I. PARTICIPANTS · Imaging is ongoing. Fully automatic 3D imaging with material characterization will be pursued during the fall of 2019 (Year 7). Operational control software and

I. PARTICIPANTS

Mohammad Nemati PhD NEU 6/2020 Mahshid Asri MS NEU 6/2020

Muhammad Ghafoor BS NEU 5/2021

Anthony Englert BS UMass Amherst 5/2021 Samuel Kebadu BS George Mason Univ. 5/2021 Emily Belk BS NEU 5/2022 Thomas Campion BS NEU 5/2022

II. PROJECT DESCRIPTION

A. Project Overview

We have been developing a custom-designed Advanced Imaging Technology (AIT) person-scanning system that represents the next generation of airport and other secure-area concealed object detectors. The currently employed systems are omnipresent in U. S. and worldwide [1-4]. This project is continuing to test an advanced millimeter wave (mm-wave) radar whole body AIT imaging system using a custom-designed elliptical toroid reflector which allows multiple overlapping beams for focused wide-angle illumination to speed data acquisition and accurately image strongly inclined body surfaces. Building on the concepts and analysis of project R3-A.1 [9-11], we have extended the Blade Beam Reflector from a single illuminating antenna into a multi-beam Toroidal Reflector, with multiple feeds. Each feed generates a different incident beam with different viewing angles, while still maintaining the blade beam configuration of narrow slit illumination in the vertical direction. Having multiple transmitters provides horizontal resolution and imaging of full 120 deg. of body. Furthermore, the reflector can simultaneously be used for receiving the scattered field, with high gain, overlapping, high vertical resolution beams for each transmitting or receiving array element. The multistatic transmitting and receiving array configuration sensing avoids dihedral artifacts from body crevices and reduces non-specular drop-outs [5, 6].

We have extended the toroidal reflector-based system from a single fixed transmitter (Tx), swinging arc receiver (Rx) design, to a fixed array of seven transmitters with overlapping coverage (Fig. 1). We are poised to test the 56 Rx fixed array. The designs for the fixed array of receivers are shown in Figure 2. This

ALERT Phase 2 Year 6 Annual Report

Appendix A: Project Reports Thrust R3: Bulk Sensors & Sensor Systems

Project R3-A.3

configuration is the result of many man-hours of work: (i) we minimized the spacing while maintaining the appropriate distance between elements to mimic the performance of an array with about ⅓ as many elements as previous studies; (ii) we positioned transmitters to minimally block receivers, keeping the antenna elements close enough to the mathematically ideal focal arc while allowing for assembly and fine-tuning for real-world optimal repositioning; (iii) we solidly supported the radar module boards in high temperature conditions to ensure that the multistatic signals are received strongly for all target positions from -50 to 50 degrees, and (iv) we designed to allow for heat sink attachments. We have simplified the cabling and positioning infrastructure for easy and fast channel assignment.



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The RF radar modules have been separated from the signal addressing and conditioning circuit boards. This lengthy redesign was necessitated by the new module configuration provided by the sole chip vendor. Four Rx chips along with their individual antennas have been incorporated into a single board, and their four separate channels have been incorporated into a “motherboard.” By separating the RF modules on a separate board, the receivers can be packed closer together. Figure 3 shows the quad RF receiver board layout, which has been custom designed for our specific application. Figure 4 shows the corresponding quad motherboard. With multiple design and debugging iterations, we feel that we have the closest possible spacing of elements for the fixed array design. Using a previously reported computationally optimized Tx/Rx array configuration, we will be able to form a rapid scanning multi-static radar with high parallel processing abilities.



Project R3-A.3

B. State of the Art and Technical Approach

The toroidal reflector antenna images in the horizontal plane, and translates vertically. As such it acquires signals faster and is prone to fewer mechanical alignment, ruggedness, and wear operation than 2D raster scan systems [7, 8]. Having multiple transmitters provides horizontal resolution and imaging of a full 120 degrees of body. In practice, a second reflector and feed array would be used for the other side of the subject under test. Each reflector can simultaneously be used for receiving the scattered field with high gain, overlapping, high vertical resolution beams for each transmitting or receiving array element. The multistatic transmitting and receiving array configuration sensing avoids dihedral artifacts from body crevices and reduces non-specular drop-outs that are present with existing fielded AIT systems [5, 6].

