Spatial resolutions and field-of-views in millimetre wave aperture synthesis security screening imagers

Salmon, Neil A.

doi:10.1117/12.2502925

Cited by 6 publications

(4 citation statements)

References 13 publications

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“…This means skin surrogates will be recognised even if they have exactly the same electrical properties as human skin. An active (coherent wave) illumination system will not have this capability, as it measures the reflectivity directly [7]. *amaniabubaha@gmail.com; The University of Manchester; mobile number +44 7402 939 756.…”

Section: Introductionmentioning

confidence: 99%

Variation in the electromagnetic signatures of the human skin with physical activity and hydration level of the skin

Owda

Salmon

2019

Millimetre Wave and Terahertz Sensors and Technology XII

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Our recent studies in the human skin signatures indicate a strong correlation between the human skin emissivity and factors such as the body mass index, the gender, the age, and the ethnicities of the participants. The key innovation in this is in recognising that signatures from the human body enable regions of the body to be identified as skin. This will enable increased the detection probabilities of anomalies, and reduced the false alarm rates in security screening portals. This is a capability that is being demanded internationally by governments and in the UK by the Home Office Future Aviation Security Solutions (FASS) programme and the Joint Security and Resilience Centre (JSaRC). In this paper, radiometric measurements conducted on human skin in the millimetre wave band region (80-100) GHz show variation in the human skin emissivity before and after conducting physical activity (jogging) subject to the same participant. The measurements were conducted on the palm of the hand and the back of the hand skin. The measurements reveal that the emissivity of the skin is significantly lower in the rest state of the body compared with the active state by mean values of 0.088 and 0.07 for the palm of the hand and the back of the hand skin respectively. The differences in the mean emissivity values were found to be linked to the length of time exercising and the hydration level of the skin i.e. (sweat). Radiometric measurements on palms of the hand and on the back of the hand skin before and after the application of an aqueous gel indicate a strong correlation between the human skin signature and the hydration level of the skin. The mean differences in emissivity values before and after the application of an aqueous gel indicate a scatter in the range of 0.02 to 0.26. These findings suggested trends in the human skin emissivity and indicate the potential of a new non-contact passive method for remote sensing of the physical state of human beings. Understanding these signatures and variations of the human skin emissivity are very important for both security screening (anomalies detection) and medical applications (non-invasive diagnosis of human body).

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Section: Introductionmentioning

confidence: 99%

Variation in the electromagnetic signatures of the human skin with physical activity and hydration level of the skin

Owda

Salmon

2019

Millimetre Wave and Terahertz Sensors and Technology XII

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“…This is due to the capability of MMW to penetrate dielectric materials such as fabric and textiles [1,2,3] and detect concealed metal and non-metallic threats. In addition, the spatial resolution, down to scale lengths of ~1.0 mm in a diffraction-limited system [4,5], is sufficient to identify many forbidden items. These properties make MMW radiation suitable for scanning people in airports [6,7], sensing hidden objects under clothing materials [8,9], and military applications [10].…”

Section: Introductionmentioning

confidence: 99%

A three-layer model for investigating the effect of clothing made of fleece, denim, and leather on the interaction of millimetre wave radiation on the skin

Owda,

Salmon,

Owda

2023

Emerging Imaging and Sensing Technologies for Security and Defence VIII

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This paper proposes a three-layer electromagnetics model for investigating the interaction of millimetre wave radiation with human skin and clothing as a means to improve security screening technology. Progress in this spectral band is only possible with a deep understanding of the interaction of this radiation with the human body, the clothing and threat items; the proposed model in this paper is implemented to provide us with this information. The model consists of three layers namely, 1) air (a semi-infinite layer and lossless layer), 2) clothing layer (finite thickness layer ranging from 0.0 mm-1.2 mm), and 3) skin layer (semi-infinite layer). Three types of clothing are investigated by the model, these being: 1) Fleece, 2) Denim, and 3) Leather. Simulation results indicate that a clothing layer, in direct contact with human skin, enhances the transmission of radiation between air and skin. This is due to the clothing layer acting as an impedance matching transformer. The simulation results indicate that the power transmission coefficient varies with the frequency and thickness of the clothing layer. For the Fleece, the power transmission coefficient was found to increase fractionally, ranging from 0.05 to 0.112 at 90 GHz when the thickness of the fleece varied between 0.5mm and 1.2 mm. For the Denim, the difference in the transmission coefficient was found to increase with the thickness of the Denim, up to a factor of 0.095, when the thickness of the Denim layer varied from 0.5 mm to 1.2 mm at 60 GHz. For the beige leather, the variation in the transmission coefficient between different thicknesses was substantial and it could be up ~10.0% when the thickness of the material varied from 0.5 mm to 1.0 mm at 60 GHz. However, when the thickness of the leather was 1.2 mm, the maximum value of the transmission coefficient of 0.83 was achieved at around 45 GHz. Simulation results obtained from the three-layer model presented in this paper are in good agreement with the measurements reported in the literature reviews at specific frequencies. The importance of having such a validated model is that security screening system parameters can be optimised with a minimal amount of costly trials and experimentation.

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“…The visibility function is formed from the cross-correlations of electric fields measured from pairs of receivers. It is calibrated in the near-field by putting a phase centre in the centre of the 3-D field-of-view (FOV), whereas for 2-D radio astronomy this is normally put at infinity [18,20]. Numerical simulations indicate that if a subject is surrounded by receivers, the Abbe microscope spatial resolution for incoherent imaging [21] of half a wavelength may be achieved in 3-D, which may be improved upon if auxiliary information is provided [15,20].…”

Section: Introductionmentioning

confidence: 99%

The Effects of Obscuration in Passive 3-D Millimeter-wave Imaging for Human Security Screening

Sun¹,

Salmon²,

Zhuge³

et al. 2023

PIER

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The possibility of near-field passive 3-D imaging using the aperture synthesis technique is theoretically proven and highlights the opportunity for imaging the entire human body by an antenna receiving array that surrounds the body. In these scenarios there will be partial obscuration of some regions of the body, by other parts of the body. This results in some receivers in the array being able to measure emission from certain parts of the body, while others are obscured from a measurement. A model is presented which enables the effects of obscuration to be assessed for planar-like, cylindrical-like, and concave-like regions of the human body. The effect the obscuration has on the spatial resolution of the imager is evaluated by examining the 3-D point spread function, as determined by a near-field aperture synthesis imaging algorithm. It is shown that over many areas of the human body, the Abbe microscope resolution of λ/2 (5 mm@30 GHz) in a direction transverse to the human body surface is achievable, an attractive proposition for security screening. However, the spatial resolution in a direction normal to the human body surface is shown to be close to λ (10 mm@30 GHz). In regions of greater obscuration, such as in the armpits, the resolution may fall to λ (10 mm@30 GHz) and 5λ (50 mm@30 GHz) in the directions transverse and normal to the human body surface, respectively. It is also shown by simulation using a human body solid model and the 3-D aperture synthesis imaging algorithm how the image quality changes with the number of receiving antennas.

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Spatial resolutions and field-of-views in millimetre wave aperture synthesis security screening imagers

Cited by 6 publications

References 13 publications

Variation in the electromagnetic signatures of the human skin with physical activity and hydration level of the skin

Variation in the electromagnetic signatures of the human skin with physical activity and hydration level of the skin

A three-layer model for investigating the effect of clothing made of fleece, denim, and leather on the interaction of millimetre wave radiation on the skin

The Effects of Obscuration in Passive 3-D Millimeter-wave Imaging for Human Security Screening

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