Optics and Lasers in Engineering 136 (2020) 106318 Contents lists available at ScienceDirect Optics and Lasers in Engineering journal homepage: www.elsevier.com/locate/optlaseng Development of prototype of electronic speckle interferometry based spirometer R Arun Kumar a,b,1 , R Sunil Kumar a,1 , S Sreejyothi a,1 , Vimal Raj a,1 , M S Swapna a,1 , S. Sankararaman a,∗ a Department of Optoelectronics, University of Kerala, Trivandrum, Kerala, 695581, India b Formerly Department of Electrical Engineering, Indian Institute of Technology, Palakkad, Kerala, 678623, India a r t i c l e i n f o Keywords: Speckle Spirometer DNM module ESPIS Peak expiratory flow rate a b s t r a c t The paper reports the design, construction, and calibration of the prototype of a spirometer based on electronic speckle interferometry (ESPI). The conventional ESPI setup is modified by incorporating a DNM (Diaphragm- Nozzle-Mouthpiece) module comprising a metallic diaphragm, regulated airflow channel, and a mouthpiece. The exhaled air after a deep breathe is channelled to the DNM module where the diaphragm gets deformed. From the circular fringe pattern obtained by subtracting the speckled images before and after deformation of the metallic diaphragm, the radius of curvature (R) due to deformation is calculated using the principle of Newton’s rings. The value of R and peak expiratory flow rate (PEFR) from the standard spirometer reading are correlated. From the 640 observations spread over the range 100 - 500 L/min in the standard spirometer, an empirical relation is set in terms of R from the scatter plot. The ESPI spirometer (ESPIS) is validated by determining the value of R corresponding to a particular PEFR from the empirical relation and also from the standard spirometer. The PEFR calculated from ESPIS matches well with the standard spirometer reading, which suggests that the system designed and constructed can be used for biomedical applications for assessing lungs’ efficiency. 1. Introduction The industrial revolution started in the 18 th century has though rev- olutionised our lifestyle, we witness a higher level of environmental pol- lution today as its direct consequence. The polluted air together with the modern lifestyle, has adversely affected human health that resulted in diseases relating to the lungs [1]. The primary five causes of death ac- cording to the Forum of International Respiratory Societies, are Chronic obstructive pulmonary disease (COPD), Asthma, Acute lower respira- tory tract infections, tuberculosis, and lung cancer [2]. The recently reported COVID 19 also affects the lungs efficiency severely [3]. The higher death rate due to respiratory problems suggests the need of its earlier and easier diagnosis. Today, there exists various diagnostic tools, such as spirometers, chest imaging, bronchoscopy, and thoracoscopy, for monitoring lungs related health issues [4–6]. Spirometers are used for measuring the amount of air inhaled and exhaled [4]. The efficiency of lungs is related to its dynamic volume, which in turn represents the volume of air involved in respiration that is being monitored in COPD . The advancement in biomedical engineering led to the development of modern, sophisticated equipment that has revolutionised the medical ∗ Corresponding author. E-mail address: drssraman@gmail.com (S. Sankararaman). 1 All are first authors field of diagnosis with the use of lasers and fibre sensors. Fibre-based spirometers enable a sensitive analysis of pulmonary function by mon- itoring the variations in the optical energy flowing through the fibre [4]. Lasers find various applications in the medical field not only in surgery but also in diagnosis techniques. The laser-assisted diagno- sis making use of advanced optical interferometric and sub micropho- tographic techniques are popular because of its high precision, non- destructive nature, sensitivity, and the availability of advanced im- age processing tools [7–9]. The optical non-destructive testing (NDT) methods include fibre optics, infrared thermography, endoscopic, elec- tronic speckle, and terahertz technology [10]. The speckle interferomet- ric technique is sensitive even to minute changes in the deformation or movement of the object as it records the phase variations in the beam that is reflected or scattered from the object. Interference patterns and its intensity are highly sensitive to the phase that leads to variations in the speckle pattern [11,12]. Speckles are the granular patterns of in- tensity distribution over a surface due to the interference of dephased and coherent wavelets. The speckle based NDT analyses the interference of speckled image of an object with a reference field [12,13]. The in- terference images are recorded using a Charged Coupled Device (CCD) camera and stored in the computer that can be processed under two https://doi.org/10.1016/j.optlaseng.2020.106318 Received 7 June 2020; Received in revised form 21 July 2020; Accepted 28 July 2020 0143-8166/© 2020 Elsevier Ltd. All rights reserved.