It’s 2014 and wireless charging still isn’t mainstream, what’s holding it back?

August 1, 2014

The wireless charger for the the Nexus 5 is coming, and soon.

Battery life is still a big weakness for our increasingly powerful and impressive smartphones. The need to plug in and recharge at regular intervals challenges their “mobile” status. It’s a pain having to take chargers and cables with you. It’s limiting to have to sit next to a power socket. How often have you inwardly cursed as you fiddled with that micro-USB plug?

You know what’s missing in every vision of the future? Wires.

Wires are ugly, they get tangled, and they end up dictating where we can have things. No one really likes them, so why can’t we just get rid of them once and for all?

The science is there

Electric toothbrushes have been wirelessly recharging since the 90’s. There’s nothing special about the technology and it’s been around for a lot longer than that. Inductive charging uses an electromagnetic field and tends to employ two induction coils, one in the device and one in the charging dock. Unfortunately they have to be very close together for this to work.

magnetic fields Hyperphysics

Thankfully some clever people worked out that resonance can be employed to transfer power over short distances of around a meter or so. The idea is that the charger and device are effectively tuned to the same frequency and this would enable the phone in your pocket to start charging when in range without you having to do a thing. It could also pave the way for battery-free smoke detectors and wireless gadgets and appliances throughout the home, but it’s not ready for prime time just yet.

What’s wrong with what we have?

Palm launched the Touchstone wireless charger for the Pre back in 2009. Since then we’ve seen various wireless charging kits that force you to splash out extra cash for a new back cover and a series of impressively ugly pads. It’s gradually becoming more common for smartphones to support wireless charging out of the box, but it’s far from ubiquitous.

samsung wireless charging

There are lots of inductive charging solutions on the market already, but they have weaknesses. You can only charge one device at a time and you have to find the sweet spot on the pad for it to charge properly. Knock your phone out of position and charging will grind to a halt. If you can get the same speed as charging from a USB port then you’re doing well, and there’s little prospect you’re going to get anywhere near wall socket speeds. You also can’t use the device while it’s charging.

There are lots of inductive charging solutions on the market already, but they have weaknesses

Having a pad on the night stand that you stick your phone on overnight is the obvious scenario, but it offers little advantage over a decent dock, especially if you have a magnetic charging port like the Z2.

The truth is that the current solutions that are available right now just aren’t that good and there’s another big barrier to their adoption.

Greed versus open standards

According to IHS the market for wireless power transmitters and receivers was worth $216 million in 2013 and it’s going to expand to $8.5 billion by 2018. Everyone wants to carve themselves a big piece of that pie and they’re still fighting about the technology, which means we can’t have a standard that will work across the board with every device.

The Wireless Power Consortium (WPC) was founded in 2008 and is driving the Qi standard, which is the most widely supported right now. A lot of big mobile players are working with it including Samsung, Sony, Nokia, HTC, LG, Asus, Qualcomm, T-Mobile, Sprint, and Verizon.

The Power Matters Alliance (PMA) was founded by Procter & Gamble and Powermat Technologies in 2012 and it has set itself up in opposition to Qi. It also has a long list of big mobile names involved including Samsung, Sony, HTC, LG, Asus, Qualcomm, ZTE, and AT&T.

best-wireless-charger-choe-2

The PMA has pushed Powermats into chains like Starbucks and McDonalds as it makes a play for public profile. General Motors just announced that it will have Powermat in its new Cadillac line, but you have to buy a case for your phone to use Powermat technology and they’re not cheap.

It’s not clear who will win and you can see that many companies are engaging in a bit of fence-sitting, waiting to see which side they should jump down on

The WPC seems to be focusing more on getting Qi technology into hardware like it did with the Nexus 4, 5, and 7, some of Samsung’s galaxy line-up, a bunch of Nokia Lumias, phones from HTC, Motorola, LG, and a bunch of others. However, it’s rarely advertised as a big feature and often requires the additional purchase of a Qi battery cover.

It’s not clear who will win and you can see that many companies are engaging in a bit of fence-sitting, waiting to see which side they should jump down on. There’s no significant difference in the technology that the WPC and the PMA are backing, in fact Powermat was in the WPC until it broke away to form the PMA.

What about magnetic resonance?

