JP2008130187A - Magnetic recorder and magnetic recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recorder and a magnetic recording method, which can perform highly accurate synchronous recording when magnetic recording is performed to a patterned medium. <P>SOLUTION: The device is a magnetic recording device recording information magnetically for a medium, and the device is provided with a laser 160 projecting light to the medium, an optical sensor 180 for detecting a property of the medium by reflected light from the medium, and a recording head 150 recording information magnetically in the medium by a clock synchronized with a detection signal of the optical sensor. The medium is the patterned medium in which a recording region consisting of a magnetic object of a first reflectance and a non-recording region consisting of a non-magnetic object of second reflectance are arranged regularly, and the optical sensor detects a magnetic object and a non-magnetic object. Since a clock synchronized with the detection signal of the optical sensor is generated and used for magnetic recording, a recording current synchronized with the magnetic object on the patterned medium can be supplied. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a magnetic recording apparatus and a magnetic recording method. The present invention is premised on application to general magnetic storage devices using patterned media such as a hard disk drive (HDD), but can also be applied to other recording devices.

  A hard disk drive (hereinafter referred to as “HDD”) is widely used as an information recording / reproducing apparatus in a computer or the like. As an HDD recording method, a patterned medium is attracting attention as a future technology in place of a conventional continuous medium (see, for example, Patent Document 1). Patterned media is a type of medium in which minute dots of magnetic material are regularly arranged along a track at regular intervals, and one bit of information is written and recorded for each dot. High density recording is possible beyond the limit of recording density. However, recording on such a patterned medium requires a complicated recording method synchronized with the medium. That is, at the time of recording, a recording current must be generated in synchronism with the magnetic material so that the individual data is stably written in the individual magnetic material, and the control becomes complicated.

  As a technique for solving such control complexity, a method of recording while synchronizing in the servo area and maintaining the synchronization in the data area has been proposed (for example, see Patent Document 2). However, when considering the separation of the medium and the rotational fluctuation, there remains an accuracy problem. On the other hand, a method of continuously detecting the magnetic field not only from the servo area but also from the entire data is conceivable, but since a strong magnetic field is generated from the head during recording, the magnetic field synchronized with the medium must be reproduced. There is a problem with SN (Signal to Noise ratio).

JP 2004-303302 A JP 2004-199806 A

  The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to perform highly accurate synchronous recording in magnetic recording on a medium (for example, a patterned medium). It is another object of the present invention to provide a new and improved magnetic recording apparatus and magnetic recording method.

  In order to solve the above problems, according to a first aspect of the present invention, there is provided a magnetic recording apparatus for magnetically recording information on a medium. The magnetic recording apparatus (100) of the present invention includes a light irradiation means (160) for irradiating the medium with light, and an optical sensor (180) for detecting the characteristics of the medium by reflected light from the medium. And a recording head (150) for magnetically recording information on the medium with a clock synchronized with a detection signal of the optical sensor (claim 1).

  In the magnetic recording apparatus of the present invention, the medium has, for example, a pattern in which recording areas made of a magnetic material having a first reflectance and non-recording areas made of a nonmagnetic material having a second reflectance are regularly arranged. Media. In this case, the optical sensor can detect the magnetic body and the non-magnetic body (claim 2).

  According to such a configuration, the reflectance of the recording area and the non-recording area of the patterned medium is different, and on the other hand, the optical sensor (180) is provided on the head side, so that the magnetic substance arranged on the patterned medium and A non-magnetic material can be detected by light (for example, laser light). A clock synchronized with the detection signal can be generated and used for magnetic recording. In this way, a recording current synchronized with the magnetic material on the patterned medium can be supplied, and a recording method for performing highly accurate synchronous recording can be provided. However, the present invention is not necessarily limited to one using a patterned medium.

  In the above description, the reference numerals in parentheses attached to the constituent elements are merely examples of the corresponding constituent elements in the embodiments and drawings described below for easy understanding. It is not limited to. The same applies to the following.

  Although various applications are possible in the present invention, several application examples are as follows.