B.1. Imaging Results

In Year 6, we produced images using all seven third generation (Gen-3) transmitters and a single rotating Gen-3 receiver, along with the synthetic aperture radar (SAR) algorithm developed in project R3-A.2. The air duct torso simulant with attached metal and dielectric (explosive simulant [22-23]) bars were imaged as seen in Figure 5 [12-19]. This image represents a 2D horizontal slice of the middle of the air duct in Figure



Project R3-A.3

1, with targets attached with black electrical tape. The y-axis represents range from the radar sensor and the x-axis represents cross range, with illumination coming from below. With seven transmitters working in sequence, almost the entire front surface of the torso is illuminated and reconstructed. We use the Radon/inverse Radon transform reported in past years to fill in the high spatial frequency image jitter. The metal target on the right side of the torso image is clearly imaged with relatively sharp corners and pronounced protrusion toward the radar, while the dielectric target produces the characteristic discontinuity and depression in the torso surface on the right side of the duct image.

Multiple images at different heights are then stacked, interpolated, and displayed as a 2D surface of the 3D torso in Figure 6, with color corresponding to range from the radar sensor.

Figure 7 shows imaging [20, 21] with a realistic body geometry. Using sprayed-on radio frequency conductive paint, the nominally non-reflective manikin is altered to respond to incident microwave radiation much the same as human skin (Fig. 7a). The geometry is clearly representative of an ideal human body surface, and with reflective paint, it becomes an effective microwave human simulant. Simulating the concavity of the upper chest (as shown in Fig. 7b) or the response from the body with a foreign object (Fig. 7c) relative to just the body response (Fig. 7d) to the can be a challenging task, but these responses allow for



Project R3-A.3

foreign object characterization, showing very different reconstructions for metal and weak dielectrics. These responses rule out non-threatening concealed objects, which image as less distinct anomalies.

C. Major Contributions

Development of elliptical torus reflector for overlapping multi-beam transmission and reception for multistatic operation (2013).

Fabrication of reflector and experimental proof of principle (2014).

Multistatic imaging with elliptical torus using original Tx/Rx chipset (2015).

Design of 60 GHz multistatic radar Tx and Rx modules, including separated mother board/daughter board configuration, as demanded by manufacturer revised specification (2016).



Project R3-A.3

Design of separated 60 GHz wideband microstrip antenna (2017).

Fabrication and testing of RF single Tx/Rx boards (2018).

Debugging and imaging using individual RF Tx/Rx boards (2019).

Design and fabrication of quad Rx motherboard and daughter board to minimize packaging and cabling (2019).

D. Milestones

We completed most of the planned measurements and reconstructions halfway through Year 6. This represents the culmination of seven years of effort: identifying ways of improving the general AIT portal concept, reducing imaging artifacts, speeding up data acquisition and image reconstruction, and improving the materials characterization of concealed foreign objects.

Working in the retooling delay, we have implemented low-cost RF hardware and successfully tested and optimized its performance. The sparse array support structure has been designed, built, and fitted with RF boards. Measurements and reconstruction (with the help of Project R3-A.2) are ongoing.

The full sparse transmit array has been fabricated, with feed positions optimized, and fully tested. Imaging is ongoing. Fully automatic 3D imaging with material characterization will be pursued during the fall of 2019 (Year 7).

Operational control software and self-contained reconstruction code have been developed to minimize operator intervention. The previous form of the system required numerous instructions from an operator. Each of these are being streamlined with appropriate engineering, preferably with help from system vendors with experience in these aspects.

E. Future Plans/Project Completion (Year 7)

Before the AIT portal system can be released for field testing and possible certification, it must be configured for operation with minimal operator involvement. Error trapping and automatic correction will be implemented. Unusual body shapes and sizes, along with difficult object cases, must be tested and evaluated.

Fully automatic scanning with material characterization is the goal for June 2020. This involves improving RF hardware reliability and imaging repeatability, creating accurate positioning and mounting of the fixed sparse receiver array, and optimizing algorithm development for multi-transmitter imaging.