The next generation of wireless charging will be the near field magnetic resonance we talked about earlier. No mats or careful alignment, much greater potential convenience. The WPC just announced plans for Qi to fold a backwards compatible magnetic resonance system into the platform, but the PMA won an important battle when it convinced the Alliance for Wireless Power (A4WP) to partner.

rezence

The A4WP was founded in 2012 and supports a magnetic resonance system which it’s calling Rezence technology. Another pioneer of resonant wireless power transfer technology, WiTricity, is also a member of the PMA. If it can get to market with these kinds of superior solutions then the WPC could see its early lead melt away.

Get on with it

Who is going to end up in the graveyard with HomeRF, Betamax, and HD DVD? To some extent we will decide with our purchases, but because the technology is going be incorporated into the devices we buy the alliances and decisions of the OEMs are vital. Who is going to choose a smartphone based on the wireless charging technology inside it? If all the big players jumped off the fence and chose the same side the argument would be over instantly.

Either way it looks as though the technology itself is going to improve drastically in the next couple of years and we can’t wait for it to deliver on its promise. No one is going to miss wires.

Comments

  • Sean

    Until a phones charge last more than a day or so, wires will remain present in portable chargers. They’re not going anywhere.

    • TheGCU

      The problem with battery life is size. I have an extended battery in my phone, and the extra size is completely worth the longer life; I get three days between charges. If people stopped obsessing about thin and small, then they’d have decent battery life.

      • wezi427

        I couldn’t agree more. I’d rather tell someone that I get 2 days on a full charge, than telling someone that my phone is 1/2 cm thinner than there phone.

  • MasterMuffin

    So you could say PMA has better solution than WPC, but WPC is still getting more attention?

    • Ivan Budiutama

      If I’m getting this right:
      – WPC focused more on Qi, that means something similar to dock charging minus port. Still the Qi “dock” needs wire on the wall socket so the differences are not that great
      – PMA while might be similar to Qi, they seems trying to adapt the “Mat” into popular places (probably airport and starbucks) in which (if not always) I found people place themselves near power stripes or wall sockets that is, so yeah it’s a good move. If they have this installed on every table, one less things to worry, but I found the case is quite expensive.

      IF only they put more research, fund and mind on Tesla Tower concept, we might have what this article tried to say as “practical” use of wireless power charge.

  • OhStopItYou!

    just wait for apple to decide which one they will partner with, then
    the competition will just melt away (I know, I know, you guys might call
    me a troll, but think about it, NFC has been here for ages, and no one
    has picked up on it, now that there are leaks that apple will include it
    in it’s iPhone 6, guess what? one by one, everyone is slowly adopting
    it.)

    • http://dribbble.com/nickchamberlin Nick Chamberlin

      that’s strange to me, I use NFC all the time to pay for things and send links and video to people who are in the same room with me. Tons of people I know use it. every new decent android phone has NFC in it, it’s everywhere.

      • OhStopItYou!

        if you don’t mind me asking where do you live? (I live in Canada, and
        NFC is so lagging in it’s implementation and spread, I still can’t use it in most shops for example to pay for whatever
        Most android phones do have it and
        are capable however the “enterprises” (like starbucks, or the like) will
        pick up and use it to do innovative things only when iPhones start to
        have it.
        (an example of something innovative would be to get rid of
        room keys at the hotels – download an app, off you go, open your room
        with NFC)

        • Tyrone_83

          Have you looked at your debit card weither it be from TD, Royal Bank, Scotia etc etc you see those three curve bend lines?? That’s show that your card has NFC on it. even I use it for my credit cards,

          • OhStopItYou!

            I have been using that since 2012. I am talking using phones to pay for it. (for example, ask them if you can tap to pay and all of them just give you blank looks)

  • Chris

    I think the main factor is Apple. Manufacturers are already divided on the WPC/PMA front, everyone else (bars, non Starbucks, third party manufacturers etc) is just waiting for Apple to throw their hat in the ring with whatever proprietary ‘magic’ solution they make for the iphone etc. Then wireless charging will become a mainstream feature so hopefully we’ll see some progress.

    • TheGCU

      Because Apple controls enough market share to dictate that? I don’t think so. And if Apple comes out with a wireless charger, it’ll be proprietary, and no one else can use it, so Apple’s not really a factor in this at all. If they’re smart, they’ll wait until one becomes standard, them they’ll adopt it, but they’ll probably come out with their own exclusive wireless charger.

