Abstract

Far-infrared to millimeter-wave bolometers designed to make astronomical observations are typically encased in integrating cavities at the termination of feedhorns or Winston cones. This photometer combination maximizes absorption of radiation, enables the absorber area to be minimized, and controls the directivity of absorption, thereby reducing susceptibility to stray light. In the next decade, arrays of hundreds of silicon nitride micromesh bolometers with planar architectures will be used in ground-based, suborbital, and orbital platforms for astronomy. The optimization of integrating cavity designs is required for achieving the highest possible sensitivity for these arrays. We report numerical simulations of the electromagnetic fields in integrating cavities with an infinite plane-parallel geometry formed by a solid reflecting backshort and the back surface of a feedhorn array block. Performance of this architecture for the bolometer array camera (Bolocam) for cosmology at a frequency of 214 GHz is investigated. We explore the sensitivity of absorption efficiency to absorber impedance and backshort location and the magnitude of leakage from cavities. The simulations are compared with experimental data from a room-temperature scale model and with the performance of Bolocam at a temperature of 300 mK. The main results of the simulations for Bolocam-type cavities are that (1) monochromatic absorptions as high as 95% are achievable with <1% cross talk between neighboring cavities, (2) the optimum absorber impedances are 400 Ω/sq, but with a broad maximum from ∼150 to ∼700 Ω/sq, and (3) maximum absorption is achieved with absorber diameters ≥1.5λ. Good general agreement between the simulations and the experiments was found.

© 2002 Optical Society of America

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References

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  1. D. C. Alsop, C. Inman, A. E. Lange, T. Willbanks, “Design and construction of high-sensitivity infrared bolometers for operation at 300 mK,” Appl. Opt. 31, 6610–6615 (1992).
    [CrossRef] [PubMed]
  2. P. L. Richards, “Bolometers for infrared and millimeter waves,” J. Appl. Phys. 76, 1–24 (1994).
    [CrossRef]
  3. R. Winston, “Light collection within the framework of geometrical optics,” J. Opt. Soc. Am. 60, 245–247 (1970).
    [CrossRef]
  4. D. A. Harper, R. H. Hildebrand, R. Stiening, R. Winston, “Heat trap: an optimized far-infrared field optics system,” Appl. Opt. 15, 53–60 (1976).
    [CrossRef] [PubMed]
  5. C. R. Cunningham, W. K. Gear, W. D. Duncan, P. R. Hastings, W. S. Holland, “SCUBA: the submillimeter common-user bolometer array for the James Clerk Maxwell telescope,” in Instrumentation in Astronomy VIII, D. L. Crawford, E. R. Craine, eds., Proc. SPIE2198, 638–649 (1994).
    [CrossRef]
  6. R. H. Hildebrand, “Focal plane optics in far-infrared and submillimeter astronomy,” Opt. Eng. 25, 323–330 (1986).
    [CrossRef]
  7. J. C. Peterson, M. A. Goldman, “Reflectance of broad band waveguide bolometers,” Int. J. Infrared Millim. Waves 9, 55–69 (1988).
    [CrossRef]
  8. J. A. Murphy, R. Padman, “Radiation patterns of few-moded horns and condensing lightpipes,” Infrared Phys. 31, 291–299 (1991).
    [CrossRef]
  9. P. D. Mauskopf, J. J. Bock, H. Del Castillo, W. L. Holzapfel, A. E. Lange, “Composite infrared bolometers with Si3N4 micromesh absorbers,” Appl. Opt. 36, 765–771 (1997).
    [CrossRef] [PubMed]
  10. J. Glenn, J. J. Bock, G. Chattopadhyay, S. F. Edgington, A. E. Lange, J. Zmuidzinas, P. D. Mauskopf, B. Rownd, L. Yuen, “Bolocam: a millimeter-wave bolometric camera,” in Advanced Technology MMW, Radio, and Terahertz Telescopes, T. G. Phillips, ed., Proc. SPIE3357, 326–334 (1998).
    [CrossRef]
  11. M. Griffin, L. Vigroux, B. Swinyard, “SPIRE: a bolometer instrument for FIRST,” in Advanced Technology MMW, Radio, and Terahertz Telescopes, T. G. Phillips, ed., Proc. SPIE3357, 404–413 (1998).
    [CrossRef]
  12. J. J. Bock, J. Glenn, S. M. Grannan, K. D. Irwin, A. E. Lange, H. G. LeDuc, A. D. Turner, “Silicon nitride micromesh bolometer arrays for SPIRE,” in Advanced Technology MMW, Radio, and Terahertz Telescopes, T. G. Phillips, ed., Proc. SPIE3357, 297–304 (1998).
    [CrossRef]
  13. High-Frequency Structure Simulator (HFSS), version A.04.01, Hewlett-Packard Company, Test and Measurement Organization, P.O. Box 50637, Palo Alto, Calif. 94303-9512.
  14. S. E. Church, B. Philhour, A. E. Lange, P. A. R. Ade, B. Maffei, R. Nartallo-Garcia, M. Dragovan, “A compact high-efficiency feed structure for cosmic microwave background astronomy at millimeter wavelengths,” in Submillimetre and Far-Infrared Space Instrumentation, E. J. Rolfe, ed., Proceedings of the 30th ESLAB Symposium, ESA SP-388 (European Space Agency, Munich, 1996), pp. 77–80.

