Abstract

We demonstrate a method based on self-referenced THz time-domain spectroscopy for inspection of aqueous liquids, and in particular alcohol solutions, inside closed containers. We demonstrate that it is possible to determine the alcohol content of an aqueous solution, and that liquids can be classified as either harmless or inflammable. The method operates in reflection mode with the result that liquids opaque to THz radiation can be characterized with little influence of the bottle shape. The method works with plastic bottles as well as glass bottles, with absorption of THz radiation by the plastic or the glass being the limiting factor. The reflection mode allows for automatic control of the validity of the measurement. The method will be useful in liquid scanning systems at security checkpoints.

© 2008 Optical Society of America

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  1. T. Ikeda, A. Matsushita, M. Tatsuno, Y. Minami, M. Yamaguchi, K. Yamamoto, M. Tani, and M. Hangyo, "Investigation of inflammable liquids by terahertz spectroscopy," Appl. Phys. Lett. 87, 034105 (2005)
    [CrossRef]
  2. N. W. Broad, R. D. Jee, A. C. Moffat, M. J. Eaves, W. C. Mann, and W. Dziki, "Non-invasive determination of ethanol, propylene glycol and water in a multi-component pharmaceutical oral liquid by direct measurement through amber plastic bottles using Fourier transform near-infrared spectroscopy," The Analyst 125, 2054 (2000)
    [CrossRef]
  3. S. Dexheimer (ed.) Terahertz Spectroscopy: Principles and Applications (CRC Press, 2007)
    [CrossRef]
  4. P. Uhd Jepsen, U. Møller, and H. Merbold, "Investigation of aqueous alcohol and sugar solutions with reflection terahertz time-domain spectroscopy," Opt. Express 15, 14717 (2007)
    [CrossRef] [PubMed]
  5. P. Uhd Jepsen and B. M. Fischer, "Dynamic range in terahertz time-domain transmission and reflection spectroscopy," Opt. Lett. 30, 29 (2005)
    [CrossRef] [PubMed]
  6. M. Naftaly and R. E. Miles, "Terahertz time-domain spectroscopy of silicate glasses and the relationship to material properties," J. Appl. Phys. 102, 043517 (2007)
    [CrossRef]
  7. H. Kitahara, T. Yagi, K. Mano, M. Wada Takeda, S. Kojima, and S. Nishizawa, "Dielectric characteristics of water solutions of ethanol in the terahertz region," J. Korean Phys. Soc. 46, 82 (2005)
  8. J.-Z. Bao, M. L. Swicord, and C. C. Davis, "Microwave dielectric characterization of binary mixtures of water, methanol, and ethanol," J. Chem. Phys. 104, 4441 (1996)
    [CrossRef]
  9. T. Sato and R. Buchner, "Dielectric relaxation processes in ethanol/water mixtures," J. Phys. Chem. A 108, 5007 (2004)
    [CrossRef]

2007 (2)

M. Naftaly and R. E. Miles, "Terahertz time-domain spectroscopy of silicate glasses and the relationship to material properties," J. Appl. Phys. 102, 043517 (2007)
[CrossRef]

P. Uhd Jepsen, U. Møller, and H. Merbold, "Investigation of aqueous alcohol and sugar solutions with reflection terahertz time-domain spectroscopy," Opt. Express 15, 14717 (2007)
[CrossRef] [PubMed]

2005 (3)

P. Uhd Jepsen and B. M. Fischer, "Dynamic range in terahertz time-domain transmission and reflection spectroscopy," Opt. Lett. 30, 29 (2005)
[CrossRef] [PubMed]

H. Kitahara, T. Yagi, K. Mano, M. Wada Takeda, S. Kojima, and S. Nishizawa, "Dielectric characteristics of water solutions of ethanol in the terahertz region," J. Korean Phys. Soc. 46, 82 (2005)

T. Ikeda, A. Matsushita, M. Tatsuno, Y. Minami, M. Yamaguchi, K. Yamamoto, M. Tani, and M. Hangyo, "Investigation of inflammable liquids by terahertz spectroscopy," Appl. Phys. Lett. 87, 034105 (2005)
[CrossRef]