      • Colts5609

        Agreed that Apple would absolutely use the own wireless charging technologies and methods. I would be in shock if Apple announced that they were going with the QI standard. I image it will be like what AT&T and LG are doing with the G3.

        • http://dribbble.com/nickchamberlin Nick Chamberlin

          I’d be shocked too if apple did something respectable.

      • abazigal

        Apple would control enough of the market share that actually matters (i.e.: the people who are able and willing to pay for such stuff) to dictate that. The people who use iPhones would be more willing to invest in this sort of thing. Charging mats aren’t all that expensive, but they still cost way more than a simple micro-USB cable.

        Conversely, do you think users in developing nations using a cheap android phone would be interested in a $60 charging mat that probably costs more than the phone itself?

        • freediverx

          I’ll go out on a limb and predict that Apple will never release products with inductive charging mats. The technology is way too clunky and provides no real benefit other than the “wireless charging” claim. They will use near field magnetic resonance instead.

      • freediverx

        Apple won’t adopt a standard if they feel it’s is inferior. Notice how they never adopted micro USB, instead developing their own Lighting cable which is much better. Fast forward two years and only now is the USB standard is being updated to provide similar features (smaller bi-directional connector). There are advantages to controlling both the hardware and the software without being beholden to advertisers or wireless operators.

        Apple could easily release their own wireless charging standard overnight, across their entire product line, and beat everyone else to market.

  • wvcadle

    What’s the point in a wireless charger if the charger has to be plugged in? And (sorry for the ignorance) if there are wireless chargers that can be charged and removed from a power source.. what’s the difference between those and power banks? It’s just not that inconvenient to carry around a usb cable.

    • Gator352

      You can leave the charger plugged in all the time and never have to mess with it. Just plop your phone down and go. Plugs never touch the phone.

      • wvcadle

        …leave it plugged in just like my regular cord, in the same place? The 3/4 of a second I’d save doesn’t justify the $40-$60 dollar difference in price between a wireless charger and a $5 cord. Novelty isn’t enough to make a product huge.

        • freediverx

          Not to mention that the cord takes up no space, while a charging pad takes up even more space than the phone, even when it’s not being used. Also the cord can be used to charge your tablet while the charging pad likely only works with a given phone.

  • Sal

    Once apple puts it out then it will explode into being mainstream then the isheep would praise apple for doing it first and accuse others for copying.

    • Gamma M

      But me personally as an Android user, will thank Apple to make some basic and obvious feature mainstream.

      • Chris

        Seriously. I really hope the next iPhone has NFC so I can use it more places with my Android.

        • Fl3mez

          It’s interesting how android has more of a market share yet to make something mainstream apple has to do it, doesn’t that seem a bit weird?

          • abazigal

            Not really. That can be summed up in a single word – control.

            Android lacks a single unifying hardware OEM powerful enough to push for this sort of standards to become mainstream. So the problem is while most Android phones may contain a feature like NFC, no one company has the resources to push for a mainstream use for NFC tech (nor would they have the inclination to, since any new feature they introduce would simply be applicable to every other Android smartphone with NFC as well). Then there are conflicts of interest, so you get problems like Verizon blocking Google wallet because they want to promote their own payment system instead. You can think of the various OEMs like small fiefdoms more interested in turing a quick profit than collaborating with other companies to advance a standard if it doesn’t benefit them financially in any way.

            Apple is somewhat of the opposite. With 800 million iTunes accounts, they have the “army” necessary to support the adoption of any new standard they wish to push. Consider the use of “continuity”, which will come with ios8 and Yosemite (and Apple has the resources to rapidly seed its users with the latest version of any software it makes). It uses bluetooth LE, a technology which Apple has been seeding its devices with as early as 3 years ago. You say that’s convenient, I say Apple has been planning that for many years now. That’s vision. That’s foresight. That’s something only a company who vertically controls the hardware and software can pull off.

