CN103954922B - The devices and methods therefor of linear frequency modulation double light beam laser heterodyne measurement magnetostriction coefficient - Google Patents

Abstract

The devices and methods therefor of linear frequency modulation double light beam laser heterodyne measurement magnetostriction coefficient, belongs to magnetostriction coefficient fields of measurement.The problem the highest in order to solve the certainty of measurement of the measuring method of current magnetostriction coefficient.It includes chirped laser device, the first plane mirror, thin glass plate, the second plane mirror, collecting lens, photodetector, signal processing system, excitation coil, fixing device and power circuit；Utilize power circuit that the sample being arranged in excitation coil is added electric current, photodetector is made to start to receive beam signal, the photoelectric current of signal processing system continuous acquisition photodetector output, and the difference frequency signal collected is processed, the current distance between thin glass plate and the second plane mirror is obtained according to the relation between frequency and distance, formula further according to magnetostriction coefficient, it is thus achieved that the magnetostriction coefficient of testing sample.The present invention is used for measuring magnetostriction coefficient.

Description

The devices and methods therefor of linear frequency modulation double light beam laser heterodyne measurement magnetostriction coefficient

Technical field

The invention belongs to magnetostriction coefficient fields of measurement.

Background technology

Can align under the magnetic domain outside magnetic field effect of ferromagnetics, thus cause the change of spacing of lattice in medium, cause The phenomenon making the change of ferromagnet generation length is referred to as magnetostrictive effect.Due to this phenomenon first by joule in 1842 Find, thus also referred to as Joule effect.Magnetostriction not only magnetic on material has important impact (particularly to initial magnetic Conductance, coercivity etc.), and the application that effect itself is in practice is the most extensive, such as: magnetostrictive technology may be used for machinery In vibration and ultrasonic transducer, there is important application at aspects such as laser radars.

Utilize material change of length under action of alternating magnetic field, can be made into supersonic generator and receptor: by one A little particularly conversion equipments, can make sensor and delay line, the wave filter etc. such as power, speed, acceleration.At identical outer magnetic Under conditions of Chang, the change of different magnetisable materials magnetostrictive length is different, generally with magnetostriction coefficient α (α=Δ L/l) size of its deformation is characterized.Therefore, the magnetostriction coefficient α accurately measuring material is very important.Owing to mangneto is stretched The length of material that contracting effect causes changes the most small relatively, and the magnetostriction coefficient of general ferromagnetic material only has 10^-5～10^-6Number Magnitude, therefore needs to use some high-precision methods to be measured.

The mensuration of magnetostriction coefficient is attributed to the measurement that micro-length (displacement) changes.Measure magnetostriction coefficient at present Method mainly has nonequilibrium bridge measurement method, differential power transformation to hold survey method, optical lever, straingauge measurement method and Through Optical Interference Spectra Deng.But all there is respective shortcoming and defect in these methods, therefore certainty of measurement is the highest.

Summary of the invention

The invention aims to solve the problem that the certainty of measurement of the measuring method of current magnetostriction coefficient is the highest, The present invention provides the devices and methods therefor of a kind of linear frequency modulation double light beam laser heterodyne measurement magnetostriction coefficient.

The device of the linear frequency modulation double light beam laser heterodyne measurement magnetostriction coefficient of the present invention,

Described device includes chirped laser device, the first plane mirror, thin glass plate, the second plane mirror, meeting Poly-lens, photodetector, signal processing system, excitation coil, fixing device and power circuit；

Sample is arranged in excitation coil, and described sample is by fixing device and the second plane mirror One fixing connection in face, described fixing device is nonmagnetic substance fixing device, and described power circuit provides energy for magnet exciting coil Commutation, the working power of regulation size of current；

The laser light incident that chirped laser device sends, to the first plane mirror, reflexes to thin through the first plane mirror Glass plate, and it is divided into a reflection light and refraction light through thin glass plate；Described refracted light incident is to the one of the second plane mirror Individual face, light and the light of a reflection after a face reflection of described second plane mirror are all incident to collecting lens, warp Collecting lens 5 converges to the optical signal receiving terminal of photodetector, at the photo-signal outfan of photodetector and signal The photo-signal input of reason system connects；

Described thin glass plate and the second plane mirror are parallel and contour.

