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Security-Oriented Sensors

#G-1644


Security-Oriented New Ultra-High Frequency Devices

Tech Area / Field

  • INF-SIG/Sensors and Signal Processing/Information and Communications
  • INF-ELE/Microelectronics and Optoelectronics/Information and Communications

Status
3 Approved without Funding

Registration date
21.05.2008

Leading Institute
Tbilisi State University, Georgia, Tbilisi

Collaborators

  • Rensselaer Polytechnic Institute, USA, NY, Troy\nFraunhofer Institute Zerstörungsfreie Prüfverfahren, Germany, Saarbrücken\n[Individual specialist]

Project summary

Among technical means to prevent terrorist acts special place is occupied by various detection devices and sensor systems. For this purpose, different devices and microcircuits of solid state electronics are used.

Sensors in which the groundwork of detection is based on the changes in electromagnetic wave characteristics (amplitude, phase) when propagating in media with different electrical parameters (e.g. permittivity, permeability or electrical conductivity) are turned out to be very productive Sensor systems built on this principle are used to detect people and luggage for concealed weapon and explosives, for example, in airports and other places of people accumulation. The biggest volume of information is given by 3D imaging of a concealed target with good side and depth resolution. In this context millimeter-wave sensor systems are rather promising. It should also mentioned that today such systems have been perfectly developed and are very close to industrial realization. Besides the resolution, important aspects also are the imaging time, the possibility to create portable systems and cut down their cost.

Ultrahigh frequency radiation (300-3000GHz) has much lower wavelength and, hence, can provide submillimeter spatial resolution which makes them even more attractive for imaging applications.However, at present, sensors operating in subterahertz and terahertz frequency ranges are at the stage of investigations.

In quadrature microwave sensors (MS) which are being studied and developed most intensively the RF signal is converted to a real (I) and imaginary (Q) parts either directly, or at an intermediate frequency. Accordingly, so-called homodyne or heterodyne MS configurations are used. The heterodyne configuration includes two oscillators (RF and local) and the I-Q demodulation is carried out at an intermediate frequency. The homodyne configuration is based on the direct conversion of the reflected RF signal to real and imaginary parts.

Though homodyne sensors have more simple design, in the majority of the works a heterodyne configuration was used.We managed to prove the definite advantage of the homodyne configuration over the heterodyne option on particular examples at gigahertz frequencies. (The work has been implemented under ISTC Project G-801).

The performed investigations allowed one to formulate and substantiate a novel concept of performance of a microwave sensor with homodyne configuration. Basic approach consists in variation of the RF frequency, f, in the range of f with discrete step fi.During preliminary estimations a set of algebraic equations for target parameters in the system sensor-antenna-target has been obtained using the well-know relation between the signal power and the distance under free-space conditions. The advantages of the proposed concept involve a possibility to exclude main parasitic effects, which will increase accuracy and reliability of evaluation of key target parameters, to estimate the distance from the target (without using separate methods) and to establish the data in real time; all this – using simple hardware and software. This, in its turn, makes this sensor for fast checking of people and luggage very attractive.

The present work involves research and development of a homodyne MS for the frequency range 55-63GHz as a finished and well characterized device using commercially available microwave monolithic integrated circuits (MMICs).In the frames of the project no finished system that could be directly used at airports and other places with checking of people is envisaged. However, all technical prerequisites will be established to provide 3D image and scanning of the target. The advantages to detect concealed weapon, explosives and other dangerous objects over other MS types will also be shown.

Taking into account the relative simplicity of sensor design containing two main units – varying frequency oscillator and mixer, of great interest is the application of this concept to subterahertz and terahertz ranges.

However, according to the preliminary estimations, to realize the concept, the frequency tuning range, f must be at least 10% of the carrier frequency, f. Direct use of such types of voltage controlled oscillators (VCO), as, for example, terahertz CMOS VCO or VCO based on Gunn oscillators and varactor diodes in V-band is impossible because the tuning range is not wide enough for envisaged applications.

