Abstract:
An eddy-current probe according to the present invention comprises: a substrate having a first surface facing to a subject to be tested and a second surface opposite to said first surface; an exciting coil formed on the second surface, having a pair of current lines in parallel with each other through which exciting currents flow in opposite directions to each other during testing, for generating an alternate magnetic field applied to the subject by the exciting currents; and at least one eddy-current sensor positioned on a central axis between the pair of current lines on the second surface of the substrate, for detecting a magnetic field generated newly from the subject by an eddy-current induced by the alternate magnetic field. The substrate has a non-planar form having at least one convex-surface portion on the first surface, and the at least one eddy-current sensor is formed on at least one concave-surface portion formed on the second surface, which is corresponding to the at least one convex-surface portion.

Description:
PRIORITY CLAIM  
       [0001]     This application is a divisional application of application Ser. No. 11/203,252, filed Aug. 15, 2005, which is a divisional application of application Ser. No. 10/938,541, filed Sep. 13, 2004.  
         [0002]     This application claims priority from Japanese patent application No. 2003-326174, filed on Sep. 18, 2003, which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0003]     1. Field of the Invention  
         [0004]     The present invention relates to an eddy-current probe that is able to detect object&#39;s shapes, defects and so on nondestructively.  
         [0005]     2. Description of the Related Art  
         [0006]     Eddy-current testing (ECT) technique is frequently utilized for nondestructive testing of distorted surfaces of important metal machine parts used in a nuclear power plant, an airplane and so on, such as turbine blades, various pipes and airplane wings. Generally, such an ECT probe using the eddy-current includes mainly an exciting coil and a detector coil for detecting a magnetic field based on an eddy-current induced by an alternating magnetic field generated by the excited coil. Such a technique is described in for example, Japanese Patent Publications Nos. 07-083884A, 09- 189682 A, 11-248685A and 2002-090490A.  
         [0007]     Further, a planar-type ECT probe for inspecting printed circuit boards is proposed, including a meander-type exciting coil and a pick-up coil for the eddy-current detection which are formed on a flexible planar substrate. Such a probe is described in for example, T. Miyagoshi, D. Kacprzak, S. Yamada and M. Iwahara, “Feasibility of Inspecting Defects in Printed Circuit Boards by Using Eddy-Current Testing Techniques”, Journal of the Magnetics Society of Japan, Vol. 23, No. 4-2, pp. 1613-1616, 1999, and S. Yamada and M. Iwahara, “Trend of Detection Techniques Using Planar-Type Micro-Eddy-Current Testing Probes”, Journal of the Magnetics Society of Japan, Vol. 23, No. 7, pp. 1817-1825, 1999.  
         [0008]     Recently, in such an ECT probe, an element for detecting the eddy-current, that is, an eddy-current sensor has been intended to be miniaturized, and to be improved in resolution and sensitivity. In order to improve its detecting resolution, as well as to miniaturize it, the ECT probe has been required to have less spacing between the sensor and a subject.  
         [0009]     It is difficult for the planar-type ECT probe using a planar substrate to constantly keep the spacing between the surfaces of the substrate and of a subject much small. In some cases, the surfaces of the substrate and of the subject are almost in contact with each other. Further, when the subject has distorted surfaces, the ECT probe using a flexible thin substrate is desirable to be utilized to follow the surfaces smoothly. However, it is impossible to follow such a flexible substrate in no contact with the subject&#39;s surface.  
         [0010]     When the surfaces of the substrate used in the planar-type ECT probe and of the subject are almost in contact with each other, an adsorption phenomenon (sticktion) is likely to occur between the surfaces of the substrate and of the subject.  
         [0011]     When the sticktion occurs, some external-force application is needed to remove the probe substrate from the subject&#39;s surface against the sticktion. The application is likely to damage the probe substrate. The weaker is the strength of the substrate, the damage by the sticktion occurs more frequently. Because the flexible substrate has a small thickness and a weak mechanical strength, the durability and lifetime of the planar-type ECT probe depend largely on the occurrence of the sticktion, especially in the measurement of the distorted surface where the substrate inevitably has a contact with the subject&#39;s surface.  
         [0012]     This problem tends greatly to appear in micro-defect detection on the smooth surface of the substrate.  
       BRIEF SUMMARY OF THE INVENTION  
       [0013]     It is therefore an object of the present invention to provide an eddy-current probe for high resolution testing, possessing very high performances of the durability and lifetime by reducing an occurrence probability of the sticktion.  
         [0014]     An eddy-current probe according to the present invention comprises: a substrate having a first surface facing to a subject to be tested and a second surface opposite to the first surface; an exciting coil formed on the second surface, having a pair of current lines in parallel with each other through which exciting currents flow in opposite directions to each other during testing, for generating an alternate magnetic field applied to the subject by the exciting currents; and at least one eddy-current sensor positioned on a central axis between the pair of current lines on the second surface of the substrate, for detecting a magnetic field generated newly from the subject by an eddy-current induced by the alternate magnetic field. Especially, according to the present invention, the substrate has a non-planar form having at least one convex-surface portion on the first surface, and the at least one eddy-current sensor is formed on at least one concave-surface portion formed on the second surface, which is corresponding to the at least one convex-surface portion.  
         [0015]     Because the first surface of the substrate facing to the subject (the measurement surface) has a non-planar form having the at least one convex-surface portion and therefore has a small facing/contact area with the subject&#39;s surface, the sticktion hardly occurs. Even if the sticktion occurs, much less external-force application should be needed to remove the probe from the subject&#39;s surface against the sticktion. Consequently, a damage probability by the sticktion is drastically reduced, and therefore, the durability and lifetime can be improved in a large extent. Further, because the at least one eddy-current sensor is formed on the at least one concave-surface portion formed on the second surface (the opposite surface to the measurement surface), which is corresponding to the at least one convex-surface portion, the distance between the subject&#39;s surface and the eddy-current sensor does not increase, and therefore, a high performance of resolution is provided.  
         [0016]     Preferably, the at least one convex-surface portion has a waved convex form where the substrate is curved along a traverse direction (X direction). In the case, it is preferable that the at least one convex-surface portion is a single convex-surface portion or a plurality of convex-surface portions.  
         [0017]     It is also preferable that the substrate is a flexible substrate.  
         [0018]     Further, an eddy-current probe according to the present invention comprises: a substrate having a first surface facing to a subject to be tested and a second surface opposite to the first surface; an exciting coil formed on the second surface, having a pair of current lines in parallel with each other through which exciting currents flow in opposite directions to each other during testing, for generating an alternate magnetic field applied to the subject by the exciting currents; and at least one eddy-current sensor positioned on a central axis between the pair of current lines on the second surface of the substrate, for detecting a magnetic field generated newly from the subject by an eddy-current induced by the alternate magnetic field. Especially, according to the present invention, the first surface of the substrate has a plurality of concaves and convexes.  
         [0019]     Because the first surface of the substrate (the measurement surface) has a plurality of concaves and convexes, the sticktion hardly occurs. Even if the sticktion occurs, much less external-force application should be needed to remove the probe from the subject&#39;s surface against the sticktion. Consequently, a damage probability by the sticktion is drastically reduced. Therefore, the durability and lifetime of the eddy-current probe show no decrease, even when a high resolution is obtained by putting the measurement surface of the probe toward the subject&#39;s surface as closely as possible to minimize the distance between the subject&#39;s surface and the eddy-current sensor.  
         [0020]     Preferably, the surface having a plurality of concaves and convexes is a rough surface by such as a blast finishing or an embossed surface.  
         [0021]     Preferably, a lubricant layer, a diamond-like carbon (DLC) layer, or both of a DLC layer and a lubricant layer are formed on the first surface having a plurality of concaves and convexes. The lubricant layer, the DLC layer, or both of the DLC layer and the lubricant layer formed on the surface can prevent the sticktion more surely, and reduce the wear-outs of the measurement surface of the substrate and of the subject&#39;s surface.  
