A step toward fully 3D-printed active electronics

Reading the article, it looks like so far they only have a working resettable fuse (a passive device), and only hypothesize that a transistor was possible with the copper-infused PLA filament. So no actual working active electronics.

And from the paper linked in the article[1], it seems the actual breakthrough is the discovery that copper-infused PLA filament exhibits a PTC-effect, which is noteworthy, but definitely not "3D-Printed Active Electronics" newsworthy.

[1] https://www.tandfonline.com/doi/full/10.1080/17452759.2024.2...

> So no actual working active electronics.

Oh so this is another scam like the MIT Food Computer. At this point I assume everything coming out of MIT is a scam until independently validated by disinterested third parties

usually even these academia hype pieces have some grain of utility but this one was so incomprehensibly bad that i was genuinely confused if i'm reading it incorrectly. what the hell?

Hang on, can you explain why this is passive and not active?

> Harnessing the described phenomenon, we created the first semiconductor-free active electronic devices fully 3D printed via material extrusion. We demonstrate this breakthrough through the implementation of monolithically 3D-printed logic gates.

Well, it is just “a step.”

Whether or not it is newsworthy… eh, I mean, what is MIT News? A campus newspaper? I’m pretty sure we had articles on particularly big games of capture the flag in mine.

It looks like the editors have amended the title of their article since this was initially posted. The original title was just “3D-printed Active Electronics”

Not to be that guy, but this is a typical situation as it occurs a thousand times per week:

1. Scientists make minor progress as part of a multi-year effort, release a paper, paper features overly optimistic outlook to get future funding

2. Institute marketing department both hypes it up and dumbs it down a little

3. Popular science press picks it up and both hypes it up and dumbs it down a little more

4. Scientific literate readers read it and complain

TL;DR: Nothing new under the sun

They've created a Polymeric Positive Temperature Coefficient (PPTC) device. As it heats up the resistance gets very high very abruptly.

While it is non-linear, diodes are also considered passive devices[2], as active is taken to mean electrical control of current flow.

In this case one could induce current control through thermal means, ie an adjacent heating element, and if you potted that in a box I guess you could argue the box is an active device. But not the PPTC itself.

[1]: https://m.littelfuse.com/~/media/electronics/technical_paper...

[2]: https://wiki.analog.com/university/courses/electronics/text/...

I want to clarify that they actually did build a transistor-like device, and not just hypothesize about it. I missed section 3.2 when I initially skimmed the paper, which demonstrates and shows the results of a working “transistor”.

Unfortunately I can’t edit my original post, so apologies for causing any confusion.

> active is taken to mean electrical control of current flow

Is a transformer an active device? Asking because current in one loop can control current in the other loop.

From there, are two copper wires an active device?

Unlike a device with positive temperature coefficient, the NTC thermistors (negative temperature coefficient) can be used by themselves as active devices that provide a negative resistance, which can be used to make amplifiers and oscillators, exactly like with any other diodes with negative resistance, e.g. tunnel diodes, IMPATT diodes, Gunn diodes, Shockley diodes, diacs and so on.

Nevertheless, I do not think that anyone has ever made amplifiers or oscillators with thermistors, because unlike the diodes where the negative resistance has electrical causes, the inertia of the heat transfer in thermistors makes the achievable upper limit for the amplified frequencies very low, typically under 1 Hz.

A device with positive temperature coefficient could be used as an amplifier or as a switch (like a relay) only together with a separate heater, as you say.

This shouldn't be a downvote or flag. It's a serious problem, especially at elite institutions, and especially at MIT and Stanford.

It's also not out-of-line with what credible sources observe:

https://blogs.bmj.com/bmj/2021/07/05/time-to-assume-that-hea...

I'm affiliated with MIT, and have been for the vast majority of my life, including at points in fairly senior roles. If you shut people out pointing problems, it will never get better.