  The first reflectivity (reflectance of the magnetic material) may be lower than the second reflectivity (reflectance of the non-magnetic material). Conversely, the first reflectance may be higher than the second reflectance (claim 4). By changing the reflectance of the magnetic body and the reflectance of the non-magnetic body, it is possible to detect light (for example, laser light) by an optical sensor. Thus, in the present invention, it is only necessary that the reflectance of the magnetic material and the reflectance of the non-magnetic material are different, and there is no design limitation such that any reflectance must be increased.

  A plurality of the optical sensors may be provided in the track direction of the medium. By providing a plurality of optical sensors, the detection accuracy of light (for example, laser light) can be increased.

  Furthermore, the tracks forming a row of the recording area and the non-recording area may be meandered at a predetermined cycle. In particular, a further effect can be obtained by combining a plurality of optical sensors with meandering tracks with a predetermined period. That is, by providing a plurality of optical sensors in the track direction and observing the difference in the amount of light reflected and returned by the medium, the signal period and signal amplitude of the meandering track can be obtained. Therefore, this signal can be used as the rotation synchronization of the medium.

  Furthermore, it is possible to superimpose predetermined information (for example, address information and synchronization signal) on the meandering track (claim 7), and recording and reproducing the information while demodulating the information makes it possible to achieve stable synchronization. Recording is possible. Further, as will be described later, since servo information can be reduced, the corresponding area can be used as a data area, so that the data capacity can be increased.

  Although any light can be used for irradiating the medium, for example, laser light can be used (claim 8).

  In order to solve the above problems, according to a second aspect of the present invention, there is provided a magnetic recording method for magnetically recording information on a medium. The magnetic recording method of the present invention includes a light irradiation step of irradiating the medium with light, a medium characteristic detection step of detecting characteristics of the medium by reflected light from the medium, and a clock corresponding to the characteristics of the medium. And an information recording step for magnetically recording information on the medium (claim 9).

  In the magnetic recording method of the present invention, the medium has, for example, a pattern in which recording areas made of a magnetic material having a first reflectance and non-recording areas made of a nonmagnetic material having a second reflectance are regularly arranged. Medium. In this case, it is possible to detect the magnetic body and the non-magnetic body in the medium characteristic detecting step.

  According to this method, the reflectance of the recording area and the non-recording area of the patterned medium is made different, and the patterned medium is irradiated with light so that the magnetic body and the non-magnetic body aligned on the patterned medium. Can be detected by light (for example, laser light). A clock synchronized with the detection signal can be generated and used for magnetic recording. In this way, a recording current synchronized with the magnetic material on the patterned medium can be supplied, and a recording method for performing highly accurate synchronous recording can be provided. However, the present invention is not necessarily limited to one using a patterned medium.

  As described above, according to the present invention, it is possible to provide a recording method for performing highly accurate synchronous recording in magnetic recording on a medium (for example, a patterned medium). Other excellent effects of the present invention will also be described in the following description of the best mode for carrying out the invention.

  Exemplary embodiments of a magnetic recording apparatus and a magnetic recording method according to the present invention will be explained below in detail with reference to the accompanying drawings. In the present specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted. In the present embodiment, a hard disk drive (hereinafter referred to as “HDD”) will be described as an example of a magnetic recording apparatus.

(First embodiment)
First, a first embodiment of the present invention will be described.

(1) Configuration of HDD FIG. 1 is an explanatory diagram showing the internal structure of the HDD according to the present embodiment.
As shown in FIG. 1, the HDD 10 according to the present embodiment includes a spindle motor 30 installed on a base member 11, a data storage disk 20 mounted on the spindle motor 30, and data reproduction and recording. And an actuator 40 for moving the read / write head to a predetermined position on the disk 20. In general, there is a cover member corresponding to the base member 11 of FIG. 1, and the base member 11 is covered with the cover member to form one housing (housing), but the illustration and description of the cover member are omitted. To do.

  The actuator 40 includes a swing arm 44 that is rotatably coupled to a pivot 42 installed on the base member 11, and a slider 48 that is installed at one end of the swing arm 44 and has a head mounted thereon. A suspension 46 that is supported so as to be biased in the surface direction and a voice coil motor (hereinafter referred to as VCM) 50 for rotating the swing arm 44 are provided.

