Nihon Dempa Kogyo Co., Ltd. or NDK (日本電波工業株式会社, Nihon Dempa Kogyo Kabushiki-gaisha) is one of the world's largest quartz crystal companies, based in Shibuya, Tokyo, Japan. Using its synthetic quartz crystals, NDK produces crystal-related products such as crystal devices (e.g. crystal units, crystal oscillators, crystal filters) and ultrasonic transducers for medical use. In recent years, the company has begun to develop frequency synthesizers and low-power wireless modules.