         [0022]     Furthermore, an eddy-current probe according to the present invention comprises: a substrate having a first surface facing to a subject to be tested and a second surface opposite to the first surface; an exciting coil formed on the second surface, having a pair of current lines in parallel with each other through which exciting currents flow in opposite directions to each other during testing, for generating an alternate magnetic field applied to the subject by the exciting currents; and at least one eddy-current sensor positioned on a central axis between the pair of current lines on the second surface of the substrate, for detecting a magnetic field generated newly from the subject by an eddy-current induced by the alternate magnetic field. Especially, according to the present invention, the first surface of the substrate has a plurality of grooves.  
         [0023]     Because the first surface of the substrate (the measurement surface) has a plurality of grooves, the sticktion hardly occurs. Even if the sticktion occurs, much less external-force application should be needed to remove the probe from the subject&#39;s surface against the sticktion. Consequently, a damage probability by the sticktion is drastically reduced. Therefore, the durability and lifetime of the eddy-current probe show no decrease, even when a high resolution is obtained by putting the measurement surface of the probe toward the subject&#39;s surface as closely as possible to minimize the distance between the subject&#39;s surface and the eddy-current sensor.  
         [0024]     Preferably, a plurality of grooves are grooves extended along a traverse direction (X direction) of the substrate, grooves extended along a longitudinal direction (Z direction) of the substrate, or grooves extended along an oblique direction to the traverse direction (X direction) of the substrate.  
         [0025]     Preferably, a lubricant layer, a DLC layer, or both of a DLC layer and a lubricant layer are formed on the first surface having a plurality of grooves. The lubricant layer, the DLC layer, or both of the DLC layer and the lubricant layer formed on the surface can prevent the sticktion more surely, and reduce the wear-outs of the measurement surface of the substrate and of the subject&#39;s surface.  
         [0026]     Further, an eddy-current probe according to the present invention comprises: a substrate having a first surface facing to a subject to be tested and a second surface opposite to the first surface; an exciting coil formed on the second surface, having a pair of current lines in parallel with each other through which exciting currents flow in opposite directions to each other during testing, for generating an alternate magnetic field applied to the subject by the exciting currents; and at least one eddy-current sensor positioned on a central axis between the pair of current lines on the second surface of the substrate, for detecting a magnetic field generated newly from the subject by an eddy-current induced by the alternate magnetic field. Especially, according to the present invention, the first surface of the substrate has a plurality of holes.  
         [0027]     Because the first surface of the substrate (the measurement surface) has a plurality of holes, the sticktion hardly occurs. Even if the sticktion occurs, much less external-force application should be needed to remove the probe from the subject&#39;s surface against the sticktion. Consequently, a damage probability by the sticktion is drastically reduced. Therefore, the durability and lifetime of the eddy-current probe show no decrease, even when a high resolution is obtained by putting the measurement surface of the probe toward the subject&#39;s surface as closely as possible to minimize the distance between the subject&#39;s surface and the eddy-current sensor.  
         [0028]     Preferably, the holes are blind holes or through holes.  
         [0029]     Preferably, a lubricant layer, a DLC layer, or both of a DLC layer and a lubricant layer are formed on the first surface having a plurality of holes. The lubricant layer, the DLC layer, or both of the DLC layer and the lubricant layer formed on the surface can prevent the sticktion more surely, and reduce the wear-outs of the measurement surface of the substrate and of the subject&#39;s surface.  
         [0030]     Furthermore, an eddy-current probe according to the present invention comprises: a substrate having a first surface facing to a subject to be tested and a second surface opposite to the first surface; an exciting coil formed on the second surface, having a pair of current lines in parallel with each other through which exciting currents flow in opposite directions to each other during testing, for generating an alternate magnetic field applied to the subject by the exciting currents; and at least one eddy-current sensor positioned on a central axis between the pair of current lines on the second surface of the substrate, for detecting a magnetic field generated newly from the subject by an eddy-current induced by the alternate magnetic field. Especially, according to the present invention, the substrate includes a lubricant layer, a DLC layer, or both of the DLC layer and the lubricant layer formed on the first surface.  
         [0031]     The lubricant layer, the DLC layer, or both of the DLC layer and the lubricant layer formed on the first surface of the substrate (measurement surface) can reduce the sticktion, and the wear-outs of the measurement surface of the substrate and of the subject&#39;s surface.  
         [0032]     Preferably, the at least one eddy-current sensor is a single eddy-current sensor or a plurality of eddy-current sensors aligned on the central axis between said pair of current lines.  
         [0033]     It is also preferable that the at least one eddy-current sensor is a magnetoresistive element. In the case, the magnetoresistive element is preferably a giant magnetoresistive element or a tunnel magnetoresistive element.  
         [0034]     It is also preferable that the at least one eddy-current sensor is a detection coil.  
         [0035]     Preferably, the exciting coil is a meander-type coil.  
         [0036]     It is also preferable that the exciting coil comprises a coil conductor layer formed on the substrate and an insulating layer covering the coil conductor layer. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0037]      FIG. 1  shows a diagram schematically illustrating a configuration of an testing system using the eddy-current according to a preferred embodiment of the present invention;  
         [0038]      FIG. 2  shows a perspective view schematically illustrating a configuration of the ECT probe according to the embodiment in  FIG. 1 ;  
         [0039]      FIG. 3  shows a cross-sectional view taken along with line III-III in  FIG. 2 ;  
         [0040]      FIG. 4  shows a perspective view schematically illustrating a configuration of the ECT probe according to another embodiment of the present invention;  
         [0041]      FIG. 5  shows a cross-sectional view taken along with line V-V in  FIG. 4 ;  
         [0042]      FIG. 6  shows a cross-sectional view schematically illustrating a configuration according to an alternative of the embodiment in  FIG. 4 ;  
         [0043]      FIG. 7  shows a perspective view schematically illustrating a subject and a configuration of the ECT probe according to a further embodiment of the present invention;  
         [0044]      FIG. 8  shows a cross-sectional view taken along with line VIII-VIII in  FIG. 7 ;  
         [0045]      FIG. 9  shows a perspective view schematically illustrating a configuration of the ECT probe according to a still further embodiment of the present invention;  
         [0046]      FIG. 10  shows a cross-sectional view taken along with line X-X in  FIG. 9 ;  
         [0047]      FIG. 11  shows a perspective view schematically illustrating a configuration of the ECT probe according to a still further embodiment of the present invention;  
         [0048]      FIG. 12  shows a cross-sectional view taken along with line XII-XII in  FIG. 11 ;  
         [0049]      FIG. 13  shows a perspective view schematically illustrating a configuration of the ECT probe according to an alternative of the embodiment in  FIG. 11 ;  
         [0050]      FIG. 14  shows a perspective view schematically illustrating a configuration of the ECT probe according to another alternative of the embodiment in  FIG. 11 ;  
         [0051]      FIG. 15  shows a perspective view schematically illustrating a configuration of the ECT probe according to a still further embodiment of the present invention;  
         [0052]      FIG. 16  shows a cross-sectional view taken along with line XVI-XVI in  FIG. 15 ;  
         [0053]      FIG. 17  shows a cross-sectional view schematically illustrating a configuration of the ECT probe according to an alternative of the embodiment in  FIG. 15 ;  
         [0054]      FIG. 18  shows a cross-sectional view schematically illustrating a configuration of the ECT probe according to a still further embodiment of the present invention;  
         [0055]      FIG. 19  shows a cross-sectional view schematically illustrating a configuration of the ECT probe according to a further embodiment of the present invention;  
         [0056]      FIG. 20  shows a cross-sectional view schematically illustrating a configuration of the ECT probe according to a still further embodiment of the present invention;  
         [0057]      FIG. 21  shows a cross-sectional view schematically illustrating a configuration of the ECT probe according to a still further embodiment of the present invention;  
         [0058]      FIG. 22  shows a cross-sectional view schematically illustrating a configuration of the ECT probe according to a still further embodiment of the present invention;  
         [0059]      FIG. 23  shows a cross-sectional view schematically illustrating a configuration of the ECT probe according to a still further embodiment of the present invention;  
         [0060]      FIG. 24  shows a cross-sectional view schematically illustrating a configuration of the ECT probe according to a still further embodiment of the present invention;  
         [0061]      FIG. 25  shows a cross-sectional view schematically illustrating a configuration of the ECT probe according to a still further embodiment of the present invention;  
         [0062]      FIG. 26  shows a cross-sectional view schematically illustrating a configuration of the ECT probe according to a still further embodiment of the present invention;  
         [0063]      FIG. 27  shows a cross-sectional view schematically illustrating a configuration of the ECT probe according to a still further embodiment of the present invention;  
         [0064]      FIG. 28  shows a cross-sectional view schematically illustrating a configuration of the ECT probe according to a still further embodiment of the present invention; and  
         [0065]      FIG. 29  shows a cross-sectional view schematically illustrating a configuration of the ECT probe according to a still further embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0066]      FIG. 1  shows a diagram schematically illustrating a configuration of an testing system using the eddy-current according to a preferred embodiment of the present invention,  FIG. 2  shows a perspective view schematically illustrating a configuration of the ECT probe according to the embodiment in  FIG. 1 , and  FIG. 3  shows a cross-sectional view taken along with line III-III in  FIG. 2 .  
