Hi Welcome to the Eev blog An Electronics engineering video blog of interest to anyone involved in electronics design. I'm your host Dave Jones I'm here with Jason What do we got? What is this cool looking robot arm? I Love it. This is our s measurement system. s what's that specific absorption rate? It's the amount of energy that's absorbed by the human body from wireless devices cool mobile phones.

It's the big one that's every about right. Yep, All right. what does it do? How does it work? Uh, this is an E-field probe. Um, essentially we dip this probe in this liquid here.

Yep. uh. the liquid's got similar dialectric parameters to, uh, the human tissue, right? So we did probe in there. We put the phone underneath here.

Yep. and uh, we measure the field inside the liquid. Fantastic. So that's just like a regular that's just water with a bit of bit of sugar and a bit of salt.

Bit of sugar and salt. and that's actually similar to brain tissue. Apparently that's right. The same yeah and is.

The idea is to heat is to measure the heat how much it Heat's up by said well. the idea is yeah to measure the heat, but because uh, the the temperature changes are too small for accurate measurements. We measure the E field and then using the dialectric parameters of the liquid, we can calculate what the S is fantastic. So you just put this at a specific height is that and then you scan over it.

That's right. So 2 mm from the surface we do a 2d scan. 2 mm. Okay, exactly nice.

It's pretty close. Y and we do a 2d scan, find the find the peak and then do a 3D scan around that to find the penetration depth and especially average value. So this is like does this rotate this? This? This isn't this. Just manually rotates right.

The phone. Yeah. phone sits on there. This is.

this is all made of plastic and fiberglass. There's no metal Parts in here cuz and same with this. Frame There's no metal Parts cuz any metal Parts can distort the field. Okay, um and yeah, this is a design so that we can get the angles exactly right.

We' actually grab that up close. Yep, let how a look. So this Phantom is actually used for body testing. It's a a flat phantom.

Um, right over here. we've got the head Phantom which you'll see has ah right? Okay, so that's a human head. y That's a they They came up with these Dimensions after measuring the 1,000 heads from the US Army This this is the average head of. that's the average US solders head.

That's right. Yes, I like it. And yeah, so we put the phone under here and we we line it up. We've got we've got little stickers to to help us line it up.

The standards are pretty specific. The angles that we test right. Um, okay, and so that's where. that's really where one of those uh, holders comes in here.

Okay, so you just move the holder over to this bench here and then we've got these musroom. Fantastic! I Love it And that's just filled with the same same very Sim yeah, I mean slightly different uh uh. dialectric parameters cuz this is the brain tissue and this is muscle tissue. Oh, got it.

Okay, so this is it in your pocket, right? and and you have to keep the room at a certain temperature? Is that right? Yeah, uh. the tests have to be done sort of between 18 and 25, but once we start a test, it's not allowed to change by more than Plus or - 1 right? So it's it has to be has to remain fairly accurate. Yeah, cuz the dialectric parameters of the liquid changes with temperature. So so if we measure it in the morning and then you know we 5 warmer in the afternoon, we're not calculating the correct s right? Got it.

And how how long does it take to scan it? Scans about half an hour. so about 15 minutes for the 2D scan and then another 15 minutes to do the fine sort of 3D scan right? So you build up so you go over it once with a 2d and build up a 2d map of it and then it's a coarse sort of 2D map around. that sort of maps the field and then once we found where the peak is, then we'll do quite a fine sort of 3D um. scan of and how do you do that? You just move it.

move the move the prob upward. It's all run by software. All right. Okay, so but but to build up a 3D map, the probe physically moves up right and that? Excellent.

So 7 by by S points? Um, fantastic. I Love it. Thanks for that. That's fantastic.

What a cool bit of Kit How much does something like that cost? Uh, about a million dollar? About a million? Buck Nice. That's just the robot. and we've got the Bace station simulators with. Okay, so this is the yeah.

so this is the Um test. This generates. The Uh simulates the yeah this mobile phone. That's right, because we're in a shielded Faraday cage here so we can't get inside so that generates into a Sim y.

It just calls up a Sim and you put the Sim inside the phone. The phone. That's right. Fantastic.

That way, we've got full control over the power that's being output by the phone and the frequency and all that. So it's a controlled environment. So these other Um tables, they've got different sort of. Yeah, it's the same setup.

it's just. um, it's originally from back in the day, the the Dual bar mobile phone, the 900 and the 1800 MHz. So have the 1800 MHz liquid in here and here and the 900 in there and there. Um, nowadays with 3G and seem to be 4G There's a lot of different frequencies and you've got Wi-Fi as well.

so we end up having to change um liquids quite a lot which is what's at the back there. The oh okay, you got all the different types of liquids and right so you can action test Wi-Fi products here as well, right? What sort of RF ranges can you do? Like power output levels? can you test? do you know? Um I'm not sure about the power output levels I mean a mobile phone's like a one or 2 wats it when it's trans so the average I think is around 250 M but um, but we we've measured 10 W transmitters in here um and that wasn't quite getting to the to the peak of it yet and it measures. It's got a huge dynamic range actually. it's all fiber optic so there's not much noise.

Okay, it's very. It's quite expensive equipment so expect pretty good specs from it. y but um yeah, so are you going to Hazard a guess as to whether or not mobile phone causes any problems? Do you? uh, use it 5 hours a day? I Don't use 5 hours a day I I Think if you use a mobile phone sensibly Sensi be fair I think that's that's the go. All right, and what else these are just.

they're the controls on the back. Uh, these are RF amplifi RF amp y Yeah, set up before any measurements we do the start of each day we'll do a sort of a measurement of a known source. Got it? So just put a um, sine wave at 250 Ms the frequency that we're planning to measure and measure the S of that to make sure it's sort of where we expect so that the system's working. Okay, got it? Have a confidence check before we start.

So how do you calibrate? how does do you have So just a reference standard is your calibration or what? Yeah, all this equipment gets calibrated once a year in Switzerland and then we we get the reports back and then before we start a test, we'll do the same thing and confirm that our results are within 10% And that's just a confidence check to make sure the system working y cuz you really wouldn't need to be terribly accurate with this thing would you? Is it's probably a relative. uh, a lot of it would might It's actually an absolute value. Okay, it's the amount of it's definitely it's It's measured in watts per kilogram. So it's it's the power.

That's okay. Yeah, got it. Fantastic. Thank you very much.

That's all right.