JP6401694B2 - Dielectric spectrometer - Google Patents

Description

  The present invention relates to a technique for measuring a component concentration using dielectric spectroscopy.

  With the aging of society, dealing with adult diseases is becoming a major issue. In the examination of blood glucose level and the like, blood collection is necessary, which is a heavy burden on the patient. Therefore, a non-invasive component concentration measuring apparatus that does not collect blood has attracted attention.

  An apparatus using dielectric spectroscopy has been proposed as a noninvasive component concentration measuring apparatus. Dielectric spectroscopy irradiates the skin with electromagnetic waves, absorbs the electromagnetic waves according to the interaction between blood components to be measured, for example, glucose molecules and water, and observes the amplitude and phase of the electromagnetic waves. However, the interaction between glucose and electromagnetic waves is small, and there is a limit to the intensity of electromagnetic waves that can be safely irradiated to a living body.

  As a conventional measurement method, there is a dielectric spectroscopy system using photoelectric conversion in the THz band (see Patent Document 1). The system described in Patent Document 1 is a homodyne detection electromagnetic spectrum measurement system using a continuously oscillating light source, and generates a terahertz wave by photoelectrically converting an optical signal in which two continuous light waves having different frequencies are combined. Irradiating the object to be measured with the generated terahertz wave, receiving the terahertz wave transmitted through the object to be measured, and inputting the reference light synthesized by modulating the phase of one of the two continuous light waves This is a configuration for homodyne mixing.

  In the THz band, it is common to measure a complex dielectric constant of a measurement object by a free space method using a pseudo optical system using a lens. The free space method is also used in the millimeter wave band as described in Non-Patent Document 1.

  As described above, the dielectric relaxation spectrum is calculated from the amplitude and phase of the signal corresponding to the observed electromagnetic wave frequency. In general, the complex dielectric constant is calculated by expressing as a linear combination of relaxation curves based on the Cole-Cole equation. In the measurement of biological components, for example, the amount of blood components such as glucose and cholesterol contained in blood and the complex dielectric constant have a correlation, and are measured as electrical signals (amplitude, phase) corresponding to the change. A calibration model is constructed by measuring the correlation between the complex dielectric constant change and the component concentration in advance, and the component concentration is calibrated from the measured change in the dielectric relaxation spectrum.

JP 2013-32933 A

Andrew P. Gregory, and Robert N. Clarke, “A Review of RF and Microwave Techniques for Dielectric Measurements on Polar Liquids”, IEEE Transactions on Dielectrics and Electrical Insulation, August 2006, Vol. 13, No. 4, pp.727- 743 Benjamin S.-Y. Ung, Christophe Fumeaux, Hungyen Lin, Bernd M. Fischer, Brian W.-H. Ng, and Derek Abbott, “Low-cost ultra-thin broadband terahertz beam-splitter”, Optics Express, February 2012 , Vol. 20, No. 5, pp.4968-4978

  However, the measurement stability of the dielectric spectroscopy system using the terahertz wave is limited by the fluctuation of the output signal of the THz wave generation unit. During long-time measurement, the signal drifted, and it was difficult to measure the change in the complex dielectric constant of the sample with a slight change in concentration. Therefore, there is a problem that a highly accurate calibration model cannot be obtained for a low concentration sample.

  The present invention has been made in view of the above, and an object of the present invention is to enable highly stable dielectric spectroscopy over a long period of time and to perform highly accurate measurement even for a low-concentration sample.

  The dielectric spectroscopic device according to the present invention includes a first photomixer that photoelectrically converts a first optical signal obtained by combining two continuous light waves having different frequencies to emit a millimeter wave or terahertz wave electromagnetic wave, and the electromagnetic wave. A half mirror for branching, a splitter for branching a second optical signal that is combined by modulating the phase of at least one of the two continuous light waves, and one of the two branched by the half mirror The second photomixer that receives the electromagnetic wave, inputs one of the second optical signals branched by the splitter and performs homodyne mixing, and is branched by the half mirror and transmits or reflects the object to be measured. A third photomixer that receives the other electromagnetic wave and inputs the other second optical signal branched by the splitter and performs homodyne mixing. And butterflies.

  According to the present invention, highly stable dielectric spectroscopy can be performed over a long period of time, and highly accurate measurement can be performed even for a low-concentration sample.

