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Through-barrier sensing and imaging

Thru Barrier figure 1

Figure 1.  STG through-barrier sensing system, showing transceiver, electronics, and display (no moving taget).

Through-barrier sensing and imaging

The Security Technologies Group (STG) develops the metrology for through-barrier sensing and imaging technologies.  These nonmetal barriers may be ordered/structured, such as building walls, barricades, bridges, etc., or disordered, such as hedges and rubble.  Because the purpose is to sense or image through these barriers, the frequencies (or equivalently, the wavelengths) of the electromagnetic energy used in these imaging systems is relatively low, typically between 100 MHz and 5 GHz (or between 3 m and 0.06 m).  The lower frequencies typically have greater penetration through nonmetal barriers than the higher frequencies, but their spatial resolution is lower, which would affect image resolution.

Through-barrier Sensing

Through-barrier sensing, based on Doppler radar technology, is used to sense and locate (range, elevation angle, and azimuth angle) a target relative to the sensing system.  The NIST through-barrier sensing system (See. Fig. 1) is a pulse-Doppler system using a narrow-band swept-frequency source operating between about 500 MHz and 3.2 GHz.  The system comprises three wideband horn antennas, the source, and control and receive electronics.  The antennas are each dual polarization, have a 35° beamwidth, and a gain of about 12 dBi. The receive electronics employ a super-heterodyne method and the output of the second microwave mixer produces a baseband signal that is converted to a digital signal and subsequently processed. The computer controls all aspects of radar transmitted waveform, receiver characteristics, data acquisition, data processing, and data display and/or archival.  All pertinent pulse-Doppler-radar system parameters are adjustable, such as, pulse duration, pulse repetition interval, and transmitted power. 

Since the ultimate purpose is to identify humans behind optically-opaque barriers (see Fig. 2), we have investigated the detection limits of motion (see Fig. 3), in terms of the period motion of a simple test target.  These results are based on the motion of a 20-cm square aluminum plate, its large surface oriented to be perpendicular to the radar beam direction. The motion of the plate emulates the displacement and frequency of motion of a chest cavity caused by heartbeat and respiration.  We have, in collaboration with NIST building researchers, developed a library of interior and exterior walls (see Fig. 4) for measuring the effect of the detectability of a test object behind these barriers.

Through-barrier Imaging

The STG currently has a large rectilinear scanner, with an aperture of about 20 m (horizontal) by 8 m (vertical).  The image formed is by scanning a single radio frequency transceiver over this aperture.  The transceiver can be changed to support different imaging applications, such as nondestructive evaluation and testing of structural forms.  The image is formed using a holographic imaging technique developed by Pacific Northwest National Lab [Sheen, McKakin, and Hall].  The phenomenology of imaging through barriers is being studied to develop the measurement science that will support test method, test artifact, and data analysis development as well as to advance this technology and its field deployment.



  • Through-barrier sensing: motion detection limitations (2015)
  • Through-barrier sensing reference wall library (2016)
  • Through-barrier imaging lab completion (2017)

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Created October 3, 2017, Updated August 15, 2023