RF/Antenna Projects, EE Department, March 2008

Current EE department projects in the RF/Antenna area include:

• Development of HFSS computer models for metamaterial structures
• Development of physical metamaterial prototypes verified through measurements taken in the Cal Poly Anechoic Chamber
• Development of an Electromagnetic Compatibility (EMC) radiated emissions chamber and establish testing capabilities
• Characterization of the EMC chamber and accompanying instrumentation; carry out radiated emissions testing on actual systems

Metamaterials Development

The development of HFSS simulation models for metamaterials has been established for split ring resonators (SRR) and capacitively loaded strips (CLS) as detailed in [1-3]. Both planar (Fig. 1)

Fig. 1: Unit Cell, Planar MetaMaterial HFSS Model

and tri-planar models (Fig. 2) have been developed and simulation results compared.

Fig. 2: Unit Cell, Tri-Planar MetaMaterial HFSS Model

The planar model (Fig. 1) is composed of a box filled with 5880 Duroid (εr = 2.2) or FR4 with (x, y, z) dimensions of (0.210, 0.756, 0.156 inches). S-parameters are calculated as a function of frequency with the goal of |S11| → ∞ dB and |S21| → 0dB to yield a double negative material [Re(ε) < 0, Re(μ) < 0] response. Fig. 3 below illustrates the S-parameter response for the planar case (Fig. 1).

Fig. 3: S-Parameter Response, Planar MetaMaterial HFSS Model

This response indicates double negative properties (|S11| = -4dB and |S21| = -10dB) at the target frequency of 5GHz. To determine if the tri-planar structure yields an improvement in performance, the same measurement was performed: see Fig. 4 below.

Fig. 4: S-Parameter Response, Tri-Planar MetaMaterial HFSS Model

This response also indicates double negative properties (|S11| = -18.5dB and |S21| = -0.05dB), but at a frequency of 6.325GHz. Material dimensions can be scaled to obtain these characteristics at the target frequency (5GHz). Additional simulations are currently underway to characterize negative material characteristics with respect to unit cell geometries. To allow fabrication, simulation models align with materials (Roger’s Duroid and FR-4) available from substrate manufacturers. To detect negative index material characteristics, a prism structure of metamaterial unit cells [4] will be fabricated: see Fig. 5 below.

Fig. 5: Prism Geometry, MetaMaterial HFSS Model (left), Expected Ray Paths (right) [4]

Incident radiation will be applied at the x = 13cm plane at normal incidence (along the x-axis), while transmitted radiation will be measured as a function of angle (xy-plane) on both sides of the normal (at expected refracted angles) to verify negative index material performance. Applications of metamaterials include the focusing of light rays using rectangular (as opposed to convex) slabs of metameterial and the focusing of RF energy from small radiating apertures [3]: see Fig. 6 below.

Fig. 6: Application of Metamaterials: Focusing Radiation [5]

EMC (Electromagnetic Compatibility) Radiated Emissions Chamber Development

The development and construction of the EMC radiated emissions chamber [6-8] involved the following components

• extension of external copper mesh frame: 14’L × 9’W × 7.5’H to 16’L × 9’W × 9’H
• design and construction of internal 2” × 4” support structure (for ferrite tiles)
• installation of 0.5” plywood – 26AWG sheet metal – 0.5” plywood mounting surface for ferrite tiles
• ferrite tile (4” × 4” × 0.25” thick) installation: 6006 tiles
• connector panel door: allows cable entry through chamber wall
• chamber door design: tile design around main entry
• turntable and motor specification
• probe antenna specification and acquisition
• spectrum analyzer, software-controlled, specification and acquisition

To accommodate test articles with maximum dimensions 18” L × 18” W × 6” H, the chamber was extended in length by 4ft and in height by 1ft: see Fig. 7 below [9].

Fig. 7: EMC Screen Room Expansion: Note new panel on right, 1ft height extension panels

Once the screen room was complete, RF (radio frequency) isolation was characterized to determine attenuation levels from outside to inside the newly-renovated chamber: see Fig. 8 below.

