An official website of the United States government
A general synthesis technique for beamforming metasurfaces is presented which utilizes accurate modeling techniques and rapid optimization methods. The metasurfaces considered consist of patterned metallic claddings supported by finite grounded dielectric substrates. The metasurfaces are modeled using integral equations which accurately account for all mutual coupling and finite dimensions. A beamforming metasurface is designed in three phases: an initial Direct Solve phase involving the solution of the integral equation via the method of moments to obtain a complex-valued initial design satisfying the desired far-field beam specifications, a subsequent Optimization phase to convert the complex-valued metasurface into a purely reactive metasurface, and a final Patterning phase to realize the metasurface as a patterned metallic cladding. The metasurface is optimized using an adjoint optimization method. The method calculates the gradient of the cost function in only two forward problem solutions. An example metasurface designed using this approach is presented.
more »
« less
Inverse design of a grating metasurface for enhancing spontaneous emission through hyperbolic metamaterials
This work is concerned with inverse design of the grating metasurface over hyperbolic metamaterials (HMMs) in order to enhance spontaneous emission (SE). We formulate the design problem as a PDE-constrained optimization problem and employ the gradient descent method to solve the underlying optimization problem. The adjoint-state method is applied to compute the gradient of the objective function efficiently. Computational results show that the SE efficiency of the optical structure with the optimized metasurface increases by 600% in the near field compared to the bare HMM layer. In particular, an optimized double-slot metasurface obtained by this design method enhances the SE intensity by a factor of over 100 in the observation region.
more »
« less
- Award ID(s):
- 2011148
- PAR ID:
- 10487223
- Publisher / Repository:
- Optical Society of America
- Date Published:
- Journal Name:
- Journal of the Optical Society of America B
- Volume:
- 41
- Issue:
- 2
- ISSN:
- 0740-3224; JOBPDE
- Format(s):
- Medium: X Size: Article No. A79
- Size(s):
- Article No. A79
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Topology optimization of nonlocal metasurfaces requires the objective-function gradient considering all angles of interest. We generalize the recent “augmented partial factorization” method to compute such gradient efficiently and inverse design a broad-angle metasurface beam splitter.more » « less
-
A technique for the design of conformal metasurfaces with two spatially disconnected space wave ports connected by a surface wave is presented. The passive and lossless metasurface absorbs the incident wave at port 1, converts it nearly perfectly into a surface wave which transports the energy along an arbitrarily shaped/curved metasurface to port 2, then reradiates the captured power as a radiated field with control over its amplitude and phase. Since the incident field is seen to disappear at the input port and reappear at a spatially dislocated port as a new formed beam, the space wave can be said to have been seamlessly transported from one point in space to another. The metasurface consists of a single, conformal, spatially variant, impedance sheet supported by a conformal grounded dielectric substrate of the same shape. It is modeled using integral equations. The integral equations are solved using the method of moments (MoM). The impedances of the sheet are optimized using the adjoint variable method to achieve the near perfect wave transportation operation from a passive and lossless metasurface. MATLAB codes and COMSOL Multiphysics simulation files for all designs presented in this paper are available for download as supplemental material files. Possible applications include channel optimization for cellular networks, inexpensive power harvesting, sensing, around-the-corner radar, and cloaking.more » « less
-
A partial differential equation (PDE) constrained design optimization problem usually optimizes a characteristic of a dynamical system around an equilibrium point. However, a commonly omitted constraint is the linear stability constraint at the equilibrium point, which undermines the optimized solution’s applicability. To enforce the linear stability constraint in practical gradient-based optimization, the derivatives must be computed accurately, and their computational cost must scale favorably with the number of design variables. In this paper, we propose an algorithm based on the coupled adjoint method and the algorithmic differentiation method that can compute the derivative of such constraint accurately and efficiently. We verify the proposed method using several simple low-dimensional dynamical systems. The relative difference between the adjoint method and the finite differences is between [Formula: see text] to [Formula: see text]. The proposed method is demonstrated through several optimizations, including a nonlinear aeroelastic optimization. The proposed algorithm has the potential to be applied to more complex problems involving large-scale nonlinear PDEs, such as aircraft flutter and buffet suppression.more » « less
-
In this paper, a broadband achromatic focusing metasurface design scheme based on the equivalent circuit theory and optimized by a deep learning method is proposed. The designed metasurface element consists of multilayer metal rings and a grounding layer, and the phase modulation effect of achromatic aberration in a wide frequency range is realized by precisely controlling the distance between the layers. The preparation of this complex structure is realized by using additive manufacturing technology, which effectively overcomes the limitations of traditional printed circuit board technology in manufacturing complex structures. To further improve the design efficiency, deep conditional generative adversarial network is introduced in this paper to quickly determine the structural parameters and realize the inverse design, which significantly improves the efficiency and accuracy of the metasurface structure design. The experimental results show that the metasurface possesses good focusing performance in the 17 to 35 GHz band with an effective bandwidth utilization of 69.2 %. The design method proposed in this study combines artificial intelligence and additive manufacturing technology, which provides new design ideas for applications in the fields of communication, optics and wireless energy transmission.more » « less