            However, the problem here is that Apple is just as likely to introduce its own payments standard to serve as an alternative to NFC (perhaps with iBeacon?), so that won’t help the problem at all. It may be great for someone like myself who is deeply invested in the Apple ecosystem, but it would also likely suck for people like you who aren’t. :/

          • Fl3mez

            Lol well that is true but it makes you wonder why google didn’t make the same contract or what ever they did caz something tells me apple put the right terms in their contract with AT&T and the others. But your wrong about one thing, i am invested in the apple ecosystem sadly I just lack a iPhone but the only reason why I don’t want to get a android is caz the UI seems bulky and could be much better I’m not sure if that’s a skin or something but that’s the only thing that’s holding me back

          • Tyrone_83

            NFC technology isn’t not mainstream?? All of Europe and the UK have machines thats been using this stuff for years. Just only in North America it hasn’t taken off.

        • Tyrone_83

          Air Drop is basically Apple version of NFC. I find it funny Tim Cook has the nerve to say it’s a useless feature yet Air Drop does the same thing NFC does.

          • abazigal

            Airdrop does sport a larger range than NFC (I can pass files to my friend seated half a room away), and come IOS8, you should be able to airdrop files from your mac to your iOS device (and vice versa), so while the concept is the same (transferring files wirelessly), the execution is quite different.

          • Harry

            Air Drop has absolutely nothing to do with NFC. Its not a version of NFC and it doesn’t do the same thing NFC does. Yes they both enable users to transfer files but one uses an NFC chip and has a range of no more than 2 inches, and the other uses Bluetooth to create a P2P WiFi network and has a range of several meters. An argument for NFC being useless for this particular application has a lot of merit. NFC can be useful for other applications but even then it doesn’t necessarily do anything that you couldn’t do with Bluetooth 4 and BLE.

            BLE operates in the 2.4GHz spectrum, which makes it license free around the world and it comes fully loaded with AES128 encryption featuring a robust connection that has cyclical redundancy checks and adaptive frequency hopping. BLE is therefore very power efficient, secure and cheaper to implement because of its range.

    • Mike Bastable

      Maybe Apple world market the damn thing better?
      Do you really need to make some snarky Apple comment here?(yes it automatically gets you lots of likes but it must be tedious).Your point however when made rationally is valid. The tech is there, works.well..we just need a major player to implement it across its product range..and market its.advantages to the general public.

      • Sal

        I have no doubt Apple can do it better. It’s their consumer fanboys and their corporate behaviour (at times) that annoys me.

        • Mike Bastable

          Well go to an Apple site and insult them there here I would rather read your opinions please. Give the fanboys hell on the fanboy sites

    • abazigal

      Apple actually has a patent for some sort of wireless charging device which would presumably sit inside a Mac computer like an iMac, and be able to wireless charge your peripherals like the bluetooth keyboard, trackpad and any nearby devices as well.

      To me, this makes more sense than a giant mat which you still have to plug in (which I find in turn defeats the purpose of the concept of wireless charging). I don’t have to worry about keeping my phone on a mat at all times, and I can still use it while it is charging. It would really be like the phone was still wired to the charging outlet, only the wire is invisible and intangible.

    • freediverx
  • Jimmy Jamm

    Main reason it’s not catching on is because wireless charging takes too long…a phone being plugged in charges in a fraction of the time as opposed to the 5+ hours it takes to fully charge via wireless…

    • mobilemann

      this. it takes me under 2 hours for my note 3

    • Gator352

      5+ hours? Ridiculous. Sure it takes longer but that’s the convenience of have not having to deal with wires. Wanna know what the great thing is? Yes? You can use both! YES!!! Phones have a USB port and if you have a qi compatible phone and charger….it’s a win-win for most.

    • http://dribbble.com/nickchamberlin Nick Chamberlin

      Actually, it takes about the same amount of time. Maybe it was slower in the past. It also might depend on the quality of your pad.

  • Stephen

    In my household, we have 2 Nexus 4’s, 3 5’s and a couple of 7’s. I think we have 4 Zens wireless charges around the place and nobody would think to plug their phone in to charge it. It’s massively convenient to be able to pick it up, use it a bit, drop it back down. We wouldn’t buy a phone that didn’t have wireless now. What I find odd is that with the recent move to waterproof phones, they don’t have wireless. A friend has just got a Z1 Compact (lovely phone by the way) but the cradle/charging fuss would put me off immediately. Wireless charging a la a Nexus 5 would be so much better.

    • mobilemann

      lol @ massively convenient, i’m sorry but the quarter second it takes to unplug something, or the second it takes to plug it in, get faster power charging, with a higher efficacy; is just not wroth it to a lot of people.

