How to detect very high frequency sound ?

[dxpwny]

I need some advice on how I might accomplish the detection of very high frequency sound. I do not know the source of the sound, or where is comes from (I don't care and can not answer any questions about that). I also do not know the exact frequency - or range. I know it is higher then what I can hear, so perhaps 20 - 50 khz <?>.


I'd be happy just detecting that a sound above a certain the frequency threshold was present - not necessarily the amplitude, and log the event to a text file with a time stamp.


As part of the project I'm already using an 8051, tied to my PCs serial port, to detect something else. So, a simple logic high when the sound is detected is fine.

Thanks for help.

 

[Harald Kapp]

• A microfone to pick up the sound. For ultrasound a special ultrasound sensor should be used
• An amplifier to get a useable signal amplitude
• A high pass filter to reject frequencies lower than the frequencies you're interested in
• A rectifier and smoothing capacitor to generate a signal proportional to the amplitude of the high frequency sound (you don't want to analyse the high frequency waves directly, you are only interested in the envelope)
• A threshold detector to register signals above a certain threshold/limit (signals belo the limit are rejected). A Schmitt-trigger circuit is suitable and incorporates hysteresis to prevent accidental switching to and fro

Connect the output of the threshold detector to the input of your µC and evaluate the events using appropriate software.

Amplifier and filter can be combined into one using an amplifying filter built from e.g. an operational amplifier with suitable frequency response.

 

[dxpwny]

The ultra sound sensor is the missing piece. Can anyone suggest a sensor that can deal with about 20 kHz to 50 kHz - not just 40 kHz ?

 

[davenn]

Can anyone suggest a sensor that can deal with about 20 kHz to 50 kHz - not just 40 kHz ?

we would have to google it ..... am sure you could do that

 

[Colin Mitchell]

Some piezo diaphragms say they will pick up this frequency but you have to test them. I have had no luck.

 

[Harald Kapp]

I'd say start with a 40kHz sensor and find out what signal you get from 25kHz to 50kHz. If the sensor's sensitivity decreases too much outside the nominal frequency range, use 2 or more sensors and amplifiers, separately optimized for e.g. 30kHz, 40kHz and 50kHz and mix the output signals of the amplifiers to cover the full range (that's the reverse of a 3-way spaker ).

 

[Alec_t]

Acccording to this article you might be lucky using an electret mic up to ~50kHz.

 

[BobK]

Please tell me that this is not to detect ultrasonic waves that someone is beaming at you for nefarious purposes.

Bob

 

[hevans1944]

Please tell me that this is not to detect ultrasonic waves that someone is beaming at you for nefarious purposes.

Bob

Well, if so, the usual suspects would be any or several three-letter Government agencies, but what makes @dxpwny worth the effort to do so? There are more than 7,404,976,783 people currently occupying space on Mother Earth, and only a very small, almost insignificant, number are persons of interest to three-letter agencies. Still... with terabytes of storage and petaflops of computing power available, why not keep tabs on everyone?

Millimeter-wave microwaves are probably better for the purpose (whatever that is) than ultrasonic acoustical waves in air. Too much dispersion with acoustical waves and its difficult to impedance-match the radiator to the emitter over a wide bandwidth for maximum power transfer. Terahertz radiation would probably be even better, but the technology for that isn't very portable yet.

 

[CDRIVE]

Here's an ultrasonic detector that produces an audible alert.

Chris

 

[hevans1944]

I really do love Man's Best Friend. Currently between dogs (and cats) right now, but we will get a puppy either this year or after we move to Florida. Blue eyes optional in either animal, but I am partial to blue-eyed, short-haired, Siamese cats and largeish dogs. Rottweiler/Labrador mixes (rotten labs) are nice. The last dog we had was a female of that mix. Dumb as a box of rocks, but very loyal and lovable.

It's really hard on the psyche not having a dog around. Cats... meh. Take 'em or leave 'em, but you never actually "have" a cat... they just tolerate you if you are acceptable to them. Our last cat was a stray I "rescued" about ten years ago. This year he jumped out our bedroom window in the early morning hours and took on a feral, very mean, and much larger cat. He lost the battle and we haven't seen him since. He was always an "inside" cat, never allowed much outside except under adult supervision. I miss him, but not enough to rush out and get another cat. Our dogs died several years ago, and wife wants to raise and train a puppy as soon as we know where we will be doing that. Between us, we have both outlived about a dozen or so dogs and several cats. Cats live, like, forever (if they stay out of trouble). Dogs, not so much. But with all our children adults now, it hurts to not have a few pets hanging around.

All cats, and some dogs, are psychics, so that fits in well with our life style. Both work together as a synergistic early warning system if you pay attention to them.

Did Chris and I just hijack this thread? Sorry 'bout that!