The design of our ambient backscattering transmitter buildson conventional backscatter communication techniques. At a highlevel, backscattering is achieved by changing the impedance of anantenna in the presence of an incident signal. Intuitively, when awave encounters a boundary between two media that have dif-ferent impedances/densities, the wave is reflected back [18]. Theamount of reflection is typically determined by the difference inthe impedance/density values. This holds whether the wave is amechanical wave that travels through a rope fixed to a point on awall or an electromagnetic wave encountering an antenna. By mod-ulating the electrical impedance at the port of the antenna one canmodulate the amount of incident RF energy that is scattered, henceenabling information to be transmitted.To achieve this, the backscatter transmitter includes a switch thatmodulates the impedance of the antenna and causes a change in theamount of energy reflected by the antenna. The switch consists of atransistor connected across the two branches of the dipole antenna.The input signal of the switch is a sequence of one and zero bits.When the input is zero, the transistor is off and the impedences arematched, with very little of the signal reflected. When the switch in-put signal is one, the transistor is in a conducting stage which shortsthe two branches of the antenna and results in a larger scatteredsignal amplitude. Thus, the switch toggles between the backscatter(reflective) and non-backscatter (absorptive) states to convey bits tothe receiver