Drive voltages to a sensorless brushless DC motor are regulated by varying the width of a single drive pulse centered in each of the commutation periods. The cryptographic devices then mutually authenticate themselves. The assembling structure of the heat dissipation device includes a heat dissipation unit, at least one latch member and at least one retainer member. A related method is also disclosed. A HIFU transducer assembly having one or more piezoelectric element is used along with at least one sensor wherein the sensor provides feed back information to the controller for the safe operation of the piezoelectric element.