What's the best way to receive ultrasonic signals? - Page 1
Forum section: electronics / projects

author: Ben321
author_rank: Frequent Contributor
timestamp: May 20, 2017, 01:06:26 am
content: I was curious about what kinds of ultrasonic signals are just in the environment around me. I've heard that bats for example can have emissions well above human hearing, and some even as high as 100kHz (higher than the highest frequency that can be detected with a 192kHz soundcard, which has a nyquist frequency of 96kHz). So I need a way to easily get ultrasonic signals into my PC. The best commercially available sound cards (which aren't pieces of dedicated science equipment) are 192kHz sample rate (which has a nyquist limit of 96kHz), but I'd like to go a bit higher than this (with a nyquist frequency of at least 100kHz). Any suggestions?Of course, I also need a microphone that can sense ultrasound. Typically microphones are designed to be most sensitive between 20Hz and 20kHz, as this is the range of human hearing. A typical microphone won't work very well even at the highest frequencies usable on a 48kHz sound card (which has a nyquist limit of 24kHz), as 24kHz is above 20kHz. So a typical microphone won't be a usable untrasound sensor. There are dedicated ultrasound transducers, which are usually sold as a pair, for transmit and receive. However, these are usually designed for one specific wavelength (like 35kHz), and don't perform well at any other frequency (either higher or lower). Are there any wideband ultrasound sensors (with a usable range maybe between 20kHz and 100kHz) out there that don't cost thousands of dollars (like it would cost for a dedicated medical/scientific device)?

author: Brumby
author_rank: Unknown
timestamp: May 20, 2017, 02:31:47 am
content: Try something as simple as a Google search for "ultrasonic microphone".I did - and this was the first reference:Low-cost ultrasonic recording - Wildlife Sound Recording Societyhttp://www.wildlife-sound.org/equipment/technote/micdesigns/ultrasonic.html"A couple of years ago, a manufacturer of bat detectors started using cheap electret microphones in some budget detectors, presumably after finding out that some capsules had a useful response up to about 60kHz. One of these capsules is the Panasonic WM61A which features in the WSRS low cost microphone design article. If you have constructed that, you are already there - go in search of bats!"There's a place to start.

author: Ben321
author_rank: Frequent Contributor
timestamp: May 20, 2017, 02:45:36 am
content: Quote from: Brumby on May 20, 2017, 02:31:47 amWhat about the soundcard part of my question? Are there any good soundcards that hobbyists tend to use for receiving ultrasonic signals? Are there any that have sampling rates over 192kHz, so as to allow the nyquist frequency to be above 96kHz? I'd hope to get a sound card with a nyquist frequency of at least 100kHz.

author: BrianHG
author_rank: Super Contributor
timestamp: May 20, 2017, 03:56:58 am
content: $$$ for anything above 192k unless maybe some instrumentation devices.Otherwise, for sound, go here:https://mytekdigital.com/brooklyn-adc/

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 20, 2017, 04:20:45 am
content: If you add a quadrature mixer, you double the available bandwidth and shift it up towards a frequency range that is more useful to you.

author: BrianHG
author_rank: Super Contributor
timestamp: May 20, 2017, 05:10:54 am
content: If 12 bit audio is acceptable, with 8 channels AD at 500KHz sample rate, there is a 149$ solution here:https://www.mccdaq.com/usb-data-acquisition/USB-200-Series.aspxYou will still need to make your own mic pre-amp.

author: BrianHG
author_rank: Super Contributor
timestamp: May 20, 2017, 05:15:50 am
content: Found what you are looking for:http://www.batsound.com/?p=116AND for portabilityhttp://www.batsound.com/?p=125

author: Bendba
author_rank: Regular Contributor
timestamp: May 21, 2017, 01:10:21 am
content: Hi,Years ago, I went on a night walk with a nature group, they had a portable device that made listening to the bats possible by reducing the frequency of their voice. I don't know what the principle was. Could have been frequency dividing, or fm demodulation, or something else. The end result was an audible sound, which allows you to identify the bat without having to actually record anything as they all have different voices, kind of like birds.If you can find a suitable microphone, that could be a way around the sampling rate limit of your sound card.PS: Now that I think about it, I remember it sounding like an analog sound so my best bet would be some sort of heterodyne demodulation.

author: Gyro
author_rank: Super Contributor
timestamp: May 21, 2017, 09:38:21 am
content: Ultrasonic transducers are often used in bat detectors - the cheap 40kHz ones that you buy in TX-RX pairs (make sure you use the RX one). They work pretty well in practice.Bertrik's bat detector page is a good resource:http://bertrik.sikken.nl/bat/It covers frequency division and hetrodyne conversion to audio.He also has a bit on detuning transducers to improve their frequency response (they normally have a fairly High-Q 40kHz peak):http://bertrik.sikken.nl/bat/detuning.htmP.S. You could also take a look at cheap Piezo tweeters.