1997 (1)

1994 (1)

P. L. Richards, “Bolometers for infrared and millimeter waves,” J. Appl. Phys. 76, 1–24 (1994).
[CrossRef]

1992 (1)

1991 (1)

J. A. Murphy, R. Padman, “Radiation patterns of few-moded horns and condensing lightpipes,” Infrared Phys. 31, 291–299 (1991).
[CrossRef]

1988 (1)

J. C. Peterson, M. A. Goldman, “Reflectance of broad band waveguide bolometers,” Int. J. Infrared Millim. Waves 9, 55–69 (1988).
[CrossRef]

1986 (1)

R. H. Hildebrand, “Focal plane optics in far-infrared and submillimeter astronomy,” Opt. Eng. 25, 323–330 (1986).
[CrossRef]

1976 (1)

1970 (1)

Ade, P. A. R.

S. E. Church, B. Philhour, A. E. Lange, P. A. R. Ade, B. Maffei, R. Nartallo-Garcia, M. Dragovan, “A compact high-efficiency feed structure for cosmic microwave background astronomy at millimeter wavelengths,” in Submillimetre and Far-Infrared Space Instrumentation, E. J. Rolfe, ed., Proceedings of the 30th ESLAB Symposium, ESA SP-388 (European Space Agency, Munich, 1996), pp. 77–80.

Alsop, D. C.

Bock, J. J.

P. D. Mauskopf, J. J. Bock, H. Del Castillo, W. L. Holzapfel, A. E. Lange, “Composite infrared bolometers with Si3N4 micromesh absorbers,” Appl. Opt. 36, 765–771 (1997).
[CrossRef] [PubMed]

J. J. Bock, J. Glenn, S. M. Grannan, K. D. Irwin, A. E. Lange, H. G. LeDuc, A. D. Turner, “Silicon nitride micromesh bolometer arrays for SPIRE,” in Advanced Technology MMW, Radio, and Terahertz Telescopes, T. G. Phillips, ed., Proc. SPIE3357, 297–304 (1998).
[CrossRef]

J. Glenn, J. J. Bock, G. Chattopadhyay, S. F. Edgington, A. E. Lange, J. Zmuidzinas, P. D. Mauskopf, B. Rownd, L. Yuen, “Bolocam: a millimeter-wave bolometric camera,” in Advanced Technology MMW, Radio, and Terahertz Telescopes, T. G. Phillips, ed., Proc. SPIE3357, 326–334 (1998).
[CrossRef]

Chattopadhyay, G.

J. Glenn, J. J. Bock, G. Chattopadhyay, S. F. Edgington, A. E. Lange, J. Zmuidzinas, P. D. Mauskopf, B. Rownd, L. Yuen, “Bolocam: a millimeter-wave bolometric camera,” in Advanced Technology MMW, Radio, and Terahertz Telescopes, T. G. Phillips, ed., Proc. SPIE3357, 326–334 (1998).
[CrossRef]

Church, S. E.

