Constant current source for an alternating magnetic field of varying frequency and constant amplitude from a solenoid

The project I am working on requires me to oscillate my sensor. I am doing this by coating a ferromagnetic material on the sensor and applying a sinusoidally varying magnetic field. I was applying the magnetic field using a solenoid and driving it using a sinusoidal wave from the function generator. The function generator was giving me a maximum of 3.33Vpp after setting 10Ohms load. I was getting enough oscillation amplitude from the setup, but I also wanted to take the frequency response of the sensor.

On increasing the frequency of drive signal from the function generator, the current in the solenoid is decreasing, which reduces the magnetic field and I am not able to get enough oscillation amplitude. To measure the frequency response I want the magnetic force to be constant throughout the sweep, but it is decreasing with increasing frequency.

I looked into designing some operational transconductance amplifiers, but couldn't find something that could give me a constant alternating current source (most of it was for DC). I also found some stuff about Howland current pump, but they say it isn't suited for reactive loads. I also looked into audio amplifiers for this purpose (since I have a very cheap guitar amplifier I can sacrifice :-D ). But I am not sure if the audio amplifier can work as a constant current source.

Experimental details:

• L = 3.387mH
• R = 12Ohms
• Z = 24.54 ohms at 1kHz & 211.9 ohms at 10kHz
• Maximum Magnetic field requirement is 40 Gauss which I get from around 150mA current in the solenoid.
• range in which i want to find out the frequency response is upto 20Khz

Any help and suggestions will be greatly appreciated! Cheers

• If you want to drive 150 mA RMS into an impedance of 424 ohms @ 20 kHz, you're going to need an amplifier that can output 63.6 Vrms (180 Vp-p). It will need to have a differentiator that causes the voltage gain to rise with frequency. Commented Sep 10, 2019 at 14:08
• Coating with ferromagnetic material may not achieve what you want. Details please. Commented Sep 10, 2019 at 14:22
• IMO first to do is to use a resin coated copper tube or litz wire of substantial cross section, then make a solenoid with fewer turns - less inductance. So you will need larger current and lower voltage. A D class amp could drive a 2 ohm up to several ohms impedance. Commented Sep 10, 2019 at 19:50