  The VCM 50 is controlled by a servo control system, for example, and rotates the swing arm 44 in the direction according to Fleming's left-hand rule by the interaction between the current input to the VCM coil and the magnetic field formed by the magnet. That is, when the HDD 20 is turned on and the disk 20 starts to rotate, the VCM 50 rotates the swing arm 44 to move the slider 48 on which the read / write head is mounted on the recording surface of the disk 20. On the other hand, when the HDD is turned off and the rotation of the disk 20 is stopped, the VCM 50 rotates the swing arm 44 so that the head is detached from the recording surface of the disk 20.

  The internal configuration of the HDD according to the present embodiment has been described above. Hereinafter, a characteristic configuration of the present embodiment will be described.

(2) Discrete media and patterned media (Fig. 2)
FIG. 2 is an explanatory diagram showing a discrete medium (FIG. 2A) and a patterned medium (FIG. 2B) as specific examples of the data storage disk 20 shown in FIG.

  As shown in FIG. 2A, the discrete track media is a medium in which continuous thin magnetic films uniformly in the track direction are arranged discretely. Then, a minute region magnetized in the plane or perpendicular to the surface is formed on the thin film by a magnetic head, and 0 and 1 information bits are written. In a discrete medium, recording data at the time of recording is recorded asynchronously on the medium. In the example shown in FIG. 2A, the distance between the tracks of the magnetic material is about 50.8 nm, and the track density is about 500 ktpi (tracks per inch). Further, the interval of 1 bit in the bit direction is about 12.7 nm, and the bit density is about 200 kbpi (bits per inch). Further, BAR (Bit Aspect Ratio) = about 4.0.

  In the case of a continuous medium, the recording data at the time of recording is recorded asynchronously on the medium as in the case of a discrete medium. The continuous medium is a medium in which a minute area magnetized in the plane or perpendicular to the plane by a magnetic head is formed on a uniform continuous magnetic thin film, and 0 or 1 information bits are written.

  On the other hand, as shown in FIG. 2 (b), a patterned medium (bit patterned media) is a medium in which minute dots of a magnetic material are regularly arranged along a track at regular intervals. This is a medium for writing and recording 1-bit information. In the example shown in FIG. 2B, the distance between the tracks of the magnetic material is about 50.8 nm, and the track density is about 500 ktpi (tracks per inch). Further, the interval of 1 bit in the bit direction is about 12.7 nm, and the bit density is about 200 kbpi (bits per inch). Further, BAR (Bit Aspect Ratio) = about 4.0.

  Recording on such a patterned medium requires a recording method synchronized with the medium, but the patterned medium is capable of high-density recording exceeding the recording density limit of a continuous medium. Therefore, in the present embodiment, a patterned medium will be described as a specific example of the medium.

(3) Format in HDD (FIG. 3)
FIG. 3 is an explanatory diagram showing an example of a format in the HDD.
For example, as shown in FIG. 3A, the HDD format includes servo areas 320-1 (Servo1) and 320-2 (Sarvo2), data areas 310-1 (Data1), 310-2 (Data2), ..., 310-N (DataN) and a gap (Gap) between the servo area and the data area. In the example of FIG. 3A, there are N data areas, and each data area holds, for example, 512 bytes of data. The format shown in FIG. 3A is repeatedly arranged as a unit.

  FIG. 3B is an explanatory diagram showing details of each data area (Data 1, 2,..., N) in FIG. For example, as shown in FIG. 3B, the format of the data area (Data 1, 2,..., N) includes a preamble part (Preamble) 311 for synchronization when data is read, and the beginning of the data. The data head part (Sync Mark) 312 indicating, a data part (Data) 313 having, for example, 512 bytes, a CRC 314 for error detection, and an ECC 315 for error correction are included.

  FIG. 3C is an explanatory diagram showing details of the servo areas (Servo 1 and 2) of FIG. For example, as shown in FIG. 3C, the format of the servo areas (Servo 1 and 2) includes a preamble part (Preamble) 321 for synchronizing data reading and a data head part ( Sync Mark) 322, a gray code 323 including head information and sector information, and a burst 324 including information for positioning.

