Abstract

We report on the highly sensitive terahertz measurement of a thin, dielectric layer using two channels formed by inserting a single slit sheet in the parallel-plate waveguides (PPWGs). When a thin layer is applied to coat the upper surface of the channel, the single resonance frequency caused by the two-channel PPWGs is shifted as a result of the layer’s properties, including length, thickness, and refractive index. The measured frequency tuning sensitivities (FTS) throughout the 20-mm layer length are 2.41 and −1.95 GHz/mm at the open upper and lower channels, respectively. The experimental results agree with those of theoretical simulations performed using the finite-difference time-domain (FDTD) method.

© 2014 Optical Society of America

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  1. M. van Exter and D. Grischkowsky, “Optical and electronic properties of doped silicon from 0.1 to 2 THz,” Appl. Phys. Lett. 56(17), 1694–1696 (1990).
    [CrossRef]
  2. M. van Exter and D. Grischkowsky, “Carrier dynamics of electrons and holes in moderately doped silicon,” Phys. Rev. B Condens. Matter 41(17), 12140–12149 (1990).
  3. X. Liu, S. MacNaughton, D. B. Shrekenhamer, H. Tao, S. Selvarasah, A. Totachawattana, R. D. Averitt, M. R. Dokmeci, S. Sonkusale, and W. J. Padilla, “Metamaterials on parylene thin film substrates: Design, fabrication, and characterization at terahertz frequency,” Appl. Phys. Lett. 96(1), 011906 (2010).
    [CrossRef]
  4. M. Theuer, R. Beigang, and D. Grischkowsky, “Highly sensitive terahertz measurement of layer thickness using a two-cylinder waveguide sensor,” Appl. Phys. Lett. 97(7), 071106 (2010).
    [CrossRef]
  5. T. H. Isaac, W. L. Barnes, and E. Hendry, “Determining the terahertz optical properties of subwavelength films using semiconductor surface plasmons,” Appl. Phys. Lett. 93(24), 241115 (2008).
    [CrossRef]
  6. J. S. Melinger, N. Laman, S. S. Harsha, and D. Grischkowsky, “Line narrowing of terahertz vibrational modes for organic thin polycrystalline films within a parallel plate waveguide,” Appl. Phys. Lett. 89(25), 251110 (2006).
    [CrossRef]
  7. W. Withayachumnankul, J. F. O’Hara, W. Cao, I. Al-Naib, and W. Zhang, “Limitation in thin-film sensing with transmission-mode terahertz time-domain spectroscopy,” Opt. Express 22(1), 972–986 (2014).
    [CrossRef] [PubMed]
  8. J. F. O’Hara, R. Singh, I. Brener, E. Smirnova, J. Han, A. J. Taylor, and W. Zhang, “Thin-film sensing with planar terahertz metamaterials: sensitivity and limitations,” Opt. Express 16(3), 1786–1795 (2008).
    [CrossRef] [PubMed]
  9. R. Mendis, V. Astley, J. Liu, and D. M. Mittleman, “Terahertz microfluidic sensor based on a parallel-plate waveguide resonant cavity,” Appl. Phys. Lett. 95(17), 171113 (2009).
    [CrossRef]
  10. S. S. Harsha, N. Laman, and D. Grischkowsky, “High- Q terahertz Bragg resonances within a metal parallel plate waveguide,” Appl. Phys. Lett. 94(9), 091118 (2009).
    [CrossRef]
  11. E. S. Lee, S.-G. Lee, C.-S. Kee, and T.-I. Jeon, “Terahertz notch and low-pass filters based on band gaps properties by using metal slits in tapered parallel-plate waveguides,” Opt. Express 19(16), 14852–14859 (2011).
    [CrossRef] [PubMed]
  12. S.-H. Kim, E. S. Lee, Y. B. Ji, and T.-I. Jeon, “Improvement of THz coupling using a tapered parallel-plate waveguide,” Opt. Express 18(2), 1289–1295 (2010).
    [CrossRef] [PubMed]
  13. O. P. Parida and N. Bhat, “Characterization of optical properties of Su-8 and fabrication of optical componenets,” in ICOP and CSIO, Chandigarh, India, 30 Oct.-1 Nov. (2009).
  14. M. Nagel, M. Först, and H. Kurz, “THz biosensing devices: fundamentals and technology,” J. Phys. Condens. Matter 18(18), S601–S618 (2006).
    [CrossRef]
  15. Z. Xu and P. Mazumder, “Bio-sensing by Mach–Zehnder interferometer comprising doubly-corrugated spoofed surface plasmon polariton (DC-SSPP) waveguide,” IEEE Trans. Terahertz Sci. Technol. 2, 460–466 (2012).
  16. M. Nagel, F. Richter, P. Haring-Bolívar, and H. Kurz, “A functionalized THz sensor for marker-free DNA analysis,” Phys. Med. Biol. 48(22), 3625–3636 (2003).
    [CrossRef] [PubMed]

