b, and the magnetic flux can be recirculated by the closed magnetic path formed by the adjacent magnetic flux inflow unit 12a.

The magnetic film 12 has its easy axis of magnetization perpendicular to the direction in which the magnetic detection portion 12b extends (longitudinal direction of the entire magnetic film 12) in the film plane as indicated by the arrow. After film formation, magnetic anisotropy is provided by annealing in a magnetic field.

With the above configuration, when the magnetic encoder is operating, a high frequency current is applied to the magnetic film 12 from terminals 16A and 16B provided at both ends of the magnetic film 12,
The magnetic flux drawn from the magnetized medium 14 into the magnetic film 12 changes the impedance between the terminals 16A and 16B at both ends of the magnetic film 12, and the change is converted into an electric signal to obtain an output.

Next, the operation and effect of the magnetic sensor of this embodiment during operation will be described with reference to FIGS.

As shown in FIG. 2, the magnetic fluxes from the individual magnetizations of the magnetized medium 14 are indicated by arrows, and the magnetic flux inflow portion 1 of the magnetic film 12 is indicated.
The magnetic flux is drawn into each of the magnetic detectors 12b from each of 2a, returns to the magnetized medium 14 from the adjacent magnetic flux inflow portion 12a, and a reflux magnetic flux is formed. Here, the magnetic flux inflow portion 12a
If the width w is too narrow, the lower limit is set to 3 μm because the magnetic resistance to the return flux increases, and if it is too wide, the change of the leakage flux from the magnetizing medium becomes ambiguous, and the width of the magnetizing pitch P is 1/2. It is desirable that the upper limit is The length d of the magnetic flux inflow portion is the width for picking up the magnetic flux from the magnetized medium 14, and corresponds to the track width of the magnetic head.

Since the nine magnetic flux inflow portions 12a are formed, the magnetic fluxes of the eight magnetizations of the magnetized medium 14 can be drawn into the eight magnetic detection portions 12b of the magnetic film 12 as reflux magnetic fluxes. The magnetic flux drawn into the magnetic detection unit 12b flows in a direction perpendicular to the easy axis of magnetization in that portion, so that a magneto-impedance effect occurs and a change in impedance appears.

Here, magnetic fluxes flow in mutually opposite directions between the adjacent magnetic detecting portions 12b, but the magnetic impedance effect has a characteristic symmetrical with respect to the direction of the external magnetic field as shown in FIG. Regardless of the direction, the overall impedance of the magnetic film 12 appears as the sum of the impedances of the magnetic flux return portions. That is, the sum of impedances due to the magnetic fluxes of the eight magnetizations can be obtained, and the magnetic fluxes of the eight magnetic fields can be detected and averaged, so that even if the magnetizing medium 14 has uneven magnetization, the influence is mitigated.

Further, as another effect, it is possible to avoid the influence of harmful external magnetic field Hex which becomes noise from other than the magnetizing medium 14 which enters along the longitudinal direction of the magnetic film 12. That is, assuming that the impedances of the portions A and B in FIG. 2 in which the adjacent reflux magnetic fluxes in the opposite directions flow correspond to Zo of FIG. 3 when Hex = 0, the portion A when Hex> 0. In, the return magnetic flux is in the opposite direction to the external magnetic field Hex, so the impedance is reduced to Zm, and in the B part, the return magnetic flux is increased in the forward direction to Zp, and the sum is almost the same as 2Zo. Almost offset. However, in order to cancel the influence of the external magnetic field in the magnetic film 12 as a whole, it is necessary to equalize the number of the reflux magnetic fluxes in the magnetic film 12 in the forward and reverse directions. Therefore, the number of the magnetic flux inflow portions 12a is 3 or more. It is necessary to set the number of the magnetic detection units 12b to an even number, which is 2 or more, as an odd number.

As described above, the sensor of this embodiment can detect a plurality of magnetizations of the magnetized medium 14 and average them, and can be suitably used for a magnetic encoder. Moreover, the stable output can be obtained by avoiding the influence of the external magnetic field which becomes noise.

Further, since the width w of the magnetic flux inflow portion 12a can be reduced to 3 μm and the pitch P between the magnetic flux inflow portions 12a can be reduced, compared with the MR element for detecting the magnetic field in the width direction of the magnetic body of the element body, It is possible to detect a magnetic field of a magnetizing medium having a short magnetizing pitch, and it can be suitably used for a magnetic encoder with high accuracy and high resolution.

Further, since the element body of the sensor is formed of a magnetic film, problems such as difficulty of handling with conventional amorphous wires and inability to deal with complicated patterns have been solved, and productivity is improved. Are better.

Next, another embodiment of the present invention will be described with reference to FIGS.
4 to 7, the same or corresponding portions as those in FIGS. 1 and 2 of the first embodiment are designated by the same reference numerals. In the description of each embodiment, the description of the parts common to the first embodiment will be omitted.