It is a figure which shows the structure of the dielectric spectroscopy system in this Embodiment. It is a figure which shows the structure of another dielectric spectroscopy system in this Embodiment. FIG. 3A is a graph comparing measurement results of the dielectric spectroscopy system according to the present embodiment and a conventional dielectric spectroscopy system, FIG. 3A is a graph showing variation in amplitude, and FIG. 3B is a graph showing variation in phase. It is a graph. It is a graph which shows the measurement result of the dielectric loss of the glucose solution of different density | concentration.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of a dielectric spectroscopy system in the present embodiment.

  The dielectric spectroscopic system shown in FIG. 1 includes first and second continuous wave light sources 1a and 1b, splitters 2a, 2b and 2c, couplers 3a and 3b, an optical phase modulator 4, first to third photomixers 5a and 5b, 5c and a THz band half mirror 6 are provided.

The first continuous wave light source 1a outputs a continuous light wave having a frequency ω ₁ (hereinafter referred to as “first optical signal”). The second continuous wave light source 1 b outputs a continuous light wave having a frequency ω ₂ (hereinafter referred to as “second optical signal”). Instead of using the first and second continuous wave light sources 1a and 1b, an optical comb generation source and a narrow band optical bandpass filter whose passbands are ω ₁ and ω ₂ may be used.

  The splitter 2a demultiplexes the first optical signal into two. The splitter 2b demultiplexes the second optical signal into two.

Coupler 3a, the second an optical signal multiplexes in while in one of the first optical signal and the splitter 2b demultiplexed by the splitter 2a demultiplexed, frequency omega ₁ - [omega] ₂ of the beat signal (hereinafter, ""THz optical signal") is output. The coupler 3b combines the other first optical signal demultiplexed by the splitter 2a and the other second optical signal demultiplexed by the splitter 2b and phase-modulated by the optical phase modulator 4, and thereby the optical signal. (Hereinafter referred to as “THz optical excitation signal”).

  The splitter 2c demultiplexes the THz optical excitation signal output from the coupler 3b.

  The optical phase modulator 4 is disposed between the splitter 2b and the coupler 3b, and receives a sawtooth control signal to modulate the phase of the second optical signal. The optical phase modulator 4 is a phase modulator using an electro-optic crystal that can be electrically phase-modulated by a control signal, and lithium niobate that produces a strong electro-optic effect when an electric field is applied is used. Another optical phase modulator 4 may be provided between the splitter 2a and the coupler 3b.

The first photomixer 5a functions as a THz wave emitter. The first photomixer 5a receives the THz optical signal output from the coupler 3a and radiates millimeter wave band or terahertz wave electromagnetic waves (hereinafter referred to as “terahertz wave signal”). The THz optical signal input to the first photomixer 5a is photoelectrically converted and radiated as a terahertz wave signal having a frequency ω ₁ -ω ₂ into free space through an integrated antenna. As the first photomixer 5a, for example, a single-running carrier photodiode (UTC-PD) can be used.

  The half mirror 6 branches the terahertz wave signal radiated from the first photomixer 5a into two branches. The terahertz wave signal radiated from the first photomixer 5 a becomes parallel light by the collimating lens 8 and is branched into two by the half mirror 6. As the half mirror 6, as shown in Non-Patent Document 2, a structure in which a metal thin film, for example, gold or aluminum, or a flake of them is laminated on plastic can be used.

  The terahertz wave signal reflected by the half mirror 6 is collected by the condenser lens 8 and detected by the second photomixer 5b. The terahertz wave signal transmitted through the half mirror 6 is collected by another condenser lens 8 and transmitted or reflected by the measurement sample 100, and then detected by the third photomixer 5c.

  The second and third photomixers 5b and 5c function as THz wave detectors. The second and third photomixers 5b and 5c receive the terahertz wave signal, receive the THz optical excitation signal, homodyne mix the THz optical excitation signal and the terahertz wave signal, and output an electrical signal. As the second and third photomixers 5b and 5c, for example, a photo conductive antenna (PCA: Photo-Conductive Antenna) can be used. The output signals of the second and third photomixers 5b and 5c are synchronously detected by a lock-in amplifier to obtain the amplitude and phase. In the present embodiment, as will be described later, the amplitude ratio between the reference sample and the measurement sample 100 is obtained using the ratio of the currents detected by the second and third photomixers 5b and 5c, and the phase difference is the second difference. , Using the difference in phase detected by the third photomixers 5b and 5c. The complex dielectric constant is derived from the obtained amplitude ratio and phase difference. Although not shown, a computer that derives the complex permittivity by inputting the amplitude, phase, current value, and the like detected by each of the second and third photomixers 5b and 5c may be provided.