There's an incredible urge to defend elite academic institutions, but it's not in the interest of those institutions. Remember your civics class (patriots criticize their government institutions).

The only way I see this fixed involves a period where MIT is viewed like a used car salesman in the public eye for at least enough years to cause enough pain to lead to reform. The endowment is big enough it'll do fine in the end. If it keeps sliding to fraud, it won't.

The current in one transformer loop does not control the current in the other loop.

The power from one loop is transferred into the other, there is no control. The same for two copper wires.

"Control" means that you can determine the value of the power in some circuit by consuming less power to do this. If you have to use the same power, not less, then you are the provider of power, not someone in control, i.e. this is the difference between bosses and the workers commanded by them. The bosses do not lift heavy parcels themselves, they order to some worker to do that.

A device that apparently looks like a transformer but it is an active device is the magnetic amplifier. There are 2 differences from a transformer, the magnetic core is saturable during normal operation (any magnetic core is saturable at a high enough magnetic field, but when that happens in a transformer this means that the transformer has failed, which leads to overcurrents that would destroy the equipment unless a protection is triggered), and the second difference is that the control coil has a very high number of turns, so that a very small current can saturate the magnetic core.

In a magnetic amplifier, the output coil is inserted in an AC circuit where the power must be controlled. When the core is not saturated, the impedance of the coil is high and the output AC current is low. When the core is saturated, the impedance of the coil is low and the output AC current is high. Whether the magnetic core is saturated or not is controlled with a very small current and power on the control coil, which makes this an active device.

Magnetic amplifiers have been heavily used during WWII, especially by the Germans, who had improved them, and they continued to be used for a few decades after the end of WWII, when USA had captured the German technology, because of their very high reliability, until the transistor amplifiers have become reliable enough.

> as active is taken to mean electrical control of current flow.

Does the building of logic gates controlling a motor not show electrical control of current flow?

But transformers don't do that. The electricity you put in one winding "comes out" on an/the other, transformed -- there isn't one current controlling another, there's just one current[0].

[0] very loosely speaking, also I am not a doctor

> The current in one transformer loop does not control the current in the other loop.

You are right about the power, but the current in one loop __does__ control the current in the other loop.

You use "control" in the wide sense of "dependency", i.e. if two quantities are constrained by an equation, you say that one quantity controls the other, only because their values are not independent (which means that fixing the value of anyone of the two quantities also determines the value of the other quantity).

According to your usage, the voltage on a resistor is controlled by its current, because the voltage is proportional with the current (by the resistance of the resistor), and also the current is controlled by the voltage, because the current is proportional with the voltage (by the conductance of the resistor), exactly like in a transformer the input and output currents and voltages are bound by proportionality relationships.

It is true that this meaning of "control" is encountered in speech, but in engineering and physics "control" has a precise meaning, more restricted that how you use it.

In the engineering use of "control", it is always possible to distinguish which is the controller and which is the controlled in a control relationship.

When "control" is used like you use it, the "control" relationship is bidirectional and you cannot say which is the controller and which is the controlled, e.g. between the primary loop and the secondary loop of the transformer, or between the current and the voltage through a resistor.

For "control" in the engineering sense, unidirectionality is an essential property. Real control devices have some internal feedbacks that make them not completely unidirectional, but this is considered a defect and serious efforts are done to improve the unidirectionality of the control devices. A device with total feedback like a transformer cannot be used to implement any of the known control methods, i.e. you cannot make amplifiers or oscillators or logic gates with it.

This image shows logic gates they made:

https://www.tandfonline.com/cms/asset/5043deae-e79e-45fc-bb7...

But when electrical power is used to drive a simple DC motor, then that power "controls" the speed of that motor. When the power is removed and the motor keeps turning (by e.g. a flywheel) then the power is delivered back to the input. So in that example there is bidirectionality, where you still "control" the speed of the motor.