      • erikiksaz

        Have fun plugging in your phone in the dark. Most people who criticize wireless charging probably haven’t used it.

        • wezi427

          Sounds like you have trouble finding a hole without light. ;-)

          • Gator352

            That’s why most phones have flashlight app. :)

      • Stephen

        each to his own I guess. You do get both on a Nexus device so it’s not like you’ve lost the choice. I guess anything with wireless charging has the option of wired as well?

        • mobilemann

          i just thought “massively” was a bit much, to be fair; the real thing that stops me is the efficacy.

      • AeroSlingShot

        It is more convenient if you factor in that the weight of the wire tends to pull the plug off the surface it’s on and you have to go hunt for it every time you want to charge.

      • Gator352

        Your point? It is more convenient. Period. Sure! Plugging it in is more efficient but having to deal with wires isn’t worth it to a lot people when they don’t have to.

      • http://dribbble.com/nickchamberlin Nick Chamberlin

        I think it’s more that if people are putting their phone down for a little bit to go do something, they’re not going to take the time to plug it in. It’s not much more work, but most people won’t. Setting it down and having it charge itself for a little bit is more convenient, because you’re just doing something you would have done anyways.

  • Shark Bait

    apple, thats whats holding it back

    • abazigal

      Apple knows better than to back a crappy standard / concept.

  • wezi427

    As it exists today, I’ll stick to the traditional ways of charging my phone.

    • Colts5609

      Someone has obviously never experienced this wireless charging. You can still plug in your phone if you need a faster charge.

      • wezi427

        If I’m going to plug it in anyway, why tie up outlets? When they charge just as fast as traditional charger then I’ll consider it. My brother in law had it, I’m not a fan.

        • Colts5609

          I see it this way. I had a few wireless charging stands that I used with my Nexus 5. One at work, an actual wireless charging stand from Tylt, and one on my night stand. Convenience is the key here. While I am at work, my phone will never run out of juice, because it is always charging, and it is fully charged on the way home. I don’t have to plug/unplug my cable 5-10 times a day. Same with home, give the phone some juice while your not using it, all you have to do is set it down. While I owned my Nexus 5, I never once plugged it into the wall after I had wireless charging capabilities.

          But it is nice to at least have the option of either or, plugged in or wireless. Would much rather have this option than some of the gimmicks they are putting in phones nowadays.

          • wezi427

            I work out of a car and it’s on the charger the entire time I’m in it. I have three batteries one in a bag that I use for work, just in case I’m not in the car for the day. I have (2) 20ft charger’s one in my bedroom that is next to my bed and another in my kitchen “junk” drawer. I also can charge my phone in my oasis in the basement using my PS4 or I could walk up 10 steps and open a drawer and grab a charger. I like the idea of wireless charging, but it’s not a game changer for me.

  • Colts5609

    Because morons would rather have a completely useless fingerprint scanner.

  • AndroidBrian

    Wireless charging is convenient, but I find I still use my micro USB 90+% of the time. When do people usually want to charge there phone? For me, I want a charge usually while I’m using my device. Try using your phone/tablet while its laying on its charging pad. Not very comfortable. If you you only charge your phone right b4 you go to sleep, a wireless charger is perfect 4 u.

    • Gator352

      You do know that phones still use a USB port right? It’s not one or the other. You can have both….at the same time. Have the plug and cord right there for your needs. Then if you need to get up and take your phone with you, unplug it. Then just before bed, place it on the wireless charger for convenience. Simple.

      • AndroidBrian

        Really? Did you read my comment? “I use my regular micro USB 90% of the time”. Isn’t that a clear indicator that I use both? Guess not…. I read a lot of your comments you posted on this article. Just stop guy, just stop. Nobody needs you to tell them the sky is blue.

  • Adon

    The wireless charging. It all come down to marketing, and the availability of wireless charging pod. Especially in emerging markets,these products are rare. And the more established markets,the wireless charging pod are niche products. Again,limited marketing,price range,availability

  • Dean Weaver

    I bought a Nexus 4 because I wanted this BUT Google kept the charger ‘USA only’ – pathetic..

    • AeroSlingShot

      Wouldn’t any charger work? Unless you’re after the style of the Nexus charger, just get a simple Qi pad from any store.

  • Will S.