         [0067]     In these figures, reference numeral  10  indicates an ECT probe,  11  indicates its flexible substrate formed of an insulative material such as polyimide,  12  indicates a meander-type exciting coil including coil conductors formed as a planar pattern turned back on the opposite surface  11   b  to the measurement surface  11   a  of the substrate  11 ,  13  and  14  indicate a pair of electrode terminals formed on the substrate  11 , which is connected electrically to both ends of the exciting coil  12 ,  15  to  19  indicate thin-film chips bonded on the exciting coil  12 , each of which is mounted with a GMR element (eddy-current sensor) such as an SVMR element,  20  indicates a subject,  20   a  indicates a defect such as a flaw and a crack appearing on the subject  20 ,  21  indicates a multiplexer connected electrically to the each GMR element in the ECT probe  10 , which applies these GMR elements with a sense current and takes out signals from the each GMR element,  22  indicates a lock-in amplifier that receives the signals from the each GMR element through the multiplexer  21  and detects the signal&#39;s level,  23  indicates a computer that processes the input signals from the lock-in amplifier, displays the results and so on, and  24  indicates a power supply for alternate magnetic field, which provide the exciting coil  12  in the ECT probe  10  with an alternate exciting current and provide the lock-in amplifier  22  with the exciting current as reference signals, respectively.  
         [0068]     The exciting coil  12  includes a coil conductor layer formed on the insulative substrate  11  and an insulating layer covering the coil conductor layer. An exciting part of the exciting coil  12  has a plurality of current lines that extend in parallel with each other to Z direction on the substrate  11 , and are turned back at both ends. During testing, alternate exciting currents with opposite directions to each other flow through the current lines adjacent to each other, respectively.  
         [0069]     The thin-film chips  15  to  19  are aligned on a central axis of a pair of current lines  12   a  and  12   b  positioned at the center in the X direction on the exciting coil  12 . These thin-film chips  15  to  19  are bonded on the opposite surface to the subject  20  in the exciting coil  12 .  
         [0070]     Each of the thin-film chips  15  to  19  includes a GMR element such as an SVMR element for example, a pair of lead conductors connected electrically to the GMR element, and a pair of electrode terminals connected electrically to the lead conductors, all of which are formed by thin-film technique on a chip substrate.  
         [0071]     According to the present embodiment, as understood from  FIG. 3 , the substrate  11  has a non-planar form curved along a traverse direction (X direction) where the measurement surface  11   a  shows a waveform of a single convex-surface. The thin-film chips  15  to  19  are mounted, via the exciting coil  12 , on the opposite surface  11   b  of the substrate  11 , which is a single concave-surface corresponding to the single convex-surface.  
         [0072]     Because the measurement surface  11   a  on the substrate showing a waveform of a single convex-surface has a small facing/contact area with the subject  20 , the sticktion hardly occurs. Even if the sticktion occurs, much less external-force application should be needed to remove the probe from the subject  20  against the sticktion. Consequently, a damage probability by the sticktion is drastically reduced, and therefore, the durability and lifetime can be improved in a large extent. Further, because the thin-film chips  15  to  19  are mounted on the concave-surface of the opposite surface  11   b  of the substrate  11 , the distance between the surface of the subject  20  and the GMR element does not increase, and therefore, a high performance of resolution is provided.  
         [0073]      FIG. 4  shows a perspective view schematically illustrating a configuration of the ECT probe according to another embodiment of the present invention, and  FIG. 5  shows a cross-sectional view taken along with line V-V in  FIG. 4 .  
         [0074]     In these figures, reference numeral  41  indicates a flexible substrate formed of an insulative material such as polyimide,  42  indicate a meander-type exciting coil including coil conductors formed as the planar pattern turned back on the opposite surface  41   b  to the measurement surface  41   a  of the substrate  41 ,  43  and  44  indicate a pair of electrode terminals formed on the substrate  41 , which is connected electrically to both ends of the exciting coil  42 , and  45  and  46  indicate thin-film chips bonded on the exciting coil  42 , each of which is mounted with a GMR element (eddy-current sensor) such as an SVMR element, respectively.  
         [0075]     The exciting coil  42  includes a coil conductor layer formed on the insulative substrate  41  and an insulating layer covering the coil conductor layer. An exciting part of the exciting coil  42  has a plurality of current lines that extend in parallel with each other to Z direction on the substrate  41 , and are turned back at both ends. During testing, alternate exciting currents with opposite directions to each other flow through the current lines adjacent to each other, respectively.  
         [0076]     The thin-film chips  45  and  46  are aligned on a central axis of two pairs of current lines  42   a  and  42   b , and  42   c  and  42   d  positioned at different locations from each other in the X direction on the exciting coil  42 . These thin-film chips  45  and  46  are bonded on the opposite surface to the subject in the exciting coil  42 .  
         [0077]     Each of the thin-film chips  45  and  46  includes a GMR element such as an SVMR element for example, a pair of lead conductors connected electrically to the GMR element, and a pair of electrode terminals connected electrically to the lead conductors, all of which are formed by thin-film technique on a chip substrate.  
         [0078]     According to the present embodiment, as understood from  FIG. 5 , the substrate  41  has a non-planar form curved along a traverse direction (X direction) where the measurement surface  41   a  shows a waveform of two convex-surfaces. The thin-film chips  45  and  46  are mounted, via the exciting coil  42 , on the opposite surface  41   b  of the substrate  41 , which has two concave-surface portions corresponding to the two convex-surface portions.  
         [0079]     Because the measurement surface  41   a  on the substrate showing a waveform of the two convex-surfaces has a small facing/contact area with the subject, the sticktion hardly occurs. Even if the sticktion occurs, much less external-force application should be needed to remove the probe from the subject against the sticktion. Consequently, a damage probability by the sticktion is drastically reduced, and therefore, the durability and lifetime can be improved in a large extent. Further, because the thin-film chips  45  and  46  are mounted respectively on the two concave-surfaces of the opposite surface  41   b  of the substrate  41 , the distance between the surface of the subject and the GMR element does not increase, and therefore, a high performance of resolution is provided.  
         [0080]      FIG. 6  shows a cross-sectional view schematically illustrating a configuration according to an alternative of the embodiment in  FIG. 4 .  
         [0081]     According to the alternative, the substrate  41 ′ has a non-planar form curved along a traverse direction (X direction) where the measurement surface  41   a ′ facing to the subject shows a waveform of a single convex-surface that has a planar central portion. The thin-film chips  45  and  46  are mounted, via the exciting coil  42 , at the different position from each other on the opposite surface  41   b ′ of the substrate  41 ′, which is a single concave-surface that has a planar central portion corresponding to a single convex-surface that has a planar central portion. The other configurations according to the alternative are almost the same as those according to the embodiment in  FIG. 4 .  
