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hello and welcome to a special bonus episode of technically speaking in our previous episode we were talking about new technology that created a rechargeable battery from cement to get some more expert knowledge for that episode antonia spoke to a very good friend chris who was an electronic engineer also knows a lot about how electricity interacts with the human body most of that conversation made it into the episode paraphrased by antonia there are some very interesting points
in the conversation she had with chris that form the focus of this episode one of the questions antonia had was about safety if we had a cement battery in a house could we get electrocuted from our own house okay i would say almost certainly not probably for a number of reasons first of all have you ever tried holding like an a battery and putting your fingers across either end of the battery and seeing if anything happens oh yeah for sure so you can normally you
can pick up an a battery which is at like 1.5 volts you can pick up a car battery which is about 12 volts and if you hold the terminals on that nothing happens but what about if you take a 9 volt battery and you put it across your tongue for example have you ever put a battery on your tongue oh yeah as a kid what did you feel just tastes really metallic like nothing else i guess what was happening when you were doing that is the current from the battery was stimulating the
taste buds in your tongue and actually causing you know the neurons to send signals to your brain and you were effectively doing neurostimulation on yourself and uh feeling a sensation that wasn't actually there and the reason it works on your tongue whereas it doesn't work on your fingers is because your tongue is inside your body and it's it's wet and it's so that means it's very conductive so it's much easier to get a connection between the contacts of the
battery and the kind of nerves in inside your tongue whereas when you're touching batch with your fingers your hands are covered in skin and the skin is often quite dry even if you lick your fingers you probably struggled to actually get a current that you could feel flowing between your fingers you'll find that just the the kind of resistance of your skin is too high to allow any sort of current to actually flow so people always say that it's the high current is what's really deadly
yes it's the current that kills you not the voltage and that's that's sort of true but when it's external to the body what you need is a big enough voltage to overcome that kind of resistance of your skin to actually get a big enough current to flow in the first place so even if you have a 12 volt battery that's capable of delivering thousands of amps instantaneously you're not going to get electrocuted from it because that 12 volts in the battery isn't sufficiently high to actually push that
current through your body chris has refreshed my memory of whether it's voltage or current that is most deadly but then that conversation took a really strange turn now if you had some uh needle electrodes that you'd placed into your skin that'll be a slightly different manner why would we want to do that uh you're piercing that kind of non-conductive layer of the skin and you're going into your tissue and what's the inside of a body is mainly made out of water and water is a great well not
perhaps a great conductor but is it is a conductor it current can flow through the water that's inside our bodies it's really clear to me now that the skin is a great barrier to the flow of electricity but it turns out there is another reason why you are unlikely to get electrocuted or even to receive an electric shock from the walls of your house if they do actually make up a cement battery the voltage of these cells is going to be very very low that we're stringing together potentially if
you strung loads and loads of concrete batteries together and made a very very high voltage you could touch them and cause a current to flow through your body but you'd have to be kind of across the battery so you can't just touch one end of the battery because it's not actually referenced to earth we say you can get electrocuted from mains when you touch the live terminal because that live terminal is reference to ground i.e the voltage where you touch it has a
potential difference between your finger and the ground that you're standing on because that's how the power supply is set up in the uk but a battery is like a floating power source so one side of a battery terminal doesn't have a voltage by itself it only has a potential difference measured to the other side of the battery is that the same of like why birds and people don't get electrocuted if they stand on train track or if they're on the overhead line yeah that's
exactly it the bird might be stood at a potential of 75 kilovolts let's say it's kind of irrelevant because there's no difference to grounds the bird doesn't get electrocuted so yeah so even with that fact these cement batteries the voltage is so low that it's probably not going to electrocute you and i imagine it's going to struggle to deliver enough current through you because of the internal resistance of the battery so these cement batteries are pretty safe
to handle and that's good news chris had more to say about how electricity interacts with the human body and what happens to our nerves you don't actually need a particularly a large amount of current to stimulate a nerve if you've got direct connection to a nerve a few microamps could actually stimulate a nerve if you've got a direct connection to it so perhaps you know it could be possible to electrocute someone with a concrete battery if all the conditions were perfect so maybe if we
had an open wound well maybe two open wounds we've got an open wound on each arm yeah and then we've got a concrete battery that will have to be physically massive in order to get a large enough voltage yeah but we're somehow going to be able to touch both ends of the battery do we want to stop the heart or do we want to just feel a tingling sensation i mean i don't know what the definition of being electrocuted even is like well i've looked up on the government's
