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hoola

piezo ceramic project

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I am working with piezo ceramics, 5.5 mm thick. I need to know the rate of a shock wave as it travels through the material.  James Woodward, et al are developing a piezoelectric Mach thruster device they are claiming develops propellantless thrust as a physical analog to the Shawyer engine. The materials to do a few simple tests are cheaply available so I figure it could be an interesting side project. Thanks for any help if you know that detail about ceramic piezos or have an interest in mach thrusters in general.

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does anyone know of a rubberlike substance with a tailored characteristic that passes a mechanical force in one direction, and absorbs force from the opposite direction? In effect a non linear stiffness profile, or  "smart rubber". A material of this nature could act as a rectifier of physical forces, and this directionality might offer a thrust potential when placed between each piezo instead of a single conventional damper used in the woodward mechanism.

Edited by hoola

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4 minutes ago, hoola said:

does anyone know of a rubberlike substance with the tailored characteristic that passes a mechanical force in one direction, and absorbs force from the opposite direction? In effect a non linear stiffness profile, or  "smart rubber". A material of this nature could act as a rectifier of physical forces, and this directionality might offer a thrust potential when placed between each piezo instead of a single conventional damper used in the woodward mechanism.

Substances don't 'absorb force'.

It is possible to build a mechanism that sort of answers your requirement using a dome shaped piece of spring steel foil set against a ring foundation.
But the foundation would have to be set against something to ultimately resist the applied force.

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substances don't absorb force?  Wouldn't an absorbed force show up (at least)as heat within the material? The domed spring idea is interesting if it produces a diode like appearance to the system. The "thing" the spring is set against in this instance would be the inherent mass of the ring, but even then it seems the dome would couple as much energy overall in one direction than the other, although I see it might have a differing directional profile. If you had maxwell demons to do the job, such as tiny trap doors that all open in one direction allowing force through and close in the other, blocking such efforts with compressive release of heat from the stopped wave .

Edited by hoola

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a purely mechanical system is what I am experimenting with now, using a double row of 24 contacts rotary switch spinning at 1800 rpm , sweep pulsing the piezos and scoping results with a 6th piezo at the end of the stack.  I am  in the process of assembling a purely electronic setup using an arduino  microcontoller to manage timing of the 5 power amps that will pulse each element individually, with the next pulse timed precisely to reinforce the previous one in the forward direction, or hit it at the next element's  "TDC". This hopefully will result in amplification of the pulse that after 5 repeated steps hits the end of the stack, and due to mechanical impedance mismatch, is reflected back in a way similar to a transmission line or an audio amp that has lost it's load. This reflected wave is the problem. It prevents thrust by equalizing forces. The driver schematic I am  drawing up has a full time negative feedback system, but with a hi Q 25khz trap in series, which is the resonant frequency of the piezos I am using.  This will suppress  the normal sideband noise but not the desired signal.  This could clean up the carrier signal and maybe even offer some added amplification due to reduced internal losses. At the end of the cycle, when the return wave is heading back through the stack, all feedback circuits remain on, but the 25khz trap is bypassed and all signals are suppressed  maximally within each element. This hopefully will cancel a portion of the  reflected wave energy within each element. So, the overall goal is to amplify kinetic forces in one direction and actively suppress it in the other. 

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the question of how to detect micro newtons of thrust is going to be a tough one for a table top experiment in the kitchen. I am going to try swinging the stack as a long pendulum of approx 55" of length,  suspended from the ceiling with fishing line. I will time the duration of the swinging without power until the mass comes to rest. Then I will power up the stack and measure swing duration with the proposed thrust direction positive to the pendulum directions. Then thrust direction will be reversed to counter the pendulum motions and that will be timed. These 3 tests averaged over many trials might offer some evidence of thrust or lack of it.

Edited by hoola

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The drive order at each limit of swing is switched in either instance. The stack will be suspended from the ceiling with two parallel fishing lines spaced equally to the distance between stack end attachment points to keep the assembly parallel to the proposed thrust vector.

Edited by hoola

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I need to know the fastest switching speed an arduino can produce. After numerous utube tutorials and asking around, no one knows what that is. The reason I need to know is that the shock wave travelling through the stack will have to be " chased" in the manner previously described, and it seems likely that since the stack is on the order of 2" long and having a far faster speed of sound being a dense ceramic,  will need microsecond gradations, and not the millisecond pulse rates that the arduino might only be capable of.  If  the arduino speed is limited to a millisecond range,  a recommendation of a laptop controlled microcontoller with a microsecond control speed would be  very much appreciated.

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