Transducers for Biomedical Measurements: Principles and Applications

Citation

Cobbold, R. S. C. (1974). Transducers for Biomedical Measurements: Principles and Applications. Wiley.

Chapter Summary

This is a single-author monograph of xiv + 486 pages, published in New York by Wiley as a Wiley-Interscience book in the series Biomedical Engineering and Health Systems. Library catalogues classify it under biomedical transducers and note that it includes bibliographical references. The title states its two halves: the principles on which transducers work, and their application to measurements on living systems. The sections below follow the topic areas the book's published front matter and subject headings point to, not a chapter list.

Signals and Systems in Measurement

The opening material is about the signals a biomedical measurement has to capture and the systems that carry them. This is the language the rest of the book relies on, the characteristics of signals and systems, and it prepares the reader to judge how faithfully a measuring chain reproduces what the body produces.

Criteria for Error-Free Measurement

Alongside signal characteristics, the early part of the book sets out criteria that a measurement must meet to be free of error. For a reader this is the framework for asking of any sensor whether its output can be trusted: how closely the recorded quantity follows the physiological one, and what distorts it.

General Properties of Input Transducers

Next the book turns to the transducer itself, the element that converts a physical or chemical quantity in the body into a signal that instrumentation can handle. The general properties of input transducers are treated before individual devices, so that devices of different physical kinds can be compared on common terms.

Transducers and Their Applications

The remainder of the 486 pages, according to the title and subject headings (biomedical transducers, biomedical engineering), covers specific types of transducer and their use in measuring physiological quantities. The book is organized around the measuring device rather than around a clinical specialty.

Key Concepts

Signals and Measurement Quality

• Signal and system characteristics: the properties of physiological signals and of the systems that transmit them, which determine what a measurement can resolve.
• Error-free measurement criteria: the conditions under which a recorded signal faithfully represents the physiological quantity.

Transducers

• Input transducer: the device at the front of a measuring system that converts a physical or chemical quantity into an electrical or other usable signal.
• General transducer properties: characteristics common to all input transducers, used to compare devices.

Critical Analysis

Strengths

• The book is devoted to one subject, the transducer, which is the first element of every biomedical measuring chain. A reader who wants the sensor level explained at length is not diverted into amplifiers, displays or clinical systems.
• Its stated structure starts from general ideas (signals and systems, measurement criteria, general transducer properties) before reaching particular devices. That order suits a reader who wants to understand why a transducer behaves as it does, not just to look up types.
• It is the work of one author, which tends to give a consistent treatment and notation across the whole text.
• Wiley-Interscience publication and the inclusion of bibliographical references make it traceable to the literature of its time.

Limitations

• It dates from 1974, so devices, materials and electronics have changed substantially since. It can explain principles of long standing but cannot be relied on for current practice.
• Its focus is transducers. Readers who need amplifiers, signal conditioning, data acquisition, safety standards and patient monitoring will need other books.
• Its length of nearly 500 pages is given over to a single stage of the measuring chain, which makes it slow going for readers who only need an overview.

Where It Fits in the Course

In the medical instrumentation group this is the oldest and the narrowest book. Webb's Principles of Biomedical Instrumentation follows the design of a medical instrument step by step, from sensor through amplification, filtering and digitization to safety. Christe's Introduction to Biomedical Instrumentation describes the equipment found in hospitals from the viewpoint of those who maintain it. Webster and Nimunkar's Medical Instrumentation: Application and Design is a standard engineering textbook covering sensors, signal conditioning and clinical measurements. Togawa, Tamura and Öberg's Biomedical Sensors and Instruments is organized by the quantity measured. Northrop's text covers the analog electronics between sensor and digitizer. Cobbold's monograph stands apart as a focused, historical treatment of the sensor stage, best read after one of the current texts has set out the whole instrument.

How to Use This Book

The book is for students who have completed an introductory instrumentation course and want to go deeper on how transducers work, or who are interested in the foundations of the field as it stood in the early 1970s. A grounding in calculus, circuits and basic physiology is the sensible preparation.

A practical plan is to start with a current instrumentation text for the overall chain, then read the early material in Cobbold on signals, systems, measurement criteria and general transducer properties as a conceptual framework. Use the later, device-specific material as a source on the physical principle of a given sensor, and check against a current book or manufacturer documentation for present-day devices, accuracy figures and safety rules. Because the book is a library-held classic and not a current course text, it works best as a supplementary reference to an assigned book, with its bibliography as a route to the original literature.