author: mark03
author_rank: Frequent Contributor
timestamp: May 24, 2017, 04:55:50 am
content: Most of the information on ultrasonic microphones is outdated. You should consider a MEMS microphone, or perhaps a closely packed array of four devices (they're cheap). Although very few are characterized above 20 kHz, most of them have good response up to 100 kHz, albeit with a resonance peak usually around 20-30 kHz. At least, this is true for analog-output, bottom-port devices. This should be far better than the cheapo 40-kHz rangefinding devices, and increasingly competitive with good electret mics.You didn't say if you would consider a custom digital front end, or require something off the shelf. I have had success with a relatively simple daughter-board for the STM32L476 "Discovery" kit. It consists of the MEMS microphones, some analog signal conditioning and a 16-bit, 500-kSPS SAR ADC. The discovery board has sufficient DSP horsepower to downconvert and shove the audio through the on-board codec to headphones. Works great! If you wanted to keep it even simpler, you could use the on-chip ADC which samples at up to 5 MSPS with ~ 11 bits of SNR. You would need to use the DFSDM peripheral to keep the computational load manageable, but after downsampling, mixing, and downsampling some more, you would gain about 4 extra bits of SNR for 15 bits total, not too shabby.

author: yannick_33
author_rank: Newbie
timestamp: October 20, 2018, 03:32:30 pm
content: Hello Mark03,what is this "daughter-board for the STM32L476 "Discovery" kit" ?Thank's, Yannick.

author: mark03
author_rank: Frequent Contributor
timestamp: October 21, 2018, 05:08:36 pm
content: Hi Yannick,The daughterboard was my own custom design (see attached PDF schematic). It is slightly more complicated than necessary because I was trying to make a generic front-end not only for bats but also a VLF software-defined radio and anything else that could use a 1 to 2 MSPS ADC. This is not a viable approach unless you have plenty of electronics (and surface-mount soldering) experience and are prepared to dig in and customize the HW/SW to your own liking.There are much simpler circuits which can do a good job; I designed this one last year for some high-school kids:https://www.eevblog.com/forum/projects/critique-my-ultrasonic-translator-circuit/

author: coppercone2
author_rank: Super Contributor
timestamp: October 22, 2018, 07:16:44 pm
content: If you go SMD I noticed that the ultrasonic microphones (one of which is no longer produced) seem to have a larger mesh-covered opening, while the audio ones have a pinhole.https://www.digikey.com/products/en/audio-products/microphones/158?k=microphone&k=&pkeyword=microphone&pv41=98&sf=1&FV=ffe0009e%2Cyr100Hz+%7E+100kHz%7C2145%2Cyr100Hz+%7E+80kHz%7C2145%2Cyr50Hz+%7E+40kHz%7C2145&quantity=&ColumnSort=0&page=1&pageSize=25

author: mark03
author_rank: Frequent Contributor
timestamp: October 23, 2018, 12:52:35 am
content: Quote from: coppercone2 on October 22, 2018, 07:16:44 pmIt was after seeing only a handful of Knowles MEMS mics rated for ultrasound that I inquired with technical support. I was told that the difference is mainly in characterization; the engineer claimed that all bottom-port analog MEMS devices have a similar ultrasonic response. I've used Invensense ICS-40720 with success.It would be a useful project to come up with a test apparatus for ultrasonic sensitivity characterization. Only relative, not absolute. A short spark discharge at close range might work, but you'd need a $$$ microphone with known ultrasonic response to test it first, and I'm too cheap for that!

author: coppercone2
author_rank: Super Contributor
timestamp: October 23, 2018, 01:01:32 am
content: Well a problem you will get is that the microphone may couple electrical fields through its wiring rather then just the acoustic signal if you use something like a spark.I shielded the crap out of one of those microphones on a stick to make a pockey probe rod (its some where in the coppercone posts I think).Also with those mics, some vendors sell the standard ones rated till 40KHz (rather then the 20 on digikey)I have yet to buy the broadband ones.. but I do have some 'ultrasonic transducers' from ebay, the standard type that look like a little dish under a mesh screen. I think if you connect them to a function generator they produce some noise, and they can receive noise too.

author: djacobow
author_rank: Super Contributor
timestamp: October 24, 2018, 03:05:03 pm
content: Has anyone asked Meredith Perry? I understand she's an expert in ultrasonics.<ducks>

author: mark03
author_rank: Frequent Contributor
timestamp: October 24, 2018, 06:13:09 pm
content: No, but when they auction off the company assets, let me know! There must be something I could use for characterizing ultrasonic microphones...