[homebrewer (OP)]

Dear Forum,

I am building a dual frequency ultrasonic generator and need some help
to design a variable inductor to individually tune either of the attached
sonotrodes .

Specification :

Tunable inductor : 

Inductance : 100 mH

Tunable range : 50 to 100 mH

Resonance Frequencies : either  20 or 40 kHz

Current : 3 Amps

Voltage : 40 volts  p.p.

Wire size : 0.5 mm dia

As you probably gather this is an intermediate coil before the LOPT
which I use to drive the sonotrodes.

Your comments are much appreciated.

Thanking you.

[RD]

Inductance : 100 mH

Tunable range : 50 to 100 mH

Current : 3 Amps

Voltage : 40 volts  p.p.

A 50 microHenry inductor capable of 8A is about the size of a thumb.

So a 100 milliHenry capable of 3A will be about the size of a fist, and cost an arm and a leg.

Maybe a (salvaged) mains step-down transformer with windings capable of 3A 40V would suffice as an large inductor.

[CliffordK]

I've seen used variable transformers that weren't that expensive.

Could one be converted into a large variable inductor?

[homebrewer (OP)]

Thanking you so much for your contribution.

One of the things I had not mentioned was the requirement for a long term
frequency stability of the circuit, taking into accounts the heat generated
by the tuning coils and the sonotrodes which impose a substantial drift
to the operating parameters of the circuit.

So I am looking for variable inductor - linked to a stepper motor and
an automatic tuning circuit to enhance the frequency stability.

I have taken note of the comments made as to the cost of the inductor and will
reduce the inductance to 25 mh and the current to 250 mA.

Once I have made a coil former next week, I will ask SOWTER to wind a couple
of inductors for testing.

Thank you for your kind contribution.

[RD]

Ultrasonic cleaners are available new on ebay for as little as £20 for cleaning jewelery / dentures,

or industrial 120Watt types costing  about £100 ... http://www.ebay.co.uk/itm/Professional-Ultrasonic-Cleaner-3L-with-heating-Free-ss-basket-and-cover-/280832408592

Resonance Frequencies : either  20 or 40 kHz

20KHz may be audible by some young people , see ... http://www.compoundsecurity.co.uk/security-information/mosquito-devices  [ which use 18.6KHz ]

[homebrewer (OP)]

Thank you RD for your comments, but my application involves ultrasonic machining of very small structures.

Please take a look at this link : www.r-s-ultraschall.com

[RD]

Thank you RD for your comments, but my application involves ultrasonic machining of very small structures.

Please take a look at this link : www.r-s-ultraschall.com

My German isn't so gut ... http://translate.google.com/translate?sl=auto&tl=en&js=n&prev=_t&hl=en&ie=UTF-8&u=http%3A%2F%2Fwww.r-s-ultraschall.com%2F

If you need circuitry which can deliver 120Watts of ultrasound at 40KHz , the industrial cleaning tank I mentioned in my previous post  allegedly has that , the company you linked to also makes 300Watt versions  , [ sometimes using the innards of a bulk manufactured item is cheaper than having something similar custom made ].

[homebrewer (OP)]

I am sorry, but my German friend is just  re-working his website.

Here is a link in English, very impressive portfolio of work:

http://www.r-s-ultraschall.com/pdf/samples_e.pdf