PIERS Proceedings, Hangzhou, China, March 24-28, 20081122 Metamaterial Techniques for Automotive Applications K. Sato, T. Nomura, S. Matsuzawa, and H. Iizuka Toyota Central Research & Development Labs., Inc., Japan Abstract— Automotive applications that metamaterials are expected to effectively contribute to are presented, and research activities of metamaterials undertaken at Toyota Central R&D Labs (TCRL) are reviewed. They include development of leaky-wave antennas for future millimeterwave radar systems, dipoles for UHF band applications, and topology design optimization techniques for periodic structures of metamaterials. 1. INTRODUCTION Metamaterials are artificially constructed materials that have unusual electromagnetic properties such as backward wave, reduced wavelength with decreasing frequency, nonlinear frequency characteristic of resonances, and so on. In the view point of engineering, metamaterials having such unusual electromagnetic properties are expected to extend significantly the design degrees of freedom for materials, devices, components and systems. Significant research efforts have been expended in the development of microwave and millimeter-wave metamaterials, such as couplers, resonators, small antennas, and beam-scanned leaky wave antennas [1–3]. In addition, there are currently considerable interests in the development of optical metamaterials such as a negative index planar lens or “superlens” [4, 5]. Metamaterials are expected to provide new applications, drastic improvement of performance, simple architectures, low cost, and so on, in future automotive electronics applications, as shown in Fig. 1. The automotive applications that metamaterials are expected to effectively contribute to include beam scanning antenna systems for radars, mobile communication antennas, novel magnetic materials for electric motors, the high-performance absorbing and shielding materials for electromagnetic compatibility. Metamaterials are also expected to be applied to optical devices such as LED headlights and night vision systems using infrared cameras. Research activities undertaken at Toyota Central R&D Labs (TCRL) are reviewed in this paper. Two types of metamaterial-based antennas are presented. One is a leaky-wave antenna for future millimeterwave radar systems that need wide scanning angle with simple architecture. The other is a dipole for UHF band applications. The dipole provides small size, or opposite polarization to conventional one. Also, design techniques are desired to maximize the performance of metamaterials. A topology design optimization technique for periodic structures of metamaterials is presented with an example model. Frequenc Frequency LE LED High Optics Laser Night vision Tera Radar Millimeter Microwa ve Mobile antenna TPMS High freq . EMC Low LEDD LE headlig ht headlight Motor Magnetic materials EMC Body Small antennas Millimeterwave wave radar Laser La se r rada radarr Magnetic field Motor Magnetic material materials Night vision sy stemusing system usin g Infrared camera TPMS :Ti re :Tire pressure pres sure monitoring system sy stem Figure 1: Automotive applications metamaterials are expected to effectively contribute to. 2. TOPOLOGY DESIGN OPTIMIZATION Topology optimization is a highly flexible optimization method that can simultaneously deal with geometric and topological configuration changes [6]. Topology optimization is being used to develop a novel method for designing the periodic microstructures of electromagnetic materials [7]. The weight or electromagnetic permittivity. 3. A novel structure for a frequency-independent steerable composite right/left handed leaky wave antenna for the millimeter-wave band applications is presented [8–9]. optimized metamaterial microstructures with a specific band-gap. εr . a field of view (FOV) covering about 20◦ over a range of 150 m is sufficient and can be provided by most sensors on the market today. In the near y Microstrip to waveguide transitions x Teflon substrate θ z Patch 0. high gain and a simple structure in the millimeter-wave band. Electric field amplitude structure Start Final 1 10 Relative permittivity Figure 2: Example of electromagnetic band-gap structure using topology optimization design. The prototype CRLH LWA shown in Fig. This approach is very attractive because of its simplicity and efficiency. An example of a periodic electromagnetic band-gap dielectric material designed using topology optimization is shown in Fig. This antenna offers the advantages of wide beam scanning. Then. The main feature involves representing the shape of a structure by the density of its micropores to allow for the free transformation of the topology of the shape. inclined polarization y z CRLH LW an antenna tenna Feed (a) Configuration (b) Prototype Figure 3: Millimeter-wave leaky wave antenna. is 5.45 9 0. For these systems. 