Crystal radio

A transceiver controlled by a computer is used to interrogate and receive the ID code of each RF tag. The transceiver antenna transmits a specially modulated, 125 kHz electromagnetic field. This field is of very low energy and not harmful. When an RF tag is held within about 1 cm from the transceiver s antenna, energy is picked up by the RF tag s antenna. A rectifier in the chip converts this energy to microwatt levels of DC power, which is enough to power-up the logic circuitry on the chip. In a very real sense, the RF tag is similar to a crystal radio (which does not require an external power source), except that the device serves as both receiver and transmitter. It is self-contained , in that the chip uses no internal batteries and has no external metallic connections. 

SCRE Single Crystal Radio-Electrochemistry IRT Indirect Radiotracer Technique SERT Secondary Effect Radiochemical Technique CRT Common Radiotracer Technique (Foil Method.)... 

Naturally occurring crystals with diode-like properties were used in amateur crystal radio sets purchased by millions of hobbyists in the middle of the twentieth century. 

Fig. 19.1 Ultra-simple "crystal radio," with optional amplifier.

As an additional exercise, the circuit of Fig. 19.2 might be built and listened to with a portable AM radio. A louder signal will be heard, compared to the experiment in Chapter 1, because of the capacitor storing energy that then gets discharged within about one millisecond. Also, the crystal radio in Fig. 19.1 should be able to pick up the signals. 

The operation of solid-state microelectronic devices largely depends on specific electrical responses occurring at the interface between materials of different nature. A representative example for this statement is the rectifying property of the metal-semiconductor contact, which has been identified as early as the end of the nineteenth century (the semiconductor properties of galena were identified by Karl Ferdinand Braun in 1874 32 years later, Greenleaf Whittier Pickard patented a crystal radio receiver [1], which used a crystal detector that was actually a metal-semiconductor diode made of galena). As a consequence, the performance of these devices critically depends on the quality and reliability of their interfaces. Organic electronic devices do not escape this universal rule. 

PbS is a / -type semiconductor when sulphur rich and an n-type semiconductor when lead rich. A conductivity of 1 -3 x 10-4 q i cm-i is found for stoichiometric PbS . Crystalline PbS is a remarkable radio detector, and was widely used in early crystal radio receivers. 

Synthetic gemstone materials often have multiple uses. Synthetic mby and colodess sapphire are used for watch bearings, unscratchable watch crystals, and bar-code reader windows. Synthetic quartz oscillators are used for precision time-keeping, citizen s band radio (CB) crystals, and filters. Synthetic mby, emerald, and garnets are used for masers and lasers (qv). 

In this biosensor a quartz radio crystal is functionalized with the enzyme glucose-6-phosphate dehydrogenase. As shown in Figure 3, a thin film of Pmssian blue [14038-43-8] C gN gFe, is then coated onto the crystal. 

Fig. 3. Detail of enzyme-modified quartz radio crystal used in a piezoelectric biocatalytic biosensor.

Other interesting thin-film studies using AES have included the growth of platinum on Ti02- and SrO-terminated (100) SrTiOs single-crystal substrates [2.154], of epitaxial niobium films on (110) T1O2 [2.155], the interaction of copper with a (0001) rhenium surface [2.156], and the characterization of radio-frequency (rf) sputtered TiN films on stainless steel [2.157]. 

It should be noted that, whereas ferroelectrics are necessarily piezoelectrics, the converse need not apply. The necessary condition for a crystal to be piezoelectric is that it must lack a centre of inversion symmetry. Of the 32 point groups, 20 qualify for piezoelectricity on this criterion, but for ferroelectric behaviour a further criterion is required (the possession of a single non-equivalent direction) and only 10 space groups meet this additional requirement. An example of a crystal that is piezoelectric but not ferroelectric is quartz, and ind this is a particularly important example since the use of quartz for oscillator stabilization has permitted the development of extremely accurate clocks (I in 10 ) and has also made possible the whole of modern radio and television broadcasting including mobile radio communications with aircraft and ground vehicles. 

Early studies on oxide films stripped from iron showed the presence of chromium after inhibition in chromate solutionand of crystals of ferric phosphate after inhibition in phosphate solutions. More recently, radio-tracer studies using labelled anions have provided more detailed information on the uptake of anions. These measurements of irreversible uptake have shown that some inhibitive anions, e.g. chromateand phosphate are taken up to a considerable extent on the oxide film. However, other equally effective inhibitive anions, e.g. benzoate" pertechnetate and azelate , are taken up to a comparatively small extent. Anions may be adsorbed on the oxide surface by interactions similar to those described above in connection with adsorption on oxide-free metal surfaces. On the oxide surface there is the additional possibility that the adsorbed anions may undergo a process of ion exchange whereby... 

Immediately that the parent is incorporated into the crystal it will start to decay to the daughter. At secular equilibrium the (radio)activity of parent and daughter, will be equal, such that ... 

Radiations outside the ultraviolet, visible and infrared regions cannot be detected by conventional photoelectric devices. X-rays and y-rays are detected by gas ionization, solid-state ionization, or scintillation effects in crystals. Non-dispersive scintillation or solid-state detectors combine the functions of monochromator and detector by generating signals which are proportional in size to the energy of the incident radiation. These signals are converted into electrical pulses of directly proportional sizes and thence processed to produce a spectrum. For radiowaves and microwaves, the radiation is essentially monochromatic, and detection is by a radio receiver tuned to the source frequency or by a crystal detector. 

A voltammetric characterization of platinum single crystal surfaces produced by these three methods shows that a very similar surface order and cleanliness are obtained in each case. The features embodied by the third method which we use for the radio-electrochemistry work, are as follows ... 

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