2014

2012

Z. Xu and P. Mazumder, “Bio-sensing by Mach–Zehnder interferometer comprising doubly-corrugated spoofed surface plasmon polariton (DC-SSPP) waveguide,” IEEE Trans. Terahertz Sci. Technol. 2, 460–466 (2012).

2011

2010

S.-H. Kim, E. S. Lee, Y. B. Ji, and T.-I. Jeon, “Improvement of THz coupling using a tapered parallel-plate waveguide,” Opt. Express 18(2), 1289–1295 (2010).
[CrossRef] [PubMed]

X. Liu, S. MacNaughton, D. B. Shrekenhamer, H. Tao, S. Selvarasah, A. Totachawattana, R. D. Averitt, M. R. Dokmeci, S. Sonkusale, and W. J. Padilla, “Metamaterials on parylene thin film substrates: Design, fabrication, and characterization at terahertz frequency,” Appl. Phys. Lett. 96(1), 011906 (2010).
[CrossRef]

M. Theuer, R. Beigang, and D. Grischkowsky, “Highly sensitive terahertz measurement of layer thickness using a two-cylinder waveguide sensor,” Appl. Phys. Lett. 97(7), 071106 (2010).
[CrossRef]

2009

R. Mendis, V. Astley, J. Liu, and D. M. Mittleman, “Terahertz microfluidic sensor based on a parallel-plate waveguide resonant cavity,” Appl. Phys. Lett. 95(17), 171113 (2009).
[CrossRef]

S. S. Harsha, N. Laman, and D. Grischkowsky, “High- Q terahertz Bragg resonances within a metal parallel plate waveguide,” Appl. Phys. Lett. 94(9), 091118 (2009).
[CrossRef]

2008

T. H. Isaac, W. L. Barnes, and E. Hendry, “Determining the terahertz optical properties of subwavelength films using semiconductor surface plasmons,” Appl. Phys. Lett. 93(24), 241115 (2008).
[CrossRef]

J. F. O’Hara, R. Singh, I. Brener, E. Smirnova, J. Han, A. J. Taylor, and W. Zhang, “Thin-film sensing with planar terahertz metamaterials: sensitivity and limitations,” Opt. Express 16(3), 1786–1795 (2008).
[CrossRef] [PubMed]

2006

J. S. Melinger, N. Laman, S. S. Harsha, and D. Grischkowsky, “Line narrowing of terahertz vibrational modes for organic thin polycrystalline films within a parallel plate waveguide,” Appl. Phys. Lett. 89(25), 251110 (2006).
[CrossRef]

M. Nagel, M. Först, and H. Kurz, “THz biosensing devices: fundamentals and technology,” J. Phys. Condens. Matter 18(18), S601–S618 (2006).
[CrossRef]

2003

M. Nagel, F. Richter, P. Haring-Bolívar, and H. Kurz, “A functionalized THz sensor for marker-free DNA analysis,” Phys. Med. Biol. 48(22), 3625–3636 (2003).
[CrossRef] [PubMed]

1990

M. van Exter and D. Grischkowsky, “Optical and electronic properties of doped silicon from 0.1 to 2 THz,” Appl. Phys. Lett. 56(17), 1694–1696 (1990).
[CrossRef]

M. van Exter and D. Grischkowsky, “Carrier dynamics of electrons and holes in moderately doped silicon,” Phys. Rev. B Condens. Matter 41(17), 12140–12149 (1990).

Al-Naib, I.

Astley, V.

R. Mendis, V. Astley, J. Liu, and D. M. Mittleman, “Terahertz microfluidic sensor based on a parallel-plate waveguide resonant cavity,” Appl. Phys. Lett. 95(17), 171113 (2009).
[CrossRef]

Averitt, R. D.

