I’ve seen the number of induction coils increase drastically over the years in The Netherlands. They are quite easily recognizable, as there’s typically a solar panel on a pole, that appears to provide power to the system.
Considering there’s a wide variety of vehicles on the road, surely each variant must have (slightly) different characteristics when passing over the coil; especially when in a specific place at a specific time.
And given that they are situated at highway exits (see picture) or after entrances, and road users unable to exit and enter elsewhere, it would be trivial to track the bulk of a vehicle’s trip.
This in context of ALPRs (in different forms) being in place at strategical locations (large junctions or at bridges or tunnels, and parking), and the address of vehicle’s owner; you’d be able to connect the dots, and end up with a pretty complete picture.
I didn’t get into energized coils and how they can be used to recognize objects because there’s much more to cover than just relatively accurately explaining how a record player cartridge and speaker work.
On the speaker end, and you’ll be familiar with this if you’ve built a metal detector before, the coil size can make it much more sensitive but that means that, and you’ll be familiar with this if you’ve ever built an am radio before, you also need to be selective in order to pick up precisely what you’re looking for. The old radio shack Forrest Mims books had compatible metal detector and am radio selectivity circuits iirc. With a change in the dropping resistor they could be daisy chained together and with an adjustable component or two in the bp filter you could stay over the same area and adjust your selectivity filter to reject all the rocks and red clay and show that one little nail buried four feet down.
The problem with using a selectivity circuit is it needs to be high order and in order to not fuck up the phase portion of the detectors chirp circuit, relatively phase linear. It’s okay if it changes the phase across the band as long as it changes it extremely consistently. That’s hard to engineer correctly and requires expensive parts so it’s less common than you would hope (thirty years ago when I was a little kid fucking around with shit in the garage).
Okay so metal detectors exist and big coils take extra circuitry, controls and training to be useful, who cares, the point is could coils like the ones pictured be used to reliably identify specific vehicles?
No. You could probably id the general weight and makeup of a car, if you knew all the other environmental factors. You gotta consider the sample size. You’re looking at a fraction of a second sample size and it’s gonna be a blip shape (just like it’s a blip sound when you sweep the metal detector coils over a nail), so you’re limited to analysis of blip shape and superimposed patterns. Blip shape is gonna just tell you general makeup, how much aluminum versus steel is there and where in the passing object, but you’d have to have an exhaustive database of different model/year/options to be able to correlate your reading to some kind of car and a good understanding of how each model ages to be able to account for the difference between a rust bucket and barn find (severely corroded pennies sound different than bright ones!).
In terms of superimposed patterns, you’re in even more difficult territory because it’s gonna be influenced by engine speed, driveshaft speed, wheel speed, and the mass of those components themselves. Go over the coils in a different gear than the last time and suddenly the reading is different enough to not be correlated.
All of the above analysis and more would require the computation power of a logging oscilloscope btw.
So if your goal is to track individual vehicles, coils are a bad choice. You need extensive knowledge, datasets to test against, repeatability, a system capable of at the very least high frequency data collection and you still get defeated by someone on the off ramp in third gear of hauling a trailer.
Or you could just use a tag reader and actually know exactly what car went where with a timestamp for likely less than a tenth of the price and no blocking off the ramp for a week while they install the coils.
I understand your skepticism, but I find it difficult to believe a (team of) professional engineer(s), being unable to design a system with sufficient selectivity and resolution. And perhaps a blip is all it takes to recognize a particular vehicle, that is statistically expected to arrive at one of the further detectors within a given time frame; it really narrows down the number of possible matches when situated between two known points.
If too noisy and low resolution, it can probably not be used reliably enough, to identify vehicles purely on the basis of detected characteristics. But in the context of ALPRs at strategic locations nearby a detector, a trail of detections could be linked to a vehicle’s license plate; which would be problematic enough. If of high enough quality, the increasing reliability of ALPRs detecting vehicle make and modell, could be utilized to store characteristics under an identifier for that detected; which could allow for pattern recognition and perhaps identification in effect.
The analysis wouldn’t necessarily have to happen on-edge, but could also be offloaded to a data center; which would drive down the computation power required per unit. And yes, installing ALPRs everywhere would be more efficient, but would simultaneously be much more controversial. These coils are already in place, and the installation of the coils in the road surface doesn’t appear to be that time consuming.
A team of professional engineers couldn’t detect terahertz radiation without grown nano scale antennas any more than they could use the coils of the size implied in your picture to differentiate between two cars of the same make and model let alone cars that aren’t in wildly different weight classes.
It’s not a question of pointing enough clever people or computing power at the problem, it’s a question of trying to dig a hole with a ball peen hammer in one swing. The tool is inadequate for the job, uses the wrong motion and doesn’t have enough time to do anything.
and for the example you gave where analysis isn’t definitive but could be paired with automated readers to clarify a picture, simple presence detection does the same thing and costs much less!
And come on, you know that just to cut those little octagons in the asphalt, drop in the coils and tar over em they’d send a ten man crew in four diesel trucks and shut the ramp down for the whole business day.
I’ve found a video that clearly demonstrates the concept I have in mind, just to make sure we’re on the same page; because I’m not sure we are. If simple presence detections, even in the context of many vehicles in close proximity of another, and changing order through vehicles overtaking others, then I would agree; but that’s something I find hard to believe. I can’t really argue with the last point though, because it should be considered universal truth…