The measuring method of the device of described linear frequency modulation double light beam laser heterodyne measurement magnetostriction coefficient, it include as Lower step:

Step one: the initial distance d between thin glass plate and the second plane mirror is set, sample is arranged on sharp Encourage in coil, make the electric current of power circuit increase, sample is carried out AC demagnetization, and makes the electric current of excitation coil to send out Magnetisation is saturated；

Step 2: signal processing system obtains the variation delta l value of sample the most in the same time, described Δ l is equal to thin Distance variation delta d between glass plate and the second plane mirror, is weighted the Δ l value the most in the same time obtained averagely Try to achieve the mean change amount of sampleTry to achieve sample magnetostriction coefficientDescribed l is equal to sample Initial length；

The method of the Δ l value of signal processing system acquisition current time:

After the photoelectric current exporting photodetector processes, it is thus achieved that the electric current of intermediate frequency I of heterodyne signal_IFFor:

$I_{\mathrm{IF}}=\frac{\mathrm{\ηe}}{\mathrm{hv}}\frac{\mathrm{\π}}{Z}{E}_0^2{\mathrm{\α}}_1{\mathrm{\α}}_2\cos (\frac{4\mathrm{knd}\cos \mathrm{\θ}}{c}t-\frac{4\mathrm{knd}\cos \mathrm{\θ}(L+\mathrm{nd}\cos \mathrm{\θ})}{c^2})$

Wherein,For the rate of change of the modulating bandwidth of chirped laser device, T is the tune of chirped laser device 1 Frequently the cycle, Δ F is the modulating bandwidth of chirped laser device, E₀The incident field of the laser sent for chirped laser device shakes Width, t is the time that chirped laser device sends laser, and the laser that chirped laser device sends arrives thin glass plate front surface Light path be L；

α₁=r, r are the reflectance of thin glass plate, α₂=β²R ', β are the absorbance of thin glass plate, and r ' is that the second plane is anti- Penetrating the reflectance of mirror, θ is the refracting light incident angle of thin glass plate, and n is the refractive index of thin glass plate, and c is the light velocity, and e is electronics electricity Amount, Z is the intrinsic impedance of photodetector surfaces medium, and η is quantum efficiency, and D is the area of photodetector photosurface, and h is Planck's constant, v is laser frequency；

Electric current of intermediate frequency I according to described heterodyne signal_IFObtain frequency f of heterodyne signal_IF；

Frequency f according to described heterodyne signal_IF, utilize d '=f_IF/ K, tries to achieve now thin glass plate and the second plane reflection Distance d ' between mirror；Wherein proportionality coefficient

The d ' that recycling obtains, seeks Δ d=d '-d, i.e. obtains Δ l.

The beneficial effects of the present invention is, by linear frequency modulation technology, the present invention will treat that measurement information is successfully modulated at intermediate frequency In the difference on the frequency of heterodyne signal.During the magnetostriction coefficient of simulation sample, the present invention obtains at frequency domain simultaneously Comprise the frequency values of the information of metal length variable quantity, after signal demodulation, obtain length variable quantity, flat by repetitive measurement weighting All can obtain the accurate sample length variable quantity with electric current.Test as a example by iron-nickel alloy, magnetostriction coefficient mould The relative error intending result is less than 0.1%, significantly improves certainty of measurement.

Compared with existing measuring method, the present invention measures magnetostriction coefficient and has high room and time resolution, survey Speed is fast, the linearity good, capacity of resisting disturbance is strong, dynamic response is fast for amount, reproducible and measure the advantages such as scope is big；Experimental provision Simple in construction, power consumption are little, easy to operate；Experimental result error is little, the high many-sided advantage of precision.Simultaneously as the present invention is real Testing phenomenon obvious, experimental data is reliable, it is possible at ultra precise measurement, detection, process equipment, coherent laser windfinding radar etc. It is widely used in engineering design field.

Accompanying drawing explanation

Fig. 1 is the device of the linear frequency modulation double light beam laser heterodyne measurement magnetostriction coefficient described in detailed description of the invention one Principle schematic.

Fig. 2 is the device of the linear frequency modulation double light beam laser heterodyne measurement magnetostriction coefficient described in detailed description of the invention three Principle schematic.

Fig. 3 is double light beam laser principle of interference schematic diagram.

Fig. 4 is the Fourier transformation frequency spectrum of the linear frequency modulation double light beam laser heterodyne signal obtained through signal processing system Figure.

Detailed description of the invention

Detailed description of the invention one: combine Fig. 1 and present embodiment is described, the linear frequency modulation dual-beam described in present embodiment swashs The device of optical heterodyne magnetostriction coefficient, described device includes chirped laser device the 1, first plane mirror 2, thin glass Glass plate the 3, second plane mirror 4, collecting lens 5, photodetector 6, signal processing system, excitation coil 11, fixing device And power circuit；

Sample is arranged in excitation coil 11, and described sample is by fixing device and the second plane mirror One face of 4 is fixing to be connected, and described fixing device is nonmagnetic substance fixing device, and described power circuit provides for magnet exciting coil Can commutation, the working power of regulation size of current；

The laser light incident that chirped laser device 1 sends, to the first plane mirror 2, reflects through the first plane mirror 2 To thin glass plate 3, and it is divided into a reflection light and refraction light through thin glass plate 3；Described refracted light incident is to the second plane reflection One face of mirror 4, light and the light of a reflection after a face reflection of described second plane mirror 4 are all incident to assemble Lens 5, concentrated lens 5 converge to the optical signal receiving terminal of photodetector 6, the photo-signal output of photodetector 6 End is connected with the photo-signal input of signal processing system；

Described thin glass plate 3 is parallel and contour with the second plane mirror 4.