2004 (1)

T. Sato and R. Buchner, "Dielectric relaxation processes in ethanol/water mixtures," J. Phys. Chem. A 108, 5007 (2004)
[CrossRef]

2000 (1)

N. W. Broad, R. D. Jee, A. C. Moffat, M. J. Eaves, W. C. Mann, and W. Dziki, "Non-invasive determination of ethanol, propylene glycol and water in a multi-component pharmaceutical oral liquid by direct measurement through amber plastic bottles using Fourier transform near-infrared spectroscopy," The Analyst 125, 2054 (2000)
[CrossRef]

1996 (1)

J.-Z. Bao, M. L. Swicord, and C. C. Davis, "Microwave dielectric characterization of binary mixtures of water, methanol, and ethanol," J. Chem. Phys. 104, 4441 (1996)
[CrossRef]

Bao, J.-Z.

J.-Z. Bao, M. L. Swicord, and C. C. Davis, "Microwave dielectric characterization of binary mixtures of water, methanol, and ethanol," J. Chem. Phys. 104, 4441 (1996)
[CrossRef]

Broad, N. W.

N. W. Broad, R. D. Jee, A. C. Moffat, M. J. Eaves, W. C. Mann, and W. Dziki, "Non-invasive determination of ethanol, propylene glycol and water in a multi-component pharmaceutical oral liquid by direct measurement through amber plastic bottles using Fourier transform near-infrared spectroscopy," The Analyst 125, 2054 (2000)
[CrossRef]

Buchner, R.

T. Sato and R. Buchner, "Dielectric relaxation processes in ethanol/water mixtures," J. Phys. Chem. A 108, 5007 (2004)
[CrossRef]

Davis, C. C.

J.-Z. Bao, M. L. Swicord, and C. C. Davis, "Microwave dielectric characterization of binary mixtures of water, methanol, and ethanol," J. Chem. Phys. 104, 4441 (1996)
[CrossRef]

Dziki, W.

N. W. Broad, R. D. Jee, A. C. Moffat, M. J. Eaves, W. C. Mann, and W. Dziki, "Non-invasive determination of ethanol, propylene glycol and water in a multi-component pharmaceutical oral liquid by direct measurement through amber plastic bottles using Fourier transform near-infrared spectroscopy," The Analyst 125, 2054 (2000)
[CrossRef]

Eaves, M. J.

N. W. Broad, R. D. Jee, A. C. Moffat, M. J. Eaves, W. C. Mann, and W. Dziki, "Non-invasive determination of ethanol, propylene glycol and water in a multi-component pharmaceutical oral liquid by direct measurement through amber plastic bottles using Fourier transform near-infrared spectroscopy," The Analyst 125, 2054 (2000)
[CrossRef]

Fischer, B. M.

Hangyo, M.

T. Ikeda, A. Matsushita, M. Tatsuno, Y. Minami, M. Yamaguchi, K. Yamamoto, M. Tani, and M. Hangyo, "Investigation of inflammable liquids by terahertz spectroscopy," Appl. Phys. Lett. 87, 034105 (2005)
[CrossRef]

Ikeda, T.

T. Ikeda, A. Matsushita, M. Tatsuno, Y. Minami, M. Yamaguchi, K. Yamamoto, M. Tani, and M. Hangyo, "Investigation of inflammable liquids by terahertz spectroscopy," Appl. Phys. Lett. 87, 034105 (2005)
[CrossRef]

Jee, R. D.

N. W. Broad, R. D. Jee, A. C. Moffat, M. J. Eaves, W. C. Mann, and W. Dziki, "Non-invasive determination of ethanol, propylene glycol and water in a multi-component pharmaceutical oral liquid by direct measurement through amber plastic bottles using Fourier transform near-infrared spectroscopy," The Analyst 125, 2054 (2000)
[CrossRef]

Kitahara, H.