S. E. Church, B. Philhour, A. E. Lange, P. A. R. Ade, B. Maffei, R. Nartallo-Garcia, M. Dragovan, “A compact high-efficiency feed structure for cosmic microwave background astronomy at millimeter wavelengths,” in Submillimetre and Far-Infrared Space Instrumentation, E. J. Rolfe, ed., Proceedings of the 30th ESLAB Symposium, ESA SP-388 (European Space Agency, Munich, 1996), pp. 77–80.

Cunningham, C. R.

C. R. Cunningham, W. K. Gear, W. D. Duncan, P. R. Hastings, W. S. Holland, “SCUBA: the submillimeter common-user bolometer array for the James Clerk Maxwell telescope,” in Instrumentation in Astronomy VIII, D. L. Crawford, E. R. Craine, eds., Proc. SPIE2198, 638–649 (1994).
[CrossRef]

Del Castillo, H.

Dragovan, M.

S. E. Church, B. Philhour, A. E. Lange, P. A. R. Ade, B. Maffei, R. Nartallo-Garcia, M. Dragovan, “A compact high-efficiency feed structure for cosmic microwave background astronomy at millimeter wavelengths,” in Submillimetre and Far-Infrared Space Instrumentation, E. J. Rolfe, ed., Proceedings of the 30th ESLAB Symposium, ESA SP-388 (European Space Agency, Munich, 1996), pp. 77–80.

Duncan, W. D.

C. R. Cunningham, W. K. Gear, W. D. Duncan, P. R. Hastings, W. S. Holland, “SCUBA: the submillimeter common-user bolometer array for the James Clerk Maxwell telescope,” in Instrumentation in Astronomy VIII, D. L. Crawford, E. R. Craine, eds., Proc. SPIE2198, 638–649 (1994).
[CrossRef]

Edgington, S. F.

J. Glenn, J. J. Bock, G. Chattopadhyay, S. F. Edgington, A. E. Lange, J. Zmuidzinas, P. D. Mauskopf, B. Rownd, L. Yuen, “Bolocam: a millimeter-wave bolometric camera,” in Advanced Technology MMW, Radio, and Terahertz Telescopes, T. G. Phillips, ed., Proc. SPIE3357, 326–334 (1998).
[CrossRef]

Gear, W. K.

C. R. Cunningham, W. K. Gear, W. D. Duncan, P. R. Hastings, W. S. Holland, “SCUBA: the submillimeter common-user bolometer array for the James Clerk Maxwell telescope,” in Instrumentation in Astronomy VIII, D. L. Crawford, E. R. Craine, eds., Proc. SPIE2198, 638–649 (1994).
[CrossRef]

Glenn, J.

J. Glenn, J. J. Bock, G. Chattopadhyay, S. F. Edgington, A. E. Lange, J. Zmuidzinas, P. D. Mauskopf, B. Rownd, L. Yuen, “Bolocam: a millimeter-wave bolometric camera,” in Advanced Technology MMW, Radio, and Terahertz Telescopes, T. G. Phillips, ed., Proc. SPIE3357, 326–334 (1998).
[CrossRef]

J. J. Bock, J. Glenn, S. M. Grannan, K. D. Irwin, A. E. Lange, H. G. LeDuc, A. D. Turner, “Silicon nitride micromesh bolometer arrays for SPIRE,” in Advanced Technology MMW, Radio, and Terahertz Telescopes, T. G. Phillips, ed., Proc. SPIE3357, 297–304 (1998).
[CrossRef]

Goldman, M. A.

J. C. Peterson, M. A. Goldman, “Reflectance of broad band waveguide bolometers,” Int. J. Infrared Millim. Waves 9, 55–69 (1988).
[CrossRef]

Grannan, S. M.

