Medical sensors turn signals from the body into numbers that clinicians can read, compare, and act on. A pulse oximeter estimates blood oxygen, an ECG measures heart electrical activity, and a pressure sensor can track blood pressure or breathing motion. These devices matter because they make invisible body processes visible in real time.
Good sensor design helps doctors detect problems earlier, monitor treatment, and keep patients safer.
Key Facts
- A medical sensor converts a physical, electrical, optical, pressure, or chemical change into an electrical signal.
- Optical sensors often use absorption: A = log10(I0/I), where I0 is incoming light and I is detected light.
- Electrical sensors measure voltage differences from the body, such as ECG signals from the heart.
- Pressure sensors use P = F/A, where pressure equals force divided by area.
- Chemical sensors relate concentration to signal, often using calibration curves such as signal = mC + b.
- Digital sampling rate must be high enough for the signal: fs >= 2fmax is the Nyquist rule.
Vocabulary
- Transducer
- A transducer is a device that converts one form of energy or information into another, such as body pressure into voltage.
- Calibration
- Calibration is the process of matching a sensor output to known reference values so its readings are accurate.
- Signal
- A signal is a changing quantity, such as voltage or light intensity, that carries information about the body.
- Noise
- Noise is unwanted variation in a measurement that can hide or distort the true body signal.
- Sampling rate
- Sampling rate is the number of times per second a digital system records a sensor signal.
Common Mistakes to Avoid
- Treating every displayed number as perfectly accurate is wrong because sensors can drift, lose contact, or be affected by motion and skin conditions.
- Ignoring calibration is wrong because the same voltage or light reading may represent different physical values unless it is matched to known standards.
- Confusing resolution with accuracy is wrong because a device can show many decimal places while still being far from the true value.
- Placing electrodes or optical sensors loosely is wrong because poor contact reduces signal strength and increases noise.
Practice Questions
- 1 A pressure sensor in a cuff detects a force of 18 N over an area of 0.0030 m2. What pressure does it measure in pascals using P = F/A?
- 2 An optical sensor sends light intensity I0 = 100 units into tissue and detects I = 25 units. Calculate absorbance using A = log10(I0/I).
- 3 A wearable heart monitor becomes noisy when a patient jogs. Explain two likely causes of the noise and one design feature that could reduce it.