Monday, 1 June 2009


To create a smoke ring, some devices use the movement of a membrane which is pulled back and then pushed forwards. This membrane is known as a diaphragm. The elastic fabric of a trampoline acts like a diaphragm. Sometimes, I imagine the magnetic field around a bar magnet (the bit that looks like a watermelon) as something like a diaphragm. The bar magnet would be the membrane at rest, and the magnetic field, as highlighted by iron filings, would be revealed as the vibrations of this membrane to and fro. I think there's something very special about a diaphragm.

A major step in the evolution of animals was taken by those that became endothermic or "warm-blooded" - the ones we call mammals. Mammals can maintain a constant body temperature over time through internal regulation. This gives them enormous independence in their surroundings compared to ectothermic, "cold-blooded" animals - such as reptiles, amphibians, and fish - which are dependent on the surrounding climate to regulate body temperature. The ability to warm the blood relies heavily on a higher metabolism. This higher metabolism is aided by a four-chambered heart (non-mammals have only three chambers) and a higher respiration capacity (oxygen fuels metabolism). This increased respiration is thanks to a muscle called the diaphragm.

The diaphragm is a sheet of muscle that seperates the abdominal cavity from the respiratory system of the chest cavity. On the in-breath the diaphragm contracts and draws down the abdominal cavity, and as it does so, it forms a vacuum in the chest cavity, which in turn forces the lungs to fill with air. On the out-breath the diaphragm then springs back into place, a bit like a trampoline, and so it forces the air out of the lungs - a bit like squeezing bagpipes. This site on You-tube offers a really good animation of the diaphragm doing its thing....

I remember reading once about how torturous crucifixion is because of the way it affects the diaphragm. As if having nails banged into the flesh (causing severe nerve damage and agonising pain) wasn't bad enough, the victim was, quite literally, left fighting for every breath. The following was taken from a piece by Cahleen Shrier Ph.D, who gives lectures on the science of Christ's crucifixion (it makes for some pretty grim reading):

Normally, to breathe in, the diaphragm (the large muscle that separates the chest cavity from the abdominal cavity) must move down. This enlarges the chest cavity and air automatically moves into the lungs (inhalation). To exhale, the diaphragm rises up, which compresses the air in the lungs and forces the air out (exhalation). As Jesus hangs on the cross, the weight of His body pulls down on the diaphragm and the air moves into His lungs and remains there. Jesus must push up on His nailed feet (causing more pain) to exhale.

In order to speak, air must pass over the vocal cords during exhalation. The Gospels note that Jesus spoke seven times from the cross. It is amazing that despite His pain, He pushes up to say “Forgive them” (Luke 23:34).

The difficulty surrounding exhalation leads to a slow form of suffocation. Carbon dioxide builds up in the blood, resulting in a high level of carbonic acid in the blood. The body responds instinctively, triggering the desire to breathe. At the same time, the heart beats faster to circulate available oxygen. The decreased oxygen (due to the difficulty in exhaling) causes damage to the tissues and the capillaries begin leaking watery fluid from the blood into the tissues. This results in a build-up of fluid around the heart (pericardial effusion) and lungs (pleural effusion).

The collapsing lungs, failing heart, dehydration, and the inability to get sufficient oxygen to the tissues essentially suffocate the victim. The decreased oxygen also damages the heart itself (myocardial infarction) which leads to cardiac arrest. In severe cases of cardiac stress, the heart can even burst, a process known as cardiac rupture. Jesus most likely died of a heart attack.

In a moving coil, or moving magnet microphone the energy in a sound wave causes a diaphragm to vibrate, and electromagnetic induction changes the acoustic energy into electrical energy. The first microphone was invented and developed to be used as a telephone voice transmitter. It converts soundwaves, existing as patterns of air pressure, into electric signals and eventually back to soundwaves through speakers. For example, in the electro-dynamic type of microphone a flexible diaphragm is made to vibrate when in the path of a stream of soundwaves. The diaphragm's movements are transferred to a coil of wire in the presence of a magnetic field, thus inducing a current in the coil through the phenomenon known as electromagnetic induction. This varying electric signal has a voltage pattern that is a replica of the sound wave pattern impinging on the microphone, ie, it is an analogue signal.

The telephone reciever (earpiece) is an electro-acoustic transducer, but works in the opposite direction to the microphone. A varying electric signal causes a diaphragm to vibrate in sympathy. In this way, the diaphragm generates a set of soundwaves, which are a reasonable reproduction of the original sound of the speaker.

Modern telephones use electret microphones for the transmitter and piezoelectric transducers for receivers. Sound waves picked up by an electret microphone causes a thin, metal-coated plastic diaphragm to vibrate, producing variations in an electric field across a tiny air gap between the diaphragm and an electrode. A piezoelectric transducer uses material which converts the mechanical stress of a sound wave upon it into a varying electrical signal.

When cystals are exposed to pressures or forces around a particular axis, they are elastically deformed. The experience of deformation produces an electric potential, which results in the flow of an electric charge for a few seconds. The same is also true in reverse - when electric current passes through a piezoelectric material they deform, they change in size (volume) by a few percent. It is the latter characteristic which enables piezoelectric materials to be used as vibrating diaphragms. Repeated application of the electric current, followed by its relaxation, enables a diaphragm to move forward and backward in one direction. The ability of the piezoelectric transducers to vibrate with an electrical signal oscillating at ultrasonic frequencies, makes them ideal for use in ultrasonic cleaning systems.

The vibrating piezoelectric diaphragm creates compression waves in the liquid if a tank which literally 'tear' the liquid apart, leaving behind many millions of microscopic voids or partial vacuum bubbles. These bubbles collapse with enormous energy; temperatures of 10,000K and pressures of 50,000 lbs per square inch have been reported; however, they are so small that they do no more than clean and remove surface dirt and contaminants. The higher the frequency, the smaller the nodes between the cavitation points, which allows for the cleaning of more intricate detail.

You might be getting a little deja-vu. We've come across ultrasonic cleaning before in a post I made about magma. I suspected ultrasonic vibrations are at work inside the planet. Ultrasonic transducers produce waves of fluid pressure by the vibration of a diaphragm immersed in fluid. The device producing the vibration is called a transducer. Does the Earth contain a transducer?

With piezoelectric transducers the frequency of vibration is high - from tens of thousands to hundreds of thousands of oscillations per second (hertz). Consequently, the effect of each cycle of vibration is negligible, but their cumulative and continuous effect can be either positively or negatively dominant. Average respiratory rate reported in a healthy adult at rest is usually given as 12 breaths per minute. The body's diaphragm is obviously going a lot slower than the transducer - but is it basically carrying out the exact same job but at a much lower frequency?

I suspect there are things we don't yet fully understand about dissolved gases, cavitation, and the collapse of bubbles in fluid. Knowing (?!) what we do now about the aether - how can it be applied to the mechanism behind electromagnetic induction, and piezoelectric transducers?

Many thanks:
Dynamic fields and waves By Andrew Norton, Open University
Understanding telecommunications networks By A. R. Valdar, Institution of Engineering

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