health and safety executive website they seem to define electric shock as a current that flows that blocks the electrical signals between the brain and the muscles oh gosh that sounds quite serious it still sounds like getting a serious injury from a concrete battery is quite unlikely although if you really wanted to set things up in a very particular way you could probably stimulate some nerves there's yet another reason why you were quite safe from any form of injury from a concrete
battery that involves electricity even if we had a concrete battery in our walls the anode and the cathode aren't exposed the concrete in in this battery is the electrolyte it's the anode and the cathode the conductive bits that we don't want to touch that could electrocute us the electrolyte is kind of just a medium for the electrons to flow in between the two of these if you imagine the concrete batteries the walls that you're touching the kind of actual terminals are inside the wall yeah i
think you're not going to get electric touching the walls for a number of reasons good to know good to know phil thank you for your expert opinion chris chris knows about far more than just electrical storage he's also done a lot of research in generating electricity from motions of the human body what's your interest in this topic how did i drag you into this this episode what how did antonio drag me into this episode okay well i did my phd in wearable electronics and as a part of
that i was looking at energy harvesting and i was particularly trying to see if we could power like a small wearable device so that's a small bit of electronics that goes on the body and potentially measures some sort of bio signal on the body and whether we could power a device that did that using just our footsteps so i made some insoles that went inside the feet in the feet in the shoes there's some insoles that went in the shoes and i did quite a lot of
work estimating looking at people's like walking speeds and putting different energy harvesters inside their shoes and looking at whether that would be able to power my electronics that i'd develop and there was once research into whether we could combine the idea of generating electricity from motions of the human body along with using the fabric of our homes to generate or store electricity interestingly someone a long time ago there was a study about putting energy
harvesting carpet in houses oh you could generate energy from like the triboelectric effect when someone shuffled along the the carpet like static electricity yeah so that basically if you put a load of triboelectric generators all over the floor and like shuffled shuffled when you walk you could use that as an energy harvester and use that to power your house that gives us an excuse to shuffle around you know some people are like oh you know don't walk like shuffly yeah
stop shuffling walk properly really you know you're just trying to help the environment you're just trying to generate electricity from your carpet in practice these things they make so little energy and it's so difficult to capture those small amounts of energy that it's really not worth the effort of making these large-scale energy harvesters for powering anything inside a home they could be useful for doing sensing where you've got a very small bit of electronics that's doing something very
simple and it's doing it very infrequently but for a house where you're doing big things like powering lights and having cookers on and you're leaving them on for long periods of time it's never going to work it's never going to scale to that sort of location so energy harvesting from moving around our own homes probably isn't feasible just yet but there are improvements in electronics all the time so maybe in the future it will make more sense everything gets smaller and more
efficient moore's law says that you can double the transistor count on the same surface area every two years or one and a half years or whatever it is so it's not infeasible to say that within 10 years time having the same device take an order of magnitude less power isn't too much more than a feasible statement to make and advances in electronics usually means that we use more elements on the periodic table this makes the devices more complicated and also raises
questions about where we'll get those elements from the cement batteries used iron and nickel as the anode and cathode but who knows what the future might hold and does this mean that we're creating a different problem adding to our our usage of metals this is something i argued before when my research looking at sustainable electricity was are we replacing fossil fuels with metals if we're not able to recover them afterwards now we're electricity generation technologies
i wonder how easy it is to recycle um not recycle what's it regenerate regenerate yeah yeah so why why does the battery lose capacity in the first place another interesting thing is how would you get so if you've got your concrete battery how are you going to get the nickel and the iron sheets out for concrete material because presumably you have to fully encapsulate the electrodes within the concrete and it has to kind of have lots of contact points yeah to get good contact so it
kind of makes you think you have to like smash it up to get it out antonia talked about recharging the cement-based batteries in the full episode and about recovering them from our homes too the big questions for any emerging technology are really about the resources that are needed to make them the useful life of that technology and what happens once it's no longer useful ultimately we're asking how these scientific advances can be useful for society the views expressed in this podcast
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