A fiber optic magnetic field sensor and its signal demodulation system

Abstract

This invention discloses an optical fiber magnetic field sensor, comprising a single-mode optical fiber, a temperature-sensing grating, a hollow glass tube, and a magnetic thin film. The single-mode optical fiber has a first end face and a second end face. The temperature-sensing grating is fabricated within the single-mode optical fiber and located near its second end face. The hollow glass tube has an optical microcavity communicating with its two ends. One end of the hollow glass tube is connected to the second end face of the single-mode optical fiber, and the other end is connected to the magnetic thin film. The second end face of the single-mode optical fiber and the magnetic thin film are parallel to each other, forming an FP interferometer between the second end face of the single-mode optical fiber, the optical microcavity, and the magnetic thin film. This optical fiber magnetic field sensor can reduce the influence of ambient temperature and improve the accuracy of magnetic field measurement. This invention also discloses a signal demodulation system for the above-mentioned optical fiber magnetic field sensor.

Description

Technical Field

[0001] This utility model relates to the field of magnetic field sensing, and in particular to an optical fiber magnetic field sensor and its signal demodulation system. Background Technology

[0002] Magnetic field measurement technology plays a crucial role in many fields. In Earth science, by measuring the distribution and changes of the Earth's magnetic field, we can study the Earth's internal structure (such as core movement), geological evolution, and even explore mineral resources. In space physics, magnetic field measurement is a core means of studying the interaction between the solar wind and the Earth's magnetosphere. In industry, by measuring the leakage magnetic field on the surface of ferromagnetic materials, we can identify defects such as cracks and corrosion. In military applications, the steel hull of a submarine can cause anomalies in the Earth's magnetic field, and the submarine's tracks can be detected by shipborne or airborne magnetometers.

[0003] Chinese patent application CN201610194409.0 discloses a fiber optic cantilever beam magnetic field sensing probe based on a giant magnetostrictive thin film. The probe includes: an optical fiber, a fixed end, a fiber optic cantilever beam, a chromium metal film, and a giant magnetostrictive thin film. The fiber optic cantilever beam is located on the end face of the optical fiber, forming an integrated optical fiber. The fiber optic cantilever beam and the end face of the optical fiber are connected through the fixed end, forming a Fabry-Perot resonant cavity. The outer surface of the fiber optic cantilever beam is sequentially coated with a chromium metal film and a giant magnetostrictive thin film. This patent uses an optical fiber as the sensing probe. The fiber optic sensing probe operates under all-optical excitation, which does not interfere with the magnetic field under test, and the magnetic field under test does not generate electromagnetic interference to the fiber optic sensing probe. The fiber optic sensing probe is small in size and suitable for magnetic field detection in confined spaces.

[0004] However, the magnetization of magnetic materials will drift at different temperatures, commonly known as "temperature drift". This will result in different degrees of deformation under the same magnetic field strength, which will cause errors in the magnetic field measurement by the magnetic field sensing probe. Utility Model Content

[0005] To address the shortcomings of the existing technology, this invention provides an optical fiber magnetic field sensor that can reduce the influence of ambient temperature and improve the accuracy of magnetic field measurement.

[0006] This invention also provides a signal demodulation system for the aforementioned fiber optic magnetic field sensor.

[0007] The technical problem to be solved by this utility model is achieved through the following technical solution: An optical fiber magnetic field sensor includes a single-mode optical fiber, a temperature-sensing grating, a hollow glass tube, and a magnetic thin film. The single-mode optical fiber has a first end face and a second end face. The temperature-sensing grating is fabricated inside the single-mode optical fiber and located near its second end face. The hollow glass tube has an optical microcavity communicating with its two ends. One end of the hollow glass tube is connected to the second end face of the single-mode optical fiber, and the other end of the hollow glass tube is connected to the magnetic thin film. The second end face of the single-mode optical fiber and the magnetic thin film are parallel to each other, so that the second end face of the single-mode optical fiber, the optical microcavity, and the magnetic thin film form an FP interferometer.