J. J. Bock, J. Glenn, S. M. Grannan, K. D. Irwin, A. E. Lange, H. G. LeDuc, A. D. Turner, “Silicon nitride micromesh bolometer arrays for SPIRE,” in Advanced Technology MMW, Radio, and Terahertz Telescopes, T. G. Phillips, ed., Proc. SPIE3357, 297–304 (1998).
[CrossRef]

Griffin, M.

M. Griffin, L. Vigroux, B. Swinyard, “SPIRE: a bolometer instrument for FIRST,” in Advanced Technology MMW, Radio, and Terahertz Telescopes, T. G. Phillips, ed., Proc. SPIE3357, 404–413 (1998).
[CrossRef]

Harper, D. A.

Hastings, P. R.

C. R. Cunningham, W. K. Gear, W. D. Duncan, P. R. Hastings, W. S. Holland, “SCUBA: the submillimeter common-user bolometer array for the James Clerk Maxwell telescope,” in Instrumentation in Astronomy VIII, D. L. Crawford, E. R. Craine, eds., Proc. SPIE2198, 638–649 (1994).
[CrossRef]

Hildebrand, R. H.

R. H. Hildebrand, “Focal plane optics in far-infrared and submillimeter astronomy,” Opt. Eng. 25, 323–330 (1986).
[CrossRef]

D. A. Harper, R. H. Hildebrand, R. Stiening, R. Winston, “Heat trap: an optimized far-infrared field optics system,” Appl. Opt. 15, 53–60 (1976).
[CrossRef] [PubMed]

Holland, W. S.

C. R. Cunningham, W. K. Gear, W. D. Duncan, P. R. Hastings, W. S. Holland, “SCUBA: the submillimeter common-user bolometer array for the James Clerk Maxwell telescope,” in Instrumentation in Astronomy VIII, D. L. Crawford, E. R. Craine, eds., Proc. SPIE2198, 638–649 (1994).
[CrossRef]

Holzapfel, W. L.

Inman, C.

Irwin, K. D.

J. J. Bock, J. Glenn, S. M. Grannan, K. D. Irwin, A. E. Lange, H. G. LeDuc, A. D. Turner, “Silicon nitride micromesh bolometer arrays for SPIRE,” in Advanced Technology MMW, Radio, and Terahertz Telescopes, T. G. Phillips, ed., Proc. SPIE3357, 297–304 (1998).
[CrossRef]

Lange, A. E.

P. D. Mauskopf, J. J. Bock, H. Del Castillo, W. L. Holzapfel, A. E. Lange, “Composite infrared bolometers with Si3N4 micromesh absorbers,” Appl. Opt. 36, 765–771 (1997).
[CrossRef] [PubMed]

D. C. Alsop, C. Inman, A. E. Lange, T. Willbanks, “Design and construction of high-sensitivity infrared bolometers for operation at 300 mK,” Appl. Opt. 31, 6610–6615 (1992).
[CrossRef] [PubMed]

S. E. Church, B. Philhour, A. E. Lange, P. A. R. Ade, B. Maffei, R. Nartallo-Garcia, M. Dragovan, “A compact high-efficiency feed structure for cosmic microwave background astronomy at millimeter wavelengths,” in Submillimetre and Far-Infrared Space Instrumentation, E. J. Rolfe, ed., Proceedings of the 30th ESLAB Symposium, ESA SP-388 (European Space Agency, Munich, 1996), pp. 77–80.

J. J. Bock, J. Glenn, S. M. Grannan, K. D. Irwin, A. E. Lange, H. G. LeDuc, A. D. Turner, “Silicon nitride micromesh bolometer arrays for SPIRE,” in Advanced Technology MMW, Radio, and Terahertz Telescopes, T. G. Phillips, ed., Proc. SPIE3357, 297–304 (1998).
[CrossRef]

J. Glenn, J. J. Bock, G. Chattopadhyay, S. F. Edgington, A. E. Lange, J. Zmuidzinas, P. D. Mauskopf, B. Rownd, L. Yuen, “Bolocam: a millimeter-wave bolometric camera,” in Advanced Technology MMW, Radio, and Terahertz Telescopes, T. G. Phillips, ed., Proc. SPIE3357, 326–334 (1998).
[CrossRef]

LeDuc, H. G.