         [0082]     In the alternative, because the measurement surface  41   a ′ on the substrate showing a waveform of a single convex-surface that has a planar central portion has a small facing/contact area with the subject, the sticktion hardly occurs. Even if the sticktion occurs, much less external-force application should be needed to remove the probe from the subject against the sticktion. Consequently, a damage probability by the sticktion is drastically reduced, and therefore, the durability and lifetime can be improved in a large extent. Further, because the thin-film chips  45  and  46  are mounted on the single concave-surface that has a planar central portion of the opposite surface  41   b ′ of the substrate  41 ′, the distance between the surface of the subject and the GMR element does not increase, and therefore, a high performance of resolution is provided.  
         [0083]      FIG. 7  shows a perspective view schematically illustrating a subject and a configuration of the ECT probe according to a further embodiment of the present invention, and  FIG. 8  shows a cross-sectional view taken along with line VIII-VIII in  FIG. 7 .  
         [0084]     In these figures, reference numeral  70  indicates a ECT probe,  71  indicates a flexible substrate formed of an insulative material such as polyimide,  72  indicates a meander-type exciting coil including coil conductors formed as the planar pattern turned back on the opposite surface to the measurement surface of the substrate  71 ,  75  indicates a plurality of thin-film chips bonded on the exciting coil  72 , each of which is mounted with a GMR element (eddy-current sensor) such as an SVMR element, and  80  indicates a subject, respectively.  
         [0085]     The thin-film chips  75  are aligned on a central axis of a pair of current lines positioned at the center in the X direction on the exciting coil  72 . These thin-film chips  75  are bonded on the opposite surface to the subject  80  in the exciting coil  72 .  
         [0086]     Each of the thin-film chips  75  includes a GMR element such as an SVMR element for example, a pair of lead conductors connected electrically to the GMR element, and a pair of electrode terminals connected electrically to the lead conductors, all of which are formed by thin-film technique on a chip substrate.  
         [0087]     According to the present embodiment, as understood from  FIG. 8 , the substrate  71  has a non-planar form curved along a traverse direction (X direction) where the measurement surface facing to the subject  80  shows a waveform of a single convex-surface. Further, the substrate  71  has flexibility where the substrate can curve flexibly along the curved surface of the subject  80 . The thin-film chips  75  are mounted, via the exciting coil  72 , on the opposite surface of the substrate  71 , which is a single concave-surface corresponding to the single convex-surface.  
         [0088]     The other configurations according to the present embodiment are almost the same as those according to the embodiment in  FIG. 1 .  
         [0089]     Because the measurement surface of the substrate showing a waveform of the single convex-surface has a small facing/contact area with the subject  80 , the sticktion hardly occurs. Even if the sticktion occurs, much less external-force application should be needed to remove the probe from the subject  80  against the sticktion. Consequently, a damage probability by the sticktion is drastically reduced, and therefore, the durability and lifetime can be improved in a large extent. Further, because the thin-film chips  75  are mounted on the single concave-surface of the opposite surface of the substrate  71 , the distance between the surface of the subject  80  and the GMR element does not increase, and therefore, a high performance of resolution is provided.  
         [0090]      FIG. 9  shows a perspective view schematically illustrating a configuration of the ECT probe according to a still further embodiment of the present invention, and  FIG. 10  shows a cross-sectional view taken along with line X-X in  FIG. 9 . Here,  FIG. 9  shows a view from the side of the opposite surface to that of  FIG. 2 , that is, of the measurement surface facing to the subject.  
         [0091]     In these figures, reference numeral  91  indicates a flexible substrate formed of an insulative material such as polyimide,  92  indicates a meander-type exciting coil including coil conductors formed as the planar pattern turned back on the opposite surface  91   b  to the measurement surface  91   a  of the substrate  91 ,  93  and  94  indicate a pair of electrode terminals formed on the substrate  91 , which is connected electrically to both ends of the exciting coil  92 , and  95  to  99  indicate thin-film chips bonded on the exciting coil  92 , each of which is mounted with a GMR element (eddy-current sensor) such as an SVMR element, respectively.  
         [0092]     The exciting coil  92  includes a coil conductor layer formed on the insulative substrate  91  and an insulating layer covering the coil conductor layer. An exciting part of the exciting coil  92  has a plurality of current lines that extend in parallel with each other to Z direction on the substrate  91 , and are turned back at both ends. During testing, alternate exciting currents with opposite directions to each other flow through the current lines adjacent to each other, respectively.  
         [0093]     The thin-film chips  95  to  99  are aligned on a central axis of a pair of current lines positioned at the center in the X direction on the exciting coil  92 . These thin-film chips  95  to  99  are bonded on the opposite surface to the subject in the exciting coil  92 .  
         [0094]     Each of the thin-film chips  95  to  99  includes a GMR element such as an SVMR element for example, a pair of lead conductors connected electrically to the GMR element, and a pair of electrode terminals connected electrically to the lead conductors, all of which are formed by thin-film technique on a chip substrate.  
         [0095]     According to the present embodiment, the entire substrate  91  has a planar form, and a part of the measurement surface  91   a  facing to subject has a large number of, preferably much small, machined concaves and convexes  91   c  such as a blasting rough surface or an embossed surface.  
         [0096]     Because the measurement surface  91   a  of the substrate has a large number of machined concaves and convexes  91   c , the sticktion hardly occurs. Accordingly, a damage probability by the sticktion is drastically reduced, and therefore, the durability and lifetime can be improved in a large extent.  
         [0097]      FIG. 11  shows a perspective view schematically illustrating a configuration of the ECT probe according to a still further embodiment of the present invention, and  FIG. 12  shows a cross-sectional view taken along with line XII-XII in  FIG. 11 . Here,  FIG. 11  shows a view from the side of the opposite surface to that of  FIG. 2 , that is, of the measurement surface facing to the subject.  
         [0098]     In these figures, reference numeral  111  indicates a flexible substrate formed of an insulative material such as polyimide,  112  indicates a meander-type exciting coil including coil conductors formed as the planar pattern turned back on the opposite surface  111   b  to the measurement surface  111   a  of the substrate  111 ,  113  and  114  indicate a pair of electrode terminals formed on the substrate  111 , which is connected electrically to both ends of the exciting coil  112 , and  115  to  119  indicate thin-film chips bonded on the exciting coil  112 , each of which is mounted with a GMR element (eddy-current sensor) such as an SVMR element, respectively.  
         [0099]     The exciting coil  112  includes a coil conductor layer formed on the insulative substrate  111  and an insulating layer covering the coil conductor layer. An exciting part of the exciting coil  112  has a plurality of current lines that extend in parallel with each other to Z direction on the substrate  111 , and are turned back at both ends. During testing, alternate exciting currents with opposite directions to each other flow through the current lines adjacent to each other, respectively.  
         [0100]     The thin-film chips  115  to  119  are aligned on a central axis of a pair of current lines positioned at the center in the X direction on the exciting coil  112 . These thin-film chips  115  to  119  are bonded on the opposite surface to the subject in the exciting coil  112 .  
         [0101]     Each of the thin-film chips  115  to  119  includes a GMR element such as an SVMR element for example, a pair of lead conductors connected electrically to the GMR element, and a pair of electrode terminals connected electrically to the lead conductors, all of which are formed by thin-film technique on a chip substrate.  
         [0102]     According to the present embodiment, the entire substrate  111  has a planar form, and a part of the measurement surface  111   a  facing to subject has a large number of, preferably much small, grooves  111   c  extended along a traverse direction (X direction) in the substrate  111 .  
         [0103]     Because the measurement surface  111   a  on the substrate has a large number of machined grooves  111   c  extended along the traverse direction, the sticktion hardly occurs. Accordingly, a damage probability by the sticktion is drastically reduced, and therefore, the durability and lifetime can be improved in a large extent.  
