When Fourier law is expressed by heat flux density, the form is as follows: q=-? (dt/dx) can be used to calculate heat conduction. The relevant formula is as follows? =-? A(dt/dx) q=-？ (dt/dx) which one? Is the thermal conductivity in w. Is the thermal conductivity, w/(m*k) A is the heat transfer area, the unit is m^2 t, the unit is K x is the coordinates on the heat transfer surface, the unit is m q is the heat flux density transmitted along the x direction (strictly speaking, the heat flux density is a vector, so q should be the component of the heat flux vector in the x direction), and the unit is w/w/m 2 dt/dx, which is the temperature gradient of the object along the x direction. gradt=-？ (dt/dx) where: gradt is the temperature gradient); At a certain point in space; N is the normal unit vector on the isotherm passing through this point, which refers to the direction of temperature rise. In the above formula, the negative sign indicates that the heat transfer direction is opposite to the temperature gradient direction? Physical parameters (? The bigger the square wave, the better the thermal conductivity)-According to Fourier's law, a square wave is composed of sine waves infinitely many times. Using square wave to test the frequency response of power amplifier can better represent the actual audio signal and reflect the dynamic performance of power amplifier equipment than sine wave test.