Microphone Design Competition Lab 8 Introduction to Engineering and Design

LAB 8: Microphone Design Competition

8.1 Objectives

The purpose of Lab 8 – Microphone Design – is to familiarize the student with piezoelectric materials. By performing this experiment, the student will learn how LabVIEW can be used as a testing mechanism. Through design, test, and analysis, the student will be able to

understand the characteristics of a microphone, and learn how a microphone works. Based on this knowledge of microphones, students will create microphones using simple household materials plus piezoelectric film.

8.2 Introduction

8.2.1 Background Information

The prefix Piezo means “Pressure”. When mechanical stress is applied to a piezoelectric material, an electric charge is produced.

8.2.2 Theory:

Piezoelectric Material

Piezo = Pressure. In piezoelectric material, mechanical stress produces electric charge. Such material has a crystalline structure. Pressure causes its molecules to compress and expand.

Fig. 8.1

Microphone

A microphone is a type of transducer, which means that is it used to convert one form of energy to another. Microphones convert variations in sound pressure to electrical signals

In a commercial microphone the sound waves first hit the Diaphragm of the microphone. A diaphragm is a thin membrane that bends and vibrates when hit by a force (i.e. Sound waves). Each sound wave hitting the diaphragm will cause it to vibrate in a unique way. The diaphragm in effect vibrates in the pattern of the sound waves that hit it. The vibrations are minute. The diaphragm has a small coil attached to it, which moves as a result of vibrations from the diaphragm. Inside the coil, a magnet creates a constant magnetic field. As the coil moves back and forth in the magnetic field, a voltage is produced at the terminals of the coil.

Fig. 8.2

Examples of Diaphragms: Examples of Transducers:

  • Drum skin ● Microphones
  • Ear Drums ● Telephones
  • Soap Bubbles ● Speakers
  • Speakers ● Voice Boxes

8.2.3 Ideal Results:

You will be using the LabVIEW VI, “TimeFreq” to test the quality of your microphone. The VI simulates an oscilloscope. TimeFreq uses two graphs to analyze the quality of your microphone. The first is a Waveform Spectrum. This graph plots voltage against time. Ideally, the graph should be smooth and continuous. The higher the amplitude of the graph, the more sound the microphone picked up (see figure 8-2). The second graph used to analyze your microphone in this experiment is called an FFT Spectrum. It plots time against frequency. An ideal FFT graph would also have a high peek that repeats itself regularly. The graph would also be smooth. A rigid graph would indicate that your microphone is not only picking up the desired sound wave, but it is also picking up unwanted background noise (see figure 8-3).

Fig. 8.3 (a)Fig. 8.3 (b)

Clear and consistent Sine WaveUnclear and disturbed Sine Wave

Fig. 8.3 (c) Fig. 8.3 (d)

High Frequency peak – ConsistentDisturbed Frequency Peak with noise background

8.3 Materials and Equipment

  • Piezoelectric film and leads
/
  • Styrofoam

  • Disposable cups
/
  • Tape

  • Plastic wrap
/
  • Amplified speaker

  • Metal Foil
/
  • Electronic keyboard

  • Rubber bands
/
  • PC with LabVIEW (TimeFreq.VI)

8.4 Rules of Competition

8.4.1 Design Specifications

  • TAs must sign your sketch before construction can begin.
  • Your microphone cannot be larger than the largest cup.
  • All materials must be placed inside the cup. The piezoelectric film and leads can be placed outside the cup.
  • You are only allowed to use the materials provided.

8.4.2 Disqualification

  • If the microphone is larger than the largest cup, the team will be disqualified.
  • If any materials are outside the cup, the team will be disqualified.
  • When testing, the cup cannot be held by anyone.

*** One team member will stop the LabVIEW program during testing. ***

8.4.3 Declaration of winners

  • The design that produces a waveform closest to the ideal in terms of waveform and FFT spectrum will be declared the winner.
  • The decision of the TA is final.
  • The winner of the competition will receive 20 extra points on the lab report.

8.5 Procedures

8.5.1 Design

  • Observe the waveform produced by a real microphone on the LabVIEW program.
  • Observe the materials provided.
  • Brainstorm within the group about possible designs for the microphone. Make notes during this process so that you can incorporate them into your lab report.
  • Sketch your design on paper. Make sure to label your design clearly and have one of the TAs sign it.
  • Construct your design based on the sketch.
  • Test your design at one of the testing stations setup by the TA.
  • If your results are unsatisfactory go back and modify your design.
  • Continue to test and modify your design until you are satisfied or the design period comes to an end.

8.5.2Test

  • When asked to do so, bring your design up to the official testing station.
  • Place your design on the keyboard and connect it to the amplified speaker.
  • Start the LabVIEW program “TimeFreq.vi”. Make sure to place the program on “continuous run”.
  • The TA will create a sound using the keyboard.
  • Observe the waveform generated by your microphone. Stop the LabVIEW program when you feel that you have the best waveform possible.
  • You will have three tries to obtain a waveform for judging.
  • At the end of the testing period, the TA will observe a representative waveform from each group and pick the winner (considering minimal design).
  • Data

You should have the following at the end of the lab:

  • A signed sketch of your design
  • A signed copy of he LabVIEW printout for your design.

8.5.4Data Analysis:

  • Not Applicable

8.6Discussion Topics

Independent Report (One report per student).

  • What results were you expecting from your design? Why?
  • Analyze and discuss the waveform for your design.
  • How does your waveform compare to the ideal waveform?
  • What aspects of your waveform are most like the ideal waveform, or may have excelled when compared to the other teams’?
  • Imagine you are a quality tester and your manager has asked you to analyze this product. Based upon your waveform analysis, what would be the strengths and weaknesses of this microphone if it were to go on the market?
  • Did you obtain the results you expected from in this experiment?
  • Why, or why not?
  • Describe your design.
  • What was your design strategy?
  • What was the role of each material?
  • Which materials failed their roles? Why was this the case?
  • Why did you win or loose the competition? Did choice of materials play a part in the outcome of the competition?
  • If you did not win the competition, how would you change your design with the goal of winning?
  • Would the shape of the materials make a difference in your results? Why or why not?
  • If only a single material was used in your design, what would happen? Explain.
  • Discuss several modern day technological applications of pressure sensors.
  • What are some other types of sensing devices that can be made with piezoelectric film?
  • Briefly describe 2 different types of microphone designs, other than the one mentioned in this experiment.

8.7 Closing

Make sure to clean up your workstation at the end of the competition. If you are going to use your design in recitation, label it and store it in a safe place. If you are not going to use your design in recitation, please dispose of it in the bins outside the labs.

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