X. Liu, S. MacNaughton, D. B. Shrekenhamer, H. Tao, S. Selvarasah, A. Totachawattana, R. D. Averitt, M. R. Dokmeci, S. Sonkusale, and W. J. Padilla, “Metamaterials on parylene thin film substrates: Design, fabrication, and characterization at terahertz frequency,” Appl. Phys. Lett. 96(1), 011906 (2010).
[CrossRef]

Barnes, W. L.

T. H. Isaac, W. L. Barnes, and E. Hendry, “Determining the terahertz optical properties of subwavelength films using semiconductor surface plasmons,” Appl. Phys. Lett. 93(24), 241115 (2008).
[CrossRef]

Beigang, R.

M. Theuer, R. Beigang, and D. Grischkowsky, “Highly sensitive terahertz measurement of layer thickness using a two-cylinder waveguide sensor,” Appl. Phys. Lett. 97(7), 071106 (2010).
[CrossRef]

Brener, I.

Cao, W.

Dokmeci, M. R.

X. Liu, S. MacNaughton, D. B. Shrekenhamer, H. Tao, S. Selvarasah, A. Totachawattana, R. D. Averitt, M. R. Dokmeci, S. Sonkusale, and W. J. Padilla, “Metamaterials on parylene thin film substrates: Design, fabrication, and characterization at terahertz frequency,” Appl. Phys. Lett. 96(1), 011906 (2010).
[CrossRef]

Först, M.

M. Nagel, M. Först, and H. Kurz, “THz biosensing devices: fundamentals and technology,” J. Phys. Condens. Matter 18(18), S601–S618 (2006).
[CrossRef]

Grischkowsky, D.

M. Theuer, R. Beigang, and D. Grischkowsky, “Highly sensitive terahertz measurement of layer thickness using a two-cylinder waveguide sensor,” Appl. Phys. Lett. 97(7), 071106 (2010).
[CrossRef]

S. S. Harsha, N. Laman, and D. Grischkowsky, “High- Q terahertz Bragg resonances within a metal parallel plate waveguide,” Appl. Phys. Lett. 94(9), 091118 (2009).
[CrossRef]

J. S. Melinger, N. Laman, S. S. Harsha, and D. Grischkowsky, “Line narrowing of terahertz vibrational modes for organic thin polycrystalline films within a parallel plate waveguide,” Appl. Phys. Lett. 89(25), 251110 (2006).
[CrossRef]

M. van Exter and D. Grischkowsky, “Carrier dynamics of electrons and holes in moderately doped silicon,” Phys. Rev. B Condens. Matter 41(17), 12140–12149 (1990).

M. van Exter and D. Grischkowsky, “Optical and electronic properties of doped silicon from 0.1 to 2 THz,” Appl. Phys. Lett. 56(17), 1694–1696 (1990).
[CrossRef]

Han, J.

Haring-Bolívar, P.

M. Nagel, F. Richter, P. Haring-Bolívar, and H. Kurz, “A functionalized THz sensor for marker-free DNA analysis,” Phys. Med. Biol. 48(22), 3625–3636 (2003).
[CrossRef] [PubMed]

Harsha, S. S.

S. S. Harsha, N. Laman, and D. Grischkowsky, “High- Q terahertz Bragg resonances within a metal parallel plate waveguide,” Appl. Phys. Lett. 94(9), 091118 (2009).
[CrossRef]

J. S. Melinger, N. Laman, S. S. Harsha, and D. Grischkowsky, “Line narrowing of terahertz vibrational modes for organic thin polycrystalline films within a parallel plate waveguide,” Appl. Phys. Lett. 89(25), 251110 (2006).
[CrossRef]

Hendry, E.

T. H. Isaac, W. L. Barnes, and E. Hendry, “Determining the terahertz optical properties of subwavelength films using semiconductor surface plasmons,” Appl. Phys. Lett. 93(24), 241115 (2008).
[CrossRef]

Isaac, T. H.

T. H. Isaac, W. L. Barnes, and E. Hendry, “Determining the terahertz optical properties of subwavelength films using semiconductor surface plasmons,” Appl. Phys. Lett. 93(24), 241115 (2008).
[CrossRef]

Jeon, T.-I.

Ji, Y. B.

Kee, C.-S.

Kim, S.-H.

Kurz, H.