Detailed description of the invention two: present embodiment be to the linear frequency modulation double light beam laser described in detailed description of the invention one outside The further restriction of the device of difference measurements magnetostriction coefficient, signal processing system include low pass filter 7, preamplifier 8, A/D converter 9 and DSP10；

The photoelectric current outfan of photodetector 6 is connected with the photoelectric current input of low pass filter 7, low pass filter 7 Filtering signal outfan be connected with the filtering signal input of preamplifier 8, the amplification signal output part of preamplifier 8 It is connected with the amplification signal input part of A/D converter 9, the digital signal output end of A/D converter 9 and the digital signal of DSP10 Input connects.

Detailed description of the invention three: combine Fig. 2 and illustrate that present embodiment, present embodiment are to detailed description of the invention one or two The further restriction of the device of described linear frequency modulation double light beam laser heterodyne measurement magnetostriction coefficient,

Power circuit includes ammeter mA, power supply V, single-way switch S₁, reversing switch S₂, the first swept resistance R₁With second Swept resistance R₂；

Reversing switch S₂A movable contact be connected with one end of excitation coil 11, reversing switch S₂Another movable contact It is connected with the other end of excitation coil 11；

The negative pole of described ammeter mA is connected with the positive pole of power supply V, the negative pole of power supply V and single-way switch S₁Moved end even Connect, single-way switch S₁Quiet end simultaneously with the second swept resistance R₂A fixing end and adjustable end connect, the second swept resistance R₂ Another fixing end and first swept resistance R₁A fixing end connect, the first swept resistance R₁Adjustable end and another With reversing switch S while of fixing end₂Stationary contact connect, the positive pole of ammeter mA and reversing switch S₂Another stationary contact Point connects.

In present embodiment, iron-nickel alloy sample is carried out AC demagnetization, slide-wire rheostat is placed on maximum position, connect The power supply of logical magnetizing coil, slowly regulates slide-wire rheostat, makes electric current monotone increasing, it is desirable to the electric current being added in magnetizing coil will not There is magnetic saturation.Meanwhile, opening chirped laser device 1, making line polarized light be reflected, mirror is oblique is mapped on thin glass plate 3, warp The light of thin glass plate 3 transmission is understood after being reflected by the second plane mirror 4 together with the light through thin glass plate 3 front surface reflection Poly-lens 5 converge on the photosurface of photodetector 6, after the signal of telecommunication after photodetector 6 opto-electronic conversion through filtering Parameter information the most to be measured is obtained after ripple device, amplifier, A/D converter and DSP.

Detailed description of the invention four: present embodiment be to the linear frequency modulation double light beam laser described in detailed description of the invention three outside The further restriction of the device of difference measurements magnetostriction coefficient,

It also includes that fixing device, described fixing device include first hold-down bars the 13, second hold-down bars 12 and fixed component 14；

Fixed component 14 is connected by the first hold-down bars 13 is fixing with one end of sample, and the other end of sample leads to The face of the second hold-down bars 12 and described second plane mirror 4 crossed is fixing to be connected.

When measuring, the both ends of the surface of sample are stained with securely with binding agent respectively nonmagnetic substance makes is fixing Rod, is fixed on the first hold-down bars 13 in fixed component after its slotting people's magnetizing coil, is pasted by the second plane mirror 4 On two hold-down bars 12, and ensure that posting the second plane mirror can move freely.

Detailed description of the invention five: the linear frequency modulation double light beam laser heterodyne measurement magnetostriction described in detailed description of the invention one The measuring method of the device of coefficient, it comprises the steps:

Step one: the initial distance d between thin glass plate 3 and the second plane mirror 4 is set, sample is arranged on In excitation coil 11, make the electric current of power circuit increase, sample is carried out AC demagnetization, and makes the electric current of excitation coil 11 Magnetic saturation will not occur；

Step 2: signal processing system obtains the variation delta l value of sample the most in the same time, described Δ l is equal to thin Distance variation delta d between glass plate 3 and the second plane mirror 4, is weighted putting down by the Δ l value the most in the same time obtained All try to achieve the mean change amount of sampleTry to achieve sample magnetostriction coefficientDescribed l is equal to detected sample The initial length of product；

The method of the Δ l value of signal processing system acquisition current time:

After the photoelectric current exporting photodetector processes, it is thus achieved that the electric current of intermediate frequency I of heterodyne signal_IFFor:

$I_{\mathrm{IF}}=\frac{\mathrm{\ηe}}{\mathrm{hv}}\frac{\mathrm{\π}}{Z}{E}_0^2{\mathrm{\α}}_1{\mathrm{\α}}_2\cos (\frac{4\mathrm{knd}\cos \mathrm{\θ}}{c}t-\frac{4\mathrm{knd}\cos \mathrm{\θ}(L+\mathrm{nd}\cos \mathrm{\θ})}{c^2})$