  For example, in the case of recording in the sector of Data 2 (310-2) in FIG. 3 (a), the position from the position calculated as the head position to the position calculated as the end position is shown in FIG. 3 (b). Data is recorded in a format, but in a discrete medium or continuous medium, the clock used at this time is asynchronous to the medium. Therefore, the length of the data length when the rotational fluctuation or the like occurs is absorbed by the gap part (Gap). Further, at the time of reproduction, the clock is drawn in the preamble part (Preamble) 311 in FIG. 3B, and then the clock is extracted from the reproduction data and synchronous reproduction is performed.

  On the other hand, in the case of a patterned medium, a magnetic material and a nonmagnetic material appear alternately, the magnetic field must be switched only in the nonmagnetic material region, and a synchronous recording method is required. As a method for realizing this, synchronization in the servo area has been proposed. This is a method in which the clock is extracted by the preamble part 321 in FIG. 3C and the frequency is held thereafter. However, when the separation of the medium and the rotation fluctuation are taken into account, there is an accuracy problem. Remain.

The accuracy problem of the patterned medium will be described. For example, if the number of data sectors N per servo frame is 5, and the maximum allowable phase error during recording is 10%, the frequency deviation due to rotational fluctuations (maximum allowable 10% = 0.0). 1 bit) / (512 bytes≈4 × 10 ³ bits) × (data sector number 5) = 00.0005% or less. However, in a general magnetic recording apparatus, the frequency deviation is about 0.01%, and cannot cope with the actual frequency deviation. Note that in the case of extracting a clock also in the preamble part (Preamble) 311 in each data area in FIG. 3B, the number of data sectors need not be taken into account, but even in that case, rotational fluctuations, etc. The frequency shift due to the frequency must be 0.0025% or less, and still cannot cope with the frequency shift actually generated.

  A method of extracting a clock while continuously reproducing the data portion during recording of the data portion as well as the servo portion has been proposed. However, due to interference by the recording magnetic field, the SN (Signal to Noise ratio) is a problem.

  Therefore, in the present embodiment, an embodiment in which a heat assist head is applied to solve the above problem will be described.

(4) Thermally assisted magnetic recording (HAMR) head (FIGS. 4 and 5)
As with the patterned medium, as a future technology, a heat-assisted magnetic recording (HAMR) head (hereinafter referred to as a “thermal assist head”) has attracted attention. The thermal assist head is a method of recording with a magnetic field at the time of recording and detecting the magnetic field at the time of reproduction. It is basically the same as the conventional head, but the medium is heated by heat such as light (heating by near-field irradiation or electron irradiation). In this method, the holding force is lowered to make writing easier.

FIG. 4 is an explanatory view schematically showing the principle of the thermal assist head.
As shown in FIG. 4, the thermal assist head 100 includes a shield 110, a read (MR) element 120, a shield 130, a return yoke 140, and a write pole 150, which are general head configurations, and further a laser 160. It is configured to include. The laser 160 irradiates the light pole 150 and the medium 200 with laser light. Reference numeral 170 in FIG. 4 indicates a laser spot irradiated on the medium 200 from the laser 160. FIG. 5 is an explanatory diagram showing a state in which the thermal assist head 100 is viewed from the medium 200 surface.

  According to such a heat assist head 100, it is possible to reduce the holding force of the medium 200 by the heat of the laser 160 and make writing easier. Therefore, in this embodiment, the patterned medium 200 and the heat assist head 110 are combined.

(5) Patterned medium when using optical sensor (FIG. 6)
FIG. 6 is an explanatory diagram showing a recording area and a non-recording area of the patterned medium. As shown in FIG. 6, the patterned medium 200 includes a convex recording area 210 and a concave non-recording area 220. In this embodiment, as an example, the recording area 210 of the convex portion is made of a magnetic material and has a low light reflectance, and the non-recording area 220 of the concave portion is filled and flattened with a non-magnetic material and a material with high reflectance. When considering a combination with a heat-assisted recording head, it is desirable to reduce the reflectance of the recording area (magnetic part) 210 and increase the reflectance of the non-storage area 220 as described above. However, the present invention is not limited to this, and the reflectance of the recording area 210 may be increased and the reflectance of the non-recording area 220 may be decreased.

