| As one of the most basic properties of materials, thermal properties are the key paremeter to research, analyse and design about particular thermal process. Also, it is the foundation of energy technology development. For a long time, the measurement of thermal properties is the basic and important requirement. Traditional technologies such as laser flash method, guarded hot plate have its restricted conditionsrespectivity, which can not meet the requirement for rapid, accurate and universal measurement. The 3ω measurement method is now widely used for thermal property characterizations. Traditional measurement process of 3ω technique needs to deposit a metal strip first on the sample, which is not cost-effective and also limits the application of the method. The freestanding sensor based on polyimide film changed the situation for its reusable characteristic. Moreover, the freestanding sensorexpands the application of 3co technique to much broader field, porous material, for example.New problem arise with the polyimide film sensor. Due to the existence of the polyimide film, the signal frequency must be low enough to ensure that it can penetrate the film and finally reach the sample.Lower frequency signal means larger time constant for the lock-in amplifier, thus the whole measurement process is time-consuming, In order to fundamentally reduce this time, new basement material for the freestanding sensor must be employed to increase the detection frequency and decrease the time constant. We choose sapphire as the basement for its high thermal diffusivity (more than one hundred times larger than the polyimide film), which is essential to determine the penetration frequency (according to the penetration depth equation). Moreover, sapphire is rigid enough (which hardness is second only to diamond in nature) to resist most damage to the nickel strip deposited on it, so the new sapphire sensor is more durable.The one-dimensional thin-film thermal conductivity method is employed to analyze the heat conduct condition of the sensor when samples are measured. Furthermore, the heat spread effects inside the sapphire which caused by the aspect ratio between heater width and sapphire thickness is required to minimized. So the validity of the one-dimensional heat conduction modeling is discussed to solve the heat spreading effects and small thermal conductivity contrast between the sapphire basement and samples in some cases.A series of standard samples are tested by the new sensor, quartz, polymethyl methacrylate, stainless steel, aluminum and copper for example. And results show that the stethoscope stylefreestanding 3co technique make the measurement more rapid, and the sensor itself is more durable. Also, the measurement results coincide with the references, which means that this sapphire-based sensor can be used to replace the polyimide film to acquire rapid measurement. Benefited from the reduction of measuring time, this technique achieves field measurement for 3ω method, which means that thermal properties of most types of materials can be acquired easily. |
PDF Full Text Request