J. J. Bock, J. Glenn, S. M. Grannan, K. D. Irwin, A. E. Lange, H. G. LeDuc, A. D. Turner, “Silicon nitride micromesh bolometer arrays for SPIRE,” in Advanced Technology MMW, Radio, and Terahertz Telescopes, T. G. Phillips, ed., Proc. SPIE3357, 297–304 (1998).
[CrossRef]

Maffei, B.

S. E. Church, B. Philhour, A. E. Lange, P. A. R. Ade, B. Maffei, R. Nartallo-Garcia, M. Dragovan, “A compact high-efficiency feed structure for cosmic microwave background astronomy at millimeter wavelengths,” in Submillimetre and Far-Infrared Space Instrumentation, E. J. Rolfe, ed., Proceedings of the 30th ESLAB Symposium, ESA SP-388 (European Space Agency, Munich, 1996), pp. 77–80.

Mauskopf, P. D.

P. D. Mauskopf, J. J. Bock, H. Del Castillo, W. L. Holzapfel, A. E. Lange, “Composite infrared bolometers with Si3N4 micromesh absorbers,” Appl. Opt. 36, 765–771 (1997).
[CrossRef] [PubMed]

J. Glenn, J. J. Bock, G. Chattopadhyay, S. F. Edgington, A. E. Lange, J. Zmuidzinas, P. D. Mauskopf, B. Rownd, L. Yuen, “Bolocam: a millimeter-wave bolometric camera,” in Advanced Technology MMW, Radio, and Terahertz Telescopes, T. G. Phillips, ed., Proc. SPIE3357, 326–334 (1998).
[CrossRef]

Murphy, J. A.

J. A. Murphy, R. Padman, “Radiation patterns of few-moded horns and condensing lightpipes,” Infrared Phys. 31, 291–299 (1991).
[CrossRef]

Nartallo-Garcia, R.

S. E. Church, B. Philhour, A. E. Lange, P. A. R. Ade, B. Maffei, R. Nartallo-Garcia, M. Dragovan, “A compact high-efficiency feed structure for cosmic microwave background astronomy at millimeter wavelengths,” in Submillimetre and Far-Infrared Space Instrumentation, E. J. Rolfe, ed., Proceedings of the 30th ESLAB Symposium, ESA SP-388 (European Space Agency, Munich, 1996), pp. 77–80.

Padman, R.

J. A. Murphy, R. Padman, “Radiation patterns of few-moded horns and condensing lightpipes,” Infrared Phys. 31, 291–299 (1991).
[CrossRef]

Peterson, J. C.

J. C. Peterson, M. A. Goldman, “Reflectance of broad band waveguide bolometers,” Int. J. Infrared Millim. Waves 9, 55–69 (1988).
[CrossRef]

Philhour, B.

S. E. Church, B. Philhour, A. E. Lange, P. A. R. Ade, B. Maffei, R. Nartallo-Garcia, M. Dragovan, “A compact high-efficiency feed structure for cosmic microwave background astronomy at millimeter wavelengths,” in Submillimetre and Far-Infrared Space Instrumentation, E. J. Rolfe, ed., Proceedings of the 30th ESLAB Symposium, ESA SP-388 (European Space Agency, Munich, 1996), pp. 77–80.

Richards, P. L.

P. L. Richards, “Bolometers for infrared and millimeter waves,” J. Appl. Phys. 76, 1–24 (1994).
[CrossRef]

Rownd, B.

J. Glenn, J. J. Bock, G. Chattopadhyay, S. F. Edgington, A. E. Lange, J. Zmuidzinas, P. D. Mauskopf, B. Rownd, L. Yuen, “Bolocam: a millimeter-wave bolometric camera,” in Advanced Technology MMW, Radio, and Terahertz Telescopes, T. G. Phillips, ed., Proc. SPIE3357, 326–334 (1998).
[CrossRef]

Stiening, R.

Swinyard, B.