[Second Embodiment] FIGS. 4 and 5 show the structure of a magnetic sensor according to a second embodiment. As shown in FIG. 4, in the present embodiment, the outer shape of the magnetic film 12 on the substrate 10 has the same zigzag pattern as the magnetic film 12 of the first embodiment, but as shown in FIG. 5, the magnetic film 12 has two layers. The magnetic films 121 and 122 are laminated. The magnetic film 1 is provided between the magnetic films 121 and 122.
The conductive film 18 is sandwiched between the thin films 21 and 122 and formed in a zigzag pattern corresponding to the magnetic films 121 and 122. The conductive film 18 is sandwiched over the entire length of the magnetic films 121 and 122, and both ends thereof are exposed from both ends of the magnetic films 121 and 122 and are formed as terminals 18A and 18B. The conductive film 18 is made of Cu, Au, or the like.

With such a configuration, the terminal 1
A high frequency current is passed through the conductive film 18 from 8A and 18B. A high-frequency current flows through the magnetic films 121 and 122 together with the conductive film 18, but since the conductive film 18 has a lower specific resistance by 1 to 2 digits, the DC resistance value of the entire sensor can be set lower than that in the first embodiment. The Q value can also be increased. As in the first embodiment, the magnetic flux from the magnetized medium flows into the magnetic films 121 and 122 to change the impedance between the terminals 18A and 18B of the conductive film 18, and the change is converted into an electric signal to output. You can get it.

With this structure, the Q value is increased by lowering the DC resistance of the magnetic film 12 as compared with the magnetic film 12 having a single layer structure as in the first embodiment, and depending on the conditions of the oscillation circuit. It is easier to handle than a single layer.

[Third Embodiment] In the first embodiment,
The magnetizing pitch P of the magnetized medium 14 and the pitch of the gap between the magnetic flux inflow portions 12a of the magnetic film 12 are made equal, but when the magnetized pitch P of the magnetized medium is extremely small, the magnetic flux drawn is the magnetic flux of the magnetic film 12. Since it is weakened by the influence of the internal demagnetizing field, it is necessary to increase the length of the magnetic detection part 12b in that case.

As a method therefor, as shown in FIG. 6 as a third embodiment, the pitch P'of the intervals of the magnetic flux inflow portions 12a.
Is an odd multiple larger than 1 of the magnetizing pitch P (in FIG. 6, P ′ =
P × 3). By doing this, the adjacent magnetic flux inflow portions 12
There is a magnetic field difference of one medium magnetization between a, magnetic flux can be drawn from the magnetized medium 14 and flown to the magnetic detection unit 12b, and the length of the magnetic detection unit 12b is long. The influence can be suppressed and the detection sensitivity can be maintained.

[Fourth Embodiment] The MI element has a small impedance when the length of the magnetic material of the entire element is short, and M
The value becomes smaller than the optimum value for the oscillation circuit that takes out the output of the I element, and there are cases where sufficient oscillation cannot be obtained. Therefore, there is a method of simply increasing the length of the entire device,
The longer surface facing the magnetized medium makes it more susceptible to variations in spacing with the magnetized medium.

A fourth embodiment in consideration of this point is shown in FIG.

As shown in FIG. 7, the substrate 1 is used in this embodiment.
0, the four magnetic films 12 in a serpentine pattern corresponding to the magnetic film 12 of the first embodiment are arranged in the direction perpendicular to the longitudinal direction, that is, in the direction in which the respective magnetic flux inflow portions 12a extend and the magnetizing medium 14 is formed. They are arranged in parallel at predetermined intervals in a direction connecting the same phase of magnetization shown as the direction of the magnetization boundary 14a and electrically connected in series.

The four magnetic films 12 are arranged so that the respective magnetic flux inflow portions 12a are aligned.
However, with respect to the four magnetic films 12, adjacent magnetic films 12 are relatively offset from each other in the longitudinal direction by one pitch in the magnetic detection portion 12b. That is, the adjacent magnetic films 12
The direction of the unevenness of the zigzag pattern is reversed between them, so that the magnetic flux inflow portions 12a at the end portions are directly extended as shown by the reference numeral 12c in the series connection portion at the end portions of the adjacent magnetic films 12. It is devised so that they can be connected to form a straight line. Note that terminals 16A 'and 16B' are formed at both ends of the entire series connection of the four magnetic films 12.

By doing so, the total length of the entire magnetic detecting portion 12b can be increased while keeping the overall length of the MI element body composed of the four magnetic films 12 short. It is possible to increase the impedance of the element body and make it less susceptible to the spacing with the magnetized medium 14. Also, the terminal 16
Since A ′ and 16B ′ are arranged on one side of the MI element body, there is an advantage that wiring is also simplified.