  Next, a method for calculating the amplitude ratio ΔA and the phase difference ΔΦ between the output signals of the reference sample and the measurement sample 100 using the output signals of the second and third photomixers 5b and 5c will be described.

When the pulse width and carrier lifetime of the THz optical excitation signal applied to the photoconductive antenna are sufficiently short compared to the pulse width of the THz electric field, the output current is the electric field intensity of the received terahertz wave signal and the THz optical excitation signal used for carrier excitation. It is proportional to the product of intensity. Here, the electric field intensity of the terahertz wave signal is E _THz , the _THz optical excitation signal intensity output from the coupler 3b is P _ex , and the terahertz waves are demultiplexed by the half mirror 6 and input to the second and third photomixers 5b and 5c. the intensity ratio of the signal _{r t: 1-r} t, the second demultiplexed by splitter 2c, third photo mixer 5b, the intensity ratio of the THz excitation signal input to 5c _r o: a _{1-r o.} If the measurement sample 100 is not installed at time t0 and measurement is performed using air as a reference, the currents I _PCA2 and I _PCA3 detected by the second and third photomixers 5b and 5c are expressed by the following equations ( 1) and (2).

_{I PCA2 (f, t0) αr} t r o E THz P ex ··· (1)
I _PCA3 (f, t0) ∝ (1-r _t ) (1-r _o ) E _THz P _ex (2)

  Similarly, when the measurement is performed with the measurement sample 100 having the absorbance A set at time t1, the terahertz wave signal input to the third photomixer 5c is attenuated to become the following expression (3). .

I _PCA3 (f, t1) ∝ (1-r _t ) (1-r _o ) AE _THz P _ex (3)

  At this time, when the ratio of the current values of the expressions (2) and (3) is taken, the following expression (4) is obtained, and the absorbance A by the measurement sample 100 can be calculated.

ΔA = I _PCA3 (f, t1) / I _PCA3 (f, t0) = A (4)

  Here, it is assumed that the proportionality coefficients in the equations (1) and (2) do not change with time or sample exchange.

  However, if drifts of ΔE (t1) and ΔP (t1) times occur in the terahertz wave signal and the THz optical excitation signal between times t0 and t1, equations (3) and (4) are expressed by the following equation (5): , (6).

I _PCA3 (f, t1) ∝ (1-r _t ) (1-r _o ) AΔE (t1) E _THz ΔP (t1) P _ex (5)
ΔA = I _PCA3 (f, t1) / I _PCA3 (f, t0) = AΔE (t1) ΔP (t1) (6)

At this time, the amplitude ratio ΔA includes a fluctuation component of intensity. When the signal change due to the absorbance A and the signal fluctuation due to drift are approximately the same, it is difficult to accurately measure the sample. Therefore, in this embodiment, using the output monitor value of the second photo-mixer 5b, the amplitude _A ref at the reference and sample 100 transmission, _{A s} the following equation (7) to (9).

A _ref = I _PCA3 (f, t0) / I _PCA2 (f, t0) = α (7)
A _s = I _PCA3 (f, t1) / I _PCA2 (f, t1) = αA (8)
α = (1-r _t ) (1-r _o ) / r _t r _o (9)

  The amplitude ratio ΔA ′ is defined as the following expression (10).

ΔA ′ = A _s / A _ref = αA / α = A (10)

Since the terahertz wave signal and the THz optical excitation signal at the same time are input to the second and third photomixers 5b and 5c, in consideration of signal drift, drift to both I _PCA2 and I _PCA3 in Expression (8). The components ΔE (t1) and ΔP (t1) are substituted to cancel the fluctuation component. As a result, only the absorption by the measurement sample 100 can be accurately measured.

  Similarly, with respect to the phase, the phase Φref, Φs and the phase difference ΔΦ ′ when transmitted through the reference and measurement sample 100 are set to the following expressions (11) to (13), thereby enabling measurement with suppressed phase drift.

_{Φ ref = Φ PCA3 (f,} t0) -Φ PCA2 (f, t0) ··· (11)
_{Φ s = Φ PCA3 (f,} t1) -Φ PCA2 (f, t1) ··· (12)
ΔΦ ′ = Φ _s −Φ _ref (13)

Here, Φ _PCA2 and Φ _PCA3 are phases detected by the second and third photomixers 5b and 5c.

  Next, another dielectric spectroscopy system in this embodiment will be described.

  FIG. 2 is a diagram showing the configuration of another dielectric spectroscopy system in the present embodiment.