H. Kitahara, T. Yagi, K. Mano, M. Wada Takeda, S. Kojima, and S. Nishizawa, "Dielectric characteristics of water solutions of ethanol in the terahertz region," J. Korean Phys. Soc. 46, 82 (2005)

Kojima, S.

H. Kitahara, T. Yagi, K. Mano, M. Wada Takeda, S. Kojima, and S. Nishizawa, "Dielectric characteristics of water solutions of ethanol in the terahertz region," J. Korean Phys. Soc. 46, 82 (2005)

Mann, W. C.

N. W. Broad, R. D. Jee, A. C. Moffat, M. J. Eaves, W. C. Mann, and W. Dziki, "Non-invasive determination of ethanol, propylene glycol and water in a multi-component pharmaceutical oral liquid by direct measurement through amber plastic bottles using Fourier transform near-infrared spectroscopy," The Analyst 125, 2054 (2000)
[CrossRef]

Mano, K.

H. Kitahara, T. Yagi, K. Mano, M. Wada Takeda, S. Kojima, and S. Nishizawa, "Dielectric characteristics of water solutions of ethanol in the terahertz region," J. Korean Phys. Soc. 46, 82 (2005)

Matsushita, A.

T. Ikeda, A. Matsushita, M. Tatsuno, Y. Minami, M. Yamaguchi, K. Yamamoto, M. Tani, and M. Hangyo, "Investigation of inflammable liquids by terahertz spectroscopy," Appl. Phys. Lett. 87, 034105 (2005)
[CrossRef]

Merbold, H.

Miles, R. E.

M. Naftaly and R. E. Miles, "Terahertz time-domain spectroscopy of silicate glasses and the relationship to material properties," J. Appl. Phys. 102, 043517 (2007)
[CrossRef]

Minami, Y.

T. Ikeda, A. Matsushita, M. Tatsuno, Y. Minami, M. Yamaguchi, K. Yamamoto, M. Tani, and M. Hangyo, "Investigation of inflammable liquids by terahertz spectroscopy," Appl. Phys. Lett. 87, 034105 (2005)
[CrossRef]

Moffat, A. C.

N. W. Broad, R. D. Jee, A. C. Moffat, M. J. Eaves, W. C. Mann, and W. Dziki, "Non-invasive determination of ethanol, propylene glycol and water in a multi-component pharmaceutical oral liquid by direct measurement through amber plastic bottles using Fourier transform near-infrared spectroscopy," The Analyst 125, 2054 (2000)
[CrossRef]

Møller, U.

Naftaly, M.

M. Naftaly and R. E. Miles, "Terahertz time-domain spectroscopy of silicate glasses and the relationship to material properties," J. Appl. Phys. 102, 043517 (2007)
[CrossRef]

Nishizawa, S.

H. Kitahara, T. Yagi, K. Mano, M. Wada Takeda, S. Kojima, and S. Nishizawa, "Dielectric characteristics of water solutions of ethanol in the terahertz region," J. Korean Phys. Soc. 46, 82 (2005)

Sato, T.

T. Sato and R. Buchner, "Dielectric relaxation processes in ethanol/water mixtures," J. Phys. Chem. A 108, 5007 (2004)
[CrossRef]

Swicord, M. L.

J.-Z. Bao, M. L. Swicord, and C. C. Davis, "Microwave dielectric characterization of binary mixtures of water, methanol, and ethanol," J. Chem. Phys. 104, 4441 (1996)
[CrossRef]

Tani, M.

T. Ikeda, A. Matsushita, M. Tatsuno, Y. Minami, M. Yamaguchi, K. Yamamoto, M. Tani, and M. Hangyo, "Investigation of inflammable liquids by terahertz spectroscopy," Appl. Phys. Lett. 87, 034105 (2005)
[CrossRef]

Tatsuno, M.

T. Ikeda, A. Matsushita, M. Tatsuno, Y. Minami, M. Yamaguchi, K. Yamamoto, M. Tani, and M. Hangyo, "Investigation of inflammable liquids by terahertz spectroscopy," Appl. Phys. Lett. 87, 034105 (2005)
[CrossRef]

Uhd Jepsen, P.