M. Nagel, M. Först, and H. Kurz, “THz biosensing devices: fundamentals and technology,” J. Phys. Condens. Matter 18(18), S601–S618 (2006).
[CrossRef]

M. Nagel, F. Richter, P. Haring-Bolívar, and H. Kurz, “A functionalized THz sensor for marker-free DNA analysis,” Phys. Med. Biol. 48(22), 3625–3636 (2003).
[CrossRef] [PubMed]

Laman, N.

S. S. Harsha, N. Laman, and D. Grischkowsky, “High- Q terahertz Bragg resonances within a metal parallel plate waveguide,” Appl. Phys. Lett. 94(9), 091118 (2009).
[CrossRef]

J. S. Melinger, N. Laman, S. S. Harsha, and D. Grischkowsky, “Line narrowing of terahertz vibrational modes for organic thin polycrystalline films within a parallel plate waveguide,” Appl. Phys. Lett. 89(25), 251110 (2006).
[CrossRef]

Lee, E. S.

Lee, S.-G.

Liu, J.

R. Mendis, V. Astley, J. Liu, and D. M. Mittleman, “Terahertz microfluidic sensor based on a parallel-plate waveguide resonant cavity,” Appl. Phys. Lett. 95(17), 171113 (2009).
[CrossRef]

Liu, X.

X. Liu, S. MacNaughton, D. B. Shrekenhamer, H. Tao, S. Selvarasah, A. Totachawattana, R. D. Averitt, M. R. Dokmeci, S. Sonkusale, and W. J. Padilla, “Metamaterials on parylene thin film substrates: Design, fabrication, and characterization at terahertz frequency,” Appl. Phys. Lett. 96(1), 011906 (2010).
[CrossRef]

MacNaughton, S.

X. Liu, S. MacNaughton, D. B. Shrekenhamer, H. Tao, S. Selvarasah, A. Totachawattana, R. D. Averitt, M. R. Dokmeci, S. Sonkusale, and W. J. Padilla, “Metamaterials on parylene thin film substrates: Design, fabrication, and characterization at terahertz frequency,” Appl. Phys. Lett. 96(1), 011906 (2010).
[CrossRef]

Mazumder, P.

Z. Xu and P. Mazumder, “Bio-sensing by Mach–Zehnder interferometer comprising doubly-corrugated spoofed surface plasmon polariton (DC-SSPP) waveguide,” IEEE Trans. Terahertz Sci. Technol. 2, 460–466 (2012).

Melinger, J. S.

J. S. Melinger, N. Laman, S. S. Harsha, and D. Grischkowsky, “Line narrowing of terahertz vibrational modes for organic thin polycrystalline films within a parallel plate waveguide,” Appl. Phys. Lett. 89(25), 251110 (2006).
[CrossRef]

Mendis, R.

R. Mendis, V. Astley, J. Liu, and D. M. Mittleman, “Terahertz microfluidic sensor based on a parallel-plate waveguide resonant cavity,” Appl. Phys. Lett. 95(17), 171113 (2009).
[CrossRef]

Mittleman, D. M.

R. Mendis, V. Astley, J. Liu, and D. M. Mittleman, “Terahertz microfluidic sensor based on a parallel-plate waveguide resonant cavity,” Appl. Phys. Lett. 95(17), 171113 (2009).
[CrossRef]

Nagel, M.

M. Nagel, M. Först, and H. Kurz, “THz biosensing devices: fundamentals and technology,” J. Phys. Condens. Matter 18(18), S601–S618 (2006).
[CrossRef]

M. Nagel, F. Richter, P. Haring-Bolívar, and H. Kurz, “A functionalized THz sensor for marker-free DNA analysis,” Phys. Med. Biol. 48(22), 3625–3636 (2003).
[CrossRef] [PubMed]

O’Hara, J. F.

Padilla, W. J.

X. Liu, S. MacNaughton, D. B. Shrekenhamer, H. Tao, S. Selvarasah, A. Totachawattana, R. D. Averitt, M. R. Dokmeci, S. Sonkusale, and W. J. Padilla, “Metamaterials on parylene thin film substrates: Design, fabrication, and characterization at terahertz frequency,” Appl. Phys. Lett. 96(1), 011906 (2010).
[CrossRef]

Richter, F.

M. Nagel, F. Richter, P. Haring-Bolívar, and H. Kurz, “A functionalized THz sensor for marker-free DNA analysis,” Phys. Med. Biol. 48(22), 3625–3636 (2003).
[CrossRef] [PubMed]

Selvarasah, S.

