The invention is concerned with a method in a communication network for invoking services, the communication network including at least one or more terminals and at least two service entities. An authorizing computer provides client computers with a data specification and remote computer address along with an authorization code that is digitally signed or encrypted and that may only be used for a limited number of times. In some embodiments, the microchannels are high-aspect-ratio grooves formed into a polycrystalline silicon cooling base, which is then attached to a cover and to the back of the chip. The associated circuitry is adapted to be powered by electro-magnetic radiation transmitted from a point remote from the sensor.