The extension of the 2D On-the-Move hallway scanner to a full 3D version must wait until the next funding period (Year 8), should funding become available. Developing this extension is a major project: conceiving the best radar module layout, optimizing 3D reconstruction algorithms, testing the system with computational simulation, purchasing radar and signal acquisition hardware, developing means of stitching together reconstructions from various poses, validation with phantoms, and eventual testing on walking humans.



Project R3-A.3

III. RELEVANCE AND TRANSITION

A. Relevance of Research to the DHS Enterprise

The multistatic radar configuration employed in Project R3-A.3 extends imaging performance by giving multiple views of each body surface pixel and helps eliminate dihedral artifacts. Reducing false alarms, improving resolution, providing material characterization, reducing scan time, and lowering costs are all important aspects of value to the Homeland Security Enterprise (HSE).

B. Potential for Transition and Transition Pathway

The Transportation Security Administration (TSA) is interested in the new technology, so they have offered to test a prototype at the Transportation Security Laboratory (TSL), hopefully after Year 6. Should tests prove successful and the scanner is shown to be superior, we will offer to partner with existing AIT manufacturers, such as L-3 Communication and Smiths Detection, or companies that are exploring entering the AIT market, such as Rapiscan Systems or Morpho Technology.

We are developing a joint project with Smiths Detection on adapting a new product line using dual frequency wideband radar as a means of reducing packaging complexity and cost. Using multiplication of the individual radar point spread functions, the imaging resolution can be improved significantly.

C. Data and/or IP Acquisition Strategy

The dual frequency PSF multiplication concept is patentable, and IP will be pursued.

D. Customer Connections

Regular telephone meetings have been held with Claudius Volz, Christoph Weiskopf, Michel Henning, Christopher Gregory, Maryann Tabacco, and Rory Doyle at Smiths Detection. (Wiesbaden, Germany; Cork, Ireland; Edgewood, MD; and Boston, MA).

IV. PROJECT ACCOMPLISHMENTS AND DOCUMENTATION

A. Education and Workforce Development Activities

1. Student Internship, Job, and/or Research Opportunities:

a. REU student interns (Summer 2018): Anthony Englert and Samuel Kebadu

B. Other Presentations

1. Seminars

a. Rappaport, C. “Multistatic 3D Whole Body Millimeter-Wave Imaging for Explosives Detection.” IEEE Distinguished Lecturer speech, Arizona State University, Tempe, AZ, November 1, 2018.

C. Technology Transfer/Patents

1. Patents Awarded

a. 10,295,644 (with Gonzalez Valdes, and Martinez-Lorenzo), On-the-Move Millimeter Wave Interrogation System with a Hallway of Multiple Transmitters and Receivers, 21 May, 2019.



Project R3-A.3

V. REFERENCES

[1] J. Skorupski and P. Uchro´nski, “Evaluation of the effectiveness of an airport passenger and baggage security screening system,” Journal of Air Transport Management, vol. 66, pp. 53–64, 2018.

[2] R. Sakano, K. Obeng, and K. Fuller, “Airport security and screening satisfaction: A case study of us,” Journal of Air Transport Management, vol. 55, pp. 129–138, 2016.

[3] A. Knol, A. Sharpanskykh, and S. Janssen, “Analyzing airport security checkpoint performance using

cognitive agent models,” Journal of Air Transport Management, vol. 75, pp. 39–50, 2019. [4] A. Pala and J. Zhuang, “Security screening queues with impatient applicants: A new model with a case

study,” European Journal of Operational Research, vol. 265, no. 3, pp. 919–930, 2018. [5] D. M. Sheen, D. L., McMakin, T. E. Hall, “Combined illumination cylindrical millimeter-wave imaging

technique for concealed weapon detection,” AeroSense, International Society for Optics and Photonics, pp. 52-60, July 2000.

[6] D. M. Sheen, D. L. McMakin, and T. E. Hall, “Three-dimensional millimeter-wave imaging for concealed

weapon detection,” IEEE Transactions on microwave theory and techniques, vol. 49, no. 9, pp. 1581–1592, 2001.