Wherein,For the rate of change of the modulating bandwidth of chirped laser device 1, T is chirped laser device 1 In the frequency modulation cycle, Δ F is the modulating bandwidth of chirped laser device 1, E₀Incident illumination for the laser that chirped laser device 1 sends Field amplitude, t is the time that chirped laser device 1 sends laser, and the laser that chirped laser device 1 sends arrives thin glass plate The light path of 3 front surfaces is L；

α₁=r, r are the reflectance of thin glass plate 3, α₂=β²R ', β are the absorbance of thin glass plate 3, and r ' is the second plane The reflectance of reflecting mirror 4, θ is the refracting light incident angle of thin glass plate 3, and n is the refractive index of thin glass plate 3, and c is the light velocity, and e is electricity Sub-electricity, Z is the intrinsic impedance of photodetector 6 surface dielectric, and η is quantum efficiency, and D is the face of photodetector 6 photosurface Long-pending, h is Planck's constant, and v is laser frequency；

Electric current of intermediate frequency I according to described heterodyne signal_IFObtain frequency f of heterodyne signal_IF；

Frequency f according to described heterodyne signal_IF, utilize d '=f_IF/ K, tries to achieve now thin glass plate 3 anti-with the second plane Penetrate the distance d ' between mirror 4；Wherein proportionality coefficient

The d ' that recycling obtains, seeks Δ d=d '-d, i.e. obtains Δ l.

In present embodiment, from $I_{\mathrm{IF}}=\frac{\mathrm{\ηe}}{\mathrm{hv}}\frac{\mathrm{\π}}{Z}{E}_0^2{\mathrm{\α}}_1{\mathrm{\α}}_2\cos (\frac{4\mathrm{knd}\cos \mathrm{\θ}}{c}t-\frac{4\mathrm{knd}\cos \mathrm{\θ}(L+\mathrm{nd}\cos \mathrm{\θ})}{c^2})$ Permissible It is seen that there is in the intermediate frequency item difference on the frequency that linear frequency modulation dual-beam heterodyne measurement method obtains and has thin glass plate 3 and the second plane mirror The information of distance d between 4.Intermediate frequency item intermediate frequency rate variance for above-mentioned formula is analyzed, because using Fourier transformation very Easily realize frequency measurement.At this point it is possible to the frequency of heterodyne signal is designated as:

$f_{\mathrm{IF}}=\frac{2\mathrm{knd}\cos \mathrm{\θ}}{\mathrm{\πc}}=\mathrm{Kd}$

Understanding, distance d between the frequency of heterodyne signal to thin glass plate 3 and the second plane mirror 4 is directly proportional, ratio Coefficient is:

$K=\frac{2\mathrm{kn}\cos \mathrm{\θ}}{\mathrm{\πc}}---\left(9\right)$

With refraction angle θ, refractive index n, modulating bandwidth rate of change k and light velocity c relevant.

Pass through $I_{\mathrm{IF}}=\frac{\mathrm{\ηe}}{\mathrm{hv}}\frac{\mathrm{\π}}{Z}{E}_0^2{\mathrm{\α}}_1{\mathrm{\α}}_2\cos (\frac{4\mathrm{knd}\cos \mathrm{\θ}}{c}t-\frac{4\mathrm{knd}\cos \mathrm{\θ}(L+\mathrm{nd}\cos \mathrm{\θ})}{c^2})$ It can be seen that light electrical resistivity survey Survey after the photoelectric current expression formula of device 6 output is fourier transformed on frequency spectrum it can be seen that heterodyne signal frequency crest, By measuring heterodyne signal frequency, it is possible to measure distance d between thin glass plate 3 and the second plane mirror 4, when d changes Time, it is possible to measure variation delta d of corresponding d it is known that Δ d, be known that Δ l.

Detailed description of the invention six: according to the linear frequency modulation double light beam laser heterodyne measurement mangneto described in detailed description of the invention five The further restriction of the measuring method of the device of coefficient of dilatation, it is thus achieved that the electric current of intermediate frequency I of heterodyne signal_IFMethod be:

In the case of not considering thin glass plate its thickness, arrive front surface anti-of thin glass plate 3 in the t-L/c moment Penetrating light field is:

$E_1\left(t\right)={\mathrm{\α}}_1{E}_0\exp \left\{i\right[{\mathrm{\ω}}_0(t-\frac{L}{c})+k{(t-\frac{L}{c})}^2\left]\right\}$

Wherein, ω₀Incident field angular frequency for the laser that chirped laser device 1 sends；

The light field expression formula that synchronization light is transmitted through front surface through thin glass plate 3 rear surface is:

