/) of a laser diode, where you can see that a typical laser has three different operation regions (taking the transfer curve at 0 °C as an example): Sub-threshold: the laser operates below the threshold current, Ith, emitting minimal light; Linear region (this is where the laser usually operates): the driving current is higher than the threshold, the laser shows the best efficiency; Saturation: the driving current is too large, and the efficiency drops again (note the behaviour in this region is not linear, but let's approximate it with a straight line for simplicity). i) iii)
Fig: 1
(A) Reverse engineer a piece of medical technology. This must include: 1. A brief history of the science leading to its development, and the development of the technology. 2. A careful, physical analysis of how the device works. This must include a schematic or diagram and the math describing the physics. 3. Evaluation of how the device is applied, the impact it has on humanity, and how it could be improved in the future. Citations of strong sources are required DEVICE: Defibrillator for each question
(A) Reverse engineer a piece of medical technology. This must include: 1. A brief history of the science leading to its development, and the development of the technology. 2. A careful, physical analysis of how the device works. This must include a schematic or diagram and the math describing the physics. 3. Evaluation of how the device is applied, the impact it has on humanity, and how it could be improved in the future. Citations of strong sources are required
3.2 Continue with 3.1 (Fig. 2). To convert the detected photon current Ip into a voltage signal, we usually use the following front-end shown in Figure 3. a) What is the absolute sensitivity of the front-end in Fig. 3 (from Ip to Vout) | Vout/IP in terms of RF, R1 and R₂? (4 marks) b) We use RF = 10k, R₁ = 9k2 and R₂ = 3k2; what is the absolute system sensitivity (from I, to Vout) | Vout/Ir? Plot Vout(t). (3, 6 marks) c) If Vout(t) shows an error of ±3mV, how big is the error irradiance measured? (4 marks) Note that the absolute value means ignoring the sign of a number, e.g. 1-3.0] = 3.0. R₂ R₁
4.1 Suppose R₁ = R₂(unstrained) = R3 = R4(unstrained) = R (12 marks). a) Which artificial limb movements, (1) bending or (II) extension (R₂ and R4 extended in the same direction), can we use the Wheatstone bridge in Fig. 4 to evaluate and why? Derive V bridge (as a function of Vin, G, and ) when the limb is bent down as shown in (1). c) What is Vbridge when the limb is extended as (II)? b) d) If we have G = 8.0, Vin = 10V, and = 5 microstrain, what is Vbridg for (a)? 4.2 Now, we bend the limb up as Fig. 5 shows and connect the output nodes Vout,12 and Vout,34 to an instrumentation amplifier (pay attention to the connection) to produce Vout. (18 marks) a) What is the transfer gain K = Vout/Vbridge (as a function of RG, RS, R6, and R₂)? b) What is Vout (as a function of Vin, G, &, and K)? Pay attention to the signal sign. c) If we have G = 8.0, Vin = 10V, &= 5 microstrain, RG = 1 ks, R₁ = 4.5 KQ, R6 = 1 ks, and Ry = 10 k2, calculate Vout and K (K in dB)? d) Suppose the gauge factor has a temperature variation coefficient per Celcius degree (AG/G)/AT = +0.02%/°C. If we have a temperature change from 0 to 100 °C, what are the voltage changes in V bridge and Vout, respectively?
Q1 (30/100) We often use laser diodes to excite biological samples and observe their fluorescence emission. Figure 1 shows a transfer function (the laser output power P vs the driving current /) of a laser diode, where you can see that a typical laser has three different operation regions (taking the transfer curve at 0 °C as an example): Sub-threshold: the laser operates below the threshold current, Ith, emitting minimal light; Linear region (this is where the laser usually operates): the driving current is higher than the threshold, the laser shows the best efficiency; Saturation: the driving current is too large, and the efficiency drops again (note the behaviour in this region is not linear, but let's approximate it with a straight line for simplicity). i) iii)
Q3 (26/100) We use a BPW34F photodiode to detect the amount of light (at a wavelength of 850nm) falling onto a surface. Its characteristics and normalised spectral sensitivity are as shown below. * Be aware of the wavelength of the incident light. Characteristics T₁ = 25 °C Parameter Wavelength of max sensitivity Spectral range of sensitivity Radiant sensitive area Dimensions of active chip area Symbol As max A 10% A LxW typ. typ. typ. typ. Values 950 nm 780 ... 1100 nm 7.02 mm² 2.65 x 2.65 mm x mm
1.1 What are the threshold currents of the laser for 25 and 100 °C? (2, 2 marks) 1.2 What are the transfer gains (we also name the transfer gain as 'sensitivity' AP/Al) of the laser operating at the linear region, for 0, 25, and 100 °C, respectively? What is your observation (2, 2, 2, 3 marks) 1.3 From Question 1.2, what are the laser diode's linear dynamic ranges (both / and P) for 0, 25, and 100 °C, respectively? (6 marks) 1.4 Suppose the fluorescence experiments require the laser diode to deliver a modulated laser power between Pmin = 1 mW and Pmax = 6 mW. What is the driving current range for 0, 25, and 100 °C, respectively? (6 marks)