Medical Applications User Guide (pdf) - Freescale Semiconductor

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Digital Stethoscope 16.1 Introduction A digital stethoscope is a device that uses ultrasound waves to detect different types of tissue and movements within the body, such as produced by heart contractions and relaxation or even blood flow through the arteries, using an ultrasonic probe. The functioning is based on the Doppler Effect, which consists of the wavelength variation of any wave sent or received by a moving object. In this case, the source sends acoustic waves to the heart. Part of the energy bounces back. However, because the heart is beating, the bounced waves are affected by the Doppler Effect. This changes their frequency. Therefore with simple algorithms the heartbeats are detected. 84 Medical Applications User Guide
16.2 Ultrasonic Probe The ultrasonic probe may consist of an oscillator (X1 in Figure 16-2) that generates an ultrasound frequency (for these applications, the range is 1–3 MHz) followed by an amplifier (U2 in Figure 16-2) to condition the sine waveform in volts. This waveform is applied to the transmitter transducer to send vibrations through the body and bounce back when the density of the medium changes. Another transducer is used to receive the bounced vibrations and convert them to electrical signals. This signal is amplified using an instrumental amplifier and is sent to a band-pass filter. The filtered signal is sent to a phase-locked loop to generate a voltage signal, which depends on the frequency applied. For implementations of the instrumentation amplifier and band-pass filter, see the Appendix of this document. 16.3 Electrical Protection Any time an AC-powered medical device comes into contact with a patient, the system must be designed with electrical protection in mind. Electrical protection limits the current to a non-harmful range of 6–10 mA maximum, avoiding the probability of electrical discharge. This also should provide isolation between the power source of the device and the sensor that is in contact with the person. In the transmitter ultrasound probe example (Figure 16-2) the resistor R3 limits the current to transformer T1. Transformer T2 provides isolation between the circuit and the patient’s body. Transformers T1 and T2 must have a 1:1 relationship, and should not be affected by the operational frequency of the transducers. Figure 16-1: Digital Stethoscope General Block Diagram Digital Stethoscope Ultrasound Transducer Freescale Technology Core • ARM ® Core • ARM Cortex-M4 Core 72/100 MHz • DSP ® Cortex-M4 Core 72/100 MHz • DSP Signal Conditioning • ADC • DAC • OPAMP • TRIAMP Audio Power Amplifier Potentiometer Volume Diagnostic and Therapy Devices freescale .com/medical 85 MCU HMI • External Bus Interface (FlexBus) Figure 15-3: 16-2: Transmitter Ultrasonic Ultrasonic Probe Probe Example Example U1 X1 C1 C2 Figure 16-3: Receiver Ultrasonic Probe Example Figure 15-4: Receiver Ultrasonic Probe Example Transducer T2 R1 Instrumentation Amplifier R2 U2 Band-Pass Filter LCD Active Speaker R3 T1 Transducer Phase-Locked Loop fin feedback Vout To MCU ADC input
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Medical Applications User Guide TM
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freescale.com/medical 3 Introductio
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Introduction 1.1 Freescale Offers T
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Monebo Kenetic ECG Algorithms Free
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Home Portable Medical 2.1 Introduct
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3.2 Home Health Hub (HHH) Reference
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3.3 Power Management Every design n
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MC34704 The MC34704 is a multi-chan
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3.7 How it Works The external capac
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eliably monitor and manage non-crit
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3.19 Standard Medical USB Communica
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Freescale has developed sample code
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4.2 Heartbeat Detection The heartbe
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4.6 Blood Pressure Monitor Referenc
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MCF51MM: Flexis 32-bit ColdFire V1
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Heart Rate Monitor 5.1 Introduction
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