A biometric authentication device for use with a host having memory, processing power and communication capabilities, such as a personal digital assistant. A filler support layer is added to the hollow side of the cover sheet and hardens. The resonance control unit adjusts a resonant frequency of the auxiliary resonator in accordance with a coil distance between the power transmission coil and the auxiliary coil, optimizing receiving power supplied to the power receiver. The present invention also provides a method for controlling the ice volume fraction of a circulating ice-containing medium using such a control system.