Abstract
This work presents, to our knowledge, the first completely passive imaging with human-body-emitted radiation in the lower THz frequency range using a broadband uncooled detector. The sensor consists of a Si CMOS field-effect transistor with an integrated log-spiral THz antenna. This THz sensor was measured to exhibit a rather flat responsivity over the 0.1–1.5-THz frequency range, with values of the optical responsivity and noise-equivalent power of around 40 mA/W and 42 pW/, respectively. These values are in good agreement with simulations which suggest an even broader flat responsivity range exceeding 2.0 THz. The successful imaging demonstrates the impressive thermal sensitivity which can be achieved with such a sensor. Recording of a 2.3 × 7.5-cm-sized image of the fingers of a hand with a pixel size of 1 mm at a scanning speed of 1 mm/s leads to a signal-to-noise ratio of 2 and a noise-equivalent temperature difference of 4.4 K. This approach shows a new sensing approach with field-effect transistors as THz detectors which are usually used for active THz detection.
Highlights
The recording of images of the human body in a passive manner, that is, using its own thermal radiation, is a well-established imaging modality in the infrared (IR) at wavelengths around 10 μm, where the black-body radiation of living beings is at its highest spectral intensity
This paper focuses on TeraFETs, THz detectors based on field-effect transistors (FETs) with integrated antennas
As a step further for this technology, we demonstrate here the first completely unaided passive imaging of a human hand with an uncooled TeraFET detector
Summary
The recording of images of the human body in a passive manner, that is, using its own thermal radiation, is a well-established imaging modality in the infrared (IR) at wavelengths around 10 μm, where the black-body radiation of living beings is at its highest spectral intensity. At IR wavelengths, detectors can be operated at room temperature. Into the THz and sub-THz regime, the power of the Planck radiation drops strongly, with the consequence that unaided passive detection at room temperature, typically using bolometers and microbolometer-based cameras as sensors [1,2,3], is impractical. Passive detection can be maintained at sub-THz frequencies when using superconducting sensor devices. Passive imaging with human-body radiation and penetration through various materials was shown for example at 350 GHz and 850 GHz using a detector array of 20 superconducting
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