[0008] Furthermore, the magnetic thin film is a terbium-dysprosium-iron alloy thin film, an iron-gallium alloy thin film, a nickel-iron oxide thin film, or a magnetite thin film.

[0009] Furthermore, the fiber optic magnetic field sensor also includes a support film, which is disposed on the surface of the magnetic film near the hollow glass tube and connected to the opening of the hollow glass tube.

[0010] Furthermore, the supporting film is a graphene film, a PDMS film, or a quartz film.

[0011] Furthermore, the fiber optic magnetic field sensor also includes a vacuum glass tube, one end of which is closed and the other end is open; the vacuum glass tube is fitted over the FP interferometer and the temperature measuring grating, and its open end is sealed to the periphery of the single-mode optical fiber.

[0012] Furthermore, the magnetic film is provided with a plurality of regularly arranged nanopores.

[0013] A signal demodulation system includes a light source device, a demodulation device, and the aforementioned fiber optic magnetic field sensor, wherein the output end of the light source device and the input end of the demodulation device are both connected to the first end face of the single-mode optical fiber.

[0014] Furthermore, the signal demodulation system also includes an optical fiber circulator, which has a first port, a second port, and a third port. The first port is connected to the output end of the light source device, the second port is connected to the first end face of the single-mode optical fiber, and the third port is connected to the input end of the demodulation device.

[0015] Furthermore, the light source device includes an excitation laser, a probe laser, a signal generator, an electro-optic modulator, a broadband laser, a first coupler, and a second coupler. The first coupler has a first input port, a second input port, and an output port. The excitation laser is connected to the first input port of the first coupler through the electro-optic modulator, and the probe laser is connected to the second input port of the first coupler. The second coupler also has a first input port, a second input port, and an output port. The output port of the first coupler is connected to the first input port of the second coupler, and the broadband laser is connected to the second input port of the second coupler. The output port of the second coupler is connected to the first end face of the single-mode optical fiber, and the signal generator is electrically connected to the electro-optic modulator.

[0016] Furthermore, the demodulation device includes a beam splitter, a first bandpass filter, a second bandpass filter, a photodetector, a spectrum analyzer, a spectrometer, and a host computer. The beam splitter has an input port, a first output port, and a second output port. The spectrum analyzer is connected to the first output port of the beam splitter sequentially through the photodetector and the first bandpass filter. The spectrometer is connected to the second output port of the beam splitter through the second bandpass filter. The input port of the beam splitter is connected to the first end face of the single-mode optical fiber. Both the spectrum analyzer and the spectrometer are electrically connected to the host computer.

[0017] The present invention has the following beneficial effects: The fiber optic magnetic field sensor of the present invention uses the FP interferometer and the temperature measuring grating to measure the ambient magnetic field and ambient temperature respectively. During demodulation, the ambient temperature measured by the temperature measuring grating can be used to calculate the magnetic drift of the magnetic thin film, and then the calculated magnetic drift can be used to compensate for the ambient magnetic field measured by the FP interferometer, thereby improving the magnetic field measurement accuracy of the FP interferometer and reducing the influence of ambient temperature on the FP interferometer. Attached Figure Description

[0018] Figure 1 The structural principle diagram of the fiber optic magnetic field sensor provided by this utility model.

[0019] Figure 2 The schematic diagram of the signal demodulation system provided by this utility model. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the accompanying drawings and embodiments, examples of which are shown in the drawings. Throughout the drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0021] In the description of this utility model, it should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.

[0022] Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first," "second," or "third" may explicitly or implicitly include one or more of that feature. In the description of this utility model, "multiple" means two or more, unless otherwise explicitly specified.

[0023] In this utility model, unless otherwise explicitly specified and limited, the terms "installation," "connection," "joining," "fixing," and "setting," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model according to the specific circumstances.