I have seen old organs which used solid state VCOs that also had an incandescent lightbulb near the circuit boards to help maintain a stable temperature, and had thought they must use a thermistor although I seem to be mistaken as I can't find much information about that.

I did find this however:

https://northcoastsynthesis.com/news/temperature-compensatio...

From https://news.ycombinator.com/item?id=40759133 :

> In addition to nanolithography and nanoassembly, there is 3d printing with graphene.

And conductive aerogels, and carbon nanotube production at scale

From https://news.ycombinator.com/item?id=41210021 :

> There's already conductive graphene 3d printing filament (and far less conductive graphene). Looks like 0.8ohm*cm may be the least resistive graphene filament available: https://www.google.com/search?q=graphene+3d+printer+filament...

> Are there yet CNT or Twisted SWCNT Twisted Single-Walled Carbon Nanotube substitutes for copper wiring?

Aren't there carbon nanotube superconducting cables?

Instead of copper, there are plastic waveguides

What seems cool about this to me is that they seem to have done it with a plain old FDM printer and copper impregnated PLA. The devices are fairly large (mm scale) so presumably anyone with a $200 ender and the correct filament could print these.

I am able to find copper PLA for sale too, although I'm not positive it is what was used in the experiment, and it's kind of pricey (~ $100/kg).

As I have said, some people, including you, are using the word "control" in this wider sense, where it is synonymous with "dependency".

Nevertheless, using "control" with this meaning in any engineering text would be a mistake, because there "control" must be used in its strict sense, to avoid confusions.

In any system there are many dependency relationships, corresponding to all the equations that are applicable to that system, but much fewer control relationships. The control relationships are quite important for the understanding of the system, so they must be identified clearly in a distinct way from other dependencies.

Etymologically, the right sense of "control" is the strict sense, because it has never been applied to a bidirectional relationship like that between the quantities connected by an equation, but it originally referred to a unidirectional relationship, between a dominant party, the controller, and a subordinate entity, the controlled, whose accounts were checked by the controller.

In proper engineering terms it is not the source of power which controls the speed of a motor, but the device that is used to vary the amount of that power. When there is no device to vary the input power, a DC motor works like a transformer, the input voltage is proportional with the output rotational speed and the input current is proportional with the output torque. The input quantities and the output quantities are dependent, so in the wide meaning of "control" you can say equally well that the input electric power is controlled by the output mechanical power or that the output mechanical power is controlled by the input electrical power. However the use of this phrases does not provide any advantage instead of just saying that you have a system of 2 equations that connect the 2 input quantities and the 2 output quantities, so given an appropriate pair of quantities the other 2 are provided by the equations. On the other hand, saying for instance that the motor speed can be controlled by the excitation current of the motor provides useful information by using the word "control", because it is implied that this method of varying the motor speed requires only a small power in comparison with the output power.

We say a changing current in one coil of a transformer induces a current in the other coil. It does not control the current of the other coil.

Any induced current is superimposed on top of whatever is already there on the other side. This is different from controlling the current.

For example, you couldn't block DC current passing through the secondary side regardless what you did on the primary side.

It’s cool for tinkering, and I think there are lots of potential use-cases for conductive filaments and printing in electronics, but I don’t think transistors are necessary. Silicon crystal development is really already a sort of “additive manufacturing”, and I’m not sure what purpose would be served by re-inventing a method that would be starting so far behind in terms of scale, precision, and cost in relation to traditional semiconductor production (anyway, I assume this idea is broadly for learning/experimentation/the lols, rather than some earnest aspiration for using metal-bearing printer filaments to produce active components).

What about the use of power transistors that don't too well as silicon crystals afaik.

Imagine i have a pencil which I'm holding in my hand. With my hand, I can control the position of the tip of the pencil. Now imagine the pencil is made of rubber. I can still control the position of the tip, but e.g. a strong wind can cause the pencil to flex and so the control is not perfect. But it is still control.

I don't see how this is fundamentally different from controlling the current through a transformer.