11 Feb History of Transducers
A transducer is any substance that converts one form of energy into another form of energy.
The best transducers are mineral crystals which transmute energy along their elemental atomic lattice. In modern physics and electrical engineering, the term transducer generally means the use of a sensor or a detector of some kind, but any system which changes energy from one form into another is considered transductive.
Transducers are found everywhere today and have been helping our society for the last hundred years. They’re widely used in all types of everyday things, including antennae, microphones, speakers and magnetic tape heads, and especially in measuring devices like hydrogen meters, pH meters, electrostatic meters and even the latest iPhone enabled sonar fishfinder device. All types of audio transmitters and receivers including BlueTooth require Piezo crystals. But this wasn’t always the case – the science is only about one hundred years old.
Man has long believed crystals are magic.
Theophrastus made the first known reference to the phenomenon of pyroelectricity in 381 BC, noting that a gem stone in his possession called the lyngourion became charged when heated. In his lapidary, Theophrastus reported that the gem would attract sawdust or bits of straw when made hot. Today we believe he was talking about amber, and perhaps a rare variety of white amber from Ligor? In any case, although amber is not a gem, it does have both pyroelectric and piezoelectric properties. Another stone described by Theophrastus as exhibiting similar properties was something he valued called electron, which although is another ancient name for amber, Theophrastus does not consider this gem to be made of the same material as Lyngourian.
Could either of these gems have been the mineral tourmaline? Boron silicate or Tourmaline makes beautiful gemstones, often considered magic for their unusual electric properties. The boron silicate molecule combines with other metallic elements to crystalize in many different shapes and colours. They are all scientifically proven transducers, and a great many ancient writers were aware of their strange properties.
Johann Georg Schmidt noted in 1707 that tourmaline attracted only hot ashes, not cold ones. In 1717 Louis Lemery wrote as Schmidt had earlier, that small scraps of non-conducting material were first attracted to tourmaline, but then repelled by it once they came into contact with the gemstone. In 1747 Linnaeus first related the phenomenon to the newly discovered concept of electricity. He called tourmaline Lapidem Electricum or “the electric stone”, even though the connection was not officially proven until 1756 by Franz Ulrich Theodor Aepinus.
Piezoelectricity was discovered in 1880 by French minerology professor Jacques Curie and his younger brother, Pierre Curie, who were working with a few different crystals including tourmaline at the University of Montpellier. They were conducting tests in pyroelectricity. These two researchers combined their knowledge of crystals and their passion for the emerging science of electricity to make some accurate conclusions about how crystals behave when subjected to thermal or mechanical stimuli. The Curies made their most impressive discoveries using Rochelle Salt Crystals, which are potassium sodium tartrate, with molecular formula is KNaC4H4O6•4H2O. This double salt was first prepared in 1675 by an Pierre Seignette, of La Rochelle, France. Rochelle salt crystals are colorless to blue-white salt crystals with an orthorhombic system and the best choice for physics professors teaching the subject.
The Curies were studying pyroelectricity (from the Greek pyr, fire, and electricity) which is the ability of certain materials to generate a temporary voltage when they are heated or cooled. While the two men were heating substances and measuring the stones to determine if electrical current was being produced through heat, they discovered some of the mechanisms behind piezoelectricity, which means electricity resulting from pressure. It is derived from the Greek piezo or piezein (πιέζειν), which means to squeeze or press, and electric or electron (ήλεκτρον), which actually stands for amber, that ancient source of electric charge.
The first practical application for piezoelectric devices was sonar, developed during World War I in France in 1917 by Paul Langevin when his team of war weary researchers developed what they titled as an ‘ultrasonic submarine detector’.
Langevin’s Submarine Detector was Top Secret in 1917. It was the most advanced science of the period, shared with the British and then with the Americans in the last days of the war. The bulky contraption was definitely larger than a bread box, and consisted of a huge transducer, made of thin quartz crystals carefully glued between two steel plates, and a hydrophone to detect the returned echo. By emitting a high-frequency chirp from the transducer, and measuring the amount of time it takes to hear an echo from the sound waves bouncing off an object, the British Navy crews could calculate the distance to the German Submarine below and use the data to set more accurate depth charges.
In the not so distant future electronics companies will grow piezoelectric crystals in orbiting labs or on the moon, which has much less gravity to warp the crystalline structures. The result will be the best fishfinders that planet Earth has ever seen!