(6) Thermal assist head equipped with optical sensor (FIGS. 7 and 8)
On the other hand, an optical sensor 180 is provided on the head side as shown in FIG. FIG. 8 is an explanatory diagram illustrating a state in which the thermally assisted head 100 when the optical sensor 180 is provided on the head side is viewed from the surface of the medium 200. The optical sensor 180 is used to detect the characteristics of the medium 200 based on the reflected light from the medium 200. That is, the magnetic substance and the non-magnetic substance arranged on the patterned medium 200 are detected by the optical sensor 180, and a clock synchronized with this detection signal is generated. Information can be recorded on the medium 200 using this clock.

  Further, by optimizing the area and patterning of this non-recording area, effective thermal assistance to the medium is possible. For this reason, heat-assisted recording by continuous irradiation is possible without performing pulse modulation as proposed in, for example, Japanese Patent Application Laid-Open No. 2004-355739.

(7) Optical Sensor-Clock Generation-Magnetic Recording Control System FIG. 9 is an example of timing control of recording current when recording on a magnetic medium.
The optical signal detected by the optical sensor 180 passes through the phase comparator 310 and is adjusted with a predetermined phase offset. Further, it is sent to the recording current driver 350 as a clock via the charge pump 320, the loop filter 330 and the oscillator 340. On the other hand, the recording data is sent to the recording current driver 350 via the data formatter 360. In this way, a recording current is sent to the thermal assist head 100.

  In the example shown in FIG. 9, a PLL (Phase Locked Loop) in a general analog circuit is used. However, when a digital circuit is used, the charge pump and the loop filter are replaced with an arithmetic unit. In addition, since the recording head and the photodetector are physically separated from each other, a phase shift occurs, so that a phase offset is necessary. This offset amount needs to be optimized in advance. As a simple method for this adjustment, it is conceivable to observe and optimize the signal-to-noise ratio (Signal to Noise ratio) or the error rate while changing the offset amount.

(Effects of the first embodiment)
As described above, according to the present embodiment, the reflectance of the recording area 210 and the non-recording area 220 of the patterned medium 200 is different, and on the other hand, the optical sensor 180 is provided on the head side. The magnetic body 210 and the non-magnetic body 220 arranged on the read medium 200 can be detected by the laser 160 and the optical sensor 180. A clock synchronized with the detection signal can be generated and used for magnetic recording. In this manner, a recording current synchronized with the magnetic body 210 on the patterned medium 200 can be supplied, and a recording method for performing highly accurate synchronous recording can be provided.

(Second Embodiment)
Next, a second embodiment of the present invention will be described as an application example of the first embodiment.
In this embodiment, a track that forms a row of recording areas and non-recording areas of the medium is wobbled at a predetermined cycle, and a plurality of optical sensors are provided in the track direction of the medium, and the difference in the amount of light returning from the medium It is characterized by observing. The duplicate description of the parts substantially the same as those of the first embodiment will be omitted, and the parts characteristic of the present embodiment will be described in detail below.

  First, wobbling will be described. Wobbling is a technique for accurately reading the recording surface of a recording DVD (Digital Versatile Disk). The recording DVD has a meandering groove on the recording surface in advance. The convex part of the groove is called a land, and the concave part is called a groove. This meandering wave is called wobble (meaning “sway” or “shake”), and the drive / recorder side detects the wave period and controls the rotation of the disk. The position on the disk can be known by counting the wobbles provided at a constant period. In the case of a DVD-R disc, an accurate position is grasped by counting both prepits and grooves in a land (hill) portion.

  In this embodiment, this wobbling is applied to the HDD medium, and the signal period and signal amplitude of the meandering track can be obtained by wobbling the track that forms a row of the recording area and the non-recording area of the medium at a certain period. it can. Furthermore, predetermined information can be superimposed on the track by wobbling the track at a certain period. For example, address information and a synchronization signal can be superimposed on the track.

  Furthermore, as shown in FIG. 10, the present embodiment is characterized in that a plurality of optical sensors 191 and 192 are provided in the track direction of the medium 200, and the light amount difference returning from the medium 200 is observed. FIG. 11 is an explanatory diagram illustrating a state in which a plurality of optical sensors 191 and 192 are provided in the track direction, as viewed from the surface of the medium 200. In this way, by providing a plurality of optical sensors 191 and 192 in the track direction of the medium 200 and observing the difference in the amount of light returning from the medium 200, the wobbling of the medium 200, that is, the signal period of the meandering track, Signal amplitude can be obtained.