         [0104]      FIG. 13  shows a perspective view schematically illustrating a configuration of the ECT probe according to an alternative of the embodiment in  FIG. 11 . Here,  FIG. 13  shows a view from the side of the opposite surface to that of  FIG. 2 , that is, of the measurement surface facing to the subject.  
         [0105]     According to the present alternative, the entire substrate  111 ′ has a planar form, and a part of the measurement surface  111   a  ′ facing to subject has a large number of, preferably much small, grooves  111   c  ′ extended along a longitudinal direction (Z direction) in the substrate  111 ′. The other configurations according to the present alternative are almost the same as those according to the embodiment in  FIG. 11 .  
         [0106]     Because the measurement surface  111   a  ′ on the substrate has a large number of machined grooves  111   c  ′extended along the longitudinal direction, the sticktion hardly occurs. Accordingly, a damage probability by the sticktion is drastically reduced, and therefore, the durability and lifetime can be improved in a large extent.  
         [0107]      FIG. 14  shows a perspective view schematically illustrating a configuration of the ECT probe according to another alternative of the embodiment in  FIG. 11 . Here,  FIG. 14  shows a view from the side of the opposite surface to that of  FIG. 2 , that is, of the measurement surface facing to the subject.  
         [0108]     According to the present alternative, the entire substrate  111 ″ has a planar form, and a part of the measurement surface  111   a  ″ facing to subject has a large number of, preferably much small, grooves  111   c  ″ extended along the oblique direction to a traverse direction (X direction) in the substrate  111 ″. The other configurations according to the present alternative are almost the same as those according to the embodiment in  FIG. 11 .  
         [0109]     Because the measurement surface  111   a  ″ on the substrate has a large number of machined grooves  111   c  ″ extended along the oblique direction, the sticktion hardly occurs. Accordingly, a damage probability by the sticktion is drastically reduced, and therefore, the durability and lifetime can be improved in a large extent.  
         [0110]      FIG. 15  shows a perspective view schematically illustrating a configuration of the ECT probe according to a still further embodiment of the present invention, and  FIG. 16  shows a cross-sectional view taken along with line XVI-XVI in  FIG. 15 . Here,  FIG. 15  shows a view from the side of the opposite surface to that of  FIG. 2 , that is, of the measurement surface facing to the subject.  
         [0111]     In these figures, reference numeral  151  indicates a flexible substrate formed of an insulative material such as polyimide,  152  indicates a meander-type exciting coil including coil conductors formed as the planar pattern turned back on the opposite surface  151   b  to the measurement surface  151   a  of the substrate  151 ,  153  and  154  indicate a pair of electrode terminals formed on the substrate  151 , which is connected electrically to both ends of the exciting coil  152 , and  155  to  159  indicate thin-film chips bonded on the exciting coil  152 , each of which is mounted with a GMR element (eddy-current sensor) such as an SVMR element, respectively.  
         [0112]     The exciting coil  152  includes a coil conductor layer formed on the insulative substrate  151  and an insulating layer covering the coil conductor layer. An exciting part of the exciting coil  152  has a plurality of current lines that extend in parallel with each other to Z direction on the substrate  151 , and are turned back at both ends. During testing, alternate exciting currents with opposite directions to each other flow through the current lines adjacent to each other, respectively.  
         [0113]     The thin-film chips  155  to  159  are aligned on a central axis of a pair of current lines positioned at the center in the X direction on the exciting coil  152 . These thin-film chips  155  to  159  are bonded on the opposite surface to the subject in the exciting coil  152 .  
         [0114]     Each of the thin-film chips  155  to  159  includes a GMR element such as an SVMR element for example, a pair of lead conductors connected electrically to the GMR element, and a pair of electrode terminals connected electrically to the lead conductors, all of which are formed by thin-film technique on a chip substrate.  
         [0115]     According to the present embodiment, the entire substrate  151  has a planar form, and a part of the measurement surface  151   a  facing to the subject has a large number of, preferably much small, blind holes  151   c.    
         [0116]     Because the measurement surface  151   a  on the substrate has a large number of machined blind holes  151   c , the sticktion hardly occurs. Accordingly, a damage probability by the sticktion is drastically reduced, and therefore, the durability and lifetime can be improved in a large extent.  
         [0117]      FIG. 17  shows a cross-sectional view schematically illustrating a configuration of the ECT probe according to an alternative of the embodiment in  FIG. 15 .  
         [0118]     According to the present alternative, the entire substrate  151 ′ has a planar form, and a part of the measurement surface  151   a ′ facing to the subject has a large number of, preferably much small, through holes  151   c ′. The other configurations according to the present alternative are almost the same as those according to the embodiment in  FIG. 15 .  
         [0119]     Because the measurement surface  151   a ′ on the substrate has a large number of through holes  151   c ′, the sticktion hardly occurs. Accordingly, a damage probability by the sticktion is drastically reduced, and therefore, the durability and lifetime can be improved in a large extent.  
         [0120]      FIG. 18  shows a cross-sectional view schematically illustrating a configuration of the ECT probe according to a still further embodiment of the present invention.  
         [0121]     In this figure, reference numeral  181  indicates a flexible substrate formed of an insulative material such as polyimide,  182  indicates a meander-type exciting coil including coil conductors formed as the planar pattern turned back on the opposite surface  181   b  to the measurement surface  181   a  of the substrate  181 , and  185  to  189  indicate thin-film chips bonded on the exciting coil  182 , each of which is mounted with a GMR element (eddy-current sensor) such as an SVMR element, respectively.  
         [0122]     The exciting coil  182  includes a coil conductor layer formed on the insulative substrate  181  and an insulating layer covering the coil conductor layer. An exciting part of the exciting coil  182  has a plurality of current lines that extend in parallel with each other to Z direction on the substrate  181 , and are turned back at both ends. During testing, alternate exciting currents with opposite directions to each other flow through the current lines adjacent to each other, respectively.  
         [0123]     The thin-film chips  185  to  189  are aligned on a central axis of a pair of current lines positioned at the center in the X direction on the exciting coil  182 . These thin-film chips  185  to  189  are bonded on the opposite surface to the subject in the exciting coil  182 .  
         [0124]     Each of the thin-film chips  185  to  189  includes a GMR element such as an SVMR element for example, a pair of lead conductors connected electrically to the GMR element, and a pair of electrode terminals connected electrically to the lead conductors, all of which are formed by thin-film technique on a chip substrate.  
         [0125]     According to the present embodiment, the entire substrate  181  has a planar form, and a part of the measurement surface  181   a  facing to the subject is applied with a lubricant  181   d  such as a lubricating oil. The other configurations according to the present alternative are almost the same as those according to the embodiment in  FIG. 1  with the exception that the substrate  181  has a planar form.  
         [0126]     Because a part of the measurement surface  181   a  on the substrate has a lubricant layer  181   d , the sticktion hardly occurs. Accordingly, a damage probability by the sticktion is drastically reduced, and therefore, the durability and lifetime can be improved in a large extent.  
         [0127]      FIG. 19  shows a cross-sectional view schematically illustrating a configuration of the ECT probe according to a still further embodiment of the present invention.  
         [0128]     In this figure, reference numeral  191  indicates a flexible substrate formed of an insulative material such as polyimide,  192  indicates a meander-type exciting coil including coil conductors formed as the planar pattern turned back on the opposite surface  191   b  to the measurement surface  191   a  of the substrate  191 , and  195  to  199  indicate thin-film chips bonded on the exciting coil  192 , each of which is mounted with a GMR element (eddy-current sensor) such as an SVMR element, respectively.  
         [0129]     The exciting coil  192  includes a coil conductor layer formed on the insulative substrate  191  and an insulating layer covering the coil conductor layer. An exciting part of the exciting coil  192  has a plurality of current lines that extend in parallel with each other to Z direction on the substrate  191 , and are turned back at both ends. During testing, alternate exciting currents with opposite directions to each other flow through the current lines adjacent to each other, respectively.  
