Spectral Signature

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Paul D Ledger - One of the best experts on this subject based on the ideXlab platform.

  • identification of metallic objects using Spectral mpt Signatures object characterisation and invariants
    International Journal for Numerical Methods in Engineering, 2021
    Co-Authors: Paul D Ledger, Ben A Wilson, Alan A S Amad, William R B Lionheart
    Abstract:

    The early detection of terrorist threats, such as guns and knives, through improved metal detection, has the potential to reduce the number of attacks and improve public safety and security. To achieve this, there is considerable potential to use the fields applied and measured by a metal detector to discriminate between different shapes and different metals since, hidden within the field perturbation, is object characterisation information. The magnetic polarizability tensor (MPT) offers an economical characterisation of metallic objects that can be computed for different threat and non-threat objects and has an established theoretical background, which shows that the induced voltage is a function of the hidden object's MPT coefficients. In this paper, we describe the additional characterisation information that measurements of the induced voltage over a range of frequencies offer compared to measurements at a single frequency. We call such object characterisations its MPT Spectral Signature. Then, we present a series of alternative rotational invariants for the purpose of classifying hidden objects using MPT Spectral Signatures. Finally, we include examples of computed MPT Spectral Signature characterisations of realistic threat and non-threat objects that can be used to train machine learning algorithms for classification purposes.

  • efficient computation of the magnetic polarizabiltiy tensor Spectral Signature using proper orthogonal decomposition
    International Journal for Numerical Methods in Engineering, 2021
    Co-Authors: Ben A Wilson, Paul D Ledger
    Abstract:

    Our interest lies in the identification of hidden conducting permeable objects from measurements of the perturbed magnetic field in metal detection taken over range of low frequencies. The magnetic polarizability tensor (MPT) provides a characterisation of a conducting permeable object using a small number of coefficients, has explicit formula for their calculation and a well understood frequency behaviour, which we call its Spectral Signature. However, to compute such Signatures, and build a library of them for object classification, requires repeated solution of a direct (full order) problem, which is typically accomplished using a finite element discretisation. To overcome this issue, we propose an efficient reduced order model (ROM) using a proper orthogonal decomposition (POD) for the rapid computation of MPT Spectral Signatures. Our ROM benefits from output certificates, which give bounds on the accuracy of the predicted outputs with respect to the full order model solutions. To further increase the efficiency of the computation of the MPT Spectral Signature, we provide scaling results, which enable an immediate calculation of the Signature under changes in the object size or conductivity. We illustrate our approach by application to a range of homogenous and inhomogeneous conducting permeable objects.

Ben A Wilson - One of the best experts on this subject based on the ideXlab platform.

  • identification of metallic objects using Spectral mpt Signatures object characterisation and invariants
    International Journal for Numerical Methods in Engineering, 2021
    Co-Authors: Paul D Ledger, Ben A Wilson, Alan A S Amad, William R B Lionheart
    Abstract:

    The early detection of terrorist threats, such as guns and knives, through improved metal detection, has the potential to reduce the number of attacks and improve public safety and security. To achieve this, there is considerable potential to use the fields applied and measured by a metal detector to discriminate between different shapes and different metals since, hidden within the field perturbation, is object characterisation information. The magnetic polarizability tensor (MPT) offers an economical characterisation of metallic objects that can be computed for different threat and non-threat objects and has an established theoretical background, which shows that the induced voltage is a function of the hidden object's MPT coefficients. In this paper, we describe the additional characterisation information that measurements of the induced voltage over a range of frequencies offer compared to measurements at a single frequency. We call such object characterisations its MPT Spectral Signature. Then, we present a series of alternative rotational invariants for the purpose of classifying hidden objects using MPT Spectral Signatures. Finally, we include examples of computed MPT Spectral Signature characterisations of realistic threat and non-threat objects that can be used to train machine learning algorithms for classification purposes.