X. Liu, S. MacNaughton, D. B. Shrekenhamer, H. Tao, S. Selvarasah, A. Totachawattana, R. D. Averitt, M. R. Dokmeci, S. Sonkusale, and W. J. Padilla, “Metamaterials on parylene thin film substrates: Design, fabrication, and characterization at terahertz frequency,” Appl. Phys. Lett. 96(1), 011906 (2010).
[CrossRef]

Shrekenhamer, D. B.

X. Liu, S. MacNaughton, D. B. Shrekenhamer, H. Tao, S. Selvarasah, A. Totachawattana, R. D. Averitt, M. R. Dokmeci, S. Sonkusale, and W. J. Padilla, “Metamaterials on parylene thin film substrates: Design, fabrication, and characterization at terahertz frequency,” Appl. Phys. Lett. 96(1), 011906 (2010).
[CrossRef]

Singh, R.

Smirnova, E.

Sonkusale, S.

X. Liu, S. MacNaughton, D. B. Shrekenhamer, H. Tao, S. Selvarasah, A. Totachawattana, R. D. Averitt, M. R. Dokmeci, S. Sonkusale, and W. J. Padilla, “Metamaterials on parylene thin film substrates: Design, fabrication, and characterization at terahertz frequency,” Appl. Phys. Lett. 96(1), 011906 (2010).
[CrossRef]

Tao, H.

X. Liu, S. MacNaughton, D. B. Shrekenhamer, H. Tao, S. Selvarasah, A. Totachawattana, R. D. Averitt, M. R. Dokmeci, S. Sonkusale, and W. J. Padilla, “Metamaterials on parylene thin film substrates: Design, fabrication, and characterization at terahertz frequency,” Appl. Phys. Lett. 96(1), 011906 (2010).
[CrossRef]

Taylor, A. J.

Theuer, M.

M. Theuer, R. Beigang, and D. Grischkowsky, “Highly sensitive terahertz measurement of layer thickness using a two-cylinder waveguide sensor,” Appl. Phys. Lett. 97(7), 071106 (2010).
[CrossRef]

Totachawattana, A.

X. Liu, S. MacNaughton, D. B. Shrekenhamer, H. Tao, S. Selvarasah, A. Totachawattana, R. D. Averitt, M. R. Dokmeci, S. Sonkusale, and W. J. Padilla, “Metamaterials on parylene thin film substrates: Design, fabrication, and characterization at terahertz frequency,” Appl. Phys. Lett. 96(1), 011906 (2010).
[CrossRef]

van Exter, M.

M. van Exter and D. Grischkowsky, “Carrier dynamics of electrons and holes in moderately doped silicon,” Phys. Rev. B Condens. Matter 41(17), 12140–12149 (1990).

M. van Exter and D. Grischkowsky, “Optical and electronic properties of doped silicon from 0.1 to 2 THz,” Appl. Phys. Lett. 56(17), 1694–1696 (1990).
[CrossRef]

Withayachumnankul, W.

Xu, Z.

Z. Xu and P. Mazumder, “Bio-sensing by Mach–Zehnder interferometer comprising doubly-corrugated spoofed surface plasmon polariton (DC-SSPP) waveguide,” IEEE Trans. Terahertz Sci. Technol. 2, 460–466 (2012).

Zhang, W.

Appl. Phys. Lett.

X. Liu, S. MacNaughton, D. B. Shrekenhamer, H. Tao, S. Selvarasah, A. Totachawattana, R. D. Averitt, M. R. Dokmeci, S. Sonkusale, and W. J. Padilla, “Metamaterials on parylene thin film substrates: Design, fabrication, and characterization at terahertz frequency,” Appl. Phys. Lett. 96(1), 011906 (2010).
[CrossRef]

M. Theuer, R. Beigang, and D. Grischkowsky, “Highly sensitive terahertz measurement of layer thickness using a two-cylinder waveguide sensor,” Appl. Phys. Lett. 97(7), 071106 (2010).
[CrossRef]

T. H. Isaac, W. L. Barnes, and E. Hendry, “Determining the terahertz optical properties of subwavelength films using semiconductor surface plasmons,” Appl. Phys. Lett. 93(24), 241115 (2008).
[CrossRef]