         [0130]     The thin-film chips  195  to  199  are aligned on a central axis of a pair of current lines positioned at the center in the X direction on the exciting coil  192 . These thin-film chips  195  to  199  are bonded on the opposite surface to the subject in the exciting coil  192 .  
         [0131]     Each of the thin-film chips  195  to  199  includes a GMR element such as an SVMR element for example, a pair of lead conductors connected electrically to the GMR element, and a pair of electrode terminals connected electrically to the lead conductors, all of which are formed by thin-film technique on a chip substrate.  
         [0132]     According to the present embodiment, the entire substrate  191  has a planar form, and a part of the measurement surface  191   a  facing to the subject has a large number of, preferably much small, grooves  191   c  extended along a traverse direction (X direction), a longitudinal direction (Z direction) or an oblique direction to the traverse direction (X direction), and is applied with a lubricant  191   d  such as a lubricating oil. The other configurations according to the present embodiment are almost the same as those according to the embodiment in  FIG. 11 , or the alternative in  FIG. 13  or in  FIG. 14 .  
         [0133]     Because a part of the measurement surface  191   a  on the substrate has a large number of grooves  191   c  and a lubricant layer  191   d , the sticktion hardly occurs. Accordingly, a damage probability by the sticktion is drastically reduced, and therefore, the durability and lifetime can be improved in a large extent.  
         [0134]      FIG. 20  shows a cross-sectional view schematically illustrating a configuration of the ECT probe according to a still further embodiment of the present invention.  
         [0135]     In this figure, reference numeral  201  indicates a flexible substrate formed of an insulative material such as polyimide,  202  indicates a meander-type exciting coil including coil conductors formed as the planar pattern turned back on the opposite surface  201   b  to the measurement surface  201   a  of the substrate  201 , and  205  to  209  indicate thin-film chips bonded on the exciting coil  202 , each of which is mounted with a GMR element (eddy-current sensor) such as an SVMR element, respectively.  
         [0136]     The exciting coil  202  includes a coil conductor layer formed on the insulative substrate  201  and an insulating layer covering the coil conductor layer. An exciting part of the exciting coil  202  has a plurality of current lines that extend in parallel with each other to Z direction on the substrate  201 , and are turned back at both ends. During testing, alternate exciting currents with opposite directions to each other flow through the current lines adjacent to each other, respectively.  
         [0137]     The thin-film chips  205  to  209  are aligned on a central axis of a pair of current lines positioned at the center in the X direction on the exciting coil  202 . These thin-film chips  205  to  209  are bonded on the opposite surface to the subject in the exciting coil  202 .  
         [0138]     Each of the thin-film chips  205  to  209  includes a GMR element such as an SVMR element for example, a pair of lead conductors connected electrically to the GMR element, and a pair of electrode terminals connected electrically to the lead conductors, all of which are formed by thin-film technique on a chip substrate.  
         [0139]     According to the present embodiment, the entire substrate  201  has a planar form, and a part of the measurement surface  201   a  facing to the subject has a large number of, preferably much small, blind holes  201   c , and is applied with a lubricant  201   d  such as a lubricating oil. The other configurations according to the present embodiment are almost the same as those according to the embodiment in  FIG. 15 .  
         [0140]     Because a part of the measurement surface  201   a  on the substrate has a large number of blind holes  201   c  and a lubricant layer  201   d , the sticktion hardly occurs. Accordingly, a damage probability by the sticktion is drastically reduced, and therefore, the durability and lifetime can be improved in a large extent.  
         [0141]      FIG. 21  shows a cross-sectional view schematically illustrating a configuration of the ECT probe according to a still further embodiment of the present invention.  
         [0142]     In this figure, reference numeral  211  indicates a flexible substrate formed of an insulative material such as polyimide,  212  indicates a meander-type exciting coil including coil conductors formed as the planar pattern turned back on the opposite surface  211   b  to the measurement surface  211   a  of the substrate  211 , and  215  to  219  indicate thin-film chips bonded on the exciting coil  212 , each of which is mounted with a GMR element (eddy-current sensor) such as an SVMR element, respectively.  
         [0143]     The exciting coil  212  includes a coil conductor layer formed on the insulative substrate  211  and an insulating layer covering the coil conductor layer. An exciting part of the exciting coil  212  has a plurality of current lines that extend in parallel with each other to Z direction on the substrate  211 , and are turned back at both ends. During testing, alternate exciting currents with opposite directions to each other flow through the current lines adjacent to each other, respectively.  
         [0144]     The thin-film chips  215  to  219  are aligned on a central axis of a pair of current lines positioned at the center in the X direction on the exciting coil  212 . These thin-film chips  215  to  219  are bonded on the opposite surface to the subject in the exciting coil  212 .  
         [0145]     Each of the thin-film chips  215  to  219  includes a GMR element such as an SVMR element for example, a pair of lead conductors connected electrically to the GMR element, and a pair of electrode terminals connected electrically to the lead conductors, all of which are formed by thin-film technique on a chip substrate.  
         [0146]     According to the present embodiment, the entire substrate  211  has a planar form, and a part of the measurement surface  211   a  facing to the subject has a large number of, preferably much small, through holes, and is applied with a lubricant  211   d  such as a lubricating oil. The other configurations according to the present embodiment are almost the same as those according to the embodiment in  FIG. 17 .  
         [0147]     Because a part of the measurement surface  211   a  on the substrate has a large number of through holes  211   c  and a lubricant layer  211   d , the sticktion hardly occurs. Accordingly, a damage probability by the sticktion is drastically reduced, and therefore, the durability and lifetime can be improved in a large extent.  
         [0148]      FIG. 22  shows a cross-sectional view schematically illustrating a configuration of the ECT probe according to a still further embodiment of the present invention.  
         [0149]     In this figure, reference numeral  221  indicates a flexible substrate formed of an insulative material such as polyimide,  222  indicates a meander-type exciting coil including coil conductors formed as the planar pattern turned back on the opposite surface  221   b  to the measurement surface  221   a  of the substrate  221 , and  225  to  229  indicate thin-film chips bonded on the exciting coil  222 , each of which is mounted with a GMR element (eddy-current sensor) such as an SVMR element, respectively.  
         [0150]     The exciting coil  222  includes a coil conductor layer formed on the insulative substrate  221  and an insulating layer covering the coil conductor layer. An exciting part of the exciting coil  222  has a plurality of current lines that extend in parallel with each other to Z direction on the substrate  221 , and are turned back at both ends. During testing, alternate exciting currents with opposite directions to each other flow through the current lines adjacent to each other, respectively.  
         [0151]     The thin-film chips  225  to  229  are aligned on a central axis of a pair of current lines positioned at the center in the X direction on the exciting coil  222 . These thin-film chips  225  to  229  are bonded on the opposite surface to the subject in the exciting coil  222 .  
         [0152]     Each of the thin-film chips  225  to  229  includes a GMR element such as an SVMR element for example, a pair of lead conductors connected electrically to the GMR element, and a pair of electrode terminals connected electrically to the lead conductors, all of which are formed by thin-film technique on a chip substrate.  
         [0153]     According to the present embodiment, the entire substrate  221  has a planar form, and a part of the measurement surface  211   a  facing to the subject is coated with a DLC layer  221   e . The other configurations according to the present embodiment are almost the same as those according to the embodiment in  FIG. 1  or the embodiment in  FIG. 18  with the exception that the substrate  221  has a planar form.  
         [0154]     Because a part of the measurement surface  221   a  on the substrate has a DLC layer  221   e , the sticktion hardly occurs. Accordingly, a damage probability by the sticktion is drastically reduced, and therefore, the durability and lifetime can be improved in a large extent.  
         [0155]      FIG. 23  shows a cross-sectional view schematically illustrating a configuration of the ECT probe according to a still further embodiment of the present invention.  
         [0156]     In this figure, reference numeral  231  indicates a flexible substrate formed of an insulative material such as polyimide,  232  indicates a meander-type exciting coil including coil conductors formed as the planar pattern turned back on the opposite surface  231   b  to the measurement surface  231   a  of the substrate  231 , and  235  to  239  indicate thin-film chips bonded on the exciting coil  232 , each of which is mounted with a GMR element (eddy-current sensor) such as an SVMR element, respectively.  
