如何实现这个功能，哪位大神指点小弟下下。
完全可以实现，现在在微信，支付宝等软件上已经应用得很成熟了。
而且有现成的库可以用：
android/iphone/windows/linux声波通讯库
声波支付，声波会员卡，声波券票，声音名片，声波签到，声波排队，做wifi和密码共享或者设定，做文件/图片分享
声波通讯库介绍：
http://blog.csdn.net/softlgh/article/details/40507623
声波通讯库下载：
http://download.csdn.net/detail/softlgh/8095263
Data-> DAC -> Anti-imaging Filter -> Speaker --(Supersonic Wave)-> Mic -> Amplifier -> ADC ->Data
Bandwith is limited by smallest one.
The DAC in the cellphone can't output a signal that frequence over 22.050kHz.
According to Nyquist–Shannon sampling theorem, the signal can be reconstructed when the sample freqency is 2X or larger of original signal. Most cellphone's sample rate of DAC is 44.1KHz, so DAC can't play it. Also, ADC can't sample it.The amplifier of cellphone can't process supersonic wave.
There is a low pass filter in the audio circuit.
However, you can try the frequence between 18000-21000Hz, but I can't make sure that cellphone's speaker can play it.
This is an example: LM4808
Gain drops when requence increases.
麦、扬声器和操作系统，软硬件三方面，既没有这个频率响应，也没有传输所需的功率或灵敏度，你死心吧。
真正可行的办法是：用蓝牙指挥单片机等设备，控制超声波发射器/传感器/成品模块，去实现你需要的超声功能。
所以最后，你的需求到底是什么？你必须详述这一点。