5. (20 pts) answer the following questions:

a) At microwave frequencies, the power density considered for human exposure is

1mW/cm². A radar radiates a wave described as

E(r) = 3000

where r is the radial coordinate which is the distance from the source. What is the radius

of the unsafe region?

b) A laptop manufacturer wants to shield her laptop such that the energy from its high-

frequency clock doesn't radiate to the outside world. Assuming a clock rate of 2.45 GHz,

what should be the thickness (how many skin depths) of the metal cladding on the laptop

cover and weight of metal required, given standard laptop dimension of 35 cm x 25 cm if

they use copper that has a o = 5.8 x 107 S/m and density = 8.96 g/cm³ and they

require 50 dB attenuation.