[0024] Example 1 like Figure 1 As shown, an optical fiber magnetic field sensor includes a single-mode optical fiber 31, a temperature-sensing grating 32, a hollow glass tube 33, and a magnetic thin film 35. The single-mode optical fiber 31 has a first end face and a second end face. The temperature-sensing grating 32 is fabricated inside the single-mode optical fiber 31 and located near its second end face. The hollow glass tube 33 has an optical microcavity 330 communicating with its two ends. One end of the hollow glass tube 33 is connected to the second end face of the single-mode optical fiber 31, and the other end of the hollow glass tube 33 is connected to the magnetic thin film 35. The second end face of the single-mode optical fiber 31 and the magnetic thin film 35 are parallel to each other, so that an FP interferometer is formed between the second end face of the single-mode optical fiber 31, the optical microcavity 330, and the magnetic thin film 35.

[0025] The fiber optic magnetic field sensor of this invention uses the FP interferometer and the temperature-sensing grating 32 to measure the ambient magnetic field and ambient temperature, respectively. During demodulation, the ambient temperature measured by the temperature-sensing grating 32 can be used to calculate the magnetic drift of the magnetic thin film 35. The calculated magnetic drift is then used to compensate for the ambient magnetic field measured by the FP interferometer, thereby improving the magnetic field measurement accuracy of the FP interferometer and reducing the influence of ambient temperature on the FP interferometer.

[0026] The working principle is as follows: A modulated excitation light signal, a probe light signal, and a broadband light signal are coupled together into the fiber optic magnetic field sensor. The excitation light signal and the probe light signal have different wavelengths. The frequency range of the modulated excitation light signal covers the resonant frequency of the magnetic thin film 35 within the influence range of the ambient magnetic field. The wavelength of the probe light signal is consistent with the operating wavelength of the FP interferometer. The wavelength range of the broadband light signal is near the center wavelength of the temperature-sensing grating 32. After reaching the magnetic thin film 35, the modulated excitation light signal drives the magnetic thin film 35 to generate forced vibrations. The probe light signal is typically selected from the reflectance spectrum of the FP interferometer in the range of -3... The wavelength value at dB is reflected for the first time when passing through the second end face of the single-mode fiber 31, and for the second time when reaching the magnetic thin film 35. The two reflected beams interfere with each other to form an interference light signal. The broadband light signal is reflected when passing through the temperature-sensing grating 32. When the temperature-sensing grating 32 is not affected by the ambient temperature, the reflection peak of the broadband light signal is at the initial wavelength position. When the temperature-sensing grating 32 is affected by the ambient temperature, due to thermal expansion and contraction, the center wavelength of the temperature-sensing grating 32 will change, thereby causing the reflection peak of the broadband light signal to drift. By demodulating the amount of reflection peak drift of the broadband light signal, the magnitude of the ambient temperature can be calculated. When the magnetic thin film 35 is not affected by the ambient magnetic field, it can generate different resonant responses under the drive of excitation light signals of different frequencies. At this time, by demodulating the light intensity of the interference light signal, a graph can be plotted to show the corresponding resonant response. The resonant frequency of the magnetic film 35 at its initial position can be obtained from the corresponding frequency response curve. First, the magnetic drift of the magnetic film 35 is compensated using the ambient temperature measured by the temperature-measuring grating 32 to obtain the resonant frequency after initial position compensation. When the magnetic film 35 is subjected to an ambient magnetic field, the resonant frequency of the magnetic film 35 in the frequency response curve drifts to a new position. Then, the magnetic drift of the magnetic film 35 is compensated again using the ambient temperature measured by the temperature-measuring grating 32 to obtain the resonant frequency after new position compensation. Subtracting the two resonant frequencies after initial position compensation and new position compensation yields the amount of frequency drift after compensation. Since the larger the ambient magnetic field, the greater the frequency change of the magnetic film 35, and the greater the frequency drift in the frequency response curve, the magnitude of the ambient magnetic field acting on the magnetic film 35 can be calculated based on the relationship curve or mathematical model between the frequency drift and the ambient magnetic field.

[0027] The temperature-measuring grating 32 may be, but is not limited to, a Bragg grating or a chirped grating; the magnetic thin film 35 may be, but is not limited to, a terbium-dysprosium-iron alloy thin film, an iron-gallium alloy thin film, a nickel-iron oxide thin film, or a magnetite thin film, etc.