M. Griffin, L. Vigroux, B. Swinyard, “SPIRE: a bolometer instrument for FIRST,” in Advanced Technology MMW, Radio, and Terahertz Telescopes, T. G. Phillips, ed., Proc. SPIE3357, 404–413 (1998).
[CrossRef]

Turner, A. D.

J. J. Bock, J. Glenn, S. M. Grannan, K. D. Irwin, A. E. Lange, H. G. LeDuc, A. D. Turner, “Silicon nitride micromesh bolometer arrays for SPIRE,” in Advanced Technology MMW, Radio, and Terahertz Telescopes, T. G. Phillips, ed., Proc. SPIE3357, 297–304 (1998).
[CrossRef]

Vigroux, L.

M. Griffin, L. Vigroux, B. Swinyard, “SPIRE: a bolometer instrument for FIRST,” in Advanced Technology MMW, Radio, and Terahertz Telescopes, T. G. Phillips, ed., Proc. SPIE3357, 404–413 (1998).
[CrossRef]

Willbanks, T.

Winston, R.

Yuen, L.

J. Glenn, J. J. Bock, G. Chattopadhyay, S. F. Edgington, A. E. Lange, J. Zmuidzinas, P. D. Mauskopf, B. Rownd, L. Yuen, “Bolocam: a millimeter-wave bolometric camera,” in Advanced Technology MMW, Radio, and Terahertz Telescopes, T. G. Phillips, ed., Proc. SPIE3357, 326–334 (1998).
[CrossRef]

Zmuidzinas, J.

J. Glenn, J. J. Bock, G. Chattopadhyay, S. F. Edgington, A. E. Lange, J. Zmuidzinas, P. D. Mauskopf, B. Rownd, L. Yuen, “Bolocam: a millimeter-wave bolometric camera,” in Advanced Technology MMW, Radio, and Terahertz Telescopes, T. G. Phillips, ed., Proc. SPIE3357, 326–334 (1998).
[CrossRef]

Appl. Opt. (3)

Infrared Phys. (1)

J. A. Murphy, R. Padman, “Radiation patterns of few-moded horns and condensing lightpipes,” Infrared Phys. 31, 291–299 (1991).
[CrossRef]

Int. J. Infrared Millim. Waves (1)

J. C. Peterson, M. A. Goldman, “Reflectance of broad band waveguide bolometers,” Int. J. Infrared Millim. Waves 9, 55–69 (1988).
[CrossRef]

J. Appl. Phys. (1)

P. L. Richards, “Bolometers for infrared and millimeter waves,” J. Appl. Phys. 76, 1–24 (1994).
[CrossRef]

J. Opt. Soc. Am. (1)

Opt. Eng. (1)

R. H. Hildebrand, “Focal plane optics in far-infrared and submillimeter astronomy,” Opt. Eng. 25, 323–330 (1986).
[CrossRef]

Other (6)

C. R. Cunningham, W. K. Gear, W. D. Duncan, P. R. Hastings, W. S. Holland, “SCUBA: the submillimeter common-user bolometer array for the James Clerk Maxwell telescope,” in Instrumentation in Astronomy VIII, D. L. Crawford, E. R. Craine, eds., Proc. SPIE2198, 638–649 (1994).
[CrossRef]

J. Glenn, J. J. Bock, G. Chattopadhyay, S. F. Edgington, A. E. Lange, J. Zmuidzinas, P. D. Mauskopf, B. Rownd, L. Yuen, “Bolocam: a millimeter-wave bolometric camera,” in Advanced Technology MMW, Radio, and Terahertz Telescopes, T. G. Phillips, ed., Proc. SPIE3357, 326–334 (1998).
[CrossRef]

M. Griffin, L. Vigroux, B. Swinyard, “SPIRE: a bolometer instrument for FIRST,” in Advanced Technology MMW, Radio, and Terahertz Telescopes, T. G. Phillips, ed., Proc. SPIE3357, 404–413 (1998).
[CrossRef]

J. J. Bock, J. Glenn, S. M. Grannan, K. D. Irwin, A. E. Lange, H. G. LeDuc, A. D. Turner, “Silicon nitride micromesh bolometer arrays for SPIRE,” in Advanced Technology MMW, Radio, and Terahertz Telescopes, T. G. Phillips, ed., Proc. SPIE3357, 297–304 (1998).
[CrossRef]

High-Frequency Structure Simulator (HFSS), version A.04.01, Hewlett-Packard Company, Test and Measurement Organization, P.O. Box 50637, Palo Alto, Calif. 94303-9512.