[0042]

As is apparent from the above results, according to the present invention, the magnetized medium is moved relative to the magnetized medium which is magnetized in the opposite polarity alternately at a predetermined magnetizing pitch. Is a magnetic sensor for a magnetic encoder that detects the magnetic field of the magnetic field by a magnetic impedance effect, and is formed by forming a high-permeability magnetic film on a non-magnetic substrate, and the magnetic film has an interval of an odd multiple of the magnetization pitch. A plurality of linear magnetic flux inflow portions arranged in parallel with each other, and a plurality of linear magnetic detection portions that are connected so as to sequentially fold the magnetic flux inflow portions are formed in a zigzag pattern, and the easy magnetization axis direction is Magnetic anisotropy is provided so as to be perpendicular to the extending direction of the magnetic detecting portion in the film surface, and the extending direction of the magnetic flux inflow portion of the magnetic film connects the same phase of the magnetization of the magnetized medium. The magnetic film parallel to the direction A high-frequency current is applied to the magnetic film from both ends thereof in parallel with each other, and a change in impedance generated between both ends of the magnetic film by a magnetic flux from the magnetizing medium is converted into an electric signal. By adopting the configuration capable of obtaining the output, it is possible to detect the magnetic fields of a plurality of magnetizations of the magnetized medium and average them, which has been difficult in the conventional MI element.

Moreover, the magnetic field of the magnetizing medium having a shorter magnetizing pitch than that of the MR element can be detected in addition to being strong against a noise magnetic field from the outside and providing a stable output. Suitable for high resolution magnetic encoders. Furthermore, since the element body is made of a magnetic film, there are no handling difficulties like conventional amorphous wires, complex patterns can be easily formed, and excellent productivity can be obtained. To be

[Brief description of the drawings]

FIG. 1 is a perspective view showing a basic structure of a magnetic sensor for a magnetic encoder according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating an operation during a detection operation of the magnetic sensor.

FIG. 3 is a graph showing a magnetic impedance characteristic of a magnetic film of the magnetic sensor.

FIG. 4 is a perspective view showing a structure of a magnetic sensor according to a second embodiment.

5 is a cross-sectional view taken along the line AA ′ in FIG.

FIG. 6 is an explanatory diagram showing a relationship between a pitch P ′ of a gap between magnetic flux inflow portions in a magnetic film of the magnetic sensor of the third embodiment and a magnetizing pitch P of a magnetizing medium.

FIG. 7 is a perspective view showing a structure of a magnetic sensor according to a fourth embodiment.

FIG. 8 is a plan view showing a structure of a conventional magnetic sensor using an MR element.

[Explanation of symbols]

 Reference Signs List 10 non-magnetic substrate 12 high-permeability magnetic film 12a magnetic flux inflow portion 12b magnetic detection portion 12c series connection portion 14 magnetizing medium 14a magnetization boundary (boundary of magnetization reversal) 16A, 16B terminal 18 conductive film 18A, 18B terminal 121, 122 Magnetic film

Claims (5)

[Claims] 1. A magnetic sensor for a magnetic encoder, which moves relative to a magnetized medium that is magnetized with opposite polarities alternately at a predetermined magnetizing pitch to detect a magnetic field of the magnetized medium by a magnetic impedance effect. It is configured by forming a high magnetic permeability magnetic film on a non-magnetic substrate, the magnetic film, a plurality of linear magnetic flux inflow portions arranged in parallel at intervals of odd multiples of the magnetization pitch, The magnetic flux inflow portion is formed in a meandering pattern composed of a plurality of linear magnetic detection portions that are connected so as to be sequentially folded back, and the easy axis of magnetization is perpendicular to the extending direction of the magnetic detection portion in the film plane. The magnetic film has magnetic anisotropy so that the direction of extension of the magnetic flux inflow portion of the magnetic film is parallel to the direction connecting the same phase of magnetization of the magnetic medium, and the magnetic film is parallel to the magnetic medium. Face both sides of the magnetic film A high-frequency current is applied to the magnetic sensor, and a change in impedance generated between both ends of the magnetic film by a magnetic flux from a magnetizing medium is converted into an electric signal so that an output can be obtained. 2. The magnetic sensor according to claim 1, wherein the width of the magnetic flux inflow portion is in the range of 3 μm or more and half or less of the magnetization pitch. 3. The magnetic sensor according to claim 1, wherein the number of the magnetic flux inflow portions is an odd number of 3 or more and the number of the magnetic detection portions is an even number of 2 or more. 4. A plurality of magnetic films formed in the zigzag pattern are arranged in parallel at a predetermined interval in a direction in which the magnetic flux inflow portion extends, and are electrically connected in series. The magnetic sensor according to any one of 3 to 3. 5. The magnetic film is a two-layer magnetic film that is laminated by sandwiching a conductive film that is thinner than the magnetic film and is formed in a serpentine pattern corresponding to the magnetic film over the entire length. Both ends are exposed from both ends of the two-layer magnetic film, and a high-frequency current is applied to the conductive film from both ends to generate impedance between both ends of the conductive film due to magnetic flux from a magnetizing medium. 5. The magnetic sensor according to claim 1, wherein the change is converted into an electric signal to obtain an output.