Enhanced Ion TweeterOur Team Members Rob Alejnikov Mark Blattner Colin Joye

Our Advisor Dr. Robert Caverly

Project ObjectivesWhat 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

Presentation Objectives

Intro, Audio Subsystem – RobHigh Voltage Generation – MarkResults and Conclusions – Colin

The Audio SubsystemNeed

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

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

High Voltage Circuit Operation

Generates high voltage necessary for Corona DischargeMajor Components

Power MOSFET MOSFET Gate Driver Coil

Uses Resonant Properties of Coil to produce High VoltagesSelf-Oscillating nature of circuit provides resilience to environmental changes

Coil ImplementationsKeys 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

Coil Implementations

10 Coils Built and TestedBuilt 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”

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

Interface MethodsNumerous 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

Interface Methods

Decided on Power Rail Modulation PWM unable to obtain clean waveforms and

oscillations Faraday Shield requires very High Voltages

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.

Testing

Power Efficiency TestTube-based:

114W at 1cm flame height.

FET-based: 67W at 1cm flame

height.

40% Power savings

Unit CostUnit 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

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 frequencyIncrease flame power

In ConclusionSpecial 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????