$E_2\left(t\right)={\mathrm{\α}}_2{E}_0\exp \left\{i\right[{\mathrm{\ω}}_0(t-\frac{L+2\mathrm{nd}\cos \mathrm{\θ}}{c})+k{(t-\frac{L+2\mathrm{nd}\cos \mathrm{\θ}}{c})}^2+\frac{2{\mathrm{\ω}}_0\mathrm{nd}\cos \mathrm{\θ}}{c}\left]\right\};$

Total light field that photodetector receives is expressed as:

E (t)=E₁(t)+E₂(t)

Then the photoelectric current I of photodetector output is expressed as:

$\begin{array}{c}I=\frac{\mathrm{\ηe}}{\mathrm{hv}}\frac{1}{Z}\∫\underset{D}{\∫}\frac{1}{2}[E_1\left(t\right)+E_2\left(t\right)]{[E_1\left(t\right)+E_2\left(t\right)]}^{*}\mathrm{ds}\\ =\frac{\mathrm{\ηe}}{2\mathrm{hv}}\frac{1}{Z}\∫\underset{D}{\∫}[E_1^2\left(t\right)+E_2^2\left(t\right)+(E_1\left(t\right){E_2}^{*}\left(t\right)+{E_1}^{*}\left(t\right)E_2\left(t\right))]\mathrm{ds}\end{array};$

The difference frequency signal DC terms of above-mentioned photoelectric current I filters after low pass filter, it is thus achieved that electric current of intermediate frequency I_IFFor:

$I_{\mathrm{IF}}=\frac{\mathrm{\ηe}}{2\mathrm{hv}}\frac{1}{Z}\∫\underset{D}{\∫}\left[(E_1\left(t\right){E_2}^{*}\left(t\right)+{E_1}^{*}\left(t\right)E_2\left(t\right))\right]\mathrm{ds};$

According to E₁(t) and E₂T (), tries to achieve electric current of intermediate frequency I_IFFor:

$\begin{array}{c}{I}_{\mathrm{IF}}=\frac{\mathrm{\ηe}}{\mathrm{hv}}\frac{\mathrm{\π}}{Z}{E}_0^2{\mathrm{\α}}_1{\mathrm{\α}}_2\cos \left\{\right[{\mathrm{\ω}}_0(t-\frac{L}{c})+k{(t-\frac{L}{c})}^2]-\\ [{\mathrm{\ω}}_0(t-\frac{L+2\mathrm{nd}\cos \mathrm{\θ}}{c})+k{(t-\frac{L+2\mathrm{nd}\cos \mathrm{\θ}}{c})}^2+\frac{2{\mathrm{\ω}}_0\mathrm{nd}\cos \mathrm{\θ}}{c}\\ =\frac{\mathrm{\ηe}}{\mathrm{hv}}\frac{\mathrm{\π}}{Z}{E}_0^2{\mathrm{\α}}_1{\mathrm{\α}}_2\cos (\frac{4\mathrm{knd}\cos \mathrm{\θ}}{c}t-\frac{4\mathrm{knd}\cos \mathrm{\θ}(L+\mathrm{nd}\cos \mathrm{\θ})}{c^2})\end{array}\left]\right\}.$

As it is shown on figure 3, owing to light beam can constantly reflect and transmission between thin glass plate 3 and the second plane mirror 4, And this reflection and transmission have contribution for reflection light and the interference at infinity or on lens focal plane of the transmission light.

In present embodiment, in the case of not considering thin glass plate 3 its thickness, total light that photodetector receives Field can be expressed as:

E (t)=E₁(t)+E₂(t)；

Then the photoelectric current of photodetector output is expressed as:

$\begin{array}{c}I=\frac{\mathrm{\ηe}}{\mathrm{hv}}\frac{1}{Z}\∫\underset{D}{\∫}\frac{1}{2}[E_1\left(t\right)+E_2\left(t\right)]{[E_1\left(t\right)+E_2\left(t\right)]}^{*}\mathrm{ds}\\ =\frac{\mathrm{\ηe}}{2\mathrm{hv}}\frac{1}{Z}\∫\underset{D}{\∫}[E_1^2\left(t\right)+E_2^2\left(t\right)+(E_1\left(t\right){E_2}^{*}\left(t\right)+{E_1}^{*}\left(t\right)E_2\left(t\right))]\mathrm{ds}\end{array};$

Owing to difference frequency signal DC terms can filter after low pass filter, therefore, the most only considering exchange item, this hands over Stream item is commonly referred to electric current of intermediate frequency, and arrangement can obtain electric current of intermediate frequency and be:

$I_{\mathrm{IF}}=\frac{\mathrm{\ηe}}{2\mathrm{hv}}\frac{1}{Z}\∫\underset{D}{\∫}\left[(E_1\left(t\right){E_2}^{*}\left(t\right)+{E_1}^{*}\left(t\right)E_2\left(t\right))\right]\mathrm{ds};$

According to E₁(t) and E₂T (), tries to achieve electric current of intermediate frequency I_IFFor:

$\begin{array}{c}{I}_{\mathrm{IF}}=\frac{\mathrm{\ηe}}{\mathrm{hv}}\frac{\mathrm{\π}}{Z}{E}_0^2{\mathrm{\α}}_1{\mathrm{\α}}_2\cos \left\{\right[{\mathrm{\ω}}_0(t-\frac{L}{c})+k{(t-\frac{L}{c})}^2]-\\ [{\mathrm{\ω}}_0(t-\frac{L+2\mathrm{nd}\cos \mathrm{\θ}}{c})+k{(t-\frac{L+2\mathrm{nd}\cos \mathrm{\θ}}{c})}^2+\frac{2{\mathrm{\ω}}_0\mathrm{nd}\cos \mathrm{\θ}}{c}\\ =\frac{\mathrm{\ηe}}{\mathrm{hv}}\frac{\mathrm{\π}}{Z}{E}_0^2{\mathrm{\α}}_1{\mathrm{\α}}_2\cos (\frac{4\mathrm{knd}\cos \mathrm{\θ}}{c}t-\frac{4\mathrm{knd}\cos \mathrm{\θ}(L+\mathrm{nd}\cos \mathrm{\θ})}{c^2})\end{array}\left]\right\}.$

Utilizing the magnetostriction coefficient of the iron-nickel alloy sample of the long 200mm of Matlab software analogue measurement, checking is linear The feasibility of frequency modulation double light beam laser heterodyne measurement method.Excitation coil 11 is 200 circles/cm；Second plane is anti-under normal circumstances Penetrate the refractive index of medium between mirror 4 and thin glass plate 3 and take n=1；Chirped laser device wavelength is 1.55 μm, frequency modulation cycle T= 1ms, modulating bandwidth Δ F=5GHz.

By emulation it will be seen that the Fourier of the linear frequency modulation double light beam laser heterodyne signal obtained through signal processing becomes Change frequency spectrum as shown in Figure 4, in the case of wherein solid line is laser oblique incidence, measure iron-nickel alloy sample length variation delta l time pair Answer the Fourier transformation frequency spectrum of linear frequency modulation double light beam laser heterodyne signal；In the case of dotted line is laser normal incidence, measure ferrum nickel The Fourier transformation frequency spectrum of correspondence linear frequency modulation double light beam laser heterodyne signal during alloy sample length variation delta l.

It can be seen from figure 4 that give the theoretical curve in the case of normal incidence in Shi Yan, it is therefore an objective to: adjust linear Frequently, in double light beam laser heterodyne signal spectrogram, linear frequency modulation double light beam laser heterodyne signal frequency during oblique incidence can be obtained simultaneously The numerical value of the mid frequency of theoretical curve when the mid frequency of spectrum and normal incidence, in this way it is easy to obtain two mid frequencyes Ratio:

ζ=cos θ

In the case of obtaining mid frequency, laser refraction angle θ after thin glass plate can be calculated by ζ=cos θ formula Size, owing to the thickness of thin glass plate can be ignored, therefore incidence angle θ₀The size being approximately equal to refraction angle is:

${\mathrm{\θ}}_0\stackrel{\·}{=}\mathrm{\θ}=\arccos \mathrm{\ζ}$

Finally byThe numerical value of the K that formula is asked, final obtain thin glass plate 3 and the second plane mirror 4 it The value of spacing variation delta d, due to Δ d=Δ l, thus in the case of can calculating any incident angle according to formula α=Δ l/l The magnetostriction coefficient of iron-nickel alloy sample.

In theoretical derivation, the thickness that have ignored thin glass plate does not the most consider that heterodyne is believed by the reflection light of device rear surface Number impact, but the thickness of actually thin glass plate be exist be generally less than 1mm, for overcoming this impact, according toIt can be seen that the linear frequency modulation dual-beam heterodyne letter that the reflection light of thin glass plate rear surface produces Number frequency distribution near the zero-frequency of frequency spectrum, add wave filter and just can filter low frequency heterodyne signal in experiment light path Interference.Utilize above-mentioned linear frequency modulation double light beam laser heterodyne measurement method, eight groups of data of continuous analog, obtain different electric current feelings The simulation result of testing sample magnetostriction coefficient under condition, as shown in table 1.

In the case of the different electric current I of table 1, the actual value α of magnetostriction coefficient_ActualWith analogue value α

It should be understood that utilize the emulation experiment data of table 1, different electric current feelings can be calculated according to formula α=Δ l/l The simulation value of magnetostriction coefficient under condition, the maximum relative error finally giving simulation result is 0.1%, so can be seen that this The certainty of measurement of method is the highest.Meanwhile, analytical data is it can also be seen that in the case of current stabilization, environment brings Systematic error and error in reading be negligible in simulations, the error in emulation experiment mostlys come from fast Fourier Trueness error after conversion (FFT) and the round-off error during calculating.

Claims (5)

1. the measuring method of the device of linear frequency modulation double light beam laser heterodyne measurement magnetostriction coefficient, described device includes linearly FM laser (1), the first plane mirror (2), thin glass plate (3), the second plane mirror (4), collecting lens (5), light Electric explorer (6), signal processing system, excitation coil (11), fixing device and power circuit；

Sample is arranged in excitation coil (11), and described sample is by fixing device and the second plane mirror (4) a face is fixing to be connected, and described fixing device is nonmagnetic substance fixing device, and described power circuit is that magnet exciting coil carries Energy supply commutation, the working power of regulation size of current；

The laser light incident that chirped laser device (1) sends is to the first plane mirror (2), anti-through the first plane mirror (2) It is incident upon thin glass plate (3), and is divided into a reflection light and refraction light through thin glass plate (3)；Described refracted light incident is flat to second One face of face reflecting mirror (4), light and a reflection light after a face reflection of described second plane mirror (4) all enter Being incident upon collecting lens (5), concentrated lens (5) converge to the optical signal receiving terminal of photodetector (6), photodetector (6) Photo-signal outfan be connected with the photo-signal input of signal processing system；

Described thin glass plate (3) is parallel and contour with the second plane mirror (4)；

It is characterized in that, described measuring method comprises the steps:

Step one: the initial distance d between thin glass plate (3) and the second plane mirror (4) is set, sample is arranged on In excitation coil (11), make the electric current of power circuit increase, sample is carried out AC demagnetization, and makes excitation coil (11) Electric current will not occur magnetic saturation；

Step 2: signal processing system obtains the variation delta l value of sample the most in the same time, described Δ l is equal to thin glass Distance variation delta d between plate (3) and the second plane mirror (4), is weighted putting down by the Δ l value the most in the same time obtained All try to achieve the mean change amount of sampleTry to achieve sample magnetostriction coefficientDescribed l is equal to detected sample The initial length of product；

The method of the Δ l value of signal processing system acquisition current time:

After the photoelectric current exporting photodetector processes, it is thus achieved that the electric current of intermediate frequency I of heterodyne signal_IFFor:

$I_{IF}=\frac{\mathrm{\η}e}{hv}\frac{\mathrm{\π}}{Z}{E}_0^2{\mathrm{\α}}_1{\mathrm{\α}}_2\cos (\frac{4kndcos\mathrm{\θ}}{c}t-\frac{4kndcos\mathrm{\θ}(L+ndcos\mathrm{\θ})}{c^2})$

Wherein,For the rate of change of the modulating bandwidth of chirped laser device (1), T is the tune of chirped laser device (1) Frequently the cycle, Δ F is the modulating bandwidth of chirped laser device (1), E₀Incidence for the laser that chirped laser device (1) sends Optical field amplitude, t is the time that chirped laser device (1) sends laser, and the laser that chirped laser device (1) sends arrives thin The light path of glass plate (3) front surface is L；

α₁=r, r are the reflectance of thin glass plate (3), α₂=β²R ', β are the absorbance of thin glass plate (3), and r ' is the second plane The reflectance of reflecting mirror (4), θ is the refracting light incident angle of thin glass plate (3), and n is the refractive index of thin glass plate (3), and c is light Speed, e is electron charge, and Z is the intrinsic impedance of photodetector (6) surface dielectric, and η is quantum efficiency, and h is Planck's constant, v For laser frequency；

To described electric current of intermediate frequency I_IFDifference on the frequency be analyzed, use Fourier transformation to obtain frequency f of heterodyne signal_IFWith d's Relation:

$f_{IF}=\frac{2kndcos\mathrm{\θ}}{\mathrm{\π}c}=Kd;$

Measure frequency f of heterodyne signal_IF, utilize d '=f_IF/ K, tries to achieve now thin glass plate (3) and the second plane mirror (4) Between distance d '；Wherein proportionality coefficient

The d ' that recycling obtains, seeks Δ d=d '-d, i.e. obtains Δ l.

The measurement side of the device of linear frequency modulation double light beam laser heterodyne measurement magnetostriction coefficient the most according to claim 1 Method, it is characterised in that signal processing system includes low pass filter (7), preamplifier (8), A/D converter (9) and DSP (10)；

The photoelectric current outfan of photodetector (6) is connected with the photoelectric current input of low pass filter (7), low pass filter (7) filtering signal outfan is connected with the filtering signal input of preamplifier (8), the amplification letter of preamplifier (8) Number outfan is connected with the amplification signal input part of A/D converter (9), the digital signal output end of A/D converter (9) and DSP (10) digital signal input end connects.

