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Chapter 22: Problem 13

One of the critical components of our modern video cassette recorders (VCRs) is the magnetic recording/playback head. Write an essay in which you address the following issues: (1) the mechanism by which the head records and plays back video/audio signals; (2) the requisite properties for the material from which the head is manufactured; then (3) present at least three likely candidate materials, and the property values for each that make it a viable candidate.

Short Answer

Expert verified
Answer: The three main points about modern VCRs' magnetic recording/playback head are: (1) the mechanism by which it records and plays back video/audio signals using magnetic fields, (2) the necessary properties required for the material used to manufacture the magnetic head, such as high magnetic permeability, wear resistance, corrosion resistance, and thermal stability, and (3) the identification of suitable candidate materials including ferrite, amorphous metallic alloys, and high-permeability metals like permalloy. These points are important as they provide an understanding of the functionality, durability, and reliability of the VCR's performance as well as the potential for future advancements in the technology.

Step by step solution

01

Introduction

Begin the essay with a brief introduction that introduces the topic, setting the stage for the subsequent sections. Mention how VCRs have significantly impacted the entertainment industry and the importance of understanding their components, specifically the magnetic recording/playback head.
02

Mechanism for Recording and Playback

In this section, explain the mechanism by which the magnetic recording/playback head records and plays back video/audio signals. Describe how it uses magnetic fields to record and reproduce signals; for example, how a changing magnetic field is induced in the tape when it is being recorded, which in turn alters the material's magnetic properties. Furthermore, discuss how the playback process works by moving the tape past the head, creating a varying magnetic field that generates an electrical signal that is then amplified and processed to play back the audio and video content.
03

Requisite Material Properties

Discuss the essential properties required for the material used to manufacture the magnetic recording/playback head. Some of these key properties may include high magnetic permeability, wear resistance, corrosion resistance, and thermal stability. Explain why these properties are important to the head's functionality, and how these aspects maintain the durability and reliability of the VCR's performance.
04

Candidate Materials

Identify at least three candidate materials suitable for manufacturing the magnetic recording/playback head. Some examples of potential materials may include ferrite, amorphous metallic alloys, and high-permeability metals like permalloy. For each material, provide a brief description of its properties and how they make it a viable candidate for use in the head. Also discuss any advantages and disadvantages of each material, such as cost, availability, and manufacturability.
05

Conclusion

Sum up the essay with a brief conclusion, tying together the main points discussed and reiterating the importance of understanding the function and properties of the magnetic recording/playback head in modern VCRs. Mention the potential for future advancement in this area, such as improved materials or recording technology that could enhance the performance of VCRs and similar technologies.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Magnetic Recording Mechanism
The magnetic recording mechanism of a VCR head is akin to a meticulous scribe, etching the nuances of sound and vision onto a receptive canvas—the magnetic tape. As the tape glides past the recording head during recording, an electrical signal representing the audio and video content is converted into a magnetic field. This field, in turn, aligns the microscopic magnetic particles on the tape's surface, effectively 'writing' the information in a magnetic language.

When it's time for playback, the roles reverse—the playback head interacts with these magnetized particles to produce a varying magnetic field. This field induces an electrical signal in the head, which mirrors the original content signal. This signal is amplified and decoded, transforming back into the sounds and images once captured by the VCR. The precision required for this process is astounding, involving aligned magnetic domains and a delicate signal retrieval, ensuring that every scene and note is faithfully preserved.
Material Properties for Magnetic Heads
The material of a magnetic head is no ordinary substance; it's carefully chosen to meet demanding criteria essential for high-fidelity recording and playback.

High Magnetic Permeability

This enables the head to respond to and influence the magnetic particles on the tape with finesse, facilitating a clear translation of data.

Wear Resistance

As the head makes continual contact with the moving tape, resistance to abrasion ensures longevity of both the head and the media.

Corrosion Resistance

It protects the head from environmental conditions, preventing loss of performance over time.

Thermal Stability

This allows consistent operation even when temperature fluctuations occur within the device.

The interplay of these properties ensures the magnetic head operates optimally, preserving the integrity of the VCR's function, whether it's rekindling old memories or recording new tales.
Candidate Materials for VCR Heads
Selecting a candidate material for VCR heads is a careful balance between desirable magnetic properties and practical manufacturing concerns.
  • Ferrite: A ceramic-like material, ferrite offers excellent magnetic permeability and corrosion resistance, yet is brittle, potentially complicating manufacturing.
  • Amorphous Metallic Alloys: These materials boast superior wear resistance and low noise during playback, but their production can be complex and costly.
  • Permalloy: This high-permeability metal is a traditional choice, providing a good balance between performance and ease of processing, although it may not match the wear resistance of newer materials.
Each material brings strengths and compromises to the table, and the ideal choice might depend on factors like cost-effectiveness, ease of mass production, or specific performance characteristics of a given VCR model. The ongoing evolution of these materials promises exciting advances in the quality and durability of magnetic recording and playback.