Wada Takeda, M.

H. Kitahara, T. Yagi, K. Mano, M. Wada Takeda, S. Kojima, and S. Nishizawa, "Dielectric characteristics of water solutions of ethanol in the terahertz region," J. Korean Phys. Soc. 46, 82 (2005)

Yagi, T.

H. Kitahara, T. Yagi, K. Mano, M. Wada Takeda, S. Kojima, and S. Nishizawa, "Dielectric characteristics of water solutions of ethanol in the terahertz region," J. Korean Phys. Soc. 46, 82 (2005)

Yamaguchi, M.

T. Ikeda, A. Matsushita, M. Tatsuno, Y. Minami, M. Yamaguchi, K. Yamamoto, M. Tani, and M. Hangyo, "Investigation of inflammable liquids by terahertz spectroscopy," Appl. Phys. Lett. 87, 034105 (2005)
[CrossRef]

Yamamoto, K.

T. Ikeda, A. Matsushita, M. Tatsuno, Y. Minami, M. Yamaguchi, K. Yamamoto, M. Tani, and M. Hangyo, "Investigation of inflammable liquids by terahertz spectroscopy," Appl. Phys. Lett. 87, 034105 (2005)
[CrossRef]

Appl. Phys. Lett. (1)

T. Ikeda, A. Matsushita, M. Tatsuno, Y. Minami, M. Yamaguchi, K. Yamamoto, M. Tani, and M. Hangyo, "Investigation of inflammable liquids by terahertz spectroscopy," Appl. Phys. Lett. 87, 034105 (2005)
[CrossRef]

J. Appl. Phys. (1)

M. Naftaly and R. E. Miles, "Terahertz time-domain spectroscopy of silicate glasses and the relationship to material properties," J. Appl. Phys. 102, 043517 (2007)
[CrossRef]

J. Chem. Phys. (1)

J.-Z. Bao, M. L. Swicord, and C. C. Davis, "Microwave dielectric characterization of binary mixtures of water, methanol, and ethanol," J. Chem. Phys. 104, 4441 (1996)
[CrossRef]

J. Korean Phys. Soc. (1)

H. Kitahara, T. Yagi, K. Mano, M. Wada Takeda, S. Kojima, and S. Nishizawa, "Dielectric characteristics of water solutions of ethanol in the terahertz region," J. Korean Phys. Soc. 46, 82 (2005)

J. Phys. Chem. A (1)

T. Sato and R. Buchner, "Dielectric relaxation processes in ethanol/water mixtures," J. Phys. Chem. A 108, 5007 (2004)
[CrossRef]

Opt. Express (1)

Opt. Lett. (1)

The Analyst (1)

N. W. Broad, R. D. Jee, A. C. Moffat, M. J. Eaves, W. C. Mann, and W. Dziki, "Non-invasive determination of ethanol, propylene glycol and water in a multi-component pharmaceutical oral liquid by direct measurement through amber plastic bottles using Fourier transform near-infrared spectroscopy," The Analyst 125, 2054 (2000)
[CrossRef]

Other (1)

S. Dexheimer (ed.) Terahertz Spectroscopy: Principles and Applications (CRC Press, 2007)
[CrossRef]

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Figures (10)

Fig. 1.
Fig. 1.

Definitions of the geometry associated with reflection of the THz signal from a bottle. (a) A thick, regular bottle shape with a paper label and (b) a thin, irregular bottle shape with a loosely attached polymer label.

Fig. 2.
Fig. 2.

(a) THz absorption coefficient and (b) index of refraction of PET, in the form of a softdrink bottle (black curves), Vivak®(red curves) and Axpet®(blue curves). The absorption and index of the glass bottle used in this study (dark olive curves) are also shown. All measurements are carried out at room temperature.

Fig. 3.
Fig. 3.

Reflected THz signals from a PET bottle containing (a) water and (b) isopropanol. The different traces show the reflected signal from a position on the bare bottle, from a position at the edge of the paper label, and from a position on the label.

Fig. 4.
Fig. 4.