         [0157]     The exciting coil  232  includes a coil conductor layer formed on the insulative substrate  231  and an insulating layer covering the coil conductor layer. An exciting part of the exciting coil  232  has a plurality of current lines that extend in parallel with each other to Z direction on the substrate  231 , and are turned back at both ends. During testing, alternate exciting currents with opposite directions to each other flow through the current lines adjacent to each other, respectively.  
         [0158]     The thin-film chips  235  to  239  are aligned on a central axis of a pair of current lines positioned at the center in the X direction on the exciting coil  232 . These thin-film chips  235  to  239  are bonded on the opposite surface to the subject in the exciting coil  232 .  
         [0159]     Each of the thin-film chips  235  to  239  includes a GMR element such as an SVMR element for example, a pair of lead conductors connected electrically to the GMR element, and a pair of electrode terminals connected electrically to the lead conductors, all of which are formed by thin-film technique on a chip substrate.  
         [0160]     According to the present embodiment, the entire substrate  231  has a planar form, and a part of the measurement surface  231   a  facing to the subject has a large number of, preferably much small, grooves  231   c  extended along a traverse direction (X direction), a longitudinal direction (Z direction) or an oblique direction to the traverse direction (X direction), and is coated with a DLC layer  231   e . The other configurations according to the present embodiment are almost the same as those according to the embodiment in  FIG. 11 , or the alternative in  FIG. 13  or in  FIG. 14 .  
         [0161]     Because a part of the measurement surface  231   a  on the substrate has a large number of grooves  231   c  and a DLC layer  231   e , the sticktion hardly occurs. Accordingly, a damage probability by the sticktion is drastically reduced, and therefore, the durability and lifetime can be improved in a large extent.  
         [0162]      FIG. 24  shows a cross-sectional view schematically illustrating a configuration of the ECT probe according to a still further embodiment of the present invention.  
         [0163]     In this figure, reference numeral  241  indicates a flexible substrate formed of an insulative material such as polyimide,  242  indicates a meander-type exciting coil including coil conductors formed as the planar pattern turned back on the opposite surface  241   b  to the measurement surface  241   a  of the substrate  241 , and  245  to  249  indicate thin-film chips bonded on the exciting coil  242 , each of which is mounted with a GMR element (eddy-current sensor) such as an SVMR element, respectively.  
         [0164]     The exciting coil  242  includes a coil conductor layer formed on the insulative substrate  241  and an insulating layer covering the coil conductor layer. An exciting part of the exciting coil  242  has a plurality of current lines that extend in parallel with each other to Z direction on the substrate  241 , and are turned back at both ends. During testing, alternate exciting currents with opposite directions to each other flow through the current lines adjacent to each other, respectively.  
         [0165]     The thin-film chips  245  to  249  are aligned on a central axis of a pair of current lines positioned at the center in the X direction on the exciting coil  242 . These thin-film chips  245  to  249  are bonded on the opposite surface to the subject in the exciting coil  242 .  
         [0166]     Each of the thin-film chips  245  to  249  includes a GMR element such as an SVMR element for example, a pair of lead conductors connected electrically to the GMR element, and a pair of electrode terminals connected electrically to the lead conductors, all of which are formed by thin-film technique on a chip substrate.  
         [0167]     According to the present embodiment, the entire substrate  241  has a planar form, and a part of the measurement surface  241   a  facing to the subject has a large number of, preferably much small, blind holes  241   c , and is coated with a DLC layer  241   e . The other configurations according to the present embodiment are almost the same as those according to the embodiment in  FIG. 15 .  
         [0168]     Because a part of the measurement surface  241   a  on the substrate has a large number of blind holes  241   c  and a DLC layer  241   e , the sticktion hardly occurs. Accordingly, a damage probability by the sticktion is drastically reduced, and therefore, the durability and lifetime can be improved in a large extent.  
         [0169]      FIG. 25  shows a cross-sectional view schematically illustrating a configuration of the ECT probe according to a still further embodiment of the present invention.  
         [0170]     In this figure, reference numeral  251  indicates a flexible substrate formed of an insulative material such as polyimide,  252  indicates a meander-type exciting coil including coil conductors formed as the planar pattern turned back on the opposite surface  251   b  to the measurement surface  251   a  of the substrate  251 , and  255  to  259  indicate thin-film chips bonded on the exciting coil  252 , each of which is mounted with a GMR element (eddy-current sensor) such as an SVMR element, respectively.  
         [0171]     The exciting coil  252  includes a coil conductor layer formed on the insulative substrate  251  and an insulating layer covering the coil conductor layer. An exciting part of the exciting coil  252  has a plurality of current lines that extend in parallel with each other to Z direction on the substrate  251 , and are turned back at both ends. During testing, alternate exciting currents with opposite directions to each other flow through the current lines adjacent to each other, respectively.  
         [0172]     The thin-film chips  255  to  259  are aligned on a central axis of a pair of current lines positioned at the center in the X direction on the exciting coil  252 . These thin-film chips  255  to  259  are bonded on the opposite surface to the subject in the exciting coil  252 .  
         [0173]     Each of the thin-film chips  255  to  259  includes a GMR element such as an SVMR element for example, a pair of lead conductors connected electrically to the GMR element, and a pair of electrode terminals connected electrically to the lead conductors, all of which are formed by thin-film technique on a chip substrate.  
         [0174]     According to the present embodiment, the entire substrate  251  has a planar form, and a part of the measurement surface  251   a  facing to the subject has a large number of, preferably much small, through holes  251   c , and is applied with a DLC layer  251   e . The other configurations according to the present embodiment are almost the same as those according to the alternative in  FIG. 17 .  
         [0175]     Because a part of the measurement surface  251   a  on the substrate has a large number of through holes  251   c  and a DLC layer  251   e , the sticktion hardly occurs. Accordingly, a damage probability by the sticktion is drastically reduced, and therefore, the durability and lifetime can be improved in a large extent.  
         [0176]      FIG. 26  shows a cross-sectional view schematically illustrating a configuration of the ECT probe according to a still further embodiment of the present invention.  
         [0177]     In this figure, reference numeral  261  indicates a flexible substrate formed of an insulative material such as polyimide,  262  indicates a meander-type exciting coil including coil conductors formed as the planar pattern turned back on the opposite surface  261   b  to the measurement surface  261   a  of the substrate  261 , and  265  to  269  indicate thin-film chips bonded on the exciting coil  262 , each of which is mounted with a GMR element (eddy-current sensor) such as an SVMR element, respectively.  
         [0178]     The exciting coil  262  includes a coil conductor layer formed on the insulative substrate  261  and an insulating layer covering the coil conductor layer. An exciting part of the exciting coil  262  has a plurality of current lines that extend in parallel with each other to Z direction on the substrate  261 , and are turned back at both ends. During testing, alternate exciting currents with opposite directions to each other flow through the current lines adjacent to each other, respectively.  
         [0179]     The thin-film chips  265  to  269  are aligned on a central axis of a pair of current lines positioned at the center in the X direction on the exciting coil  262 . These thin-film chips  265  to  269  are bonded on the opposite surface to the subject in the exciting coil  262 .  
         [0180]     Each of the thin-film chips  265  to  269  includes a GMR element such as an SVMR element for example, a pair of lead conductors connected electrically to the GMR element, and a pair of electrode terminals connected electrically to the lead conductors, all of which are formed by thin-film technique on a chip substrate.  
         [0181]     According to the present embodiment, the entire substrate  261  has a planar form, and a part of the measurement surface  261   a  facing to the subject is coated with a DLC layer  261   e , and is applied with a lubricant  261   d  such as a lubricating oil. The other configurations according to the present embodiment are almost the same as those according to the embodiment in  FIG. 1  or the embodiment in  FIG. 18  with the exception that the substrate  261  has a planar form.  