[7] Cooper, K.B.; Dengler, R.J.; Llombart, N.; Thomas, B.; Chattopadhyay, G.; Siegel, P.H., "THz Imaging Radar

for Standoff Personnel Screening," IEEE T. Terahertz Science and Technology, , vol.1, no.1, pp.169-182, Sept. 2011.

[8] Roe, K. and Gregory, C., "Wave-based sensing and imaging for security applications," 2015 9th European

Conference on Antennas and Propagation (EuCAP), Lisbon, 2015, pp. 1-5. [9] Rappaport, C.M.; Gonzalez-Valdes, B., "The blade beam reflector antenna for stacked nearfield

millimeter-wave imaging," IEEE Antennas and Propagation Society Int’l Symp. , vol., no., pp.1-2, 8-14 July 2012.

[10] B. Gonzalez-Valdes, Y. Alvarez, J. A. Martinez, F. Las-Heras, C. M. Rappaport, “On the Use of Improved

Imaging Techniques for the Development of a Multistatic Three-Dimensional Millimeter-Wave Portal for Personnel Screening,” Progress In Electromagnetics Research, PIER, Vol. 138, pp. 83-98, 2013.

[11] Alvarez, Y.; Gonzalez-Valdes, B.; Angel Martinez, J.; Las-Heras, F.; Rappaport, C.M., "3D Whole Body

Imaging for Detecting Explosive-Related Threats," IEEE T. Antennas and Propagation, vol.60, no.9, pp. 4453,4458, Sept. 2012.

[12] Y.Alvarez, B. Gonzalez-Vaedes, J. A. Martinez-Lorenzo, C. M. Rappaport, and F. Las-Heras, “SAR imaging

based techniques for low permittivity lossless dielectric bodies characterization,” IEEE Antennas and Propagation Magazine, vol. 57, no. 2, pp. 267–276, 2015.

[13] S. Alekseev and M. Ziskin, “Human skin permittivity determined by millimeter wave reflection

measurements,” Bioelectromagnetics, vol. 28, pp. 331–9, 07 2007. [14] S. I Alekseev, A. Radzievsky, M. Logani, and M. C Ziskin, “Millimeter wave dosimetry of human skin,”

Bioelectromagnetics, vol. 29, pp. 65–70, 01 2008.



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[15] M. Sadeghi, E. Wig, A. Morgenthaler, and C. Rappaport, “Modeling the response of dielectric slabs on ground planes using cw focused millimeter waves,” in 2017 11th European Conference on Antennas and Propagation (EUCAP), March 2017, pp. 759–763.

[16] M. Sadeghi and C. Rappaport, “Virtual source model for ray-based analysis of focused wave scattering of

a penetrable slab on pec ground plane,” in 2018 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting. IEEE, 2018, pp. 1177–1178.

[17] M. Sadeghi, E. Wig, and C. Rappaport, “Determining the dielectric permittivity and thickness of a

penetrable slab affixed to the human body using focused cw mm-wave sensing,” in 2018 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting. IEEE, 2018, pp. 621–622.

[18] M. Sadeghi, “Characterization of penetrable dielectric slab affixed to the human body using focused cw

mm-waves,” Master’s thesis, Northeastern University, 2018. [19] E. Wig and C. Rappaport, “Modeling focused ray scattering by a penetrable dielectric slab over skin

surface with a finite air gap for millimeter-wave person scanning,” in 2018 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting. IEEE, 2018, pp. 1335–1336.

[20] D. J. Griffiths, “Introduction to electrodynamics,” 2005. [21] D. H. Staelin, A. W. Morgenthaler, and J. A. Kong, Electromagnetic Waves. Pearson Education, 1994. [22] A. L. Higginbotham Duque, W. L. Perry, and C. M. Anderson-Cook, “Complex microwave permittivity of

secondary high explosives,” Propellants, Explosives, Pyrotechnics, vol. 39, no. 2, pp. 275–283, 2014. [Online].

[23] A. R. von Hippel and S. O. Morgan, “Dielectric materials and applications,” Journal of The Electrochemical

Society, vol. 102, p. 68C, 01, 1955.



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Documents

I. PARTICIPANTS · Imaging is ongoing. Fully automatic 3D imaging with material characterization will be pursued during the fall of 2019 (Year 7). Operational control software and