"Wide Band" ultrasonic transducers.

[G6Tanuki]

Does anyone know of a source of 'wide band' ultrasonic transducers (like the TV remote-control types).

I'm resurrecting a bat-detector whose transducer failed some years back after being left out in the rain and ending up full of water: fitting a traditional 40KHz type salvaged from a dead 1980s TV chassis has a rather narrow bandwidth compared with the original (which has now been lost).

[The bat-detector is remarkably simple - ultrasonic transducer, a single common-emitter amplifier and a balanced modulator fed with a variable-frequency square-wave from a 555. Result goes to a LM386. Essentially it's a 20-80KHz direct-conversion receiver!].

[vidjoman]

There used to be some about 1 inch dia that were used in alarm systems. Don't know how wideband they were.

[Andrew2]

I use a 40 KHz piezo transducer on my bat-detector and it is indeed rather narrow. I did experiment with electret mic inserts but found they all rolled off below about 20 KHz.
My detector is similar to yours but uses an NE602 balanced mixer driven by a cmos oscillator.

[Andrew B]

Nowadays a lot of cars have reversing sensors, they look a lot like the old transducers. Maybe a visit to the local car breakers may be an idea?

[dseymo1]

Certainly worth a try, but the electronics usually seem to have a tuning arrangement, so I suspect that they are resonant at a nominal frequency.
Would a piezo sounder, stripped of its casing, work perhaps?

[G6Tanuki]

Hadn't thought of reversing sensors - I'm not sure if these combine both a transmitter and receiver in the same unit, or if there are a pair of transmitters and a separate pair of receivers per vehicle.

In another place someone's also suggested the "volumetric sensors" used in car-alarms to protect the insides of the vehicle against people breaking windows, slashing hoods on convertibles etc.

The other thing I was wondering about are the flat circular piezoelectric transducers used as bleepers and pingers in things like digital clocks/watches/microwave-ovens.

Definitely this is giving me things to think about - I'm now wondering about modifying the Bat-detector and using several switchable ultrasonic transducers [sort-of frequency-diversity?] to cover different Bat-channels? For example, the common Pipistrelle bat uses a call centred on 45 kHz, while the Soprano Pipistrelle echolocates at 55 kHz. The two species are sometimes called the 45 kHz Pipistrelle and the 55 kHz Pipistrelle.

[dseymo1]

The reversing sensors I've seen are all single dynamic devices, but some have built-in electronics (pre-amp?).

[Andrew2]

Oops my post above (#3) was badly edited and gave the impression that electrets roll off *below* 20 KHz. I meant above. Ahem.

[ms660]

Originally Posted by G6Tanuki

Definitely this is giving me things to think about - I'm now wondering about modifying the Bat-detector and using several switchable ultrasonic transducers [sort-of frequency-diversity?] to cover different Bat-channels? For example, the common Pipistrelle bat uses a call centred on 45 kHz, while the Soprano Pipistrelle echolocates at 55 kHz. The two species are sometimes called the 45 kHz Pipistrelle and the 55 kHz Pipistrelle.

Don't forget the Horseshoe (if they are around at your location) they are around 100khz.

Lawrence.

[G6Tanuki]

Yes there's a Greater Horseshoe roost about 1/4 mile from my house. Getting them is one of the reasons I want a wideband transducer!

[Hmmmm... in the style of the 1950s "HAC" - Heard All Continents - single-valve shortwave radios I propose a HAB - "Heard All Bats" - receiver]

[KeithsTV]

The piezo sounders we used in some fire alarm sounders were normally resonant at around 2kHz so may not be suitable.

What frequency do the reversing sensors work at?

Keith

[ms660]

Originally Posted by pwdrive

Don't forget the Horseshoe (if they are around at your location) they are around 100khz.

Bats I guess are a bit off topic so I'll keep it as short as poss....You are fortunate to have the Greater Horsehoe close by, not too many of them around these days, we have a colony near us (Prideaux Wood Mine) I went in there a few years ago at the invite of the local batman who does stuff for the wildlife trust (they were doing the yearly count) fascinating to watch, we have in the past had the Lesser Horseshoe in some old mine workings which we own, got bats at our house too but not had chance to identify the species yet.

Good luck with the detector and enjoy your bat detecting.

Lawrence.

[G4_Pete]

Hi,
There was a discussion on bat detectors microphones a while back. Some electrets give an extended response and it is posible to make capacitance types by streatching capacitor film over a pitted surface like sintered filter material.

https://www.vintage-radio.net/forum/...d.php?t=102454

Pete

[MotorBikeLes]

I am fairly certain I have a load of unused CTV rem con receiver units. GEC type, maybe some Grundig. PM me if you want some.
Les.

[boxdoctor]

I woud guess that very few ultrasound sensors are "wide band", as the majority would be designed for a specific purpose, and use a frequency optimum for that purpose.
The sensitivity probably falls away quite dramatically when they are used off resonance. Tony.