# Enhanced Second-harmonic Generation Using Nonlinear Metamaterials

## TL;DR

This paper presents a nonlinear metamaterial with enhanced second-harmonic generation at microwave frequencies, achieved through structural engineering and array phase matching, resulting in significant harmonic signal amplification.

## Contribution

The study introduces a novel DSRR-based metamaterial with engineered resonance frequencies and demonstrates enhanced second-harmonic generation through constructive interference and cavity effects.

## Key findings

- Enhanced second harmonic with a factor of 70 compared to single ring structures.
- Constructive interference and cavity mechanisms boost harmonic signals in arrays.
- Resonance engineering enables phase matching for maximum harmonic enhancement.

## Abstract

We demonstrate a nonlinear metamaterial which enhance higher order harmonics in microwave frequency regime. Nonlinearity in the structure is introduced by adding a varactor diode in the common slit of the double split ring resonator (DSRR) design. By engineering the structure such that inner ring resonance frequency of the DSRR is twice as the outer ring resonance frequency, we have demonstrated that the second harmonic of the outer ring can be enhanced significantly. By comparing with a single ring (SRR) unit cell structure, DSRR has an enhancement factor of 70. Furthermore, we elucidate that the second harmonic signals generated by two identical double split rings interfere and we can use its constructive interference positions to construct an array of DSRRs that gives a maximum second harmonic signal with phase matching condition. When the phase matching condition occurs the enhancement factor of an array is more than the contribution of individual unit cells which proves that the enhancement is due to not only constructive interference of the second harmonic generated by individual unit cells but also due to cavity mechanism occurred in the array structure.

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Source: https://tomesphere.com/paper/1705.07720