  • efficient computation of the magnetic polarizabiltiy tensor Spectral Signature using proper orthogonal decomposition
    International Journal for Numerical Methods in Engineering, 2021
    Co-Authors: Ben A Wilson, Paul D Ledger
    Abstract:

    Our interest lies in the identification of hidden conducting permeable objects from measurements of the perturbed magnetic field in metal detection taken over range of low frequencies. The magnetic polarizability tensor (MPT) provides a characterisation of a conducting permeable object using a small number of coefficients, has explicit formula for their calculation and a well understood frequency behaviour, which we call its Spectral Signature. However, to compute such Signatures, and build a library of them for object classification, requires repeated solution of a direct (full order) problem, which is typically accomplished using a finite element discretisation. To overcome this issue, we propose an efficient reduced order model (ROM) using a proper orthogonal decomposition (POD) for the rapid computation of MPT Spectral Signatures. Our ROM benefits from output certificates, which give bounds on the accuracy of the predicted outputs with respect to the full order model solutions. To further increase the efficiency of the computation of the MPT Spectral Signature, we provide scaling results, which enable an immediate calculation of the Signature under changes in the object size or conductivity. We illustrate our approach by application to a range of homogenous and inhomogeneous conducting permeable objects.

Bodil Gesslein - One of the best experts on this subject based on the ideXlab platform.

  • unique Spectral Signature of human cutaneous squamous cell carcinoma by photoacoustic imaging
    Journal of Biophotonics, 2020
    Co-Authors: Jenny Hult, Ulf Dahlstrand, Aboma Merdasa, Karin Wickerstrom, Rehan Chakari, Bertil Persson, Magnus Cinthio, Tobias Erlov, John Albinsson, Bodil Gesslein
    Abstract:

    Cutaneous squamous cell carcinoma (cSCC) is a common skin cancer with metastatic potential. To reduce reoperations due to nonradical excision, there is a need to develop a technique for identification of tumor margins preoperatively. Photoacoustic (PA) imaging is a novel imaging technology that combines the strengths of laser optics and ultrasound. Our aim was to determine the Spectral Signature of cSCC using PA imaging and to use this Signature to visualize tumor architecture and borders. Two-dimensional PA images of 33 cSCCs and surrounding healthy skin were acquired ex vivo, using 59 excitation wavelengths from 680 to 970 nm. The Spectral response of the cSCCs was compared to healthy tissue, and the difference was found to be greatest at wavelengths in the range 765 to 960 nm (P <.05). Three-dimensional PA images were constructed from spectra obtained in the y-z plane using a linear stepper motor moving along the x-plane. Spectral unmixing was then performed which provided a clear three-dimensional view of the distribution of tumor masses and their borders. (Less)

Ferran Martin - One of the best experts on this subject based on the ideXlab platform.

  • multistate multiresonator Spectral Signature barcodes implemented by means of s shaped split ring resonators s srrs
    IEEE Transactions on Microwave Theory and Techniques, 2017
    Co-Authors: Cristian Herrojo, Ferran Paredes, Javier Matacontreras, Simone Zuffanelli, Ferran Martin
    Abstract:

    Spectral Signature barcodes functional at the $S$ frequency band are presented in this paper. The barcodes are implemented by loading a coplanar waveguide transmission line by means of multiple S-shaped split ring resonators (S-SRRs), each one tuned to a different frequency. The main particularity of this paper is the fact that more than two logic states (i.e., three or four, depending on the implementation) are assigned to each resonant element. By this means, the total number of bits of the barcode (for a given number of resonators) is increased, as compared with previous approaches based on two logic states per resonator. This multistate functionality is achieved by rotating the S-SRRs. Such rotation modulates the line-to-resonator coupling intensity, and consequently the notch depth at the S-SRR fundamental resonance. Therefore, by considering three or four fixed rotation angles (or orientations) between the line axis and the S-SRR (for the tri- and four-state multiresonator barcodes, respectively), intermediate levels between the maximum and minimum attenuation are achieved. This multistate strategy only exploits a single frequency per resonant element (the fundamental one). Therefore, the data capacity per bandwidth are improved as compared with two-state-based barcodes or to multistate barcodes that use two frequencies per resonant element. As illustrative examples, two different four-state multiresonator barcodes with eight S-SRRs (providing $4^{8}= 65.536$ different codes, or 16 bits) and with nine S-SRRs (equivalent to 18 bits), occupying a Spectral bandwidth of 1 GHz and less than 6.75 and 8.2 cm2, respectively, are designed, fabricated, and characterized.

