ECE5320 Mechatronics Assignment#01: Literature Survey on Sensors and Actuators Topic: Microphone

1. ECE5320 MechatronicsAssignment#01: Literature Survey on Sensors and Actuators Topic: Microphone Prepared by: David D Bradshaw Dept. of Electrical and Computer Engineering Utah State University E: davbradshaw@cc.usu.edu ; T: (435)797-1000; F: (435)797-3054 (ECE Dept.) W: http://mechatronics.ece.usu.edu 3/9/2007

2. Outline • Reference list • To probe further • Major applications • Basic working principle illustrated • A typical sample configuration in application (application notes) • Major specifications • Limitations ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

3. Reference list • Microphones: Technology and Technique, Borwick, John. 1990. Focal Press. • Shure SM57, Shure SM81, Shure PG-52, Rhode NT-2A product manuals • Yamaha Sound Reinforcement Handbook, Davis & Jones, 1989. Hal Leonard. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

4. To explore further • http://www.mediacollege.com/audio/microphones/how-microphones-work.html • http://members.aol.com/mihartkopf/ • http://www.coutant.org/1.html • http://www.panasonic.com/industrial/components/audio/aud_mic.htm ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

5. Major applications • Professional Recording Studios • Public Address Systems • Hearing Enhancement • Voice / Audio Communication Systems • Television and theatrical Studios • Surveillance and Intelligence Agencies • Any system used to store, transmit or amplify signals in the human hearing range (20Hz – 20KHz) ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

6. Basic Working Principle • Conversion of acoustic vibrations to electrical Energy Acoustic vibrations are transmitted through the air as compression waves. http://www.privateline.com/TelephoneHistory/soundwaves.html ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

7. Basic Working Principle • Conversion of acoustic vibrations to electrical Energy A microphone converts these acoustic pressure variations into alternating current signals http://www.privateline.com/TelephoneHistory/soundwaves.html ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

8. Sample Configuration Voice Activation Circuit This circuit closes a relay when a strong enough signal is sensed by the microphone ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

9. Major Specifications • Frequency Response • Directivity • Sensitivity • Output Impedance • Transducer Type ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

10. Major Specifications • Frequency Response Specified as the range where the magnitude is above -3dB Example: 15Hz - 40 KHz Complex frequency response can also be specified using a Bode plot Example: ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

11. Major Specifications • Frequency Response Microphone should be selected based on frequency content of sound source Instrument Microphone Bass drum Microphone ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

12. Major Specifications • Frequency Response Some microphones have a configurable frequency response. The response is changed by changing pickup elements or selecting it via a toggle switch. (Usually an onboard low-pass or high-pass filter) ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

13. Major Specifications • Directivity Also known as “polar” or “pickup” pattern. This specification refers to the microphones response to sounds approaching the pick-up element from different angles Example Polar Patterns: ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

14. Major Specifications • Directivity Some microphones offer configurable polar patterns ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

15. Major Specifications • Sensitivity • Sensitivity in measured in dB units or Sound Pressure Level. There are several ways this is specified: • dBv • output compared to 1V RMS signal • dBu • output compared to 0.775V RMS signal • SPL • millivolts per Pascal ( mV / PA ) ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

16. Major Specifications • Output Impedance • Specifies the impedance seen across the output terminals. • Microphones used for sound reinforcement or professional sound recording are is usually on the order of 150 to 600 ohms. • Microphones for industrial or commercial purposes are often in the order of 1 Kohm to 10 K ohms ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

17. Major Specifications • Output Impedance • Specifies the impedance seen across the output terminals. • Microphones used for sound reinforcement or professional sound recording are is usually on the order of 150 to 600 ohms. • Microphones for industrial or commercial purposes are often in the order of 1 Kohm to 10 K ohms ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

18. Major Specifications • Transducer Type • The properties of a microphone are highly dependant on the type of transducer used to translate pressure waves into electrical energy • Most Common Transducer Types: • Dynamic • Condenser • Piezoelectric ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

19. Major Specifications • Transducer Type - Dynamic Most common type of microphone in sound reinforcement systems. It consists of a flexible diaphragm coupled to a moving coil which is suspended in field permanent magnet . ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

20. Major Specifications • Transducer Type - Dynamic • Dynamic transducer microphone Characteristics: • Highly rugged and reliable. • Low sensitivity to disturbances • Good frequency response ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

21. Major Specifications • Transducer Type - Condenser Condenser microphones function as a variable capacitor. A thin diaphragm coated with a conductive material is suspended above a conductive back plate. A DC voltage bias is applied across these two elements. Output voltage is proportional to the vibration of the diaphragm. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

22. Major Specifications • Transducer Type - Condenser • Condenser microphone characteristics: • require a DC bias supply (usually 9 – 48 VDC) • require a buffering amplifier • flat frequency response • high transient response ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

23. Major Specifications • Transducer Type – Piezoelectric • Piezoelectric microphones are constructed of a flexible diaphragm coupled to a crystal element. The vibration of the diaphragm creates an electrical response across the crystal. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

24. Major Specifications • Transducer Type – Piezoelectric • Characteristics of piezoelectric microphones: • inexpensive • lower frequency response • can be directly mounted to a surface to sense vibrations ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

25. Limitations • Limitations of microphones: • low voltage output levels require external voltage amplifiers • low power output requires power amplifier for sound reproduction • frequency response is usually optimized around the range of human hearing ( 20 Hz to 20 KHz ) ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators