Electricity is fundamental to biomedical engineering, powering diverse devices from pacemakers to diagnostic equipment. Understanding the sources of electricity and the principles of electrolysis allows biomedical engineers to design, maintain, and innovate medical devices that rely on controlled electrical energy. In Kenya, where healthcare infrastructure is rapidly advancing, mastery of these principles enhances the reliability and safety of biomedical equipment used in hospitals, clinics, and research institutions. This chapter explores the main sources of electricity relevant to biomedical applications and the process of electrolysis with its practical uses in the biomedical field.

2.1 Sources of Electricity

In biomedical engineering, reliable and safe sources of electricity are critical for operating medical devices and laboratory instruments. Kenya’s healthcare facilities depend heavily on electrical power supplied through various means to ensure continuous service delivery, especially in rural and off-grid locations. This section examines the different sources of electricity, focusing on their characteristics and suitability for biomedical applications.

2.1.1 Primary and Secondary Cells: Definitions and Differences

Primary and secondary cells are the two fundamental categories of electrochemical cells that serve as portable sources of electrical energy in biomedical devices.

• Primary Cells: These cells generate electrical energy through irreversible chemical reactions. Once depleted, they cannot be recharged or reused. Common examples include alkaline batteries used in disposable medical devices such as glucose meters. Their advantage lies in convenience and immediate availability, but they generate waste and incur recurring costs.
• Secondary Cells: These cells involve reversible chemical reactions, allowing them to be recharged multiple times. Lithium-ion batteries in implantable devices like pacemakers illustrate secondary cells’ critical role in biomedical engineering. Secondary cells reduce operational costs and environmental impact over time.
• Energy Density: Primary cells usually have higher initial energy density, making them suitable for short-term use. Secondary cells have lower energy density but longer lifecycle, essential for devices requiring continuous power.
• Cost Implications: Primary cells have lower upfront costs but higher long-term expenses due to replacement. Secondary cells require investment in charging infrastructure but are cost-effective for repeated use.
• Environmental Impact: Disposal of primary cells contributes to environmental pollution, while secondary cells mitigate this through reuse and recycling programs, aligning with Kenya’s environmental sustainability goals.

2.1.2 Characteristics of Cells and Batteries in Biomedical Devices

The performance of cells and batteries in biomedical devices depends on several electrical and physical characteristics crucial for device reliability and patient safety.

• Voltage Output: Biomedical devices require stable voltage to function correctly. Variations can lead to inaccurate readings or device malfunction. For example, infusion pumps in county hospitals need consistent voltage to administer precise medication doses.
• Capacity and Energy Density: Capacity determines how long a battery can power a device. High energy density cells reduce the size and weight of wearable health monitors, enhancing patient comfort.
• Internal Resistance: Low internal resistance improves efficiency and reduces heat generation, critical in implantable devices to prevent tissue damage.
• Shelf Life: Long shelf life is essential for emergency medical kits stocked in rural clinics, ensuring readiness when needed.
• Safety Features: Cells designed for biomedical use often include protective circuits to prevent overcharging, overheating, and leakage, ensuring patient safety.

2.1.3 Common Types of Batteries Used in Biomedical Engineering

Different types of batteries serve specific biomedical applications based on their chemical composition and performance characteristics.

• Alkaline Batteries: Widely used in portable diagnostic tools like blood pressure monitors due to their availability and moderate cost.
• Lithium-Ion Batteries: Favoured for implantable devices such as neurostimulators because of high energy density and rechargeability.
• Nickel-Cadmium (NiCd) Batteries: Historically used in some medical equipment but less common now due to memory effect and environmental concerns.
• Silver-Oxide Batteries: Used in small devices like hearing aids because of stable voltage and compact size.
• Zinc-Air Batteries: Employed in cochlear implants and some hearing aids, offering high energy density but limited rechargeability.

2.1.4 Selection Criteria for Batteries in Biomedical Applications

Selecting an appropriate battery for a biomedical device requires balancing technical, economic, and safety considerations.

• Device Power Requirements: The battery must meet the voltage and current needs without compromising device function. For instance, dialysis machines in county hospitals require high-capacity power sources.
• Size and Weight Constraints: Wearable and implantable devices demand lightweight, compact batteries to minimize patient discomfort.
• Operational Environment: Batteries must withstand temperature variations and humidity typical in Kenyan healthcare settings without degradation.
• Regulatory Compliance: Batteries must meet medical device standards and certifications to ensure safety and efficacy.
• Cost and Availability: Affordability and supply chain reliability influence battery choice, especially in resource-limited healthcare facilities.

Chapter Summary

This chapter explored various sources of electricity, highlighting their fundamental role in electrical circuits. It examined the process of electrolysis and its practical applications in industry and technology. The concept of simple cells was introduced as the basis for understanding how chemical energy converts to electrical energy. Differences between primary and secondary cells were clarified, emphasizing their distinct rechargeability features. Various types of cells and batteries were discussed in detail, including dry cells, Leclanché, mercury, lead-acid, alkaline, and lithium batteries, each with unique characteristics and uses. The chapter also covered electromotive force and internal resistance, explaining their influence on the performance of cells. Proper maintenance techniques for batteries were outlined to ensure longevity and efficiency. Finally, the chapter reviewed the wide range of applications for batteries across different sectors, demonstrating their importance in everyday electrical devices.