Acoustic Sensors for Biomedical Applications

The interface between the physical sciences, electronics, and life sciences becomes inhabited by several researchers to fulfill the needs of the medical/life scientist in the biomedical community. Based on the chemical, biological, and physical principles, the instruments improvement burgeoned. Conversely, the analytical instruments require several types of sensors extending from elementary devices for temperature and flow measurements, nonionizing and ionizing radiation to biological, chemical, ultrasound, and acoustic sensing transducers [1–9].

In our daily life, sensors are corporate in several devices and applications for a better life. Such sensors as the tactile sensors are included in the touch screens and the computers’ touch pads. The input of these sensors is from the environment that converted into an electrical signal for further processing in the sensor system. The sensor’s main role is to measure a specific quantity and create a signal for interpretation. The human bodies continuously communicate health information that reflects the status of the body organs and the overall health information. Such information is typically captured by physical devices that measure different types of information, such as measuring the brain activity, blood glucose, blood pressure, heart rate, nerve conduction, and so forth. According to these measurements, physicians decide the diagnosis and treatment decisions. Engineers are realizing new acquiring devices to measure noninvasively the different types of signals for further analysis using mathematical algorithms and formulae. This chapter includes classifications of the biosignals based on several principles. In addition, the different biosensors are highlighted including the role of the biopotential amplifier stage within the sensor system. Finally, the biomedical signal acquisition and processing phases are also included.

Sound is the generalized name of the acoustic waves that have frequencies within the range of one to tens of thousands Hertz, where the maximum human hearing ability is 20 kHz. The main role of the sound sensors/transducers is to use electrical energy for creating mechanical vibrations that disturb the surrounding air to produce sound at the inaudible or audible frequencies, which requires a transmission medium. The sound waveform can be characterized by the velocity (m/s), the frequency (ƒ), and the wavelength (λ), like the electrical waveform. The sounds wave shape and frequency are determined by the vibration/origin that created the sound, while the velocity depends on the sound wave transmission. Discovery of the quartz resonator to stabilize the electronic oscillators leads to the detection of the piezoelectricity. Piezoelectricity can be defined as the electrical charges production by the mechanical stress imposition. This creates a revolution in the acoustic wave sensors and devices using a piezoelectric material for generating acoustic waves. Applying a fluctuating electric field by the piezoelectric acoustic wave sensors, a mechanical wave is created that propagates via the substrate and transformed to electric field for further measurements. This chapter reveals about the fundamentals of the acoustics with a detailed explanation of the several body acoustic sounds sources.

An acoustic wave biosensor employs mechanical or acoustic waves as a detection instrument to attain biochemical, biophysical, and medical information. It senses changes in elasticity, mass, dielectric properties, and conductivity from the electrical or mechanical variations. At an input transducer, the piezoelectric effect is employed in these devices to stimulate the acoustic waves electrically and to obtain the waves at the output transducer. Acoustic biosensors are implemented with robust piezoelectric crystals such as lithium tantalite, lithium niobate, or quartz that can detect various biomolecules. Sound waves are generated by different compression and expansion of the medium at specific frequencies. For auscultation and listening to body sounds, the stethoscope instrument is used to hear the sounds produced from the heart, intestinal tract, lungs, stomach, the blood flow in the exterior vessels, venous, arterial, uterine, and the sound of human’s/animal fetuses. Acoustic wave sensors are convenient in several applications as predominantly mass sensitive devices capable of the respond to small environmental perturbations. New surface acoustic wave devices using different materials for chemical and biological sensing are developed. The improvement of a broad sensor system for biomarker and chemical sensing attracts several researchers. This chapter introduces in details the piezoelectricity effect as well as the acoustic sensor design and the acoustic stethoscope. Finally, the acoustic wave sensors including the bulk acoustic wave sensors, the surface acoustic wave sensors, and the acoustic wave propagation modes are introduced.

The biomedical engineering domain is concerned with physiological modeling, biomaterials, biomechanics, control and simulation, etc. Biomedical sensors are considered the most vital parts in the biomedical engineering. These sensors enable the biologic events detection and conversion to signals. The biomedical sensors receipt signals that represent the biomedical measurements and convert them into optical or electrical signals. Thus, the biomedical sensor acts as an interface between the biological feature and the electronic system. Sensor specialists and biomedical engineers are interested to process and design sensors for several application problems. This chapter introduces some examples of the acoustic sensors in different biomedical applications.

This book introduces the basic definitions of the sensors, the biosensors and their features, and the equivalent components, amplifiers, filters, and bio-measurement systems for further circuit design. It describes and categorizes the mainstream acoustic wave biosensors, including the utilization of the bulk acoustic waves and analysis devices, which imply surface acoustic waves. In addition, the use of the piezoelectric substrates of the acoustic sensors design is included. The different types of the biosensors are presented. Several applications of the acoustic biosensors are introduced.