BME 201 Found. of BME Fall 2017 HW #4 Due Wednesday, November 8 Name: 1. You may work together but each person should turn in his/her own work in his/her own handwriting. Problems #1 (10 pts) _____________ #2 (15 pts) _____________ #3 (10 pts) _____________ #4 (5 pts) _____________ /40 Total: _______________ 1. Bioinstrumentation: Voltage Divider [10 pts] You are developing a portable medical device for measuring the conductivity of skin, which is related to several conditions. The device is powered by a standard 9V battery, but your conductivity sensor requires only 4V to power it. Design a voltage divider circuit to deliver 4V to the sensor from your 9V battery. A diagram is shown below to help get you started. Note that the max current the circuit can handle is 100 mA, so make sure to stay below that value. Once you have calculated your desired values of R1 and R2 (show work), mathematically demonstrate that your voltage divider in fact delivers 4V to the sensor, and limits the current in the network to under 100 mA. [10 pts] 2. Bioinstrumentation: Temperature Sensors [15 pts] Voltage (mV) A. You are developing a temperature sensor to be used inside an autoclave system, which is used for sterilizing surgical instruments. During its operation, the system needs to monitor temperature up to 200°C to ensure the instruments are sterile. Your other specification is that the sensor should maximize sensitivity. Using the curves below as a guide, select the thermocouple type you will use for this application and provide your reasoning. [5 pts] 70 60 50 40 30 20 10 S. Chatterjee, Biomedical Instrumentation Systems, Delmar Cengage Learning, Clifton Park, NY, p. 685 B. The table below shows the relationship between resistance and temperature for a thermistor. Temperature (°C) 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 Resistance (RT) 57.0 40.7 29.4 21.5 15.9 11.9 8.9 6.8 5.2 4.0 3.2 2.5 2.0 1.6 1.3 i. Plot the temperature (x-axis) vs. resistance (y-axis) curve for this thermistor. [5 pts] ii. Given that Ro = 10 kΩ at To = 298 K, calculate the coefficient β. Hint: make sure you convert your temperature to K before running the calculation. [5 pts] 3. Ultrasound Imaging [10 pts] A. If the time required to receive an ultrasound echo from the ascending aorta is 90 µs, what is the depth of the structure? Report answer in units of cm. [5 pts] B. Doppler ultrasound imaging is being used to measure the blood flow velocity for a patient. The transducer is operating at 7 MHz and the angle between the transducer and the artery is 50°. If the Doppler shift is measured at 2.5 kHz, what is the blood flow velocity? Report answer in units of cm/s. [5 pts] 4. Image Processing and Analysis [5 pts] A 2D image was been spatially digitized with a 7-bit processor. If the area imaged is 23 cm x 23 cm, and pixels are square elements, what is the pixel size? Report answer in units of mm x mm. [5 pts]
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