Managing energy usage in mobile devices
摘要
說明書
In another example embodiment, a pulse-amplitude technique can be used. A piezoelectric ceramic crystal (PCC) acts as a transmitter and launches an ultrasonic pulse through a delay line to the surface being monitored. After initial excitation, the PCC acts as a receiver and detects an echo returning from the surface. The delay line guarantees that the PCC has recovered from the initial excitation before it receives the returning echo. When an air interface is present at the surface being measured (i.e., no frost) a maximum amount of energy is reflected. When frost is present, approximately 30 percent of the transmitted ultrasonic energy propagates in the ice, thus reducing the level of the reflected signal the PCC receives. This level reduction provides an indication of the presence of thin ice layers (frost). Once the ice has exceeded the threshold thickness, the sensor continues to detect the presence of ice. The presence of fog also affects the reflected energy. Detection of the changes caused by fog can also be characterized and used as an indication that a heating element should be activated.
In another embodiment, a pulse-echo technique can be used. In this technique, there are two PCC's. One acts as a pulse transmitter, and the other acts as a pulse echo receiver. A high-frequency excitation signal is sent to the first PCC, which transmits an acoustic pulse toward the sensing surface. Either the sensing face or the surface of the frost, when frost is present, reflects the acoustic pulse. The second PCC receives the returning echo. The processor measures the transit time between excitation and receipt of the returning echo, thereby determining the amount of accumulated ice (frost). The presence of fog also affects this transit time and can be characterized for a particular device to determine that fog is present.