    As long as I see wires coming out of something, its not “wireless charging”!

    • Gator352

      The phone is wirelessly charging….not the charger.

      • abazigal

        Which still kinda defeats the point. So if I want to charge my phone outside, I need to bring the whole mat with me?

        The ideal wireless charger would be a device which can emit waves that charge your devices from a distance away. Imagine walking into a room with such a charger, and your phone automatically starts charging in your pocket without you needing to do anything. Now, that’s wireless charging.

        • Gator352

          If you want to go outside…..take your USB cable/charger with you….it’s not like your USB cable is tied down anymore.
          Now I agree with rest wholeheartedly! That would be TRUE wireless charging!

  • abazigal

    Has nobody considered the most likely explanation of all – that maybe wireless charging, while cool, hasn’t taken off simply because it is a crappy piece of technology to begin with?

    It has been mentioned a few times below, and I still think it’s silly to have to plug in a mat to a power socket just so I can place my phone on it to charge. And I can’t even move my phone from the mat without disrupting the charging process. I am pretty sure wireless charging is less efficient than wired charging itself, so that’s extra power consumption already.

    People say it’s great for the choice, which seems to be a recurring theme for Android, but as a primary Apple user, I personally prefer 1 single solution that works great, compared to having to juggle with multiple different options that usually don’t really work very well to begin with. I can choose to either plug in my phone or place it on the mat? So now I need 2 cables and 2 usb ports (one for the phone, one for the charger)? Huh? That seems like 1 step forward, 2 steps back to me.

    The Apple way (and what I deem to be the best solution moving forward) would be to create a charger which emits waves that charges a device from a short distance away. Either that or improve wireless charging to the point where it charges your phone faster than via a dedicated cable. Then we can talk.

  • Alt

    The technology for wireless charging is not here.
    1. It’s a hassle. Finding the correct distance or location for optimal charging requires too much work. Distance is limited. Will the case on a phone need to be removed also? Or a special case purchased?
    2. Power loss is inherent (due to resistance of the coil for instance) resulting in a higher electricity bill and probably longer charge time. Efficiency can largely vary, although high efficiency can achieved it will cost (prohibitively?) more and based on how electronics are made nowadays, I wouldn’t bet on long life or high efficiency for the average product.
    3. Not as portable. Roll up a mat and cord and wall adapter (and battery adapter?) vs. a cable?
    4. Not universal. A certain mat for a certain device?
    5. Overcharging? In an ideal wired battery charger, the charger shuts off when the battery is fully charged (resistance between terminals is very high). With wireless? The mat will continue to waste power, and the mat and battery may overheat and cause damage.
    6. Interference. Shielded cables are available (although why you would charge a device in such an environment is beyond me). What about the electronics inside the device? Microprocessors can be seriously screwed up in noisy (i.e. electromagnetic noise) environments. What about a competing electromagnetic field from a fluorescent light? How will they affect each other? What about a nearby radio? Chances are one or both or those will be near where you charge the device.
    7. Cost. Goes without saying.

    Any more reasons you know?

  • MGB

    There is no problem with ‘laying it in the right spot’ with the new 3 coil Qi charging plates that are appearing now.

  • Harry

    Wireless charging in its current form is stupid thats why it hasn’t taken off. A wire at least lets me hold onto my phone and use it while I’m sitting on the couch next to the powerpoint. If I have to put it on a mat on the bench and stand over the bench to interact with it how has it added anything of value? I cant even play some of my games because a lot of them require me to be able to pick up the phone and use accelerometer gestures. That’s why it hasn’t taken off.. its a gimmick. It will take true wireless charging that works just like wi-fi through and around walls for the tech to take off.

  • tharrat143

    theres much boom in every aspect of mobile technology but BATTERY still remians in doom

  • freediverx

    Inductive charging is a joke. As the article points out, it requires a ridiculous charging pad and careful alignment of the device to the charger (among other limitations.)

    On the other hand, near field magnetic resonance sounds like the real future of wireless charging given its range of about a meter and ability to extend this range with “repeater” devices.

    So aside from bickering over competing standards, is NFMR technology currently ready for production and if not, what is holding it back? Because while most players in the market sit on the fence waiting for one of the standards to win out, I can think of one $600 billion company in Cupertino who could successfully roll out this tech across its entire product line without worrying about anyone else’s standards.