Fig. 8: Ferrite Tile Support Structure inside EMC Screen Room

The worst-case measured isolation is 19dB at 1GHz, while the best-case is 64dB at 100MHz. Between these frequency limits, the average attenuation is approximately 30dB. Since commercial chambers have minimum isolation levels of 90dB to 100dB, additional measures to increase isolation will be employed including the installation of fingerstock to both sides of the door jamb and patching holes in the copper mesh. The addition of steel sheet metal between plywood layers should improve isolation values taken without the support structure. Results will be communicated in a future report.

To support the plywood sandwich structure mounted on the ceiling, vertically placed 2” × 6” boards were installed across the double-stacked 2” × 4” top layer: see Fig. 9 below.

Fig. 9: Ferrite Tile Support Structure inside EMC Screen Room: 2” × 6” Ceiling Joists

In conjunction with the screen room expansion, a wooden support structure was developed to accommodate a plywood structure (plywood - sheet metal - plywood) upon which ferrite tiles will be mounted: Fig. 10 below. The layered structure consists of two ½ inch thick plywood sheets attached to either side of a 26AWG steel sheet mounted onto the support frame.

Fig. 10: Plywood – Sheet Metal – Plywood (1⁄2 inch thick) Sandwich Structure

With the mounting structure in place, ferrite tiles (4” × 4” × ¼” thick each) are attached to the structure with zinc-coated steel screws: See Fig. 11 below

Fig. 11: Ferrite Tile Installation

Through C3RP/ONR support, a total of 6,006 ferrite tiles (143 boxes, 42 tiles/box) [9, p. 107] were purchased from Samwha Corporation, in addition to 6,006 plastic inserts and mounting hardware. The chamber is currently under construction (see Figure 12 below).

Fig. 12: Ferrite Tile Installation; Ceiling, Back, and Side Wall

A turntable, stepper motor, and angular position control system will also be designed and implemented inside the new chamber to enable radiated emissions measurements as a function of angular direction from the equipment under test (EUT). A cardboard cutout indicating the size of the proposed turntable and required location on the chamber floor is shown in Fig. 13 below.

Fig. 13: Turntable Size and Location Relative to Front Wall

Since the motor must be located outside the chamber, two holes for the belt drive must be established through the screen room wall, and plywood-sheet metal and ferrite tile layers. Techniques to minimize the impact to isolation and tile absorption performance will be examined and the optimum method or combination employed.

The chamber will undergo characterization testing to compare radiated emissions performance against pre-compliance requirements, including isolation. Adjustments (isolation techniques mentioned above) will then be applied to improve overall performance.

References:

1. D.R. Smith, W. Padilla, D.C. Vier, S.C. Nemat-Nasser, S. Schultz, “Negative Permeability from Split Ring Resonator Arrays,” Lasers and Electro-Optics Europe, 2000, Conference Digest, 10-15 Sept 2000.
2. R.W. Ziolkowski, “Design, Fabrication, and Testing of Double Negative Matematerials,” IEEE Trans. Antennas Progat., Vol. 51, July 2003, pp. 1516-1529.
3. J.B. Pendry, A.J. Holden, D.J. Robbins, W.J. Stewart, “Magnetism from Conductors and Enhanced Nonlinear Phenomena,” IEEE Trans. Microwave Theory & Techniques, Vol. 47, No. 11, Nov 1999, pp. 2075-2084.
4. J.B. Pendry and D.R. Smith, “Reversing Light with Negative Refraction,” Phys. Today, 57, June 2004, pp. 37-43.
5. J.B. Pendry, “Negative Refraction Makes a Perfect Lens,” Phys. Rev. Lett., Vol. 85, No. 18, Oct 2000, pp. 3966-3060
6. ANSI C63.4-2003: Methods of Measurement of Radio-Noise Emissions from Low-Voltage Electrical and Electronic Equipment in the Range of 9 kHz to 40 GHz, American National Standards Institute.
7. CISPR 22: Information technology equipment, radio disturbance characteristics, limits and methods of measurement, Comité International Special des Perturbations Radioélectriques.
8. FCC, Part 15 (Radio Frequency Devices): Subpart A: General, Subpart B: Unintentional Radiators, Subpart C: Intentional Radiators
9. M.I. Montrose, E.M. Nakauchi, Testing for EMC Compliance, Approaches and Techniques, Wiley & Sons, 2004

For More Information

Dean Arakaki
darakaki@calpoly.edu