Resonant Inc. /zigman2/quotes/200913816/composite RESN -0.70% said Friday that Chief Financial Officer Michael Seifert has resigned, after less than three weeks in the role. He had joined the radio frequency front-ends company on Sept. 4 from Analogix Semiconductor. The company did not give a reason for the sudden departure. Resonant said Seifert will be replaced on an interim basis by former CFO Jeff Killian, who is currently a company consultant. the stock, which was still inactive in premarket trade, has tumbled 27% over the past three months, while the S&P 500 /zigman2/quotes/210599714/realtime SPX +1.01% has gained 6.6%.