[0028] In the preparation process, one of the aforementioned magnetic materials is first deposited on a copper substrate using vapor deposition or other deposition methods. Then, the copper substrate with the magnetic thin film 35 is placed in a ferric chloride solution with a concentration of 0.075 g / ml to allow the ferric chloride solution to completely corrode the copper substrate. Next, the waste liquid from filtering the ferric chloride solution is rinsed multiple times with deionized water, causing the magnetic thin film 35 to float in the deionized water. Then, one end of the hollow glass tube 33 is slowly brought into contact with the magnetic thin film 35 in a parallel manner to complete the transfer of the magnetic thin film 35. Finally, the magnetic thin film 35 on the hollow glass tube 33 is naturally dried, allowing the magnetic thin film 35 to adhere and fix to the hollow glass tube 33 through its own van der Waals forces.

[0029] In this embodiment, the thickness of the magnetic thin film 35 is between 150-300 nm.

[0030] For some magnetic films 35 that are difficult to attach directly to the hollow glass tube 33, or magnetic films 35 that are tough and easily damaged after attachment, preferably, the fiber optic magnetic field sensor further includes a support film 34, which is disposed on the side surface of the magnetic film 35 near the hollow glass tube 33 and connected to the opening of the hollow glass tube 33.

[0031] In this embodiment, the supporting film 34 may be, but is not limited to, a graphene film, a PDMS film, or a quartz film.

[0032] The graphene film has a thickness between 0.3-10 nm and can be attached to the opening of the hollow glass tube 33 using the wet transfer method described above. The PDMS film has a thickness between 20-100 μm, and the quartz film has a thickness between 1-10 μm. Both the PDMS film and the quartz film can be attached to the opening of the hollow glass tube 33 using adhesive bonding. After attaching the support film 34 to the opening of the hollow glass tube 33, magnetic material is then deposited directly onto the support film 34 using vapor deposition or other deposition methods.

[0033] In addition, to further reduce the influence of ambient temperature on the FP interferometer, preferably, the fiber optic magnetic field sensor also includes a vacuum glass tube 36, one end of which is a closed end and the other end is an open end; the vacuum glass tube 36 is sleeved outside the FP interferometer and the temperature measuring grating 32, and its open end is sealed to the periphery of the single-mode fiber 31 (such as by fusion splicing or by using sealant).

[0034] The vacuum glass tube 36 allows the FP interferometer to operate in a vacuum environment. This high vacuum environment effectively reduces the interference of ambient temperature's heat conduction and convection on the magnetic thin film 34, decreases the frequency of heat transfer through molecular collisions, and eliminates conditions for heat transport by macroscopic fluid flow. This makes it difficult for these two strong heat transfer paths to continuously affect the magnetic thin film 34, significantly weakening the influence of ambient temperature on its measurement. In this state, the temperature-measuring grating 32 only needs to measure the temperature change caused by ambient thermal radiation to compensate for the magnetic drift of the magnetic thin film 34.

[0035] Meanwhile, high vacuum sealing can improve the Q value (quality factor) of the magnetic thin film 34, thereby increasing the sensor sensitivity and lowering the detection limit.

[0036] Preferably, in order to eliminate the pressure difference between the hollow glass tube 33 and the vacuum glass tube 36, the magnetic thin film 35 (and the supporting thin film 34) are provided with a plurality of regularly arranged nanopores (not shown in the figure). The nanopores can be formed by micro-nano etching of the magnetic thin film 35 (and the supporting thin film 34) using a focused ion beam, but are not limited to this process.

[0037] Example 2 like Figure 2 As shown, a signal demodulation system includes a light source device 1, a demodulation device 2, and the fiber optic magnetic field sensor 3 described in Embodiment 1. The output end of the light source device 1 and the input end of the demodulation device 2 are both connected to the first end face of the single-mode fiber 31.

[0038] Preferably, the signal demodulation system further includes an optical fiber circulator 4, which has a first port, a second port and a third port. The first port is connected to the output end of the light source device 1, the second port is connected to the first end face of the single-mode optical fiber 31, and the third port is connected to the input end of the demodulation device 2.

