您要查找的是不是：
- undercurrent n. 暗流；潜流
- frequenter n. 常客；常常来访者
- under-frequency 欠频
- infrequence n. 很少发生,罕见
underfrequency 低于额定频率，[物] 频率过低
网络短语:
underfrequency card 频率过低卡
underfrequency protection 欠频保
underfrequency relay 低频继电器
underfrequency rela 欠频继电器
underfrequency pc card 低于额定频率百分数卡