         [0182]     Because a part of the measurement surface  261   a  on the substrate has a DLC layer  261   e  and a lubricant layer  261   d , the sticktion hardly occurs. Accordingly, a damage probability by the sticktion is drastically reduced, and therefore, the durability and lifetime can be improved in a large extent.  
         [0183]      FIG. 27  shows a cross-sectional view schematically illustrating a configuration of the ECT probe according to a still further embodiment of the present invention.  
         [0184]     In this figure, reference numeral  271  indicates a flexible substrate formed of an insulative material such as polyimide,  272  indicates a meander-type exciting coil including coil conductors formed as the planar pattern turned back on the opposite surface  271   b  to the measurement surface  271   a  of the substrate  271 , and  275  to  279  indicate thin-film chips bonded on the exciting coil  272 , each of which is mounted with a GMR element (eddy-current sensor) such as an SVMR element, respectively.  
         [0185]     The exciting coil  272  includes a coil conductor layer formed on the insulative substrate  271  and an insulating layer covering the coil conductor layer. An exciting part of the exciting coil  272  has a plurality of current lines that extend in parallel with each other to Z direction on the substrate  271 , and are turned back at both ends. During testing, alternate exciting currents with opposite directions to each other flow through the current lines adjacent to each other, respectively.  
         [0186]     The thin-film chips  275  to  279  are aligned on a central axis of a pair of current lines positioned at the center in the X direction on the exciting coil  272 . These thin-film chips  275  to  279  are bonded on the opposite surface to the subject in the exciting coil  272 .  
         [0187]     Each of the thin-film chips  275  to  279  includes a GMR element such as an SVMR element for example, a pair of lead conductors connected electrically to the GMR element, and a pair of electrode terminals connected electrically to the lead conductors, all of which are formed by thin-film technique on a chip substrate.  
         [0188]     According to the present embodiment, the entire substrate  271  has a planar form, and a part of the measurement surface  271   a  facing to the subject has a large number of, preferably much small, grooves  271   c  extended along a traverse direction (X direction), a longitudinal direction (Z direction) or an oblique direction to the traverse direction (X direction), and is coated with a DLC layer  271   e , and is further applied with a lubricant  271   d  such as a lubricating oil. The other configurations according to the present embodiment are almost the same as those according to the embodiment in  FIG. 11 , or the alternative in  FIG. 13  or in  FIG. 14 .  
         [0189]     Because a part of the measurement surface  271   a  on the substrate has a large number of grooves  271   c , a DLC layer  271   e  and a lubricant layer  271   d , the sticktion hardly occurs. Accordingly, a damage probability by the sticktion is drastically reduced, and therefore, the durability and lifetime can be improved in a large extent.  
         [0190]      FIG. 28  shows a cross-sectional view schematically illustrating a configuration of the ECT probe according to a still further embodiment of the present invention.  
         [0191]     In this figure, reference numeral  281  indicates a flexible substrate formed of an insulative material such as polyimide,  282  indicates a meander-type exciting coil including coil conductors formed as the planar pattern turned back on the opposite surface  281   b  to the measurement surface  281   a  of the substrate  281 , and  285  to  289  indicate thin-film chips bonded on the exciting coil  282 , each of which is mounted with a GMR element (eddy-current sensor) such as an SVMR element, respectively.  
         [0192]     The exciting coil  282  includes a coil conductor layer formed on the insulative substrate  281  and an insulating layer covering the coil conductor layer. An exciting part of the exciting coil  282  has a plurality of current lines that extend in parallel with each other to Z direction on the substrate  281 , and are turned back at both ends. During testing, alternate exciting currents with opposite directions to each other flow through the current lines adjacent to each other, respectively.  
         [0193]     The thin-film chips  285  to  289  are aligned on a central axis of a pair of current lines positioned at the center in the X direction on the exciting coil  282 . These thin-film chips  285  to  289  are bonded on the opposite surface to the subject in the exciting coil  282 .  
         [0194]     Each of the thin-film chips  285  to  289  includes a GMR element such as an SVMR element for example, a pair of lead conductors connected electrically to the GMR element, and a pair of electrode terminals connected electrically to the lead conductors, all of which are formed by thin-film technique on a chip substrate.  
         [0195]     According to the present embodiment, the entire substrate  281  has a planar form, and a part of the measurement surface  281   a  facing to the subject has a large number of, preferably much small, blind holes  281   c , and is coated with a DLC layer  281   c , and is further applied with a lubricant  281   d  such as a lubricating oil. The other configurations according to the present embodiment are almost the same as those according to the embodiment in  FIG. 15 .  
         [0196]     Because a part of the measurement surface  281   a  on the substrate has a large number of blind holes  281   c , a DLC layer  281   e  and a lubricant layer  281   d , the sticktion hardly occurs. Accordingly, a damage probability by the sticktion is drastically reduced, and therefore, the durability and lifetime can be improved in a large extent.  
         [0197]      FIG. 29  shows a cross-sectional view schematically illustrating a configuration of the ECT probe according to a still further embodiment of the present invention.  
         [0198]     In this figure, reference numeral  291  indicates a flexible substrate formed of an insulative material such as polyimide,  292  indicates a meander-type exciting coil including coil conductors formed as the planar pattern turned back on the opposite surface  291   b  to the measurement surface  291   a  of the substrate  291 , and  295  to  299  indicate thin-film chips bonded on the exciting coil  292 , each of which is mounted with a GMR element (eddy-current sensor) such as an SVMR element, respectively.  
         [0199]     The exciting coil  292  includes a coil conductor layer formed on the insulative substrate  291  and an insulating layer covering the coil conductor layer. An exciting part of the exciting coil  292  has a plurality of current lines that extend in parallel with each other to Z direction on the substrate  291 , and are turned back at both ends. During testing, alternate exciting currents with opposite directions to each other flow through the current lines adjacent to each other, respectively.  
         [0200]     The thin-film chips  295  to  299  are aligned on a central axis of a pair of current lines positioned at the center in the X direction on the exciting coil  292 . These thin-film chips  295  to  299  are bonded on the opposite surface to the subject in the exciting coil  292 .  
         [0201]     Each of the thin-film chips  295  to  299  includes a GMR element such as an SVMR element for example, a pair of lead conductors connected electrically to the GMR element, and a pair of electrode terminals connected electrically to the lead conductors, all of which are formed by thin-film technique on a chip substrate.  
         [0202]     According to the present embodiment, the entire substrate  291  has a planar form, and a part of the measurement surface  291   a  facing to the subject has a large number of, preferably much small, through holes  291   c , and is coated with a DLC layer  291   c , and is further applied with a lubricant  291   d  such as a lubricating oil. The other configurations according to the present embodiment are almost the same as those according to the alternative in  FIG. 17 .  
         [0203]     Because a part of the measurement surface  291   a  on the substrate has a large number of through holes  291   c , a DLC layer  291   e  and a lubricant layer  291   d , the sticktion hardly occurs. Accordingly, a damage probability by the sticktion is drastically reduced, and therefore, the durability and lifetime can be improved in a large extent.  
         [0204]     In the above-mentioned embodiments, the thin-film chip includes the GMR element such as the SVMR element. However, it is evident that the thin-film chip may include a TMR element instead of the GMR element, which has higher sensitivity than the GMR element.  
         [0205]     Further, it is also evident that the detection coil with high sensitivity may be used instead of the GMR element.  
         [0206]     All the foregoing embodiments are by way of example of the present invention only and not intended to be limiting, and many widely different alternations and modifications of the present invention may be constructed. Accordingly, the present invention is limited only as defined in the following claims and equivalents thereto.  
         [0207]     The eddy-current probe according to the present invention is extremely useful for a remarkably fine nondestructive testing such as an inspection of the micro-defects, the cracks, the scratches and so on in an object&#39;s surface and inside and an inspection of the micropatterns on a printed circuit board, as well as nondestructive testing of distorted surfaces of important metal machine parts of a nuclear power plant, an aircraft and so on, such as turbine blades, various pipes and airplane wings.