# Experimental Testing of Passive Linear TMD for Postural Tremor Attenuation
## 1 Introduction  
Essential tremor (ET) is one of the most common tremor diseases [1]. The muscles of the patient with ET operate in the frequency range of 4-12 Hz [2]. ET is characterized by postural and kinetic tremors, mostly affecting the hands [3]. Postural tremor (PT) is presented during a voluntary movement to maintain a body part at a position against gravity, whereas kinetic tremor occurs during a voluntary movement towards a target. Propranolol and primidone are the most effective pharmacological treatments for ET; however, a large number of patients do not respond to either of these treatments [2], leaving severe side effects on the patient's quality of life [3]. Recent studies have been conducted to provide a non-invasive, wearable mechanical device to attenuate the tremor [4, 5]. [PERSON] et al. [6] modeled the forearm as a 305 mm \(\times\) 25 mm \(\times\) 25 mm aluminum beam attached to the hand. The test bench is fabricated as one segment pinned at the elbow joint and is attached rigidly to the hand at a position reflecting the wrist joint. The system is excited by an electro-dynamic shaker using ET signals in the horizontal direction to reflect the flexion-extension motion. A 120 g proportional-integral-derivative (PID) controller was able to provide a 20-60% reduction in the lineardisplacement amplitude of the segment at the position of the wrist, within the 6-13 Hz bandwidth. [PERSON] et al. [7] modeled the forearm as a 1088 g rectangular beam made up of wood and excited using a shaker by a signal of Parkinson's disease (PD) in the vertical direction. A TMD with variable weight was adapted to reach the tuning frequency by controlling the level of water entering or leaving the piezoelectric micro-pumps. A 200-400 g TMD operating between 4.5-6 Hz is placed near the free end of the beam. It causes a 57% reduction in the amplitude of acceleration at the resonance frequency of 5.32 Hz. [PERSON] et al. [8] manufactured a forearm as an inertial rod attached rigidly to the hand and excited by a direct-current (DC) motor at the wrist joint to apply a pronation-supination motion. The system is operating at the resonance frequency in a range of 4.40-5.78 Hz, measured for patients with PD using an inertial measurement unit (IMU). A 280 g passive bracelet is tuned to the resonance frequency to reduce the simulated tremor. The passive device reduced to 86% of the angular displacement amplitude at 4.75 Hz, measured using the IMU at the wrist. [PERSON] and [PERSON] [9] fabricated an experimental setup with a 1690 g mannequin hand excited by a sinusoidal signal of 50 mm amplitude and a frequency of 4.5 Hz, representing the measured tremor behavior of a patient with PD. Two TMDs designs as a 109 mm \(\times\) 72 mm \(\times\) 9 mm metallic rectangular box each, of 530 g total mass, are placed symmetrically on the top and the bottom of the hand, at the wrist joint, to reduce the motion in the horizontal direction. These TMDs were tested on a real patient by tracing the pre-drawn line on a whiteboard. This resulted in a 70-80% reduction in the tremor amplitude, which validates the numerical study. [PERSON] and [PERSON] [10] designed a prototype of a wearable small and comfortable gyroscope-based mechanism device with low power consumption, weighing 268 g and of 105 mm \(\times\) 84 mm \(\times\) 50 mm physical size. It is prepared to reduce uniaxial hand tremors in the range of 1.41 \(\pm\) 2.58\({}^{\circ}\) and with a frequency between 4-6 Hz of PD. Its effectiveness is validated by a simulation using Matlab; it results in a 92.6% reduction in the amplitude. However, the high-quality testing equipment used was not enough to produce exact tremor data of PD. [PERSON] et al. [11] used two seesaw-like actuators with magnetic discs of 120 g mass to reduce a tremor simulated by a wearable tremor simulator device composed of 32 g eccentric mass and a DC motor. The effectiveness of the device was estimated by visualizing the water level in a beaker held by the participant.