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Most popular questions from this chapter

In a manner similar to the treatment of Section \(22.2,\) perform a stiffness- to-mass performance analysis on a solid cylindrical shaft that is subjected to a torsional stress. Use the same engineering materials that are listed in Table 22.1 . In addition, conduct a material cost analysis. Rank these materials both on the basis of mass of material required and material cost. For glass and carbon fiber-reinforced composites, assume that the shear module are 8.6 and \(9.2 \mathrm{GPa},\) respectively.

(a) Using the expression developed for stiffness performance index in Problem 22.D3(a) and data contained in Appen\(\operatorname{dix} \mathrm{B},\) determine stiffness performance indices for the following polymeric materials: high- density polyethylene, polypropylene, poly(vinyl chloride), polystyrene, polycarbonate, poly(methyl methacrylate),poly(ethylene terephthalate), polytetrafluoroethylene, and nylon \(6,6 .\) How do these values compare with those of the metallic materials? (Note: In Appendix B, where ranges of values are given, use average values.)(b) Now, using the cost database (Appen\(\operatorname{dix} C),\) conduct a cost analysis in the same manner as Section \(22.2 .\) Use cost data for the raw forms of these polymers. (c) Using the expression developed for strength performance index in Problem \(22 . \mathrm{D} 3(\mathrm{a})\) and data contained in Appendix B, determine strength performance indices for these same polymeric materials.

(a) Using the procedure as outlined in Section 22.2 ascertain which of the metal alloys listed in Appendix B have torsional strength performance indices greater than \(10.0\left(\text { for } \tau_{f} \text { and } \rho \text { in units of } \mathrm{MPa} \text { and } \mathrm{g} / \mathrm{cm}^{3}\right.\) respectively \(),\) and, in addition, shear strengths greater than \(350 \mathrm{MPa}\). (b) Also using the cost database (Appendix C), conduct a cost analysis in the same manner as Section \(22.2 .\) For those materials that satisfy the criteria noted in part a, and, on the basis of this cost analysis, which material would you select for a solid cylindrical shaft? Why?

Consider the plate shown below that is supported at its ends and subjected to a force \(F\) that is uniformly distributed over the upper face as indicated. The deflection \(\delta\) at the \(L / 2\) position is given by the expression $$\delta=\frac{5 F L^{3}}{32 E w t^{3}}$$ Furthermore, the tensile stress at the underside and also at the \(L / 2\) location is equal to $$\sigma=\frac{3 F L}{4 w t^{2}}$$ (a) Derive stiffness and strength performance index expressions analogous to Equations 22.9 and 22.11 for this plate (Hint. solve for \(t\) in these two equations, and then substitute the resulting expressions into the mass equation, as expressed in terms of density and plate dimensions.) (b) From the properties database in Appendix \(\mathrm{B},\) select those metal alloys with stiffness performance indices greater than 1.40 (for \(E\) and \(\rho\) in units of \(\mathrm{GPa}\) and \(\mathrm{g} / \mathrm{cm}^{3}\) respectively). (c) Also using the cost database (Appendix C), conduct a cost analysis in the same manner as Section \(22.2 .\) Relative to this analysis and that in part b, which alloy would you select on a stiffness- per-mass basis? (d) Now select those metal alloys having strength performance indices greater than 5.0 (for \(\sigma_{y}\) and \(\rho\) in units of \(\mathrm{MPa}\) and \(\mathrm{g} / \mathrm{cm}^{3}\) respectively \(),\) and rank them from highest to lowest \(P\).(e) And, using the cost database, rank the materials in part d from least to most costly. Relative to this analysis and that in part d, which alloy would you select on a strength-per-mass basis? (f) Which material would you select if both stiffness and strength are to be considered relative to this application? Justify your choice.

A helical spring is to be constructed from a 4340 steel. The design calls for 5 coils, a coil-to-coil diameter of \(12 \mathrm{mm},\) and a wire diameter of \(3 \mathrm{mm}\). Furthermore, a maximum total deflection of \(5.0 \mathrm{mm}\) is possible without any plastic deformation. Specify a heat treatment for this 4340 steel wire in order for the spring to meet the above criteria. Assume a shear modulus of \(80 \mathrm{GPa}\) for this steel alloy, and that \(\tau_{y}=0.6_{y} .\) Note: heat treatment of the 4340 steel is discussed in Section 10.8.
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