In particular, we looked at transverse waves on a string, which have an energy density and energy-current density that were essentially expressed as () () So divide 127 by 4, then multiply by power. That's nothing more than converting the power and range to the proper units. Peak spatial power density depends on individual components within the system tied to specific design aspects. Power density is the measure of the power from an antenna to a certain distance D. This assumes that an antenna radiates power in all directions. One reason for this variation is the changing earth-sun distance. some surface gives the average power per unit area incident on that surface. To get the power density of a 1 mm diameter beam one must simply multiply the power (in Watts) by 127 cm-2 to get power density (in W/cm2). Or, Power Density = 127×Power (of 1 mm beam) If the beam diameter is 2 mm instead of 1 mm, then the power density will drop by 22 or 4. Power Density in radar applications, is typically described by the non-directional power density multiplied by the gain of the radar.Notice that the distance D is an exponential component to the equation, due to the three-dimensional "spreading" of the waveform as it propagates through space. An Analogy Between Mechanical and EM Waves We previously studied the energy contained in mechanical waves. The power spectrum () of a time series describes the distribution of power into frequency components composing that signal. This value varies slightly throughout the year but by no more than 0.1 percent. IV. The solar output on the earth is called the power density. This calculator computes for the value of power density if the output power and gain are given. The power density of the sun's radiation on the surface of the earth is approximately 1.4 kW/m 2. For safety (radiation hazard) and EMI calculations, power density is usually expressed in milliwatts per square cm. 100 watts = 1 x 10 2 watts = 1 x 10 5 mW 100 feet = 30.4785 meters = 3047.85 cm. Power density is the amount of power (time rate of energy transfer) per unit volume. With spatial power density variation, the average spatial power density is dependent upon the data center’s size and often is correlated with infrastructure capacities. In the phasor domain, the average power delivered to a load in a circuit is P= 1 2 RefV~I~⁄g Similarly, the time-average Poynting vector indicates the average real power density of a time-harmonic wave: Sav= 1 2 RefE £H⁄g(5.156) whereS=E £H⁄is the complex Poynting vector.