To build VCO, application of elements with I-C characteristics with negative differential conductivity (NDC) which is preserved up to the terahertz range seems rather attractive. According to the literary sources, these properties are characteristic, e.g. to planar diodes based on highly doped short-period GaAs/AlGaAs superlattices.

However, it requires complex investigations in the field of material science, technology and design. Nevertheless, with correct approach to the problem, theoretical and technological prerequisites can be created and sub-and terahertz devices can be designed.

Thus, the objectives of the project are:

  • practical realization of the novel concept of the quadrature microwave sensor of homodyne configuration for millimeter-wave range, which involves full theoretical description of the concept of sensor performance, fabrication and characterization of this device, as well as its technically substantiated advantages for security –oriented systems with 3D imaging of the target and
  • study of theoretical, technological and design prerequisites for creation of such sensor based on III-V semiconductor superlattices with NDC to broaden the operating range up to terahertz frequencies.

Though each of the posed problems has its own scientific and practical interest, they are inexorably related to the general principle of sensor system design and to the main field of sensor application. Moreover, precisely the development of millimeter-wave sensor will make it possible to estimate such important parameters as the required range and step of oscillator frequency variation in the transmitting part of the sensor, which will form the basis for selection of VCO types of terahertz device.

Thus, the proposed project refers to rather an important field of science and technology – development of highly efficient and relatively low cost sensor systems, including portable ones, operating at room temperature in quasi-real time and used to detect concealed weapon and explosives. Part of results (millimeter-wave), will make practical contribution to solution of this problem in the near future and the other results (terahertz) will be realized later.

The expected results are:

  1. Heterodyne millimeter-wave sensor based on a new concept of discrete frequency variation of the transmitting part of the sensor and possessing a number of obvious advantages over other similar devices for security applications will be investigated and developed.
  2. Prerequisites will be studied and technological principles for expanding the frequency range of the sensor up to submillimeter waves will be investigated on the basis of III-V semiconductor superlattices with NDC on the I-V characteristic.

In the first case: comprehensive theoretical description of a new concept of heterodyne microwave sensor (analysis, theoretical approach, set of algorithms) will be given; functional and electric circuits as well as millimeter-wave sensor design based on commercially available MMIC will be developed; such sensor characteristics as output power, frequency stability, sensitivity depending on the frequency variation step, distance from the target and data processing method will be established and conditions for optimization of these characteristics will be defined; conditions for development of algorithms for 3D reconstruction of data, i.e. a system consisting of one millimeter-wave oscillator and several phase-matched devices will be described.

In the second case: choice of III-V semiconductor structures to be grown by molecular beam epitaxy (MBE) will be substantiated based on investigation of highly doped III-V superlattices with maximum current drop on the negative portion of the I-V characteristic; methods of minimization of transient contact resistance in diode structures will be studied theoretically and experimentally; influence of various methods of intercomponent insulation (mesa-etching and ion implantation) on diode parameters will be investigate; circuit design to create integrated ultrahigh-frequency VCO and mixer on the developed diodes will be performed.

The scope of activities is defined by the project goals and expected results and is given in detail as 9 Tasks, 8 of which will be implemented in parallel.

Thus, after project completion, first, a new microwave sensor having a number of advantages over the available sensors will be developed and after fabrication of a system demonstrator with 3D image of the object will allow fast, reliably and qualitatively detect concealed weapon and explosives in the luggage and personal control. The sensor system is supposed to operate both in stationary and portable regimes, which facilitates solution of a number of security problems. Preliminary estimations show that the sensor system will be economically more attractive. However exact figures will be known only after creation of a demonstrator with all necessary software and hardware.

Second, in the course of project implementation, new knowledge on possibility to create a monolithic terahertz sensor with specified characteristics will be obtained. However, practical application of such devices is rather a long-term outlook.


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