[0039] The light source device 1 includes an excitation laser 11, a probe laser 12, a signal generator 13, an electro-optic modulator 14, a broadband laser 15, a first coupler 16, and a second coupler 17. The first coupler 16 has a first input port, a second input port, and an output port. The excitation laser 11 is connected to the first input port of the first coupler 16 through the electro-optic modulator 14, and the probe laser 12 is connected to the second input port of the first coupler 16. The second coupler 17 also has a first input port, a second input port, and an output port. The output port of the first coupler 16 is connected to the first input port of the second coupler 17, and the broadband laser 15 is connected to the second input port of the second coupler 17. The output port of the second coupler 17 is connected to the first end face of the single-mode optical fiber 31, and the signal generator 13 is electrically connected to the electro-optic modulator 14.

[0040] The demodulation device 2 includes a beam splitter 21, a first bandpass filter 22, a second bandpass filter 23, a photodetector 24, a spectrum analyzer 25, a spectrometer 26, and a host computer 27. The beam splitter 21 has an input port, a first output port, and a second output port. The spectrum analyzer 25 is connected to the first output port of the beam splitter 21 in sequence through the photodetector 24 and the first bandpass filter 22. The spectrometer 26 is connected to the second output port of the beam splitter 21 through the second bandpass filter 23. The input port of the beam splitter 21 is connected to the first end face of the single-mode optical fiber 31. Both the spectrum analyzer 25 and the spectrometer 26 are electrically connected to the host computer 27.

[0041] The electro-optic modulator 14 generates a frequency comb or sweep signal (typically, the frequency comb acts directly, which is faster than the sweep signal acting frequency by frequency) to modulate the excitation light signal emitted by the excitation laser 11 under the control of the signal generator 13; the probe light signal emitted by the probe laser 12 is mixed with the excitation light signal in the first coupler 16 to output a first mixed light; the broadband light signal emitted by the broadband laser 15 is mixed with the first mixed light in the second coupler 56 to output a second mixed light; the second mixed light enters the transmission fiber 1 of the ultra-high precision fiber optic FPI sensor through the circulator 57.

[0042] In this embodiment, both the first coupler 16 and the second coupler 17 are 90:10 couplers, that is, in the first mixed light, the excitation light signal accounts for 90% of the total light signal and the probe light signal accounts for 10% of the total light signal; in the second mixed light, the first mixed light accounts for 90% of the total light signal and the broadband light signal accounts for 10% of the total light signal.

[0043] When the excitation light signal coupled into the fiber optic magnetic field sensor 3 acts on the magnetic thin film 34 through optical force or photothermal effect, it drives the magnetic thin film 34 to generate forced vibration.

[0044] The probe light signal coupled into the fiber optic magnetic field sensor 3 is reflected for the first time when it passes through the second end face of the single-mode fiber 31, and is reflected for the second time when it reaches the magnetic thin film 34. The two reflected lights interfere with each other to form an interference light signal, which then re-enters the fiber optic circulator 4 and enters the beam splitter 21 from the reflecting end of the fiber optic circulator 4.

[0045] After the broadband optical signal coupled into the fiber optic magnetic field sensor 3 is modulated and reflected by the temperature measuring grating 32, a portion of the optical signal corresponding to the center wavelength of the temperature measuring grating 32 is reflected back and re-enters the fiber optic circulator 4. Then, it enters the beam splitter 21 from the reflecting end of the fiber optic circulator 4, while other optical signals located outside the center wavelength of the temperature measuring grating 32 continue to propagate forward.

[0046] The beam splitter 21 divides all reflected light signals into two beams. One beam passes through the first bandpass filter 22, which filters out the excitation light signal and broadband light signal. After being collected by the photodetector 24, it is output to the spectrum analyzer 25 for light intensity demodulation, thereby obtaining the frequency response curve of the FP interferometer. The other beam passes through the second bandpass filter 23, which filters out the excitation light signal and probe light signal. It is then collected by the spectrum analyzer 26, thereby obtaining the reflection spectrum of the temperature measuring grating 32.

