Enhanced Ion Tweeter

1. Enhanced Ion Tweeter • Our Team Members • Rob Alejnikov • Mark Blattner • Colin Joye • Our Advisor • Dr. Robert Caverly

2. Project Objectives • What did we do? • Created an audio transducer that offers the same frequency content in all directions. • Concentrated on high frequencies since they tend to beam the most. • How we did it: The Ion flame • What is it? • Voltage --> flame size --> sound • Existing devices use vacuum tubes, creating excessive heat • Goal • Raise power efficiency • Decrease unit cost

3. Presentation Objectives • Intro, Audio Subsystem – Rob • High Voltage Generation – Mark • Results and Conclusions – Colin

4. The Audio Subsystem • Need • Ion tweeter cannot implement low frequencies --> Filter • Output of source device (CD, cassette) up to 1 V; power rail modulation requires ~ 30 V --> Gain • Design Criteria • Flat frequency response for high audio frequencies • Sufficient gain on signal passed to high voltage circuit

5. The Audio Subsystem • 3-stage implementation • Buffer for high input impedance • Low Pass • High Pass • Performance measures • Cutoff at 4 kHz and 40 kHz • Total gain factor up to 60

6. High Voltage Circuit Operation • Generates high voltage necessary for Corona Discharge • Major Components • Power MOSFET • MOSFET Gate Driver • Coil • Uses Resonant Properties of Coil to produce High Voltages • Self-Oscillating nature of circuit provides resilience to environmental changes

7. Coil Implementations • Keys to producing High Voltage • Resonant Frequency between 3MHz and 8MHz to avoid audible hiss and limitations of technology • High Quality Factor (Q) causes near open circuit • Low DC resistance

8. Coil Implementations • 10 Coils Built and Tested • Built with Varying Specs • Dimension, wire gauge, and number of turns • Coil Chosen • 16 Gauge Wire • 45 Turns • 5 MHz Resonance • D=3” H=2.5”

9. Field Effect Transistor (FET) • FET rapidly switches a small current in the coil. • Optimal FET • High Voltage handling • >500 volts • High Transconductance • Greater current in coil • Low Gate Capacitance • <500 pico-Farads • Reduces stress on Gate Driver

10. Interface Methods • Numerous Approaches Tried and Tested • Pulse Width Modulation (PWM) via Gate Driver • Power Rail Modulation via Audio Transformer • Ground Rail Modulation via Audio Transformer • Faraday Shield Modulation

11. Interface Methods • Decided on Power Rail Modulation • PWM unable to obtain clean waveforms and oscillations • Faraday Shield requires very High Voltages

12. Noise versus Coil Frequency • Flame Flicker Noise present up to 3MHz, as noted by Siegfried Klein in 1956. • This noise is virtually inaudible 7MHz and up. • At 30MHz, the flame has a different appearance and no noise.

13. Testing • Power Efficiency Test • Tube-based: • 114W at 1cm flame height. • FET-based: • 67W at 1cm flame height. • 40% Power savings

14. Unit Cost • Unit Cost (45% savings): • FET: $48.46 (to us), $65.44 (industry) • Tube: $120.53 • Total man-hours: • 750 man-hours • Estimated industry cost: • $45,270

15. Recommendations • For Increased Linearity: • Pulse Width modulation of the FET. • Requires high speed, high precision circuitry. • Requires virtually zero extra power. • Occupies almost no space. • Faraday Shield Modulation. • Affects the voltage gradient directly. • Requires high voltage audio. • Increase operation frequency • Increase flame power

16. In Conclusion • Special Thanks to: • Texas Instruments (gate drivers) • BGR-WYK Distributors (ST FETs) • International Rectifier (FETs) • Fairchild Semiconductors (FETs) • Alpha Industries (diodes) • Join us for a demo in CEER 210. • Questions????