Vertical panels of mmWall (IMAGE) Princeton University, Engineering School Caption The mmWall is an accordion-like array of 76 vertical panels that can both reflect and refract radio waves at frequencies above 24 gigahertz, the lower bound of mmWave signals. Credit Tori Repp/Fotobuddy Usage Restrictions Noncommercial use License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.