Microsystems for Bioelectronics

independent of the position and orientation. The limits of such convenience-based ubiquitous

communication will be the focus of this chapter.

An important notion is that communication is the transmission of physical effects from one system to

another [1], and therefore the limiting cases can be analyzed using the principles of fundamental physics,

similar to those used in Chapter 3. The principal physical effect used for ubiquitous communication is

electromagnetic radiation. The analyses offered in this chapter center on the electromagnetic transducer

(e.g. the antenna) since its scaling directly impacts communication system performance.

5.2 ELECTROMAGNETIC RADIATION

Time varying electrical or magnetic fields produce self-propagating waves of electromagnetic (EM)

energy, which propagate in space at the speed of light, c (in vacuum, c ¼ 310

8

m/s), and are used to

transfer energy and information. Specifically, if an electron moves with acceleration (or deceleration),

it produces electromagnetic radiation. When an alternating current (AC) of frequency

n

is flowing in

a conductor, electromagnetic radiation of the same frequency is emitted from the conductor into its

external environment. The generated electromagnetic wave propagates through space and it can affect

the behavior of other electrons at large distances from the emitter. This constitutes the basic principle

of ‘wireless’ communication, e.g. radio.

Electromagnetic waves are, as all other waves, characterized by their frequency,

n

, and wavelength,

l

(see Box 5.1). Electromagnetic radiation is classified according to the frequency/wavelength, as

shown in Figure 5.1. For wireless communication, radio, microwave and infrared parts of the spectrum

are typically used. In the case of nanomorphic cell, radiation wavelengths in the THz to PHz regime

(

l

w10–100

m

m) are comparable to the physical size of the cell.

While in classical electrodynamics and in most engineering treatments electromagnetic radiation is

regarded as a continuous phenomenon, quantum physics has revealed the granular nature of electro-

magnetic radiation, which is primarily manifested through the interaction of radiation with matter, e.g.

in emission and absorption processes. The smallest amount of radiation energy, which can be emitted

or absorbed, is called the quantum of radiation or photon (Box 5.2). The quantum nature of the

electromagnetic radiation becomes especially apparent when the scale of objects and interactions is

small, e.g., in the micrometer and nanometer range – the nanomorphic cell.

Although an electromagnetic signal can be physically analyzed in various ways, it will be

instructive to consider extreme cases only. One extreme is a classical continuous-wave detection,

which implies a large number of photons. This case typically occurs in radiofrequency (RF)

communication. The other detection extreme is a ‘counter’, an instrument which records the incidence

of single photons. The discrete photon regime is more typical for optical communication. In the

following the basic principles of both RF and optical communication will be considered.

5.3 BASIC RF COMMUNICATION SYSTEM

A schematic block diagram for a radio communication system is shown in Figure 5.1. It consists of

a transmitter and a receiver. The essential components of a radio transmitter are:

T1: An oscillator that generates AC current of certain carrier frequency, which is the source of EM

radiation.

124 CHAPTER 5 Nanomorphic cell communication unit