  • Spectral Signature barcodes implemented by multi state multi resonator circuits for chipless rfid tags
    International Microwave Symposium, 2016
    Co-Authors: Cristian Herrojo, Jordi Naqui, Ferran Paredes, Ferran Martin
    Abstract:

    This paper presents the first Spectral Signature barcodes, operative at the S frequency band, implemented by means of multi-state resonators, each one able to provide more than 1-bit of information using a single frequency. The barcodes consist of a coplanar waveguide transmission line loaded with S-shaped split ring resonators (S-SRR), which are etched in the back substrate side. The S-SRRs are electrically small, hence providing compact size to the barcode. Moreover, and most important, each S-SRR provides three or four logic states for the tri-state and the four-state multi-resonator based barcode, respectively. This multi-state functionality is achieved by rotating the S-SRRs. By this means, the coupling level between the line and the resonator is controlled, and the notch depth in the transmission coefficient at the S-SRR resonance can thus be set to intermediate levels between the maximum and minimum rejection. This is a clear improvement as compared to previous bi-state (1-bit) resonator based barcodes, where the logic states ‘0’ and ‘1’ are achieved by the presence or absence of notch. This work also represents a progress as compared to other approaches of multi-state resonators that exploit their two first resonance frequencies (hence allowing for size reduction but not for an improvement of data capacity in a given bandwidth). As illustrative example, a tri-state resonator based barcode with 10 resonators (giving 310 = 59.049 different codes, or more than 15 bits) and 1 GHz Spectral bandwidth is designed and fabricated. An approach to achieve four states (2-bits) per resonator is also discussed.

  • Spectral Signature barcodes based on s shaped split ring resonators s srrs
    EPJ Applied Metamaterials, 2016
    Co-Authors: Cristian Herrojo, Jordi Naqui, Ferran Paredes, Ferran Martin
    Abstract:

    In this paper, it is shown that S-shaped split ring resonators (S-SRRs) are useful particles for the implementation of Spectral Signature (i.e., a class of radiofrequency) barcodes based on coplanar waveguide (CPW) transmission lines loaded with such resonant elements. By virtue of its S shape, these resonators are electrically small. Hence S-SRRs are of interest for the miniaturization of the barcodes, since multiple resonators, each tuned at a different frequency, are used for encoding purposes. In particular, a 10-bit barcode occupying 1 GHz Spectral bandwidth centered at 2.5 GHz, with dimensions of 9 cm2 , is presented in this paper.

William R B Lionheart - One of the best experts on this subject based on the ideXlab platform.

  • identification of metallic objects using Spectral mpt Signatures object characterisation and invariants
    International Journal for Numerical Methods in Engineering, 2021
    Co-Authors: Paul D Ledger, Ben A Wilson, Alan A S Amad, William R B Lionheart
    Abstract:

    The early detection of terrorist threats, such as guns and knives, through improved metal detection, has the potential to reduce the number of attacks and improve public safety and security. To achieve this, there is considerable potential to use the fields applied and measured by a metal detector to discriminate between different shapes and different metals since, hidden within the field perturbation, is object characterisation information. The magnetic polarizability tensor (MPT) offers an economical characterisation of metallic objects that can be computed for different threat and non-threat objects and has an established theoretical background, which shows that the induced voltage is a function of the hidden object's MPT coefficients. In this paper, we describe the additional characterisation information that measurements of the induced voltage over a range of frequencies offer compared to measurements at a single frequency. We call such object characterisations its MPT Spectral Signature. Then, we present a series of alternative rotational invariants for the purpose of classifying hidden objects using MPT Spectral Signatures. Finally, we include examples of computed MPT Spectral Signature characterisations of realistic threat and non-threat objects that can be used to train machine learning algorithms for classification purposes.