The survey of the device of linear frequency modulation double light beam laser heterodyne measurement magnetostriction coefficient the most according to claim 1 and 2 Metering method, it is characterised in that power circuit include ammeter (mA), power supply (V), single-way switch (S1), reversing switch (S2), One swept resistance (R1) and the second swept resistance (R2)；

One movable contact of reversing switch (S2) is connected with one end of excitation coil (11), and another of reversing switch (S2) is dynamic tactile Point is connected with the other end of excitation coil (11)；

The negative pole of described ammeter (mA) is connected with the positive pole of power supply (V), the negative pole of power supply (V) and the moved end of single-way switch (S1) Connecting, the quiet end of single-way switch (S1) is connected with a fixing end and the adjustable end of the second swept resistance (R2) simultaneously, and second is sliding Another fixing end end fixing with of the first swept resistance (R1) of galvanic electricity resistance (R2) is connected, the first swept resistance (R1) Adjustable end and another fixing end are connected with a stationary contact of reversing switch (S2) simultaneously, the positive pole of ammeter (mA) and commutation Another stationary contact of switch (S2) connects.

The measurement side of the device of linear frequency modulation double light beam laser heterodyne measurement magnetostriction coefficient the most according to claim 3 Method, it is characterised in that described fixing device includes the first hold-down bars (13), the second hold-down bars (12) and fixed component (14)；

Fixed component (14) is connected by the first hold-down bars (13) is fixing with one end of sample, and the other end of sample leads to Another face of the second hold-down bars (12) and described second plane mirror (4) crossed is fixing to be connected.

The measurement side of the device of linear frequency modulation double light beam laser heterodyne measurement magnetostriction coefficient the most according to claim 1 Method, it is characterised in that obtain the electric current of intermediate frequency I of heterodyne signal_IFMethod be:

In the case of not considering thin glass plate its thickness, arrive the reflection of the front surface of thin glass plate (3) in the t-L/c moment Light field is:

$E_1\left(t\right)={\mathrm{\α}}_1{E}_0\exp \{i\[{\mathrm{\ω}}_0(t-\frac{L}{c})+k{(t-\frac{L}{c})}^2\]\}$

Wherein, ω₀Incident field angular frequency for the laser that chirped laser device (1) sends；

The light field expression formula that synchronization light is transmitted through front surface through thin glass plate (3) rear surface is:

$E_2\left(t\right)={\mathrm{\α}}_2{E}_0\exp \{i\[{\mathrm{\ω}}_0(t-\frac{L+2ndcos\mathrm{\θ}}{c})+k{(t-\frac{L+2ndcos\mathrm{\θ}}{c})}^2+\frac{2{\mathrm{\ω}}_{0}ndcos\mathrm{\θ}}{c}\]\};$

Total light field that photodetector receives is expressed as:

E (t)=E₁(t)+E₂(t)

Then the photoelectric current I of photodetector output is expressed as:

$\begin{array}{c}I=\frac{\mathrm{\η}e}{hv}\frac{1}{Z}\underset{D}{\∫\∫}\frac{1}{2}\[E_1\left(t\right)+E_2\left(t\right)\]{\[E_1\left(t\right)+E_2\left(t\right)\]}^{*}ds\\ =\frac{\mathrm{\η}e}{2hv}\frac{1}{Z}\underset{D}{\∫\∫}\[E_1^2\left(t\right)+E_2^2\left(t\right)+\left(E_1\right(t\left){E_2}^{*}\right(t)+{E_1}^{*}(t\left)E_2\right(t\left)\right)\]ds\end{array};$

D is the area of photodetector (6) photosurface；

The difference frequency signal DC terms of above-mentioned photoelectric current I filters after low pass filter, it is thus achieved that electric current of intermediate frequency I_IFFor:

$I_{IF}=\frac{\mathrm{\η}e}{2hv}\frac{1}{Z}\underset{D}{\∫\∫}\[\left(E_1\right(t\left){E_2}^{*}\right(t)+{E_1}^{*}(t\left)E_2\right(t\left)\right)\]ds;$

According to E₁(t) and E₂T (), tries to achieve electric current of intermediate frequency I_IFFor:

$\begin{array}{c}{I}_{IF}=\frac{\mathrm{\η}e}{hv}\frac{\mathrm{\π}}{Z}{E}_0^2{\mathrm{\α}}_1{\mathrm{\α}}_2\cos \{\[{\mathrm{\ω}}_0(t-\frac{L}{c})+k{(t-\frac{L}{c})}^2\]-\\ \[{\mathrm{\ω}}_0(t-\frac{L+2nd\cos \mathrm{\θ}}{c})+k{(t-\frac{L+2nd\cos \mathrm{\θ}}{c})}^2+\frac{2{\mathrm{\ω}}_{0}nd\cos \mathrm{\θ}}{c}\]\}\\ =\frac{\mathrm{\η}e}{hv}\frac{\mathrm{\π}}{Z}{E}_0^2{\mathrm{\α}}_1{\mathrm{\α}}_2\cos (\frac{4knd\cos \mathrm{\θ}}{c}t-\frac{4knd\cos \mathrm{\θ}(L+nd\cos \mathrm{\θ})}{c^2})\end{array}.$