2 shows that the microstructure is generated as the iteration step progresses and finally either a void or a filled/solid material is produced. topology optimization can be used to produce new. China. However. Fig. Hangzhou. The initial design is of a homogenous material in which the relative permittivity. . COMPOSITE RIGHT/LEFT-HANDED LEAKY WAVE ANTENNA (CRLH LWA) There is a greatly increased interest in the development of automotive radar sensors for adaptive cruise control and pre-crash safety systems using a millimeter-wave band from 76 to 77 GHz. the density distribution is optimized for a desired specification by applying a mathematical non-linear programming technique.45 λ 00 x 45 deg. over a maximum range of 60 m in order to adequately deal with cut-in situations. The density of the material is translated to gradual changes in the physical properties such as the stiffness.Progress In Electromagnetics Research Symposium. 2. In this manner. 3 was fabricated and tested in the millimeter-wave band. March 24-28. 2008 1123 design algorithm used for the variable change method is based on the density method. new developments like “stop & go” adaptive cruise control and collision avoidance assistance systems require a broader FOV up to 60◦ . C. LEFT-HANDED DIPOLE ANTENNAS A new concept for forming a dipole antenna using a left-handed transmission line is next described [10]. The straight dipole worked in the fundamental mode.. Computer Methods in Applied Mechanics and Engineering. and left-handed dipole antennas have been presented along with some thoughts for future investigation. it may be possible to realize automotive radar antenna systems with a high gain in excess of 20 dBi by using the proposed antenna.77 wavelengths in free space. REFERENCES 1. shown in Fig. 2000. CONCLUSIONS A topology design optimization technique for electromagnetic materials. a left-handed leaky wave antenna for millimeter-wave applications... Eleftheriades. Rev. Balmain. Caloz. 2. Phys Rev. 1988. Phys. 4(a). IEEE. J. and T. Electromagnetic Metamaterials. 4.. Bendsøe. 5. 2008 1124 future. 3966.. ACKNOWLEDGMENT The authors would like to express their sincere gratitude to research collaborators. D. Pendry. March 24-28. The antenna of 0. The first is a small dipole.18 wavelengths in free space provided a gain of −3. and G.. Lett. Lett. 2006. John Wiley and Sons. Inc. Hangzhou. Phys. Metamaterials will clearly open up a whole new field for automotive electronics applications. These novel dipoles offer a great promise for future automotive mobile communications. 2000. 71. Polarization orthogonal to a right-handed one was achieved at 643 MHz by the induced current of nine half wavelengths on the meander having 0.. We believe that the LHLWA is a promising design for automotive millimeter-wave applications. 197–224. 2005. China. et al. These have been the subjects of recent metamaterial studies at TCRL. 4(b). Smith. . Rev. 6. 84–18. et al. z z θ 20 Inductor y x θ y φ x φ Feed point 180 100 Feed point Inductor Capacitor 10 (a) Straight dipole Capacitor Unit: mm Unit: mm (b) Meandered dipole Figure 4: Left-handed dipole antennas. Kikuchi. 4184. IEEE. Lett. shown in Fig. The concept is applied to two antennas. The second is an orthogonally polarized dipole. Engheta. The meandered dipole worked in the higher order mode.PIERS Proceedings. 3.. 4.. N. 095504. Adding capacitors to one side of the network leads to out-of-phase currents with different amplitudes that produce high levels of radiation.9 dBi at 547 MHz and bandwidth of 1. 95. The unit cell has a shunt inductor and two serious capacitors. John Wiley and Sons. V. and N. The antenna has a unique feature in that the wavelength decreases with the frequency. 2005.7% for |S11| < −10 dB. Itoh. 85–18. P. 5.. Negative-refraction Metamaterials. The antenna is composed of a ladder network periodic structure of unit cells. . S. Rio de Janeiro. New York. March 24-28. Vol. Hall. 1246–1253.. T. . Matsuzawa. 55.. E89-C. Workshop on Antenna Tech. Int. 420–424. “Topology optimization of periodic microstructures in electromagnetic material. May 2007. Hangzhou. et al. 2005. No. Antennas Propag... 2008 1125 7. and P. Brazil. 2006. Sato.. China.. et al. 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