Need RX Coil whose size is smaller than 30x30mm

Xiaofei,

There are many coil vendors that produce smaller coils.  If you review the bq51013B EVM User's Guide, you'll see several vendors listed that we work with and have confirmed have standard sized coils that work on the EVM. They also produce smaller coils that may be of interest to you.

For dual mode coils, the bq51221 EVM User's Guide also shows several vendors.

We are constantly evaluating small coils for wearable applications.  It is difficult to list the vendors and specific coil numbers because each wearable application is unique and the solutions may not have the same success in each application.

Regards,

Dick