S. E. Church, B. Philhour, A. E. Lange, P. A. R. Ade, B. Maffei, R. Nartallo-Garcia, M. Dragovan, “A compact high-efficiency feed structure for cosmic microwave background astronomy at millimeter wavelengths,” in Submillimetre and Far-Infrared Space Instrumentation, E. J. Rolfe, ed., Proceedings of the 30th ESLAB Symposium, ESA SP-388 (European Space Agency, Munich, 1996), pp. 77–80.

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Figures (6)

Fig. 1
Fig. 1

(a) Bolocam (214 GHz), manufactured at the Jet Propulsion Laboratory Micro Devices Laboratory, is composed of a silicon wafer 75 mm in diameter and 400 µm thick. It has 151 micromesh absorbers etched into it and semiconductor thermistors attached to each absorber. The absorber meshes and thermistors are too small to see in this rendering. (b) Geometry of a single 214-GHz bolometer integrating cavity seen in cross section edge-on. There are 144 integrating cavities in Bolocam, one for each bolometer in the array. The cavity is circularly symmetric about the axis of the waveguide. The aluminum feedhorn block (on top, containing the hollow waveguide) and Invar backshort plate were modeled as perfectly reflecting boundaries. There is no gap between the Invar backshort plate and the silicon wafer substrate. The absorber was modeled as an infinitely thin sheet with the appropriate surface impedance. The vacuum gap between the silicon wafer and the feedhorn block leads to adjacent cavities and was modeled as a radiation-absorbing boundary. The wafer used for cryogenic testing in Bolocam was 200 µm thick, so cylindrical pockets were milled in the Invar backing plate to form the λ/4 backshorts.

Fig. 2
Fig. 2

Configuration used for the HFSS simulations showing the ports and the boundaries in an oblique view. A magnetic symmetry wall was employed to take advantage of the structural symmetry and reduce the numerical computation time.

Fig. 3
Fig. 3

Simulated TE11 reflection (return loss) S 11 at port 1 as a function of absorber impedance. The absorber diameter was fixed at 2.0 mm. Maximum absorption occurs for a surface impedance of 400 Ω/sq.

Fig. 4
Fig. 4

Simulated reflection (return loss) S 11 at port 1 of the 3.0-mm-diameter cavity as a function of absorber diameter. The absorber impedance was fixed at 400 Ω/sq. For this cavity configuration, an absorber diameter of 2.0 mm affords a low return loss and a minimum absorber area.

Fig. 5
Fig. 5

Instantaneous electric field strengths |E| from the simulations. Red is maximum field strength and blue is minimum. The color stretches are linear. (a) TE11 mode propagating in the waveguide, with a cut along the waveguide axis. Absorption by the bolometer spanning the center of the cavity is apparent. (b) Distribution of the field strength in the plane of the absorber. |E| falls nearly linearly from the center of the cavity (waveguide axis) to the edges, which are defined by the silicon and upper cavity walls.

Fig. 6
Fig. 6

Scale model 90-GHz measurements of return loss as a function of frequency for a 4.8-mm-diameter absorber λ c /4 from the waveguide termination and backshort, 5.6-mm absorber λ c /4 from the waveguide termination and backshort, 4.8-mm absorber λ c /2 from the waveguide termination and backshort, and 5.6-mm absorber λ c /2 from the waveguide termination and backshort. It is clear that, with the absorbers present, the cavities are tuned for absorption with λ c /4 spacings and tuned for reflection with λ c /2 spacings.

Tables (1)

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Table 1 Summary of HFSS Simulations and Experimental Results

Equations (1)

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A=1-R-T=4gaZ0l2+gaZ0l2,

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