(Effect of 2nd Embodiment)
As described above, according to the present embodiment, the signal period and signal amplitude of the meandering track can be obtained. Therefore, this signal can be used as the rotation synchronization of the medium 200.

  Furthermore, the address information and the synchronization signal are superimposed on the meandering track, and recording and reproduction is performed while demodulating the address information, and stable synchronous recording can be performed, and servo information can be reduced from the current servo area. Since this area can be used as a data area, the data capacity can be increased.

  The preferred embodiments of the magnetic recording apparatus and the magnetic recording method according to the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious for those skilled in the art that various modifications or modifications can be conceived within the scope of the technical idea described in the claims, and these are naturally within the technical scope of the present invention. It is understood that it belongs.

  For example, in the second embodiment, the case where two optical sensors (191, 192) are provided has been described. However, the present invention is not limited to this, and three or more optical sensors may be provided.

  The present invention is applicable to a magnetic recording apparatus and a magnetic recording method. The present invention is premised on application to general magnetic storage devices using patterned media such as a hard disk drive (HDD), but can also be applied to other recording devices.

It is explanatory drawing which shows the internal structure of HDD roughly. It is explanatory drawing which shows a discrete medium and a patterned medium. It is explanatory drawing which shows the format in HDD. It is explanatory drawing which shows a heat assist magnetic recording (HAMR) head. It is explanatory drawing which shows the state which looked at the head from the medium surface. It is explanatory drawing which shows the patterned medium in the case of using an optical sensor. It is explanatory drawing which shows the head for thermal assistance carrying an optical sensor. It is explanatory drawing which shows the state which looked at the head of FIG. 7 from the medium surface. It is explanatory drawing which shows the control system of optical sensor-clock generation-magnetic recording. It is explanatory drawing which shows the head for heat assistance carrying a some optical sensor. It is explanatory drawing which shows the state which looked at the head of FIG. 10 from the medium surface.

Explanation of symbols

10 HDD
20 Disc 30 Spindle motor 40 Actuator 42 Pivot 44 Swing arm 46 Suspension 48 Slider 50 Voice coil motor (VCM)
DESCRIPTION OF SYMBOLS 100 Thermal assist head 110 Shield 120 Read element 130 Shield 140 Return yoke 150 Light pole 160 Laser 170 Heat spot 180 Optical sensor 191, 192 Optical sensor

Claims (10)

A magnetic recording apparatus for magnetically recording information on a medium,
A light irradiation means for irradiating the medium with light;
An optical sensor for detecting characteristics of the medium by reflected light from the medium;
A recording head for magnetically recording information on the medium with a clock synchronized with a detection signal of the optical sensor;
A magnetic recording apparatus comprising: The medium is a patterned medium in which recording areas made of a magnetic material having a first reflectance and non-recording areas made of a non-magnetic material having a second reflectance are regularly arranged.
The magnetic recording apparatus according to claim 1, wherein the optical sensor detects the magnetic body and the non-magnetic body.   The magnetic recording apparatus according to claim 2, wherein the first reflectance is lower than the second reflectance.   The magnetic recording apparatus according to claim 2, wherein the first reflectance is higher than the second reflectance.   The magnetic recording apparatus according to claim 2, wherein a plurality of the optical sensors are provided in a track direction of the medium.   The magnetic recording apparatus according to claim 1, wherein tracks forming a row of the recording area and the non-recording area meander in a predetermined cycle.   7. The magnetic recording apparatus according to claim 6, wherein predetermined information is superimposed on the meandering track.   The magnetic recording apparatus according to claim 1, wherein the light irradiation unit irradiates the medium with laser light. A magnetic recording method for magnetically recording information on a medium,
A light irradiation step of irradiating the medium with light;
A medium characteristic detecting step of detecting the characteristic of the medium by reflected light from the medium;
An information recording step of magnetically recording information on the medium with a clock according to the characteristics of the medium;
A magnetic recording method comprising: The medium is a patterned medium in which recording areas made of a magnetic material having a first reflectance and non-recording areas made of a non-magnetic material having a second reflectance are regularly arranged.
The magnetic recording method according to claim 9, wherein in the medium characteristic detection step, the magnetic body and the non-magnetic body are detected.

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