J. S. Melinger, N. Laman, S. S. Harsha, and D. Grischkowsky, “Line narrowing of terahertz vibrational modes for organic thin polycrystalline films within a parallel plate waveguide,” Appl. Phys. Lett. 89(25), 251110 (2006).
[CrossRef]

R. Mendis, V. Astley, J. Liu, and D. M. Mittleman, “Terahertz microfluidic sensor based on a parallel-plate waveguide resonant cavity,” Appl. Phys. Lett. 95(17), 171113 (2009).
[CrossRef]

S. S. Harsha, N. Laman, and D. Grischkowsky, “High- Q terahertz Bragg resonances within a metal parallel plate waveguide,” Appl. Phys. Lett. 94(9), 091118 (2009).
[CrossRef]

M. van Exter and D. Grischkowsky, “Optical and electronic properties of doped silicon from 0.1 to 2 THz,” Appl. Phys. Lett. 56(17), 1694–1696 (1990).
[CrossRef]

IEEE Trans. Terahertz Sci. Technol.

Z. Xu and P. Mazumder, “Bio-sensing by Mach–Zehnder interferometer comprising doubly-corrugated spoofed surface plasmon polariton (DC-SSPP) waveguide,” IEEE Trans. Terahertz Sci. Technol. 2, 460–466 (2012).

J. Phys. Condens. Matter

M. Nagel, M. Först, and H. Kurz, “THz biosensing devices: fundamentals and technology,” J. Phys. Condens. Matter 18(18), S601–S618 (2006).
[CrossRef]

Opt. Express

Phys. Med. Biol.

M. Nagel, F. Richter, P. Haring-Bolívar, and H. Kurz, “A functionalized THz sensor for marker-free DNA analysis,” Phys. Med. Biol. 48(22), 3625–3636 (2003).
[CrossRef] [PubMed]

Phys. Rev. B Condens. Matter

M. van Exter and D. Grischkowsky, “Carrier dynamics of electrons and holes in moderately doped silicon,” Phys. Rev. B Condens. Matter 41(17), 12140–12149 (1990).

Other

O. P. Parida and N. Bhat, “Characterization of optical properties of Su-8 and fabrication of optical componenets,” in ICOP and CSIO, Chandigarh, India, 30 Oct.-1 Nov. (2009).

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Figures (6)

Fig. 1
Fig. 1

(a) Schematic diagram of the thin layer THz sensing system. (b) The waveguide structure. A single slit sheet is located in the middle of the PPWG air gap to divide the two channels. The front part of the sheet can be bent in an upper or lower direction (indicated by the dashed lines) to open only one of the channels. A thin dielectric layer (SU-8) is on the upper PPWG block surface.

Fig. 2
Fig. 2

Measured transmission spectra for different layer lengths. Lower right insets show the normalized reference spectrum (no coated layer). Lower left insets show the slit sheet bent in a lower or upper direction. (a) The input THz beam travels to the upper channel only. (b) The input THz beam travels to the lower channel only.

Fig. 3
Fig. 3

Measured time delay and frequency shift. The red and blue fitting lines indicate the upper and lower channel open only respectively. (a) Time delay for different layer length. (b) Frequency shift for different layer length as shown in Fig. 2.

Fig. 4
Fig. 4

Measured transmission spectra for different layer thickness. Lower right insets show the resonance frequency shift. Lower left insets show the slit sheet bent in a lower or upper direction. (a) The input THz beam travels to the upper channel only. (b) The input THz beam travels to the lower channel only.

Fig. 5
Fig. 5

Simulated transmission spectra for 1 mm length, 1.00 μm thickness, and 1.7 refractive index. The insets show frequency shifts with respect to variations in the different parameters. (a) Differences in layer length (b) Differences in layer thickness (c) Differences in layer reflective index

Fig. 6
Fig. 6

Comparison of the experimental (blue) and simulated (red). The solid and dashed lines indicate linear fitting for the data. (a) Frequency shifts for different layer lengths. Layer thicknesses used in experimental and simulation conditions are 1.33 ± 0.18 and 1.50 μm, respectively, for the open upper channel (red triangles) and 1.04 ± 0.08 and 1.00 μm, respectively, for the open lower channel (inverse blue triangles). (b) Frequency shifts for different layer thickness. Layer lengths used in experimental and simulation conditions are both 5 mm for the open upper channel (red triangles) and for the open lower channel (inverse blue triangles).

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