If u want to generate a frequency then fix a oscilator of your required frequency in series to the electromagnet. (OR one capacitor or inductor calculated for your frequency. Do u need help in it???)
Delta 0.1-3 Hz deep sleep, lucid dreaming, increased immune functions, hypnosis
Theta 3-8 Hz deep relaxation, meditation, increased memory, focus, creativity, lucid dreaming, hypnagogic state
Alpha 8-12 Hz light relaxation, "super learning", positive thinking
Low Beta 12-15 Hz relaxed focus, improved attentive abilities
Midrange Beta 15-18 Hz increase mental ability, focus, alertness, IQ
High Beta above 18 Hz fully awake, normal state of alertness, stress and anxiety
Gamma 40 Hz associated with information-rich task processing and high-level information processing
These r the frequency for the mind wave generation