Reflected THz signals from a thin (0.17 mm wall thickness) PET bottle containing water (lower two traces, shown in blue color) and and the same bottle containing isopropanol (upper two traces, shown in red color). Each trace was recorded at a new position on the bottle.

Fig. 5.
Fig. 5.

(solid lines) (a) Real and (b) imaginary part of the modeled dielectric function of water-ethanol mixtures, in 10% increments. The experimental data for neat water and neat ethanol were recorded by reflection THz-TDS. Experimental data for water and ethanol is shown with solid squares.

Fig. 6.
Fig. 6.

(a) Simulated and (b) measured reflected THz signal from a PET bottle with 0.65 mm wall thickness, containing mixtures of water and ethanol. The red, lower traces represent the reflection from neat water and each successive curve represents a 10% increase in ethanol mass fraction.

Fig. 7.
Fig. 7.

Simulated reflected THz signal from a glass bottle with 3.0 mm wall thickness, containing neat water. The inset shows the shape of the second reflection in dependence of the ethanol concentration in the mixture. The red, lower trace represents the reflection from neat water and each successive curve represents a 10% increase in ethanol mass fraction.

Fig. 8.
Fig. 8.

Measured reflected THz signal from a glass bottle with 3.0 mm wall thickness, containing neat water. The inset shows the shape of the second reflection in dependence of the ethanol concentration in the mixture. The red, lower trace represents the reflection from neat water and each successive curve represents a 10% increase in ethanol mass fraction.

Fig. 9.
Fig. 9.

The ratio of the strengths of the second to the first pulse reflected off an (a) 0.65 mm PET bottle and (b) a 3.0 mm glass bottle, as functions of the ethanol concentration of the water-ethanol mixture in the bottles. Red curves represent a simulation, square symbols represent measurements.

Fig. 10.
Fig. 10.

(a) Time traces of the the difference sample signal reflected from a glass bottle for various ethanol concentrations. (b) The ratio Rdiff (x) of the strength of the difference signal with respect to the reference signal, as function of alcohol concentration.

Equations (17)

Equations on this page are rendered with MathJax. Learn more.

E ref ( ω ) = r ̂ 12 E in ( ω )
E sam ( ω ) = t ̂ 12 t ̂ 21 t ̂ 23 exp ( α 2 d eff + 2 in 2 ω d eff c ) .
r ̂ 12 = n ̂ 2 2 cos ϕ + n ̂ 2 2 sin 2 ϕ n ̂ 2 2 cos ϕ + n ̂ 2 2 sin 2 ϕ ,
t ̂ 12 = 2 cos ϕ n ̂ 2 cos ϕ + 1 sin 2 ϕ n ̂ 2 2 ,
t ̂ 21 = 2 n ̂ 2 1 sin 2 ϕ n ̂ 2 2 n ̂ 2 cos ϕ + 1 sin 2 ϕ n ̂ 2 2 ,
r ̂ 23 = n ̂ 3 2 n ̂ 2 2 sin 2 ϕ + n ̂ 2 2 n ̂ 3 2 sin 2 ϕ n ̂ 3 2 n ̂ 2 2 sin 2 ϕ + n ̂ 2 2 n ̂ 3 2 sin 2 ϕ .
ε ̂ ( ω ) = ε + Δ ε i 1 i ω τ i
Δ ε 1 ( x EtOH ) = 69.01 48.41 x EtOH
Δ ε 2 ( x EtOH ) = 2.01 0.62 x EtOH
Δ ε 3 ( x EtOH ) = 2.08 0.87 x EtOH
ε ( x EtOH ) = 2.10 0.76 x EtOH
τ 1 ( x EtOH ) = 9.02 + 68.78 x EtOH
τ 2 ( x EtOH ) = 0.80 + 0.73 x EtOH
τ 3 ( x EtOH ) = 0.05 + 0.03 x EtOH
R ( x ) = E sam , x 2 ( t i ) E ref , x 2 ( t j )
R diff ( x ) = E diff , x 2 ( t i ) E ref , x 2 ( t j )
d max 1 α ln ( DR )

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