Spirits of Stone: Chapter 7 -- Quartz Crystals and Digital Technology
Pierre and Jacques Curie first demonstrated the piezoelectric effect in quartz crystals in 1880, stimulating a flood of technological advances utilizing quartz crystals. Who could have predicted at that time that experiments using tin foil, glue, magnets, wire and a jeweler's saw would set the stage for the development of electric guitars, radar, sonar, computers, and a vast range of digital technologies within the next 100 years?
“Piezoelectricity is the ability of certain crystals to produce a voltage when subjected to mechanical stress,” according to the Wikipedia. “The word is derived from the Greek 'piezein', which means to squeeze or press. The effect is reversible; piezoelectric crystals, subject to an externally applied voltage, can change shape by a small amount. The effect is of the order of nanometres, but nevertheless finds useful applications.”
“In a piezoelectric crystal, the positive and negative electrical charges are separated, but symmetrically distributed, so that the crystal overall is electrically neutral. When a stress is applied, this symmetry is destroyed, and the charge asymmetry generates a voltage. A 1 cm cube of quartz with 500 lb (2 kN) of correctly applied pressure upon it, can produce 12,500 V of electricity.”
The piezoelectric property of quartz crystals enables them to receive energy, process it, and transmit the oscillations outward in precise patterns.
Quartz crystal’s piezoelectric properties became the foundation of Twentieth Century digital technologies. Scientists found that the vibration patterns quartz crystals receive and transmit could be manipulated to augment, store, amplify, transfer, transform and focus other vibrational frequencies of energy, including sound, electricity and even information in the form of precise periodic pulses.
Sonar, radios, piezoelectric cigarette lighters, transistors, computer chips, liquid crystal displays, digital watches, satellites and many other technological pillars of today’s global society utilize quartz crystals in their manufacture.
In 1917, Paul Langevin, a French inventor, introduced an ultrasonic submarine detector called sonar, which utilizes a quartz crystal inducer to generate high-pitched sound frequencies which were transmitted through the water and bounced off objects to return to their source, where they are detected by a hydrophone.The time it takes for the sound waves to return is a measure of the distance from the sonar device to the objects in the water.
Quartz crystals were used in ham radios for the first time in the 1920s and 1930s, transmitting and receiving the human voice and music across vast distances. Between 1935 and 1940 Motorola made crystal control the foundation for a system of two-way radios that would work in a wide range of temperatures. The US military made the decision to incorporate crystal control into all their communications systems in 1939, and military historians say this decision contributed greatly to the Allied victory in World War II.
Pressing the button of a piezoelectric cigarette lighter squeezes a quartz crystal, and the resulting high-voltage discharge of electricity ignites the gas in the lighter as the spark jumps over a small gap.
Piezoelectric sensors power the amplifiers in electric guitars and powerful microphones.
Imagine a bell shaped by grinding a single crystal of quartz. “It would ring for minutes after being tapped,” explains Douglas Dwyer, the founder of Frequency Precision Ltd, a company that provides consulting and design services to the world-wide electronics industry. “Almost no energy is lost in the material. A quartz bell -- if shaped in the right direction to the crystalline axis -- will have an oscillating voltage on its surface, and the rate of oscillation is unaffected by temperature. If the surface voltage on the crystal is picked off with plated electrodes and amplified by a transistor or integrated circuit, it can be re-applied to the bell to keep it ringing.” This unusual property of quartz is the basis for the manufacture of digital watches.
“Quartz clocks employ a tuning fork made from quartz that uses a combination of both direct and converse piezoelectricity to generate a regularly timed series of electrical pulses that is used to keep track of the passage of time,” explains the Wikipedia. “The quartz crystal (like any material) has a precisely defined natural frequency (caused by its shape and size) at which it prefers to oscillate, and this is used to stabilize the frequency of a periodic voltage applied to the crystal.”
“The same principle is critical in all radio transmitters and receivers, and in computers where it creates a clock pulse,” according to the Wikipedia. Both of these applications usually use a frequency multiplier to reach the megahertz and gigahertz ranges.”
Tiny quartz crystals now comprise the heart of all digital electronic devices. “Currently, quartz crystals -- precision-cut and polished single-crystal silicon dioxide (a main ingredient of sand and window glass) -- serve as the clock source,” reports Sandia National Laboratories. “A piezoelectric material, the crystals expand and change shape when an electric field is applied, storing up electric charge. When no current is administered, the crystals release the charge. Electrical energy sloshes back and forth at a fixed frequency between the crystal and the timing circuit in a feedback loop. This fixed frequency generates timing signals, which allow calculations in digital electronics to occur in synchronized steps.”
Computer chips have a fascinating birth history. Silicon dioxide forms naturally as quartz crystals. Over time, quartz erodes into beach sand, which is the non-crystalline form of silicon dioxide.
Computer manufacturers extract pure silicon from the sand, heat the silicon to 1,500 degrees Celsius, and dip a tiny quartz crystal into the super-heated solution. The crystal is rotated and slowly extracted from the mixture, creating a larger mass shaped like a cone. The cone is turned on its side, and sliced into flat disks, which are then sub-divided into the tiny computer chips so ubiquitous in our homes, offices, cars, airplanes and briefcases.
It is no exaggeration to say that the digital age is the age of the quartz crystal.
READ NEXT CHAPTER: Chapter 8: Clearing, Cleansing and Using Quartz Crystals