[0047] The host computer 27 finally demodulates the reflection spectrum and frequency response curve to obtain the magnitude of the ambient magnetic field.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present utility model and not to limit them. Although the present utility model has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present utility model, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the scope of the technical solutions of the present utility model.

Claims

1. A fiber optic magnetic field sensor, characterized in that, The device includes a single-mode optical fiber, a temperature-sensing grating, a hollow glass tube, and a magnetic thin film. The single-mode optical fiber has a first end face and a second end face. The temperature-sensing grating is fabricated inside the single-mode optical fiber and located near its second end face. The hollow glass tube has an optical microcavity connected to its two ends. One end of the hollow glass tube is connected to the second end face of the single-mode optical fiber, and the other end of the hollow glass tube is connected to the magnetic thin film. The second end face of the single-mode optical fiber and the magnetic thin film are parallel to each other, so that the second end face of the single-mode optical fiber, the optical microcavity, and the magnetic thin film form an FP interferometer.

2. The fiber optic magnetic field sensor according to claim 1, characterized in that, The magnetic thin film is a terbium-dysprosium-iron alloy thin film, an iron-gallium alloy thin film, a nickel-iron oxide thin film, or a magnetite thin film.

3. The fiber optic magnetic field sensor according to claim 1 or 2, characterized in that, The fiber optic magnetic field sensor also includes a support film, which is disposed on the surface of the magnetic film near the hollow glass tube and connected to the opening of the hollow glass tube.

4. The fiber optic magnetic field sensor according to claim 3, characterized in that, The supporting film is a graphene film, a PDMS film, or a quartz film.

5. The fiber optic magnetic field sensor according to claim 1, characterized in that, The fiber optic magnetic field sensor also includes a vacuum glass tube, one end of which is closed and the other end is open. The vacuum glass tube is fitted over the FP interferometer and the temperature measuring grating, and its open end is sealed to the periphery of the single-mode optical fiber.

6. The fiber optic magnetic field sensor according to claim 5, characterized in that, The magnetic thin film has multiple nanopores arranged in a regular pattern.

7. A signal demodulation system, characterized in that, It includes a light source device, a demodulation device, and the fiber optic magnetic field sensor as described in claim 1, wherein the output end of the light source device and the input end of the demodulation device are connected together to the first end face of the single-mode fiber.

8. The signal demodulation system according to claim 7, characterized in that, The signal demodulation system further includes an optical fiber circulator, which has a first port, a second port, and a third port. The first port is connected to the output end of the light source device, the second port is connected to the first end face of the single-mode optical fiber, and the third port is connected to the input end of the demodulation device.

9. The signal demodulation system according to claim 7 or 8, characterized in that, The light source device includes an excitation laser, a probe laser, a signal generator, an electro-optic modulator, a broadband laser, a first coupler, and a second coupler. The first coupler has a first input port, a second input port, and an output port. The excitation laser is connected to the first input port of the first coupler through the electro-optic modulator, and the probe laser is connected to the second input port of the first coupler. The second coupler also has a first input port, a second input port, and an output port. The output port of the first coupler is connected to the first input port of the second coupler, and the broadband laser is connected to the second input port of the second coupler. The output port of the second coupler is connected to the first end face of the single-mode optical fiber, and the signal generator is electrically connected to the electro-optic modulator.

10. The signal demodulation system according to claim 7 or 8, characterized in that, The demodulation device includes a beam splitter, a first bandpass filter, a second bandpass filter, a photodetector, a spectrum analyzer, a spectrometer, and a host computer. The beam splitter has an input port, a first output port, and a second output port. The spectrum analyzer is connected to the first output port of the beam splitter sequentially through the photodetector and the first bandpass filter. The spectrometer is connected to the second output port of the beam splitter through the second bandpass filter. The input port of the beam splitter is connected to the first end face of the single-mode optical fiber. Both the spectrum analyzer and the spectrometer are electrically connected to the host computer.

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