  The dielectric spectroscopy system shown in FIG. 2 has a configuration in which optical power monitors 7b and 7c are installed between the splitter 2c and the second and third photomixers 5b and 5c of the dielectric spectroscopy system shown in FIG. By correcting the intensity ratio of the THz optical excitation signals input to the second and third photomixers 5b and 5c by the optical power monitors 7b and 7c, the variation in drift of the THz optical excitation signals after being branched by the splitter 2c is suppressed. In addition, the measurement accuracy can be further improved. The input / output characteristics of the second and third photomixers 5b and 5c with respect to the input of the terahertz wave signal may be recorded in advance as a reference table and used as correction terms in the above equations (10) and (13).

  1 and 2, by making the optical path length of the terahertz wave signal between the first photomixer 5a and the second and third photomixers 5b and 5c the same, a beat signal is obtained. Since the noise component contained in is canceled out as the intensity ratio or phase difference, a more stable signal can be obtained.

  Next, the stability of the dielectric spectroscopy system in the present embodiment and the conventional dielectric spectroscopy system will be compared.

  FIG. 3 is a graph showing a result of measuring amplitude and phase fluctuations by performing continuous operation for 1 hour with the frequency of the terahertz wave signal as 300 GHz using the dielectric spectroscopy system of FIG. FIG. 3A shows amplitude fluctuations, and FIG. 3B shows phase fluctuations. The measurement result using the correction by the second photomixer 5b indicated by the solid line in FIG. 3 is longer than the measurement result using only the output of the third photomixer 5c indicated by the broken line because fluctuations in both amplitude and phase are reduced. It can be seen that the time stability is improved. Accordingly, it can be said that the use of the dielectric spectroscopy system according to the present embodiment can suppress the influence of time fluctuation caused by sample exchange or the like.

  As shown in the measurement results of dielectric loss of aqueous glucose solutions with different concentrations shown in FIG. 4, the complex permittivity measurement in the terahertz band is performed by sweeping the frequency of the second continuous wave light source 1b of the present dielectric spectroscopy system, and the multivariate analysis is performed. Create a calibration model of the target sample.

  According to the present embodiment, the first photomixer 5a that photoelectrically converts a THz optical signal obtained by combining two continuous light waves having different frequencies to emit a terahertz wave signal, and the terahertz wave signal are branched into two. The half mirror 6, the splitter 2 c that splits the THz optical pumping signal that has been combined by modulating the phase of one of the continuous light waves, and the terahertz wave signal that has been split by the half mirror 6 are received, and the THz optical pump is received. A second photomixer 5b that inputs a signal and performs homodyne mixing, and a third photo that receives the other terahertz wave signal that has been branched by the half mirror 6 and transmitted through the measurement sample 100, and that receives the THz optical excitation signal and performs homodyne mixing. A mixer 5c is provided to measure the reference sample from the amplitude, phase and current values detected by the second and third photomixers 5b and 5c. By calculating the amplitude ratio and phase difference of the output signal of the sample 100 and deriving the complex dielectric constant, even when the terahertz wave signal or THz optical excitation signal radiated by the first photomixer 5a changes during long-time measurement, Highly stable dielectric spectroscopy is possible, the measurement sample 100 having a small difference in dielectric constant can be measured with high accuracy, and a highly accurate calibration model can be created.

DESCRIPTION OF SYMBOLS 1a, 1b ... Continuous wave light source 2a, 2b, 2c ... Splitter 3a, 3b ... Coupler 4 ... Optical phase modulator 5a, 5b, 5c ... Photomixer 6 ... Half mirror 7b, 7c ... Optical power monitor 8 ... Lens 100 ... Measurement sample

Claims (2)

A first photomixer that photoelectrically converts a first optical signal obtained by combining two continuous light waves having different frequencies to emit electromagnetic waves of millimeter waves or terahertz waves;
A half mirror for branching the electromagnetic wave;
A splitter for branching a second optical signal that is combined by modulating the phase of at least one of the two continuous light waves;
A second photomixer that receives one of the electromagnetic waves branched by the half mirror and inputs the second optical signal branched by the splitter and performs homodyne mixing;
A third photomixer that receives the other electromagnetic wave that has been branched by the half mirror and transmitted or reflected by the object to be measured, and that receives the other second optical signal branched by the splitter and performs homodyne mixing When,
A dielectric spectroscopic apparatus comprising:   The optical path length between the first photomixer and the second photomixer and the optical path length between the first photomixer and the third photomixer are the same. Item 2. The dielectric spectroscopy apparatus according to Item 1.

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