20-Bio-B6 Analytical Biochemistry · May 2013
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Paper format: National Exams, May 2013 — 04-Bio-B6 Bioinstrumentation. Three hours, open book, non-communicating calculator permitted. Six questions of equal value (25 marks each); four constitute a complete paper and only the first four appearing in the answer book are marked. All six are solved here as a complete study resource. Every question is a design/essay question (block-diagram instrumentation-system design, or descriptive explanation).
Reference texts (the books a candidate should have reviewed for this subject):
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
A miniature piezoelectric contact microphone (or a small piezoresistive accelerometer) is used to pick up the joint sound: the piezoelectric element generates a charge proportional to the mechanical vibration/pressure applied to it, which a charge amplifier converts to a voltage. It is taped directly to the skin over the TMJ (immediately anterior to the tragus of the ear, the standard auscultation point for joint sounds), using a low-mass adhesive pad so its own inertia does not load or damp the vibration being measured, with light, consistent contact pressure. Chewing force is measured with a thin force-sensing resistor (FSR) or strain-gauge load cell embedded in a bite plate/occlusal splint the subject bites down on; the sensor's resistance (FSR) or strain-gauge bridge imbalance changes proportionally with the applied bite force, converting a mechanical force into an electrical signal.
The microphone/accelerometer signal passes through a charge (or high-impedance voltage) preamplifier, then a bandpass filter set to 50 Hz-2 kHz to match the stated joint-sound spectrum and reject out-of-band noise, followed by an anti-aliasing low-pass filter ahead of the ADC. The force-sensor bridge is amplified by an instrumentation amplifier (specified for low offset drift, since the signal of interest is near-DC) and low-pass filtered at ~10-20 Hz to match the stated 0-10 Hz chewing-force bandwidth while rejecting higher-frequency mechanical noise, again followed by an anti-alias filter matched to its own (much lower) sample rate.
The sound channel is sampled at ≥4 kHz (Nyquist rate for the 2 kHz upper band edge), and the force channel at 50-100 Hz (ample margin above its 10 Hz content). Both channels are sampled from a common clock so every joint-sound sample can be time-tagged against the simultaneous chewing-force value. The processor computes a short-time spectrogram (sliding-window FFT) of the sound channel to show amplitude vs. frequency vs. time, and overlays or time-aligns this with the chewing-force trace so the clinician can see how the joint-sound spectrum and amplitude change as bite force is applied and released. The synchronised sound-spectrum/force data are shown on a real-time display and logged for offline diagnostic review.
Both transducers are non-invasive, biocompatible, contact-only sensors: the contact microphone uses a hypoallergenic adhesive pad, and the bite-force sensor is built into a smooth, inert (medical-grade polymer) occlusal splint with no sharp or rigid metal parts that could injure the mouth. The entire signal chain from patient-attached sensors through to any mains-powered instrument is electrically isolated (battery-powered front end or an isolation amplifier/optocoupler at the interface, as detailed in Question 5) so no hazardous current path exists between the subject and line power.
