ํŒŒ๋ฅด์ฝ” ๋ ˆ์ง€์˜ค๋‚ ๋ ˆ ๋ฒ ๋„คํ†  ๋ธ ๋ธํƒ€ ๋ธ ํฌ์˜ Hertz ๋ Œํ„ฐ์นด